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Transient response?

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John Roberts {JR}:

--- Quote from: Ivan Beaver on February 22, 2021, 08:58:14 am ---
And then you have the latency of the LP filter to add to the whole mess-------------

--- End quote ---
Better known as phase lag...

JR

duane massey:
Thanks, everyone. Back in "the day" we called it the "boom or thump" comparison. If you put on a recording of a heavy kick drum or thumping a mic, did the cabinet go "boom" or "thump"? We always strove for "thump", especially at higher volume levels. Built a lot of very large straight bass horns back then, and one of the biggest differences to our unscientific minds was the excursion of the woofers. Seemed to us that woofers in ported boxes really started flopping after a certain level, whereas the horns had significantly less excursion at the same output, and we assumed this was part of the boom vs bump that we were hearing. I will probably never build any horns of that magnitude again, so this is just idle curiosity on my part.

Ivan Beaver:

--- Quote from: duane massey on February 22, 2021, 10:08:11 am ---Thanks, everyone. Back in "the day" we called it the "boom or thump" comparison. If you put on a recording of a heavy kick drum or thumping a mic, did the cabinet go "boom" or "thump"? We always strove for "thump", especially at higher volume levels. Built a lot of very large straight bass horns back then, and one of the biggest differences to our unscientific minds was the excursion of the woofers. Seemed to us that woofers in ported boxes really started flopping after a certain level, whereas the horns had significantly less excursion at the same output, and we assumed this was part of the boom vs bump that we were hearing. I will probably never build any horns of that magnitude again, so this is just idle curiosity on my part.

--- End quote ---
Here is what I have found that is interesting, through various testing I have done. 

The "thump" or kick or punch is more due to a NON FLAT response.  Or one in which the upper part of the bass range is louder than the lower part of the response.  This can be due to either non proper alignment between tops and subs, eq boost, or just ragged response.

A flat accurate response will not sound as "punchy".

This can happen in a couple of different ways.  In horns,, there could be more horn gain at the upper end of the response than at the lower end (very common in shorter horns).

in front loaded cabinets this can often be harmonic distortion (which is simply higher freq that are not in the original signal-free sound if you think of it that way) or the rising response of the driver at higher freq of the bass range.

Most people have never looked at distortion with even a simple RTA.

Just put in a sine wave (preferably in the passband) at a low to moderate level, and look at the response on a RTA.  You should see a single spike (but there will be some skirts on the sides due to the way most RTAs overlap bands).

Now turn up the level and watch for freq that start to rise up that are harmonically related to the original (ie multiples of the original freq).  So if you put in 60Hz, you will see spikes at 120, 180, 240 etc.

The relative level of the other freq in relation to the original is the amount of distortion at those harmonics the cabinet is producing. 

This works well for full range cabinets as well.

Just don't get stupid or you can tear things up.

Mark Wilkinson:

--- Quote from: Ivan Beaver on February 22, 2021, 08:58:14 am ---

Even something like "arrival" of a low freq signal. Is it when the first part of the signal gets to you? or the peak?  Since low freq wavelengths can be very long, it gets into a whole different discussion.

Just look at the auto delay finders on various measurement platforms.  "If" they can give you a repeatable number, it is much longer than the distance you are away from the loudspeaker.  That is because they are adding the distance from the source AND the distance to the center part of the wavelength together.

Higher freq are much easier, because the wavelengths are much shorter.



--- End quote ---

With all due respect, I don't think auto delay finders work like that...."adding the distance from the source AND the distance to the center part of the wavelength together."
(italics added to part i disagree with)

Because like you were saying just before that, when does the low freq arrive?  The first part of the wave, or the peak?
And the answer as I know it, is the first part of the wave, the very first initial rise of the wave.   
That's the time a good auto delay finder works to calculate, not the arrival of the peak of the wave.

My 2c...
Transient response predominantly equals frequency response.....flat full spectrum frequency response.
But even perfect frequency response can have it's transient response improved, when phase rotation/group delay are reduced/eliminated.

Perfect transient response is when the initial rise of all frequencies begins at the exact same time (which spreads their peaks out in time... )
This also gives a perfectly flat zero degree phase curve.  (not something likely to have with live sound, huh?)


Ivan Beaver:

--- Quote from: Mark Wilkinson on February 22, 2021, 11:28:12 am ---With all due respect, I don't think auto delay finders work like that...."adding the distance from the source AND the distance to the center part of the wavelength together."
(italics added to part i disagree with)

Because like you were saying just before that, when does the low freq arrive?  The first part of the wave, or the peak?
And the answer as I know it, is the first part of the wave, the very first initial rise of the wave.   
That's the time a good auto delay finder works to calculate, not the arrival of the peak of the wave.



--- End quote ---
So use a auto delay finder, with just a sub (no full range cabinets) with low pass filter engaged.  See what it tells you.  Now see if that distance is what the distance from the sub to the mic is.  I have never seen it be anywhere near close.

If you disengage the low pass filter, it will be more accurate, because there is more high freq information available (ie shorter wavelengths).  Of course the actual phase trace will tell you (depending on how it tilts) how close the measured distance is from the actual distance.  Of course you also have to take into account any digital delays (either actually set or AD/DA convertors).

It is not necessarily the peak, but is not the "onset" of the waveform getting there.

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