Would this crazy subwoofer idea work? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 34 Old 02-08-2018, 03:03 PM - Thread Starter
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Would this crazy subwoofer idea work?

I accidentally posted this in the subwoofer section, and they sent me here. I an pretty new to audio, but have been learning.


I just finished the 5.1 setup for my wife and kids. It is all Klipsch, but even it is a little odd. I have an RC-7 center and then RF-5 fronts, but the RF-5 have tweeters and crossovers from some RC-7. Since the woofers in the RC-7 and RF-5 are identical, kind of have 3 RC-7 up front, albeit in different cases. My surrounds are the two RC-7 with the RF-5 tweeters and crossovers. It creates what I perceive to be a unified field of sound with no edges or gaps. I may hook up the RS-7 surrounds instead, but that is for later.

My subwoofer is an SVS PB2 Plus, which weighs 175 pounds and has 2 12-inch drivers. I quite like it, but I have minimal experience with subwoofers. I wanted a B4 Plus that is for sale in San Diego. It has 4 drivers and weighs 200 pounds. Must have been made around 2000. The guy wants $900, and I could get it to Seattle for under $200. But people have warned me about old subwoofers. So I turned my attention to newer subwoofers.

The SVS round subs really caught my eye. And from what I have read, they are acoustically the same. Not sure about that. And then a few people told me to just build my own, that it was relatively easy and a lot cheaper. So that led naturally to the idea of making my own round subwoofer. I am told that people do or have, but I have not seen much about it.

And once that set my mind going, it just took off, and I realized that that circle would actually be considerably smaller that the square ones, and then that made me consider a taller round sub to make up, say 6 feet tall, and that made me think about multiple drivers, which reminded me of the B4.

So here is the question. Would it make sense to try a six foot tall round sub with a 20 inch interior diameter, and then put 6 drivers in it, three pointing out from each half, and set them up with a push-pull system? That may be a stupid idea, but it actually is the one I am trying to evaluate.

I thought I was the only one, and then I came across this. Any thoughts or comments are welcome. And if this is stupid, just tell me, I can take it.

http://spinditty.com/instruments-gea...nder-subwoofer

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post #2 of 34 Old 02-08-2018, 03:05 PM
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Quote:
Originally Posted by SeattleDavis View Post
I accidentally posted this in the subwoofer section, and they sent me here. I an pretty new to audio, but have been learning.


I just finished the 5.1 setup for my wife and kids. It is all Klipsch, but even it is a little odd. I have an RC-7 center and then RF-5 fronts, but the RF-5 have tweeters and crossovers from some RC-7. Since the woofers in the RC-7 and RF-5 are identical, kind of have 3 RC-7 up front, albeit in different cases. My surrounds are the two RC-7 with the RF-5 tweeters and crossovers. It creates what I perceive to be a unified field of sound with no edges or gaps. I may hook up the RS-7 surrounds instead, but that is for later.

My subwoofer is an SVS PB2 Plus, which weighs 175 pounds and has 2 12-inch drivers. I quite like it, but I have minimal experience with subwoofers. I wanted a B4 Plus that is for sale in San Diego. It has 4 drivers and weighs 200 pounds. Must have been made around 2000. The guy wants $900, and I could get it to Seattle for under $200. But people have warned me about old subwoofers. So I turned my attention to newer subwoofers.

The SVS round subs really caught my eye. And from what I have read, they are acoustically the same. Not sure about that. And then a few people told me to just build my own, that it was relatively easy and a lot cheaper. So that led naturally to the idea of making my own round subwoofer. I am told that people do or have, but I have not seen much about it.

And once that set my mind going, it just took off, and I realized that that circle would actually be considerably smaller that the square ones, and then that made me consider a taller round sub to make up, say 6 feet tall, and that made me think about multiple drivers, which reminded me of the B4.

So here is the question. Would it make sense to try a six foot tall round sub with a 20 inch interior diameter, and then put 6 drivers in it, three pointing out from each half, and set them up with a push-pull system? That may be a stupid idea, but it actually is the one I am trying to evaluate.

