HOLMImpulse: Measuring Frequency- & Impulse-Response - Page 85 - diyAudio
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Old 21st November 2013, 02:51 PM   #841
yoke is offline yoke  Croatia
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thanks jtalden
will play with it, try to understand, learn how to use HOLMi...
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Old 5th May 2014, 12:04 AM   #842
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This is a really long thread and have wondered about this for a long time. Sorry have not read this very long thread for a while but, would really like this clarified.

It is my understanding the stimulating impulse (test signal) has a maximum amplitude at some point along the impulse curve, the peak amplitude at time say t-zero for convenience. The response of the speaker under test also produces a maximum amplitude and then is received at the microphone returning to the analyzer at time t-zero+nTime. It is the time from the driving impulse maximum amplitude to the speaker under test maximum amplitude which is used to determine the "excess time" or delay from the speaker under test to the microphone. This is used to determine the distance from microphone to the speaker is what I understand. Small times like delay through amplifiers and so on also add to this time but are small compared the the delay from speaker to microphone.

Is this correct? If wrong, how is this time determined to allow calculation of driver phase response and so on?
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Old 5th May 2014, 01:28 AM   #843
gedlee is offline gedlee  United States
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There are several options in HolmImpulse for determining the exact delay, but for the most part what you say is correct.
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Old 7th May 2014, 01:06 AM   #844
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Thanks for that.

If plausible, would really like to hear from the people responsible for the actual software. Are you one or are you an experienced user only?
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Old 7th May 2014, 06:12 AM   #845
Shaun is offline Shaun  South Africa
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If you could find the leading edge of the impulse with any amount of certainty, that would be a more accurate means to determine "excess". This is because the timing of the peak of the impulse is dependent on the driver's bandwidth; more specifically: high frequency response. Anyway, try to home in on the point where the measured impulse begins to rise (some estimation/judgment required) and you're good to go: that should effectively eliminate excess time.

While trying to find online references I found this blog, which may help some (I have not yet read all of it myself, but it looks relevant): Phase Alignment of Subs Ė Why I donít use the impulse response

I personally don't use the phase generated by HOLMImpulse. I import the SPL response into SoundEasy, do a Hilbert-Bode transform to determine minimum phase. I then use this method: Finding Relative Acoustic Offsets Empirically to determine relative acoustic offset.

Here's some more info (you may have to log in at PartsExpress Tech Talk forum to get the file): How To Use Passive Crossover Designer To Find The Relative Acoustic Offset.
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Old 7th May 2014, 03:28 PM   #846
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Thanks for posting this info and links. I am glad I did not have to point out,
LOUDNESS=DISTANCE
as a ridiculous conclusion. The problem then turns into, without knowing the distance, the impulse mapping into response cannot be made therefore, this whole impulse testing method without accurate distance (excess time through everything) is more or less a complete waste of time whereas the results are meaningless.
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Old 7th May 2014, 04:36 PM   #847
Shaun is offline Shaun  South Africa
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It is not clear why you think it might be a waste of time. Perhaps if you share what it is you are trying to achieve you will get an answer that addresses your problem more directly.

On your earlier request for HOLMImpulse software writers to respond... askbojeson did a lot of development here in the early days, but has not posted here since the software reached maturity. I am sure that here are others who understand the workings of the software well enough to answer your original question.
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Old 7th May 2014, 07:41 PM   #848
jtalden is offline jtalden  United States
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Quote:
Originally Posted by sumaudioguy View Post
Thanks for posting this info and links. I am glad I did not have to point out,
LOUDNESS=DISTANCE
as a ridiculous conclusion. The problem then turns into, without knowing the distance, the impulse mapping into response cannot be made therefore, this whole impulse testing method without accurate distance (excess time through everything) is more or less a complete waste of time whereas the results are meaningless.
I a hobbyist with experience aligning drivers in a multiway system. I agree with Shaun that if we knew the context for the question then the answer will become easier to convey.

Your concept of relating loudness to time/distance is erroneous. The level of the sweep signal is constant across the frequency range. The IR that is calculated by the analysis of the mic measurement results in an initial large peak in the IR that closely relates to the time the highest frequencies captured arrive at the mic. This time is (mostly) independent of the level of the signal and the mic input level. As Shaun indicated, the initial rise is really the better indicator of the delay of the first arriving (highest) freqs.

The phase response and group delay of a driver is changing over the its frequency range so there is no single "acoustic center" or "delay" for all frequencies.

These are general comments and may not help answer your question, but if not, they may help you form a more detailed one. Are you trying to align drivers in a multiway speaker design? Do you have a way to introduce a set delay in your system with a speaker management box like a DCX2496? Is it just an academic question?

Holm is not very well documented, but REW, Arta, and many other speaker measurement packages are. You may get your answer by reading their docs.
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Old 14th May 2014, 09:26 AM   #849
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Default Manipulation Feature in Holmimpulse

Hi all,

I am working on vinyl EQ measurements and my idea was to use the manipulation feature of HOLMimpulse to calculate the difference of a DUTs Trasfer Function from the ideal RIAA (or Columbia, Decca,...).

First I generated the RIAA transfer function (txt file, frequency, magnitude phase) in Scilab. It imports fine in HOLMimpulse using the import function. Second I measured the actual transfer function of the phono-pre. Unfortunately the manipulation (e.g. C = A/B) does not work properly. As a result I can only see a 0 degree phase line but no magnitude. It works well if I use two imported FR (e.g. Decca + RIAA) so I assume the problem is related to different sampling/frequency resolution, however I used 96kHz samplerate and 32768 FFT size for both, measurement and TF calculation in Scilab.

Any idea what the problem might be?

kind regards, Daniel
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Old 14th May 2014, 07:25 PM   #850
jtalden is offline jtalden  United States
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Have you reduced the dB scale enough to be sure the SPL plot is not just falling off the chart range?
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