# Different kind of audio subwoofer



## Howard Ferstler (Sep 27, 2007)

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 Research 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 acoustically 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.

Sonotube is normally 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 top plates have large cutouts for the woofers and the bottom plates have smaller cutouts for the ports.) 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 in the future. 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


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## H. A. S. (Sep 23, 2010)

That is very impressive! For the true audiophile, I see. The Crown amps can't be beat, IMO. Clarity, and power. Would have liked to see the build pics.


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## woodnthings (Jan 24, 2009)

*Beautiful, beautiful*

Not only do they look great, but I'll take your word on the sound!
I've been wondering what to do with a pair of 18" Electrovoice paper cone subs that are in a ported bass reflex enclosure. Would they work in this vertical application? Or are they just too old to bother with? Another question...the covers you have on the tops, are they for protection or do they serve an additional function?
Nice work out, very sophisticated in my opinion. :thumbsup: bill


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## knotscott (Nov 8, 2007)

Nice job Howard! That's a great look. :thumbsup: Did you consider doing a transmission line at all?

The Merlin loudspeakers used to be made from Sonotube material, but they had a rectangular shape. I also seem to recall a cylindrical downfiring subwoofer that used a membrane on the top that worked like a passive radiator....I think they might have been called Tymphany, but this was back in the early 90's and am not all that clear about it.

Enjoy!


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## aardvark (Sep 29, 2011)

Howard, I like this a ""Whole Lot"".
I'm also a audiophile, and yet at present am just running a Harmon Kardon amp/receiver which is a surround unit.
I've built many speakers in the past and was a subscriber to Speaker Builder Magazine, before sold to whoever has em now. I have 9 speakers up and hooked up at present, but run 7 of them. I made 2 pyramid shaped sub , 3 sided and a base, holding a 10" downfiring spkr. The unit is 4" up from the floor. 3" ported.. It sits under the couch and shakes up as well as surprises whoever sits there when the couch rumbles. For those are matching pyramid (3 side, triangular) satellites. 4 each plus 1 more for the voice (center mode) speaker. They hold a 5.25 mid and a piezo.

My faves, however, I'm running towers made out of 3/4" MDF hi density and painted with Flektone paint and then clearcoated, also using oak edgings cut in radiuses. The enclosures have 6 sq ft for the 12" downfiring to the floor subs. Also ported 3". The mid/highs are in the same case but separately enclosed to keep freq's from crossing over into the other area cavity.

But I LOVE this sonnetube idea, and now you might have me dissecting these towers and trying something new.
"""Could you post the crossover circuit you used? """
I got stock units from Parts Express. They seem ok, and the ranges I worked with seemed fine. 

Oh, and any concrete store has sonnetubes in nearly any size you want , or can quickly get them. 
I'm thinking 2 sizes of tubes with an airgap filled with solid foam would insulate very well too.

LOVE THIS THING !


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## H. A. S. (Sep 23, 2010)

woodnthings said:


> Not only do they look great, but I'll take your word on the sound!
> I've been wondering what to do with a pair of 18" Electrovoice paper cone subs that are in a ported bass reflex enclosure. Would they work in this vertical application? Or are they just too old to bother with? Another question...the covers you have on the tops, are they for protection or do they serve an additional function?
> Nice work out, very sophisticated in my opinion. :thumbsup: bill




Those 18s you have, remind me of one of the finest bass rigs I ever owned, back when I played METAL. It had 2--18" folded horns reflex cabinets. 1000 watt SUNN head. That bad boy made your heart and lungs vibrate; probably the cause of my current problems:laughing: No, just kidding about that. Make you a couple of folded horn cabs, Bill.:thumbsup:


That SUNN head only needed to be turned up to 5, to play large venues. Putting it up to 11, would have caused another stage collapse.


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## Howard Ferstler (Sep 27, 2007)

To H.A.S. I am kind of mad at myself for not taking photos during the project, but I was caught up in the work and did not think of using a camera until they were done. The units are really so simple that photos are not really required, but here is some more descriptions to paint a picture in print. 

Picture the tubes coated on the inside with 2-inch thick fiberglass normally used to wrap furnace pipes. They come with the fiber material glued to metalized paper, but I removed the paper and just used the fibers. I used spray adhesive to hold the stuff in place. Fiberglass actually allows the driver to "see" a larger volume than simple empty space. It is not functioning as any kind of vibration-damping material.

