Peerless
Peerless does offer a good value for the buck. Have a look at the 850146 for a decent 10" at affordable price. For a medium size room they should be fine doubled up in p/p, or separate boxes.
I like stereo bass (as you've probably gathered). There is really much more "there" there than one would imagine. The soundscape grows fuller, and much more realistic. I wouldn't have thought this possible since bass below 100 Hz is supposedly omnidirectional. Not so, in my experience - the source is easily localized if the crossover is up near 100 Hz, and especially easy with a 12 dB (only) high pass filter is in use. Crossed low with 24 dB HP filters, and things get much harder.
The other problem that I can see with p/p is an application which requires high output due to room size, along with deep extension. Many of the true subwoofers are 4 ohm impedance only, and doubling these up requires a very substantial amplifier for the 2 or less ohm load, or the use of an isobaric pair each side for impedance matching. Ha! That might be interesting.
Tim
Peerless does offer a good value for the buck. Have a look at the 850146 for a decent 10" at affordable price. For a medium size room they should be fine doubled up in p/p, or separate boxes.
I like stereo bass (as you've probably gathered). There is really much more "there" there than one would imagine. The soundscape grows fuller, and much more realistic. I wouldn't have thought this possible since bass below 100 Hz is supposedly omnidirectional. Not so, in my experience - the source is easily localized if the crossover is up near 100 Hz, and especially easy with a 12 dB (only) high pass filter is in use. Crossed low with 24 dB HP filters, and things get much harder.
The other problem that I can see with p/p is an application which requires high output due to room size, along with deep extension. Many of the true subwoofers are 4 ohm impedance only, and doubling these up requires a very substantial amplifier for the 2 or less ohm load, or the use of an isobaric pair each side for impedance matching. Ha! That might be interesting.
Tim
Another reason for bracing could be to keep the sealed cabinets' walls from physically puffing out and sucking in at sub-resonant frequencies. Granted the actual displacement could be quite small, perhaps 1mm or less, but if you factor in the surface area it seems it could start to steepen your low-end rolloff.
-Casey Walsh
-Casey Walsh
DIY Active
Planet10
4 channels? Actively, I presume?
I just got the MCM flier which shows the AudioSource AMP offerings with the AMP 300 capable of 235 watts each (2) channel into 4 ohm, is 2 ohm stable, has auto sensing, some adjustable gain limiting on the back, but level adjustment on the front, balance, a pass through line level feature on one of two inputs, and can be 375 bridged watts, 8ohm. $400. Also, $300 for the AMP200 at 125watts x 2, 200 w bridged, same features.
Smarmy
Not sure I'm following. Yes, a poorly built box can expand and contract minutely, I suppose. But more likely it will have a lot of spurious energy in the panels generating their own racket and muddying up the sound. It may sound bad, but it shouldn't effect roll-off. It might effect rolling out to the curb for pick up.
Tim
Planet10
4 channels? Actively, I presume?
I just got the MCM flier which shows the AudioSource AMP offerings with the AMP 300 capable of 235 watts each (2) channel into 4 ohm, is 2 ohm stable, has auto sensing, some adjustable gain limiting on the back, but level adjustment on the front, balance, a pass through line level feature on one of two inputs, and can be 375 bridged watts, 8ohm. $400. Also, $300 for the AMP200 at 125watts x 2, 200 w bridged, same features.
Smarmy
Not sure I'm following. Yes, a poorly built box can expand and contract minutely, I suppose. But more likely it will have a lot of spurious energy in the panels generating their own racket and muddying up the sound. It may sound bad, but it shouldn't effect roll-off. It might effect rolling out to the curb for pick up.
Tim
I myself have built subwoofer enclosures using quite a few mountings. Push Push definately did get the ENTIRE box to vibrate less, as a whole. Panel resonance has nothing to do with push push mounting. Push push merely cancels out the intertia forces created by the drivers. If the speaker cone moves out, then it will push the box backwards (in the opposite direction of the cone movement). Its not causing a panel to vibrate, its causing the box as a whole to vibrate. I've built a push push design and used the same drivers that I formerly had mounted on the same side of a similar alignment. The push push design had a slightly higher Q but both enclosures sounded very similar. I do not think push push design gives much, if any, audible advantage. I have used upward firing woofers in sealed enclosures and found that it does make the floor and walls of the building structure resonate ALOT more. This might cause slight coloration, but what I really noticed was pictures rattling etc... It did give tremendously more impact to the sound however. Bass drum hits could be felt much more than they could before at the same level, explosions on movies etc... I'd say side firing woofers push push or not shouldnt have much problem with whole enclosure vibration. As for panel vibration 3/4 MDF shouldnt have any resonance below 100hz unless you're using long and moderately wide panels. I'd say bracing is needed at least every 12 - 15 inches. Bracing every 8 inches will work fine, but it might be slightly excessive. As for the Box in a Box design, its an interesting idea, but I'd bet if we did a listening test comparing the same driver in the same alignment crossing over below 100hz at 24db/octave no one could tell a difference. The extra time, and extra weight of the enclosure are particularly unattractive. My sub already weighs 130lbs with the driver.
Even if your panels don't hit a resonance, if your total panel area is large compared with the driver effective cone area it won't take very much flexing of the panels to almost equal (and therefore undo) the air displacement of the driver. The panel area of mine is about 52 times that of the 12" cone.
"Even if your panels don't hit a resonance, if your total panel area is large compared with the driver effective cone area it won't take very much flexing of the panels to almost equal (and therefore undo) the air displacement of the driver. The panel area of mine is about 52 times that of the 12" cone."
