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- Newsgroups: rec.audio.tech,rec.audio.opinion,rec.audio.misc,rec.audio.marketplace,rec.answers,news.answers
- Subject: FAQ: rec.audio.* Speakers 2/99 (part 5 of 13)
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- Organization: Texas Instruments Corp.
- Summary: Answers to common questions about audio equipment, selecting,
- buying, set-up, tuning, use, repair, developments, and philosophy.
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- Archive-name: AudioFAQ/part5
- Last-modified: 2000/02/02
- Version: 2.15
-
- 12.0 Speakers:
-
- 12.1 What should I listen to when evaluating speakers?
- The most important thing is to listen to recordings that
- you *know*. Any good salesman will play you recordings
- that highlight that particular speaker. Do not be embarrassed
- about bringing a stack of CDs with you to the hi-fi shop.
-
- Do not spend your valuable listening time switching between a
- dozen pairs every 3 seconds. If you are shopping at a quality
- store, the dealer will, from the description of your room, your
- size requirements, your musical tastes, and your budget, be able
- to show you a couple of pairs that will be close to what you
- want. Spend several minutes listening to each. When you think
- you're close, don't be embarrassed about spending half an hour
- or more listening to the speakers. You're going to have them in
- your home for a lot longer, and many speakers will cause
- "listening fatigue" after a short time. Make sure you really
- like them before you hand over money.
-
- One thing to try is well recorded "Spoken Word" records; most
- people have a very good ability to tell when a speaking voice
- sounds unnatural, even if they've never heard the person
- speaking live. If you play an acoustic instrument, find
- something that features that instrument solo, or in a small
- group; make sure it really sounds like it should. Almost
- everyone has heard a live piano. Piano can be very revealing.
-
- Blues, jazz, folk, or 'easy listening' music with simple
- instruments and a female vocalist is also revealing. Well done
- female singing voices provide a very good test of a system's
- response. Try something simple and soft, which will let you
- hear any noises coming from the system; and something complex,
- with lots of instruments all happening at once, to make sure the
- system doesn't go muddy when things get complicated. And, of
- course, try a few of your favorites, and see if you like what
- happens with them.
-
- If a sales person suggests some music to listen to, the odds are
- that it isn't the most revealing. Sales people tend to suggest
- things which sound great. Anything you own and like is good,
- because you know it and are happy to listen to it carefully. No
- matter how good the recording, if you don't like Opera, you
- won't listen to it as carefully as your favorite, scratchy,
- 1940's rhythm and blues.
-
- Most important is to listen to something you are familiar with.
- Even if a recording is flawed (and what ones aren't?), how is it
- different from your normal setup? Some of the most important
- differences are "Gee, I never heard that instrument before!"
-
- 12.2 What should I listen for when evaluating speakers?
- When comparing two speakers side-by-side, doing an AB
- comparison, be extremely careful to match the levels before
- evaluating. A slight level difference can make one speaker
- sound better, even though the difference may not be perceived
- as a level difference. Some claim that you will be influenced
- by a difference of less than 1/2 dB!
-
- First and foremost, the sound should be natural. If you listen
- to vocals, close your eyes and try to picture someone singing in
- the same room with you. Does it sound realistic? Likewise with
- instruments. You selected recordings of instruments that you
- like and have heard live. Do they sound like what you remember
- them sounding like live?
-
- Your very first impression should be something like "what nice
- sound". If your initial gut reaction is "gosh, what a lot of
- detail", the system is likely to be heavy in the treble (often
- interpreted by beginners as "more detailed") and you'll probably
- find that annoying after a while. If your first reaction is
- "hey, what powerful bass", then the system is probably
- bass-heavy, rather than ideal. The most common mistake for
- beginners is to buy a system with REALLY powerful bass, because
- it sounds "impressive" at first. After a while, though, you'll
- get tired of being thumped on the head by your music.
-
- Not to say that good bass and treble aren't important. But your
- first realization should be that the music is all there, and
- that it comes together as good music, without one particular
- part trying to dominate it. Sit back and listen to it for a
- bit. You should be able to pick out the individual instruments
- if you want. They shouldn't force themselves on you, and you
- should also be able to hear the music as a single piece, the sum
- of its parts, without feeling like each of the instruments is
- trying to grab your attention away from the others.
-
- You should check how things sound with the amp turned up, and
- also with it turned down to a fairly low volume level. Some
- speakers which sound very nice at low levels begin to sound
- confused, like they can't cope, when turned up. On the other
- hand, some sound nice loud, but sound thin and bodiless when you
- turn them down a bit. With the spoken word or female vocalist,
- listen for "sibilance", a pronounced 'hiss' at the end of 's'
- and 'z' sounds. It shouldn't be there. Most planar speakers
- just can't play very loud. Whatever you hear, do some
- auditioning at the maximum volume you anticipate ever wanting.
-
- It is acceptable and sometimes desirable to switch the stereo to
- mono to evaluate naturalness. Mono is a good test of both the
- room and the speakers. The image should be rock-solid dead
- center, and not move with signal or level. If it isn't perfect
- mono, it will be nearly impossible to create a good stereo.
-
- A speaker in a large box is capable of producing low frequencies
- at higher volumes with more efficiency than a small box, but
- that doesn't mean that a small box can't have great bass, it
- just won't be as efficient and can't play as loud.
-
- Good speakers can "recreate a natural stereo sound stage",
- placing some instruments to the left of the left speaker, some
- sounds in the middle, and some to the right of the right
- speaker. Poorer speakers make it harder to localize voices.
-
- 12.3 Why use a subwoofer? Will it help? One or two?
- One reason to get a subwoofer is to add bass to a feeble system.
- A second reason is to move the lowest frequencies to a separate
- driver, and thereby reduce a particular kind of distortion
- caused by the nonlinear mixing of different sounds, called
- "intermodulation distortion". A third is to increase the power
- handling ability of the system and the overall reliability. All
- are valid reasons, but it isn't so simple.
