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midlife
05-25-2009, 08:03 AM
How large would a speaker enclosure have to be for it to function as an infinite baffle? And does this eliminate the need for enclosure tuning? As a reference; horn HF, horn MID, 18" cone LF.

spkrman57
05-25-2009, 09:46 AM
When the cabinet size approaches the Vas of the LF driver the alignment is considered a "infinite-baffle" design.

This would be a "sealed" cabinet the way I'm looking at it.

Let's see if anyone else chimes in on this topic.

Regards, Ron

Hoerninger
05-25-2009, 10:22 AM
How large would a speaker enclosure have to be for it to function as an infinite baffle?
As Ron said, fairly big.

But what is your intention? With a real open baffle you can get loose of enclosure resonances. But with a maintained enclosure you will miss this advantage. And you will presumably have an early bass roll off which must be compensated. :blink:

Which 18 inch speaker do you have in mind?
____________
Peter

4313B
05-25-2009, 10:26 AM
Usually anything over a Qtc of 0.5 tends towards acoustic suspension and anything under tends towards infinite baffle.

midlife
05-25-2009, 11:18 AM
Usually anything over a Qtc of 0.5 tends towards acoustic suspension and anything under tends towards infinite baffle. A formula, I may be able to figure that one out...what is Qtc?

4313B
05-25-2009, 11:41 AM
Qt of a closed box

Here's a handy gadget to measure such things in real life:

http://www.woofertester.com/wt2product.htm

Loren42
05-26-2009, 04:06 AM
How large would a speaker enclosure have to be for it to function as an infinite baffle? And does this eliminate the need for enclosure tuning? As a reference; horn HF, horn MID, 18" cone LF.

Once the volume of air inside a cabinet is so large that the air's compliance is greater than the compliance of the woofer's suspension, then the box is considered an infinite baffle.

Loren42
05-26-2009, 04:14 AM
Usually anything over a Qtc of 0.5 tends towards acoustic suspension and anything under tends towards infinite baffle.


Um, I thought a Qtc < .5 tended toward a vented enclosure.

I am not aware of a guideline for infinite baffle, but I will look that up.

4313B
05-26-2009, 04:44 AM
I am not aware of a guideline for infinite baffle, but I will look that up.I just posted it above.

Basically it is when the sealed enclosure volume loses the ability to offer any kind of restoring force.

Qtc relates to sealed volumes. Qtc < 0.5 tends towards infinite baffle.


Just go with #2, #3, #7 above, it's easier to understand.

badman
05-26-2009, 08:00 AM
Um, I thought a Qtc < .5 tended toward a vented enclosure.

I am not aware of a guideline for infinite baffle, but I will look that up.

Cabinet large (>=Vas) is a pretty good guideline. Qts and Qtc are different. Qts is the driver in free air, the Q of the combined electrical and mechanical components of the driver at Fs (Qes and Qms). This determines (largely) what sort of box you want to use. Higher tends to need less help from a port, hence the preference for sealed. Lower tends towards vented, and very low belongs in a horn (for bass anyway).

Qtc is the Qts with the influence of the enclosure. When this is close to Qts, it's an infinite baffle enclosure.

Loren42
05-26-2009, 08:15 AM
Cabinet large (>=Vas) is a pretty good guideline. Qts and Qtc are different. Qts is the driver in free air, the Q of the combined electrical and mechanical components of the driver at Fs (Qes and Qms). This determines (largely) what sort of box you want to use. Higher tends to need less help from a port, hence the preference for sealed. Lower tends towards vented, and very low belongs in a horn (for bass anyway).

Qtc is the Qts with the influence of the enclosure. When this is close to Qts, it's an infinite baffle enclosure.


Thanks! I was confusing my Qtc with Qts.

What happens when you put a low Qts driver (i.e., .28) into a sealed enclosure of small volume?

I have a specific reason for asking the question.

4313B
05-26-2009, 08:47 AM
and very low belongs in a horn (for bass anyway).Well... that might be some generallity found somewhere but I'm not real sure I'd want a 124/2203 or 136/2231 in a horn.
What happens when you put a low Qts driver (i.e., .28) into a sealed enclosure of small volume?Note that JBL puts low Qts midbass drivers in small sealed boxes.


The problem with these kinds of forum discussions is that they probably shouldn't exist (especially since they all go to Google now). Read the AES papers and myriad books instead. They do the subject a hell of a lot more justice than anything you'll find on some Internet forum. We went over this with Zilch early on and he dove right in as suggested.

Hoerninger
05-26-2009, 10:55 AM
More than the definition and relationship of speaker parameters by Claus Futtrup (former Dynaudio employee):

http://home1.stofanet.dk/cfuttrup/dpc/dpc.htm
____________
Peter