I thought I was the only one, and then I came across this. Any thoughts or comments are welcome. And if this is stupid, just tell me, I can take it.

https://spinditty.com/instruments-ge...nder-subwoofer
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post #3 of 34 Old 02-08-2018, 03:09 PM - Thread Starter
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Originally Posted by David Varner View Post
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Let's try this. This worked for me. And I think first one is now fixed. Thanks.

http://spinditty.com/instruments-gea...nder-subwoofer
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post #4 of 34 Old 02-08-2018, 05:46 PM
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look up sono tube subs
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post #5 of 34 Old 02-08-2018, 07:02 PM - Thread Starter
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I have pretty thoroughly researched Sonotube and am in discussion with a guy named Tim McKee there. I need to call him back. That might work and simplify things for me. The odd thing was that he said 20 inches by 12 feet long would have a wall thickness of 0.180. As I read the chart it would be 0.97. I am trying to figure out what the chart means. I am attaching it.

One of my struggles is getting a clear grasp of some of the basics. I seem be finding conflicting information

Do I want thicker walls or thnner walls. Can walls be too thick?

DO I want tight spaces inside the sub or more space?

How close to the tube size and driver size need to match. is 20/18 good or would 22/18 be the same, worse or better.

I feel stupid for asking these questions, but after a lot of research, I just do not know the answers.
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post #6 of 34 Old 02-08-2018, 08:02 PM
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Vanu u seriously need to chill out my friend.
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post #7 of 34 Old 02-08-2018, 08:05 PM
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Take the time to understand the basics of sub design first. You need to know that. More research!
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post #8 of 34 Old 02-08-2018, 09:36 PM - Thread Starter
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Originally Posted by RoboAVS View Post
Take the time to understand the basics of sub design first. You need to know that. More research!
I am very keenly aware of that. Fortunately, research is what I love to do, and I already am deep into it. I guess my question was whether this idea is worth researching. Of course, I will learn the basics along the way, but it would be a lot more fun if I thought that this was actually a possibility.

With the 5.1 setup, my problem was that I kept doing more research instead of doing something, so I finally made myself just act. This is all very intriguing. When I first got started, I equated sound waves with light waves and assumed that they were part of the same spectrum, but they are as different as can be. I have learned a lot of things, but I still feel just as dumb.
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post #9 of 34 Old 02-08-2018, 09:58 PM
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Originally Posted by SeattleDavis View Post
I have learned a lot of things, but I still feel just as dumb.
I got hooked on speakers as a teen and decided to become a loudspeaker design engineer because of that! The more I learned, the more I found out "it's actually more complicated than that!" Fortunately, I found it fascinating, not discouraging.

Now to some of your questions. First off, I really don't get what you mean by "6 drivers in it, three pointing out from each half, and set them up with a push-pull system?" Are you talking about stacking several cylinders on top of each other? But then what is "three pointing out from each half"? Do you mean the woofers would be vertical, i.e. pointing out along a radius from the centerline of the tube?

A cylinder due to its geometry has very strong walls compared to boxes. They can be available formed from cardboard maybe much less expensively than building an equivalently strong box. A thicker wall will resonate less, though the thickness can affect the internal volume somewhat. To go a step further, you could even have an inner and an outer cylinder, and fill with sand &/or shot in between. Or concrete, like a buddy of mine was doing with some quasi-KEF 103s. The cylinder radius does not need to match the woofer diameter exactly.

Some folks make the radius extra large so they can fire the port out the same end as the woofer &/or to offset the woofer to make any internal resonances less symmetrical.

