HOLMImpulse: Measuring Frequency- & Impulse-Response - Page 84 - diyAudio
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Old 24th October 2013, 08:14 PM   #831
KSTR is offline KSTR  Germany
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The problem is for HF we know that the phase must roll off corrsponding to the rolloff of magnitude shape, but we don't know how much in detail. We know that a speaker cannot have a phase going more positive while the response falls at the same time with the correct time zero, as well we know that the phase cannot roll off negative like crazy when we see a moderate response rolloff. So we can only eyeball correct time zero (much easier to see a dead-time related rolloff in linear frequency scale, btw, as it becomes a superimposed slope on the real phase response). Only way to find the exact point (for academic interest, that is) is to covert to minphase which makes the HF start at the first sample, reload it without auto zero detection and move the original pulse in time in 1/10th sample fractions until you see the same rolloff at HF. Largest or first peak is typically very close so that should do in most situations.

Example of the "linear view eyeballing" here : Synergy Horns. No drawbacks, no issues?

Last edited by KSTR; 24th October 2013 at 08:18 PM.
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Old 24th October 2013, 09:54 PM   #832
gedlee is offline gedlee  United States
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Simple question, seems appropriate here. What is the program "rephrase"? What does it do and why would someone want to use it?
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Old 24th October 2013, 10:08 PM   #833
ra7 is offline ra7  United States
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Thanks KSTR... I think I understand.

Earl,
rePhase, a loudspeaker phase linearization, EQ and FIR filtering tool

Allows you to play with phase and output corrected impulse that can be inserted in the signal chain to fix phase (and other things).
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Old 25th October 2013, 01:54 AM   #834
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What is the best way to show phase?

What is the best way to measure phase?

My 3 ways so far. Any of them work?
TweeterL: DNA-159 driver on an EOS 6 waveguide
xover around 2300hz
Mic was about 1" from waveguide mouth

Click the image to open in full size.

[IMG]Click the image to open in full size.[/IMG]

[IMG]Click the image to open in full size.[/IMG]

Last edited by makingmoney; 25th October 2013 at 02:11 AM.
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Old 25th October 2013, 07:44 AM   #835
AllenB is offline AllenB  Australia
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I find if you look at the highest frequencies while changing the start time, it will be easier to find where they aren't rolling upward or downward. Phase doesn't have to be level, just free of this extra shift.

An exception to this is where you are taking two measurements from one location. Then you can choose which one will be the 'correct' one.
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Old 26th October 2013, 01:08 PM   #836
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Causal means no output commences before the stimulus input. (Drivers are not clairvoyent!).

If we consider most drivers to be bandpasses (limited bandwidth with rolloffs both sides) then we will always see the phase roll up on the low side and roll down on the high side. All we need is to figure out the magnitude of the longest delay on the high side. With the "t equals minus d phi over d omega" understanding then the right delay gets the stop band phase to bend up to just level ( which will equal zero delay for that frequency region).

This would be equivalent to creating the group delay curve ( calculating the d phi d omega curve) and looking for the earliest part and then setting it to zero ms.

This should also be the delay required to get the measured phase to match calculated minimum phase.

It isn't quite the first peak in the impulse response, as energy preceeds that. I believe the peak of the impulse is roughly equal to the group delay of the center of the unit's band pass. Note that I have seen designers attempt time allignment by setting the impulse peaks of several sections in line. This gets their respective midbands in allignment but very likely gets their crossover region out of phase. Wrong!

My understanding, at least.

David
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Old 21st November 2013, 07:29 AM   #837
yoke is offline yoke  Croatia
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I nead help understanding measurments

Click the image to open in full size.

I'm using
- pc - behringer DCX2496 - amplifiers - speaker
- mic / behringer - monacor micpriamp - pc

cut is 12db L-R at 2.4kHz

what I don't understand is why is ti measure low frequencies on twitter ?
and have high on mid bas ?

is there something I'm doing wrong ?

( pc audio card have flat response )

this is with 1/6 smoothing

Last edited by yoke; 21st November 2013 at 07:42 AM.
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Old 21st November 2013, 08:19 AM   #838
yoke is offline yoke  Croatia
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Here is the frequency response of mid/bas with twitter (green)
with 1/6 smoothing

How does it look to you ?
I think it's bad, because all those up and down under 1kHz
Is it room or just a bad speaker cabinet ?
(drivers are scan speak 18W8545)


Click the image to open in full size.

or is there some holmi user guide how to measure for dummies ?
(practical stap by stap..I have searc net and this is the simple one...
Red Spade Audio: How to measure your crossover with Holm Impulse

In those grafs I didn't use gating ?
would that help ?
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Old 21st November 2013, 01:44 PM   #839
jtalden is offline jtalden  United States
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Quote:
Originally Posted by yoke View Post
...
what I don't understand is why is ti measure low frequencies on twitter ?
and have high on mid bas ?
Once the SPL reaches the noise floor (550 Hz for the TW and maybe 40 Hz for the MW) the SPL response follows the noise floor and the phase response will go wild.

It's a good idea to measure the noise floor so you can understand where it is.

In "Options" there is ability to hide the phase when SPL falls below a level you can set. This can help clean up the traces if it is set correctly.

The MW trace has the phase rolling up at a fast rate. This is due to the position of its IR relative to 0 ms. Its peak must be before 0 ms.
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Old 21st November 2013, 01:51 PM   #840
jtalden is offline jtalden  United States
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Quote:
Originally Posted by yoke View Post
...I think it's bad, because all those up and down under 1kHz
Is it room or just a bad speaker cabinet ??
This is typical room influence.

If you can't find detailed info regarding Holm try reading the info provided on any other measurement software package. The concepts are all identical and once those are understood then it is easy to learn how to use the controls provided in Holm.
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