Large format Coaxial designs

[bfish]

Originally posted by Old Guy:
Holy **** - $30 for a manual. I'd have to have my conscience amputated to be an Ebay dealer.

If you'd asked me 10 years ago I'd probably have sold my whole set for $30.

Hi Dave- I know Altec marketed something similar in the 90's- but didn't it have the 1" throat? I thought the 1.4 spec was new?

<font size="2" face="Verdana, Helvetica, sans-serif">Yeah, but it's market-driven, what burns me is the guys that sell spec sheets for $10 that they printed from Todd's and other's online librarys.

I've only got $50 in the 8550.....

You guys are talkin' about The Engine, IMHO one of the brightest ideas in recent audio (look at GPA's logo sometime). Bill took a 515-8GHP, machined out a gap in the backplate and installed a 299 'fram and tangerine, modified the polepiece to be a 1.4" throat, connected a 60x40 MR horn on the front, and stuck it in a modified 816 cab. A Duplex with a single, dual-purpose mag. Exactly what Charles has in mind, only no 299 hanging in front. There's a 12" also. Think some of them ended up in EVs DTS lineup for awhile. Such a brilliant concept, yet seldom seen, it almost seems there's a plot to hide it. Don't know if Bill DOES still make 'em, but I'd bet my bippy he CAN.

[Old Guy]

Ten bucks for a spec sheet is high. I wouldn't be beyond charging $5 if someone other than from here needed one. Would depend on my mood and how they asked.

As far as the Duplexes, I suspect blueprints still exist, if you know what I mean.

Wouldn't be surprised if Bill doesn't make them for AlPro. $4000 is a lot for a Chinese speaker, so I suspect they aren't.

[Russ Farrell]

bfish: A correction on my post - the built-in 200V supply is only on the OI-8050A version. The standard 8050A just has a BNC input. Input range 3.6 mV to 3.16V rms. I reread the whole spec sheet today (I have to stop my 3 AM replies). Never heard of an OI version or saw one on any price list.

For you and Old Guy: When I worked for an Altec contractor we had an 8050 plus GR and B&K test gear. We tried the 8050 with the different mics in our big demo room. It was hard to tell what if any difference there was. I remember us talking about how moving the test mic position one foot made more difference than the mic type. IMHO any B&K, GR, or HP 1/2" omni mic would work fine for all practical purposes.

Interesting (I hope) tidbit: Between contractor and OEM I was district manager for NE & upstate NY. General Radio bought 15" woofers (418's) for the hearing test booths they made. One visit they told me they used an Altec hf driver to calibrate the expensive ultrasonic (about 32 kHz) microphones they sold. I thought they were joking, especially when they showed me the 808-8A in their calibration lab. But they weren't joking. Even though the response was WAY down and very ragged at the test frequencies, they had written software to normalize the test results. I offered to get them a tangerine 802 but they said no - the response from they 808 was very repeatable so it worked fine!

[bfish]

Hi, O.G.,

Hope Charles forgives me for dragging his thread OT....again...

I've found the AES papers, but haven't yet commited to buy. Just found an original manual on eBay today (for $30), but now that I know I may have trouble finding the right mic, I may hold off, or forget it. I use a 1/20 octave software RTA that does way more than the old HP would, just thought it would be cool to get the old greenie up to par. May just see if Bill or Todd want it for nostalgia's sake, those old geezers used them when they came out (yuk, yuk). Ooops, 'bout forgot who I was talkin' to......

Since Russ gave me the mic #, I found a little info on it, including a response plot, so maybe I can find a close match (not shure about the 200V though). What was more interesting was the 90p document that contained the info, a study of atmospheric acoustic sensors, including WWII acoustic arrays used to steer searchlights to track aircraft. Any serious audio nut should check it out, the pictures on p1 alone are worth it;

http://www.nps.navy.mil/se/harney/cbt2ch11.pdf

[selmerdave]

Old Guy,

I think they were sold in the 90's, there was a guy who was selling four of them here a few months ago. Sounds like an interesting concept anyway, 104 db sensitivity on the LF.

http://www.lansingheritage.org/html/...akers/9894.htm

Dave

[Todd W. White]

I'm not sure if Bill has the parts to build an entire ENGINE or not - I know for certain he doesn't have the specially-built MANTARAY horns they used, but one could get around that...

He COULD, I am sure, do it, IF there was a market for them.

I installed several of the 9864's and they worked GREAT! You have to add sub's, though, if you want the system to go BOOM BOOM!

[bfish]

Originally posted by Russ Farrell:
bfish: A correction on my post - the built-in 200V supply is only on the OI-8050A version. The standard 8050A just has a BNC input. Input range 3.6 mV to 3.16V rms..snip...

<font size="2" face="Verdana, Helvetica, sans-serif">Thanks, Russ, that simplifies things a lot. I'll makeup a BNC adapter and try my Behringer measurement mic out with the 8050A. The response curve matches your HP model up to 16kHz, but I can compensate for the remaining top band. I've got a mini-pre with phantom power that will get me in the upper sensitivity range of 2.5V. As a precaution, I checked the BNC jack for bias V., nothin' there.

[Old Guy]

Hi Bfish- I've always been told to figure in the mic curve when making measurements. Theoretically as long as you do that any decent mic should work.

I can't remember any specs on the HP's power. I'm drawing a complete blank.

Will it power the Behringer? If not there are other ways.

[bfish]

Hi, OG,

I suppose with most any hardware RTA, user compensation is required as you say. Guess I'm just spoiled with the software version I use (TrueRTA), in that it has a cal file for the ECM-8000 Behringer (and a few other mics), that eliminates the need to compensate otherwise, so the displayed plot is a true representation. If you have the response plot for a different mic, you can use it the same way by writing a text cal file for TrueRTA to reference. To interface the condenser mic to my sound card, I use an ART MicroMix mini-preamp that provides the phantom power and signal boost required, and has an unbalanced out to plug right into my soundcard mic input. TrueRTA has a self-calibration routine for the souncard too, you just loop the soundcard out back to the in, run the cal routine and save it. With 1/24-octave resolution, a pink/white/sine generator, spectrum or oscilloscope displays, automatic compensation, and a screensave feature, it's a very functional RTA. I've got <$200 in the software, mic, and preamp, so it's affordable as well. If you're interested, check it out at TrueAudio.com. They have a nice audio resource library as well.

[Old Guy]

[QUOTE]Originally posted by bfish:
[QB],

I suppose with most any hardware RTA, user compensation is required as you say. Guess I'm just spoiled with the software version I use TrueRTA

LOL. Also bear in mind we're talking about a 30 year difference in technologies.

I'm not sure but I think some hardware RTA's will allow you to calibrate for the mic.

BTW I've used that Behringer mic. I get just as good results with it as I do the ones I paid a lot more for.This includes some costing a few hundred.

I've heard good things about True RTA. It pops up in net discussions. I've been using hardware.

I'm curious about that preamp. Does it work well for you? I need to buy one.

I have Smaart,just never used it. Got a deal at a show about a year ago,it was marked way down. I'm looking at a USB pre but it's expensive.

Incidentally, if anybody needs an el cheapo but decent RTA program, Allen & Heath have one for ten bucks. Doesn't do nearly what True RTA does. Free download to try but only works for like a week. Then you gotta pony up.