Another consideration is that long cylinders have resonances-think "organ pipes"-so you would want to stuff the interior or you could even have baffles I suppose. Now, you can't do that to the port, so the port may self-resonate at higher frequencies.
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post #10 of 34 Old 02-08-2018, 11:38 PM - Thread Starter
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RoboAVS I sometimes wish I could chill out but at 53 I am not hopeful. My mind is a constant hurricane. I am a lawyer and that seems to help there, but I find it hard to sleep with my mind racing. So I just run with it.
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post #11 of 34 Old 02-09-2018, 01:57 AM - Thread Starter
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Head_Unit that was extremely helpful

My concept starts with the idea of a large vertical cylinder instead of a box. So instead of 18x25x28 PB2 Plus, I would have a 6 foot tall column 30 inches in diameter. The box has a volume of 12,600 cubic inches or 7.29 cubic feet, and the cylinder has 50,892 cubic inches or 29.45 cubic feet. Just for comparison purposes, the AuraSound NS18-992-4A 18" has a Vas of 322 liters or 11.37 cubic feet. That is one and half times as much as the eternal size of my PB2 Plus, and four would fit in the column I am describing. A Dayton RSS460HO*4 18" has a Vas of 9.6 cubic feet. Assuming that it would otherwise work doesn't is make more sense to use taller towers than bigger boxes?

Subwoofers with two drivers are designed more ways that I can count or understand. The more I read about isobaric and push-pull, the more confused I get. Having read some more, I am just going to say however many drivers in whatever configuration makes sense. I had been thinking that the top having 3 facing up and bottom having 3 facing down and the two halves wired out of phase might have benefits, but now I am not at all sure. It did seem that if all 6 drivers worked in tandem good things might happen. But yeah, as I imagined it there would 3 drivers stacked in each half.

For the tube itself, I am inclined to go with a product made by shapes unlimited.com. The are made from multiple layers of heavy-weight fiberboard. The bent wood you see on chairs and other rounded corners are made from the same thing. They can make tubes from 3" to 48" diameter, and they can even put wood veneer on the outside. I would guess a quarter of an inch thick.

Assuning no space problems or WAF issues, the diameter certain could be increased, and volume increases rapidly. At 48 inches instead of 30, a four-foot tall tube would have a volume of almost 49 cubic feet.

From what I have read the layered laminate will not resonate easily. I have also looked into new high tech sound absorption materials, but they mostly such at lower frequencies.

Thanks again, you have given me much to think about.
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post #12 of 34 Old 02-09-2018, 04:11 AM
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Can you post a diagram of what your wanting to build? You keep saying "stacking 3 drivers" in each end so I'm kinda confused on your goal. If you goal is like the pic I attached just with 3 drivers instead of 2 I highly recommend against it. The only real benefit is reduced box requirements. So in a home setting you would be way better off making one dual opposed box at twice the volume that one box like the pic I attached. If you want 6 drivers in sonotubes make 3 dual opposed enclosures and enjoy your new amazing subs.
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post #13 of 34 Old 02-09-2018, 04:49 AM
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Sounds like a standard opposed driver sub in a sonotube, it'd probably work great, just that if it has 6 real woofers in it, it's probably going to need to be taller than 6 feet.

With that many drivers though, I might be tempted to build smaller and use multiples spread around a bit.
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post #14 of 34 Old 02-09-2018, 09:18 AM - Thread Starter
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Sounds like a standard opposed driver sub in a sonotube, it'd probably work great, just that if it has 6 real woofers in it, it's probably going to need to be taller than 6 feet.

With that many drivers though, I might be tempted to build smaller and use multiples spread around a bit.
Thanks. I guess the question is whether it is possible or makes sense to have multiple drivers in each direction with an opposed driver system. And my thought was that is they were out of phase, they might be symbiotic instead of opposed. In other words if the drivers were pointed opposite directions but actually moving in tandem.

As for more smaller, that is my other question. Better with smaller moved around or huge in on location. And here I am ignoring for a moment room acoustics and the benefits of multiple subs, just looking at total output and output quality.
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post #15 of 34 Old 02-09-2018, 10:02 AM
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I'm still happy with my 1990s Hsu TN-1220 HO, which was one of the very first cylindrical subs made with sonotube. Only 4' long by 1' in diameter with just a single 12" driver and a big, long, flared port it's flat to 20Hz and -3dB at 16Hz. Since the amp is separate the sub is amazingly light at just 30 pounds and is easily tucked under one arm and carried around. I started with it standing vertically which my wife tolerated but ended up laying it on the floor behind a sofa which scored extra spouse points. If the driver ever dies I'm just going to replace the driver as it gives me all the low bass I need.

