I've confused myself. I am struggling to find the right "V" for my calculations.
JL MHX 280/4 amp running 2 channel bridged into 4 ohm Arc Moto 692.

As I follow the cheat sheet for setting with the 1000Hz test tone I'm overthinking my math.

Calculation 1 - I believe this is incorrect.
50w x 4 = 200W (doesn't matter because I'm not using this)
140w x 2 @4 ohms (bridged) = 280W

P= 280
R= 4
280x4=1120 square root is 33.46 (V)

Calculation 2 - I "think" this is right
140x2 = 280/2 (because I'm measuring one channel?)
P=140
R= 4
140x4=560 square root is 23.66 (V)

Seems to me that 23.66 is the correct V for me to measure. Can someone please verify? The whole bridging piece has me totally lost. I tried!

 

http://www.ohmslawcalculator.com/ohms-law-calculator


Takes the guessing out. Just input your desired wattage and the speaker ohm.

 

so this is the problem or the misunderstanding. do I enter total power (140x2=280) or per channel power (140)

this is where I'm getting lost.

But thank you Matt!!

 

140 watts x 4 ohms = 560. sq root 560 is 23.66.

 

Watts per Channel times the load of the speakers - then take the square root

Since you're bridging the amp, you use the rated watts per channel in bridged-mode.

FYI -

From what I've read, those Moto's like and can really handle lots of power. The JL Audio MHX280/4 is under-rated at 140 watts (bridged) with a 4 ohm load. Realistically, it's putting out close to 185 watts RMS. I'd set the gains (with the bike warmed-up & running) midway between 140 & 185 watts, which is 162.5 watts. That would put your target voltage at 25.5 VAC. The square root of (162.5 x 4) = 25.49 VAC
You could possibly go higher, but 25.5 volts will give you a little cushion. That's where I'm running my DD speakers on the MHX - bridged.

 

Can you hurry up and get yours all finished up so we can start on mine... JK
Man you are doing a heck of a nice job

Pete

 

Thanks Guys, I just wanted to check and make sure I was using the right number. I set it up today without the bike running but will take it out in the driveway tomorrow and run my tone and DMM again and dial it in. I used the 23.66 because the higher number seems way off so I did it right the first time...now time to fine tune.

 

Ummmm, don't talk to me about hurrying up...I've been impatiently waiting for Haze's return for a month. I'm about to fly to Miami and give him a ride home from the airport and help him pack up the rest of my gear.

 

I like ur strategy on the VAC figure!!! Run this shix within the most restrictive published limits and get to know it. Minor tweaks after u ride for a while will be inevitable as things break in, but damn good idea to identify the smart sandbox and to remain within it!!!!

Good on u bro!!!

T.

 

I may be misunderstanding your post, but I think he was referring to his original (incorrect) voltage calculation of 33.46 VAC, not my recommendation to bump the correct voltage calculation from 23.66 VAC up to 25.5 VAC.

Haze recommended a conservative initial increase up to 25.0 VAC on this amp. I'd also contacted JL Audio with another question, so I took the opportunity to ask them for an "unofficial" maximum gain setting, other than the "published" 23.66 VAC. They told me that the MHX-280/4 (bridged & 4 ohms) should perform well up to 26.0 VAC.

I do agree that a conservative starting point (23.66) might be better. The speakers need a little break-in time before being pushed to their limits and there is always a chance that the DMM isn't reading 100% accurate.