Measured monopole and dipole room responses

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Hello,

I did some measurements with monopole and dipole bass in a room.

Particularly I try to pay attention to temporal behaviour since as I believe steady state measurements in this case are pretty useless when considering human perception. Also I try to match the measurement excitation signal to represent the final situation, that is music.

Music is no impulse nor steady state sinusoid, thus I'm using short tone bursts with shaped envelope. It will give quite good visuality to what is happening in the room due the reflections.

I plotted some spectrograms. Note the horisontal axis is the time in periods. Vertical axis is frequency.

Also note that each frequency the maximum value of the burst envelope is normalised to 0dB. In this way it is possible to compare the room responses in perceptual sense since each frequency the amplitude is the same.

To start here's the ideal case for a reference, response of a laptop soundcard:


- Elias
 

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From these measurements it can be said that in the case of the dipole the time the envelope maximum occurs follows quite well the original envelope, but in the case of the monopole the envelope maximum occurs in almost a randomly manner. With monopole at some freqs the envelope maximum and thus the energy that reaches the listener is delayed - it has a poor energy delay (if one not like to use the term group delay).

Is this a reason for a perceived 'slow bass'? In this sense the dipole is 'faster' - the energy delay is smaller.

The beauty of using this excitation signal is you can listen how the room sounds like while doing the measurement. I can state that comparing dipole and monopole in this room one can hear big difference. I think in this case the visualisation yields the same result as the ear hears: In the case of the dipole the bass notes are clearly separated and it is easy to follw the bass line, whereas in the case of the monopole the bass sounds like it's never going to die out and the bass line is mudded.


- Elias
 
Hello,

Originally posted by David_Web
However -10dB is not that interesting as "direct sound" is what you mostly get. -40dB is a lot more useful. -60dB even more so. RT60 and all.

10ms is only 3,4m so you can't really tell me that you are showing any "in room" response.

Take a another look at equal loudness contours at bass frequencies. 10dB is a huge perceived difference. 60dB dynamic range at bass in a small room is a wishfull thinking only - the signal has to go above pain level to achieve that.

And I think RT60 is not much of a use in small rooms.

Note again that the time axis is in periods, not linear time!

- Elias
 
Originally posted by David_Web
I find it hard to translate to cycles as time matters to me.


That's just the key! :) One needs to get rid of the traditional idea of having looking the room in linear time. For a human linear time have little perceived importance at different frequencies.

For example, take a 10ms reflection: At 20Hz it would be very hard to detect by ear as one period of 20Hz is already 50ms. But at 20kHz (one period is only 50us) 10ms reflection should be easily detectable by the ear.

Thus it is better, in my opinion, to scale the time axis to the frequency in question one is making the observation.

Keep the end user in mind! :)

- Elias
 
Elias said:

Particularly I try to pay attention to temporal behaviour since as I believe steady state measurements in this case are pretty useless when considering human perception.

- Elias

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.

Above 500 Hz the situation is quite different and in fact changes 180 degrees - transients and <10ms impulses are the most important.
 
Elias said:
In the case of the dipole the bass notes are clearly separated and it is easy to follw the bass line, whereas in the case of the monopole the bass sounds like it's never going to die out and the bass line is mudded.


- Elias

I also hear this as well, particularly that image depth is preserved in this region. The classic example is a drum kit moving forward (toward the loudspeakers) vs. a drum kit preserved further into the "background" (no matter where you put them in the room comparing one type to the other at the same position).

On the other hand I've gotten *very* similar results paying careful attention to the driver/baffle coupling, overall weight, and significant attention paid to the in-box pressure and any fiber-fill restricting driver motion.
 
ScottG said:


I also hear this as well,

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. I don't think that the comparison should be between dipoles and monopoles, but between dipoles and multiple subs. Small numbers of monopoles, like one, is pretty much a disaster.
 
gedlee said:


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. I don't think that the comparison should be between dipoles and monopoles, but between dipoles and multiple subs. Small numbers of monopoles, like one, is pretty much a disaster.

Given the radiation pattern of dipoles, one could say that they're mimicking multiple sub, as the front and rear waves are exciting different portions of the room.
 
badman said:


Given the radiation pattern of dipoles, one could say that they're mimicking multiple sub, as the front and rear waves are exciting different portions of the room.

I would tend to agree with this. In a room simulation, one models a dipole as two sources, close together, and out of phase. How close, depends on the "dipole moment" (which is seldom talked about). The larger the dipole moment the more a dipole acts like two sources - correlated, to be sure, but still two sources.

So I tend to agree with you, but there isn't any real way to prove it that I can see.

In simulations of multiple dipoles versus multiple monopoles, they tend to be about the same as far as smoothness and spatial uniformity go (on the average, but each specfic case is different), but a huge difference in power required.
 
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