cs004017@cs.brown.edu (Steve Liebling) (04/12/91)
I am considering building a subwoofer and I have a few questions: 1) Has anyone had experience with Parts Express? Are their drivers and crossover decent? How are their prices? 2) I read about using a tube for a subwoofer, but how do you set-up the woofer in a room? Does it go with the woofer firing downward using short stands on which to rest the tube? Do you lie the tube on its side and have the woofer fire sidewides? How about suspending the tube upright using string from a ceiling? It seems that this method might better isolate the speaker from the room acoustically but might not be good for resonances. (I don't mean to be pretentious as to understanding all this, I'm just putting forth some possibly imaginative hypothesis). 3) What type of material might be good for an enclosure (if I opt for the non-tube type)? Plywood? How thick? 4) What about amplification? I mean, the most efficient use of the subwoofer would be to amplifiy only the low end, but this entails, having a crossover before the amplifier stage, right? How would this be possible? 5) What in the world is a double voice-coil driver? Simply an electrodynamic transducer with two voice coils suspended in a cylindrical magnet hooked to a cone? Why two, and not just one bigger one? 6) If I use the same amp for my speakers (Boston Acoustics A60's) as for my subwoofer, then do I need a dedicated attenuator for the subwoofer to match the efficiency of my speakers? If so, would it go after the crossover or before? Thanks in advance, Steve cs004017@cs.brown.edu
gstead@maestro.mitre.org (Graham Stead) (04/15/91)
In article <10976@uwm.edu>, cs004017@cs.brown.edu (Steve Liebling) writes: |> |> I am considering building a subwoofer and I have a few questions: |> |> 1) Has anyone had experience with Parts Express? Are their drivers |> and crossover decent? How are their prices? Nope, sorry. I've ordered stuff from Madisound and A&S Speakers, and I much prefer Madisound. |> 2) I read about using a tube for a subwoofer, but how do you set-up |> the woofer in a room? Does it go with the woofer firing downward using |> short stands on which to rest the tube? Do you lie the tube on its side |> and have the woofer fire sidewides? How about suspending the tube upright |> using string from a ceiling? It seems that this method might better |> isolate the speaker from the room acoustically but might not be good |> for resonances. (I don't mean to be pretentious as to understanding all |> this, I'm putting forth some possibly imaginative hypothesis). I don't know if I'd suspend it from the ceiling. The driver and enclosure wouldn't be coupled or "connected" to anything, and swing, bounce, or vibrate in a way that's detrimental sound reproduction. The other possibilities would work fine, because the very low frequencies you're reproducing should be omnidirectional. |> 3) What type of material might be good for an enclosure (if I opt for |> the non-tube type)? Plywood? How thick? Most people use 5/8" particleboard. It's cheap! I read an article where a guy built a box using aluminum and vinly siding - the box was great but expensive. |> 4) What about amplification? I mean, the most efficient use of the |> subwoofer would be to amplifiy only the low end, but this entails, |> having a crossover before the amplifier stage, right? How would this |> be possible? True. You could build a dedicated amplifier (Velodyne, who make great subwoofers, use a Class D because it only reproduces < 100 Hz. or so). Then you would need an active crossover. But you can still use your subs with a single amp: run the output into a passive crossover, with the low output going to the sub and the high output going to your regular speakers. |> 5) What in the world is a double voice-coil driver? Simply an |> electrodynamic transducer with two voice coils suspended in a |> cylindrical magnet hooked to a cone? Why two, and not just one bigger one? I don't know how they're constructed...but in my experience they're used for connecting left & right amplifier outputs to the same driver. |> 6) If I use the same amp for my speakers (Boston Acoustics A60's) as for |> my subwoofer, then do I need a dedicated attenuator for the subwoofer to |> match the efficiency of my speakers? If so, would it go after the |> crossover or before? I think "L-pads" are commonly used. It's common practice to put them in series with the satellite speakers' signal because they're typically more efficient and can be lowered to the correct level. -Graham
