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Bi-Amping: How can I determine relative output?

Long Story Short:  I have a 50w/channel pair of tube monos, and a 300w stereo solid state amp playing through a set of JBL 4367s. two way monitors.

The tubes are on the horn tweeter and the solid state is on the 15" woofer, crossover is apparently 700hz.

Doing absolutely nothing, some music sounds completely "normal" and some music sounds artificially bass heavy.

The solid state amp has gain adjustments for each channel.

I have a Fluke 115 multimeter, and access to plenty of test tones, but nothing to read SPL.

Is there a way to measure output at the speaker terminals such that I could dial the woofer amp down to "match" the tube amps?

If so, would this be more or less constant as the preamp driving the amps changes  volume, or would it only "match" (to the extent that it actually matches at all) at one volume level?

 

 

 

gthirteen
russ69's avatar
russ69
3,554 posts
 

@erik_squires  Voltage out does not equal SPL out. You may get the amps giving the same output but differences in driver efficiency will make the SPL different.

erik_squires
16,478 posts
 

@russ69 - Assuming passive biamping, meaning the original crossover is still in place, SPL matching is done in the speaker's crossover.

Did I misunderstand the OP's problem?

russ69's avatar
russ69
3,554 posts
 

@erik_squires Oh shoot I was thinking about the way I do it with an outboard crossover. You are right.

 

mulveling's avatar
mulveling
2,082 posts
 

The issue is that even if you can measure, WHAT are you measuring? Which frequency? The SS and tube amps will respond differently over the impedance curve of your speakers! The SS amp will dump more power into impedance dips and less into peaks. The tube amp will remain more consistent, but generally reduces its output on both peaks and dips. Therefore, the calls to just use your ears are not wrong. However, perhaps you can use your ears more effectively. Here's what I'd do, to "broadband" level-match the tube and A23+, easy peasy:

  1. Hookup both amps for VERICAL bi-amping (e.g. tube amp Left; A23+ Right, or vice versa). That's not how you'll run them obviously, because vertical usually requires identical stereo amps. Here we'll just be doing it temporarily to find the A23+'s level. 
  2. Ideally you'd have a test track with broadband pink noise (NOT white noise, ouch) that's perfectly equal in Left and Right channels. I have a vinyl source and the HiFi News Test LP has a band that's *perfect* for this. Failing this, use a mono switch (e.g. on your preamp) or mono adapter to absolutely guarantee the played track is identical to Left and Right sides.
  3. Play the track. Adjust the A23+ pots (careful to keep them equal) until the image seems as centered as possible.
  4. Now reconfigure to a horizonal biamp. 

Note I haven't tried this; just kinda what I thought up now given your situation. I do have an A23 floating around here and the gain pots can be handy. 

gthirteen OP
358 posts
 

Thanks everyone.  Those are some great suggestions and information.

for those more electronically endowed, how would I measure as Erik suggested- what’s the pretty picture look like?

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