The air pressure wants to expand and contract the box by balloning and concaving the walls. Your braces are the most direct at countering that; especially on a small box where the cross-brace is short it is much better (effectiveness versus weight) to connect opposed walls than to stengthen those walls; and your braces also stengthen the walls. Internal wires in tension have even been used, or threaded rods.
The best thing about MFD cabinets – if they are too big, cut them down, re-glue the back or face baffle ~ sand, re-paint.
The cubic foot “range” of a sealed enclosure appears to be forgiving.
I’ll use the rubberizing spay and line apply thin foam on the braces.
The cubic foot “range” of a sealed enclosure appears to be forgiving.
I’ll use the rubberizing spay and line apply thin foam on the braces.
Yes, the size changes the total system Q. That will affect how fast it rolls off below resonance.
I installed one woofer in the 50 Liter box ~ pretty disappointing actually. I heard some bass, but there was more mid bass then low. Even with the crossover set very low, the 60 – 200 (guessing) frequency was dreadful.
For damping, I used a lot of foam blocks, but did not fill it all the way.
Well the plan is isobaric, I need to install the 2nd woofer clamshell – or I might build an outer tunnel and use long screws.
Not how the advertisement read: “sub that you can continue to turn up until your foundations are in danger”.
For damping, I used a lot of foam blocks, but did not fill it all the way.
Well the plan is isobaric, I need to install the 2nd woofer clamshell – or I might build an outer tunnel and use long screws.
Not how the advertisement read: “sub that you can continue to turn up until your foundations are in danger”.
Update:
Update: I realized the box need more “stuffing”, so added misc. foam blocks and damping wool. That helped a lot, so added the second woofer.
It works fairly well, it really hits hard some of the low notes, and it did actually shake the house a bit. Not bad for woofers that were bought back in the 80s.
The upper part of the bass was a bit overbearing, I had the crossover set at 40hz, to try to roll that off; it just wouldn’t disappear.
Any ideas? Better woofers, more damping?
Update: I realized the box need more “stuffing”, so added misc. foam blocks and damping wool. That helped a lot, so added the second woofer.
It works fairly well, it really hits hard some of the low notes, and it did actually shake the house a bit. Not bad for woofers that were bought back in the 80s.
The upper part of the bass was a bit overbearing, I had the crossover set at 40hz, to try to roll that off; it just wouldn’t disappear.
Any ideas? Better woofers, more damping?
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IMHO good idea tusting your ears instead of just the math.
Sounds like it's still too resonant and you want a lower "Q" broader response curve less peaky and more usable extension lows. Still needs a bigger box. When the box is that small even a little additional volume makes a big difference. Could also be how it's interacting with the room; whee did you place it?
Then make the other one and put the other two drivers in it. Two dispersed can excite the room modes more randomly and pleasantly nearly evenly, or placed together they make more low bass.
Consider making the bottom board stick out under the woofer to make it better balanced, and make the box a bit deeper; nobody will even notice.
What are the cones made of? You could add weight (spray varnish or paint or brush-on epoxy if it's paper; don't know what to put on poly cones) then sweep w/ oscillator and measure voltage across a resistor in series with the speaker to find resonance and get them all the same. Would still want a larger box.
Sounds like it's still too resonant and you want a lower "Q" broader response curve less peaky and more usable extension lows. Still needs a bigger box. When the box is that small even a little additional volume makes a big difference. Could also be how it's interacting with the room; whee did you place it?
Then make the other one and put the other two drivers in it. Two dispersed can excite the room modes more randomly and pleasantly nearly evenly, or placed together they make more low bass.
Consider making the bottom board stick out under the woofer to make it better balanced, and make the box a bit deeper; nobody will even notice.
What are the cones made of? You could add weight (spray varnish or paint or brush-on epoxy if it's paper; don't know what to put on poly cones) then sweep w/ oscillator and measure voltage across a resistor in series with the speaker to find resonance and get them all the same. Would still want a larger box.
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I admire your persistence; I don’t think I’m ready for a death box yet, not any time soon. Seriously, these woofers are old, they could quit anytime. I’m using 2 out of the 4, so I’ll have back up woofers just in case they give out. If I was to build a death box, I’d go with new woofers.
www.whitledgedesigns.com check his audiosystem photos for the ultimate isobaric-more suited to home than vehicle use-unless you have a van anyway!
For sealed clamshell with two drivers, QTC .707 25l will be spot on, for four drivers clamshelled just double it.
For vented clamshell with two drivers, 4.058cf 114.9l, Ql of 7 and tuned to 21Hz. If you wished to keep the box volume small I modeled a 1.5cf box, vented and tuned to 28Hz but barely had any more output than the sealed at half the box volume.
The thread did get a little confusing because we changed direction; the short version:
Peerless recommended sealed box 40/80 liter divided by 2 for Isobaric = 40liter.
This box is sealed, 50 liter with a good deal of bracing. One of undercoating spay, a mix of wool and chunks of foam, pretty darn full.
Typical when I build a sub, the low bass is hard to bring out. This is sealed box is backwards, the low bass is terrific, with some overhang issue. (which was worse with only one driver)
Some of the low bass notes are really hitting a home run, however, the box did not respond well with the crossover.
Peerless recommended sealed box 40/80 liter divided by 2 for Isobaric = 40liter.
This box is sealed, 50 liter with a good deal of bracing. One of undercoating spay, a mix of wool and chunks of foam, pretty darn full.
Typical when I build a sub, the low bass is hard to bring out. This is sealed box is backwards, the low bass is terrific, with some overhang issue. (which was worse with only one driver)
Some of the low bass notes are really hitting a home run, however, the box did not respond well with the crossover.