-
- To improve the sound of a good speaker system, a subwoofer must
- "integrate smoothly" into the system, extending the bass without
- causing peaks or dips. Many subwoofers have a crossover that
- goes between your amp and your main speaker which sends the lows
- to the subwoofer and sends the higher frequency signals to the
- main speakers. This may damage the perfect sound of a good
- system, it may sound similar, or it may sound better.
-
- Most good small speaker systems have a bass peak at resonance,
- which attempts to compensate for the absence of lower bass.
- Like it or not, this is the only way to make a small system
- sound realistic. If the small system is done well, the
- improvement you will get from a subwoofer will be small, but
- still real and, to many, significant.
-
- Correctly done, a good subwoofer will enhance the sound of a
- good small-box system. Done wrong or haphazardly, anything is
- possible. Even a fine large speaker system might benefit from
- careful addition of a subwoofer. However, the better the
- original system, the more likely it will be that a modest
- subwoofer will do more harm than good.
-
- Low frequencies travel less directionally than high frequencies,
- so many people say that only one subwoofer is required for good
- sound. This is true to some extent, but not completely true.
-
- There are a few reasons for getting two subwoofers. Some feel
- that you need two subwoofers to accurately reproduce the stereo
- image, no matter how little low-frequency stereo information
- there is. Others feel that two subwoofers are much easier to
- set up in a room, less likely to excite standing waves in the
- room, and give smoother sound.
-
- A third reason is that two subwoofers can produce twice the
- sound of one. Finally, even though subwoofers produce very low
- frequency sound and very low frequency sound is non-directional,
- subwoofers also have output at 100 Hz, and sound at 100 Hz is
- directional, so two subwoofers will give a slightly better
- stereo image than one. Assuming, of course, that the two are
- separated by at least two feet.
-
- Finally, even though original source signals rarely contain any
- music with stereo components below 50Hz, there may be some noise
- component with low-frequency out-of-phase noise. This unusual
- noise might add a sense of space to a recording if it is
- reproduced by a system in which the woofers are very far apart.
-
- It is still true that a single good subwoofer, correctly added
- to a system will help the sound but two will probably help more.
-
- 12.4 How do you connect a subwoofer to a stereo?
- Many subwoofers contain their own amplifier and crossover.
- For these, take the preamp output and feed it into the subwoofer
- amp input and also into the main amplifier.
-
- For other subwoofers, just run them in parallel with your main
- speakers, or combine them into your system with your own bass
- amplifier and crossover.
-
- Some A/V receivers contain a splitter specifically for use with
- subwoofers. If you have one of these, you will either want a
- separate amplifier for your subwoofer or an amplified subwoofer.
-
- Consult the manual which comes with the subwoofer.
-
- 12.5 What do I need for surround sound?
- "Surround Sound" has referred to a number of different products
- over the years. Many mass-fi receivers have "Surround Sound"
- buttons that do little more than muck up the imaging.
-
- In recent years the term "Surround Sound" has become synonymous
- with the surround systems produced by Dolby Laboratories. Dolby
- Surround comes in several flavors, such as passive surround
- (which simply decodes the phase information and sends it to the
- rear speakers) and the more advanced system called Pro Logic.
- Pro Logic system uses computer circuitry to route directional
- information to the appropriate speakers.
-
- Generally, one needs at least two more speakers beyond the main
- stereo pair. Advanced Pro Logic systems such as the Lexicon and
- Fosgate can accommodate several more speakers beyond the two
- additional ones (usually placed in the rear). Often one can
- find Pro Logic systems with two front, two rear, two side, as
- well as a center channel speaker for dialogue.
-
- 12.6 I was just approached (accosted?) by a couple of kids driving a
- van that said they had some GREAT speakers to sell. They are
- overstocks, used by major recording studios and DJs or even
- hot, and they normally sell for $1000/pr, but they'll let
- me have them for just $399. Am I getting ripped off?
-
- Yes, you most certainly are. The speakers these people sell
- are none of what they describe. They are never used in
- studios. There might be one or two DJs out there that use
- them because they can't afford anything else. They are not
- overstocks, and in all likelihood, they are NOT HOT!.
-
- Are they good speakers? No, they're, at best, no better than
- the big boom boxes you find in $400 rack systems in department
- stores. They are worth no more than what the kids paid for
- them ($100/pr).
-
- The speakers go under names like "Acoustic Monitor DB IV",
- "Acoustic Linear," "Pro-Poly," "Audio Reference 4350", "Omni
- Audio", and so on. They all "feature" things like "liquid
- cooled 3" tweeter", poly-cone 12" woofer, fantastic (but
- impossible) frequency response, 98 db/watt sensitivity, and so
- on. The brand names are remarkably similar to reputable firms,
- but different enough to delay law suits.
-
- These speaker are made by a couple of manufacturers with the
- intent of being sold exactly this way. They cost the kids in
- the van about US $100 a pair, and the kids are given minimal
- training about what kinds of stories to use, what parking lots
- are the most likely to generate sales (department store parking
- lots near colleges in September is a great time for these guys).
- Anything over the US $100 the kids paid is pure profit.
-
- Stay away, you're getting ripped off. For more information on
- these speakers, see:
- http://bigsun.wbs.net/homepages/o/m/n/omniaudioscam/
- http://www.frii.com/~rjn/audio/whitevan.htm
-
- 12.7 What speakers should I consider in the $XXX/pair price range?
- This is probably the most commonly asked question on rec.audio,
- and also the most impossible to answer. The market keeps
- changing, everyone has different tastes, and no one has the time
- to listen to even 10% of the products available in any country.
- Also, many good products are only available in specific regions
- or countries.
-
- If you really want recommendations and are willing to listen to
- the opinions of others, check the past few issues of Stereophile
- Magazine. Although they are strongly biased towards very
- expensive gear and have their own particular other biases, they
- do steer you to some very good equipment in their
- frequently-updated list of "RECOMMENDED COMPONENTS".
-
- 12.8 Can you build better speakers than you can buy?
