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post #1 of 43 Old 08-22-2012, 06:29 AM - Thread Starter
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What do you prefer for your sealed sub, Qtc .5 , Qtc ,57 or Qtc .7?
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post #2 of 43 Old 08-22-2012, 09:29 PM
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I don't know the theory of now, but back a few decades ago when I first played around with DIY speaker building .7 was the goal of accurate bass for music in a sealed system. I know things change but for my old ears I still like the sound of some of the classic builds of speakers and amps.

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post #3 of 43 Old 08-23-2012, 12:59 AM
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for a sealed subwoofer configuration, the q of the system determines how much damping there is.

the lower the q, the more quickly the system will return to its initial state. the higher the q, the longer it will resonate.

most people untrained in listening like a higher q as it makes explosions in movies really resonate, same with the hip hop bass heads--mo is betta.

those with a critical ear listening to an upright bass or cello don't want any more resonances what is in the recording, so they are most pleased with a very low q.

so, there really isn't a universal better or worse. accurate vs. enjoyment. i have no idea how to reconcile the two other than to say it kind of depends on the person, their preferences, and the recording.

or put another way, what sounds better to you, might not sound better to me. that doesn't make either one of us more right or wrong...

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post #4 of 43 Old 08-23-2012, 06:41 AM
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Originally Posted by awblackmon View Post

I don't know the theory of now, but back a few decades ago when I first played around with DIY speaker building .7 was the goal of accurate bass for music in a sealed system.
It was, but that was before the advent of modeling software. Now you model the driver/box and let the Q end up where it may for the desired result.

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post #5 of 43 Old 08-23-2012, 11:08 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

It was, but that was before the advent of modeling software. Now you model the driver/box and let the Q end up where it may for the desired result.

Yeah, my son does installs for car audio and some of his models are way out of the ball field I was playing in decades back.

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103 inch AT screen with 9.x playback. IB subs. Two with dual 15s and one with dual 12s. Screen channels with Minimus 77s. Minimus 7 on front wide and front high and wides and sides. Room is perfect size for smaller speakers like the Minimus speakers. Approx. 17x13x8. Tower speakers were taking up to much room. Onkyo 818 used as pre-amp. Power amp duties handled by HK 2.1 Kenwood KM-X1. Hafler DH200.
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post #6 of 43 Old 08-23-2012, 08:12 PM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

It was, but that was before the advent of modeling software. Now you model the driver/box and let the Q end up where it may for the desired result.

and what do you prefer for music Bill? .5 , .57, .7 or higher?
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post #7 of 43 Old 08-24-2012, 12:13 AM
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Originally Posted by j.d. View Post

and what do you prefer for music Bill? .5 , .57, .7 or higher?
I prefer flat in-room response.

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post #8 of 43 Old 08-24-2012, 09:53 AM
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I shoot for 3. At least.

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post #9 of 43 Old 08-24-2012, 04:06 PM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

I prefer flat in-room response.


If you have eq and can get flat response with all three of the above, do you prefer any and is there much of a difference in how tight and controlled the bass is?
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post #10 of 43 Old 08-24-2012, 04:22 PM
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Originally Posted by j.d. View Post

If you have eq and can get flat response with all three of the above, do you prefer any and is there much of a difference in how tight and controlled the bass is?
When I design a sealed cab I don't pay much, if any, attention to Q.

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post #11 of 43 Old 08-24-2012, 10:10 PM
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Quote:
Originally Posted by j.d. View Post

Quote:
Originally Posted by Bill Fitzmaurice View Post

I prefer flat in-room response.


If you have eq and can get flat response with all three of the above, do you prefer any and is there much of a difference in how tight and controlled the bass is?
Changing response via EQ changes final system Q.

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post #12 of 43 Old 08-24-2012, 10:18 PM
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"Changing response via EQ changes final system Q."

+1, but not completely.

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post #13 of 43 Old 08-25-2012, 06:50 AM
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Identical final response curves have, by definition, identical final Q. It doesn't matter how you get there.

Unlikely to achieve identical curves using eq on two different alignments (unless a tailored eq like a linkwitz transform), but it illustrates the problem with the question.

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post #14 of 43 Old 08-25-2012, 08:08 AM
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Quote:
Originally Posted by Bigus View Post

Identical final response curves have, by definition, identical final Q.
That's not the case. You can use drivers with different specs in different cabs to arrive at identical response curves with very different Q values, or identical Q values and very different response curves. That's why I pay little mind to Q, as arriving at a set Q value is not a worthwhile goal in and of itself.
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Changing response via EQ changes final system Q.
Q is defined by the driver and enclosure, and is unaffected by external factors such as EQ. EQ will change response, emulating a change in Q, but it won't affect all of the other factors that an actual change in Q by modifying the enclosure will result in.

