Measured monopole and dipole room responses

[KSTR]

Originally Posted by KSTR

I'll open a new thread for this, here it will get lost and it is slightly off-topic anyway.

Here we go : Low Frequency Sine-Burst Test Signals for Room and Loudspeaker Evaluation

[john k...]

Originally Posted by Baseballbat

Of course not, I didn't meant that.

In modal region, a null (pressure node) at the listener position is (can be) a peak (velocity node) at another position in the room. So if you reduce the level at a null at the measured position, you can reduce the level of the peak at the other position.

Yes, of course. That is why I said source-to-listener transfer function. And that is the problem with room eq. EQing a what appears to be a peak at one position may result in a deeper null at another.

[Baseballbat]

But if there's already a deep null, it is no problem if you set a notch on it, thus reducing energy of that mode. It can give you more uniform response all over the room (with, of course, deeper nulls, but reduced peaks).

The problem is to define what's a "deep" null. And to conclude from the null on the right parameters for the notch.

That's the difficulty when EQ'ing based on only one measurement at the listener position. I wrote a commercial software (will run in the subwoofers processor) that does exactly that: measure at one position, calculate the parameters for the PEQs. Only for peaks, not for the nulls, I disabled that feature because it was not possible to automate that. But from my experiments, you can get very good results if you place the mic on a corner of the room; and maybe have bad luck that at your listening position you suddenly have nearly no bass. But this is rare.

[Elias]

Originally Posted by john k...

There is no need to actually "play and measure" the test signal.

There is definitely a need to do both: measurements and listening tests.

When one chooses to do the measurement using signals which can be listened it becomes possible to achieve 1-to-1 correlation with the measurement results and auditory perception. This is the whole purpose.

The perception is all the matters. If I wouldn't hear any difference, say between monopoles and dipoles, I propably wouldn't bother about all this.


- Elias

[Rudolf]

Originally Posted by Elias

When one chooses to do the measurement using signals which can be listened it becomes possible to achieve 1-to-1 correlation with the measurement results and auditory perception. This is the whole purpose.

Well said. I am curious what degree of 1-to-1 correlation you can reach. Is it just "dipoles are more open" or can you relate individual visual details of your diagrams to details of your listening impression? Would you also be able to relate those details to things in the physical world?

Rudolf

[john k...]

Ok. I have made some measurements for monopoles, dipole and cardioid. I willmake several posts.

This first figure shows the near field response of the front source of the monopole (blue), dipole (green) and cardioid (violet). The individual responses have been Eq'ed such that when the dipole and cardioid front and rear sources are summed in the far filed all three formats will have the same on axis response.



This next figure confirns that when the front and rear sources of the dipole and cardioid are summed in the far field the response matches themonpole.



The next three plots are the in room response of the three sources. Note the lables in the lower left corner of the plots. The front source of each format was at the same position. That is, all sources had the acoustic center at the same location.







Note that the dipole and cardioid are very similar and that the monopole shows some room pressurization.

[john k...]

Next, here are burst respons eplots presented in sonogram and CSD form. Note that the plots are in cycles so a line of constant time is shown in the sonograms for aid in interpretation. Again. see the lower left corner of the plots for the label.

Monopole:



Dipole:



Cardioid:




CSDs:

Monopole:



Dipole:



Cardioid:



Make what you like of the results. IMO, the dipole and cardioid preform pretty similarly. But recall that the cardioid is 6dB more efficient and cabn play 6dB louder. I may add some EQ to extend the bass response flat to 30 Hz.

[markus76]

Thanks John. Is this a room with rigid walls or a typical stud wall?

[gedlee]

Thanks John - completely plausible results. Its good to see real data.
It's clear that there is some effect below the first mode and hence the "room pressurization" (its not a dominate effect, but it is clearly there.). It's really the only significant difference in the results that I see.

I am sure people will see huge differences where I see little, but in these last few weeks before the election that's pretty common place.

[StigErik]

At what distance are those CSD taken?