Very interesting, may be worth a try.Originally Posted by bfish
Maybe not specifically for an Altec, but this '86 EV patent is certainly adaptable:
Loudspeaker and acoustic transformer ... - Google Patent Search
"[I]We're going all the way, till the wheels fall off and burn[/I]!"
Bob Dylan, from [I]Brownsville Girl[/I]
[I]"Time wounds all heels"[/I]
John Lennon, referring to the Nixon/Hoover deportation fiasco.
Very interesting, may be worth a try.
Greets!
Not really, 'aperiodic' means 'without period' or a ~complete damping of any impedance peaks which typically takes a high stuffing density, acoustically large TL whereas I'm suggesting merely damping them a bit (lowering their Q). Big difference. I recommend doing it to any cab that's not highly damped by design which typically means an acoustically large, low tuned alignment.
Driving an acoustically small bass bin with a high output impedance completely changes the scenario though since the driver's Qts is raised enough to be audible, ideally requiring a larger cab tuned lower to keep it from sounding 'loose'/'flabby'/'bloated'. In this case, critically damping the speaker may very well require a high enough stuffing density that moves it towards aperiodic, potentially 'sucking the life' out of its HF performance, so sealing it up may wind up being the best trade-off.
Hmm, a phase plug typically increases driver loading over some portion of its BW, ergo it 'honks' if the horn's profile isn't changed to complement it, i.e. made 'faster' as shown in the EV patent, so in the case of the 825's horn and its variants requires either changing out its curved side walls and/or finding the right density/shape of a foam plug mounted in the ~first third of its expansion. Easier/quicker to design/make a new horn cab IMO. That, or raise its F3, Fb with an acoustically small sealed rear chamber to damp it down same as done on compression drivers by using a loading cap, reducing it to basically a HF waveguide (WG).
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
interesting EV patent....post. Thanks.
Is there a model of Cab that EV put out that follows this design?
I have just listened to my VOTT 515 G and 288B & 805 horn a bit.....(its in the garage) and getting a bit of experience with its sound.
You're welcome.
Some of their MTH series used it, might be others, but I don't know them that well.
Should qualify that I posted it just to answer part of the Q out of context ("know of any phase plugs?"). As originally written, 'to reduce horn honk', including the phase plug becomes misleading. The purpose of the plug is the same for all applications, to reduce cancellations when the WL becomes smaller than the diaphragm, i.e. to flatten and extend HF. As GM correctly added, it (can) actually increase "honk", and is just another tradeoff.
"[I]We're going all the way, till the wheels fall off and burn[/I]!"
Bob Dylan, from [I]Brownsville Girl[/I]
[I]"Time wounds all heels"[/I]
John Lennon, referring to the Nixon/Hoover deportation fiasco.
[QUOTE=GM;1780167]
Greets!
Driving an acoustically small bass bin with a high output impedance completely changes the scenario though since the driver's Qts is raised enough to be audible, ideally requiring a larger cab tuned lower to keep it from sounding 'loose'/'flabby'/'bloated'. In this case, critically damping the speaker may very well require a high enough stuffing density that moves it towards aperiodic, potentially 'sucking the life' out of its HF performance, so sealing it up may wind up being the best trade-off.
GM
I suppose I should get back to the original problem and not diverge. I blocked off the vents of the pseudo 816 with a strip of 1" acoustic poly fill and placed minimal fibreglass in box. What a difference this made, the bass boom has been reduced by heaps and the bass sounds warmer, more natural than before, peaks are not as noticeable. I know whilst this box size is not optimal to the 416-8B, this simple mod has made it more enjoyable to listen to.
Regarding the 825 box, what size should the damped vent be, is it the same as aperiodic vent e.g 10 sq inches per cubic foot of enclosure volume. When sandwiching the 1" fibreglass between the 1/4" wire mesh, how much compression is needed or do you just compressed it to the thickness of the panel (5/8").
Regarding the 825 box, what size should the damped vent be, is it the same as aperiodic vent e.g 10 sq inches per cubic foot of enclosure volume. When sandwiching the 1" fibreglass between the 1/4" wire mesh, how much compression is needed or do you just compressed it to the thickness of the panel (5/8").
Hi,
New guy here. I hope I'm not showing my ignorance but I thought the Port (vent) size was determined by a formula using the free air resonance of the driver and the cabinet volume. Am I confusing something?
MM
Greets!
Amazing what a little damping in the right spot(s) can do for a vented alignment, eh? Starting with a smaller and/or longer vent to lower tuning hastens the process. Tuned low enough and little/no vent damping is required with some alignments.
I've never tried Weems' R-O-T or to work through Ted Jordan's original design math, so about all I can say is that with a piece of hardware screen affixed to the inside of a 3/4" thick panel (thinnest I've used) you can fill the vent with 1" acoustic fiberglass insulation and compress it flush with another piece of hardware screen or expanded double knit fabric (which adds a little extra damping) without compromising its damping ability.
Doing a bit of simming though using polyfil which can be fairly highly compressed, Weems' ROT is close enough if ~0.6 lbs/ft^3 is used in a 3/4" long vent. This results in a fairly high tuning though, so all things considered, tuning the cab lower with a ducted vent system is a better way to go about it if it's not going to be used in a max SPL app.
Tuning between driver Fs - ~1.4142x Fs works well, especially with a high output impedance, though I imagine damping the popular 75"^2 vent will too.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Greets!
Not really, Weems and other's thoughts on 'Aperiodic' alignments pre-date T/S filter theory derived cab alignments by many years, same as the old Altec nomographs and simple bass reflex (BR) vent design routine I began with.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
GM,
I can't believe the difference that applying this resistive vent has made to a once boring box. I will apply these principles to the 825 boxes once I have finished painting them (soon I hope) I'm sure to be satisfied.
It amazes me that people haven't mentioned about this simple mod in the past posts, it's certainly worth the effort.
Thanks a lot, keep up the good advice!!!!!
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