# How to set Xover gains?



## Glimmie (Apr 26, 2012)

This is how I am setting my Minidsp (actually MiniSharc) crossover levels with REW:

1) Set all EQ to flat

2) Turn off HF amp.

3) Send pink noise to LF driver amp and adjust gain for 75db on SPL meter.

4) Now switch off the LF amp and turn on the HF amp.

5) Adjust HF gain for 75db reading.

This seems to be too much HF. I also worry about tweeter damage.

Is this correct for setting crossover LF/HF gain ratio, that is to simply match tem with a SPL meter?


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## AudiocRaver (Jun 6, 2012)

Glimmie said:


> This is how I am setting my Minidsp (actually MiniSharc) crossover levels with REW:
> 
> 1) Set all EQ to flat
> 
> ...


That is not the way to do it, and yes, you could damage your tweeter. The approach you are using does not take into account the portion of the audio spectrum being covered by the tweeter, which is much smaller than that covered by the low-mid driver.

You can get closer with filtered pink noise. Room EQ Wizard (REW) will give a two-octave band that you can select the filter points for. Use a 750 Hz to 3 kHz band for low-mid and a 3 kHz to 12 kHz band (assuming 3 kHz crossover) for the HF, and you will be close. This assumes a reasonably accurate (frequency response) SPL meter, which is not the case with most SPL meters above 4 kHz or so.

Far better is using a calibrated mic with REW. Then you can see the frequency response as a whole and make accurate adjustments for flat response.


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## Glimmie (Apr 26, 2012)

AudiocRaver said:


> That is not the way to do it, and yes, you could damage your tweeter. The approach you are using does not take into account the portion of the audio spectrum being covered by the tweeter, which is much smaller than that covered by the low-mid driver.
> 
> You can get closer with filtered pink noise. Room EQ Wizard (REW) will give a two-octave band that you can select the filter points for. Use a 750 Hz to 3 kHz band for low-mid and a 3 kHz to 12 kHz band (assuming 3 kHz crossover) for the HF, and you will be close. This assumes a reasonably accurate (frequency response) SPL meter, which is not the case with most SPL meters above 4 kHz or so.
> 
> Far better is using a calibrated mic with REW. Then you can see the frequency response as a whole and make accurate adjustments for flat response.


Thanks for the suggestions. I should mention that while there is no EQ in line, the crossovers are still set up when I do this. Meaning the HF is HP filtered from 2K to 20K. Does that make any difference in your suggestions?

BTW, I use REW and have a UMIK plus I also use a USB to SPDIF converter for the generator side and run SPDIF into the MiniDSP so my calibration should be very accurate. I don't have to worry about sound card calibrations.


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## Wayne A. Pflughaupt (Apr 13, 2006)

My suggestion, just use broadband pink noise and REW’s RTA feature. Get the woofer up to somewhere between 0-75 dB, then start rolling up the gain for the tweeter ’till it matches the woofer – i.e., flat response on the display. Do some listening, if things sound too bright, then reduce the tweeter level accordingly. 

When you’re satisfied with things, you can take separate SPL measurements, for your own edification. You’ll find that the tweeter will be at a lower level. This is because pink noise drops at a rate of 3 dB/octave from the lowest octaves to the highest, which is a rough logarithmic equivalence of the way our hearing naturally processes frequencies. By SPL-matching the woof and tweet, you were essentially calibrating with _white noise,_ which has equal energy at all frequencies. There’s a reason on one uses white noise to calibrate audio systems – you just heard it. 

Regards, 
Wayne


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## AudiocRaver (Jun 6, 2012)

Glimmie said:


> Thanks for the suggestions. I should mention that while there is no EQ in line, the crossovers are still set up when I do this. Meaning the HF is HP filtered from 2K to 20K. Does that make any difference in your suggestions?


No, that was my assumption, that the tweeter signal is HP filtered and the woofer signal is LP filtered by crossover only.



> BTW, I use REW and have a UMIK plus I also use a USB to SPDIF converter for the generator side and run SPDIF into the MiniDSP so my calibration should be very accurate. I don't have to worry about sound card calibrations.


Very good, you are set for precision measurements. Wayne P's suggestion:T is a fast/easy way to get the tweeter vs. woofer level roughed in and may be all you want to do, but the measurement will be a little rougher & jump around a bit. For finer setting, the sweep measurement approach will give a more stable and more detailed plot. Your call how much trouble you want to go to, of course.

Good luck!


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## Glimmie (Apr 26, 2012)

Thank you both. I give this a try ASAP.

But the first thing I need to do is get rid of my 170wpc tweeter amps. That right, 170w RMS per tweeter. That was stupid. I got some used late model QSC theater amps so why not? Now six tweeters later, I am looking at some 20w DIY class A capacitor coupled amps for the LCR tweeters. Previoulsy before I tried the 4 channel QSC monster I was using 10w PP tube amps and never had any tweeter risks, although I did have clipping at times.

Oh and another lesson learned. Fuses are useless to protect tweeters. After I blew the first three original tweeters I installed 1.5a fast blow fuses in line. The new $180 ScanSpeak tweeters did a great job protecting those expensive fuses :hissyfit: !


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## AudiocRaver (Jun 6, 2012)

Sounds like lessons learned well. Hopefully you will be able to chuckle about it all before too long.


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