Crossover and compensation filters

[speakerdave]

I am experimenting with the Altec 288-16 on a 511E for midrange and am looking for information about several things related to this project.
1) Are there response curves published for the driver either on a horn or on a standard test tube?
2) I saw a reference to the use of this driver with the 501 crossover. Is the schematic for this crossover (and other stock Altec crossovers) available?
3) Is there a source of information about the compensation to use on Altec driver/horn combinations to make their response more linear and less midrangie?
4) I have seen references to the sonic quality of the Model 19. I think I have read that part of this quality arises from the fact that the treble response is compensated to make it more linear. Is that true? If so, is the scematic for the Model 19 filter available?
5) I have read that Doug Sax uses (or did until recently) the 288-16G/511E combination for midrange on his big monitors. Does anyone know what the rest of these speakers consist of? Does anyone know the details of his crossovers?

I'm new here and have been enjoying eavesdropping on your forum exchanges.

Thanks,

David

[GM]

>1) Are there response curves published for the driver either on a horn or on a standard test tube?
====
Yes, but I no longer have them. Really, it is just a typical compression driver response.
====
>2) I saw a reference to the use of this driver with the 501 crossover. Is the schematic for this crossover (and other stock Altec crossovers) available?
====
Never seen any, but they are textbook butterworth based on 8-16-whatever ohms with a hi-pass shelving pot so you can easily calc/draw your own.
====
>3) Is there a source of information about the compensation to use on Altec driver/horn combinations to make their response more linear and less midrangie?
====
I have never seen any, but as a rule-of-thumb, use a series resistor (8 ohms for a nominal 8 ohm driver, etc., though you may need more/less) with a cap in parallel to 'lift' up the HF. Been awhile, but IIRC a 2uF cap is about right for a 288, so you might want to have a few lower/higher values to experiment with.

Obviously, if a tube amp is used then the series resistor value will be somewhat less. Anyway, I normally dialed them in with a pot at a low level (to keep it from heating up too much), measured its resistance and made an appropriate power resistor from several small ones.
====
>4) I have seen references to the sonic quality of the Model 19. I think I have read that part of this quality arises from the fact that the treble response is compensated to make it more linear. Is that true? If so, is the scematic for the Model 19 filter available?
====
It certainly will make a positive difference, though it will not do you any good. Probably, but I have not seen it.
====
>5) I have read that Doug Sax uses (or did until recently) the 288-16G/511E combination for midrange on his big monitors. Does anyone know what the rest of these speakers consist of? Does anyone know the details of his crossovers?
====
Not me.
====
>I'm new here and have been enjoying eavesdropping on your forum exchanges.
====
Welcome!

GM

[Earl K]

Hi Dave,

In addition to the above posts :

(1) Download Tech Letter on the new 288 / 91 / 90 drivers .
You'll find some 2" PWT response studies plus response curves of your driver on a large radial ( exponential/conical mix ) horn ( 329a).

(3) My biamped 288-8K drivers are on small exponential round-mouthed horns ( Selenium ). For HF compensation , the effective capacitance in my circuit is @ 3 uf. This is parralleled with an 8 ohm resistor. This RC combo is in series with the driver. This gives a HF lift that starts around 5 Khz.. You'd want to start with a 16 ohm resistor . ( The resistor depresses the midrange below the caps crossover point ).
I don't use tweeters since this combo takes the driver out in a linear fashion to where my hearing drops ( 13.5Khz - coincidentally, right where my 288s die off ). As GM mentioned the final values for the resistor and/or capacitor ought to be judged by ear.

(4) Jeff has nicely posted the schematics you seek.

<. Earl K

[jmarkwart]

David,

1) Altec 299 response on a plane wave tube shows a suspension resonance peak around 350-400Hz, with essentially flat SPL output from 500Hz to 6.5kHz on a Manta Ray horn. The 288 is probably very similar. Your 288 should make a good midrange from 500-5000Hz.

2) GM said it all here

3) Go to www.soundpractices.com/altec.html and follow the Hiraga's EQ Crossover link.

4) Yes, the Model 19 used mid range EQ on the compression driver, as did the 604-8H duplex. The implementation is very similar. You can view both schematics on my pages at http://home.earthlink.net/~jmarkwart/

5) Not me either

Jeff

[ckdf]

I investigated a bit on the same topic recently. Could not find much but somewhere found a reference that says:

"Speakers designed by Sherwood Sax use (per channel) two Altec 15 inch woofers, one Altec 288-G horn loaded midrange crossing over at 600hz, and one hand selected Electro-Voice horn tweeter. The same tweeter that topped the old Patrician speaker system. The drivers are time aligned (the midrange horn sticks out in front) and crossovers are 6dB per octave. 70 watt tube amps designed by Sherwood Sax. Stanton 881 moving magnet cartridge and solid state preamp designed by Sherwood Sax. Doug Sax indicated that it is very important to be able to monitor recordings at realistic, meaning loud playback levels".

I stored that as plain text, so unfortunately I can?t give the exact reference anymore.

[speakerdave]

This is so cool! This is the real stuff!

Hey, GM, Jeff, ClausK and Earl. Thanks for the information, insights and links. I feel as though I have a much better sense of where to go with these drivers now.

I had a hunch Sax may have used the T350. Now I have cause to bemoan all over again the pair I sold in the late seventies. Even though the 288 has response out to 10k and above, walking back and forth in front of the 511E tells me I will want a lower crossover. I will begin by experimenting with the JBL 2404.

This is great! Thank you very much.

David

[Art J.]

>2) I saw a reference to the use of this driver with the 501 crossover. Is the schematic for this crossover (and other stock Altec crossovers) available?
====

>3) Is there a source of information about the compensation to use on Altec driver/horn combinations to make their response more linear and less midrangie?

I recently mapped out a schematic of my newly
aquired Altec 9846's which includes the 501 xover and the 30923 compensation network for
the 511 horn. I scanned it to jpeg but I havent figured out how to post it yet. I know how to
e-mail it if you want to drop me a line.
Its for this combination.

http://www.lansingheritage.org/image...-8a/page03.jpg