How to Measure Group Delay

[DigitalMan]

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[JimmyM]

Step it off and guess...I believe it's 1 ms per foot, but I could be wrong.

 

[B-string]

Don't know the software, I would imagine the sample rate would be dependent on the sound card and computer processor. Not a true lab measurement but maybe close enough for general use.
Behringer PA equipment is generally pretty decent so if it has a model profile sounds like a good match.

 

[B-string]

Kudos for actually taking this on BTW . Yes to zero axis, but I would use a standard one meter distance, then a one foot measurement. As frequency goes up the portion of the speaker cone that is producing the frequency narrows towards the center of the speaker. This where the metal "dust caps" came from, they are an attempt to enhance high frequency performance.

Measure direct in front of both your monitors, same plane same distance to check for individual differences.

For mixed speaker size cabs, if this is where you are going, one meter at the vert. center of the two cabs. Be sure to line the cabs up so the speaker fronts are on the same plane. Don't rely on the front of the cab as distance from speaker basket to grill can vary.
Have some fun in the journey!

 

[B-string]

Your computer setup should give some good results, use the highest sample rate that provides stable results.
Be sure to do a complete defrag on your drive to be positive the SSD is properly handling file fragments.

 

[dhsierra1]

For mixed speaker size cabs, if this is where you are going, one meter at the vert. center of the two cabs. Be sure to line the cabs up so the speaker fronts are on the same plane. Don't rely on the front of the cab as distance from speaker basket to grill can vary.

the speaker dust covers should be lined up for different sized speakers for proper ZDP (zero delay plane). That's your best approximation.

 

[B-string]

the speaker dust covers should be lined up for different sized speakers for proper ZDP (zero delay plane). That's your best approximation.

For high frequencies yes, for overall response not really best IMHO. But disagreement is good and easily made part of the test.

 

[walterw]

As frequency goes up the portion of the speaker cone that is producing the frequency narrows towards the center of the speaker.

huh?

my tenuous understanding of this is that the Invalid Link Removed;

it's just that as the sound waves get smaller relative to the speaker size, the waves from the far side of the speaker get canceled by the waves from the near side when you're not in front of it.

when you're right in front, the treble (from all over the speaker) is hitting you at the same time in-phase, creating the coherent beam.

that's why the bigger the driver, the narrower the dispersion.

(and why beam blockers don't really work; they're fixing the wrong problem.)

 

[dhsierra1]

For high frequencies yes, for overall response not really best IMHO. But disagreement is good and easily made part of the test.

ZDP varies most at lower frequencies, ergo the group delay issue we're discussing. Agreed, though, might as well vary the horizontal plane as well

 

[JimmyM]

Sorry...I thought you were talking about the delay you get between your gear and the PA.

 

[dhsierra1]

huh?

my tenuous understanding of this is that the Invalid Link Removed;

it's just that as the sound waves get smaller relative to the speaker size, the waves from the far side of the speaker get canceled by the waves from the near side when you're not in front of it.

when you're right in front, the treble (from all over the speaker) is hitting you at the same time in-phase, creating the coherent beam.

that's why the bigger the driver, the narrower the dispersion.

(and why beam blockers don't really work; they're fixing the wrong problem.)

as frequency increases the radiating area decreases. Beaming is a function of speaker diameter relative to the frequency wavelength, so larger diameter speakers beam at lower frequencies than their smaller sized brethren. Roughly when the frequency wavelength is about the same as the speaker's circumference is when beaming begins to occur.

 

[B-string]

ZDP varies most at lower frequencies, ergo the group delay issue we're discussing. Agreed, though, might as well vary the horizontal plane as well

Can we also agree than the true center resting point if the voice coil to cone attachment point is the least ascertainable plane on a completed speaker system? We "stack" cabs with fronts close to flat whether its right or wrong and a half inch or so most might be able to live with?

 

[will33]

as frequency increases the radiating area decreases. Beaming is a function of speaker diameter relative to the frequency wavelength, so larger diameter speakers beam at lower frequencies than their smaller sized brethren. Roughly when the frequency wavelength is about the same as the speaker's circumference is when beaming begins to occur.

