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Old 13th October 2012, 03:25 PM   #361
KSTR is offline KSTR  Germany
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Originally Posted by Elias View Post
Modulated wavelets are good because you can also play them and listen how they sound with the real speakers in a real room.
Exactly. That's why I programmed a little tool many years ago (probably before SL put out his CD) that creates a set of shaped burst sequences (.WAVs, 16bit, 44.1kHz) in quarter-tone steps from 27.5Hz to 440Hz. Each sequence is based on a burst of several cycles with raised cosine fade-ins/fade-outs of 3 periods (IIRC). Several parameters are varied systematically within each sequence: The total burst lenght, the gap in between (in multiples of cycles) plus the phase realationship between the bursts (so that the next burst starts either in phase with the room hangover or in counter-phase by making the gap half a period longer), and the interchannel phase/polarity. The sequence consist of four blocks, each block starts with long bursts reaching steady state, and long gaps in between. Then burst and gap length is successivly shortened. The next block has antiphase gap lengths (x.5 periods). These two blocks are then repeated, with one channel inverted.

From listening to this broad variety of repeatable and systematic but music-like modulations I learned more about room behaviour than from any measurments or any elaborated mental efforts before. Burnt on CD, with some additional test signals for convenience, it became several people's main tool for quickly judging and adjusting the PA sound at smaller clubs (the original application) and for helping friends to find bass-friendly positions of speakers/subs and listening chair as well as for checking the effectiveness of room treatments.

Markus knows these signals already. I may upload the (DOS) .exe and source-file (for Turbo-C++) if anybody is interested.
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Old 13th October 2012, 03:30 PM   #362
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Originally Posted by Baseballbat View Post
I am wondering what exactly do you mean with "modulated wavelets". Do you mean those cosine shaped bursts of Linkwitz?



No, it's not useless, but there are better methods of visualize the same data. That's what you are doing with your wavelet CSD.

But it is not hard to find important differences in your frequency responses. Below 40 Hz both work nearly the same. Then there's a mode at 45 Hz, still both with same level. But the next mode at 50 Hz is less excited from the dipole. Above the monopole seems to produce a null at the measurement position, while the dipole seems to work very uniform. Then, at 65 Hz, there's another very deep null from the monopole, a hint to a long decaying mode*. Above 65 Hz, both are nearly the same again, with the dipole having a slightly deeper null at 85 Hz. And all this is also visible in your CSD, although the modes are not clearly visible. That's because the used wavelets have to much bandwidth to show it. Reducing the bandwidth will give a better distinction of each mode, while sacrificing time resolution.

I would not damn the frequency response visualization. It is well enough for showing the modal behaviour of a room, and much better suited when designing EQs oder absorbers for single modes.

* I once experimented with notch filters placed on nulls, and it was quite successful. The frequency response was much more uniform across different places in the room. The perception at the listening position was not much affected.
What you are saying about nulls doesn't make sense. Nulls are the result of several modes which cancel each other. Second, the room source-to-listener transfer function is linear. The response at the listener is the source response times the room source-to-listener transfer function. Reducing the source output at a null frequency will not reduce the depth of the null.
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Old 13th October 2012, 03:33 PM   #363
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Markus knows these signals already.
I don't have them because at that time I had no PC available and you didn't want to make the sound files available for download. Maybe now is a good time, please, pretty please
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Old 13th October 2012, 05:47 PM   #364
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Originally Posted by gedlee View Post
Have you heard a room with multiple EQ'd subs?

A kickdrum is a fairly HF instrument. Are you sure its the bass difference that you are hearing. Even I see a justification for a dipole in the 125-500 Hz region.

In that region directionality is just begining to be effective and pistons are still not directional enough while the dipole is. Its very hard to get a directional source < 500 Hz. except with a dipole or a dipole derivative like a cardiod.

But < 125 Hz I just do not buy the dipole argument.
Thanks Dr. Geddes. So it seems that starting at 125 Hz, the narrower radiation pattern of a dipole compared to a monopole is more suited to delivering constant directivity over a wider BW than monopoles....which is a desired goal for all speakers.

Secondly, as JohnK pointed out, the lack of room pressurization by a dipole might be a reason a dipole sounds more natural to "some". Thinking more broadly, most bass musical instruments also do not pressurize the listening environment. True that a monopole can be equalised and LF extension decreased depending on the room, so that pressurisation does not occur. However it requires sophisticated measurements. OTOH, a dipole with sufficient displacement and LF extension could just fit in into any small to moderate sized room with minimal need for tailoring its response to the room.

