This is something I've wondered about for a while. This might be best done with a driver that already works well enough in a sealed box. Build to Vb resulting in Qt~0.7, add a vent tuned so the obligatory EBS peak is ~10dB down or more, stuff the vent to a simulated Qp~5.0-10. f3 and f10 seem like they would extend an extra ~10Hz in the case here. Roll-off is similar and perhaps a tad shallower than sealed Qtc=0.7.
To avoid a ridiculously long vent, it needs to be kept rather small in diameter. I have 1.5" x 6.375" in the below simulation. This would be problematic if unstuffed, but stuffing the vent appears to reduce air-speed and group delay to reasonable levels, where the response is already down 10dB+ by then anyway. Cone motion is generally better on the damped-vent version, except really down low, ~25Hz and less. This should not affect performance too much unless you enjoy huge pipe-organ or dubstep at high SPL or intend to watch action movies.
Faital Pro 6FE100 in 20L:
I don't think I'm the first one to come up with this idea. Is it done and does it go by any specific name? I don't see too much drawback from simulation. Would there be issues I did not consider here?
To avoid a ridiculously long vent, it needs to be kept rather small in diameter. I have 1.5" x 6.375" in the below simulation. This would be problematic if unstuffed, but stuffing the vent appears to reduce air-speed and group delay to reasonable levels, where the response is already down 10dB+ by then anyway. Cone motion is generally better on the damped-vent version, except really down low, ~25Hz and less. This should not affect performance too much unless you enjoy huge pipe-organ or dubstep at high SPL or intend to watch action movies.
Faital Pro 6FE100 in 20L:
I don't think I'm the first one to come up with this idea. Is it done and does it go by any specific name? I don't see too much drawback from simulation. Would there be issues I did not consider here?
Not quite aperiodic, the way I see it at least. IMO, aperiodic should contribute zero output and the physical 'vent' dimensions should result in a tuning well below 20Hz. I'm trying to gain a tad of output in my proposed scheme and the tuning would often be 20Hz-30Hz to do so. Maybe the idea is just nuts? 🙂 I should test it to really know.
Way back, maybe 35 years ago, when Infinity built the 1001, we had a ported 12" cabinet, stuffed full of dacron, port, too. It sounded pretty good, went quite deep, and used inexpensive drivers. At that time, we called it "transmission line", though it certainly wasn't what the definition of a tl is.
I suppose you may have had something akin to what I describe going on there.
I may have good test mules come to think of it...
I guess I better add my Infinity 1001s to my refoam list. The driver has an interesting basket, not to mention an Advent like treatment at the dust cover.
Really? Most of the 1001s had cloth surrounds. We were getting woofers from CTS, Becker, Emenence, etc. I think the Beckers had butyl surrounds, but I don't remember any foam ones. All stamped baskets. Yes, a ring of "perma gum" around the dust cap. Surprised any of those are still playing.
We're talking about the two way with a rear firing tweeter yes? Mine are in storage at the moment.
Cordell has written a paper about something very similar: http://www.google.se/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCAQFjAA&url=http%3A%2F%2Fwww.cordellaudio.com%2Floudspeakers%2FEQSS_White_Paper.pdf&ei=DR-lU-PXOaGGywOq9IDQDA&usg=AFQjCNHG7Y22oF1i8y_wLQnVDmxNkLtUPg&bvm=bv.69411363,d.bGQ
EQSS Equalized Quasi-Sealed System
EQSS Equalized Quasi-Sealed System
Yep, those are the ones. 12" woofer, 2 2" Peerless tweeters. Crossover had two 6.8 uF caps in series, and, depending on the particular woofer, 1, 2, or 3 resistors. No inductor. I remember building hundreds of them.
Thanks for that link!
What I propose does have similarities, but EQSS has no damping in the vent and uses Linkwitz transform.
Come to think of it, I may already know of a few designs 'round these parts that already do something similar, but implement it differently (not a stuffed cylindrical vent).
Like the old Variovent (SEAS/Dynaudio)= box fulled with dacron or others damping materials ? Van DIckason book...
QTC raise if a resistive hole + more damping Inside the box? I'm asking about a Jensen load than Supravox used but with resistive material to approach a sealed load ? In this scenario the resistive hole is just behind the front bafle and around the driver back cone : depth is set up with 4 screws in front of another bafle with the hole of the diameter of the cone to the sealed box! off topic but same idea behind this need. Difficult to find the good VAS but screws help... here the resistive material can be a round of dense foam ?!
QTC raise if a resistive hole + more damping Inside the box? I'm asking about a Jensen load than Supravox used but with resistive material to approach a sealed load ? In this scenario the resistive hole is just behind the front bafle and around the driver back cone : depth is set up with 4 screws in front of another bafle with the hole of the diameter of the cone to the sealed box! off topic but same idea behind this need. Difficult to find the good VAS but screws help... here the resistive material can be a round of dense foam ?!
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Not quite Variovent, where a leak to de-Q a too-small sealed box is the goal, as most things aperiodic, the way I understand.
