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Old 3rd November 2003, 05:14 PM   #1
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Default boomy box?

I have been experimenting with an 8” woofer. The Fs of the speaker is 48 Hz and I have now housed it in a 3000 Cu in box (20”X15”X10) with a PVC tube (3”diameter, 3” length).
The box is adequately lined with absorbent material inside. In the box the speaker now exhibits the two usual impedance peaks on either side of the Fs, -- characteristic of all bass reflex designs -- one at 30Hz and the other at 77Hz. The peaks, as can be seen, are not exactly balanced on either side of the Fs.

I have no further instrumental help available. Performance wise, the speaker seems to give uncoloured bass at low volumes but at higher volumes seems to boom a little. Why? The cabinet is well constructed – 18 mm plywood etc. I am yet to fix the mid and high speakers into the box. Is it because I am just listening to the woofer alone that I feel that the output is a little boomy?

TS parameters for this woofers are not very desirable (the elementariness of my measuring equipment has made its own contribution). So I have used an ounce of science with gallons of commonsense and the empirical method of cut-and-try.
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Old 4th November 2003, 12:17 PM   #2
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With speaker brand/model and/or T/S parameters, we may be able to offer some assistance.

cheers
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Old 4th November 2003, 01:33 PM   #3
rabbitz is offline rabbitz  Australia
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Check for any leaks in the box. If you already have holes cut for the mid and tweeter make sure they are sealed off.
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Old 4th November 2003, 09:51 PM   #4
Ap is offline Ap
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A boomy box can be cused by a couple of things >
1 - too small a volume. A driver put in a very small bass reflex enclosure will most likely have a high q & as a result "ring".
Basically when it is fed a signal it takes a while for it to stop - observed in impulse response graphs.
Try sealing the box by stuffing the port & listen to what happens.

2- box walls resonating (this maybe your case) - as at low volumes you dont really notice it, but as the gain increases the walls start to sing along.
Put your hand on the enclosure if it vibrates a lot at high volume then this maybe the cause.
Try bracing the box as much as possible, use corner braces, plus shelf braces every 8" or so. Then apply some damping - heavy vinyl tiles (or similar) bonded with 'liquid nails' works well.
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Old 10th November 2003, 08:58 AM   #5
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Thanks for all your tips.

To AP,

Your first tip (too small a volume) is what I suspected myself. I have also tried closing up the port altogether. Port or no port, the output doesn't seem (or sound) to make much difference. On closing the port, I would have expected the Fc (in-box speaker resonance) to go up.

The box itself doesn't seem to vibrate -- at least at the level at which I am playing it, say around 10W RMS.

Further tips?
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Old 10th November 2003, 09:19 AM   #6
Volenti is offline Volenti  Australia
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Default Re: boomy box?

Quote:
Originally posted by r_s_dhar
I am yet to fix the mid and high speakers into the box. Is it because I am just listening to the woofer alone that I feel that the output is a little boomy?

This can have an effect depending on where the woofer is crossed over/rolls off at, a lot of "tight" bass, especially natural acoustic bass has a lot of higher frequency harmonics that, if missing, can cause undesirable effects.

ie; tight bass is the whole speaker working seamlessly, not just the bass woofer.

[edit] also if the tuning frequency is too low that can cause a dip in the response followed by a peak (from high to low freq) that can cause a boomy sound too.
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