Altec 811b + what driver?

[Al Klappenberge]

MP,

Here's why I'm scared of used drivers. This is the condition of the JBL 2420 I got from Jammin Jersey. Note the condition of the foam on the back cover and the square "dimple" near the middle of the diaphragm.

In fairness though, Jemmin' Jersey DID give me my money back with no argument at all after I tried replacing the diaphragm. All I lost was the shipping and I did learn something in the process.

Al K.

[thevott]

Al,
That does look a bit neglected doesn't it? Seems like they should have inspected that driver and either repaired it or properly represented it before the sale.

There are a number of good sellers (with excellent feedback) on Ebay, some who specialize in Altec and JBL components even. Many auctions have clear pictures as well. I suppose there is always a risk though.

MP

[Tom Loizeaux]

That kind of deterioration of the foam in the back of JBL drivers is not uncommon. I cleaned mine out and put in new foam/felt pads. Dented diaphragms, on the other hand, can be a concern.

Your post is a little confusing. It sounds as if you're trying to get the 811B horns down to 700Hz. The dispersion pattern on these 811s becomes a bit beamy in the lower range. To get that low you should consider going to the Altec 511B horn. I don't know a lot about the 904? driver, but the older 802s went to 500 Hz very well.
I just finished a small PA where I used old Altec 802Ds (with fresh aluminum diaphragms from Great Plains Audio) on 811 horns, but I crossed them in at 1200Hz @ 12 dB/ because the 15s can go that high and I wanted to be able to push the output of the horns without worrying about them so much.

Tom

[Al Klappenberge]

Guys,

I untimately solved the problem of the foam and diaphragm by returning them and buying brand new 2426h drivers. If I had it to do over I suppose I would have gotten them fixed by somebody who knows what they are doing.

Jamin Jersey admitted to me that they do not have the equipment to test drivers. All they do is connect them to a signal generator and check for alive or dead condition!

As to the low end of the 811 horn, I think the beaming happens high not low. I doubt if there is anyhting made by the hands of man that will beam low frequency! Anyhow, I had 511 horns for a while. They were just too big to go into the Belle Klipsch without the driver sticking out the back (Pix attached). When I put the 811s in they sounded the same but LOOKED a lot better!

Al K.

[thevott]

700 Hz is theoretically below the H811's limit but the final test is always the human ear! I imagine that you simply lose some efficiency and directivity below the cutoff of the horn. You do have your baffle area around the horn to help out too. Personally, I am quite a fan of the 511 horn but, then again, thrive on the industrial look. Drives my wife crazy!

MP

PS: I didn't mean to sound critical of Jamin' Jersey as they were quite accommodating to your requests. It is actually very cool to have so many products and information available these days due to the 'internet phenomenon'.

[Al Klappenberge]

MP,

Yes, I still keep Jammin Jersey on my explorer favorites list. I just haven't thought of buying any other drivers until just now. They were very agreeable to all my requests. I figure buying a horn from them would be zero risk if I ever needed another one. It's pretty hard to f___ up a horn!

I was very happy with the 511 horn too. It was just to balsted BIG! I think the danger in running a horn too low is that you may go below where the horn loads the driver effectively. That will leave the diaphragm in danger of excessive motion. I did impedance measurements on the driver on the 811 horn and concluded it was safe to stretch it down 100 Hz below it's specks. I don't think I am sticking my kneck out too far. I am also using a crossover that goes down like the side of a barn below 700 Hz. It's well over 100 (one hundred) dB / octave. The driver simpy dosn't see anyhting below 700 Hz. The frequency response was fine even lower the 700 too.

Al K.