From time to time it's crossed my mind how a similar sonotube sub might sound in sealed configuration with a driver at each end. But I'm so satisfied with the performance of Hsu's ported design that I always end up thinking, why bother? Even though I rarely have to move it I still appreciate the fact that a relatively small 30 pound cylinder can produce so much deep bass. While there are bigger, more powerful options available today the old TN-1220HO already rattles my wife's china cabinet to the point that I'd be pushing my luck to go any further. I'm so fortunate that I was able to find the perfect subwoofer for me and still be satisfied with its performance after 20 years.

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post #16 of 34 Old 02-09-2018, 10:11 AM - Thread Starter
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Here is a schematic showing the overall idea. I am discussing 18 in drivers, but they could be 15 depending on what works and quality. I suspect that the desired quality might be available in a 15.

Having problems figuring out posting a pic. Image is at https://imgur.com/8wqb7Bl

A Rhythmik DS1510 15" driver has a 300 liter Vas, or 10.59 cubic feet. As I understand it, 6 of those in most configurations would require 63 cubic feet of space. That would require a 44 inch diameter tube that was six feet tall. In my face, that would be doable, but I am not sure that it would be the best demonstration of concept.

A 12 inch Rhythmik DS1204 has a 110 liter Vas or 3.88 cubic feet, or 23.28 total. That could be achieved with a 28 inch diameter tube 6 feet high.

But them I think I am missing something here because Rhythmik has a 12 inch driver designed for 1.5 cubic feet in a sealed box that has a 3.53 cubic foot Vas. And just when I thought I was starting to understand this. I used Rhythmik because I happen to like their subwoofers.

In any event, the idea is a vertical round column subwoofer with 6 drivers to see how much output could be obtained from a smaller but taller footprint. Thanks all, I appreciate the insights, and i apologize for everything I am getting wrong. I am reading everything I can get my hands on, but I am not yet good at distinguishing accurate information from bad.




http://www.rythmikaudio.com/GR_drivers.html

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post #17 of 34 Old 02-09-2018, 10:33 AM
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The Vas parameter does not equal the enclosure size.

Your design in the picture wastes the output of 4 of your subs.
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post #18 of 34 Old 02-09-2018, 10:50 AM
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Look up a LAT subwoofer.


In your sonotube idea, going isobaric or multi isobaric is a waste of drivers. Especially where you are mentioning the size of the cylinders. Run dual opposed (sub at each end) sealed or ported. Will help.
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post #19 of 34 Old 02-09-2018, 10:54 AM
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Hey Van,

Spend some time with WinISD modelling actual woofers and enclosure volumes, both ported and sealed. Vary driver size, enclosure volume port diameter and port length to see how each parameter influences subwoofer performance. You will come away with a much better understanding of the factors that influence subwoofer performance and will end up with a much better design.

For subwoofers, room placement plays a huge role in frequency response. As a general rule, more subwoofers distributed around your room will be better than a single massive subwoofer. After you have four subwoofers, adding subwoofers will produce diminishing returns on both output and linear frequency response. There are still benefits to more, it's just that the marginal improvement diminishes.

Mike
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post #20 of 34 Old 02-09-2018, 11:29 AM - Thread Starter
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The Vas parameter does not equal the enclosure size.

Your design in the picture wastes the output of 4 of your subs.
Thanks, then I completely misunderstood Vas. As I read the definition, it seemed like the point of balance between the sub and the environment. I guess I assume that meant it was the ideal. I will go read more.

I am not surprised about your statement that I would be wasting 4 drivers, and that is a big part of my question. Would stacking drivers increase their efficiency or output, perhaps by sequencing their timing? This may be a stupid question, but I am asking it earnestly. I see pictures of stacked drivers in Isobaric setups. I have read posts from here that are years old asking the same question about running dual opposed subs "in phase" but they seem to have generated more arguments than answers.