km456265@longs.LANCE.ColoState.EDU (Kevin Melsheimer) (04/15/91)
As to your first question: 1) Has anyone had experience with Parts Express? Are their drivers and crossover decent? How are their prices? I have personally ordered many times from Parts Express and they are a reputable company. When you call their 800 number you can expect to see your order in no more than two weeks, one week usually being the case. I have found that their quality is good to excellent, the latter being attributed only to their line of Polydax speakers. The prices are compared to many other mail order houses, but their sale prices have yet to be topped by any mail order firm that I know of. I don't have any experience with their crossovers; but my friends that have ordered them have been quite satisfied. As for your second question concerning using a tube as an enclosure for speakers, I have looked at this method for building speaker boxes and have dismissed it due to the length of tubes required to tune subwoofers properly. With the 15" Thruster woofers I am currently using it would be impossible to fit a properly tuned 15" tube within the length of any room in my house. Your third question asks about speakerboxes. I currently am using a box of 11.3 cubic feet with a tuned port of eighteen inches in length and eleven inches in diameter. This tunes the box to around 29 Hertz and the frequency cuttoff for the box is about 28 Hz. My box is made out of 3/4 inch plywood and I would recommend going with inch thick plywood if you can afford it. Bracing is also very important in a subwoofer enclosure. I use two x twos throughout the structure of the box, which I might add is quite big. As to your fourth question of having a crossover before your amplifier, yes it is possible. I am currently using a 100db per octive active crossover crossed over at 112 Hz. If your would like more information on active crossovers and speakerbuilding in general, I would advise you to read "Enhanced Sound: 22 projects for the audiophile." It is my opinion that this book is the most comprehensive book on Audio that exists for the beginning audiophile. Your fifth question asks about dual-voice coil subwoofers. These units sole purpose in life is to be driven by an amplifier that fails to have the capacity of beign bridged into mono. I would not recommend using a dual voice coil woofer if you are a true audiophile. The bass will get quite distorted if the bass from the two channels being input are different from each other. This is due to the speaker trying to go in two directions at once--the net result is distortion. Dual voice-coil units do have one practical use though. If you own an amp that can put power into two ohms, you will find that you can wire the woofer in parallel (if the speaker was originally four ohms) and have a lot more power available from your amp. In your fourth question you ask about matching speaker efficiencies. This is important if you are driving the subwoofer off the same amp as your main speakers (your Boston Acoustics A60's). I would not recommend doing this, however. A subwoofer requires a lot of power and if you want to use an active crossover, you will be forced to use another amp. Matching efficiencies are unimportant when you can control the amount of power going into each speaker. If your subwoofers are more efficient than your A60's (which will probalby be the case) you can simply put less power into them to compensate for this. The speakers I would recommend to you for building subwoofers would be the Thruster 12" found in Parts Express. This speaker has a very good frequency response if ported properly (down to 18 Hz). The box size will be quite large, however. Using a box size of 10.8 cubic feet will provide a speaker that has no dips or peaks larger than +/- .5 dB under 150Hz. If you have the space, I would go with these. I have found that the Thruster line of speakers have the best sound quality for the price for woofers (For bass-reflex applications). If you find a better speaker for the money, please notify me. I hope you find my information usefull, write me if you have any more questions on subwoofers, Kevin Melsheimer km456265@longs.LANCE.ColoState.Edu
mbk@jacobi.UCSD.EDU (Matt Kennel;I11 CMRR;534-4511) (04/16/91)
