Channel Separation/ Isolation testing

OK folks, recent topics on the "dual-mono" subject prompted me to perform some rudimentary testing to try to prove the channel crosstalk differences of various amplifiers as being audible by actually measuring their "audibility" in dB and removing all variable possible in doing so. This isolates the actual channel separation, or "cross-talk" occuring in the amplifiers in this test, and reinforces some theories concerning stage width differences between the amps and/or amplifier designs. Granted, this test procedure is "simple" in nature, and this is on purpose so that laypersons may relate to the set up and test equipment used. Let's read on, shall we

To remove the possibility of extraneous sources of "interference" with these measurements in a vehilce (processors, EQs, wiring, passive or active crossovers, phase shifts, etc etc etc), i used a very simplistic setup as the testing "system"--a single stereo head unit on my work bench to drive the amplifiers directly via standard RCA cables, and the amps then sending output to a stereo pair of full-range home speakers. I then used a test tone , in this case 800Hz, which is planted firmly within the freq range of the 4" midrange driver of the bookshelf monitors. An Audio Control RTA meter was used with a stationary mic stand to record the measurements. Let's look at the setup...

TESTING SET-UP>>>
Pioneer DEH-P1700 cd player
el-cheapo coax RCA cable pair, 3 foot length
Astron 100A DC power supply juicing an SVR gel cell battery
equal-length 16 ga. speaker wire pairs
1 pr Pioneer S-HF21-LR surround speakers
Audio Control SA3055 real-time analyzer
Canare XLR mic cable, full-range audio control mic
Bass Mechanic audio toolbox cd, track 30, 800Hz test tone at 0dBu level unclipped

Now, here are some pics to show the set-up>>>
here's the head unit

here's a shot of an amp hooked up on the bench

Here's the meter, mic, and speaker setup

OK, HERE ARE THE AMPS BEING TESTED....

we already saw one of the amps, but here's the list of amps>

Amp 1- JL Audio 300/2
Amp 2- DLS A3 The Twin Mono
Amp 3- Sinfoni Amplitude 150.2X
Amp 4- Arc Audio 2150SE
Amp 5- JBL Power Series PX300.4

Ready, set, TEST!

First, the outputs of the h/u were checked with a sine wave and a DMM to measure the A/C voltage to make sure the channels were close, and they were within .03V, so we were good to go.

Next, I hooked up the JL audio amp

Next, I level-set the JL amp so that volume level 20 on the head unit (the reference volume for this test will be 27 for all the amps---the max h/u vol is 30, but 27 is chosen to avoid clipping the signal) revealed a 100dB level. All the amps were consequently level-matched in this identical fashion.
Here's the JL amp level-setting measurement playing the test tone, mic position is 1/2 meter from speakers, placed directly in the center position.

and, here is a Real-time analysis response curve of the 800Hz test tone

OK, so now I moved the mic to 2.5" from the center of the right speaker while the head unit was playing the 100.2 reference level tone. This mic position will be used for all the testing of the independant amp channels.

At this mic distance and head unit volume, the right driver measures 102.2 dB playing the test tone

OK, now that all the dogs in the neighborhood are barking and I have temp hearing loss LOL i shut off the h/u. TESTING shall now begin!

First, I want to test the left channel of the JL amp. I position the mic to be 2.5" from the left speaker. I measure the ambient room volume with the system OFF, in dB.

AMBIENT ROOM VOLUME = 59.8dB

Next, I turn the balance all the way to the right, and DISCONNECT the right speaker so it does NOT interfere with the measurement.

Next, I play the test tone at the reference volume level of 27 on the head unit...here is the result.

Next, I position the mic at the 2.5" position in front of the right speaker, shift the balance all the way to the left, disconnect the left speaker, and following the same steps, get this measurement-

wow. The h/u balance control MAY be causing these readings above ambient room level. I can clearly hear the tone being played thru the non-driven speaker, so I decide to do a 2 part test for all the amps. First, using the balance control of the h/u. The second test will be a balance set to CENTER, but I will actually REMOVE the RCA cable from the amp that drives the speaker being tested. I will also disconnect the opposite speaker ( the one actually playing) so it can not interfere with the measurements. THerefore, if any signal IS getting to the speaker being tested, it is coming from the OPPOSITE CHANNEL RCA via internal amplifier crosstalk between the channels.
heres a quick shot of the rt channel RCA disconnected

Now, following the same procedure for playing the tone, here's how the rt speaker measures when the rt RCA is disconnected (following the standard procedure above)

And then the left channel tested after removing the left RCA cable-

HOLY SMOKES! The Head unit does a better job of channel isolation than the amp! YIKES! Well, let's look at the rest of the playing field on the test bench real quick, then I will post all the measurements and we can discuss the data.

I'm gonna post the results in the next reply to keep this easily navigated