The uninformed person in me thinks that 3 drivers stacked should combine their effects if timed.
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post #21 of 34 Old 02-09-2018, 11:33 AM - Thread Starter
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Thanks cubdenno all of this has really helped. Assuming that I ran one opposed at each each end, would a 6-foot length just dissipate the sound or could it have some beneficial effect? I guess is there any way that one could effectively use 4 or 6 drivers in a single tube, is would it always lead to waste and inefficiency or worse?

Bear in mind that what got me started on this is that my PB2 Plus has 2 drivers, and SVS made a B4 Plus at the same time with 4 drivers.
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post #22 of 34 Old 02-09-2018, 11:51 AM - Thread Starter
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mhutchins that is awesome and a lot of fun. Wish it took into account shape, but maybe that does not matter. You just wasted my whole weekend.
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post #23 of 34 Old 02-09-2018, 11:56 AM - Thread Starter
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Look up a LAT subwoofer.
Just caught the reference to the Linear Array Transducer subwoofer. Looks like all of them have been discontinued, but heck yeah, this seems like exactly what I had in mind. But 6 feet long and bigger drivers. There are patents which would give me a design and specs. This really might be my answer.
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Would stacking drivers increase their efficiency or output, perhaps by sequencing their timing?
It doesn't increase their efficiency. It allows them to work properly in a smaller sealed box. Essentially you have the strength of both drivers compressing the air in the box.

All of the output of one driver at twice the cost!
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post #25 of 34 Old 02-09-2018, 12:20 PM
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All of the output of one driver at twice the cost!
That reminds me of a get rich quick scheme a guy once offered me. He said that you lose a little bit on each transaction but make it up in volume.
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post #27 of 34 Old 02-09-2018, 12:37 PM
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Push-pull doesn't increase SPL and costs twice as much (including amplification).

Dual-opposed does though, it also reduces box motion to near-zero.

As you probably have guessed: All of this has been done before. (This isn't the first wheel in existence.)

A sonotube is cheap, light and strong, but a wood box is a better use of space.
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post #28 of 34 Old 02-09-2018, 12:50 PM - Thread Starter
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Thanks BassThatHz. You say that "s you probably have guessed: All of this has been done before." I did guess that but then could not find it. I found round subs that were appealing because they were not big boxes, but I could not find anyone extending them higher. And that made me wonder if it was because more space would be wasted or because everyone was used to working with limited volumes. I now get that my idea to have multiple drivers doing the same thing just won't work, and that lesson alone was the worth the price for the time I have spent on this. I learn things better by trying ideas out than by reading.

And I get the idea that 2 opposed drivers is probably the most I could get out of this. I am not interested in Isobaric. That still has me wondering about the difference between a 3 foot column and a six foot one as well as driver selection. Mach 5 makes a 32 inch driver. I have no idea if it is any good, but maybe it would be happy in a 6-foot tube, or maybe 2 of them opposed would be great. That would be expensive, but there must be other giant drivers that are worth using.

If this all seems scattered and random, it pretty much is, But this process really helps me learn things in a way that sticks and makes it possible to figure other things out. I have learned more in a few days asking dumb questions here than in a month reading online sources. Many thanks to all of you.
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post #29 of 34 Old 02-09-2018, 01:01 PM
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Quote:
Originally Posted by SeattleDavis View Post
but there must be other giant drivers that are worth using.
Yes, the SI HS24 is a great choice

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johnson636 is offline  
post #30 of 34 Old 02-09-2018, 01:36 PM - Thread Starter
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Originally Posted by johnson636 View Post
Yes, the SI HS24 is a great choice
Dang @johnson636 you are right on this. The SI HS2k MkII apparently requires 16 to 20 cubic feet ported, and a 36 inch tower 6 feet tall would have 42.4. So maybe a pair of those top and bottom is the answer if it works that way. At $1,275.99, even a pair woul dbe cheaper than six 18 inch drivers. Of course, they have an SHS-24 that sells for $2,500, and if I am reading this right, they say it works with 3 cubic feet. Seems impossible.

The HS24 displace .75 cubit fee, so a pair of them would get me close to 40, and with everything else, it should be in their stated range. I am going to focus my efforts on this. Thanks so much.
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