Best DIY design with Altec 411-8A,511B,802-8G,3000-H

[brombo]

Back in the early 1970's I built a tri-amped system (without knowing what I was really doing) with the following Altec Lansing components -

411-8A 15" dynamic force woofer
511B midrange horn + 802-8G driver
3000H tweeter

I still have the components (I am putting new surrounds on the woofers, the old ones turned to dust) and would like to know what system design would best complement the components assuming a crossover frequency of 500 Hz for the woofer and midrange. Basically I would biamp the woofer and midrange (leaving the question of the tweeter for later) and would like to know for the current state of the art what would be the best enclosure design for the woofer?

 

[Swerd]

Back in the early 1970's I built a tri-amped system (without knowing what I was really doing) with the following Altec Lansing components -

411-8A 15" dynamic force woofer
511B midrange horn + 802-8G driver
3000H tweeter

I still have the components (I am putting new surrounds on the woofers, the old ones turned to dust) and would like to know what system design would best complement the components assuming a crossover frequency of 500 Hz for the woofer and midrange. Basically I would biamp the woofer and midrange (leaving the question of the tweeter for later) and would like to know for the current state of the art what would be the best enclosure design for the woofer?

What size cabinet did you previously have?

A google search came up with this:
http://www.greatplainsaudio.com/vintage_altec/411-8A_lfspkr_spec_sheet.pdf. It suggests a sealed cabinet 4.5 to 8.0 cubic feet. That is a large range, so I'm afraid that doesn't help too much. I'll take a guess that the larger volume will produce better sounding results.

To calculate a cabinet size you need to know the woofer's Thiele/Small parameters. Again using google, I found this Driver database

The 3 important numbers you need for the Altec 411-8A are:

Vas = 899.4 liters
Qts = 0.3256
Fs = 18.3 Hz
​

Maybe someone can plug those values into a bass cabinet calculator and see what volume a sealed cabinet would be that is reasonably tuned with a total system Q of 0.5 to 0.7.

I'm afraid you're on your own when it comes to a woofer-to-midrange crossover. Without knowing more about those two drivers, you can't just guess a good crossover point. The best way to do it is to build a cabinet, mount the drivers, take measurements, and use that as a start to design a crossover.

 

[Swerd]

The 3 important numbers you need for the Altec 411-8A are:

Vas = 899.4 liters
Qts = 0.3256
Fs = 18.3 Hz
​

Using this calculator, mh-audio.nl - Home,

At Q = 0.707, resonant frequency is 39.7 Hz, and the cabinet volume is 242.11 liters or 8.55 cu. ft.

At Q = 0.5, resonant frequency is 28.1 Hz and the cabinet volume is 662.22 liters or 23.4 cu ft.

 

[TLS Guy]

Using this calculator, mh-audio.nl - Home,

At Q = 0.707, resonant frequency is 39.7 Hz, and the cabinet volume is 242.11 liters or 8.55 cu. ft.

At Q = 0.5, resonant frequency is 28.1 Hz and the cabinet volume is 662.22 liters or 23.4 cu ft.

Basically what he has are the components for the Altec Santiago. I have a pair of those 411-8A drivers. I used them for many years in cabinets for sound reinforcement, Bi-amped with 4 JW modular drivers per box and and extra tower that could be added on top to make a total of 8 JW drivers per side. I used to use this in large auditoriums like the Chester Fritz auditorium on the UND campus. I reinforced the ND centennial production of Sakakawea with the big rig, and it was very effective.

Do not use a very large cabinet. This driver have a very soft suspension and you will destroy them in a large cabinet. The optimal cabinet volume is 3.5 cu.ft. By the time you allow for driver and brace displacement you will have a cabinet with internal volume of around 3.8 cu.ft. This gives you an F3 of 48.9 Hz and a Qt of 0.7. Although the Qt seems on the high side, for some reason they don't sound like it. The bass is very tight and punchy. With my rig voices sung and spoken sounded very natural.

What are you going to use for the active crossover? The Shure SR 106 was in essence designed around that Altec 15" driver horn combination. With modern electronic crossover programs, I'm sure that crossover could be improved upon.

The 411-8A drivers are in my opinion very good drivers. They MUST be put in a relatively small cabinet.

The horns are OK in a large space, but frankly the horns are fierce in a domestic space. The Altec Santiago was quite a popular domestic speaker back in the seventies, at least in Manitoba where I lived back then. The horns really bored a hole in my head. That is why I used a different top end, and you might want to think about that also. I manufactured and supplied the cabinets with the JW top end to studios who also did not like the horn top end. I had plenty of JW drivers, as I was the Canadian agent and importer for JW.

 

[Swerd]

Thanks, your prior experience with that driver is useful. I was concerned that an 8.5 cu ft cabinet was getting rather large, not to mention 23.4 cu ft. The cabinet size you described is a lot more reasonable.

 

[brombo]

Thank you for you comments. I have enough to get started with my design now.