Proper Bi-amp settings for the following - Need help

[aaadougford]

I’m going to try bi-amping for the first time with some DIY Altec Santiago speakers I’ve recently acquired because of the current crossovers (N800-D) don’t have any control over the efficiency of the horn drivers versus the woofers. Here are the speakers/specs:

Altec 902-8B Horn drivers on 811B’s
Pressure Sensitivity:
104db SPL measured 4’ mouth of Altec 511B horn with 1 watt input of pink noise, band limited from 1200 Hz – 5000 Hz.
Frequency response:
500 Hz to 20 kHz
The 902-8B is fitted with a loading cap to permit operation at crossover frequencies from 500 Hz to 1200 Hz.

Altec 411-8A Woofer drivers:
Pressure Sensitivity:
93db SPL with 1 watt input of band-limited pink noise from 250 Hz to 1000 Hz measured on axis 4’ from the cone when mounted in a suitable airtight enclosure.

Frequency response: 250 Hz to 1000 Hz

I will be using a BBE DS26 Speaker Management System for the crossovers for each amp.

So my question is what should I be setting the frequency limits to each?
Example:
LF - 250 Hz to 800 Hz
HF - 800 Hz to 20 kHz

Or should I have some overlap between LF and HF?
Or am I completely off base?
Any other suggestions from the experienced bi-ampiers will be appreciated.

I know I’ll need to adjust the gain between the HF and the LF because of the 11db difference of efficiency which is the reason I’m attempting this in the first place. The HF drivers just over-power the woofer in a big way. I think the Altec 30904 crossover bridge is what brought the efficiency levels closer together on the original factory Santiago’s.


Thanks,
Doug

[yggdrasil]

I would start off with a crossover frequency of 800Hz, at least 12dB/octave slopes.

Assign a 800Hz low pass filter to the 411's, and a 800Hz high pass filter to the 902's.

You should not assign band pass filter's for either driver.

[aaadougford]

Altec 411-8A Woofer drivers:
Pressure Sensitivity:
93db SPL with 1 watt input of band-limited pink noise from 250 Hz to 1000 Hz measured on axis 4’ from the cone when mounted in a suitable airtight enclosure.

Frequency response: 250 Hz to 1000 Hz



So my question is what should I be setting the frequency limits to each?
Example:
LF - 250 Hz to 800 Hz
HF - 800 Hz to 20 kHz

Corrections to the original thread:

Altec 411-8A Woofer drivers:
Pressure Sensitivity:
93db SPL with 1 watt input of band-limited pink noise from 250 Hz to 1000 Hz measured on axis 4’ from the cone when mounted in a suitable airtight enclosure.

Frequency response: 20 Hz to 1000 Hz

So my question is what should I be setting the frequency limits to each?
Example:
LF - 20 Hz to 800 Hz
HF - 800 Hz to 20 kHz

[aaadougford]

Here are a couple of images of the settings for HF and LF. I'm wondering if I should set these so that they stay to the limits of the drivers capabilities, even at it's lowest roll off point or set the low frequency to that drivers specs or documented capability and let the "Butterworth 12db" make the default rolloff? Here's the LF image. I have it set at 50 Hz so that the roll off stays within 20 Hz. 20 Hz is the low frequency limit of the driver, per Altec Lancing. If I set the low frequency to 20 Hz then the Butterworth 12db would take the roll off to almost 10 Hz which is below the drivers documented limits:


Here's the HF settings that I again have mostly limited to the documented limits of the driver. Or, should I set the low frequency to the 800 Hz which is my estimated crossover between the drivers and let the rolloff fall where the Butterworth 12db setting is at default. Here's the image. The same here, I could set the low frequency to 500 Hz, but the rolloff would end up being a much lower frequency:



Hope you understand what I'm trying to ask. I'll show more images if necessary of what you would like to see.

thanks,
Doug

[yggdrasil]

Unless you plan on playing insanely loud, you should remove the LF rolloff on your woofers.

Also it has no meaning applying a HF rolloff to your HF drivers. My guess is that you actually need to add a bit of HF gain with the parametric EQ available.

You should set the crossover points so that both LF and HF drivers are ~3dB down at the same frequency. This sums relatively flat.

[aaadougford]

Unless you plan on playing insanely loud, you should remove the LF rolloff on your woofers.

Also it has no meaning applying a HF rolloff to your HF drivers. My guess is that you actually need to add a bit of HF gain with the parametric EQ available.

You should set the crossover points so that both LF and HF drivers are ~3dB down at the same frequency. This sums relatively flat.

My thought about your comment on the HF gain, is I thought because of the 11db efficiency difference, the woofer is less efficient, that I should reduce the gain of the horn by 11db to make them more even.

I'm actually going to create a couple different cossovers as you mentioned at approx. 800 Hz; one will be at ~3db and another at ~6db to see the difference or more like hear the difference.

[yggdrasil]

My thought about your comment on the HF gain, is I thought because of the 11db efficiency difference, the woofer is less efficient, that I should reduce the gain of the horn by 11db to make them more even.

This comment was addressing the possibility of a reduced HF efficiency above ~7-10KHz, not the average efficiency difference. Save it for later tweeking. You will need a measurement microphone.

Good luck.

[aaadougford]

Here's an update to this project:

This weekend was time to put all the pieces/parts together that were ordered and remove the old crossovers (N800-D).

* Installed biamp binding posts direct to each driver
* Replaced 806A drivers with 908-8B
* Wired Phase Linear 300 Series II to HF drivers 902-8B
* Wired Phase Linear 200 Series II to LF drivers 411-8A
* Installed BBE DS26 to both amps and ran saved crossover -3db at 800 Hz and with a 11db reduction of gain to the 902-8B drivers because of their more efficient nature.

Without fine tuning the crossover yet, these speakers have taken on a whole new sound! They are fantastic. I can't wait to give the parametric EQ some changes for tuning. So far these 2 way speakers are missing nothing that I can detect by ear and they are no longer the unbalanced, even shrill HF sounding that they were with the N800-D network.

Thanks,
Doug