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post #15 of 43 Old 08-25-2012, 09:22 PM
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Bill, you're speaking nonsense. You can have two different response curves with the same q (obviously, as a high pass response and a low pass response can have the same q), but two identical response curves by definition will also have the same q.

And what other factors are you speaking of that are only affected by changes in "actual" q? RLC effects are just as real as MKD effects. EQ doesn't emulate a change in q, it IS a change in q. The whole system is electromechanical. You can't ignore half the system.

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post #16 of 43 Old 08-25-2012, 09:45 PM
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Quote:
Originally Posted by Bigus View Post

Bill, you're speaking nonsense. You can have two different response curves with the same q (obviously, as a high pass response and a low pass response can have the same q), but two identical response curves by definition will also have the same q.
And what other factors are you speaking of that are only affected by changes in "actual" q? RLC effects are just as real as MKD effects. EQ doesn't emulate a change in q, it IS a change in q. The whole system is electromechanical. You can't ignore half the system.
I'm not sure what Q you're referring to. I'm referring to Qtc of a sealed speaker, to which your comments do not apply.

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post #17 of 43 Old 08-26-2012, 07:55 AM
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I'm speaking of the q you actually hear, the one defined by the final response of the speaker. I don't see the point in talking about qtc when that isn't what we hear when eq is in play. Changing q electrically has the same effect in both frequency and time domains as were it achieved by driver and alignment alone.

Which is what the question specifically stated... q in the context of eq. To which my answers assuredly apply. So why are you talking about something else?

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post #18 of 43 Old 08-26-2012, 08:53 AM
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Originally Posted by Bigus View Post

Which is what the question specifically stated... q in the context of eq.
Not as I understood it; he did specify Qtc. To clarify for those interested, neither EQ nor any other form of processing alters the Qtc, and therefore the transfer function, of a speaker.

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post #19 of 43 Old 08-26-2012, 09:15 AM
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Maybe a misunderstanding of what is being discussed. The original question was about qtc. Once eq is introduced we aren't talking about qtc as you can't hear it in isolation. You only hear final q, effective q, effective qtc, or whatever other name you wish to apply to it. In any case, once he asked about eq and what was preferred it was correct to point out that by altering frequency response you alter q. You seemed to object to this, even going so far as to make flatly wrong statements such as two enclosures with the same response can have different q, and also suggesting that electrically altering q somehow doesn't produce the same effects as altering "actual" q via enclosure alignment.

I suspect these comments simply arise from a common tendancy to forget that eq alters time domain behavior just as it does frequency domain, and changing q electrically has the same effects on ringing etc as does altering it via alignment.

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post #20 of 43 Old 08-26-2012, 11:14 AM
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To the original poster: given access to in-room measurement and PEQ, the box's qtc only really matters in the context of driver choice, box size, available power, and desired output SPL and bandwidth, and is not directly applicable to final sound quality. What you actually hear at your seat is the combination (well, technically, convolution...) of system and room responses.

In short, don't worry about the "sound" of a particular box qtc. Build the box according to your application constraints, measure it in the actual position in the actual listening room at the actual listening position(s), and move and/or (parametric) eq accordingly. Because that's what you finally hear. Qtc is a useful measure, but not nearly as useful as many would have you believe.
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post #21 of 43 Old 08-26-2012, 02:14 PM
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Quote:
Originally Posted by Bigus View Post

. In any case, once he asked about eq and what was preferred it was correct to point out that by altering frequency response you alter q.
Not the Qtc of the speaker. Yes, system response will be altered, but only by dint of the alteration of the signal going into the speaker. That's an entirely different proposition than actually changing the Qtc of the speaker by either making the cab larger or smaller, or by adding stuffing, which alters F3, excursion, sensitivity and maximum SPL. EQ has no effect on those parameters.

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post #22 of 43 Old 08-26-2012, 09:12 PM
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Quote:
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Originally Posted by Bogus 
In any case, once he asked about eq and what was preferred it was correct to point out that by altering frequency response you alter q.
Not the Qtc of the speaker. Yes, system response will be altered, but only by dint of the alteration of the signal going into the speaker.
Well of course. How else could it work? But he asked about sound preference of the alignments. Who cares about qtc when eq is on board and the question is about how various Q's sound.
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That's an entirely different proposition than actually changing the Qtc of the speaker by either making the cab larger or smaller, or by adding stuffing
Not different when the question is about how a particular q sounds in the presence of eq. That was the question. You don't hear qtc, you hear the final q. There may be peripheral differences regarding power compression and other thermal effects, amplifier distortion, etc, but that wasn't the question.
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which alters F3, excursion, sensitivity and maximum SPL. EQ has no effect on those parameters.
F3 is certainly affected by eq, and theoretical max spl in a sealed system (what the thread was about) as frequency lowers is not altered by box size. Efficiency of course changes. No one has suggested a cheat to Hoffman's law.