Thirdly, if a dipole woofer is used beyond 125hz as in most 2 way applications, the bidirectional radiation at mid frequencies (around and above 500 Hz) weaves a more ambient/natural soundfield, as opposed to the almost unidirectional radiation by monopoles at these frequencies.

So in summary, even if there is no agreement (or scientific evidence) about the "perceived" difference of bass transient response between dipoles vs monopoles, based on the three ideas above, it should be logical as to why a dipole woofer may just sound more "natural" and real to some.

Last edited by soundaatma; 13th October 2012 at 05:51 PM.
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Old 13th October 2012, 06:40 PM   #365
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Soundaatma - that dipoles sound different is not contested. That they are inherently "better" is. People can convince themselves that "their dipoles" "sound better", but thats not proof of anything.

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the narrower radiation pattern of a dipole compared to a monopole is more suited to delivering constant directivity over a wider BW than monopoles....
is not really correct, I would say that both have about the same bandwidth of CD, but the dipoles is higher in directivity. People often seem to misunderstand that CD and directivity are completly different things. There can be one without the other and visa-versa. What I strive for is CD with high directivity and in the range of 125 Hz - 500 Hz a dipole has an advantage in that it can achieve a narrower directivity than a direct radiator. Below 125 Hz, I don't believe that the source type makes a difference and above 500 Hz the dipole and the direct radiator are converging on the same directivity.

I don't really buy room pressurization as a factor because it is simply not a major effect. It is true that monopoles are more efficient as the frequency falls, and this could be a factor. Room pressureization only occurs below the first mode and then only if the room is highly sealed, which is extremely rare. My room is probably sealed far better than most and I don't see any response below the first mode with my five monopoles. I have seen this effect in small cars, but the volumes are vastly different than a home listening room.

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However it requires sophisticated measurements. OTOH, a dipole with sufficient displacement and LF extension could just fit in into any small to moderate sized room with minimal need for tailoring its response to the room
There may be some truth to a dipole placed at random being preferable to a monopole placed at random, but that's simply a dumb thing to do, so what's the point? Isn't the question "How do I get the best bass in my room?" To that question, I do not find the dipole to be an advantage, more of a disadvantage due to its low efficiency. And the dipole has to be EQ'd, not doing so is not an option, so it should only be compared to an EQ'd monopole and then I think the results might be a wash.

The measurements aren't hard, the equipment can be obtained for < 100$ and the software is free. So taking the measurements is not an issue. Knowing what to do with them, as always, can be. Someday the software that I have to adjust the subs EQ will be available because its not difficult to do, but for now I need to keep it proprietary because its my only value added.

Last edited by gedlee; 13th October 2012 at 06:46 PM.
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Old 13th October 2012, 06:47 PM   #366
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I don't have them because at that time I had no PC available and you didn't want to make the sound files available for download. Maybe now is a good time, please, pretty please
I would be interested as well, but I can certainly understand not diseminating your work for free!
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Old 13th October 2012, 07:52 PM   #367
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It's pretty easy to generate a text file with any signal you like using Excel or writing your own short code. Then all you need to is convolve it with the system impulse response as measured at the listening position. There is no need to actually "play and measure" the test signal.
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Old 13th October 2012, 08:26 PM   #368
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Originally Posted by john k... View Post
It's pretty easy to generate a text file with any signal you like using Excel or writing your own short code. Then all you need to is convolve it with the system impulse response as measured at the listening position. There is no need to actually "play and measure" the test signal.
This surely is true (as long as we stay in the linear regime which can be quite safely assumed) but it's not our point. It's about listening to the effect in realtime with known and controlled properties of the signal. OK, your method can be used to listen to it as well -- with headphones. Further, you can walk along the room and probe with your ears, again in realtime.

Also, another purpose is to check what noises the room (plaster walls, doors, windows, furniture) does make, as well as to check the speakers themselves (distortion, rattling, port chuffing).

It was meant as a quite versatile and useful tool for evaluation of several perceptional aspects of LF reproduction in rooms.

I'll open a new thread for this, here it will get lost and it is slightly off-topic anyway.
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Old 13th October 2012, 08:48 PM   #369
gedlee is offline gedlee  United States
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I always use a swept tone in a room to search for buzzes and the like. But I do like the idea of having some controlled tone bursts to listen for the effects. I can see value in that.

John, I was not aware that Excel could write wav files (but I am not much of an Excel user), but anyways its very easy to generate files like this in MathCAD. But heck, if someone else has done the work for me I'll bite!
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Old 13th October 2012, 09:36 PM   #370
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Originally Posted by john k... View Post
Reducing the source output at a null frequency will not reduce the depth of the null.
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.
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