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Old 19th October 2020, 03:12 PM   #31
CharlieLaub is offline CharlieLaub  United States
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Originally Posted by David McBean View Post
Just to clarify, the acoustical impedance changes BECAUSE of the additional air mass. The two are intimately related, with the mass contributing to the reactive (imaginary) component of the complex impedance.
I was thinking of the situation more as the air mass in the tunnel being tightly coupled to the driver and becoming part of its moving mass. This would leave the "external" air to have the same acoustic impedance. But perhaps that is the wrong way to think about it. Honestly I am not well versed in that kind of driver modeling - it's a one step down towards first principles that I am used to worrying about!
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Old 20th October 2020, 08:46 AM   #32
David McBean is offline David McBean  Australia
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Originally Posted by CharlieLaub View Post
I was thinking of the situation more as the air mass in the tunnel being tightly coupled to the driver and becoming part of its moving mass. This would leave the "external" air to have the same acoustic impedance.
Ah, now I understand :-). I had incorrectly assumed that for both the normal H-Frame and the "unfolded" system, when you referred to "acoustical impedance", that you meant the resultant load at the diaphragm (which is required by the simulation model to calculate the response).
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Old 20th October 2020, 03:20 PM   #33
CharlieLaub is offline CharlieLaub  United States
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Originally Posted by David McBean View Post
Ah, now I understand :-). I had incorrectly assumed that for both the normal H-Frame and the "unfolded" system, when you referred to "acoustical impedance", that you meant the resultant load at the diaphragm (which is required by the simulation model to calculate the response).
Honestly, I do not know which is the right way to think about it and model it. I just measure the nearfield response so that I don't need to be concerned about how to model the driver in the 'frame. I can easily construct the far field response from front and rear nearfield measurements.
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Old 20th October 2020, 03:42 PM   #34
bentoronto is offline bentoronto  Canada
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Help to design H frame subwoofer
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Originally Posted by CharlieLaub View Post
Honestly, I do not know which is the right way to think about it and model it....
The nice thing about most other driver mounting systems (including corner horn) is that you can get away with simplifying the environment into which they play. You can, as McBean does, provide for one or more "walls", and I suppose there's simulation of the entire room impact too.

Not so with dipoles because that kind of simplification is too much. Dipoles always have a wall behind them at some non-standardized distance and non-standardized angle. And that wall has, as we say now-a-days, has "consequences".

Perhaps if the International Dipole Standardization Committee (IDSC) specified a room environment, then skillful model-coders like McBean could craft the software.

B.
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Old 20th October 2020, 05:09 PM   #35
CharlieLaub is offline CharlieLaub  United States
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The nice thing about most other driver mounting systems (including corner horn) is that you can get away with simplifying the environment into which they play. You can, as McBean does, provide for one or more "walls", and I suppose there's simulation of the entire room impact too.

Not so with dipoles because that kind of simplification is too much. Dipoles always have a wall behind them at some non-standardized distance and non-standardized angle. And that wall has, as we say now-a-days, has "consequences".

Perhaps if the International Dipole Standardization Committee (IDSC) specified a room environment, then skillful model-coders like McBean could craft the software.

B.
You seem to be stuck on dipoles and their reflections from walls? Didn't we agree, hearing is not like a microphone?

If the wall is near the dipole, the reflection from it (the wall) will just be combined with the first arrival by the brain as part of the "hearing" process. It's completely natural. It's how we can make sense of sounds in reflective spaces (all indoor spaces) and locate objects with our eyes closed.

As a result, I only worry about what the dipole is radiating into 2Pi or 4Pi space and do not at all worry about what the reflections will do. In fact, the best and most spacious imaging I have had with a dipole was in a very sparsely furnished and lively room using my first nude dipole prototype. The soundstage was incredible.
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Old 20th October 2020, 05:16 PM   #36
scottjoplin is offline scottjoplin  Wales
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How many times will low frequencies reflect around the room before your ears register them?
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Old 20th October 2020, 05:23 PM   #37
CharlieLaub is offline CharlieLaub  United States
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How many times will low frequencies reflect around the room before your ears register them?
At low frequencies dipole will stimulate room modes. It's less about reflections.

