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Old 30th October 2011, 12:13 PM   #21
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by william2001 View Post
Hi,

Interesting paper with some interesting numbers in there. IMO it does not
sufficiently explore the rather more succinct method of an overdamped
low tuned 4th order system combined with a peaking high pass filter
to provide the EQ and the subsonic filter in one go.

IMO there are a lot of smoke and mirrors arguments in that paper, that
whilst true, are actually misrepresenting the practical reality by some
clever misdirection, the pudding is being severely over egged IMO.

It is a more flexible EQ system than an overdamped 6th order, and
more complicated, and doesn't include the subsonic filter, and it
would allow you to use driver not suited to what I'd call a sensible
6th order alignment in what is effectively a similar alignment.

However if you do go for an overdamped 6th order, you can make
the Q of the highpass filter adjustable, for room matching, but
you do need to choose the driver and enclosure carefully.

It does illustrate what you can do with low tuned overdamped vented
alignments compared to sealed boxes, the advantages are overwhelming,
as low bass actually needs SPL more than purely frequency extension.

rgds, sreten.

Vented boxes will end up rolling off at 24dB/octave. 6th order 36dB/octave.
The trick is to forget maximally flat alignments and overdamp the alignment
such that the roll-off starts off near first going towards second order for
most of the bass range of interest, accelerating to higher orders basically
below the real area of reproduction interest, combined with room gain works.
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Last edited by sreten; 30th October 2011 at 12:28 PM.
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Old 30th October 2011, 01:37 PM   #22
bbggg is offline bbggg  United States
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My ultimate preference would be for a sealed box Bessel alignment with LT and judicious EQ that takes room effects into account to produce a flat response. This does not have to involve very big boxes. For example, using two big woofers, one on each side wall, can make for a relatively slim and rigid box. Low Fs woofers should be used for the lowest possible group delay. This will minimize the boost required of the LT circuits and, if excursions are not very large, there will be relatively little air nonlinearity. A slick marketeer might even call it the "Stepford" alignment.
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Last edited by bbggg; 30th October 2011 at 01:40 PM.
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Old 30th October 2011, 10:54 PM   #23
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Quote:
Originally Posted by bentoronto View Post
True, there is less movement of the cone (and hence less distortion) in vented enclosures north of the system resonance when the vent augments the sound by feeding out system upper-resonance into the room. But I believe at box resonance and below, the situation is different.

But hard to say if distortion is harder to take in the Hz region above resonance compared to sound below resonance.

Ben
Sending signal below the tuning frequency of a subwoofer is a bad idea. (unless someone likes distortion ) That's why I always have the High-pass set 4hz above the tuning frequency of a BR sub.
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Old 30th October 2011, 11:18 PM   #24
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Quote:
Originally Posted by william2001 View Post
What about Mr. Cordell's EQSS? Low tuned vented enclosure with the LT applied. Replace the big port with a passive radiator if you need to. Reduced cone excursion like a vented but group delay more similar to a closed box. (I've not tried this yet myself, just something interesting.)

http://www.cordellaudio.com/loudspea...hite_Paper.pdf
I've been building these for years. Bob is just describing a LLT sub + LT. I have no problems with his maths, although using a comparison sub tuned to 65hz is a little silly, Also using a very low Q sealed sub with LT would sound like IMO. A properly designed LLT does not need a LT circuit to achieve flat in-room response to below 20Hz.

Last edited by revboden; 30th October 2011 at 11:22 PM.
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Old 30th October 2011, 11:31 PM   #25
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Quote:
Originally Posted by bbggg View Post
"Stepford" alignment.
I like

As an added bonus if you buy in the next 20 min., they come with a wife who just loves to listen to you go on and on about the nuances of wizzer cones.
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Old 31st October 2011, 12:12 AM   #26
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You may be right, I was just thinking that with this extra low tuning you would still need a bit of help with the EQ as it rolls off, not quite able to keep up with the room gain without it. In my own situation the far bigger problem is the havoc created by the room modes...
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Old 31st October 2011, 01:25 AM   #27
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Quote:
Originally Posted by revboden View Post
Sending signal below the tuning frequency of a subwoofer is a bad idea. (unless someone likes distortion ) That's why I always have the High-pass set 4hz above the tuning frequency of a BR sub.

That makes very good sense. I think it is vital to use such filters for all systems I can think of but for BR, seems like an odd mixture of techniques.

But then why use BR if you are throwing away so much "baby with the bath water"?

Ben
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Old 31st October 2011, 05:08 PM   #28
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Additional 2-cents:

while it is somewhat helpful not to direct any signal to the BR below some point (say, 4 Hz above resonance), it still does not control the cone below that point, the way a sealed box does. These are different techniques.

Perhaps the benefit of a BR-plus-high-pass arises from being able to create a pretty small BR box (without raising the system resonance, as with a sealed box), using the tuning to control the system resonance peak, an using the filter to limit uncontrolled cone motion in the low bass.

Ben
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Old 31st October 2011, 09:57 PM   #29
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Quote:
Originally Posted by bentoronto View Post
That makes very good sense. I think it is vital to use such filters for all systems I can think of but for BR, seems like an odd mixture of techniques.

But then why use BR if you are throwing away so much "baby with the bath water"?

Ben
I have to say, some of your analogies confuse me...

What is being thrown away?

I should point out that if I build a BR box they are semi-LLT tuned ~14hz and High-pass at 18Hz. I suspect you're thinking about tunings well above that. (which i don't like for many reasons)
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Old 31st October 2011, 10:07 PM   #30
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Quote:
Originally Posted by william2001 View Post
You may be right, I was just thinking that with this extra low tuning you would still need a bit of help with the EQ as it rolls off, not quite able to keep up with the room gain without it. In my own situation the far bigger problem is the havoc created by the room modes...
With an undersized low tuned sub some EQ could be used as bob suggests.

If you can't treat the room properly (low WAF ) have you tried notch filters, I use them all the time and the brain dosen't notice the missing frequencies as much as it notices the drone of standing waves.
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