Back in the day many ported enclosures used a simple slot opening with no duct. I have often wondered about that approach but I have noticed in running simulations that such an arrangement looks especially good for drivers with a Qts in the transition region between sealed and BR/horn drivers (eg. 0.4x).
With these drivers the sealed box usually lacks in bass but a normal port has a rather large cross sectional area. With these drivers the length can be very short (just panel thickness) and still have reasonable area.
Thoughts?
With these drivers the sealed box usually lacks in bass but a normal port has a rather large cross sectional area. With these drivers the length can be very short (just panel thickness) and still have reasonable area.
Thoughts?
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Back in the 1960s, in the days before T/S parameters, Wharfedale issued cabinet construction sheets. Issue 12 includes a design for a 2 cubic foot cabinet which is reflex tuned by a narrow 12" x 0.75" slot. Surprisingly, the cabinet is said to be suitable for the company's entire range of 8", 10" and 12" speakers! Is it possible that a narrow slot 'tunes' the cabinet over a broader band of frequencies than the more familiar round, ducted port? 
It worked for the pioneers and anyone else 'in the know' WRT duct damping in the ensuing decades and still does, especially acoustically large MLTLs, with proper speaker grill cloth voicing historically being the most common way for 'finished' products and stretching [fine mesh] screen [sometimes combined with cloth] over vents to primarily give some measure of pest control for PA/cinema apps with vent damping being a bonus.
Lots of folks claim to not like/want audible distortion from their speakers, yet when preferring removing a cab's stock grills having these big, simple reflex vents, its 'noise' adding lower mids harmonic distortion is the dominant reason IME.
GM
Lots of folks claim to not like/want audible distortion from their speakers, yet when preferring removing a cab's stock grills having these big, simple reflex vents, its 'noise' adding lower mids harmonic distortion is the dominant reason IME.
GM
Yes, as the aspect ratio increases it moves towards ~aperiodic [> ~9:1] empirically arrived at before my time AFAIK while investigating flow Vs noise levels in sheet metal heat/AC duct shapes.
For sure, Altec's stretched screen 12:1 slot tuning for its 'compact' A8 Vott works great to smoothly provide the necessary mid-bass/roll-off of a period correct small cinema, large HT or HIFI app: http://www.lansingheritage.org/images/altec/catalogs/1983-vott/page05.jpg
GM
hey GM - Karlons's K12 of ~1956 used 6 slits about 1/8" high in some cases and 10" wide. That cabinet when driven by sine in the vicinity of its small signal fb, produces many harmonics vs a single vent. (Dr. Geddes IIRC said to me that this was not distortion but rather "modulated noise")
we need a discussion of the distributed port type seen in many of the 1950's cabinets
Look here for an interesting 1935 patent re: resistance
https://patentimages.storage.googleapis.com/62/98/78/6176b06154093c/US2065751.pdf
we need a discussion of the distributed port type seen in many of the 1950's cabinets
Look here for an interesting 1935 patent re: resistance
https://patentimages.storage.googleapis.com/62/98/78/6176b06154093c/US2065751.pdf
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that 's interesting. Briggs in the book "Loudspeakers", used a partition with narrow slots and 2:1 chamber ratio for a type of DCR. I'd like to try that Hutton vent formula with some speakers in the Karlson cabinet which aren't really suited to full flow venting.
There was a point in time of that era of mix and match speakers to cabinets where many had distributed hole ports or slots. I think even EV had one (which looked like their Aristocrat IIRC -?). GE's distributed port cabinet was one of the more famous and there's an article on it (probably Audio Engineering magazine). i made a 5 cubic foot cabinet in ~1966 for a whizzerr cone 12" Allied Knight fullrange and tuned it 3/4" holes bored in the baffle. It was "ok" - then later tried tuning it via a nomogram with a ducted port which worked worse for the high qts speaker.