- Some people can build better than you can buy. These people are
- either experts, golden ears, extremely well equipped, inspired,
- or a combination of the above.
-
- Some companies have plans available to entice you into buying
- their drivers: Audio Concepts, Audax, Dynaudio, Focal, KEF, and
- Scanspeak. Your success rate with these plans will probably be
- very good IF your cabinetry skills are very good and IF you
- follow the plans precisely. If you deviate (as everyone does),
- anything is possible.
-
- Stereophile has published three different plans designed by Dick
- Olsher which are similar two-way ported systems. A recent one of
- these was in Stereophile Nov '90, pages 94-127. Audio Magazine
- published a plan called "The Pitts" by Ken Kantor, in Audio, Nov
- '88 pages 65-71 continued in Dec '88 pages 73-77. This plan is
- a two-way sealed box.
-
- I have built one published design and one manufacturer's design.
- I believe that both met my expectations. They took me a long
- time to build, taught me a lot, were fun projects, and sounded
- good when finished.
-
- I also believe that a commercial system which cost what my parts
- cost will never sound anywhere near as good as the one I build.
- If you consider $2/hour for my time, however, building is
- financial suicide.
-
- Designing your own system is even more a can-of-worms, and
- should be left to those with either a strong stomach, a very
- forgiving ear, infinite resources, or excellent guidance.
-
- 12.9 Where can I read more about speaker building?
- Europe's Greatest Speaker Designs
- Solen Electronique
- 4470 Avenue Thibault
- St.-Hubert, QC J3Y 7T9 Canada
- Voice 514-656-2759
- FAX 514 443-4949
- High Performance Loudspeakers by Martin Colloms
- Speaker Builder Magazine
- Audio Amateur Publications
- PO Box 494
- Peterborough NH 03458 USA
- 603-924-9464
- Synergetic Audio Concepts Classes and Newsletters
- Syn-Aud-Con teaches classes on Audio and Acoustics
- 12370 W. Co. Rd. 100 N.
- Norman IN 47264 USA
- 812-995-8212
- The Loudspeaker Design Cookbook, Fifth Edition
- by Vance Dickason (C) 1995
- ISBN 1-882580-10-9
- $34.95 + $4.45 S&H from:
- Old Colony Sound Lab
- PO Box 243
- Peterborough NH 03458-0243 USA
- 603-924-9464
- $30.00 + approx. $3 Shipping from:
- Madisound
- 8608 University Green; Box 4283
- Madison WI 53711 USA
- 608-831-3433
- $30.00 + ??? S&H from:
- Parts Express
- 340 E. First St
- Dayton OH 45402 USA
- 800-338-0531
-
- 12.10 Where can I buy speaker drivers?
- Audio Concepts (Their own kits plus drivers)
- 901 South 4th Street
- LaCrosse WI 54602 USA
- Voice 608-784-4570
- http://www.audioc.com
- Phil Baker (Surplus cabinets only)
- 546 Boston Avenue
- Medford MA 02155 USA
- Bandor Design & Development Studios (Aluminium coned speakers)
- 11 Penfold Cottages
- Penfold Lane
- Holmer Green
- Bucks, HP15 6XR United Kingdom
- Tel. (01494) 714085
- DBS Audio (Speaker kits and crossovers)
- PO Box 91, Bury St.
- Edmunds, Suffolk, IP30 0NF United Kingdom
- Tel (0284) 828926
- Drexler Audio Systems (Bandor Speaker Distributor)
- 14 Rose Lane
- Rosemont PA 19010 USA
- Falcon Electronics (Drivers and cross overs)
- Tabor House
- Mulbarton
- Norfolk, NR14 8JT United Kingdom
- Tel. (0508) 78272
- Faraday Sound (Concrete loudspeaker cabinets)
- 248 Hall Road
- Norwich, NR1 2PW United Kingdom
- Tel. (0603) 762967
- Gold Sound (Broad line including pro speakers)
- PO Box 141
- Englewood CO 80151 USA
- 303-789-5310
- Madisound (Broad line)
- 8608 University Green
- Box 4283
- Madison WI 53711 USA
- 608-831-3433
- http://www.itis.com/madisound/
- Meniscus (Broad line)
- 2442 28th Street SW Ste D
- Wyoming MI 49509 USA
- 616-534-9121
- Parts Express (Broad line)
- 340 East First Street
- Dayton OH 45402-1257 USA
- 513-222-0173
- Solen Electronique (Airborne, Audax, Ceratech, Dynaudio, Eton,
- Lpg, Morel, Peerless, Scan-Speak, Seas, Solen, Vifa)
- 4470 Avenue Thibault
- St.-Hubert, QC J3Y 7T9 Canada
- Voice 514-656-2759
- FAX 514 443-4949
- The Speaker Co (Large range of drive units plus speaker kits)
- Unit 9, Waterside Mill
- Waterside, Macclesfield, SK11 7HG. United Kingdom
- Tel. (0625) 500507
- Speakers Etc.
- 2728 West Thomas Road
- Phoneix AZ 85017 USA
- 602-272-6696
- SRS Enterprises (Pyle, Pioneer, Eminence, Ultimate, Fane, MG)
- 1839 N Circle Dr
- Colorado Springs CO 80909 USA
- Voice 719-475-2545
- FAX 719-475-0359
- Wilmslow Audio (Kits and drive units. KEF, Dynaudio, Audax, SEAS,
- Peerless, Scanspeak, Morel)
- Wellington Close
- Parkgate Trading Estate
- Knutsford, Cheshire, WA16 8DX United Kingdom
- Tel (0565) 650605
- Zalytron (Broad line including kits)
- 469 Jericho Turnpike
- Mineola NY 11501 USA
- 516-747-3515
-
- 12.11 Where can I buy loudspeaker kits?
