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Old 3rd February 2020, 04:30 AM   #10451
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by SamAnytime View Post
I meant that calculating after putting in other parameters should not allow the locked parameters to be altered.
Using your first example:

Quote:
Originally Posted by SamAnytime View Post
1. lock throat area and segment length to set values, and only allow the 'calculate' routine to change the other values (mouth area etc.).
Attachment 1 shows the settings required to "lock" S1 = 200 and L12 = 120 and allow the value of AT to be entered before calculating the other parameter values.

Attachment 2 shows the settings required to "lock" S1 = 200 and L12 = 120 and allow the value of S2 to be entered before calculating the other parameter values.

Attachment 3 shows the settings required to "lock" S1 = 200 and L12 = 120 and allow the value of F12 to be entered before calculating the other parameter values.

The are no other solvable input options for an exponential segment with S1 and L12 "locked". You can confirm this for yourself by studying the equations defining the geometry of an exponential horn.
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Old 3rd February 2020, 10:42 AM   #10452
Brian Steele is offline Brian Steele  Grenada
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Originally Posted by David McBean View Post
Hi Mårten,

The acoustic path length is the length of the shortest acoustic path between the two outputs (assumed to be point sources). For your example, that means the length of the red line shown in the attachment, or in other words, the value of L23. It is not the difference in the distances from each output to the listener.

Kind regards,

David
Hmm... then I stand corrected on that issue, because I always thought it to be the latter. Does this apply to offset TLs as well?
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Old 3rd February 2020, 03:41 PM   #10453
bolserst is offline bolserst  United States
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Hornresp
A change was made to the calculation method for combined responses in Hornresp Update 4060-170521
The new method is a power response calculation that considers the total sound power radiated.
This makes the combined response consistent with the individual source responses which have always been power response.

The combined power response of two sources is dependent on their individual magnitude/phase, and the separation distance between them. The pressure response @ 1m is then calculated for a point source having the equivalent power response. The relative distances between listener and sources does not come into play, only the separation distance between the sources.

Additional information/clarification can be found here:
Hornresp Post #7383
Hornresp Post #8516
Hornresp Post #8521
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Old 3rd February 2020, 03:53 PM   #10454
more10 is offline more10  Sweden
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Quote:
Originally Posted by David McBean View Post
Hi Mårten,

The acoustic path length is the length of the shortest acoustic path between the two outputs (assumed to be point sources). For your example, that means the length of the red line shown in the attachment, or in other words, the value of L23. It is not the difference in the distances from each output to the listener.

Kind regards,

David
Thanks for the clarification David.

Just out of curiosity, is the port a point source in the simulation? Having mass but no depth?
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Old 3rd February 2020, 04:14 PM   #10455
Brian Steele is offline Brian Steele  Grenada
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I'm trying to "wrap my brain" around this change, and the reason for it, and I'm not sure I get it.

Consider the following extreme example (see attached image). Say the drivers and vent in each box are separated by 1/2W @ 400 Hz, where the first vent resonance effect appears. Are we saying that the "path" information for them would be the same and therefore the predicted response from Hornresp would be the same?

Because I expect that they would measure very differently around 400 Hz at the given listening position, because the phase relationship between the two sources would be different at that position.
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Old 4th February 2020, 04:03 AM   #10456
bolserst is offline bolserst  United States
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Quote:
Originally Posted by Brian Steele View Post
…Are we saying that the "path" information for them would be the same and therefore the predicted response from Hornresp would be the same?
Yes. The power response for both examples is the same. Power response is not dependent on mic position, as it is in essence a summation of all mic positions on the surface of a sphere(or part of a sphere) around the sources(which are considered to be point sources). This is no different than how Hornresp calculates acoustic output for individual sources(ie point source power response). DMcBean will likely have some additional comments on why Hornresp was developed as a power response calculator.

Quote:
…I expect that they would measure very differently around 400 Hz at the given listening position, because the phase relationship between the two sources would be different at that position.
Not sure about 400Hz since the vent likely won’t have much output, but if you are making measurements near the enclosure where distances (mic-to-vent) and (mic-to-woofer) have significant differences you will see differences in summation as you move around the enclosure. But, at low frequencies you will find that the power response is a better match for what you would measure in an outside ground-plane test at a typical listening distance of a couple meters.
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Old 4th February 2020, 06:08 AM   #10457
David McBean is offline David McBean  Australia
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Just out of curiosity, is the port a point source in the simulation? Having mass but no depth?
Hi Mårten,

In your bass reflex example, for the purposes of combining the two sound outputs, both the driver and the port are considered to be point sources. A point source is simply an acoustic radiator having dimensions that are small compared to the wavelength.

The air in the actual port tube has mass and depth, both of which are taken into account in the simulation.

Kind regards,

David
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Old 4th February 2020, 06:40 AM   #10458
David McBean is offline David McBean  Australia
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Hi bolserst,

Quote:
Originally Posted by bolserst View Post
The power response for both examples is the same.
Thanks for providing the detailed explanation and the reference links - you have saved me some work :-).

Quote:
Originally Posted by bolserst View Post
DMcBean will likely have some additional comments on why Hornresp was developed as a power response calculator.
Determining the directivity characteristics necessary to enable the pressure response to be calculated would require the use of finite element analysis. Testing has shown that this slows the operation of Hornresp (on my computer at least) to an unacceptable level. A simple one-parameter directivity model has however been included, which gives indicative results. At low frequencies the difference between the power and pressure responses is not that large anyway, due to the omnidirectional nature of the sources at those frequencies.

Kind regards,

David
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Old 4th February 2020, 06:42 AM   #10459
David McBean is offline David McBean  Australia
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Does this apply to offset TLs as well?
Yes.
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Old 4th February 2020, 07:17 AM   #10460
David McBean is offline David McBean  Australia
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At low frequencies the difference between the power and pressure responses is not that large anyway
Just to clarify - this statement applies to a bass horn system.
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