High Efficiency Speaker Asylum

RE: JBL Scoop

128.115.27.10

Hornlover

In Reply to: RE: JBL Scoop posted by AFP on September 27, 2007 at 18:57:54

I agree, these are not the best for Hi-fi, or home use. You can get better bass extension in a bass reflex, with better fidelity. A 6th order bass reflex is even better. For info on 6th order alignments, check out the paper titled 'Loudspeaker Alignments', and scroll down to example 3.
This is my favorite BR alignment, and am puzzled why it isnt more popular. It outperforms a 4th order BR box by a mile!

6th order alignments (Open in New Window)

Follow Ups:

Low Qts - djk 03:03:05 09/29/07 (0)
The optimum Qts for minimum box size and maximum bass extension is 0.312

Qts in the range of 0.25~0.40 is OK.

If much higher than 0.40 a sealed box is indicated, if much lower than 0.25 a horn is indicated.

***********************************************************************

A little known fact is you can 'burn' Qts if it is lower than what you need(no more than 20%).Another tactic would be to use the low Qts to reduce the box size and raise the Fb to keep it flat.

The optimum Qts for an equalized 6th order Butterworth design(not to be confused with a bandpass design)is .312 .The formula for box size is Qts*Qts*4.1*Vas=Vb.The formula for Fb is (Fs/Qts)*.312 .For a Qts of .312 the Faux(eq frequency)=Fb with a Q of 2 .

***********************************************************************

Box size is roughly proportional to the square of the Qts, so the lower the Q the smaller the box. Also the lower the Q, the higher the efficiency. Bass rolls off though if the Q is too low, the magnet can be too big for its own good.

For a vented box, the optimum Qts is 0.312

0.312 gives the best bass extension, minimum box size, and highest efficiency.

Posted by djk ( M ) on July 25, 2005 at 00:55:59

A 2 cu ft 2nd order sealed box with an F3 of 30hz can only be 0.18% efficient (84.55dB).
A 2 cu ft 4th order vented box with an F3 of 30hz can only be 0.36% efficient (87.56dB).
A 2 cu ft 6th order vented box with an F3 of 30hz can only be 0.90% efficient (91.54dB).

The correct box size for a Qts=0.312 woofer for the 6th order vented design is Vas*4.1, Fb=Fs=Faux, Q=2 for Faux.

Without the Q=2 filter the box is an SBB4, with the best transient response of all the standard vented alignments, with the filter it is a B6(maximally flat).

The link describes a couple of DIY 6th order sub designs from JBL.

http://www.lansingheritage.org/html/jbl/reference/technical/1983-subs.htm

*****************************************************************

The Qts of the old JBL drivers is way to low to be optimum for bass reflex.

Will they work?

Sure.

But they will sound more balanced in a BLH.
interesting... - JoshK 13:31:10 09/28/07 (0)
This is pretty new to me. I haven't built many enclosures. That document however was lacking in some details. What eq do you need? What if anything about the enclosure is different?

I have some Lambda TD15X's that might be good for this application (94db). Based on quick number crunching, they would allow me to have an Fb of 25hz with a little less than 4cuft box. That sounds quite appealling.

Post a Followup:

FAQ

Post a Message!

Forgot Password?

Moniker (Username):
Password (Optional):
	Remember my Moniker & Password (What's this?) Eat Me
E-Mail (Optional):
Subject:

Message:	(Posts are subject to Content Rules)

Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:	Automagically notify you when someone responds.

To view your new posting or follow-up, click on the RELOAD or REFRESH button on your browser.

This post is made possible by the generous support of people like you and our sponsors:

VH Audio