Ok, what is group delay? It is rated in ms, so i assume it has to do with time. and when looking at a group delay curve, what is generally good? a flat line, or an increasing line with constant slope or what? Does group delay have anything to do with overhang?
thanks for any help you can give me.
thanks for any help you can give me.
DEFINITIONS
Hi,
I'll take the easy way out.
I suggest you take a look at these definition tables:
GROUP DELAY
Cheers,
Hi,
I'll take the easy way out.
I suggest you take a look at these definition tables:
GROUP DELAY
Cheers,
Group Delay as it relates to what?
In live concert sound If a speaker line is set up halfway to the back of the arena a delay must be set up so when the sound from the stage reaches the delay line the phasing stays correct.
The same must also be done on the stage line between the lows to mids to highs if the drivers are not in line in order to maintain the proper phase relationship between the frequencies
As far as a group delay curve, I have no idea. Is this someones design of a multi driver speaker or just a term you heard?
In live concert sound If a speaker line is set up halfway to the back of the arena a delay must be set up so when the sound from the stage reaches the delay line the phasing stays correct.
The same must also be done on the stage line between the lows to mids to highs if the drivers are not in line in order to maintain the proper phase relationship between the frequencies
As far as a group delay curve, I have no idea. Is this someones design of a multi driver speaker or just a term you heard?
Here are a few thoughts.
I'll leave the nitty gritty to the link already posted. Here's what I've come to understand over the past couple months since getting into vented systems.
For one, sealed systems have extremely low group delay, typically under 7 ms at all frequencies. Ideal group delay would be zero, but this just isn't going to happen, although the higher in frequency you go, the closer to zero it will become.
For vented systems, the peak in the group delay curve will come at the box tuning frequency, Fb. For a given woofer and box size, lowering the Fb will increase the peak value of group delay. The peak is generally quite narrow however, and so lowering Fb will have the effect of reducing group delay at higher frequencies.
I was talking with Dan Wiggins from Adire Audio about this last week. His rule of thumb is to design the box/woofer/vent combination so that the product of group delay and frequency is about 400 or less. So, ideally, you'd have group delay of no more than 20 ms at 20 Hz, 13 ms at 30 Hz, 10 ms at 40 Hz, etc.. He also mentioned that if your system response is down, then you are allowed higher group delay without it being audible. For example, I believe he mentioned that if your response is 10 dB down at 20 Hz, then you could have 2-3 times the group delay of a system that was flat to 20 Hz, without audible detriment.
As for overhang, I do believe it's somewhat related, yes. Group delay, in my understanding, is the difference in time between when a signal is applied to the speaker driver, and when it actually is output into the room as sound. So when you think about it, use for instance a kick drum or any other kind of drum that has a high frequency content. The high frequency portions will be output almost instantaneously, while the low frequency portions will be delayed by an amount dependent upon your speaker system. It can get very high in poorly designed vented systems.
The ideal group delay curve would be a straight line at 0 ms.
Hope this made some sense.
Aaron Gilbert
I'll leave the nitty gritty to the link already posted. Here's what I've come to understand over the past couple months since getting into vented systems.
For one, sealed systems have extremely low group delay, typically under 7 ms at all frequencies. Ideal group delay would be zero, but this just isn't going to happen, although the higher in frequency you go, the closer to zero it will become.
For vented systems, the peak in the group delay curve will come at the box tuning frequency, Fb. For a given woofer and box size, lowering the Fb will increase the peak value of group delay. The peak is generally quite narrow however, and so lowering Fb will have the effect of reducing group delay at higher frequencies.
I was talking with Dan Wiggins from Adire Audio about this last week. His rule of thumb is to design the box/woofer/vent combination so that the product of group delay and frequency is about 400 or less. So, ideally, you'd have group delay of no more than 20 ms at 20 Hz, 13 ms at 30 Hz, 10 ms at 40 Hz, etc.. He also mentioned that if your system response is down, then you are allowed higher group delay without it being audible. For example, I believe he mentioned that if your response is 10 dB down at 20 Hz, then you could have 2-3 times the group delay of a system that was flat to 20 Hz, without audible detriment.
As for overhang, I do believe it's somewhat related, yes. Group delay, in my understanding, is the difference in time between when a signal is applied to the speaker driver, and when it actually is output into the room as sound. So when you think about it, use for instance a kick drum or any other kind of drum that has a high frequency content. The high frequency portions will be output almost instantaneously, while the low frequency portions will be delayed by an amount dependent upon your speaker system. It can get very high in poorly designed vented systems.
The ideal group delay curve would be a straight line at 0 ms.
Hope this made some sense.
Aaron Gilbert
Group Delay is directly related to the change of phase of a driver as it rolls off -- usually referring to the roll-off at the bottom of a woofer. The higher the order of the roll-off, the greater the Group delay.
A flat curve would be best, but would require a speaker to be flat to DC. It's not going to happen. The shallower (and smoother) the rise the better.
This is a tool best used when trying to minimize the group delay problems that come along with a ported speaker.
dave
A flat curve would be best, but would require a speaker to be flat to DC. It's not going to happen. The shallower (and smoother) the rise the better.
