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Using Altec 30904 atteuator with 511/416

When I built my A7/1505 system, the 1505s were something like 10db louder than the 515B A7 cabs. I ended up tri amping the system with an Rane active crossover and adjusted the volume on each individual amp. Cheers.
 
What's to tri-amp in A7/1505?

Does the Rane have CD compensation?

Are you using it?

There's more than simple attenuation the subject here.... :yes:
 
Zilch said:
I assume 500 Hz capability matters to you. Go to the BMS site and look up the specs of their 1.4", 1.5", and 2" drivers. 511E horns are 1.4", as I recall, but they are merely 511s with the throat lopped off at the appropriate diameter and a mounting flange added, which any competent machine shop can do.

The most direct solution to your problem is an active crossover with CD compensation like Behringer CX3400, ~$150 complete with cables at Guitar Center or similar source. AK members have been securing them there for $99 for the unit itself lately....
Click to expand...

Hi Zilch.
I've read most of your posts regarding compensation and I've wondered if when you mention CD compensation you're talking about Constant Directivity horns or Compression Drivers. Often you suggest CD compensation with older Altec horns which are Non-constant directivity. Does it work equally well on these types? The Behringer CX3400 sited above has Constant Directivity compensation above 3.5KHz.
Thanks in advance
 
The necessity for compensation derives from the inherent characteristic of compression drivers rolling off high frequency response above mass breakpoint, so it's really compression driver compensation being done. In typical audio compression drivers, mass breakpoint occurs in the region of 3.5 kHz:

http://audioheritage.org/vbulletin/showthread.php?t=4410

Some horn designs such as exponentials do compensation acoustically by progressively concentrating increasing frequencies having lower energy into a narrowing beam, in effect equalizing the response.

Constant directivity horns and waveguides don't do that, as their purpose is to produce a controlled and constant beamwidth across the spectrum. Thus, they roll off with the driver, and require compensation to "boost" the higher frequencies, which is generally accomplished via midband attenuation in passive designs. As may be seen in the curves I posted above for 30923, that attenuation is contoured to be the reciprocal of the driver/horn rolloff.

The Altec horns are basically radials, rotating an exponential contour horizontally about a vertical line pivot in the area of the throat. Thus, they exhibit rolloff of higher frequencies and require compensation as well. They are not constant directivity; the exponential contour beams the high frequencies in the vertical dimension, partially compensating for the driver rolloff, but equalization is still required for extended high-frequency response....
 
Does the CX3400 CD compensation filter/booster do an adequate job with 811 horns or is the Altec HF crossovr filter needed as well?
I would be able to answer the question myself if Parts Express would send me the caps I ordered last week but have not received them as yet. :no: I have the Behringer, ready to go active, and am looking forward to using it.
 
OK let's see if I got this right, off terminal 2 of the L-pad I run a 2-ohm resistor back to the negative, this should take the place of R2 in the 30923 schematic? Does the 2 ohm resistor provide the circuit with extra resistance when the L-pad is at zero ohm's?
 
srm51555 said:
OK let's see if I got this right, off terminal 2 of the L-pad I run a 2-ohm resistor back to the negative, this should take the place of R2 in the 30923 schematic? Does the 2 ohm resistor provide the circuit with extra resistance when the L-pad is at zero ohm's?
Click to expand...
Yes. It prevents the impedance from getting too low, although you'll see even that starts pulling the whole works down, including the HF, at the lowest resistance settings....
 
Can this do any harm or is it just a matter of adjusting the HF/MF more? Thanks again, you have really helped me on this. I will be donating some money to AK next payday to help the cause.
 
It's a standard circuit used in many Altec products to correct the excessive midrange inherent in their basic designs.

It may harm some perceptions of what sounds good, is all.

Nobody's gonna lose an eye using it.... :p:
 
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