- Audiocab (Speaker kits and cabinets)
- 9 Skewbridge Close
- Wooten Bassett, Swindon, SN4 7DW United Kingdom
- Tel (0793) 848437
- Audio Concepts, Inc. (Wide range of kits. Catalog available)
- (see 12.10, above)
- Fried Products (Parts kits starting $550. Catalog available)
- (Emphasizes high-end transmission line speakers)
- (Parts kits have plan, crossover, and driver)
- 1323 Conshocken Road
- Norristown, PA 19401 USA
- 610-277-1014 or 800-255-1014
- IPL Acoustics (Kits using SEAS, Morel, Audax, and Visaton)
- 2 Laverton Road
- Westbury, Wiltshire, BA13 BRS United Kingdom
- Tel (0373) 823333
- Mahogany Sound (Parts kits and Woodstyle kits)
- (Parts kits have plan, crossover, and driver)
- (Woodstyle kits also have 3/4" MDF veneered boxes)
- (Prices $150/pair to $500/pair. Catalog available)
- (Two way, three way & subwoofer kits)
- 2610 Schillingers Rd #488
- Mobile AL 36695 USA
- 205-633-2054
- Tabula Rasa (Wide range of speaker kits)
- 1 Silkin Dalton Close
- Broadfield, Crawley
- W. Sussex, RH11 9JD United Kingdom
- Tel. (0293) 531190
- Visaton UK Ltd (Drivers, crossovers, kits, designs, software)
- 2 Bentfield Road
- Stansted Mountfitchet
- Essex
- CM24 8HN
- UK
- Tel. +44 (0)1279 817604 Fax: +44 (0)1279 817601
- E-Mail visaton@visaton-amc.demon.co.uk
- Also see above, under suppliers for speaker drivers.
-
- 12.12 How can I improve the sound of my speakers?
- The best way to change the sound of your speakers is to change
- where you put them. Ideally, the speakers should be located at
- ear level, in front of you, squared off between you. It's then
- a matter of fiddling with a) the angles, b) the distance apart,
- c) the distance from you, and d) the distance from the wall.
- Just moving the speakers around in the room or putting them onto
- stands can make a major difference. For more on speaker
- placement, see 13.1 below.
-
- Other than that, speaker modifications can be a can of worms, or
- can produce very subtle changes, which you might prefer. For
- example, you might improve a speaker by adding some cross braces
- of 1"x1" wood from left to right and from front to back. This
- will stiffen the cabinet and reduce speaker cabinet wall
- vibrations, which probably hurt sound quality. Alas, this will
- be most effective with lower-cost and poorly built speakers.
-
- Along similar lines, some claim success putting lead wire or
- epoxy putty on thin parts of the speaker to damp out resonances.
- You can try doing this to the thinner parts of the speaker
- "basket" or frame, or to the front "baffle" or supporting panel.
-
- Still another "tweak" is to add sound deadening felt pads to the
- inside walls of the speaker. Instead of felt pads some advocate
- sand-filled latex coatings on the inside walls of speakers.
- Others advocate ceramic tiles held in place with "thinset".
- Still others rave about commercial products like AC Glop,
- Acoustic Magic, and Bostik Sheet. However, the people who rave
- about these products tend to be the same people who sell them.
-
- Any change along the lines of adding felt, cross-bracing, or
- putty will have subtle effects on the sound.
-
- For the brave at heart, you can replace old or cheap drivers
- with better ones, but the results of this one change can be very
- dissatisfying if you happen to get the wrong type of driver for
- that application, and may never sound right, even if you use a
- similar driver. Speaker system design is still somewhat of a
- science and somewhat of an art. Throwing paint on a canvas
- often makes a mess.
-
- Whatever change you try, don't "burn your bridge" home. Be sure
- that you can undo whatever change you did, just in case. Many
- tweaks to good speakers, no matter how well thought through,
- will correct for one flaw, but create others, or correct a flaw
- that the designer had cleverly used to his advantage.
-
- 12.13 How can I replace/re-cone my old speakers?
- The best chance of success is to buy an identical replacement
- speaker driver from the manufacturer of the system.
-
- Second choice is to buy the exact same driver from a
- distributor. This is sometimes difficult because it is hard to
- learn exactly what driver the manufacturer used. In addition,
- EVEN IF the manufacturer used stock speakers, they might have
- used matched pairs or selected speakers by hand for an exact set
- of specific characteristics.
-
- There are companies that rebuild drivers, but they charge quite
- a bit. I have heard $75 per driver. This is rarely done for
- anything but very expensive commercial drivers. Speaker
- manufacturers will often sell owners the materials that they
- need to repair a speaker. If you are handy with delicate
- things, it is worth a try.
-
- In addition to speaker manufacturers, there are companies which
- sells rebuild kits for approximately $30 per pair, containing
- new foam, a special glue, and instructions. If you have a blown
- or distorted voice coil, this still won't help. A few netters
- have used rebuild kits from this company successfully. Contact:
- Stepp Audio Technologies
- PO Box 1088
- Flat Rock NC 38731 USA
- 800-747-3692
-
- Two other vendors of speaker repair parts are:
- Parts Express (sells 8", 10", 12", & 15" repair kits)
- 340 E First St
- Dayton OH 45402-1257 USA
- 513-222-0173
-
- Simply Speakers
- P. O. Box 22673
- St. Petersburg FL 33742 USA
- 800-767-4041 or 813-571-1245
-
- Also check out: http://www.decware.com/surround.htm and
- http://www.les.safety.net/stepp.html for directions on
- replacing speaker foam.
-
- Some speaker manufacturers have very good warranties.
- Electro-Voice warranties all professional products for life.
- KEF has a similarly broad warranty on their speakers. Contact
- the manufacturer first.
-
- 12.14 What computer programs can I use to design speakers?
- There are many useful programs available, but none are complete
- without a good knowledge of speaker design. Further, you will
- NEED to supplement any program with hand tweaking for the best
- sound. Finally, no simulation program is ever useful without
- good model parameters, and the parameters which manufacturers
- give you are often imperfect, so many good designers strongly
- recommend your own lab measurements. The Loudspeaker Design
- Cookbook (see 12.9) tells you how to measure a speaker, and also
- gives enough theory to feel confident with a good program.
