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Old 23rd July 2009, 05:52 PM   #81
gedlee is offline gedlee  United States
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Klaus

320 Hz is well above the modal region. When you see decays like that it can only be due to reflections. There is a strong reflection from somewhere and the impulse response should tell you that. I'm betting on a floor or ceiling bounce. There is nothing "modal" about this problem.
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Old 24th July 2009, 08:33 AM   #82
Elias is offline Elias  Finland
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Hello,

Quote:
Originally posted by gedlee
multiple subs is accepting extremely wide acceptance.
In theory that would be great because one could assume that would generate more comparative measurement results of different systems. But nobody seems to optimise the time response. What I've seen to be done they use white noise and long averaging to optimisation.

Nobody interested to check the time response?!? Amazing.



Quote:
Originally posted by gedlee
I would question the validity of "time response" for LFs in small rooms. It has no relavence and this has been shown. What we hear at LF, where the periods of the sound are greater than our ears averaging time, is the steady state. We do not hear LF transients, or "time response".
Well, to your post to have any relevance you should change "we" to "I" where the "I" is meaning you. Transients below 100Hz are very easy to hear.

Have you ever done the Linkwitz test? What you are listening to is the modulation of the envelope. That is the transient.
http://www.linkwitzlab.com/images/graphics/mlt-bst1.gif



Quote:
Originally posted by KSTR
For lower bass multiple subs (DBA included) looks easier to me to get best results.
About ten years ago I was thinking to make similar system like DBA but sideways for stereo. But the WAF of such things is too bad.

- Elias
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Old 24th July 2009, 06:16 PM   #83
gedlee is offline gedlee  United States
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Quote:
Originally posted by Elias
Hello,



In theory that would be great because one could assume that would generate more comparative measurement results of different systems. But nobody seems to optimise the time response. What I've seen to be done they use white noise and long averaging to optimisation.

Nobody interested to check the time response?!? Amazing.

Well, to your post to have any relevance you should change "we" to "I" where the "I" is meaning you. Transients below 100Hz are very easy to hear.

Have you ever done the Linkwitz test? What you are listening to is the modulation of the envelope. That is the transient.

- Elias
I have no idea what the attached link is supposed to show, but you would have to go a long way to convince me that we can hear a transient for a sound with a period of 10 ms or more. And hearing the envelope is not the same thing as a transient. From all that I know what we sense at LF is a steady state sound. There were studies of "modal decay" in the AES which showed that people did not hear these decays. They heard the integrated sound level, i.e. a more steady state sound.
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Old 24th July 2009, 07:39 PM   #84
KSTR is offline KSTR  Germany
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Same freq. as im my previous post, this time with a short shaped burst. Doesn't look like a single reflection from a simple floor/ceiling bounce. More like a repeated reflection that will become a mode when the exitation is long enough. The shorter pulse has wider spectrum, though, which mus be taken into account.

The Linkwitz graphs is just exactly what Elias and I are concerned with. My understanding (and perception) also is that we hear the envelope pretty well. Also we know that in the bass region the hair cells fire only during the positive (relative) pressure halves of a waveform, which explains a lot of otherwise unexplainable phenomena (like sub-harmonics, ear "IMD", and audibilty of absolute poarity with transient asymmetric waveforms -- the latter I recently backed up with a clean ABX blindtest using sort of an "electric bass drum" as test signal).

- Klaus
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Old 24th July 2009, 07:44 PM   #85
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Click the image to open in full size.

Quote:
Originally posted by gedlee
I have no idea what the attached link is supposed to show
The top trace is the signal and the bottom trace is what the mic recorded. The first one is at a frequency where there aren't any significant room effects and the recording is pretty clean. The others are at frequencies where there are significant room peaks or notches and they don't look so pretty.

Try it for yourself. Download and play http://www.linkwitzlab.com/images/sound/100mbst4.wav . It's "a signal consisting of four bursts with cosine envelope over 10 cycles of a 100 Hz sine-wave", repeated 3 times. If you can distinctly hear the 4 bursts, your system is doing okay at 100 Hz. If it sounds like one long burst, it isn't doing so well.
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Old 24th July 2009, 08:31 PM   #86
gedlee is offline gedlee  United States
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Ok, I tried it. I could hear the modulation on all the systems that I have, including my PC speakers. SO what? The bass in the PC speakers is awful and the bass in my HT is superb and this test came out the same in both situations. I simply don't get the relationship between this test and anything relevent about the subjective perception of bass.

And lets go one step further. In an auditorium the reverberation time could be seconds long and this signal will get almost completely lost in the reverberation. Does this mean that the bass in ALL large auditoriums is bad?

Sorry, but the real situation is just not that simple.
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Old 24th July 2009, 08:37 PM   #87
KSTR is offline KSTR  Germany
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Quote:
Originally posted by gedlee
And lets go one step further. In an auditorium the reverberation time could be seconds long and this signal will get almost completely lost in the reverberation. Does this mean that the bass in ALL large auditoriums is bad?
If you only have the recorded sound and not any visual clues this could sound pretty bad -- even though due to the long reverberation time the effect is more like a rather slowly changing overall noise floor that is decorelated to a greater extent (compared to normal listening room sizes).

Quote:
but the real situation is just not that simple.
On *this* we'll most probably all agree, don't we?

- Klaus
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Old 24th July 2009, 08:44 PM   #88
KSTR is offline KSTR  Germany
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Quote:
Originally posted by catapult
Try it for yourself. Download and play http://www.linkwitzlab.com/images/sound/100mbst4.wav . It's "a signal consisting of four bursts with cosine envelope over 10 cycles of a 100 Hz sine-wave", repeated 3 times. If you can distinctly hear the 4 bursts, your system is doing okay at 100 Hz. If it sounds like one long burst, it isn't doing so well.
The structure of my test signals show the effect even more pronounced than Linkwitz'. This is because of the longer/stronger exitation and the nature of the shrinking gaps between the individual bursts, plus the phase relationsships I mentioned.

And (@Earl), all this types of signals are not too far away from real music signals unless one were very limited in genres.

- Klaus
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Old 24th July 2009, 08:48 PM   #89
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I think the fact that we can all hear the bursts is significant. It shows that there's more to bass than the steady-state condition. The bursts are similar to certain musical sounds so it's not an unrealistic test.

The next step is to compare 'good' and 'bad' systems/rooms and actually look at the traces on a scope to compare the waveforms, testing over a number of different frequencies. It gives a better test than just 'can I hear it.' Computer speakers don't really count as a 'bad' system because you're listening in the nearfield where the sorts of room effects being tested are minimal.
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Old 24th July 2009, 10:09 PM   #90
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Gedlee... Your choice of words for discerning the tones is interesting. Modulation vs distinct tones does imply that they don't sound like separate bursts. Do you not notice a difference in character between difference frequency bursts when they are exciting room modes?
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