Ive recently built a subwoofer for my home theatre using a shiva driver. I am really happy with the result, and am currently hunting all the things vibrating in the room to eliminate them! (damn those steel frame homes!)
Anyway, when I built the sealed enclosure, I used generous amounts of silicon at every joint (and waited for it to cure before I installed the driver). I used 25mm MDF with 16mm bracing. I also mounted the amplifer separate to the main box.
I was just wondering what the best method is to test for any leaks. I keep hearing how important this is but dont hear anything about how to test for it after the box is built.
Any suggestions??
Anyway, when I built the sealed enclosure, I used generous amounts of silicon at every joint (and waited for it to cure before I installed the driver). I used 25mm MDF with 16mm bracing. I also mounted the amplifer separate to the main box.
I was just wondering what the best method is to test for any leaks. I keep hearing how important this is but dont hear anything about how to test for it after the box is built.
Any suggestions??
Minor leaks in a closed box are not tragic. If the impedance curve comes out where you want it, you're probably OK. If not, you can run an infrasonic signal to the sub (maybe 10 Hz or so) at a moderate excursion, then wet your lips and move your mouth around the joints of the box (keeping it a cm or so away!). You'll feel any air leaks. Just don't let anyone see you do this 'cause it looks so silly. Works, though.
Alternatively, you can do the same thing with a stethascope, but I think the wet lip thing works better.
Alternatively, you can do the same thing with a stethascope, but I think the wet lip thing works better.
Well I gotta admit I would’ve never guessed the wet lips method!
I’ll give it a go but I gotta be careful coz I got aluminum sheets stuck on all sides!
I was thinking of somehow surrounding it in smoke and seeing whether any leaks created movement. Could I try dry ice or do I have to crack open the cubans?
Actually we test for gas leaks here at work with soapy water, but I reckon that sounds a bit messy.
My main concern is around the driver itself because that was the last thing I installed and hence I couldn’t seal it from the inside.
I’ll give it a go but I gotta be careful coz I got aluminum sheets stuck on all sides!
I was thinking of somehow surrounding it in smoke and seeing whether any leaks created movement. Could I try dry ice or do I have to crack open the cubans?
Actually we test for gas leaks here at work with soapy water, but I reckon that sounds a bit messy.
My main concern is around the driver itself because that was the last thing I installed and hence I couldn’t seal it from the inside.
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SkinnyBoy said:Ummmm what can I sugest... I know.. don't look for leaks, seal them, even if they are not there. .hmm, not sure how that works of a metal covered box, perhaps making sure it was sealed should have been don't first..
I found a leak in my tempest ported ebs enclosure when I was playing a 10hz wave at full power on a 250w plate amp. I had put a screw in the bottom to secure the two 3/4" baltic birch plywood pieces together when gluing, and forgot to plug it. It was quite noticable.
It is amazing how much stuff that 20hz can shake in my apartment. It makes the walls resonate. I did some frequency sweeps with a tone generator, and it seemed to find the resonant frequencies of everything in my apartment. Definately too big of a sub for a small apartment.
--
Brian
To SVeRD
That should indicate that you do have a leak.
If your cabinet is absolutely tight, you will only compress the air, and the cone will return to zero immediately.
If there is a leak, - by pushing and holding, some air will leak out. When you release the push, the diaphragm support will try to return to zero by the suspension forces, thus creating an under pressure inside, which will slowly be corrected by a small leak, - cone will travel almost to zero rest imediately, but slowly for the last few mm, depending on the size of the leakage,- and the sze of you diaphragm and box..
That should indicate that you do have a leak.
If your cabinet is absolutely tight, you will only compress the air, and the cone will return to zero immediately.
If there is a leak, - by pushing and holding, some air will leak out. When you release the push, the diaphragm support will try to return to zero by the suspension forces, thus creating an under pressure inside, which will slowly be corrected by a small leak, - cone will travel almost to zero rest imediately, but slowly for the last few mm, depending on the size of the leakage,- and the sze of you diaphragm and box..
Hold on folks,
Be careful with making your box too airtight. Air is a non-linear medium. When the cone goes inside it is pressing more air out of the leaks of the box than when is goes out and sucking air back in. This is in fact a rectifying effect. When you put a sine of say 30Hz and with sufficient amplitude on your box, an under pressure will built up in the box pulling the cone steady inwards. This effect is the strongest in relatively small closed boxes. Luckily music is not of pure sinuses so the effect is not that harmful.
Leakage only lowers the total Q of the box. In some occasions this can be even of advantage. One of the nasty things of leaks is the “breathing” sound or noise they can generate.
The leakage itself has a time constant. I have found that this time constant must be shorter than the repetition time of the bas notes reproduced to avoid the rectifying effect. A time constant of app. 0.1 sec is a good compromise without lowering the Q of the box much. But it is only of relevance if you are playing at high levels.
Be careful with making your box too airtight. Air is a non-linear medium. When the cone goes inside it is pressing more air out of the leaks of the box than when is goes out and sucking air back in. This is in fact a rectifying effect. When you put a sine of say 30Hz and with sufficient amplitude on your box, an under pressure will built up in the box pulling the cone steady inwards. This effect is the strongest in relatively small closed boxes. Luckily music is not of pure sinuses so the effect is not that harmful.
Leakage only lowers the total Q of the box. In some occasions this can be even of advantage. One of the nasty things of leaks is the “breathing” sound or noise they can generate.
The leakage itself has a time constant. I have found that this time constant must be shorter than the repetition time of the bas notes reproduced to avoid the rectifying effect. A time constant of app. 0.1 sec is a good compromise without lowering the Q of the box much. But it is only of relevance if you are playing at high levels.
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