Passive crossovers: Making Lpads for MTMs (1 Viewer)

[GaryLP]

If I made a 2-way passive crossover for a 4 ohm tweeter (with a 92dB SPL) and a 4 ohm midrange (with a 89dB SPL), I would need to make a 3dB Lpad for the tweeter.

But say I wanted to use (2) 8 ohm mids (with a 86dB SPL) in parallel instead…how much should I pad down the tweeter?

 

[ThomasW]

Doesn't get much easier than this

http://www.lalena.com/audio/calculator/lpad/

 

[GaryLP]

Thanks for the response Thomas, but it doesn't answer my question...I already know how to make an Lpad.

What I'm asking is...If I made a 2-way passive crossover for a 4 ohm tweeter (with a 92dB SPL) and a pair 8 ohm mids in parallel (with a 86dB SPL)...how many dB's should I pad the tweeter down? 3dB? 6dB?

 

[ThomasW]

Given the variability of the acoustical characteristics of any given room; the usual proceedure is to measure the output level in the room, and adjust the tweeter level from those measurements.

So most designers use a variable L-pad to adjust the level, then pull it out of the circuit, and measure the values for their fix unit.

Unfortunately Phoenix Gold, the only supplier of variable 4 ohm L-pads, has stopped production.

 

[GaryLP]

Hi Thomas, I just wanted to use the textbook answer as a starting point. I will be experimenting, but don't want to buy too many resistors.

 

[Michael R Price]

Gary, if those are the exact sensitivity numbers for the drivers... since 4db is a typical amount for baffle step compensation, the mids will be have a sensitivity of (86+6)-4 = 88db at low frequencies so you will want to pad down the 92db tweeter by around 4db to match. Of course there is a lot of variability but that is what I would use as a starting point.

 

[GaryLP]

Hi Michael,

Thanks for the response.