Measured monopole and dipole room responses

[markus76]

Originally Posted by john k...

So the imulse has to be in the form of a wav file? That's not too convinient. All my impulse data is in the form of text files which are generated using an MLS burst.

Can you send me such a file?

[gedlee]

Originally Posted by Elias

Modulation transmission function.

Thats not what you use in your paper, you use Coherence. And I know of no work that say that this or the MTF has been shown to correlate with perception. Your are simply assuming that a higher value of coherence is better. In room acoustics for instance a lower coherence would imply better spaciousness, i.e. lower coherence is "better". Unless you show the connection between what you maesure and subject and that it is stable, you are simply showing a bunch of numbers that could mean anything.

[Elias]

Originally Posted by john k...

Elias,

Is your software available anywhere? If I had it and could run it I might be interested in reconstructing my CRAW woofer to look at all three: Monopoles, dipoles and cardioid.

Yes, there is a version available for free on my home page. It can be used to plot wavelets from impulse response . It does not have modulation analysis though (the one I posted just now).

May I know what software you use to measure impulse responses ?

ASCII to WAV conversion is the least of difficulty. Does the file have a header ? Can you post a few lines from such a file, so I can make a conversion script ?


- Elias

[gedlee]

Originally Posted by john k...

So the imulse has to be in the form of a wav file? That's not too convinient. All my impulse data is in the form of text files which are generated using an MLS burst.

John

Its an easy matter to convert a text file into a wav file with MathCAD. If you don't have that software I can do it for you because I do it all the time.

I found Elias plot interesting but unlike him I did not see anything that I thought was conclusive in the results. I did not see what significance a modulated wavelet has. There might be something there I am not sure, but it wasn't obvious to me.

The bass in a large room is always very good and yet its impulse response at LFs is very long. So why is a shorter LF impulse response in a small room a "good thing"? I'm just not convinced that these "metrics" are a valid surrogate for perception. I have not seen any tests that prove that they are.

[markus76]

Originally Posted by gedlee

The bass in a large room is always very good and yet its impulse response at LFs is very long.

Is it? Listening to a bass solo in a church is probably not a very pleasant experience.

[Elias]

Originally Posted by gedlee

Thats not what you use in your paper, you use Coherence. And I know of no work that say that this or the MTF has been shown to correlate with perception. Your are simply assuming that a higher value of coherence is better. In room acoustics for instance a lower coherence would imply better spaciousness, i.e. lower coherence is "better". Unless you show the connection between what you maesure and subject and that it is stable, you are simply showing a bunch of numbers that could mean anything.

This I wrote in diyaudio in August in another thread:

There exists several academic articles on modulation transfer function MTF applied to speakers in rooms. Internet search engine is your friend.


Modulation transfer function as a measure of room low frequency performance
By BM Fazenda, KR Holland, PR Newell and SV Castro


Excess phase effects and modulation transfer function degradation in relation to loudspeakers and rooms intended for the quality control monitoring of music
By KR Holland, PR Newell, SV Castro and BM Fazenda

...

What you don't seem to grasp is the freq response, modal notches etc are symptoms the listener is fully being exposed to only under steady state signal conditions. Most music will not do that. Thus the perceptionally derived differences between, say monopole vs dipole, cannot be concluded from steady state measures.


I recall MTF was introduced with MLSSA in the 80's (?), and while their definition of MTF differs from mine since I'm expanding the wavelet analysis for the task so I'm more into temporal aspects. But then there is TMTF (temporal MTF) which could find it's use here too. TMTF is in good use in the research field at the moment. Hope to see it's usage would spread.


- Elias

To repeat, I'm not using MTF in the traditional sense. MTF is another steady state signal analysis, not very usefull when music is being considered. In music the modulation is temporally compact, not continuous.

What you propably need to do is first analyse any music sample to find out the temporal aspects of the modulation it contains.

And what you say:

In room acoustics for instance a lower coherence would imply better spaciousness, i.e. lower coherence is "better".

is generally incorrect and may apply only to interaural difference (similar to IACC).
Here the first hand question is how to reproduce the information from the recording in a small room. The information = modulation = music.


- Elias

[john k...]

Originally Posted by Elias

May I know what software you use to measure impulse responses ?

ASCII to WAV conversion is the least of difficulty. Does the file have a header ? Can you post a few lines from such a file, so I can make a conversion script ?


- Elias

I use the old Liberty IMP. I'll have to see what the format is. I believe it has a header and some info at the end about sampling rate and number of samples. That is easy enough to edit out. This I believe it just has a single column of data which is the sampled impulse. I'll that a look tomorrow (Sunday).

[soundaatma]

Hi Elias,
I completely agree with your graphs comparing impulse responses between dipoles and monopoles, as being the most representative of subjective perceptions, by many including me. For music with rapidly changing bass lines, indeed a dipole "sounds" as the one with the most definition, in any room big or small.

However, perhaps the only reason dipoles ( in passive systems)are not so common, is because of the limited bass extension needing equalization. From the views of John and the quoted paper , "Backman, J. Low-frequency polar pattern control for improved in room response, AES
paper 5867, 115th AES Convention, October, 2003", it seems a cardioid is the best midway compromise between a sealed and pure dipole (H-frame of flat panel) in terms of better bass extension than a dipole but better transient response than sealed.

It would be most interesting to know if you have used your excellent software to compare a sealed and cardioid bass unit, as your experiments are indeed the most representative of subjectve perception by many.

Thanks for your remarkable contributions and measurements !

[john k...]

Soundaatma,

I am planing to do a comparison of monopole (sealed), dipole and cardioid in the same room assuming I can get my impulse files converted to the necessary wav format. I'll also have to learn how to run Elias' code and Octave.

Perhaps the better way to do this would be for me to just email my impulse files to Elias for processing? I still want to learn how to use Elias' code but I'm interested is seen the results. Still I have to set up the woofer systems which will take a little time. I'm a little busy at the moment.

[bolserst]

Originally Posted by john k...

...assuming I can get my impulse files converted to the necessary wav format.

HolmImpulse is very handy for creating *.wav files from tabular impulse files using the Import/Export functions.
One thing to watch out for is the Holm assumes "," or "." are decimal point.
The Holm recognized column separators are semicolon, space, or tab.