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post #23 of 43 Old 04-10-2014, 08:44 AM
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Resurrecting this thread because I've been curious about this as well. I understand that we can EQ the final response to be flat but what is missing is even with the same frequency response won't each alignment sound different due to the different characteristics of each QTC alignment? Transient response is supposed to be better at Qtc .5 compared to Qtc 1 for example, so even if the frequency response is EQ'd flat, won't the Qtc of .5 Sound better due to having a more damped driver?
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post #24 of 43 Old 04-10-2014, 08:53 AM
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I understand that we can EQ the final response to be flat
Knowing this a potential third rail:
EQ is not a panacea:
http://www.roomeqwizard.com/wizardhelpv5/help_en-GB/html/iseqtheanswer.html

If response if uneven from a directivity standpoint - EQ only adjusts for a single position not all positions.
EQ on the bass end has to take into consideration the impact on excursion demands.

Professionals ( such as Bob McCarthy ) also write extensive about such issues.

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post #25 of 43 Old 04-10-2014, 09:11 AM
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Quote:
Originally Posted by WVSyd View Post

Knowing this a potential third rail:
EQ is not a panacea:
http://www.roomeqwizard.com/wizardhelpv5/help_en-GB/html/iseqtheanswer.html

If response if uneven from a directivity standpoint - EQ only adjusts for a single position not all positions.
EQ on the bass end has to take into consideration the impact on excursion demands.

Professionals ( such as Bob McCarthy ) also write extensive about such issues.

I get that but it's kind of a separate issue altogether, I'm just saying assuming EQ can effectively make each different QTC alignment equal, will they all sound the same or do the differences in internal pressure on the driver make them sound different? Since the transient response and group delay numbers are different for each alignment, I would think there would be a difference but without building 3 different boxes with the same drivers I can't know for sure.
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post #26 of 43 Old 04-10-2014, 09:18 AM
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You are correct.. smile.gif
EQ in this case would be an attempt to compensate for Frequency response via signal adjustment.
It would Not alter the mechanical aspect ( compliance ) of the speaker/cab system combination or the transient response ( a time based event ).
To work ( EQ ) would have to be adaptive - adjusting over time.

Of course - the very audibility and perception of low frequency is often used to dismiss transient response rolleyes.gif

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post #27 of 43 Old 04-10-2014, 11:11 AM
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Quote:
Originally Posted by aarons915 View Post

even if the frequency response is EQ'd flat, won't the Qtc of .5 Sound better due to having a more damped driver?
The advantage to a Qtc of 0.5 versus 0.7 is that 0.5 goes lower. The disadvantage is that it takes a larger box to do it. When designing a cab and deciding on what Qtc you want to end up with it's a matter of comparing all of the results with regards to response, maximum output and cab size, making the final choice based on where you want to compromise, and where you don't. More often than not cab size is where you prioritize, especially if going from a Qtc of 0.7 to 0.5 requires tripling the volume of the box.

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post #28 of 43 Old 04-10-2014, 11:52 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

The advantage to a Qtc of 0.5 versus 0.7 is that 0.5 goes lower. The disadvantage is that it takes a larger box to do it. When designing a cab and deciding on what Qtc you want to end up with it's a matter of comparing all of the results with regards to response, maximum output and cab size, making the final choice based on where you want to compromise, and where you don't. More often than not cab size is where you prioritize, especially if going from a Qtc of 0.7 to 0.5 requires tripling the volume of the box.

So you mentioned the box size and that the lower Q has an extended low frequency response (Due to a shallower rolloff) but didn't mention transient response or group delay benefits. Are you of the opinion that transient response doesn't matter in the subwoofer frequencies?
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post #29 of 43 Old 04-10-2014, 12:13 PM
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Originally Posted by aarons915 View Post

... I would think there would be a difference but without building 3 different boxes with the same drivers I can't know for sure.
Went looking for a link to address that part:
http://www.neumann-kh-line.com/neumann-kh/home_en.nsf/root/prof-monitoring_knowledge_faqs_general-answers_question13

"The subjective effect of excessive group delay is a “loosening” of the bass or a “less dry” bass quality. Currently there is insufficient psychoacoustic research on the threshold of group delay at low frequencies."
In light of that:
It would be down to the DIYer to determine if it's perceptible.
Ya may have to build, listen and decide. biggrin.gif

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post #30 of 43 Old 04-10-2014, 12:31 PM
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If you have the space, I don't see any good reason to not design for a Q of .5.

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