I was talking about above the point where room modes become dense. There is some name for the transition from sparse to dense room modes but I can't recall it.
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Old 20th October 2020, 06:28 PM   #38
bentoronto is offline bentoronto  Canada
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.....As a result, I only worry about what the dipole is radiating into 2Pi or 4Pi space and do not at all worry about what the reflections will do. In fact, the best and most spacious imaging I have had with a dipole was in a very sparsely furnished and lively room using my first nude dipole prototype. The soundstage was incredible.
Charlielaub, its called the Schroeder point. His office was just down the hall from mine at Bell Labs.

You seem to be contradicting yourself, first by saying the room doesn't matter in modelling a dipole and then by effusively elaborating your experience.

BTW, I really, really do not need your patronizing remarks about human hearing ("Didn't we agree, hearing is not like a microphone?"). What cred do you have in the subject of perception?

B.
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Old 20th October 2020, 09:23 PM   #39
CharlieLaub is offline CharlieLaub  United States
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Ben why are you so worked up over this?

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Charlielaub, its called the Schroeder point. His office was just down the hall from mine at Bell Labs.
Ah yes, the Schroeder frequency. That's it. Thanks.

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You seem to be contradicting yourself, first by saying the room doesn't matter in modelling a dipole and then by effusively elaborating your experience.
Contradicting myself? What I said was when I model the dipole I don't (on purpose) take into account any room reflections. Is this so different from modeling a closed box loudspeaker? What I said about room reflections is that they contribute to the listening experience with a dipole. Too often (not pointing fingers here) I have seen, especially with lovers of horn loudspeakers, that the idea is to take the room "out of the picture" by using lots of adsorption and traps, because anything but the direct sound is "bad". I am not in favor of that, and I feel that with dipoles you can actually use the room reflections to a sonic advantage. A more lively the room is actually better in this regard. The room and reflections become your friend, rather than the enemy.

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Originally Posted by bentoronto View Post
BTW, I really, really do not need your patronizing remarks about human hearing ("Didn't we agree, hearing is not like a microphone?"). What cred do you have in the subject of perception?

B.
Hmmm, patronizing? (looking up it now...) Let's see, according to Webster it is
showing or characterized by a superior attitude towards others : marked by condescension
OK, I had thought patronizing meant telling people what they wanted to hear, so you had me scratching my head there for a minute. But alas, you are not correct. I know you are both knowledgeable and experienced in many areas of audio. No, I 100% honestly thought we both were participating in a recent (e.g. past 6 months) thread where the topic of hearing versus microphone measurements was brought up, and that we were in agreement that they are not the same. Look, I am sorry if I am remembering incorrectly and this pushed your buttons in the wrong way. Believe me, I was not trying to be condescending in any way, shape of form and if that is how you felt it was completely unintentional on my part. I'm happy to say that right here, out in the open.

But honestly Ben, now that I have said that, there were probably 100 different and better ways that you could have raised the issue with me. You chose a rather low road there, calling out my "cred" and so on. Nice one.
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Last edited by CharlieLaub; 20th October 2020 at 09:28 PM.
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Old 21st October 2020, 07:14 AM   #40
David McBean is offline David McBean  Australia
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Originally Posted by bentoronto View Post
Not so with dipoles because that kind of simplification is too much. Dipoles always have a wall behind them at some non-standardized distance and non-standardized angle.
Hornresp takes into account the solid angle into which the H-Frame or U-Frame system radiates. The simulation model is valid at those frequencies where the dimensions of the system and the distance from the wall or walls are small compared to the wavelength, and where the system radiates symmetrically into the solid angle.

To illustrate, Attachment 1 shows the on-axis pressure response of a resistive U-Frame system optimised for cardioid directivity, radiating into quarter space (pi steradians solid angle). Attachment 2 shows the polar directivity pattern for the same system under the same radiation conditions, at a frequency of 100 hertz.
Attached Images
File Type: png Attach_1.png (56.6 KB, 84 views)
File Type: png Attach_2.png (54.1 KB, 84 views)
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