The top end cap is a 14 inch disc inserted, with a 16 incher screwed and glued to it. Both sections have 11-inch holes cut to accommodate the surface-mounted woofer driver. On the bottom, a similar 14-inch mdf disc was inserted and glued in place, and two 16 inchers were glued and screwed to that. A proper-sized hole had been cut through all three to accommodate the 20-inch long, 4-inch diameter port tube. I painted the attached-together plates before installing them, using blue tape to keep the surfaces of the glue points free of paint. 

To woodnthings. If the 18 inchers are not in bad shape you could use them, but of course the tube diameter would have to be considerably bigger than what I used. The result would be a short sub that might actually serve as an end table. 

The idea is to get the internal volume of the enclosure to dovetail with a certain port length and diameter. The actual size of the woofer and its excursion limits and its thermal capacity will determine how loud the unit can play, but the volume of the enclosure and the port size will determine the extension below the point where the driver itself begins to roll off. Port size calculations used to be problematical (the Thiele/Small parameters are for math geeks), but now there is a web site that can do the calculations for you:

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

With box-shaped inclosures all you need to calculate is internal volume, using H x W x D (internal measurements). Of course, with a cylinder enclosure things are a bit more involved, but there is a web site that calculates circle areas for you at:

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

Once you have the area in square inches you just multiply it by the internal length of the tube in inches and you have the volume in cubic inches. Divide that by 1728 and you have the volume in cubic feet. Then, just go back to the previously noted site and let it calculate the port parameters. Once you have those, you can buy a port kit from Parts Express. 

The standoff plates on tops are there just to protect the drivers. The space is about 2.5 inches. The plates on the bottoms are 2 inches from the port exit, and they probably do dampen port noise a bit down there. 

To knotscott. I did not consider a transmission line. Both Hsu Research and SVS have done well with basic ported designs in cylindrical enclosures, and so I figured that if it worked well for them it would work well for me.

To aardvark. The subs and amp have no crossover in operation. Instead, the on-board crossover in my Yamaha DSP-A1 surround integrated amp is used. The frequency is 90 Hz, with 24-dB slopes. The Yamaha has both mono and stereo subwoofer outputs, and since the amp is a stereo job and there are two subs I am using it that way. The acoustic advantages are probably nil, compared to if the two subs were getting a split mono signal, but, heck, the processor offers the feature so why not use it. 

Note that the subs roll off slightly below 30 Hz, and so I am using a Hsu Research "Optimizer" equalizer to moderately boost the bass below 40 Hz. The rise is about 6 dB at 20 Hz, which compensates for the acoustic rolloff. In many rooms such EQ would not be requred, especially with paired subs like mine, which add together coherently (+6 dB instead of +3 dB) at very low frequencies. Where this happens depends upon the distance between the subs. Still, I like what the Optimizer does in this case.

Howard Ferstler


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## woodnthings (Jan 24, 2009)

*Great response, thanks*

I think Howard needs his own sub forum here....just sayin'.
Speakersnthings? :yes: bill

Audiofiles?


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## aardvark (Sep 29, 2011)

Woodnthings
I'm up for that.
It is it's own artform , just like guitar bodies and such.

Howard, thanks I get the crossover point and the process. Generally I'll run the sub/bass at a cut off point of 100-125hz(125 is actually a shade high), since the mids that I use aren't taxed as hard on the low end. 

Beautiful job, (again). I was sharing the photo's and processes with a friend this morning, who is an audiophile and also worked in the radio industry for 30 years. He runs higher power than I am accustomed to.
He likes as well.


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## aardvark (Sep 29, 2011)

Oh, and thanks for the On-line calculators.
I never looked on-line to see if they existed. I had books on the matter.

I saved the links.


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## Dadoo (Nov 21, 2011)

New here, been lurking a bit but speaker building actually got me the wood working bug. I deal with speakers/speaker design and audio as my day job, and those are indeed very nice subs Howard. I am currently running two Aura 18 inch beasts is sealed boxes eq'd to the room and there just is no substitute for having oodles of clean deep bass available on demand. For any that are interested there is a lot of free software out there for the crossover design, box sizing and that sort of thing. Winisd and passive crossover designer are the most popular.


