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Multi-Way Conventional loudspeakers with crossovers

Group Delay Question
Group Delay Question
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Old 1st November 2005, 12:37 AM   #1
69stingray is offline 69stingray  United States
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Default Group Delay Question

I don't think I understand group delay. Can someone give my the "Group Delay for Dummies" version of what it means and how it effects loudspeakers?

For example, I have attached the group delay plot from WinISD for the same driver (Dayton 7" Aluminum Cone) with 5 different volumes (the 5 different alignments available in WinISD).

What should I learn from the group delay of each alignment?

Click the image to open in full size.
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Old 1st November 2005, 12:48 AM   #2
soongsc is online now soongsc  Taiwan
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The definition of group delay is -dphase /dfrequency. Are the larger peaks the higher volume setting?
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Old 1st November 2005, 01:04 AM   #3
Sjef is offline Sjef  Netherlands
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Group delay is nothing more than the phase characteristic corrected to frequency.

In simple words, When a loudspeaker has a group delay of 2mS at 200 Hz and a group delay of 20 mS at 40 Hz (not uncommon for reflex enclosures) this means that when two tones of 40 and 200 Hz are played at the same time the 40HZ tone whil come out 20-2=18mS later than the 200Hz tone. in other words, the low frequencies are walking behind the low-mid frequencies in this example.

hope this helps.
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Old 1st November 2005, 01:22 AM   #4
69stingray is offline 69stingray  United States
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Thanks Sjar-

In that case, using the sample of the graph I posted. Looking from 40 Hz on up, the Light Cyan curve (the real peaky one) would be "better" from a group delay standpoint?

How audioable is group delay? Is there a time lapse that starts becoming objectionable? For example, will the group delay difference at 40Hz be noticeable between the light cyan curve and the red curve?
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Old 1st November 2005, 01:28 AM   #5
ShinOBIWAN is offline ShinOBIWAN  United Kingdom
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Keep the group delay(GD) below 10ms in the 30-40hz+ range if possible.

Be aware that ported designs generally have worse GD than sealed at lower frequencies because of the 180degree phase shift at the tuning frequency.

Group delay is really only problem for the lowest frequencies, which one of the reasons why I much prefer sealed with a LT.
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Old 1st November 2005, 01:31 AM   #6
Sjef is offline Sjef  Netherlands
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I'm sorry, somehow I don't see your attacement.

There ar lot's of discussions of how audible the group delay is, but it's controversial. Every loudspeaker suffers from group delay. When you really want the least group delay just build the biggest enclosure you can and this problem is solved. But that means you won't get any bass from your system anymore. So it's all about compromise. The only choose the least worst alligment
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Old 1st November 2005, 01:35 AM   #7
carlosfm is offline carlosfm  Portugal
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Quote:
Originally posted by ShinOBIWAN
Group delay is really only problem for the lowest frequencies, which one of the reasons why I much prefer sealed with a LT.
Group delay is a problem over the entire spectrum, crossovers also have group delay.
The higher the slope the worse it gets, and also the crossover type.
For instance, 2nd order Bessel has much less group delay than 2nd order Butterworth.
It is clearly audible in the midband and treble.
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Old 1st November 2005, 01:40 AM   #8
ShinOBIWAN is offline ShinOBIWAN  United Kingdom
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Quote:
Originally posted by carlosfm


Group delay is a problem over the entire spectrum, crossovers also have group delay.
The higher the slope the worse it gets, and also the crossover type.
For instance, 2nd order Bessel has much less group delay than Butterworth.
It is clearly audible in the midband and treble.
Do what I do and use FIR filters

Seriously though, you've got to really mess up your design to get anything like 10ms in the mids. According to SW I've got 2ms as a worst case from 100hz-20Khz
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Old 1st November 2005, 01:40 AM   #9
69stingray is offline 69stingray  United States
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Thanks everyone for your replies, very interesting.
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Old 1st November 2005, 01:50 AM   #10
carlosfm is offline carlosfm  Portugal
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Quote:
Originally posted by ShinOBIWAN
Seriously though, you've got to really mess up your design to get anything like 10ms in the mids. According to SW I've got 2ms as a worst case from 100hz-20Khz
Try it, listen and compare.
It's audible, the mid/treble gets slower and less detailed.
It's even audible in active filters, simpler is (sounds) better.
Software doesn't make the whole speaker, some decisions are made later, depending on the priorities.
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