ALTEC 825 Cabinets - A5 A7 VOT

[Wardsweb]

I'm thinking of picking these up or if someone wants them I can take them to Forward Air freighters for shipping.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1383308181

http://ebay3.ipixmedia.com/abc/M28/_EBAY_8a4b171c9e4878590bf00b3861a636db/i-1_B.JPG

[Kamakiri]

I was kind of thinking of those as I had seen the auction actually. Hmmm....I'll have to see where they close.

Thanks for the offer!

[Wardsweb]

Anyone know what drivers and crossovers were used in the 825 cabinets? Were they always the same or did they use an array of drivers? I know the 811B horn, but what driver? What's the difference in 802,806,808 drivers for these?

[Wardsweb]

I went and saw these cabinets and they are very pretty. So, I'm making a run for them on Ebay. Get ready for the snipage.:D

[bully]

Great snipe, Wards!!
The wood alone is worth more than what yer gonna pay.
And they're already shaped into a great cabinet.

far out

pete

[Wardsweb]

I got new cabinets, I got new cabinets. Now I need drivers. :D

The good news I saved so much on the cabinets, I can still afford drivers. :D

[THOR]

Now all you need are some altec woofers and horns ;)

[ProAc_Fan]

Great score buddy! Hell I was gonna bid but I figured shipping charges would break me. Plus I knew you wanted them and I wouldn't outbid another AK member unless it was for a kickass TT.

Mike

[Don McR]

Originally posted by Wardsweb
Anyone know what drivers and crossovers were used in the 825 cabinets? Were they always the same or did they use an array of drivers? I know the 811B horn, but what driver? What's the difference in 802,806,808 drivers for these?

The most common 825 configuration was the A7 which used 416 bass driver with the 811 horn, 806 driver and N801 cross-over. To complicate matters there are many versions of the 416, small format compression driver and cross-over depending on age. In general, the later the better.

The A7-500 swapped out the 811 horn for the larger 511 horn, 802 driver and N501 cross-over. The 416 bass driver was common with the A7.

The A5 used the 825 cabinet loaded with the 515 bass driver and large format 288 compression driver with a multicell horn.

For home use, the best configuration is generally considered to consist of the 416-8B bass driver from the mid to late 70's, the 511 horn, the 802-8G compression driver with the "Tangerine" phase plug and N501 cross-over.

[gonefishin]

What about a pair of 650Hz saladbowls with jbl 2420's to go with them?

[Wardsweb]

Thanks Don, I'm going to build these for home use so your last suggestion seems fitting.

Lovely cabinets, someone spent some bucks having them veneered. They are a little shiny in the pic because I just oiled them. Should tone down overnight.

[Don McR]

For details on rebuilding 825's, you have to read this:

http://www.soundpractices.com/images/smallVOT.pdf

The article is primarily targeted at pro use of the 825, but most of what is written is applicable to home use as well.

The author, Jim Dickinson, posts regularly on the Altec forum as "Jim D" and can answer any detailed questions

http://members3.boardhost.com/AltecUsersBoard/

[Rob]

Wards,

You stole those A-7 cabinets. They sure look nice.

My experience with A-7's, either with the 800Hz horn or the 500Hz horn is that they do not work in an average living room. These speakers were designed to 'throw' the sound out into the audience of a theatre. I have observed that you need to be about 35 feet out in front of them before they 'phase' properly.
I have owned a sound system with four A-7's setting atop four 816-A bass bins (the bass horn half of an A-7) for the past ten years and tried a lot of room setups with them. They sound best outdoors, hands down!!!!

I'm not trying to discourage experimentation. I am also sure that some others will disagree with what I think, so buy some real Altec drivers and complete those beauties and have some fun playing with them. They are very efficient, about 105dB/1W with OEM drivers.

Rob

[Wardsweb]

Rob these should give me plenty to play with especially when I get a set of your tube amps. :D

I know they are not best suited for my small house, but for the price I couldn't pass them up. Most likely will I play with them for a while and then sell them. That's why I want OEM Altec drivers. My father always told me to do things only one way - the right way or don't bother.

[Thatch_Ear]

Could be the Tangarine phase plugs cause enough "turbulance" in the horn to shorten the throw a bit, but you are still going to have to really turn those in towards the center of the room compared to domes with baffles.
I was playing around with 811Bs with 808B(phenolic diaphragm) drivers using 421s in some Jensen cabinets. That didn't work too well.
When I used one of the horn/driver sets with the folded bass bin the closer I could get the mouth of the horn to being over the voice coil of the woofer the better the phasing was. The Tangerine might be a help in moving the horn forward and keeping the speed of the compression driver down.
Oh and congrats, the cabinets look great, have fun.