Regarding that Jensen-load for Supravox, are you talking about the R-J? I remember reading about Supravox using R-J, but do not remember if any damping material was used in the concentric vent. Perhaps this might be a bit like my scheme, provided some output from the vent is desirable. In any case, there is no link between R-J and Jensen that I know of, but to complete that triangle, do I remember correctly something with Supravox and Ultraflex (Onken) load?
Like CLS said laws of physics can't be fooled, excursion is limiting spl. QSS is better than sealed however. I think that this low-tuning works best for double drivers when we often must use a too small box for ideal BR tuning.
I snipped this from the paper linked in previous message #10
I snipped this from the paper linked in previous message #10
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Jeff Macaulay had done a series of articles in wireless world on sealed box sized vented boxes in the 1990s. He found that there was no phase inversion if the tuning port was small enough, even though the small port limits the bass benefit.He is now available at macaulayaudio.co.uk
Yes, this one http://www.supravox.fr/kits/bafflescompenses.pdf
What is the meaning of R-J and who is the inventor of this load ?
There is no resistive material around the space between the two bafle but myt idea is to put one circle damping material between both bafles to simulate something near the Variovent concept to approach the advantage oa a sealed cabinet but with a more direct absorption of the rear wave and the back wave with this damping material to low more the problem of the time+1 wave back behind the cone.
The difficulty if the concept would be ok is to choose a material which can absorb enough but stay close a sealed load or at least an aperiodic one and to find the Vas of the driver for box dimension (the screw may help to set up it ?!).
I was thinking about a two layer resistive material : the first concentric near the rear driver with a sort of reticuled open cell foam à la Gedlee, the second a dense material à la Seas Variovent : maybe even more dense as the open surface is nearer of a BR port than a resistive hole like Variovent !
My thinking comes to the fact I would like an Open bass mid bass (from 100-150 hz to ....) with less distance from the front wall than an OB which needs minimum 1 or 2 feets and to reduce the need of bass-EQ with reducing the bad effect of the reflexions in a sealed box while staying with a low Qts driver for the transcient (<= 0.3 e.g.) ! A sort of hybrid between resistive-sealed cabinet and inverted U-frame near 2Pi beaming... Certainly a crasy idea by laking of technical background with empirical development !
Theoric as I have no experience, nore money to test it ! I'm looking for a mid bass of 10" to match with the 94 db of a Neo 8 or 8s (starting at 350 to 400) to theorize this speaker ! So the mid bass load is problematic if the Neo 8 stay in an OB or U-frame load to match its fastness and have sweet transition with few octaves and a problematic high slope for the life of the mid-bass register... well second order should be a maximum in theory with mid-bass to keep so liveness here... maybe active filtering and amp do not act as passive filter here ? I don't know !
I am for a specific mid-bass as this register is a talon d'Achile in many design !
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From WinISD simulation, again with Faital 6FE100 in 22L, both sealed and ported to 30Hz, the port being stuffed to Qp=5, I get the same benefit in increased ELSPL, until the vent simply unloads, below 25Hz or so, as also shown on Cordell's above graph.
I think I came relatively from the same place with my idea, but higher ultimate SPL was not my aim as much as lowering f3/f10 a bit on a sealed box. It seems like medium-high Qt drivers, such as the 6FE100 would pretty much require some vent stuffing to mostly kill the peaky output at this frequency. Doing the same with Fostex FF225WK, 19L stuffed versus vented to 30Hz and no vent stuffing (Qp=100), the response is about the same as sealed, ~10Hz lower kneepoint but no port peak output because of the lower Qt.
Can't fool physics and can't re-invent or (hardly) re-discover them. The Cordell scheme pretty much is what I was after, save for his implementation of EQ. I think I'm satisfied with it answering my initial question of "is it being done and what's it called". 🙂
Going back to the Supravox kit site, the one called Baffle Compensé RJ is the same one you linked to.
R-J (Robbins-Joseph) was a baffle scheme from the 50ies I believe. Like the Supravox, the speaker is mounted on a baffle spaced from the front of the speaker, but this one is inside the enclosure and the resulting space is the bass-reflex vent. The exit is also somewhat smaller than the cone area and of irregular shape, often seen as a lopsided lemon in commercial offerings. The Elliptoflex was somewhat similar. I suppose the RJ's slot shape was meant to provide a different type of dispersion and a sense of space in the monophonic days.
http://downloads.bbc.co.uk/rd/pubs/reports/1955-08.pdf
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The R-J was one of those gimmick loudspeakers of the 50s, more marketing than engineering (much like the Carlson in that regard). The BBC paper seems to describe its attributes well.
Resistive vented cabinets are always a very mixed bag as well. If the box is too small then you can reduce the bass hump, but you are then tossing out any benefits in reduced excursion. In the end the difference between that and fully sealed is minimal.
I don't see anything inherently wrong with an overdamped vented alignment that approaches a sealed box in response. You should be able to get to some blend of sealed and vented attributes.
Resistive vented cabinets are always a very mixed bag as well. If the box is too small then you can reduce the bass hump, but you are then tossing out any benefits in reduced excursion. In the end the difference between that and fully sealed is minimal.
I don't see anything inherently wrong with an overdamped vented alignment that approaches a sealed box in response. You should be able to get to some blend of sealed and vented attributes.
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