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Old 20th May 2005, 05:18 PM   #1
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Default Low Qe or High Qe?

I have heard this many times, but now i need it, i just can't remember. Now how is it?

Low Qe driver is suitable for a closed cavity
0,7 Qe is suitable for bass reflex and
Higher Qe is suitable for open baffle.

Right ???
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Old 20th May 2005, 07:24 PM   #2
Raoul is offline Raoul  United States
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Hi Lars,

Dickason said of driver selection in the Loudspeaker Cookbook:

"In terms of driver Qts, closed-box loudspeakers generally require woofers with a fairly high Qts of greater than 0.3..."

(of vented system) "...only Qts between 0.2-0.5 generally provide satisfactory responses."

Not sure if that helps, but there you go.
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Old 20th May 2005, 07:33 PM   #3
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Qts<0.3 hornloading

0.3<Qts<0.4 basreflex

0.4<Qts<0.55 closed box

Qts>0.55 infinite baffle/dipole

It isn't stricktly like that. Things overlap and depend on other T/S-parameters as well (like Fs). Fs/Qts gives Efficiency Bandwith Product (EBP) which is also used as a rule of thumb.

Qts combined with Xmax gives an good idea what kind of quality (sub)speaker you're dealing with, high Qts , low Xmax being the worse.

Simulating will sometimes show supprising facts, so don't go totally out on rules-of-thumb anyway.

Mvg Johan
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Old 20th May 2005, 10:01 PM   #4
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Thanks Guys! I did some simulations and it seems if i take a Qts 0.7 and put in a too small closed box, it will peak severely at 100-200 Hz. But if i take a low Qts (0.4) it will only peak 1-2 dB. But the low Qts unit will also give a slightly higher spl than the high Qts unit. Is this in compliance with reality?

The project in question is a flat panel subwoofer with 64 drivers 6 inch each. Each in closed boxes of 4 liters. The size is 2 x 2 meters but only 6 inches in depth. (A wall of bass!!)

The simulator program (Waldo) shows 105,6 dB / 1 Watt (100 Hz up) and -18 dB at 35 Hz. I think the large baffle will give some help on the -18 dB. (???)
So i'm going to compensate the -18 dB (or whatever) with a gainer stage, and some power. The total loadability of the 64 units is 6 kW so with the right amplifier it can be made linear to the 35 Hz, and with 40W per driver a spl of 139 dB should be possible. (Total 2.5 kW). (log(2500) x 10 + 105.6) = 139 dB
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Old 21st May 2005, 08:50 PM   #5
simon5 is offline simon5  Canada
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Forget about the 139 dB at 35 Hz, your drivers will run out of excursion. But you can get 139 dB at higher frequencies for sure...
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Old 23rd May 2005, 02:52 PM   #6
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Quote:
But the low Qts unit will also give a slightly higher spl than the high Qts unit. Is this in compliance with reality?
Yes, a lower Qts indicates a more efficient speaker. But also the lower the Qts becomes, the less it's suited for low-frequency reproduction.

I don't know what on earth you would need a SPL of 139 dB for, except bassheavy parties starting at 200 people outside or so. So what is the intended use?

Mvg Johan
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Old 23rd May 2005, 06:17 PM   #7
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The purpose is 'discrete' club sound. Since the speaker is only going to be 6 inch thick, it can fit over the dancefloor, and not take up any space in the club.
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Old 24th May 2005, 12:39 AM   #8
mike.e is offline mike.e  New Zealand
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Lars: You will want to use a subwoofer modeling program in order to see the full picture.

'bassbox6'
'winisd pro'
'subsim'

Cheers!
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Old 24th May 2005, 12:42 AM   #9
simon5 is offline simon5  Canada
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'unibox'
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