-circlotron-
Have you tested this? I dont really have anything to back me up here, but I would imagine that panel vibration works somewhat like the vibration of a Passive Radiator because that is in fact what the panels are doing, passively radiating the sound. Anyhow, if your 12" sub movies even 2 inches p-p then your panels will have to move over a 32nd of an inch to cancel out the driver's acousitc output. Thats a serious underestimation considering not every square inch of surface on your box is going to move that much. Only the middle of the panels will move a significant amount, not the corners where the boards join. I'd say you'd be getting near 1/16 or 1/8 of an inch of movement. Unless your building your box from some cheesedick 4 ply 1/2 inch pine (which you should NEVER do) that much panel flexing should not occur. As I said before bracing every 12-15 inches should make your box solid. If you have a box less than 15x15x15 I'd say bracing is very optional. It would only be needed with a extremely powerful 12" driver, probably more powerful than those currently on the market. I'd put a few braces for something like a brahma, but I really dont think it would make a big difference.
-circlotron-
Have you tested this? I dont really have anything to back me up here, but I would imagine that panel vibration works somewhat like the vibration of a Passive Radiator because that is in fact what the panels are doing, passively radiating the sound. Anyhow, if your 12" sub movies even 2 inches p-p then your panels will have to move over a 32nd of an inch to cancel out the driver's acousitc output. Thats a serious underestimation considering not every square inch of surface on your box is going to move that much. Only the middle of the panels will move a significant amount, not the corners where the boards join. I'd say you'd be getting near 1/16 or 1/8 of an inch of movement. Unless your building your box from some cheesedick 4 ply 1/2 inch pine (which you should NEVER do) that much panel flexing should not occur. As I said before bracing every 12-15 inches should make your box solid. If you have a box less than 15x15x15 I'd say bracing is very optional. It would only be needed with a extremely powerful 12" driver, probably more powerful than those currently on the market. I'd put a few braces for something like a brahma, but I really dont think it would make a big difference.
Hmm, I was thinking about how to estimate the actual movement of the box. How about this: Play some loud music. Feel the vibration using the fingers on the box. Then lower the volume, and put the fingers on the woofer. Raise the volume until the vibration feels equally strong. Check the level difference in between the two cases. Add 20*log(Sb/Sd) to compensate for the larger box area (Sb). I think there will be plenty of margin until the box palys as loud as the speaker, even with pretty thin walls.
Hmm, I'll have to test it.
Edit: I did it, I had to lower the level by some 50 dB using a 100 Hz sinusoid on my pretty weak boxes (18mm softwood, box is 0.2x0.2x1 m) without bracing. 50 dB corresponds to 316 times when it comes to surface, assuming that the entire surface moves like the spot where I put the fingers. I don't think it does. Sb is 61 times Sd on my system. Not very scientific, but it gives an idea about the order of magnitude of the vibs.
Hmm, I'll have to test it.
Edit: I did it, I had to lower the level by some 50 dB using a 100 Hz sinusoid on my pretty weak boxes (18mm softwood, box is 0.2x0.2x1 m) without bracing. 50 dB corresponds to 316 times when it comes to surface, assuming that the entire surface moves like the spot where I put the fingers. I don't think it does. Sb is 61 times Sd on my system. Not very scientific, but it gives an idea about the order of magnitude of the vibs.
FWIW, acoustic guitars, which function like very poorly made bass-reflex boxes, typically have a Helmholz air resonance around 20% lower than calculations would predict. This is due to the top and back flexing... the stiffer the top and back the higher the resonant frequency. I agree, though, that in most decently constructed sub boxes the frequency shift would likely be unmeasureable, but wall stiffness may have a slight effect nonetheless.
I have an accelerometer somewhere around here so I will try to fine it and scope my subs whivh are 6.25 cubic feet divided in half made of 1.5 " MDF whith 36 internal braces. I know what I feel at the box is not of the signal frequency. Additionally two variovents and 13 lbs of wool and 2 30w-100s
Furthermore in a system in which multiple frequecies are introduced additional tones are generated by the sumation and difference of the initial tones and the generated tones
f1 + f2 +f3, f1+f2-f3, f1+f2, f1-f3, ...
Furthermore in a system in which multiple frequecies are introduced additional tones are generated by the sumation and difference of the initial tones and the generated tones
f1 + f2 +f3, f1+f2-f3, f1+f2, f1-f3, ...
I'm very much in favour of making very rigid boxes but this sounds overstated.
eg. let's look at a 1 cu ft sealed sub with a 12" driver like the Stryke AV12.
VD is 2.3L.
The surface area of the box is 0.7m2.
For the box to move as much air as the driver requires the walls to move on average 1/14th of the p-p xmax of the driver at most, which is
1/14 x 46mm = 3.3mm
1.65mm ~ -6db
0.8mm ~ -12db
0.4mm ~ -18db
0.2mm ~ -24db
0.1mm ~ -30db
The walls would have to be very thin for you to be able to see them flexing this much.
In circlotron's box, the box has 3.7x more surface area, so it would need to be more rigid to achieve the same effect, however it seems hard to credit that the contributation from the box could be close to that of the driver.
The theoretical maximum output of the box should be 6db. This is output from the rear of the driver. If you achieve any more than this, then the rear of the box is acting as an acoustic lever. In the case of a sealed box, you could consider this in terms of transmission loss (TL) through the enclosure material. I would think that as long as you can achieve 10db TL without significant coloration, then this should be acceptable.
Most of us diyers like to go well beyond acceptable. We like to put our hands on the box and feel nothing when the speakers are playing. Many of us have a love of over-engineering. This is why I prefer to make boxes a minimum of 36mm thick
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