Cabinet Port size for combo amps

[heisthl]

I found a forum on Altec 417s that discussed the HAD cabinet design - does anyone know the actual dimensions of some of his combo cabs, including the oval size?
Here's what I found:
http://www.hostboard.com/cgi-bin/ultima ... 223&f=3729

On this cabinets thing, HAD (H. Alexander Dumble) used to use the 417 exclusively until they were discontinued. Like most he moved to EV 12Ls afterward. When he built my amp years ago, (Long ago sold, idiot!) I think maybe 1972?, he had a very precise formula for cutting the rear cabinet hole to match some formula that he either arrived at himself or found somewhere. I built the cabinet to save some money. I just don't recall how I cut the hole. It was something like two 9.5" circles cut 6.75" apart and the middle section cut out. How in the heck did he arrive at that? If I could get the TS parameters for the 417-8C I could fool with the numbers until something made sense. Vas divided/multiplied by total Q expressed in square inches? Something times something else divided by what? I've played with a tubular vent the same depth as the box (using boxplot) and come up with some interesting numbers for other known speakers but the answer just elludes me. In the mean time I have a pal with access to an original to measure but I sure would like to know what he based it on. It sounded like no other open back cabinet you've heard. I'm building an amp. Great to see there are a bunch of Guitar speaker nuts around here.
Dan

quote:

Originally posted by airboss:
.......he had a very precise formula for cutting the rear cabinet hole to match some formula that he either arrived at himself or found somewhere.
In the mean time I have a pal with access to an original to measure but I sure would like to know what he based it on.

Greets!
Probably the max flat impedance alignment that was popular with tube systems. Wayne Parham has been pushing it for years as his Pi-Align: http://www.pispeakers.com/PiAlign.doc
Sure would be nice to have the cab dims and T/S specs though.
GM

[Funkalicousgroove]

send me a PM or an email, I'll get you the plans.

[secretriches]

Funk,

Do you have any info regarding a speaker cab (not combo) and the rear port size? I will be building a speaker cab (1x12, 2x12, etc) and would like to experiment with the rear hole shape and size to see if I can come up with a similar "tuning".

[AcePepper]

I've been fooling with cabinet design also and I came across this freebie cabinet design program called WinISD. I think you can find/download it at linearteam.org It lets you design a cabinet with T/S parameters for a bunch of speakers and/or you can enter your own speaker specs. You can also mess with ports and tuning and will show a frequency response graph for the cabinet/driver combination. Folks use this to design subwoofers, but you can put in whatever cabinet size and see what it'll do.

There's another program called Boxnotes for cabinet design. this one fine-tunes the resonances inside the box and between the sides and the driver. I've been using both to design some 1x12" ported guitar speaker cabs.

I've just built a 1x12" combo cab based on ideas/suggestions from WinISD, as far as cabinet depth and port size. I haven't finished it yet, it's being covered now, but I'll let ya know how it works.
Hope this helps,
Ace!8-)>

[Sven]

Greetings,

The first question to be answered about speaker cabinet design is WHAT is one trying to achieve, WHAT is desirable speaker enclosure performance, translated into key parameters and the final result/output. When one answers that question, than one can approach the design.

Obviously, the GOAL of guitar amplifier speaker enclosure design is not the same as with the Hi-Fi speaker enclosure, nor a bass horn for a low end of a PA system, etc.

All the best,

Sven

[Sven]

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[Sven]

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