Altec 811b + what driver?

[Al Klappenberge]

Hi guys,

I'm new here. This is my very first post..

Question: I have Altec 811B horns with JBL 2426H drivers on them. The response drops off in a smooth droop. What driver do you suggest I put on these horns to use in a 3 way system crossed at 700 Hz and 7500 Hz?

Al K.

[Alex Lancaster]

2404 or 2405's.

[Al Klappenberge]

Alex,

The 2404 and 5 are tweeters. I am using Beyma CP-25 and am pretty happy with them. What I want to do is REPLACE the 2426H drivers with something that works better on the Altec 811b horn.

AL K
:confused:

[Al Klappenberge]

Ok then, I'll be specific --> 802, 806, 902?

Does anybody make new new ones now or do I buy a pig in a poke off eBay?

Al K.

[Alex Lancaster]

OK, then IMHO You are all set, an Altec driver will not make it sound "better", but Your horns and the 2426´s are designed to be x-overed at 800 Hz.

Alex.

[Al Klappenberge]

Alex,

I am stretching the crossover down a bit to 700 Hz becasue that's the upper limit of the Belle Klipsch woofer. The crossover has extremely sharp slopes, so there is no danger of damage from lows. I am just hoping a driver desinged for the 811 / 511 horns would not show the frequency response droop the JBL driver shows with the 811 horn. I have tried an Altec 902-8 driver and it is beautifull but I only need flat response to 7500 Hz where I am crossing to a tweeter. What I am looking for is a NEW alternitive to buying a used driver in unknown cndition. That is why I bought the JBLs.

I have response plots I can post if it will illustrate my point.

I may have to get a used driver and fix it up, I just don't want to!

To see what I have done, click on the "My stereo stuff" link below.

Al K.

[maxwedge]

You could try a 2461 with the phenolic diaphragms, if you can find them they go down to 500 hz. I have a pair and they sound great as long as you have a tweeter, cause they crap out about 12k. I've seen them from time to time on ebay but you have keep looking. Also if you can find only the diaphragms they may fit your 2426's but an expert here will have to confirm this.:)

Looks like Jammin Jersey (http://www.jamminjersey.com/speaker2.htm#Tweeters) has some.:cool:

EDIT: Looks like he has 2470's also but I'm not sure what the difference is to the 2461 except that it has a bigger magnet. Same price.

[Al Klappenberge]

Maxwedge,

I have tried to attach my plot of the 2426H + 811b horn.

Do you think the phenolic diaphragm would solve this problem up to 7500 Hz. I an thinking it's some sort of throat mismatch between JBL and Altec. What I don't know about horns would write the book though!

Al K.

[maxwedge]

I'm not the one to really the one to answer your tech questions, as there's far more experienced people here, but I do know that the responce you get is the result of your 'combo' of the horn and driver combined. Looking at your graph it looks like you have more of a HF problem (I didn't quite get that point before:()....I was thinking of your 700hz crossover point for the 2461. I don't really know if it would help in the HF range you need.

Scott

[Al Klappenberge]

Scott,

Ok... Here's a plot done at the same time with an Altec 902 driver on the very same horn. It is much better. Since I would have to get used ones and I only need it to go flat to 7500, I was hoping that there would be an alternitive driver. I think also that the JBL drivers just don't match the Altec horn. Since Altec isn't making them any more I guess I'm stuck with what I got or a used Altec.

Al K.

[maxwedge]

Yes, thats a much nicer plot. I'd say you must be correct about the JBL/Altec combo. Another alternative would be to use a JBL horn but that may involve some modifications to your cabinet. I take it the 902's don't belong to you?

[Al Klappenberge]

Scott,

No.. The 902 driver was on loan from a fellow I desinged a set of crossover netwroks for. He was going to use the 902 with a 511 horn, my network and a Klipsch LaScala woofer. I just had the driver to measure the complex impedance of it across it's frequency range. (I'll post that plot if anybody's interested)

Actually, I have an R-C equalizer in the squawker circuit now that flattens out the response. I just don't like equalizers. I think I am just going to try a better equalizer next. It will certainly cost me less money than replacing 3 drivers!

Al K.

[thevott]

902 drivers in excellent and /or new condition are frequently available on Ebay and replacement diaphrams should be available for many years to come. These staple drivers are only out of production because of corporate Bologna Sausage, not because of obsolescence or the normal 'end of production'. The demise of Altec is a truly sad and disappointing reality:(

[Al Klappenberge]

thevott,

Have you ever replaced a diaphragm in an Altec driver? How much trouble is it?

I treid to do it in a set of older JBLs (2420s I think) and didn't have much luck. I know about the "rubber hammer" centering method. I did two of them. One came out ok but the other wouldn't center. The new diaphragms I was given were an unknown quantity though. They may have been used ones! They were from Jammin' Jersey as were the drivers themselves. I finally made J-J take the drivers and the diaphragms back, which he did with no argument.

Al K.

[thevott]

Al,

I have removed and inspected almost all of my Altec diaphragms (both large and small) with no problems. It is so easy that I've even performed the operation just to show my friends how they're assembled. I guess I'm a speaker nerd though, what can I say. Anyway, the only JBL's I have disassembled are my 075 bullets when I replaced the diaphragms---which was also a piece of cake---but that's another animal entirely. I expect most JBL drivers are just as easy to service as their Altecs cousins if the proper manufacturing tolerances are met and if there is no oxidation/corrosion on the screws and centering pins.


MP

[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.