simple biamp question

[mrkramer]

Hi all,
I am building up some 3 way speakers. Decided to biamp them.
This is REALLY diving into the deep end for me but so far so good.
The good news is that I made a power supply that seems to work great. Yea! And I made 4 lm3886 modules that work great. Yea!

Now I'm wondering about something. My mid/high speakers are about SPL 96 or a little higher. My Woofer is around SPL 94 or a bit lower. What are my best options for changing/matching the relative volume/sensitivity? Would it work to just lower the gain a little on the mid/high amps?

MrKramer

[Michael Bean]

Active or passive crossovers?

[mrkramer]

line level passive between bass and mid/tweet. 1st order.

MrKramer

[Francec]

For the extra cash and a little more complexity (not that much), an active 24 db cross-over is a worthwhile inclusion. Plus with an adjustable output buffer, you can match levels after testing.

Frank

[mrkramer]

I appreciate the suggestion but right now "a little more complexity" is something I'd like to avoid. This is my first amp and I'd like to keep it as simple as possible.

Thanks

MrKramer

[pacificblue]

Originally posted by mrkramer
My mid/high speakers are about SPL 96 or a little higher. My Woofer is around SPL 94 or a bit lower. What are my best options for changing/matching the relative volume/sensitivity? Would it work to just lower the gain a little on the mid/high amps?

For a 2 dB difference the gain for the mid/high amps would have to be set to around 80 % of the woofer amp's.

Another simple solution would be to use a voltage divider for the mid/high parts of the cross-over. Either two resistors, e. g. 2k + 8k2 or a potentiometer/trimmer. You should post a schematic of the cross-over to make sure, where to put it without changing the cross-over characteristic.

[mrkramer]

I don't have an active preamp before this, only a stepped attenuator. The XO is just a simple RC filter like the one here:
http://www.t-linespeakers.org/tech/f...ssiveHLxo.html
If I was going to pad down the mid/tweet I thought of putting the 2 resistors after the filter. So Attenuator>XO>Pad>Amp
Since I don't have an active pre, I thought it might be better to reduce the gain a little rather than drop down the signal. Make any sense?
How would I relate gain to DB?

MrKramer

[pacificblue]

Originally posted by mrkramer
If I was going to pad down the mid/tweet I thought of putting the 2 resistors after the filter. So Attenuator>XO>Pad>Amp

Yes, as long as Pad and Amp together have the same impedance as before R2 and Amp.

Originally posted by mrkramer
How would I relate gain to DB?

Here is a calculator. Scroll about half-way down the page and use the Voltage V to Voltage Level Lu calculator. Makes it easy to calculate. 0 dB are 1 V and -2 dB are 0,79... V Those numbers are proportional to the gain. So, e. g. if the woofer amp has a gain of 20, the mid/tweeter amp should be set to ~16.