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Different kind of audio subwoofer

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Project by ferstler posted 11-19-2011 06:11 PM 2545 views 12 times favorited 8 comments Add to Favorites Watch

I am a retired audio writer and have had various subwoofers and other components installed in my home over the years, both as items to be reviewed and for personal use. I recently have had a pretty impressive pair of subwoofers in my main audio system (Hsu and SVS models), but while both worked just fine, they wer not visually complementary, and so I decided that I wanted a matched pair of subs that I built myself pretty much from scratch.

The new subs, like the classic Hsu Research TN-1220 (that I also owned for a while) and the SVS cylinder models, were made from 58-inch long, 14-inch diameter Sonotube sections. (Hsu and SVS models varied from 12 to 16 inches.) While Sonotubes are not exactly wood, I did use woodworking tools to build the subs and the top and bottom sections did at least involve the use of mdf boards cut to proper size and shapes.

With the end plugs, caps, and standoff plates (the standoffs and plates are 16-inches in diameter) the subs are each 68 inches tall. The enclosure volume of each is 5 cubic feet, and with the 20-inch-long, 4-inch-diameter, bottom-located ports the tuning frequency is 17.5 Hz. (The woofer drivers are mounted on top, facing upwards.) Each Sonotube interior surface is lined with 2 inches of fiberglass batting to simulate an even larger enclosure volume. I purchased most of the electrical and mechanical parts from Parts Express, with the Sonotube purchased from a local lumberyard and the mdf purchased from Home Depot.

The Sonotube is only available in 12-foot lengths, and it was easy to cut that item down to the two lengths I needed. The top and bottom plugs are mdf (glued and screwed into position just inside the top and bottom rims, and with larger plates glued and screwed to them. above and below. The bottom actually has double thick mdf plates, and then both the top and bottom have additional plates, each held away by three hollow standoff dowels that are secured to the plates by long screws. Each tube was painted flat black, and then standard black speaker grill cloth was wrapped around them and secured in back by Gorilla tape for removal should the cloth be torn or damaged by accident. To serve as hems top and bottom 50-inch long, black-leather belts were wrapped around the perimeters. The top and bottom plates were spray painted with several coats of satin-finish black enamel.

Outboard power to the subs is provided by the first new component I have purchased for some time: a Crown XLS1000 stereo power amp. The vintage (but still working just fine) Yamaha DSP-A1 integrated amp in the installation has both mono and stereo subwoofer outputs, and, well, I have the subs hooked up stereo style. It may not mean much to do it that way, but, heck, it is an offered feature with the Yamaha, so why not use it? The drivers are massive 12 inchers, and the pair, as driven by the 350 watts-per-channel amp, is able to generate 105 dB peaks at 20 Hz at the listening couch 17 feet away from each unit. At 30 Hz (where even most deep-bass music cuts off), even higher peaks are possible. However, most sane listening will never involve levels that loud. As a retired audio writer, I just had to run them up that high to make sure they were able to hold together.

The subs can easily match the performance of any commercially made subs I have auditioned in that room over the past two decades.

Howard Ferstler





8 comments so far

View vipond33's profile

vipond33

1405 posts in 1187 days


#1 posted 11-19-2011 06:38 PM

Invisible sound made visibly pretty. A very attractive pair.
I’m curious if the Sonotube would flex given the strength of those low notes or does it not matter because it is a cylindrical shape? I made my own sub-woofer in a square design and used figure 8 braces internally. The unit doesn’t buzz or rattle at all but connected to my DBX BX-3 everything else in the house does.
Did you design it all yourself in terms of the electronics and dimensions or are there formulas I can consult to make a pair very similar to these (albeit, a little smaller).

-- gene@toronto.ontario.canada : dovetail free since '53, critiques always welcome.

View Brian Strothcamp's profile

Brian Strothcamp

111 posts in 1383 days


#2 posted 11-19-2011 11:27 PM

What did you use for the 20” port? PVC?
If I remember back from my audio days… would this be considered a ‘horn loaded’ sub with the plate on top? I assume that plate is solid (duh i see it is now).

View ferstler's profile

ferstler

333 posts in 2210 days


#3 posted 11-20-2011 03:10 AM

Sonotube enclosures, because they are cylindrical, as vipond33 noted, cannot flex their side panels at all. Poh Ser Hsu, who I have corresponded with for years (and who’s products I have reviewed) was one of the first to use Sonotubes as enclosures for really “serious” subwoofers. Later on, Tom Vodhanel, at SVS used the material for their cylidrical-enclosure subwoofers. During the design phase, I contated Poh Hsu and also contacted Ed Mullen, at SVS, for design pointers.