This^^

Center placement to capture as high as the driver will play. Hence the reason, or rather one of them, for 2 and 3-way speakers

 

[dhsierra1]

Can we also agree than the true center resting point if the voice coil to cone attachment point is the least ascertainable plane on a completed speaker system? We "stack" cabs with fronts close to flat whether its right or wrong and a half inch or so most might be able to live with?

yes, it is pretty challenging to measure but I figure with all the recent dust-ups on the subject we might as well do these expts as accurately as possible.

This is why I agree with you that there should be "real world" measurements as well as tests as maximally controlled for variables as possible. And at the end of the day I run with and use the real world test results, and then publish the highly controlled experiments for academic thrills

Edit, well, it won't be "we" running the experiments, that's up to the OP to decide how to set things up since he's buying the gear and going through the exercise.

 

[walterw]

as frequency increases the radiating area decreases. Beaming is a function of speaker diameter relative to the frequency wavelength, so larger diameter speakers beam at lower frequencies than their smaller sized brethren. Roughly when the frequency wavelength is about the same as the speaker's circumference is when beaming begins to occur.

but is the actual radiating area decreasing, or is it just getting canceled off-axis?

if the speaker really didn't emit the highs on the outer edges, the highs coming from the center would be effectively coming from a smaller driver and would have a wider, not narrower pattern.

(wait, did you mean "radiating area" on the speaker cone or out into the world?)

 

[dhsierra1]

but is the actual radiating area decreasing, or is it just getting canceled off-axis?

if the speaker really didn't emit the highs on the outer edges, the highs coming from the center would be effectively coming from a smaller driver and would have a wider, not narrower pattern.

(wait, did you mean "radiating area" on the speaker cone or out into the world?)

my understanding is that the radiating area on the cone actually decreases to just the center portion of the driver. This was taken advantage of by whizzer cones and as B-String pointed out the metal dust caps (eg JBL ). The highs wind up decreasing in the radiating area because of cone mass issues. Again, the reason you have the beaming is because of the effect of the overall size of the cone, regardless of the amount of cone area that's doing the actual radiating. How and why that's so is something BFM or DLJ would have a far better grasp of than me.

 

[will33]

Agreed re: time alignment. It'd be intersting to see 1 with voice coils aligned and 1 with a flat cab face, the way most people set up.

 

[dhsierra1]

Thanks.

I had a thought that just occurred in this conversation.

If a measurement is taken from from an equidistant location (e.g. 1 inch, 1 foot, 1 meter) in front of the grille, it may not perfectly measure each cabinet when accounting for ZDP. However, would it be the most accurate reading if the derivative information desired is the actual delay experienced in the real world from a listener?

I would be trading off an accurate "factory style" spec for what might be a more applicable "relative" reading. In short, the listener in a real world spot considered ideal would be roughly equidistant from the front of the grilles.

Therefore this measurement would be group delay plus propagation delay (travel time) accounting for differences in ZDP. Given 1.1ft/ms speed of sound and the overall ZDP range possible, what is the maximum time delta I am looking at here? Is is around 0.1 ms?

Testing from equal distances might actually compensate for ZDP assuming people line up their cabs front-flush rather than according to ZDP.

Am I thinking this through correctly?

If you're going to go through all of this then I would suggest you pick up a copy of Vance Dickason's "Loudspeaker Design Cookbook" or something similar and read up how it's all done.

 

[billfitzmaurice]

huh?

my tenuous understanding of this is that the Invalid Link Removed;

it's just that as the sound waves get smaller relative to the speaker size, the waves from the far side of the speaker get canceled by the waves from the near side when you're not in front of it.

when you're right in front, the treble (from all over the speaker) is hitting you at the same time in-phase, creating the coherent beam.

that's why the bigger the driver, the narrower the dispersion.

(and why beam blockers don't really work; they're fixing the wrong problem.)

Most of that is factual, but not all. While the cone radiates the same frequencies from its entire surface the dome also can be configured to operate as a separate high frequency radiator, improving high frequency response and dispersion, though not nearly to the extent that a separate midrange or high frequency driver can.
Beam blockers do work, as phase plugs via diffraction. The effect isn't huge , but it's there.
As for group delay, it's a non issue and not worth considering. A speaker with group delay bad enough to be audible would have so many other issues as to make it unlistenable at all. Oddiophiles who worry about anything that can be measured fret about it, but strangely enough the same oddiophiles claim to hear things that even the best gear can't measure, defying the laws of both physics and biology.

 

[B-string]

Don't feel bad, he told me he was putting me on Iggy also. I'm so heartbroken
It's an honor roll I think?