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## aardvark (Sep 29, 2011)

Probably the most impressive speakers I ever heard were the large Magnaplaners , but the bass was a tad light, and it took an incredible amount of power to drive those magnetic sheets. Backed up with a good sub, they came alive.

Likewise speakers got me into shop building with wood, but I had been doing construction for years prior.
Not the same as shop stuff. Actually straight wood is not the best for cabinets. MDF High density is the way to go, and the whole point is to eliminate cabinet resonances, and sound escaping causing a reverse wave interfering with the forward wave. Even ported speakers can conflict and either become too false and boomy or without a port, too tame. I experiment when done with the design, by partially plugging off the ports with foam and listen for obvious changes till I get what I like....and everyones ears hear differently.


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## Howard Ferstler (Sep 27, 2007)

Yes, mdf has the weight and density needed to help quash cabinet resonances. For me, the problem with mdf is that I have an aesthetic revulsion to veneer. Of course, with mdf you can also just paint the stuff black or some color, and I suppose that is more straightforward than laminating it with veneer wood.

Those subs of mine are actually made of hard-pressed cardboard. The stuff is stiff, of course, (Sonotubes are designed to be used as concrete post molds), and the main advantage is that a round shape cannot be bent to a curved shape like what we have with flat-sided boxes. Consequently, the sides are essentially inert. The tops and bottoms are thick mdf (1.5 inches on top, 2.25 inches on the bottom, and with the top most of the surface is made up of installed woofer driver, anyway.

I have made speakers with wood other than Sonotube materials or mdf. The center speaker in that main system has top, bottom, and side panels made of 1.5-inch-thick cedar, with the front and back panels mdf. In another part of the house there is a home-theater rig that has speakers with the tops, bottoms, and sides made of simple pine, but with the front and rear panels mdf. Internal cross bracing was also used in all of them. This mix of materials helps to prevent resonances at specific frequencies being too loud.

The photos show the center speaker in the main room and one of the units in the AV system. (Both build projects for them have been profiled some time back on this site.) Both use vertical MTTM arrays, with small woofers on the bottom. The woofers can be small, because subwoofers handle the low bass in both systems.

Howard Ferstler


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## aardvark (Sep 29, 2011)

I Like that as well. Rather large for a center channel. but very cool.
That cedar is unique.

Exactly on the round shape to a speaker radius vs a squared cavity. Resonances flow better and (in your case) straight line. No bouncy bouncy in the cavity. Very desirable and it would be a pleasure to hear em, to see how they perform. Guess I might have to consider doing something like it to try em.

I get your dislike of speakers that are veneered , and worse yet is plastic contact paper finishes. I like mdf for it's density, and likewise don't veneer boxes. Mine are 3/4" mdf, painted with Flekstone paint, giving them a stone like finish. Wood finishes sometimes don't fit a very modern decor. They don't fit in mine at all, since we are heavily ultra contemporary. A piece here or there is fine, but we gotta watch it.

I had a cabinet maker friend that handed me some bendable plywood. All grain patterns ran the same direction and picking up a sheet was a trick due to it's flexibility. It's thickness varied, depending on the application and radiuses you wanted to bend it to. It has possibilities in the "round" format. It also was grained with a variety of wood finishes to choose from, BUT, again, the face is a veneer. and it's not cheap per sheet.


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## 240sxguy (Sep 13, 2010)

Looks nice, I have seen a bunch of the sonotube built subwoofers but I really like the endcaps you did. They look great. I am going to be building a few subs shortly which will end up looking like plant stands. Fun stuff. Who did you review for?


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## aardvark (Sep 29, 2011)

Seen em (tubes) in automotive applications, but rarely in household setups.
This is a particularly modern smooth project, which has me inspired.


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## Howard Ferstler (Sep 27, 2007)

240sxguy said:


> Looks nice, I have seen a bunch of the sonotube built subwoofers but I really like the endcaps you did. They look great. I am going to be building a few subs shortly which will end up looking like plant stands. Fun stuff. Who did you review for?


My early articles, back in the 1970s and 1980s, were for High Fidelity and Stereo Review, although they did not allow many outsiders to publish stuff. I also wrote one article for Audio, working with an electrical engineer who helped to keep me from making too many errors.

