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Robh3606
07-27-2003, 10:37 AM
I have a question for you guys. Since group delay is a phase issue how audible is it?? What are "good" numbers?? Also with a sub and woofer set-up is it advantageous to have the group delay numbers as close as possible at crossover or is this made irrelevant buy the crossover because of the inherrenant phase shift.

Thanks Rob:)

Robh3606
07-27-2003, 03:44 PM
"I suppose you've already read Blauert & Laws?"

Well no actually I have seen the graph often enough. Thanks for the article I can always get the AES reprint. Thanks for the page from Bass Box.

Rob:)

Tom Loizeaux
07-27-2003, 06:52 PM
Wouldn't have JBL engineers worked on this in designing their crossovers?
Couldn't you correct any remaining group delay by using an active crossover (when bi-amping a 3-way system) by adjusting the delay of the woofer output?

Tom

GordonW
07-27-2003, 09:57 PM
Seigfried Linkwitz has continued working with this concept; apparently, he is convinced (if I read him right) that group delay in the bass and midbass, is far more audible, at lower levels than the Blaeurt and Laws study indicated.

If you want, you can check on lots of Linkwitz's work:

www.linkwitzlab.com

Fascinating site, from an extraordinarily bright man...

Regards,
Gordon.

Ian Mackenzie
07-28-2003, 06:53 AM
Rob,

This topic is a bit of a brain teaser, It depends on the frequency and sensitivity of the ear/brain to percieved changes in amplitude.

The Rane site has some excellent reads on this by Debono.

I'm inclined to think that its a more difficult problem to tame at lower frequencies as the wave lengths are obviously longer.

Hence, if the group delay of the crossover is xx milliseconds and you get 20 feet of lag on the high pass, how can one create that sort of displacemet correction in their living room without resorting the electronic delay.

This is why the asymetric all pass crossovers are popular at frequencies below 150hz, as they have minimal group delay if any.

At higher frequencies, the problem resembles more of an amplitude bump or peak around the crossover point and can be seen as lopes if one can measure the vertical polar response of the drivers.

I just try and avoid too much displacement according to the Curves then adjust the crossover values for flat response in the listener positon. ie I dont think 2 ms matters much, 3-5 ms yes maybe.

hope this helps

Ian

Robh3606
07-28-2003, 08:33 AM
Hey Giskard. where did your posts go??

Hello Ian

I have been doing some reading on the net about the audibility of phase diferences. I have found a couple of good studies but they don't agree on the numbers ie miliseconds of delay. Some say it is more audible some not. I was concerned about what is going on with my 300Hz 24db L/R and my 60Hz 24 Db L/R crossover points. As you say with 360 of phase change that is some delay! And without a digital crossover to correct you have a significant and rather drastic change at crosover phase wise. If you look at Dr Linkwitzs site he now feels that the effects of the high order crossovers are not audible which seems to be a reversal of his previous work. Or should I say not as audible. Lots of contradictions if you look at the references. Well I certainly don't have a good grasp yet but I figure just keep looking and asking questions. I will take a look at the Rane site you mention. It gets a little crazy with combining an all pass crossover function with the L/R filters??? I just have to read up and get a better understanding of the different filter functions as the light is still off:idea: :banghead:

Rob:)

Earl K
07-28-2003, 09:41 AM
Hi RobH
I actually thought you began this thread to inquire about the audibility of acoustic group delay ( specifically in bass frequencies ) - induced as a consequence of adding a helmholtz resonator into a speaker enclosure. My assumption was based on you mentioning subwoofers and bass - my mistake .

I did have thoughts about that first premise - though somewhat long winded :blah: and not germaine to bessel / butterworth / LR / linear phase / electrical discussions .

regards <> Earl K

Robh3606
07-28-2003, 10:15 AM
Hello Earl

"I actually thought you began this thread to inquire about the audibility of acoustic group delay ( specifically in bass frequencies ) - induced as a consequence of adding a helmotz resonator into a speaker enclosure. My assumption was based on you mentioning subwoofers and bass - my mistake ."

No you are correct but its a 2 parter. I was curious how audible it was and what good numbers are and even if you did match or have the group delay of 2 different driver/enclosure combinations reasonably close or matched would not the phase shift in the crossover throw it out the window. Especially down low between a subwoofer and a woofer where the delays are in 10 of milliseconds. Say at 50 hz 24db 4 order 360 degree delay 20 milliseconds. A little knowledge is dangerous if I am way off track someone smack me please.

"though somewhat long winded"

I am all ears!

Rob:)

boputnam
07-28-2003, 10:36 AM
"...Giskard. where did your posts go??"

Dang them moderators! They have almost Orwellian powers - can rewrite the past!! ;)

Giskard has done that occasionally - sometimes he's refining the thought, other times scampering from copyright infringement... :eek:

I've learned to "get 'em while they're hot". But, alas, I had my arms into way too many cabinets this weekend, and was going to give this Thread a good read during the work week ;) .

Those graphs were pretty helpful. Dang it!

More on the topic here: http://www.trueaudio.com/post_010.htm, and a proper reference to Blauert and Law's article. If anybody has a "authorized" copy :D , please pm me...