posted
I havent had much time to get into this but here is what group velocity is. Im still need to sit down and derive the formula for this.
There is something called phase velocity. It is a function of frequency. What this means is that at different frequencies, the phase travles at different speeds. so when two different frequencies are sent to your speakers the one with the slower phase velocity will arive later then the other one. This is refered to as group delay.
I still dont totally under stand this 100% and how a speaker can have set group delay. maybe it is assumed the measurement would be takin at 1m. I would think group delay is a funtcion of the distance from the speakers. This would be a good question for Richard clark. it would save me some time.
Sorry if this doesnt help. I wouldnt worry about it though. theres not much you can do anyway.
------------------ 2-DD 9512's 2-2000X's (for now) 8.0ft^3 box in a civic trunk One big ass port ?????dB's
It's not the size of your woofer, It's the size of the waves your woofer makes!
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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posted
Group delay is really only a concern in ported enclosures. It can severly effect the sq of a ported enclosure system.
Group Delay:The rate of change of phase shift with respect to frequency. Mathematically, the first derivative of phase verses frequency. The rate of change is just a measure of the slope of the phase shift verses linear (not log) frequency plot. If this plot is a straight line, it is said to have a "constant" (i.e., not changing) phase shift, or a "linear phase" (or "phase linear" -European) characteristic. Hence, constant group delay, or linear group delay, describes circuits or systems exhibiting constant delay for all frequencies, i.e., all frequencies experience the same delay. Note that pure signal delay causes a phase shift proportional to frequency, and is said to be "linear phase," or "phase linear." In acoustics, such a system is commonly referred to as a "minimum phase" system.
------------------ Ron Hawkins
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posted
SO, in simpler terms, it it when the port is out of phase with the woofer, or vice versa, or something totally different? (bear with me!) and how can i read a group delay graph and use it to help me design a box? A sealed boxes phase change is very low, so are you shooting for a really low one? ONe thing i have noticed is that there is more of a delay at resonances like tuning freq, woofer impedance, stuff like that. how and why does that affect it?
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Posts: 58 | From: Ogden, Utah, USA | Registered: Jan 2001
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Group delay is the difference in phase between the driver output and port output. Its not too important unless the box is wierd, anything under around 25 msec is inaudible.
ShadowStar
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Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
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posted
when modeling my stryke HE15 sub in an 8 cu ft PR box (three 15" lambda PRs), around the tuning frequency the group delay shoots up ALOT. everywhere else it is WELL under 25 msec.
perhaps this table will help:
Driver : Stryke HE15 Number of drivers : 1 Box type : Vented Box size : 8.000 ft^3 Tuning frequency : 24.00 Hz Vent : 3 vent(s) 292.98 in length for each 15.00 in round
posted
I think that's what it should do isn't it, looks about right, I don't think it's a modelling problem. Should sound like a normal ported box. Verrrry flat response though, I think it was fathered by table mountain and mothered by the fens round here (that's to say not a bump for miles). To make sure though run a few other speakers through and see what results it churns out. Make sure they're comparable speakers though. As asked elsewhere, and I don't know if you've already responded to this, what is the Fs of the driver? Colin
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