416-8A Cabinet

[Martyh]

I am looking for some opinions on the best cabinet for a 416-8A for home use. The system would consist of 511B, 808-8A ,416-8A and n501-8A or 8B. I will probably build a separate sand *****d box for the 511s to sit on top of what ever cabinets I build. I like the vintage look of the Valencia but I have never heard a pair. Any thoughts?

[Martyh]

Sorry for the omissions, Room size is about 11.5x14x7.5 high. speakers would be on the short wall with listener about 1.5' off the opposite wall. As for size, Smaller than an 825 is what I had In mind. Cones are original. 40~50 cps is plenty low. The horns would be on top. In the perfect world, I would need the speakers to work with varying flavors of tube amps, mostly 1568As. I guess a 7~8' reflex is in order but I don't have near the experience that many of the people that post here do and I worry about the transition from the horn to the woofer in that type of installation. I realize the Valencia has this same transition but I would feel allot better about investing 20 hours and a couple of hundred dollars in building a pair if I had some input from those in the know.

[GM]

With such an old driver, without measuring them there's no telling what an ideal cab would be. Have they been reconed? Do you use a SS or tube amp? If tube, what's its output impedance? What kind of LF extension are you looking for? How big is the room? Are there any cab size/dims restraints? Will the 511 sit on top or in the cab?

GM

[GM]

Well, any of the Altec cabs would require extensive bracing, so might as well build. I have specs for the "A" series done by a mag back in the early '70s, so who knows how they compare to yours, but it's all we've got. They're actually very close to the much later 604-8G published specs.

A T/S max flat alignment with an SS amp is 6.65ft^3 net/37.5Hz Fb. Pushing it to ~7.25ft^3 net (~8ft^3 gross) at this Fb or a little lower looks good also. If this size was chosen and driven with various amps of differing output resistance, then to keep it from sounding boomy will require tuning lower to suit each one.

If we assume a worst case scenario of 4ohms, then the T/S max flat alignment cab size goes ballistic to 25.95ft^3 net/24.9Hz Fb! Shrunk to 7.25ft^3 net requires you to seal it up since you can't tune it low enough to get rid of the underdamped response.

Obviously, any series resistance value in between requires a longer vent to tune it lower with increasing resistance, so I suggest mounting the vent tube on a separate little baffle that can be removed and resealed so you can insert different lengths. Even small leaks, like around a screw, destroys cab tuning so be forewarned.

Anyway, I tend to like my horns above my head angled down, with the 15" at ~face height since a 15" is beaming in the 500Hz XO BW and accept the floor bounce issue, while some prefer the horns at face level, or a little below, with the driver close to the floor to reduce floor bounce and get some LF/midbass boost.

That said, assuming the specs I'm using are relatively close, driven with an SS amp the driver wants to 'feel' a rather squat cab, with a 22"id height, requiring the other dims to be 31.5"id/19.95"id. As series resistance increases, so does height. The worst case scenario bumps it up to 34.66"id tall, so I compromised on an acoustic ratio cab with two dims close to these and averaged cab tuning WRT driver/vent placement since this is a *****hoot anyway:

35.75"id h
15.5"id d
24.88"id w
driver 16.5" down from top
vent 6"dia. x 1.25"L (for SS driven) 6" up from bottom

Line one wall, top, and back with fiberglass or equal to damp lower mids, and I assume you know how to make a rigid cab/mass load the driver.

If you prefer more floor gain/HF horn lower, then of course you can lay it down with the horn relocated.

GM

[Steve Burger]

A little recommendation for the horn drivers in a home application would be to use 902 aluminum or 909 pascalite diaphragms instead of the symbiotik 808 that would have been stock. They are available from GPA. Better yet send them to him in case there is a need for re-magnetizing. The improvement would be tremendous.

[Martyh]

Thanks guys, I appreciate the input. I did plan on having both the 808s and 416s re-conditioned. Gm, I bet allot of cabs will be built to the dimensions you gave, there is a distinct lack of information on the 416-8a and I don?t think allot of people go to the trouble of measuring their drivers. I don?t quite understand the design process used pre TS but I am under the impression that the older Altec cabs sound pretty good with a wide variety of woofers especially if you quiet down the panel resonance. My only experience with Altec speakers is in auditoriums. In this setting they obviously trounce the competition. Do the conditions in the average listening room make cabinet selection more critical? Thanks again, M

[GM]

Cab Vb was chosen by factories based on the driver's Fs/Cms/BL product (very similar to T/S) and tuned by damping the in-box impedance peak.

Yes, a typical HIFI listening room is much smaller and has boundary gain and many standing wave issues not found in an auditorium, etc., so blending it to the room is a must for ~accurate sound reproduction. Fortunately, T/S allows us to more quickly do this than the old tedious sinewave sweeps/impedance mapping.

GM