OB, Fequal and effective distance D

e-side · 26th December 2006, 10:07 AM

Hi,

After having read the Design Models and FAQ pages on Linkwitz's site and a couple of threads on this forum, I'm still unsure about the effective distance between the front and rear wave in an OB speaker.
According to Linkwitz the frequency at which the output of an OB speaker equals the output of a closed box with the same driver can be calclauted as Fequal = 0.17 v / D

D is the effective distance between the front and rear wave, right? In case of a circular baffle with the driver in the center, does D equal the radius of the baffle (half the width of a rectangular baffle) or the diameter (total width of a rect baffle)?

Maybe I missed something, but here Linkwitz takes the total width ('diameter') of the Phoenix as D, while here half the baffle width ('radius') is used...

Could someone help me with this question?

Erwin

johninCR · 27th December 2006, 02:51 AM

D is the extra distance the rear wave must travel, so on a flat circular baffle D is the radius. For example, I've played around a little with 15" drivers with no baffle at all, so the driver itself is the baffle. D=7.5" and Fequal predicted at 306hz. 15's don't display the 6db peak above Fequal because Linkwitz's stuff assumes a center point of origin, but a 15 launches it's wave from a wide range of surface to edge distance, so the response was surprisingly smooth. It just starts rolling off at 6db/oct at about 300hz. Smaller drivers don't fair as well with circular baffles.

Davey · 27th December 2006, 03:51 AM

Erwin,

It can get a bit confusing, but the first case you noted is for the Phoenix woofer which is more complicated than a simple flat baffle.

SL explains it much better on this page..IMHO:

http://www.linkwitzlab.com/models.htm#B

Cheers,

Davey.

26th December 2006, 10:07 AM	#1
e-side diyAudio Member Join Date: Jun 2005 Location: The Netherlands	OB, Fequal and effective distance D Hi, After having read the Design Models and FAQ pages on Linkwitz's site and a couple of threads on this forum, I'm still unsure about the effective distance between the front and rear wave in an OB speaker. According to Linkwitz the frequency at which the output of an OB speaker equals the output of a closed box with the same driver can be calclauted as Fequal = 0.17 v / D D is the effective distance between the front and rear wave, right? In case of a circular baffle with the driver in the center, does D equal the radius of the baffle (half the width of a rectangular baffle) or the diameter (total width of a rect baffle)? Maybe I missed something, but here Linkwitz takes the total width ('diameter') of the Phoenix as D, while here half the baffle width ('radius') is used... Could someone help me with this question? Erwin

27th December 2006, 02:51 AM	#2
johninCR diyAudio Member Join Date: Apr 2004 Location: Costa Rica	D is the extra distance the rear wave must travel, so on a flat circular baffle D is the radius. For example, I've played around a little with 15" drivers with no baffle at all, so the driver itself is the baffle. D=7.5" and Fequal predicted at 306hz. 15's don't display the 6db peak above Fequal because Linkwitz's stuff assumes a center point of origin, but a 15 launches it's wave from a wide range of surface to edge distance, so the response was surprisingly smooth. It just starts rolling off at 6db/oct at about 300hz. Smaller drivers don't fair as well with circular baffles. __________________ Everyone has a photographic memory. It's just that most are out of film.

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27th December 2006, 03:51 AM	#3
Davey diyAudio Member Join Date: Dec 2001 Location: Bremerton, WA.	Erwin, It can get a bit confusing, but the first case you noted is for the Phoenix woofer which is more complicated than a simple flat baffle. SL explains it much better on this page..IMHO: http://www.linkwitzlab.com/models.htm#B Cheers, Davey.

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