In article <11040@uwm.edu> km456265@longs.LANCE.ColoState.EDU (Kevin Melsheimer) writes: >Your fifth question asks about dual-voice coil subwoofers. These units >sole purpose in life is to be driven by an amplifier that fails to have >the capacity of beign bridged into mono. I would not recommend using a >dual voice coil woofer if you are a true audiophile. The bass will get >quite distorted if the bass from the two channels being input are >different from each other. This is due to the speaker trying to go in >two directions at once--the net result is distortion. This is bogus. All that happens is that the forces generated by each coil ADD. Remember _Sum_ (\vec{F}) = ma. The forces are being applied in the same place. You're not going to create enough force to physically rip apart the coil assembly, so don't worry about it. It has the same effect as if you added two low-level signals together (via some type of amplifier circuit) to create a monophonic signal, and then amplified that and passed it to the speaker coil. (It's possible that there may be odd electrical effects as there's a mutual inductance between the two coils, so it may screw up a badly designed amplifier.) Matt K mbk@inls1.ucsd.edu
ivanov@imag.imag.fr (eric ivanov) (04/16/91)
In article <11039@uwm.edu> gstead@maestro.mitre.org (Graham Stead) writes: >In article <10976@uwm.edu>, cs004017@cs.brown.edu (Steve Liebling) writes: >|> >|> 5) What in the world is a double voice-coil driver? Simply an >|> electrodynamic transducer with two voice coils suspended in a >|> cylindrical magnet hooked to a cone? Why two, and not just one bigger one? > >I don't know how they're constructed...but in my experience they're >used for connecting left & right amplifier outputs to the same >driver. > Cantilene (french speaker builder) utilize double voice-coil drivers in its three-way two-driver designs (bass and midrange are directed to the two coils of the double voice-coil driver, high frequencies are handled by an ordinary tweeter.) Another french speaker, Vecteur Premiere, uses double voice-coil drivers, but I don't remember in which manner. I guess this is to reduce intermodulation distortion, but that's only a guess. Both speakers received rave reviews in France (and in Germany for the latter.) >-Graham eric -- eric ivanov@imag.fr "-Fishing ? -Not today."
rubin@cis.ohio-state.edu (daniel j rubin) (04/17/91)
> I am considering building a subwoofer and I have a few questions: > > 1) Has anyone had experience with Parts Express? Are their drivers > and crossover decent? How are their prices? > I live in Dayton, Ohio and I buy parts from Parts Express all the time. The drivers they offer are good quality, I am partial to Pyle, and are priced way below retail. I have never used one of their crossovers, but I have seen them up close and they are very well made. They are great about returns so if you have a speaker and use it for 15 days and don't like the way it sounds you can return it for a full refund as long as the terminals have not been soldered. After 15 days you have 90 days to exchange the speaker. You may also want to take a look at MCM electronincs in Dayton, Ohio, they sell pretty much the same stuff so both tend to keep each others prices low. MCM sells more Plye products, including auto amplifiers at great prices. - Dan Rubin
UCHUCK%UNC.BITNET@ncsuvm.ncsu.edu (Chuck Bennett (919)966-1134) (04/18/91)
The best sounding subwoofers I ever heard were in the home of a TAS reviewer. They were simplicity at its quintessence. Two 18" Hartley drivers mounted in the floor with a 20" x 20" cold-air return grate as the cover and insulation batting hung loosely around the underside. The crossover was at 50Hz. The sound was tight, accurate and AWESOME all the way down to where it became a "feeling" not a sound (<16Hz). Chuck
jhenders@wimsey.bc.ca (John Henders) (04/18/91)
On a different note concerning subwoofers. JBL seems to be useing something called a triple bandpass design on their newer boxes. Has anyone seen any articles on the theory behind this? I'd like to see some info on volume and porting for various drivers. The club I work for just put in a pair that have 2 15' drivers mounted in a centre chamber, magnet to magnet, facing into two other ported chambers. These boxes are speced to be +/- 3db down to 32hz, and run at around 90db 1watt/meter. They handle 800 watts and I can attest that for their size, they are very efficient. I saw the subwoofers JBL is using with their Control series sattallites recently, and they seem to be using the same design. Anyone have further info, as our local JBL rep knows less about this stuff than I do? John Henders Vancouver,B.C.