[Don McR]

Rob

The issue of the Altec horns being “long throw” devices is really a function of their frequency response and not due to any phase or timing issue. The A7-500 is actually better time aligned than many home speakers since the acoustic center of the bass driver and compression driver are nearly coincident when installed properly. The network is also designed so that the drivers are phase aligned at the cross-over frequency.

Nonetheless, I know exactly what you are talking about when you say that the A7, A7-500 needs about 35’ to sound coherent. In my opinion, this is strictly a frequency response issue. These systems all have a peaked midrange response that results in the “in-your-face” presentation. Due to the dissipation of high frequency energy in air, they tend to sound much smoother at a distance. However, the upper high frequency response will have disappeared at that point.

The biggest culprit for this peaked response is horn resonance. The aluminium 811 and 511 horns have their resonant frequency within their passband. In other words, they ring like a bell under normal operating conditions. Altec took a long time to realize this, and only by around 1980, did they start modifying these horns. The later sectoral horns had their webs cut, and a rubber spacer placed between the web halves that damped the resonance. Prior to this, there were numerous home brewed solutions to damping Altec horns. A quick search of the AA High Efficiency forum on “Altec horn damping” will yield detailed advice.

To Thatch

The “Tangerine” phase plug is not designed to cause turbulence in the horn throat. Instead, it is intended to pass more high frequency energy than the more standard annular slit design. This addresses the falling high frequency response that plagues virtually all small format compression drivers used in a two-way system. Most compression drivers have a high frequency response that drops off rapidly after 10khz. Competitors, like EV and JBL, added UHF drivers to their midrange compression drivers to address this issue in high-end home systems and studio monitors. However, Altec always believed in the superiority of the simpler two-way design and sought out a means of extending the HF response of their midrange drivers. The 802-8G of 1976 was the first driver to successfully accomplish this. This is why I don’t recommend the 802’s that pre-date the “G” series unless you want to consider a 3-way design.

In summary, an unmodified A7 from the 50’s into the late 70’s will have a limited frequency response that is very aggressive and ragged sounding. Most listeners will find this troublesome in a home environment. However, a few simple modifications to damp the horn and extend the HF response will tame this beast to be a very acceptable home system with unmatched dynamics.

[Rob]

Don,

Thank you for the detailed explanation above. I Knew my 511B horns ring like a bell but never bothered playing with damping techniques. In my previous home system I used them with 802-8D drivers and I liked the sound, but had them installed actively bi-amped (18dB/octave 500 Hz) with a pair of 15" woofers in an infinite baffle enclosure. They sounded terrific up close in an average living room.

Ron

[Thatch_Ear]

Great explanation. I knew that turbulance was not the correct way to say it but I was under the impression that the sound would have to bend around the plug and not knowing really how sound waves work thought it might help with dispersing the sound waves better. There certainly is enough spread on the mouth of the horns that they shouldn't need 35' for you to get the stereo effect.
I didn't want to go as far as putting putty on my horns because I thought them harsh and wasn't sure that I would keep them. I tried bags of pebbles (which I had), bags of sand which was messy, and had the best luck with cloth bags of lead bird shot. The shot comes that way in the sporting goods shop for reloaders.

[Tom Brennan]

I've messed around with many horn flares and it's hard to beat the 511B horn that's been damped. I used the much praised Edgar "saladbowls" for awhile but went back to the 511s. I find that in my room the horizontal pattern of the 511 is just right for the kind of presentation I like, using horns with wider patterns resulted in too spacious a sound, too difuse.

The 511 also extends the frequency response of the driver because it's vertical dispersion narrows with increasing frequency, on axis this compensates for the driver's power roll-off. Using 908 drivers with Radian aluminum diaphragms I get flat response out to 16,000hz on axis, that's the highest reading available on my RTA.

As for damping; cutting the welds in the vanes with a sawzall and filling the kerfs with silicon is very worthwhile, as Don mentioned Altec did this on later models of the horn. The "lips" area of the horn that extends past the mounting flange is highly resonant, some non-hardening modeling clay pressed into the lips damps the horns a great deal.

The other day I went from the 511s to 1005 multi-cells, great sounding horns in the midrange but difficult to dial-in because of their constant directivity, I need to use tweets with these horns even though I'm using 1" JBL drivers that extend to 16,000hz on 511s. On the 1005s the response drops off at 8,000hz on axis. I'm gonna use a pair of JBL 076 "catseyes" as soon as a new diaphragm for one of them arrives. To make do I'm using the pair of 908s, hornless, brought in at 10,000hz, 1st order. This is working OK for the time being.


www.chicagohornspeakerclub.org

[THOR]

:eek: So many numbers! Is this math class??? :D