Measured monopole and dipole room responses

[gedlee]

Originally posted by john k...
"(not room pressurization)." was a typo. No "not". Room pressurization is the same old same old. ... I know, rooms leak, but put a dipole in a small room and the bass will not be over loaded below the room's first non-zero mode, or room fundamental, what every you want to call it.

Hi John

I knew something was wrong. (Editing can prevent a lot of arguments down the road - I should have attacked you on this one!! )

As I have said, I have never been able to measure this "pressurization mode" in a real room (at least not at a significant level, i.e. comparable to a room mode, like 1,0,0 in my room) and I can only assume that leakage is the issue. That dipole bass sounds better in many rooms than the typical single monopole is, I think, fairly well established, but I am not sure that I'd jump to "pressurization" as the answer. I think that it might be more complicated than that. I do know that if you get multiple monopole subs setup properly in any room then the bass will sound as good or better than the typical dipole setup. This would tend to discount the "pressurization" explaination.

[john k...]

I did measurements several years ago when developing the NaO II and I certainly saw differences between monopole, diopole and cardioid below the room fundamental in my room. The dipole pretty much followed the anechoic roll off, the monopole showed a definate lack of such roll off and the cardioid was somewhere in between. The monopole was a sealed box. All three sources had the same free field on axis response, Q = 0.5, Fs = 25 Hz.

Don't care to argue about it. If you see diferently in your room then it must be so there.

[gedlee]

Originally posted by john k...
I did measurements several years ago when developing the NaO II and I certainly saw differences between monopole, diopole and cardioid below the room fundamental in my room.

John

Of course you will see differences, thats not the point at all.

[john k...]

Originally posted by gedlee


John

Of course you will see differences, thats not the point at all.

Yes, it is. Dipole did not pressurize the room. Cardioid and monopole did to differening degrees. The pressurization effect or lack of it was quite obvious. That would tend to NOT discount pressurization.

[Elias]

Hello,

Originally posted by jeepee
I like your approach described here. Could you post a graphic of the special waveform you are using?

Originally posted by jason_watkins
I also would love to hear more about how these measurements were done.

I'm using sinusoidal bursts of 5 to 10 cycles with a raised cosine envelope (Hanning window). I think it is very suitable and informative for measuring speakers in a room.

Originally posted by catapult
ARTA can calculate those from the impulse response using the Burst Decay function. Here's a sonogram of a cheap sound card.

Yes, burst response can be calculated, but I prefer using the bursts as real excitation signals because I can listen at the same time how the speakers (and the room!) sounds like.

One can also observe and hear for example room structural resonances in a very interesting way with the bursts. When one turns up the volume a bit, window glasses, room doors and some furnitures start to make noise. It is interesting to hear how a resonanse slowly builds up when burst begins and then continues ringing after the burst has died out. Very informative I think, because the music will do the same thing. Something that cannot be heard in the same way with steady state sinusoids, nor with MLS noise.

It is a good idea to try bursts of different number of cycles as the bandwidth depends on it. A very short burst may not excite a (structural) resonance above the hearing threshold but a longer burst can.

Music is a temporal experience! Thus we should optimise the system keeping that in mind. I think

- Elias

[Elias]

Hello,

Originally posted by gedlee
I think that a strong case could be made that we hear LF ONLY in the steady state. It is well know that the ear has an integration time of about 10-20 ms. over which all sound arrivals are integrated into a single event. This corresponds to a period of about 100 Hz, meaning that a 100 Hz signal is basicaly not even recognized by or hearing until more than antire period has ellapsed. How is it then that we could "perceive" transients of these LF signals?

I only ever look at steady state signals at LF because I am convinced that this is all that we can perceive.

I don't know what is your definition of a steady state, but for me it means a state where signal variation is over and signal is continuous or zero. That situation will never happen during music where signal envelope is constantly varying.

If we could hear only steady state bass, we could not hear the bass at all from most of the records. There is integration time indeed, but it does not mean the sound will appear like a snap shot after the time has passed, rather the perception immediately begins and only the final touch will be set after integration is over. It makes things sound 'smoother' so to say. But it does not prevent us from hearing the temporal effects.

Bass transients are easy to hear and can be seen as envelope modulations at the ear signals. This low frequency modulation is one good thing to increase the perception of envelopment as Griesinger states it.

It's easy to try out and listen with your own ears. Linkwitz has it:
http://www.linkwitzlab.com/images/graphics/mlt-bst1.gif

When I do this test comparing monopole and dipole bass, monopole seems (hears?) to lose the ability to reproduce the envelope variation, and dipole does it better. As I see why this is so, it's because the monopole sparays more waste energy into the room in a wider radiation angle than a source which has some directivity like a dipole.

- Elias

[Elias]

Originally posted by gedlee
The thing that impresses me most about speakers like the Orion, is the bass, it is very good, better than monopoles at the same locations. But its NOT better than multiple subs, in fact I don;t think that its as good. Basically once you go to multiple subs the type of source is almost irrelavent, except that monopoles require less power.

Would you have some temporal (not steady state please) measurement of the multiple bass configuration comparing it's performance with a single monopole or perhaps a dipole? That would be very interesting comparison I think.

I don't have multiple bass boxes at hand to do the test myself because evolution brought me away from boxes

- Elias

[gainphile]

Hi Elias,

Thanks for this post. I've been following it but I'm not up to your level with data etc. to contribute.

Even SL can only subjectively say that dipole bass is better (and he admits so), your measurements take this dipole-monopole perception to different level!

I've had monopole and dipole bass and definitely the dipole sound more realistic. In fact I can't live with monopole sub. It's signature is everywhere. It's good to understand better why.

If there's suggestion that there is something "better" than dipole bass, let's see the data

Keep it coming!

[Elias]

Hello John,

Things are getting most interesting when some mathematics is involved

I agree with your statement you made in your link that one dimensional room analysis is pretty useless to see the real efects. About 10 years ago I wrote a code to calculate 3D room responses using the ray tracing method.
Here's some old results of comparing monopole, dipole and cardioid burst temporal efects:
http://www.diyaudio.com/forums/showt...20#post1629620

And here's the simulated impulse responses:
http://www.diyaudio.com/forums/showt...19#post1631119

Now I find it interesting for myself when comparing the 3D simulations with the room measurements and to the perceived responses.

All the modal analysis and eigenfunctions you present are interesting, but how are they perceived? A room mode, as I see it, is a steady state response and does not occur in most of the real music signals.

- Elias

Originally posted by john k...
I'll present this link for those interested. http://www.musicanddesign.com/Dipole_modesA.html

...

At this time I find that the major differences between the sound of different woofer systems is due the radiated power and the the room pressurization effects, and room pressurization may be the biggest issue, positive or negative, as the case may be.
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[john k...]

As you can see, the resonse at any frequency is composed of the sum of contributions for all modes. (However, at low frequency only the first 4 or 5 modes make a significiant contribution.) Each individual mode has the form of a 2nd order low pass filter with fc = the modal frequency and Q determined by the damping. As such, the impulse response is the sum of the impulse response from each mode. The Fourier transform relationship between frequency response and impulse response still holds.

Of course, the impulse response is dependent on source and listening position. But for a given source position the impulse at any point in the room can be obtained through an IFFt which could be convolved with any signal applied to the source to to get the time response at the listening position.