enclosure for Altec 904 8A

[Sibi]

Hello Altec fans,

I'm looking for an appropriate enclosure for my two 904 8A Altec speakers.

They came in an Altec 930c encolsures, but they where not in a good shape. Therefore I need some hints and tips in this case.

I'm not a professional speaker builder and therefore I scanned the Internet an this forum for some hints an tips.

I found some post regarding the 620 and the Stonehenge V enclosure with the 604 mounted (post "604e cabinet and crossover"). I personally would prefer the Stonehenge V enclosure but I don't know, if there is the need for some adjustments regarding the use of the 904 8A's.

I also tinker with the idea to use the Onken enclosures which Michael Methe uses, but they are to broad for me and they must be lifted to ear height aditionally.

The second issue is regarding the original 904-8A crossovers. Should I go on using them or should I go for another solution?

Helpful comments are welcome!

Thank you!

Regards
Thomas, Germany

[bowtie427ss]

Have your 904's been reconed and re-diaphramed?

I'm assuming you are looking for the "604 sound" from the 904. Important to understand that the 904 is a hi power sound reinforcement speaker with limited bandwidth. In it's stock form i'm not sure the enclosure is all that important.

In order to get the "604 sound" from the 904, the woofer section needs to be reconed, as well as changing the HF diaphrams from the mylar surround type to the all aluminum tangential surround type.

I'm pretty sure that the 904 woofer cone, and voice coil assembly are heavier than that of the 604, it likely differs in other ways too, preventing it from being able to reproduce midrange dynamics and detail the way the 604 does.

IMO, the 904's most outstanding attribute is it's ability to play at extreme SPL's for extended periods, i'm sure this was probably also it's main design goal.

I cannot comment on the 904 network as i'm quite unfamiliar with it.

There are others on this board who are quite familiar with the steps necessary to bring the 904 up to the fidelity level of the 604, hopefully they will chime in and confirm/correct the exact differences between these 2 speakers.

[RonSSS]

Ths 904-8A is very much like a 604-8K in it's T.S parameters.

I modeled it using Boxplot. The resultant enclosure is ported and 2ft^3.

Response is 3db down at 60hz.....so these won't go real low. An ideal candidate for a sub.

The HF section really comes alive with new diaphrams from GPA. Also remove the loading cap and add felt to the inside of the rear cover. GPA sells kits to do this. Need shorter screws too, preferably stainless steel. I also removed the bug screens which I think is a big help.

Anyway, the results are very good. with subs, it's the best sound I've ever had in my system.

Here is a photo next to a Santana for comparrison. Nearly identical size. The ports on my 904's fire out the rear.

The stock crossover is the same as the late 604's and are quite good. You can fiddle with caps to get them even better.

I'll add the photo in the next post....

Ron

[RonSSS]

Here it is.

Ron

[RonSSS]

My 904 cabs are reasonably industrial aren't they?
Actualy, I should have recessed the speaker into the fron baffle and had the front baffle flush with the sides.
But not knowing how they would sound, this was a first cut.
Seeing them side by side with the Santanas, I am very tempted to canabalize the Santana enclosure with a new front baffle and put the 904's in them.
But, even though the Santana is,t all that great, it would be hard to destroy what I remember as a classic speaker.

Now, I don't know about the LF cone in the 904. Yes it's probably heavier, with maybe a different voice coil, but I think the setup sounds wonderful. And I don't know if a 604 cone is a direct replacement. And there were more than a few 604 cones. Mine are in such good shape, I will just leave them be.

I also have model 19's, and despite the fact that they are good, my 904 with the sub setup is just simply better.

I have too many Altecs.....aint it great?

Ron

[Jim Butler]

HI Ron,
Nice 904's! What are the subs you're running with them. I'm always looking for a better sub situation and am interested in how folks cross over to them. Any info is great.

Jim

[RonSSS]

Hi Jim,

My subs are Altec 411-8A (reconed by GPA) in 8ft^3 vented enclosures.
I have 2 of them, a right and left channel.

I run the 904's full range and just add in the subs with a line level 24dB/oct active SS crossover....home brew.

I didn't want any extra electronics in line with the 904's.

One thing about this is the phase between the 904's and the subs is not correct. The subs need some sort of phase correction, it's audible. But I've never persued fixing it.

Ron

[GM]

Greets!

Assuming you don't plan to use a sub, if they were mine I'd put them in a ~10 ft^3 tower cab (aka MLTL) tuned to ~Fs and use either a high output impedance tube amp or high power SS amp with as much series resistance as required to 'fill' the cab up till it's ~flat in-room. Assuming a ~38" driver height and 19 mm material thickness (all dims inside and approximate):

L = 61.53"
WxD = 281.84"^2 - recommend 21.312" W x 13.187" D
driver up from bottom = 35.75"
vent = 8" dia. or other equal area shape x 3" long near the bottom for flattest response and up 20" for a more traditional Altec alignment.

Damp to suit, recommend lining top, back and one wall with 1" acoustic fiberglass insulation or similar.

GM

[Jim Butler]

Ron,
Thanks for the sub info. I'm running 411's also although I'm just using a PE plate amp at the moment crossing with 604's in 620 cabs. Like you I always find there is a bit of a phase issue.

GM,
Thanks again...in the MLTL cab for a 904 what would the 3db down be in the flattest configuration? If the 10^3 cab is good for a 904, what would be the best config. for a 604-8g? The 620 cabs are good but perhaps a MLTL is better.

By the way, I have shared your description of your (and your inebriated buddies') house/trailer shattering sub experiments with some sound artists I work with. There is definite interest in art applications of using LF sound this way.

Jim Butler

[Old Guy]

Nice work Ron. My stuff looks more "industrial'.