This is a tool best used when trying to minimize the group delay problems that come along with a ported speaker.
dave
see, the thing is i'm looking for a car audio woofer mainly for sound quality, well my definition at least. I don't know what exactly to look for in that regards. I was thinking about making a sealed box that has a relatively flat delay over the range it would play. I was thinking of getting an alpine HU with time correction and using it to push the woofers slightly closer to the rest of the speakers in terms of delay. then i though: what if group delay is something other than what i think it is?! of course all of you can see the problem with designing something and building it based upon a false assumption! thanks. guess it's back to the drawing board.
the woofers i have now have a predicted group delay of 5.5ms +- 0.1ms from 15hz to 44hz. playing with winISD, it looks like a Qtc of .5 gives a line for group delay. I don't regard my woofers as extemely high quality though.
all the woofers people seem to like (for car audio) model terribly IMO. like a woofer I looked at modeled well in a 3 cubic foot box, but was reccomended for a 0.75 cubic foot box! the Qtc was above 1.
the woofers i have now have a predicted group delay of 5.5ms +- 0.1ms from 15hz to 44hz. playing with winISD, it looks like a Qtc of .5 gives a line for group delay. I don't regard my woofers as extemely high quality though.
all the woofers people seem to like (for car audio) model terribly IMO. like a woofer I looked at modeled well in a 3 cubic foot box, but was reccomended for a 0.75 cubic foot box! the Qtc was above 1.
What to look for in a car woofer.
theChris,
Just about any sealed box configuration is going to give you excellent group delay figures. I would not say that it's worth going to a Qtc of 0.5 instead of 0.7, as the box will be three times larger and group delay in fact may not be any lower. I seriously doubt that anyone could hear the difference between a group delay of 5 ms and 5.5 ms.
For a car woofer, generally people look for mid to low Qts, low Vas, and somewhat higher Fs than a home driver of similar size. All these factors combine to give you very accurate bass in a very small box, with a relatively high F3, which will be compensated for by the cabin gain of your car. That's not to say you cannot put a subwoofer with a low F3 (low by my definition being about 45 hz and below) in a car. You can, but you'll almost certainly have a big peak in the response in the 30-60 hz region. My Shiva should have an F3 of about 44 Hz, and my car has a peak of 8 dB at 50 Hz. That would definitely be reduced if the F3 was 60 hz or higher, though I would of course have less output.
I've found that getting smooth bass in my car is really tough for various reasons. Output is not a problem, or low end extension, it's getting the response to be free of giant dips and peaks at the listening position...
The sealed box woofer will not be your enemy in getting sound quality, it's about 95% the car and your implementation of the crossover.
Using the head unit to add delay to the other speakers to bring them in sync with the subwoofer is a neat idea, but does the head unit provide fine enough adjustment? I suppose getting close is better than nothing, and for it to work, as you mention, it would be best to have a sub box whose group delay is as constant as possible.
Aaron Gilbert
theChris,
Just about any sealed box configuration is going to give you excellent group delay figures. I would not say that it's worth going to a Qtc of 0.5 instead of 0.7, as the box will be three times larger and group delay in fact may not be any lower. I seriously doubt that anyone could hear the difference between a group delay of 5 ms and 5.5 ms.
For a car woofer, generally people look for mid to low Qts, low Vas, and somewhat higher Fs than a home driver of similar size. All these factors combine to give you very accurate bass in a very small box, with a relatively high F3, which will be compensated for by the cabin gain of your car. That's not to say you cannot put a subwoofer with a low F3 (low by my definition being about 45 hz and below) in a car. You can, but you'll almost certainly have a big peak in the response in the 30-60 hz region. My Shiva should have an F3 of about 44 Hz, and my car has a peak of 8 dB at 50 Hz. That would definitely be reduced if the F3 was 60 hz or higher, though I would of course have less output.
I've found that getting smooth bass in my car is really tough for various reasons. Output is not a problem, or low end extension, it's getting the response to be free of giant dips and peaks at the listening position...
The sealed box woofer will not be your enemy in getting sound quality, it's about 95% the car and your implementation of the crossover.
Using the head unit to add delay to the other speakers to bring them in sync with the subwoofer is a neat idea, but does the head unit provide fine enough adjustment? I suppose getting close is better than nothing, and for it to work, as you mention, it would be best to have a sub box whose group delay is as constant as possible.
Aaron Gilbert
Hi Chris
If you are only building a IB or ported box you need not worry too much about group delay at the bottom end, as it is proportional to the slope of the driver roll off, ( as Dave said), it only really becomes a problem with complex boxes, such as bandpass boxes.
Bandpass boxes have many air loads in circuit, and the time taken for an impulse to filter through these can lead to a large group delay, and very slow bass.
If you are only building a IB or ported box you need not worry too much about group delay at the bottom end, as it is proportional to the slope of the driver roll off, ( as Dave said), it only really becomes a problem with complex boxes, such as bandpass boxes.
Bandpass boxes have many air loads in circuit, and the time taken for an impulse to filter through these can lead to a large group delay, and very slow bass.
Hi,
As already stated, group delay is nothing else than the rate of phase change regarding to frequency change. It tells something about the Q of the filter action and hence ringing of a loudspeaker at fs. Up to a Q of 0.6 the group delay is showing no peak en hence no ringing at the step response. At higher Q-values the group delay shows a peak. In other words, the higher the peak in de group delay-curve, the more the systems “rings”. Regarding to closed box woofers: Boxes with a high peak in the group delay-curve tend to sound “boomy”
As already stated, group delay is nothing else than the rate of phase change regarding to frequency change. It tells something about the Q of the filter action and hence ringing of a loudspeaker at fs. Up to a Q of 0.6 the group delay is showing no peak en hence no ringing at the step response. At higher Q-values the group delay shows a peak. In other words, the higher the peak in de group delay-curve, the more the systems “rings”. Regarding to closed box woofers: Boxes with a high peak in the group delay-curve tend to sound “boomy”
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