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Old 4th October 2012, 10:02 PM   #141
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Originally Posted by gedlee View Post
BTW - a closed box does not "ring" (add a tail) if its Q is < .7. And even if the Q is 1.0 the ringing is minimal.
Correct. No ringing but an exponential decay. I also agree that Q =1 isn't a bad thing. In fact years ago we were discussing this at Madisound and at that time, as I recall, SL and I agreed that the biggest difference between Q = 1 and Q = 0.5 woofer alignment was the difference in the amplitude response. The obvious example is that with Q = 1 a note with fundamental at the box Fs will have an amplitude of 1. and the Q = 0.5 box will reproduce the same note with amplitude = 0.5, 6dB lower. We often hear about fast woofer with Q = 0.5 when what we really have is a woofer system with attenuated bass.

With sealed woofers, or any woofer, I have way felt that the first thing of importance was to match the woofer cut off and Q properly to the room. Nothing sounds worse than a woofer which is flat to significantly below the room's first mode if the room augments the response due to pressurization. The exception is a dipole which can pressurize a room. You can see this in my previous post. There it is apparent that the monopole has significant boost below the room fundamental of 28 Hz, the cardioid less so, and the dipole drops off like a stone, following the woofer alignment. (There is a little noise around 10 Hz).

The thing that always shocked me in those measurement was the way the dipole behaved centered around 100 Hz.
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Old 5th October 2012, 12:15 AM   #142
gedlee is offline gedlee  United States
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Nothing sounds worse than a woofer which is flat to significantly below the room's first mode if the room augments the response due to pressurization. The exception is a dipole which can pressurize a room.
I think that you said this backwards "a dipole which can pressurize a room" - should be "cannot". But I am still not sure that I understand. Isn't the room augmenting the LF response a good thing? Less excursion and less power. If It weren't for this effect my room response could never have gotten down to 20 Hz as it does now. Maybe I misunderstood something.
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Old 5th October 2012, 12:36 AM   #143
Elias is offline Elias  Finland
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But I am still not sure that I understand. Isn't the room augmenting the LF response a good thing? Less excursion and less power.
No. Because less modulation transfer, less articulation and less small detail.
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Old 5th October 2012, 06:52 AM   #144
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Hi Earl

John already addressed most of the arguments so I just want to add some comments to the practical aspects.

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I did find and read that paper, it was quite interesting. [...] They did not test a multi-woofer magnitude response situation.
Unfortunately they also didn't test more advanced equalization techniques. Nevertheless the study shows the beneficial effects of reduced modal decay.

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One thing I should point out in reading the comments here is that the "modal decay" depends entirely on the room and not on the subs or there positions. Even if the direct sound does overwhelm the modal contribution, the modal decay remains the same and will appear after the direct sound has passed.

Only an active system can affect the modal decay and this was clearly shown in the subject paper. Unless you can add-in a sound to cancel the decay (active absorption) it will always remain the same no matter what you do.
Agreed and active absorption isn't hard to achieve. The study showed that even a two-sub configuration could reduce modal decay significantly (one sub at the center of the front wall and one sub at the center of the back wall).
I could achieve remarkably good results in combining near field sub and active absorption. Hope to have supporting measurements soon.

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[...] I have long recommended heavy room damping at LFs.
This is the most expensive and complicated approach. It requires major structural work which is not practical for most people.
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Old 5th October 2012, 09:53 AM   #145
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This is the most expensive and complicated approach. It requires major structural work which is not practical for most people.
Yeah, directional woofers are much more practical in every respect.
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Old 5th October 2012, 10:36 AM   #146
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Yeah, directional woofers are much more practical in every respect.
They are? Care to elaborate?
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Old 5th October 2012, 10:47 AM   #147
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Originally Posted by john k... View Post
With sealed woofers, or any woofer, I have way felt that the first thing of importance was to match the woofer cut off and Q properly to the room. Nothing sounds worse than a woofer which is flat to significantly below the room's first mode if the room augments the response due to pressurization.
Agreed, sometimes "less" becomes "more".

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The thing that always shocked me in those measurement was the way the dipole behaved centered around 100 Hz.
What exactly was shocking you ?
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Old 5th October 2012, 10:55 AM   #148
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Originally Posted by gedlee View Post
I think that you said this backwards "a dipole which can pressurize a room" - should be "cannot". But I am still not sure that I understand. Isn't the room augmenting the LF response a good thing? Less excursion and less power. If It weren't for this effect my room response could never have gotten down to 20 Hz as it does now. Maybe I misunderstood something.
Thanks for the correction. That is what I meant.

My point about room pressurization was more about the need to tune woofer systems to the room if they are capable of pressurization. Dipoles are not, so it is not such an issue. But with a sealed box woofer for example, there is little point is spending the money (IMO) for a woofer with cut off well below the room's first mode (F1) if the room is going to boost the bass below F1. You will just end up cutting the low bass with eq to compensate for the excess pressurization. Of course this is probably my antiquated thinking since I listen to music. If it's earth moving HT bass you’re after I guess that's a different story. But I'm not in that camp. I actually took the subs out of my HT system because after a while I found the room shaking bass that often accompanies action movies to be annoying. ( )
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Old 5th October 2012, 10:56 AM   #149
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No. Because less modulation transfer, less articulation and less small detail.
I don't know what this means.
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Old 5th October 2012, 11:01 AM   #150
gedlee is offline gedlee  United States
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Thanks for the correction. That is what I meant.

My point about room pressurization was more about the need to tune woofer systems to the room if they are capable of pressurization. Dipoles are not, so it is not such an issue. But with a sealed box woofer for example, there is little point is spending the money (IMO) for a woofer with cut off well below the room's first mode (F1) if the room is going to boost the bass below F1. You will just end up cutting the low bass with eq to compensate for the excess pressurization. Of course this is probably my antiquated thinking since I listen to music. If it's earth moving HT bass you’re after I guess that's a different story. But I'm not in that camp. I actually took the subs out of my HT system because after a while I found the room shaking bass that often accompanies action movies to be annoying. ( )
Agreed, I did misunderstand. It just doesn't make sense to tune the sub very low, not so much that the sound is any worse - not once the low end is EQ'd as it should be. I have often made the point that the free field specs on a sub do not say much about how it will work in a room.
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