The enclosures have the same internal volume as an SVS 16-46 model (and somewhat more than a Hsu TN-1220 model), but is taller and narrower than that SVS. It also uses a 16-46 port tube, with the port tube for my second unit being a Parts Express model the same diameter and length. The top panel is made of stacked mdf, 1.5 inches thick, and the bottom panel is triple stacked and 2.25 inches thick. The top, of course, is also mostly driver area (driver diameter is 12.5 inches), so both the top and bottom are not about to flex much in the wrong way.

Brian, the port is a special flared job (both at the input end and at the output end) and is available in sections from Parts Express, at:

http://www.parts-express.com/

This is a very good company to do business with, although there are others out there, like even Amazon, that will be able to supply similar items. I got the Crown amp, grill material, and binding posts from Parts Express, too. The internal wire is regular old 16 AWG lamp cord.

The flared ends are important with a port, because they minimize turbulance noise. The system is a tuned, bass-reflex resonator that has the direct driver output covering the spectrum down to about 40 Hz (the system crossover point to the satellites is 90 Hz), with the driver backing off and the port gradually taking over below that frequency, on down to below 20 Hz. In my 3400 cubic foot room the combination of the subs and the 700-watt Crown amp can deliver 110 dB levels at the center of the listening couch, 17 feet from the two subs. At 30 Hz the combo can put out about 114 dB at that listening distance. The drivers are making a bit of cone-flutter noise that loud, and the practical upper output limits of both working together are 105 (20 Hz) and 110 dB (30 Hz), respectively. Nobody in their right mind (rockers excepted) would care to listen at that level. In addition to being a retired audio writer and hardware reviewer, I was also a recording reviewer for a while, and now I am a Baroque and Classical enthusiast (much of the stuff I listen to does not even require a subwoofer at all) who listens at levels low enough to protect my old ears. So even with pipe organ music the low-bass levels rarely go past 95 dB. The subs are absolutely clean at such levels.

There are internet programs that help a designer skip the Thielel/Small math work and calculate port sizes quickly. One is at:

http://www.psp-inc.com/tools.html

This allows easy calculations once you feed in the internal volume of the enclosure. Of course, figuring that for cylindrical enclosures is tricky, but another web site allows you to quickly calculate the area of a circle:

http://www.calculatorsoup.com/calculators/geometry-plane/circle.php

Once you have that, you can multiply the area number by the internal length of the tube and get the volume. From there, just go back to the first site and calculate the port requirements.

This dual-sub package has no crossover at all, instead making use of the network within the integrated amplifier/controller in the installation. (This is standard procedure with home-theater receivers these days, anyway.) However, the Yamaha DSP-A1 integrated surround-sound amp has both mono and stereo sub-output abilities, and since I have two subs and a stereo power amp I use the stereo feed. It probably means little in terms of acoustic advantages, but it is there, so I use it.

Note that the two drivers are not quite mechanically and electrically matched. One is a big TC-Sounds job sent to me by SVS to beta check years ago. The other is an early stock SVS unit made by Destijl that is roughly equal to the Eminence-built versions that Hsu Research put in its VTF and TN subs. Both SVS units are strong enough to handle any input situation I care to create for them, and since the port and driver-areas determine the spectral balance the differences are meaningless. Parts Express has a bunch of probably equally good subwoofer drivers at reasonable prices.

Howard Ferstler

View Brian Strothcamp's profile

Brian Strothcamp

111 posts in 1383 days


#4 posted 11-21-2011 03:36 AM

Back in the mid 90’s I had a computer program that would help you design 5th order, bandpass boxes and such. It was very good for those days. Do you know of any good software that does such a thing today? I am familiar with Thielel/Small parameters to spec a speaker.

At one time I wanted to build an entertainment stand (a very large one cause I have the room) with built in (speaker) cabinets. I intended to implement some mid-bass specific enclosures, along with subs, center channel and all. I’m afraid components (tv) may not hold up to the vibrations… and reailize I couldnt store anything that would vibrate (photo frames). I would most likely make it a 3pc to try and isolate any bad vibes.

Thoughts on doing such a thing?

View vipond33's profile

vipond33

1405 posts in 1187 days


#5 posted 11-21-2011 03:39 PM

Thank you much for the so very detailed response and links. Given your background I appreciate your advice more amid the clutter of competing claims I find in my searches. And you’re an LJ to boot! Nice to see regular old 16 gauge wire used.

