Rational Acoustics

December 2nd, 2015, 08:57 AM
We're trying to figure out a way to empirically measure the 'quality/characteristics' of a tube amp turned up to happy volume.

Application - how to prove to people that you can get the 'same' sound from an amp turned up to eleven by using an iso box or a power soak for the speaker line.

My hope/thought was use SMAART any my analyzer mic to capture some trace/RTA w/ harmonics or whatever directly off the amplifier then do it w/ the amp in another room (same settings) but w/ a regular mic thru a good PA and measure the PA's response w/ SMAART for comparison. Then put the amp in an iso box and do the same, then with a power soak on the speaker line.

How could/would i measure this w/ some validity in SMAART so i can show the fancy church guitarist that he doesn't have to blast everyone to get 'the perfect tone'?

Chris Tsanjoures
December 4th, 2015, 10:58 AM
The problem with using an analyzer for this is you will see just how insane a guitar amp's response is - which will be alarming to someone not used to seeing traces on an analyzer. Also, a lot has to do with the equal loudness curves, and just turning the bass level up on the amp and the master down may help out a bit. It really all comes down to how good your relationship is with the guy. Work with what he has first, and if you can't get a good enough improvement, then start suggesting other options. A lot of times, he just may not realize how difficult he is making everyones lives, and you need to help him come to that realization.

While providing empirical evidence that the guitar player is ruining the sound is a neat idea, it may rub the guy the wrong way, especially if you don't already have a good relationship with him - and I say this as a former full time touring guitarist. Before going the iso route, there are some other things you can try if you haven't already. I don't think you need to prove that you can get the same sound with iso or direct line cab emulation or whatever, what you need is for him to understand that it's not all about him and he needs to work with you for the good of all. I've had this conversation many times with guitar players, and I always start with something like "I'm having a really hard time getting the band mix to settle at a comfortable level. Now, your guitar sounds awesome, but the direct sound off the amp is a bit too much for the audience. Would you mind working with me on its positioning so I can control your level in the mix more musically?"

Usually aiming the amp/cab away from the audience is all you need. They can still have the amp reasonably loud, but the direct sound becomes more diffuse and you can manage the level better. Also, suggesting a lower wattage amp or something like an AxeFX is a godsend for these applications - mind that the guitar player may not be keen to spend more money on something he may or may not trust. Hopefully the guy is willing to work with you. Since I'm a sound guy now, when I do get to play gigs I show up with my 50watt Marshal Plexi and freak out the sound guy, then I put it on top of my cab, and face the cab backwards and immediately become best friends with the sound guy cause he knows he will be able to control my level, and I'll be able to get my sound. Win Win!

Good Luck - C

December 8th, 2015, 08:22 AM
tks for your well written comments.

I'm approaching this from the sound side of things, and have had that same conversation w/ many guitar players AND it helps that i also play (did it with a drummer just last week) and own all of the 'rock band' instruments.

We were musing about finding any way that had some sense of objectivity to prove the validity of using alternatives to a fully cranked tube amp. Hadn't done any measuring yet to even 'see' what the result might be - I've previously taught a class/session on this topic (mostly focused on church application because the buildings are comparatively small) but am dreaming of a way to show on a screen that our presented alternatives really are 'close enough'.

The reality is that in most live applications, especially churches, there's only a small percentage in the audience who can tell the nuances anyway. Many can't even discern the difference between a Roland drum kit and a live kit if the patches are good and the mix is right!


December 28th, 2015, 08:57 AM
The mechanics of doing the measurement are not different to measuring any other system, but I'm concerned about compression. Is there something Smaart does not like is compression, it wreaks havoc with coherence. A guitar amp at 11 is doing a lot of compression, which is part of the "tone" of it, making the validity of a dual channel measurement questionable at best. You'll get away with doing single channel measurements though, so to see a valid curve (in my opinion) you might want to inject pink noise into the amp and use the single channel measurements (RTA, Spectrograph). This might not be what you envisioned doing though. Maybe if you record a part with the amp at 11, then with the power soak (in adjacent channels of a multitrack program/device), then in the iso box, match levels and then A/B/C it to the Musician(s)/Student(s)? it might be more meaningful to hear the differences (or lack of them) and show the RTA as eye candy or the Spectrograph as a way to compare content?

I hope this makes sense and help