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Old 4th February 2014, 03:43 PM   #1
Speakerholic
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Default Arrival delay in subwoofers question

I have been pondering this for a while now. In Vance Dickason's Loudspeaker Design Cookbook, he talks about QTC alignment and arrival delay. .577 has max flat delay response, .707 has max flat amplitude response. He further discusses the use of EQ on a sub to achieve extended flat amplitude, but notes this practice wreaks havoc on delay response.

My question is slightly different but closely related. Is there a difference delay-wise in overall system response between examples:

A) Use the sub to cover a range of 25-100hz, boosting the low end with EQ to achieve desired response.

B) Cross the sub lower and simply increase gain on the amplifier to achieve a flat system response to 25hz, as frequencies now not reproduced by the sub can be represented by separate drivers elsewhere in the system.

Intuitively, it seems like increasing the volume at the amplifier level should not negatively impact arrival delay.
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Old 4th February 2014, 04:01 PM   #2
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A and B basically are the same thing in terms of amplitude, which in turn will give similar phase (delay) response.
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Old 4th February 2014, 04:04 PM   #3
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Quote:
Originally Posted by richie00boy View Post
A and B basically are the same thing in terms of amplitude
That's what I was thinking, and the reason for my question.

Quote:
Originally Posted by richie00boy View Post
which in turn will give similar phase (delay) response.
So wait, are you saying louder volume levels have higher delay universally and without regard?
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Old 4th February 2014, 04:33 PM   #4
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Quote:
Originally Posted by Thetwinmeister View Post
That's what I was thinking, and the reason for my question.



So wait, are you saying louder volume levels have higher delay universally and without regard?
Generally, the transfer function is what is going to drive the group delay- so if you get equivalent frequency response, you'll get similar phase/group delay.
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Old 4th February 2014, 04:48 PM   #5
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Ah, transfer function. That is something I can sink my Googleteeth into. Thanks! I will do research.
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Old 19th February 2014, 11:29 PM   #6
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Default Time alignment of biamped systems, subs included...

Hi im a sound engineer doing live and studio sound for 20 years.
Ive listened and mixed in all types of subs, good , awfull, medium etc..
You mentioned a good point about time control of sub boxes.
IT MAKES A HELL OF A DIFERENCE.
You need to know about the phase-shifting that all filters aply to your signal path.
Once you hear a time-aligned system with no resonance dependent subs playing, you will never forget what you felt...

Bagend has very good info on that, and ive mixed live jazz, classic, metal, and pop on a bagend system with 4 quartz subs and 10 crystal tops.

I have never heard and felt a better sound system.

I could hear feel and understand every separate note, beat, cluck or whatever my mix had, SOOOOO much better. And Flat too.

I now know that phase and time-alignment of the system is much more inportant to good clean and transparent sound than flat frequency respond or pure spl...

Think... most of the extra dBs you gain from conventional subs is done by controlled rossonance of the box. +/-.
But ressonance is usualy our enemy right...

Search about phase-shifting problems with any x-over filters and eqs (analog or digital) and impedance problems regarding ressonances of drivers in different types of tunned boxes.

Go to this page and take a good look at their TechLibrary link http://www.bagend.com/

Time alignment changed my way of thinking and mixing both live and in the studio.

And if you can go listen to good bagend system then you will "see" the difference.

Regards
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Old 1st March 2014, 01:46 AM   #7
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To clarify, Bag End makes a sub setup where the driver is in a very small box. the resonance is up in the midbass, so the speaker is operating actually IN the roll off region. then they apply a very low frequency low pass with a lot of gain (kinda like option B above). Their contention is that by avoiding resonance the sound better, although this approach requires far more amplifier power.
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Old 1st March 2014, 02:03 AM   #8
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Wow, that is incredible. I am intrigued. So much new information here, I will come back with questions I am sure once I bring myself up to speed with readily available literature.
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Old 1st March 2014, 05:11 PM   #9
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Read up on miniphase(minimum phase) and excess phase. Although you should have encountered both terms in your research already.

In terms of bass and alignment I did things a bit different in my home system.
I delayed the top speakers so that the impulse response peaks (strongest one) aligned.
This will not add up phase properly and they won't sum proper in the crossover region.
But it sounds great even if the group delay is a bit whacked. You could argue that I get a tiny bit of pre ringing but unlike at HF it's not a problem.
Big orchestras does this where the bass instruments start a fraction before the rest to not appear saggy or slow.
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