Fender Tone Master FR-10 and FR-12 FRFR cabs

[jay mitchell]

I am curious to measure it myself. The Archangel guy claims it is louder with the upgraded pre-amp

That's pretty delusional as well. The limit on maximum amplifier output is never due to limitations imposed by a preamp. It may well have more gain (aka "voltage amplification") at given settings, but a different preamp won't increase the power amp's maximum output.

and measured 126 db

His measurement is in error. Assuming his equipment calibration is accurate, if he placed the mic on or close to the floor at a 1-meter distance, he'd get an extra 6dB from the boundary reinforcement. That's the mistake I pointed out here: IK TONEX CAB.

How did you come up with the 117 figure?

That's actually too generous by a significant amount. The internal amp is rated at - but probably can't actually deliver - 350 watts into 4 ohms, whereas the woofer is 8 ohms. I generously started with the assumption of 175 watts (half the 4-ohm figure) continuous power with a sine wave input into 8 ohms. That's absolute best-case. A sine wave has a 3dB crest factor (the ratio of peak to average power), and my best-case assumption has the amp beginning to clip at this level. The signal from a guitar has a much higher crest factor - even a compressed/high gain sound will have approximately 10dB - so, assuming you want all the clipping to come from the modeler and not the FR-10/12 - trust me on this, you really do - that reduces available continuous power by 7dB as compared to a sine wave.

Now, 175 watts = log(175)*10 = 22.4dB re: 1 watt. Subtract the 7 dB due to crest factor, and you get 15.4dB maximum continuous power referenced to 1 watt. Assuming a close-to-incredible woofer sensitivity of 100dB 1W/1M, the speaker could produce 115.4dBSPL at a 1 meter distance. Again, generously assuming your ear to be only two meters from the speaker, this translates to 109dBSPL.

Do you know the sensitivity of the drivers used, or did you measure one?

No 12" woofer exceeds 100dB/1W sensitivity. If that's a whole space figure, it implies an efficiency of 12.6%, a figure that no cone transducer can reach.

 

[Chocol8]

Understood Jay, and thanks for the explanation. Personally I am OK with the 6db from the ground plane as that is how it would normally be used, but there is still a 5+ db discrepancy. I wonder if the 126 db was measured with the FR-12 in the corner of a small room?

I think the story is that the replacement preamp board increases output because the Fender pre-amp was clipping before the power amp, so it was unable to get full output.

At some point I will try to get a reasonable ground plane measurement, but my wife needs to not be home and it can’t be too late to piss off the neighborhood!!!