- You can get a lot done with a simple spreadsheet and the
- equations in a book like The Loudspeaker Design Cookbook.
-
- For more information on programs for speaker design and on
- speaker-design hardware, such as measurement systems, get
- the archive "sahfsd**.doc" from directory:
- usenet/rec.audio.high-end/Software
- on "ftp.uu.net". In addition, there are other interesting
- audio-related files in that directory. Look around.
- That file is also available on ftp.graphics.cornell.edu in
- /pub/rahe/software
-
- 12.15 Can I magnetically shield my speakers for use near a TV?
- You probably will need to buy speakers that are made with an
- integral magnetic shield. Magnetic shielding is usually done
- by either shielding the speaker magnet or by cancellation of the
- magnetic field very close to the magnet, or by both. Shielded
- speakers are NOT built by lining the enclosure with metal.
- While it sounds like a good idea, it doesn't work.
-
- A common magnet shield is a mild steel cup around the magnet.
- This is the cheapest shield, and is usually fairly ineffective.
- It also will interfere with the speaker's critical magnet gap,
- so this type of shield can hurt speaker performance by shorting
- the magnetic field and reducing the magnetic flux density in the
- gap, which can reduce efficiency and affect the speaker's low
- frequency performance.
-
- Cancellation is done using a reverse-polarized magnet glued to
- the back of the main magnet. If done right, it can almost
- completely cancel the rear stray field. In some cases it can
- also increase the magnetic flux density in the gap, which may
- or may not be desirable.
-
- 12.16 What are all of these abbreviations people use for speakers?
- Most of these parameters are well documented in the Loudspeaker
- Design Cookbook. (see 12.9) In summary:
-
- Fs Driver free air resonance, in Hz. This is the point at
- which driver impedance is maximum.
- Fc System resonance (usually for sealed box systems), in Hz
- Fb Enclosure resonance (usually for reflex systems), in Hz
- F3 -3 dB cutoff frequency, in Hz
-
- Vas "Equivalent volume of compliance", this is a volume of
- air whose compliance is the same as a driver's
- acoustical compliance Cms (q.v.), in cubic meters
-
- D Effective diameter of driver, in meters
- Sd Effective piston radiating area of driver in square meters
- Xmax Maximum peak linear excursion of driver, in meters
- Vd Maximum linear volume of displacement of the driver
- (product of Sd times Xmax), in cubic meters.
-
- Re Driver DC resistance (voice coil, mainly), in ohms
- Rg Amplifier source resistance (includes leads, crossover,
- etc.), in ohms
-
- Qms The driver's Q at resonance (Fs), due to mechanical
- losses; dimensionless
- Qes The driver's Q at resonance (Fs), due to electrical
- losses; dimensionless
- Qts The driver's Q at resonance (Fs), due to all losses;
- dimensionless
- Qmc The system's Q at resonance (Fc), due to mechanical
- losses; dimensionless
- Qec The system's Q at resonance (Fc), due to electrical
- losses; dimensionless
- Qtc The system's Q at resonance (Fc), due to all losses;
- dimensionless
-
- n0 The reference efficiency of the system (eta sub 0)
- dimensionless, usually expressed as %
-
- Cms The driver's mechanical compliance (reciprocal of
- stiffness), in m/N
- Mms The driver's effective mechanical mass (including air
- load), in kg
- Rms The driver's mechanical losses, in kg/s
-
- Cas Acoustical equivalent of Cms
- Mas Acoustical equivalent of Mms
- Ras Acoustical equivalent of Rms
-
- Cmes The electrical capacitive equivalent of Mms, in farads
- Lces The electrical inductive equivalent of Cms, in henries
- Res The electrical resistave equivalent of Rms, in ohms
-
- B Magnetic flux density in gap, in Tesla
- l length of wire immersed in magnetic field, in meters
- Bl Electro-magnetic force factor, can be expressed in
- Tesla-meters or, preferably, in meters/Newton
-
- Pa Acoustical power
- Pe Electrical power
-
- c propogation velocity of sound at STP, approx. 342 m/s
- p (rho) density of air at STP 1.18 kg/m^3
-
- 12.17 What are fluid-filled (fluid-cooled, ferro-fluid) tweeters?
- These tweeters are built almost exactly the same as other
- tweeters. They look and act almost exactly the same, too.
- The only difference is that they have a small, controlled
- amount of a special fluid inserted into the gap between the
- magnet and the voice coil.
-
- One big effect of adding this fluid to a tweeter (or to any
- speaker) is that it makes the voice coil capable of dissipating
- more heat. This means that the speaker can have a lighter voice
- coil, for better performance, or a higher power rating for the
- same voice coil. The other big effect of this fluid is to add
- mechanical damping. The frequency response and transient
- response of the driver will change, possibly for the better.
-
- In addition, this fluid may help center the voice coil, may
- lubricate the voice coil, and may help keep dirt out of the gap.
- This fluid will not increase the magnetic field, concentrate the
- magnetic field or otherwise change the magnetic circuit. Nor
- will it cushion impact if the voice coil bottoms.
-
- The fluid used for this purpose is often called "ferrofluid".
- It consists of sub-microscopic particles of magnetic material
- suspended in special oil. This fluid stays in the gap because
- of the strong magnetic pull of the magnet. There is some debate
- over whether these fluids can dry out with time. Manufacturers
- claim that the oil used is non-volatile.
-
- It is possible to use ferrofluids in mid-range drivers and
- woofers. However, as tweeters tend to have the most fragile
- voice coils, tweeters have the most to gain from ferrofluid.
- There are various different fluids on the market, some of which
- have characteristics tailored to tweeters, some to woofers, etc.
-
- It is very risky to blindly add fluid to a driver. It may not
- be compatible with the adhesives used in the driver, may not be
- practical with the particular driver layout, and is impossible
- to remove. Permanent driver damage is possible.
-
- 12.18 Should I use spikes under my speakers? Pennies under the spikes?
- Spikes prevent speakers from rocking. They also couple the
- speaker directly to the floor. Spikes will pierce carpet.
