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.
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.
No. Because less modulation transfer, less articulation and less small detail.
Hi Earl
John already addressed most of the arguments so I just want to add some comments to the practical aspects.
Unfortunately they also didn't test more advanced equalization techniques. Nevertheless the study shows the beneficial effects of reduced modal decay.
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.
This is the most expensive and complicated approach. It requires major structural work which is not practical for most people.
John already addressed most of the arguments so I just want to add some comments to the practical aspects.
Unfortunately they also didn't test more advanced equalization techniques. Nevertheless the study shows the beneficial effects of reduced modal decay.
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.
This is the most expensive and complicated approach. It requires major structural work which is not practical for most people.
Agreed, sometimes "less" becomes "more".
What exactly was shocking you ?
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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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.
Agreed but how would the average consumer ever know what the first mode in his room is? And for 115dB SPL movie reference at the listening position (!) I have yet to see a case where one would want a woofer to have a higher cut off (or better, less air-moving capabilities).
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HT and music are different applications that need different systems or "tactics" unless you are often listening to organ music or what not. In typical music there is not much information below..say 25Hz.
I don't think they need different "tactics". From a practical standpoint only max. SPL requirements differ.
Different use cases allow for different implementations, yes, but any use case benefits from less modal ringing and a smooth frequency response.
At the time, the fact that the dipole excited the modes in that frequency range so much more than the monopole or cardioid. I was not expecting that. Maybe shocking is too strong a word. I was surprised might be better stated. The only explanation I could think of is that the cardioid and monopole excite additional modes in that frequency range which have opposite phase and lead to smoother over all response. It's like I have said before; that a dipole excites fewer modes doesn't necessarily lead to smoother response. It's a mixed bag.
Very uncommon for someone advocating (?) dipoles to present such data. Kudos to you. At times the monopole/dipole discussion gets way too dogmatic which really prevents progress.
That's why I supplied a spread sheet with the plans. The build would input his room dimensions and the suggested woofer cut off would pop out. The speaker were design with music in mind.
Well, like I said, I find HT bass annoying, both at home and in theaters.
Do you get a lot of feedback how good this works in real rooms? I'd think there are more variables to account for than just room dimensions.
What does that mean?
Everybody has his preference
Thanks, I was not sure if you were referring to the picture 2 pages back.
Could this be a placement / room issue or did you observe that in multiple rooms ?
In a word, no.
It means I would not recommend my speaker for the typical HT/movie set up. If movies are your thing you should look for something else. If your HT is for viewing concert DVDs that's another issue. But then you don't need 115 dB at 20 Hz.
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