Karlson's K12 which was sold with a blank port panel (and presumably instructions on how
many holes to drill for a particular speaker) - this one factory drilled
there was no resistive material over the port but the cabinets typically had grille cloth over the aperture
and that aperture acts as the final "port"
here's a nabbed picture of the GE cabinet and GE speaker
There was a point in time of that era of mix and match speakers to cabinets where many had distributed hole ports or slots. I think even EV had one (which looked like their Aristocrat IIRC -?). GE's distributed port cabinet was one of the more famous and there's an article on it (probably Audio Engineering magazine). i made a 5 cubic foot cabinet in ~1966 for a whizzerr cone 12" Allied Knight fullrange and tuned it 3/4" holes bored in the baffle. It was "ok" - then later tried tuning it via a nomogram with a ducted port which worked worse for the high qts speaker.
Karlson's K12 which was sold with a blank port panel (and presumably instructions on how
many holes to drill for a particular speaker) - this one factory drilled
there was no resistive material over the port but the cabinets typically had grille cloth over the aperture
and that aperture acts as the final "port"
here's a nabbed picture of the GE cabinet and GE speaker
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The internal horizontal partition (with four slits 1/16" wide) was referred to as an 'acoustic filter', and suppressed internal resonances.
The filter only suited drivers with foam or cloth surrounds in the rectangular cabinet shown in the book, but suited all surround types in columns and pipes.
I had the notion that "filter" was to suppress over excursion from record warp with the very compliant speakers of that day - ? (don't know how to simulate it in hornresp - ?) any "wheezing" noise generated by the filter would probably be reduced by the second chamber. It would be interesting to make a box with that filter.
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Re Distributed Port, and quoting from the Wharfedale cabinet construction leaflet:
"The distributed port is the main design novelty in the leaflet and takes the form of a slotted back. The main advantages are that enclosure tuning is not necessary and any type of cone surround can be used. The ventilated back reduces resonance and improves the reproduction of speech, and the cabinet can be placed within an inch of the wall without upsetting the performance. The actual number of slots is not critical, but reducing them raises the frequency and the Q of the main cone resonance. The slots can be replaced by rows of holes which are easily drilled in plywood. The distributed port has been used with success in our W4 and Airedale speakers and also in line source models."
The leaflet shows a design for a 3 cubic foot cabinet, the back of which has ten slots, 12" x 0.25", placed 2" apart. Each slot can be replaced by fifteen holes of 0.5" diameter. The design was especially recommended for the Super 12/RS/DD and RS/12/DD full range speakers.
"The distributed port is the main design novelty in the leaflet and takes the form of a slotted back. The main advantages are that enclosure tuning is not necessary and any type of cone surround can be used. The ventilated back reduces resonance and improves the reproduction of speech, and the cabinet can be placed within an inch of the wall without upsetting the performance. The actual number of slots is not critical, but reducing them raises the frequency and the Q of the main cone resonance. The slots can be replaced by rows of holes which are easily drilled in plywood. The distributed port has been used with success in our W4 and Airedale speakers and also in line source models."
The leaflet shows a design for a 3 cubic foot cabinet, the back of which has ten slots, 12" x 0.25", placed 2" apart. Each slot can be replaced by fifteen holes of 0.5" diameter. The design was especially recommended for the Super 12/RS/DD and RS/12/DD full range speakers.
Yes, I've checked the 'Loudspeakers' book.
"The acoustic filter reduces the LF cone excursions, the power handling is increased and the net result is better bass with small enclosures. Only very low frequencies pass through the slits, and it is therefore unnecessary to line the lower compartment with absorbent material."
The book also mentions that the dip in response due to the vertical standing wave is reduced, while the leaflet states that the filter cuts down harmonic resonance in columns and pipes - so we were both right!
"The acoustic filter reduces the LF cone excursions, the power handling is increased and the net result is better bass with small enclosures. Only very low frequencies pass through the slits, and it is therefore unnecessary to line the lower compartment with absorbent material."
The book also mentions that the dip in response due to the vertical standing wave is reduced, while the leaflet states that the filter cuts down harmonic resonance in columns and pipes - so we were both right!
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