- Some spikes will damage carpet. Most will just put a small
- hole in the carpet which is invisible. Putting a heavy
- speaker directly on carpet will cause a permanent mark on
- the carpet. Spikes can prevent this.
-
- If you have a pretty hardwood floor, then spikes will definitely
- damage the finish. A rigid disc under the spike will distribute
- the load and lessen the damage. Any coin should work fine. Using
- a coin will not change the speaker/floor interaction. Do not use
- a coin with a carpeted floor. Alternatives to spikes for wood
- floors are Blu-Tack and similar products. (see 12.19)
-
- If your floor is extremely rigid, then the spikes will make
- the speaker more rigid. If the floor is more conventional,
- such as a suspended floor or a wooden floor over joists,
- spikes can have a positive or negative effect, depending on
- the resonant characteristics of the floor/speaker system.
-
- The counterforce resulting from a forward cone motion in a
- speaker may try to move the speaker backwards, but spikes will
- have little or no effect on this. Most audible effects from
- spikes are due to coupling the speaker to the floor, so it
- will be less likely to resonate on its stand. Some argue that
- in most cases, spikes will have no audible effect at all.
- Try it for yourself.
-
- 12.19 How do you couple speakers to speaker stands?
- Ideally, your speakers should sit flat on the speaker stand
- or floor. They shouldn't see-saw back and forth if nudged.
-
- One good way to accomplish this is to use a small dab of
- putty under each corner of the speaker. There are a few
- common putties used for this, but all share the properties
- of being very elastic and staying flexible indefinitely.
- These putties are inexpensive, removable, and reusable.
-
- Try either Blu-Tak, which is available in the UK from office
- supply stores for cleaning typewriter elements, Faber Castell
- UHU Hold-It, which is available in the US from office supply
- stores for holding up pictures, DAP's Fun-Tak, which is sold
- in hardware stores for holding up pictures, or Pritt Buddies.
-
- 12.20 What is a Sealed, Ported, Bass Reflex, Acoustic Suspension,
- Bandpass, and Coupled Cavity Speaker? Which is better?
-
- All are "direct radiator" enclosures, so called because the
- sound is produced directly from the driver (the "radiator")
- without the assistance of a contrivance such as a horn.
-
- SEALED BOX:
- The simplest direct-radiator system. The rear of the driver
- sees a sealed enclosure, and none of the rear output of the
- driver contributes to the sound output. Depending upon how
- stiff the mechanical suspension is vs how stiff the enclosed
- air in the enclosure is (and that's a function of the size of
- the box), you can have either an Infinite Baffle enclosure,
- in which the mechanical suspension is the dominant source of
- system stiffness and the box is large; or an Acoustic
- Suspension enclosures, where the air in the box is the
- dominating stiffness, and the box is small.
-
- Sealed boxes tend to be the lowest efficiency systems for a
- given box size and bass cutoff frequency.
-
- VENTED ENCLOSURES:
- Also the same as Bass Reflex, Ported, or Passive Radiator.
- Here, an aperture in the box provides a means for the rear
- output of the cone to contribute to the total output of the
- system. However, it only contributes over a very narrow range
- of frequencies. In fact, in a properly designed system, the
- front output of the cone is reduced at the same time the
- output of port increases, so the port DOES NOT ADD to the
- output of the woofer, it REPLACES the output of the woofer at
- these frequencies. This, if done properly, can significantly
- reduce distortion and increase power handling at very low
- frequencies, a region that can be difficult for drivers.
-
- Vented systems can be up to 3 dB more efficient than a sealed
- box system that has the same bass cutoff frequency and size.
-
- BANDPASS:
- These are compound systems in that they have at least two
- enclosures: one on the front and one on the rear of the driver.
- The enclosure on the front, which looks remarkably like a vented
- box (because it is), acts as a low pass filter, and, can couple
- the output of the woofer more efficiently to the outside. They
- have several useful advantages. For example, the front enclosure
- can be used as a very effective acoustic crossover, filtering
- out mechanical noises generated by the woofer, something
- no electronic crossover can do. For very low frequencies,
- such an acoustic crossover can be far less expensive and
- more easily designed than an equivalent electronic crossover.
-
- They are called "bandpass" because the combination of the rear
- enclosure and the driver form the high pass portion while the
- front enclosure forms the low pass section. Making the bandwidth
- of the system narrower raises the efficiency of the system.
-
- COUPLED CAVITY:
- A variation of bandpass and vented systems, they are the results
- of a designers attempt to solve specific problems. They consist
- of two or more rear enclosures, each coupled to the next by a
- vent. Each enclosure/vent combination is another resonant system,
- and the combination is, essentially, a high order, multi-tuned
- resonant system.
-
- Generally, these systems have quite complex response and are
- difficult to design. No comprehensive theory on their operation
- exists like that for sealed, vented and bandpass systems.
-
- 12.21 What is the best material to make speaker boxes out of? Why?
- An ideal speaker cabinet material would be very stiff, so that
- it would not tend to move with variations in box air pressure.
- It would also be very well damped, so that if it ever does
- deflect from air pressure, it will come back to the original
- position without resonating. It would also have a very high
- resonant frequency (supersonic), so that low frequency box air
- pressure would not cause it to resonate. An attractive material
- is preferred, and additional credit is given for a material
- which is easy to cut, glue, and finish. A great material would
- be cheap, too. Finally, it would be nice if the material were
- light, because we all have to move our speakers sometimes,
- and it's hard to appreciate good speakers with a sore back.
-
- With all of those attributes, it would seem that no
- material is perfect. However, there are many materials that
- have enough of the above good attributes to make excellent
- speaker cabinets. Yet each has advantages and disadvantages.
-
- In the list of good speaker box materials below, letters are
- used to indicate which attributes the material possesses.