-- gene@toronto.ontario.canada : dovetail free since '53, critiques always welcome.

View Bertha's profile

Bertha

12951 posts in 1383 days


#6 posted 11-21-2011 04:27 PM

Thanks for sharing this! I used to build speakers but kind of got away from it due to the difficulty of getting supplies. It looks like things have changed for the better. I’m kind of a middle of the road hack audiophile/stereophile but I do have a Velodyne DD18+ and a Mirage bipolar for the gap ;)

-- My dad and I built a 65 chev pick up.I killed trannys in that thing for some reason-Hog

View ferstler's profile

ferstler

333 posts in 2210 days


#7 posted 11-21-2011 11:57 PM

Brian, I am not familiar with any computer program for designing speakers. When building satellite speakers, basically, I follow primary design parameters and then diddle away at refining the results with lots of measurements and component-shifting work. The satellites I have built for my second system (mostly for movies) use sealed-box enclosures with woofers from Allison Acoustics (Roy Allison, who was once chief designer at AR, is a friend of mine) and Allison tweeters, too. The mids are Tang Band Chinese jobs that seem OK. The subwoofer in that installation is a Hsu VTF-3 (MK3) model that works fine. The main system in the other part of the house (the one with the huge subs that I built) has a home-built center speaker that I profiled on this site a while back (the enclosure is mostly solid cedar), with the left and right main speakers being refurbished (by me) Allison IC-20 units. The system also has four surround speakers: Allison Model Fours that I have also refurbished. Allison has been out of business for a while (Roy is 83 and retired), so all of the drivers in those systems are 20+ years old.

Gene, yes, 16 AWG wire will work for all but the longest runs, and even then all you lose is a bit of resistance-related gain. While the interior wire on the subs is that size, I did get a heck of a deal at Parts Express a while back and purchased 250 feet of 14 AWG wire for fifty bucks. I use that for all of the speaker runs (the clear insulation is less visually obtrusive than black-insulated wire), some of which, say, to the more distant surrounds, as well as to the more distant sub, are about 35 feet. Not a bad idea to go up a grade in wire size with runs that long.

Al, you have one heck of a sub with that Velodyne. I never reviewed a DD model, but I have reviewed the HGS-15 and HGS-12 models, and of course I recently sold my F1800. Some would say that wanting bass distortion as low as what Velodyne offers with its servo models is kind of gilding the lily, since writers like Tom Nousaine (a friend of mine) have shown that any low-bass distortion below 10 percent should be inaudible. Still, it is nice to push the design limits, and Velodyne surely has done that. Great subs, if you can afford them. I never reviewed a Mirage speaker, but I have heard very good things about them.

Howard Ferstler

View ferstler's profile

ferstler

333 posts in 2210 days


#8 posted 11-22-2011 01:12 AM

Brian, I forgot to mention that vibrations these days probably will not have any negative impact on electronic components, including LED, LCD, andf plasma-type TV sets. With tube gear (TV or audio) in the old days it could, and back when the LP turntable was the way to play recordings vibration could be a problem then, too. However, with today’s solid-state stuff vibration is no big deal. If it were, powered subwoofers (those with the amps mounted in the enclosure along with the driver) would be having big problems in a big way.

On the other hand, any kind of stand or rack or equipment cabinet that has knick-knack style items sitting on it could be in trouble if the speakers are in the same box or rack. Even knick knacks some distance from the speakers can be a problem. I solve that (kind of) by putting fet pads under most such items, and I even put felt pads on the backsides of the various oil and acrylic paintings hanging on the walls in my wife’s art collection. Some of those are up to four feet square.

Interestingly, some people think you can localize bass that reaches up to, say, 80 or 90 Hz, making a solo subwoofer set up off to the side problematical. Actually, it should not be (I have proved this to myself both during tests and accidentally), but any artifacts sitting near a subwoofer may buzz or vibrate enough to call attention to themselves, and that is sometimes interpreted by the listener as if the sub itself doing so. The only way a sub could actually call attention to itself in terms of localization if the crossover is at 90 Hz or lower would be if the sub has excessive amounts of harmonic distortion. Those harmonics would be high enough up in frequency for them to deliver directional clues as to the location of the sub. Solution: make sure the sub is a low-distortion device. Anything below 10 percent THD at 90 Hz and below is low enough. Most good models achieve this goal, at least down to, say, 35 Hz. The super-duper jobs can do it down to 20 Hz.

Howard Ferstler

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