Can you EQ it? 40Hz is pretty low anyway, though if your sub is more efficient than your mid/FR you could find that the 40Hz LPF is actually crossing the sub much higher with your mids then you think, excuse the truely awful "paint" sketch below, but you can see line A and line B are the same sub, both crossed at 40Hz, but if you have the gain up on the sub that 40Hz crossover point quickly becomes 80Hz (in my shoddy illustration anyway😉
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I think the illustration may be spot on. There is something strange going on, I have other subs right next to this sealed box, and not nearly as many problems.
I think the cabinet is the right size.
I will go back and re-dope the cones (which is a shame, I just removed a layer of silicon).
No equalizer here.
I think the cabinet is the right size.
I will go back and re-dope the cones (which is a shame, I just removed a layer of silicon).
No equalizer here.
Up date, new build 105L
Gave up on the red box, too small. Can't figure out what Peerless was thinking. I should have checked instead of winging it.
The new box is about double the size, 105 Liters.
I don't know if this is a good idea, but I put cheesecloth over the big hole in the brace, so the damping wool won't all just fall to the bottom section.
I guess I could simply turn it over, and let gravity hold it in place.
Gave up on the red box, too small. Can't figure out what Peerless was thinking. I should have checked instead of winging it.
The new box is about double the size, 105 Liters.
I don't know if this is a good idea, but I put cheesecloth over the big hole in the brace, so the damping wool won't all just fall to the bottom section.
I guess I could simply turn it over, and let gravity hold it in place.
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surprised this worked
I was surprised this worked ~~ the 12" speakers (2 clamshell) are old but in good shape.
The bass is pretty crazy (only the bottom sub is hooked up).
I loaded up the top chamber with poly fill/damping wool and a couple of pices of foam. I may go back and add 1/2" MDF layer to the outside, but not sure if that would sound significantly better.
I do see where many would vote for a sealded box system, over a ported Bass Refex.
I was surprised this worked ~~ the 12" speakers (2 clamshell) are old but in good shape.
The bass is pretty crazy (only the bottom sub is hooked up).
I loaded up the top chamber with poly fill/damping wool and a couple of pices of foam. I may go back and add 1/2" MDF layer to the outside, but not sure if that would sound significantly better.
I do see where many would vote for a sealded box system, over a ported Bass Refex.
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I have a pair of large ported isobarics made years ago by Dennis Boyle here in Dallas. The guy who he had made them for had returned them after the foam surrounds failed on the sub drivers. The subs originally had been part of 3 way speakers that had 7" Focals in sealed compartments (2 each speaker) for mid bass and the large dipole Heil AMTs for tweeters. The subs will go down to 15 Hz which is great, but the isobaric set up was done to add speed to the 12" DVC drivers that were bought from Madisound. Since there was a stereo pair I ended up with 4 subs and gave a pair to a friend after I refoamed the drivers. The sub compartments were connected by a chimney so I cut them in half, removed the mids to get the space lost from removing the chimney and put tops on them. They are 36" tall and have tilted baffles so I am don't know the interior space. They are stuffed and the port pipes are made from 2" PVC pipe that go deep into the box, make a 90 degree turn and were tuned by stuffing them with folded up foam sheets.
Being able to be DB up with the bass really adds to the music and the great thing is that they are fast enough to keep with any tweeter made. Bass and speed together is not easy to do. They are big and ugly but my wife has never given me a hard time about having them. When I die though you will want to be at that estate sale, you could probably get them for $20 but be sure to bring a truck and some strong backs.
I found this great thread doing a search. Are there more isobaric lovers out there now than 5 years ago?
Thatch
Being able to be DB up with the bass really adds to the music and the great thing is that they are fast enough to keep with any tweeter made. Bass and speed together is not easy to do. They are big and ugly but my wife has never given me a hard time about having them. When I die though you will want to be at that estate sale, you could probably get them for $20 but be sure to bring a truck and some strong backs.
I found this great thread doing a search. Are there more isobaric lovers out there now than 5 years ago?
Thatch
What do you mean by 'speed'...as it's probably the most misused word applied to subs ("FAST" takes second place). I assume you imply upper extension to bandwidth?
(Disclaimer: haven't read the whole thread so I may be being redundant)
I'm going to have to agree. "Speed" is pretty meaningless. And usually the measurable properties people usually describe in nebulous terms like "speed", isobaric loading tends to have little effect on.
What I think is important to realize is that isobaric loading is effectively a T/S parameter transformation. There's no real acoustic magic involved. When you load 2 drivers isobarically, you are essentially creating a single driver with different T/S parameters. Depending on your design goal, that can be useful or not.
In the most basic generalized terms, isobaric loading allows you to reduce your cabinet size by half in exchange for cutting your efficiency in half. But given that your power handling is doubled from a single driver, you can theoretically achieve the same peak SPL with twice the power.
I'm going to have to agree. "Speed" is pretty meaningless. And usually the measurable properties people usually describe in nebulous terms like "speed", isobaric loading tends to have little effect on.
What I think is important to realize is that isobaric loading is effectively a T/S parameter transformation. There's no real acoustic magic involved. When you load 2 drivers isobarically, you are essentially creating a single driver with different T/S parameters. Depending on your design goal, that can be useful or not.
In the most basic generalized terms, isobaric loading allows you to reduce your cabinet size by half in exchange for cutting your efficiency in half. But given that your power handling is doubled from a single driver, you can theoretically achieve the same peak SPL with twice the power.
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