-
- S = Stiff
- D = Damped
- H = High Resonance
- A = Attractive
- M = Machinable
- C = Cheap
- L = Light
-
- MEDIUM DENSITY FIBERBOARD (MDF): SDMC This is the most practical
- material for quality speakers. It is harder to find than plywood,
- but most lumber yards can special order it. It cuts very nicely
- and has a smooth surface. It takes veneer very well. However,
- bring a helper when you pick the stuff up. One sheet is very
- heavy. MDF is harder on tools than common wood, but easier than
- particle board. This is the material that many great speaker
- makers use. US $45 for a 4'x8'x1" sheet. Density: 50 lbs/cu ft.
-
- POLYCARBONATE (LEXAN): DM A clear or solid-color polycarbonate
- box can look strikingly good. However, this is not a cheap
- material. To locate it, look in the classified directory under
- PLASTICS. US $400 for a 4'x8'x0.5" sheet. Density: 75 lbs/cu ft.
- Acrylic (Plexiglass) is cheaper than Polycarbonate, but weaker
- and poorer damped (not recommended).
-
- CORIAN (tm), FOUNTAINHEAD (tm), AVONITE (tm), SURELL (tm),
- GIBRALTAR (tm): SDA Regardless of the brand, these synthetic
- countertop materials come in a wide array of colors and look
- beautiful. They are hard to buy, and different to work with.
- They take special glue to bond and require wet sanding with
- very fine paper to finish. You can tap it, but it's too brittle
- for wood screws. Helicoil inserts are very effective. Yet an
- experienced builder can complete a cabinet in under an hour,
- from raw material to final finish. Corian is acrylic mixed with
- powdered aluminum trihydrate clay filler. Avonite, Gibraltar,
- and Surell are polyester resin mixed with filler. One user
- commented that Corian is easier to use and is easier to make
- invisible seams than the other synthetics. It has been said
- that Corian is actually easier to use than wood, but that
- depends on your equipment and experience level. Estimated cost
- for Corian is US $20 per 1'x1'x0.5". Density: 100 lbs/cu ft.
- Available from:
- Art Specialties
- 74 North Aurora St
- Lancaster, NY 14086
- 800-724-4008
- Ask for their free information pack on working with Corian.
- Note: These product names are registered trade marks and apply
- to specific materials from specific manufacturers.
-
- MARBLE: SDHA One challenge with marble speaker enclosures is
- cutting holes for the drivers. A carbide bit on a router will
- work, but it will dull quickly. Marble is also difficult to glue,
- so bracing is difficult. But it sure is pretty when you're done!
- US $25 to $45 per 1'x1'x1.25". Density: 160 lbs/cu ft.
-
- PLYWOOD SHEETS SPACED AND FILLED WITH SAND OR LEAD SHOT: SDAMC
- If you have time on your hands and want a great impractical box,
- try this. Make a simple box out of common plywood. Then glue
- cleats on the outside of the box to space the outside plywood
- from the common plywood. Glue hardwood-veneered plywood to the
- cleats and pour sand or lead shot into the spaces between the
- cleats. It won't be light, but with the filler, it will be
- extremely well damped. In addition, if you use strong cleats
- and glue well, the box will be extremely stiff. One person used
- different size Sonotubes as an alternative to plywood, and
- filled the space between them with sand. Be sure to sterilize
- the sand in your oven before putting it in the box.
-
- ALUMINUM SHEETS SPACED AND FILLED WITH ALUMINUM HONEYCOMB
- (Aerolam): SDHL Airplanes use this material for flooring. Next
- time a plane crashes in your neighborhood, see if you can get
- the wreckage for your next speaker project. You can't get a
- better, light-weight material. Celestion has exploited this for
- some great products. If you're really ambitious, you can make
- your own sandwich out of high-quality plywood faces and a thick
- honeycomb core. You will probably need an epoxy to glue the
- honeycomb to the plywood. A home-brew sandwich is easier to cut
- and glue than Aerolam.
-
- FORMED CONCRETE: SDHC There are tricks to working concrete, such
- as to cast braces, rebar, and steel-wire right into the mix.
- Also, some concrete is better damped than other. Remember to oil
- your concrete forms so that they can be removed. Most concrete
- speakers use an MDF front panel, but you can pour one if you use
- cardboard tubes or plywood rings to mold the concrete into the
- shape of a speaker cutout. Alternately, you can make a common
- veneered plywood speaker box and cast concrete inside it for
- stiffening.
-
- Any box can be improved by making the walls thicker, by bracing
- the walls, and by stiffening the walls. The stiffness of a
- material goes up as the cube of the thickness, so a slightly
- thicker material is much stiffer. A thicker panel will also have
- a higher resonant frequency because the stiffness goes up faster
- than the mass.
-
- Consider lining the inside of your speaker with ceramic tile,
- attached with thinset mortar. You can get tile remnants cheaply.
- They are easy to apply and can be added as an afterthought to
- an imperfect box. However, be sure to attach all braces before
- tiling, because it is hard to attach anything to tile.
-
- Also consider bracing any weak parts of the box. For example,
- all joints will benefit from a wooden cleat. The back of the
- box will benefit from stiffeners where the speaker terminals
- are attached. Most importantly, brace the front panel, or
- make it out of a double thickness of material.
-
- 12.22 What size fuse or circuit breaker should I put in my speaker to
- protect it from damage?
- Most modern speakers consist of a box containing more two or
- more drivers interconnected through a network of inductors,
- capacitors, and resistors. One fuse or circuit breaker in
- series with that array can't possible protect all drivers.
-
- Conventional circuit breakers are a very bad choice for speaker
- protection. They add series resistance, series inductance, and
- lousy electrical contacts, all tending to degrade performance.
- Moreover, breakers have a trip characteristic that does not
- match the damage mechanisms of speakers.
-
- Fuses are a better choice, but still are not very good. This
- is because speakers have complex thermal behavior. Loud
- playing will warm up the voice coil making it more sensitive to
- damage. No fuse takes this into account correctly. A fuse
- will do a better job of protecting tweeters, but is still not
- perfect.
-
- If you want to protect a speaker with a fuse, use the lowest
- current, fast-blow fuse which will not blow during normal
- listening. This may trip prematurely in a very loud passage,
- or may degrade sound quality, but it is your best bet for fuse
- protection. For a woofer, start with a 1 Amp fuse and work up.
