How to Solve High-Frequency Suckout in Room?

I thought there had to be a load on the amp to measure this  with multimeter but I might be wrong.  

@theaudiomaniac I think you might be right, in terms of AC voltage output being close enough. That said, there is a 1.2% variance at 5,000Hz, and close to a 1% variance around this frequency. While small, wouldn’t that be audible

@djones51 , I think the voltage output should be sufficient to compare the differences (without needing to convert to power which should give the same readings. Unless, of course, you are thinking there might be differences in the resistance between left and right and I should measure that too? As I said the problem was evident to a lesser degree on my old speakers, and I also tried swapping the speakers with each other and the problem remained on the right.

I highly doubt testing with the speakers connected will show much difference (but I will try later today). This is because I won’t be able to play the 1kHz tone at the same volume as I did without connecting the speakers, and therefore I am guessing there will be an even smaller difference between left and eighth channels.

I did read an old forum post that indicated that subtle differences may not be detectable using a voltmeter. The ultimate test is to use a dual channel oscilloscope, inverting one of the channels phases, then using the “sum” function of the scope. Because you’ve inverted one of the phases, the channels should cancel out each other when you sum them, and any variance from 0V that the scope shows would indicate an imbalance. I used to have an oscilloscope that hooked up to your PC but it’s so old it won’t work anymore.

Thinking my next step could be to rent a dual channel oscilloscope.

And, I’m going to book a frequency response hearing test just to totally rule that out! Although my wife also detected the problem without being told exactly what the issue was first.

I will also try to measure the frequency response playing the test tones, 1m from each speaker playing one side at a time.

Finally, I will also try rotating my entire system 90 degrees in my room.  Just as one final “room test”.  This will require me to dismantle my couch again so might be a while…

I do have a good relationship with my local dealer who I did not buy my amp from.  I could potentially ask them to borrow one of their high end Moon amps for troubleshooting.  I’ve tested Moon gear before and I found their stuff to be very highly resolving, so if the issue is not present with a Moon integrated, I’d think that would prove definitively that my amp is at fault.

The things we do for our hobby!

@theaudiomaniac I think you might be right, in terms of AC voltage output being close enough. That said, there is a 1.2% variance at 5,000Hz, and close to a 1% variance around this frequency. While small, wouldn’t that be audible

That is at best 0.1db. Left to right, your system could be off 3,4,5 or more db. It will not be audible.

I did read an old forum post that indicated that subtle differences may not be detectable using a voltmeter. The ultimate test is to use a dual channel oscilloscope, inverting one of the channels phases, then using the “sum” function of the scope. Because you’ve inverted one of the phases, the channels should cancel out each other when you sum them, and any variance from 0V that the scope shows would indicate an imbalance. I used to have an oscilloscope that hooked up to your PC but it’s so old it won’t work anymore.

Don’t waste your time. A wide bandwidth multimeter is accurate enough. The difference in time between measurements and thermal differences are smaller than what you are measuring. It is your room. Didn't you already say you swapped channels and the issue is still there? That rules out the electronics.

What you need to do is figure out how to measure room response. There are many resources on the web. It will cost you $100-200. If you have a noticeable difference, then then it will be easy to see them. Measure with one speaker, measure with the other, then compare.

@theaudiomaniac , I swapped the cables at the amp end (only) and the problem changes from the right side being too soft in the upper mids and into the treble, to the left side being too soft in these frequencies. This leads me to believe it’s not the room.

That said I am planning to completely rotate my system in the room as a test (setting up my system against the side wall.

Update: I have also questioned if the source material is causing the issue since the problem is not apparent on all music, mildly apparent in some music, and blatantly obvious in other tracks. As above, vocals sound centered but the upper end of vocals seem more fleshed out on whichever speaker is NOT being driven by the amp’s right channel.

So it's not the room, it's somewhere in your system.  Further swapping and substitution of cables/channels will reveal where it is.  Proceed by using logic and focus on one component at a time.