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Old 9th December 2011, 04:06 PM   #1
soren5 is offline soren5  Denmark
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Question How to deal with high QTC?

I need your help.

I have two 10 liter (0.35 cu ft) cabinets and two Peerless SLS 8" woofers and would like to make some low-end stereo support for my sealed Alpair 7 full-range speakers - crossed at ~300Hz. This is for music only in a 6x6x3 meter (19x19x9 ft) room. Power handling of the woofers is quite good and I got powerful amps, so LT is also a possibility. I'm going active and using a miniDSP for the crossover.

The problem is that WinISD gives me a QTC of 1.1 with this driver in a 10 liter box (probably QTC will be a bit lower when filling, but still far from 0.707). So how should I go about this in the best way?

I see three possibilities:

1) The EAS/ELF/Bagend approach where you utilize the high QTC and add EQ. I'm not sure how this will work (if it will work at all) with a 300Hz XO.

2) The aperiodic enclosure approach. I could add glass wool stuffed “vents” to the cabinets and in this way lower the Q.

3) A combination of 1 and 2.

What are your thoughts on this? I've attached the driver specs and also a WinISD frequency response of the driver in a 10 liter box.

Advice appreciated
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Old 9th December 2011, 04:17 PM   #2
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I would try 2

dave
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Old 9th December 2011, 07:17 PM   #3
soren5 is offline soren5  Denmark
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I knew you were going to suggest that, Dave

But does the aperiodic enclosure prevent me from boosting the low end? If going aperiodic could lower the QTC to 0.707 I would get an f3 of 48Hz, which is still not amazingly deep.

The woofer's relatively high power handling and excursion tells me I could improve the low end by adding a LT.
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Old 9th December 2011, 07:34 PM   #4
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I'd be wary of using a LT. WinISD has the capability of adding one, but be sure to check the apparent amplifier load - this gives an indication of how much power they'll be taking right at the bottom end. Excursion gets scary, too.
That said, a Linkwitz Transform offers (I suspect) more flexibility to pick and choose Qtc & LF extension than an aperiodic design.

Chris
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Old 9th December 2011, 07:52 PM   #5
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Quote:
Originally Posted by soren5 View Post
But does the aperiodic enclosure prevent me from boosting the low end? If going aperiodic could lower the QTC to 0.707 I would get an f3 of 48Hz, which is still not amazingly deep.
But what is F10? It is a small driver in a small box, you can't expect to go too low.

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Old 9th December 2011, 10:15 PM   #6
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Quote:
Originally Posted by soren5 View Post
I need your help.

I have two 10 liter (0.35 cu ft) cabinets and two Peerless SLS 8" woofers and would like to make some low-end stereo support for my sealed Alpair 7 full-range speakers - crossed at ~300Hz. This is for music only in a 6x6x3 meter (19x19x9 ft) room. Power handling of the woofers is quite good and I got powerful amps, so LT is also a possibility. I'm going active and using a miniDSP for the crossover.

The problem is that WinISD gives me a QTC of 1.1 with this driver in a 10 liter box (probably QTC will be a bit lower when filling, but still far from 0.707). So how should I go about this in the best way?

I see three possibilities:

1) The EAS/ELF/Bagend approach where you utilize the high QTC and add EQ. I'm not sure how this will work (if it will work at all) with a 300Hz XO.

2) The aperiodic enclosure approach. I could add glass wool stuffed “vents” to the cabinets and in this way lower the Q.

3) A combination of 1 and 2.

What are your thoughts on this? I've attached the driver specs and also a WinISD frequency response of the driver in a 10 liter box.

Advice appreciated
The 10 liter box shows a bumped up response above F3, what does the QTC look like in a larger box?
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Old 9th December 2011, 10:47 PM   #7
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So you need a bigger box. My favorite solution to that problem:

Get two more of the same woofers, and mount each pair clamshelled (drivers facing each other) isobaric-style in a 10-liter box. That gives you a "Q" like a box twice the size, and a much shallower rolloff. Spend on drivers, save on wood?

Then you can add EQ until the xmax limitation is reached, and it will handle (and need) more power.

But that assumes you don't mind the sight of a magnet sticking out into the room.

Last edited by cyclecamper; 9th December 2011 at 10:52 PM.
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Old 9th December 2011, 10:59 PM   #8
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Quote:
Originally Posted by cyclecamper View Post
So you need a bigger box. My favorite solution to that problem:

Get two more of the same woofers, and mount each pair clamshelled (drivers facing each other) isobaric-style in a 10-liter box. That gives you a "Q" like a box twice the size, and a much shallower rolloff. Spend on drivers, save on wood?

Then you can add EQ until the xmax limitation is reached, and it will handle (and need) more power.

But that assumes you don't mind the sight of a magnet sticking out into the room.
And don't mind the chuffing noises coming from the vent hole...
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Old 9th December 2011, 11:06 PM   #9
sreten is offline sreten  United Kingdom
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Hi,

Maximum SPL in the excursion region of a sealed driver only depends on cone
area and excursion, not box size or response. If you curtial the response
then you need more power to reach the excursion limits, if you EQ the
response for deeper bass (an LT) this needs more power and overall
SPL (due to the extended bass) limits will be lower.

Aperiodic loading is not a good idea, it chucks away cone excursion by
allowing vent output to cancel driver output, its not wanted for a sub,
and no sub I'm aware of uses it for this reason.

I can't see anything wrong with the LT approach, in moderation, LT's
are all about good bass extension but at inevitably limited SPL levels.

Limited SPL ? did somebody mention FR drivers ?

rgds, sreten.
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Last edited by sreten; 9th December 2011 at 11:29 PM.
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Old 10th December 2011, 12:59 AM   #10
Pallas is offline Pallas  Pakistan
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Quote:
Originally Posted by weltersys View Post
And don't mind the chuffing noises coming from the vent hole...
The SLS 8 is pretty quiet. And it doesn't have a standard pole-vent hole. Pole venting is through a radial holes under the dustcap.

Still, it's a pretty deep woofer. So deep that one may as well just make the box wider, and thus bigger.
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