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why NOT a 2nd external restrictor vent?
The NAIM 2-way 8 inch wall/floor mount enclosures being a case in point. With these and IIRC, the two enclosures are separated by a resistive diaphragm, AND the join between the two forms an external port to the larger lower enclosure. This port being formed by the gap between the two enclosures using precisely sized standoffs, IE a distributed port.
. So, for free space floor-standers, what advantages - if any - might an external port on the driver baffle OR rear, provide?
- Noting that I have at least 5 db of room/node gain - below 50Hz.
- Bass extension to 30 or more, or a more controlled mid/upper bass?!
. In MY case this is for a pair of bass-only /baffle-step-Eq enclosures, under the existing items. Still in the build stage for the plinth cum smaller enclosure. The larger internal encl? will be a ~25l Vb (circle baffle) sphere* facing down into a larger circular plinth. *[Matching the main pair and its mid-woofer.]
. I will be driving the 'bass-onlies' with a third amp - off a 2nd order low-pass filtering on a parallel output from the existing mid-bass power amp! I can thus try 2nd-order boost Eq for low bass, and parametric Eq.
How many Para knobs might I need below 150?
. I would guess that the q /gain of the 2nd order boost might be able to approach that for sealed enclosures @ 2/3rds Fs.
Thoughts?
WarmestTimbo in Oz
The Skyptical Mensurer and Audio ScroungerAnd gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
http://www.theanalogdept.com/systems_gallery.htm
Follow Ups:
The earliest examples I recall of this design was the Dynaco A35(followed by the A50 and A40XL) in the 70's.
In the 80s a friend thought of it independently and produced the JG Acoustics speakers(low production). His reason was for deep bass the woofer saw the larger, complete box and for the lower mids it only saw the top box which was supposedly a better loading at that frequency.
Some time later Northcreek Music designed a variation(also independently) on the design with much more specific volume choices. They used to produce kits but are dropping them but it might be worth contacting them. They are one of the few designers out there who know what they are doing and why it works.
George Augspurger's classical dual-chamber reflex of the late 1950's had 2:1 chamber volumes, 3 indentical vents, one innner connecting vent and two external vents. It could be used with any reflex "alignment" giving ~the same LF and a mild dip - I should have the late Bob Bullock's program somewhere - it had a few bugs requiring some double checking so values between the sytems werne't shared - its in DOS so XP can't freeze the screen.you would select the vents all equal and with two to tune the whole volume. the inner vent drops out at low frequencies.
I can't figure yours out.
I think that's in one of my old speakerbuilding books by David Weems.
Pretty please!?
;-)!
WarmestTimbo in Oz
The Skyptical Mensurer and Audio ScroungerAnd gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
http://www.theanalogdept.com/systems_gallery.htm
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