Currently running a 3500 at 1ohm.

Haven't clamp metered it yet but what sort of voltage should i be seeing across the speaker terminals.

Reason i ask is sub sound awesome at 71-72v but one notch more on the vol sends it up to 75v and I loose output and the sub makes a fart noise.

Cheers your brother from across the water.

The sub(s)maybe be bottoming out what subs are these?

if it sounds awesome at X volts, but not at Y volts and you lose output/good sound then use X volts? no question really.

It's a brand x audio bA18.

Yes i understand only go until just before this happens but it should be louder than it is so something is wrong.

Sounds like your enclosure is the limiting factor.

What are the specifications of your enclosure?

Going to get an exact measurement of what the enclosure is. It is possible it's too small.

Also possible I'm getting DC offset so will change HU out and try this.

Have you also measured output current ? Voltage alone doesn't say a whole lot.

If your current is 50% of voltage (rise to 2 ohms) you are still looking at 2592 watts at that frequency at 72 volts... so it's most likely a good bit of power and you could be clipping the amp stepping up to 75 volts.

As far as the loudness this is just as much a function of woofer / enclosure as it is of amplifier power. I would also make sure your LPF and Subsonic are set appropriatly.

So this farting could be the sub/box's reaction to clip.

Meaning I'm actually at full power.

I shall get hold of a scope, DMM, clamp meter, do a complete test and report back.