- For a tweeter, start with 100mA and work up.
-
- There are also cheap tweeter protectors available which contain
- a light bulb and a resistor potted in a small tube. They work
- pretty well, and if you reduce the tweeter network's series
- resistance by a few tenths of an ohm, they are not terrible for
- the sound. But they are audible and not failsafe.
-
- 12.23 Why are speakers labeled + and - or Red and Black?
- Speakers make sound my pushing and pulling at the air with the
- motion of their cones or diaphrams. When a positive voltage is
- applied to the red or "+" terminal on a standard speaker, it
- causes the cone to move outwards and push air.
-
- If you have two speakers side by side and one cone moves out
- while the other moves in, air will move between the two
- speakers but not much sound will escape. The two cone motions
- will cancel eachother. So when you have two speakers close
- together, it is vital that they be wired "in phase", with
- positive voltage going to the "+" terminal of both speakers at
- once. You can do this by wiring the speakers in parallel or
- series. In almost all cases, parallel is preferred. If wiring
- speakers in parallel, the "+" output should go to both "+"
- terminals and the "-" output should go to both "-" terminals.
- If wiring speakers in series, the "+" output should go to one
- "+" terminal. The other terminal ("-") should go to the second
- speaker "+" terminal. The other terminal ("-") of the second
- speaker should go to the "-" output. See the FAQ section on
- amplifiers for more on series and parallel connections.
-
- Even if speakers are not side by side, it is good to wire them
- in phase. For very low frequencies, speakers 15 feet apart
- are effectively close together and the same cancellation
- effects mentioned above apply. For higher frequencies, the
- effects are more subtle but still important. One symptom of
- wiring speakers wrong is that the stereo effect is imperfect.
- Instead of a main sound seeming to come from the center, the
- sound of the lead vocalist, for example, may seem to come from
- outside the room. Other odd effects are also possible.
-
- So when in doubt, always wire "+" to "+".
-
- 12.24 What is the best "stuff" to fill a speaker cabinet with?
- The following discussion will focus on practical facts on speaker
- cabinet stuffing and on sealed systems. Theory is limited help
- in selecting speaker stuffing. Vented system do share a few of
- these same issues and will also be mentioned, but the goals and
- physics of stuffing a vented box are different than those of a
- sealed box.
-
- NHT speakers use polyester fill. Some use a Danish polyester that
- mimics the properties of fiberglas very closely. Excluding this
- special poly, there are two kinds of polyester available: pillow
- stuffing, and audio-spec polyester.
-
- Forget common pillow fill. It's cheap and easy to get. If you
- use enough, it will damp the midrange, and that's a lot better
- than an empty box but it has little effect on lower frequencies.
- "Mountain Mist Polyester Fiberfill" from Stearns Technical
- Textiles is a common, inexpensive material that is said to
- perform as well as audio-spec polyester. Stearns also sells
- "Fiberloft Premium Grade Polyester" to some speaker makers.
- Mountain Mist is a coarser fiber than Fiberloft, but both are
- the same composition. We have no information on differences in
- acoustic properties between Fiberloft and Mountain Mist, but
- Fiberloft makes softer pillows and costs more. Both are
- available from these chain cloth stores:
- Cloth World
- Hancock Fabrics
- House of Fabrics
- Jo Ann Fabrics
- Minnesota Fabrics
- For more information, contact:
- Stearns Technical Textiles
- 100 Williams Street
- Cincinnati OH 45215
- 513-948-5252 or 800-345-7150
- http://www.palaver.com/mountainmist/
- E-mail: stearns@fuse.net
-
- For lining the walls of a vented enclosure to reduce internal
- reflections, or filling a transmission line to absorb the back
- wave, highly absorptive wool or fiberglas are ideal. However,
- these materials do not provide the desired results in a sealed
- system. They will provide more reflection absorption than
- polyester, but the latter is quite good in this regard in the
- critical midrange. In a sealed system you don't want
- absorption at lower frequencies anyway; you want damping and
- isothermal conversion. (Author's note: I have tried "all-out"
- efforts using fiberglas lining and polyester fill to achieve
- the best of both worlds. I found little practical benefit over
- polyester alone.)
-
- Most professional designers agree that practical experience,
- combined with trial and error is the best way to get optimum
- stuffing material, quantity, and method for a given design.
- This is why good designers routinely experiment with fill in
- the development of a new system. If you are designing a system
- that differs substantially in shape or volume or source
- impedance (passive crossover) from one of known reference, you
- will need to experiment to get best performance.
-
- Adjusting the filling is the last step in getting bass right,
- and is used mostly to fine-tune the system Qtc and resonance.
- As increasing amounts of polyester are added to a sealed box,
- the resonance and Q gradually go down. This can be shown
- mathematically to be due in roughly equal parts to the effects
- of simple resistive damping and isothermal conversion. At some
- point, a minimum is reached, and further material reverses the
- trend by taking up volume. An experienced designer can find the
- optimum amount of fill in a few trials by monitoring the
- impedance versus frequency curve as stuffing is added or
- removed.
-
- Filling also has the important effect of reducing internal
- reflections, to reduce standing waves and comb filtering.
- However, the amount of filling has comparatively little effect
- on this.
-
- COPYRIGHT NOTICE
- The information contained here is collectively copyrighted by the
- authors. The right to reproduce this is hereby given, provided it is
- copied intact, with the text of sections 1 through 8, inclusive.
- However, the authors explicitly prohibit selling this document, any
- of its parts, or any document which contains parts of this document.
-
- --
- Bob Neidorff; Texas Instruments | Internet: neidorff@ti.com
- 50 Phillippe Cote St. | Voice : (US) 603-222-8541
- Manchester, NH 03101 USA
-
- Note: Texas Instruments has openings for Analog and Mixed
- Signal Design Engineers in Manchester, New Hampshire. If
- interested, please send resume in confidence to address above.
-