My first big run, while still writing occasional stuff for the publications listed above, was with Fanfare Magazine, which specialized in record reviews, but did have a trio of audio columnists. (One was rational, one was a lunatic, and then there was me, Mr. Ultra Rational.) From there I went to The American Record Guide (Fanfare decided that there were too many audio writers on the "staff" and my often cynical and cold-blooded approach tended to alienate some of the more impressionable subscribers.) The ARG eventually was sold to a guy who had little use for audio writers (he was very nice, and we parted company amicably), so from there I went to The Sensible Sound (a kind of rational, but still "fringe" magazine), and wrote for them until the magazine folded. (The reader market kept shrinking.) After that, retirement was the remaining option. Note that audio writing was a sideline for me. My main career involvedf working for a university library, where, in addition to other tasks I was the purchasing agent for the music library's score and recording collections. 

During this journalistic romp, I also managed to publish four books on audio-video (well, two were actually recording-review books) and also helped to edit and write for the second edition of The Encyclopedia of Recorded Sound and The Routledge Guide to Music Technology. A quick Google search will pull up the details.

Howard Ferstler


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## Howard Ferstler (Sep 27, 2007)

aardvark said:


> Seen em (tubes) in automotive applications, but rarely in household setups.
> This is a particularly modern smooth project, which has me inspired.


 
Actually, a few years back Hsu Research started out its subwoofer business with cylinder subs designed specifically for in-home use. A bit later on SVS started out doing the same kind of work, and in the process ended up stealing a fair amount of business from Hsu, who had the original idea of making super-performance subs for home use that normal people could afford. It is a dog-eat-dog world out there in audio land. Both companies are competent.

Howard Ferstler


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## Howard Ferstler (Sep 27, 2007)

aardvark said:


> I Like that as well. Rather large for a center channel. but very cool.
> That cedar is unique.
> 
> Exactly on the round shape to a speaker radius vs a squared cavity. Resonances flow better and (in your case) straight line. No bouncy bouncy in the cavity. Very desirable and it would be a pleasure to hear em, to see how they perform. Guess I might have to consider doing something like it to try em.
> ...


It is large for a center channel, but even with two mids, and two tweeters, and a woofer it is small compared to the flanking Allison IC-20 models, each of which has four mids, four tweeters, and two woofers. These were Roy Allison's signature units. Roy was once the chief engineer at Acoustic Research Corporation (AR), back in the days when the AR-3a and AR-LST were industry reference standards.

Two shots of one of the Allison units are attached. One shows it with the grills installed. The other shows it uncovered, in the same room before we had the walls redone some time back. I refurbished those 20-year-old speakers last year, rebuilding the crossover networks (changed out the resistors and capacitors, but retained the copper-wire chokes), and making some changes to the woofer mounts. Each weighs in at 100 pounds and is 4 feet high, so the 53 pound weight and 38-inch height of the center unit I built to work with them (they use the same mid and tweeter drivers) is not all that extreme.

I like the idea of the Flekstone paint you used.

Howard Ferstler


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## aardvark (Sep 29, 2011)

Gotcha on the other speakers to match the center.

I hadn't realized how dog-eat-dog it was out there until I tried to market a line we put together.
It added complications when we were doing our best (and can't be done totally) to use USA made parts.
In the end, we sold a few to some locals who were quite impressed with the setups, and decided we really couldn't compete, be profitable and hold to our original intent.... an american made speaker.

We dealt with Pyle out of Indiana, which made a pretty good speaker (yeah, there are better). Most of their products were automotive based in design. We used em in home units. Did a lot with Parts Express for hardware and a few small items like crossovers, and some smaller stuff. 
In the end, we gave it up before we dumped big money in it, and moved on. I still love playing though.

And yeah, I remember Roy Allison and the AR series.
I also remember those boxes. They were a nice sounding unit. Quite directional , almost to a fault if not set in the right surroundings. Very smooth even sound.
......
On the cylinder design, I simply don't recall seeing them out there, but understand who HSU was and really never followed em close either. I see it is a design from a cavity reflectivity (or lack of) standpoint that make very good sense, however.

Oh, and hope you had your fill of turkey and don't have to put up wit 2 weeks of leftover bird. Happy Thanksgiving and may you and yours be blessed.


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