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Old 17th March 2004, 03:31 PM   #1
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Default Using subwoofer as a piece of furniture...

Construction of my subwoofer is almost underway - the enclosure is going to be 100 litres. I'm a student and don't have a huge amount of space - so is it possible to use this (totally unshielded) sub as a TV stand, where the TV will not be switched on at the same time as the sub? If the (standard CRT) TV is not switched on, will any damage occur? The motor structure is going to end up around 30cm away from the bottom of the television set.
Also, I've heard that the box can be made to appear larger than it is by stuffing it with fibrous material. Does anyone have anything to say on this? Materials/suggestions?
The box is sealed, in case that makes a difference.

Thanks a lot!
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Old 17th March 2004, 03:50 PM   #2
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Whether the TV is on or not is irrelevant. The magnet, especially from a sub, is going to magnetize the TV. The best thing would be to either use a shielded driver or find someplace else for the sub.
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Old 17th March 2004, 03:54 PM   #3
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Also, the intense vibration produced by many subs will probably shorten the life of the tv. It could knock the convergence or whatever on the tube, or cause problems elsewhere. Mind you, you have to run the sub pretty loud to do this, but I've had it happen.

(The tv usually goes wonky before the windows break.)
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Old 17th March 2004, 03:59 PM   #4
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The recommended ratio is one pound per cubic foot of enclosure volume. The recommended stuffing is either Miraflex or Accustuff but people have been known to use pillow stuffing. Stuffing has the most effect below 100 Hz. Open cell foam is a better damping material above 100 Hz.
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Old 17th March 2004, 04:43 PM   #5
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Quote:
Originally posted by Duo
Also, the intense vibration produced by many subs will probably shorten the life of the tv. It could knock the convergence or whatever on the tube, or cause problems elsewhere. Mind you, you have to run the sub pretty loud to do this, but I've had it happen.

(The tv usually goes wonky before the windows break.)
If he installs 2 drivers, one front-firing and the other rear-firing, there will be minimal vibration (that is, if he doesn't accidentally connect them out of phase).
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Old 17th March 2004, 04:53 PM   #6
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Thanks guys

Yeah I thought the magnet might be a problem even with it switched off, but was hoping it wasn't.

Quote:
The recommended ratio is one pound per cubic foot of enclosure volume. The recommended stuffing is either Miraflex or Accustuff but people have been known to use pillow stuffing. Stuffing has the most effect below 100 Hz. Open cell foam is a better damping material above 100 Hz.
how much saving in volume would the Miraflex/Accustuff give me for a 100l enclosure?

Quote:
If he installs 2 drivers, one front-firing and the other rear-firing, there will be minimal vibration (that is, if he doesn't accidentally connect them out of phase).
Not an option - there's only one driver (Dayton Titanic 15" mkIII)
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Old 17th March 2004, 04:55 PM   #7
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The sub VLR from the sub will cause the CRT cathode and other gun elements to vibrate. When turned on this will be observable as micrphonic effects in the picture.

The CRT mask will also be subject to the same effects. Prolonged exposure at high levels could cause the mask to loosen or distort.

The TV may also get big green and purple splotches (purity) from the effect of the permanent magnets in the drivers. Again, not dependent on weather the TV is operating.
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Old 17th March 2004, 05:01 PM   #8
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The recommended sealed enclosure volume for the Mk III is 65 liters.

http://www.partsexpress.com/pdf/295-420sealed.pdf

I've not modeled it myself.
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Old 17th March 2004, 06:10 PM   #9
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I think the comments so far are on target. The description below likely does not meet your needs in SPL etc, but I would like to relay a success in getting subs near a TV.

The design problem is that we have a TV that is in a recessed spot in a wall. In this room the goal was to upgrade the sound by getting more bass as well as adding new mid and upper range. For now ., the only available space (SAF) is below the TV. About 30" wide and no more than 8 1/2 inches high. In otherwords the speakers all have to sit about 2" below a 25" TV. This is not the main HT viewing area but I still wanted to see what I could do to improve the sound of TV, DVD and background music within the constraints.

I am using two Dayton 6.5" sheilded woofers (#295-306) in a 17 1/2" wide x 18 5/8" deep by 8 1/2" high 1 cf cabinet. It has a 2" wide 6" long port. -3db point without bass boost is about 40Hz. It has a plate amp with bass boost driving it, extending the low end range. Although the boost is near the port tuning frequency (~33 Hz) [danger, danger] this works fine at the listening levels we have used with the DVD's we have watched.

It's not the same SPL and depth as the main HT area but the family seems to like it and chooses this room now and then for a movie.

The sub is flanked on either side by small sealed Tangband TB W3871S speakers based on the J. Krutke design. These normally also sit in the area under the TV, although they get spread out wider sometimes for a movie.

So far I have seen no issue with the TV, either while viewing or when the TV is moved to another location in order to check for effects. I saw an effect when I had the sub pulled out and the back of the sub was facing the TV, but no effect when it is under the TV.

On the other hand:
A few years back I had a low-end sattelite system that had a bandpass box (not tuned very low) that has two small woofers that appeared to have reasonably small magnets. This sat about 2 ft. from the TV. Then I replaced the speaker setup I had the shocking scene of the TV with color smears on one side of it. I was horrified to think the TV was trashed. Turned out that the DeGaussing the TV does at startup corrected it after turning it on and off a few times. Whew, that was a relief.
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Old 17th March 2004, 11:25 PM   #10
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Quote:
The recommended sealed enclosure volume for the Mk III is 65 liters.
I find this quite strange. I've modelled the driver in WinISD. A Q of 0.707 is to be had at around 97.5 litres. I have a 500W of amplifier power (ESP P68 sub amp) and a little larger than the said 97.5l allows me to just about reach the xmax of +/-20mm at 20Hz (and get 104dB anehcoic - hopefully much more in room) with this 500W.
65 litres gives a Q of 0.8 (which is still fine) but I only get 101dB with this same 500W (+/-15mm excursion).

I guess the difference between sizes isn't too big, and 65l sure is more attractive than 100l, but then again 3dB isn't that small a difference, is it?

I'll double-check my figures in WinISD - if anyone knows that I've done something wrong, please point it out!

Thanks
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