BillFitzmaurice.info

Simple quesiton - I experimented with a Crown XLS1500 powering a single 3012LF T39. I ran a sine wave at 60HZ through the amp, set the BSS DSP crossover to 45HZ lo pass and 100 HZ high pass and set the limiter to 50 volts and tried the following:

1) Unbridged with our kick drum - not loud at all - sounded weak and lifeless. With the sine wave it hit 53 volts exactly - very little limiting needed. But it clipped the amp on some hits of the kick.

2) Bridged - nice and loud and full. Limited it to 50 volts also. No clipping.

Here's where I can't wrap my head around it. If the signal is limited to 50 volts for both scenarios why in heaven's name is the output not the same? Isn't voltage just voltage? Why would a regular (non-bridged) amp at 50 volts sound significantly weaker than a bridged amp at 50 volts?

I don't know, but rather than looking at the sound aspect, I would instead be wondering why on earth my limiter, when set to 50V, allows a voltage of 53V to be measured on my amp.
What slope are you using?

With clipping and 53V if it was me, I would have considered it lucky to not have blown the 3012lf.

Other than that, I'm really surprised your BBE lets you limit voltage by 41V (1050W/8ohms bridged = 91V )

I hope you don't use this as an excuse to bridge.
Here's what Bill says about bridging:
http://billfitzmaurice.info/forum/viewt ... =6&t=19292

As per your figures, you already get over 50V without bridging, so ther's no need to do that...

Sorry - the 53 volts was what the max I could get out of the unbridged XLS1500 before I limited it. I limited it down to 50 volts.

I have to say - if the SPL with the 50 volt limit on the unbridged channel of the XLS1500 is the loudest it should be then these speakers are not what I was led to believe. This is in my basement and I assume they should be rattling the heck out of it. But I don't believe that is it. Everything I have read here has said how ridiculously loud 50 volts is through the T39.

Again - same exact voltage going into the amp - I tested it - amp limited to 50 volts whether bridged or not. Yet one (the bridged one) is stupidly louder than the other (and I assume this is what he output of the T39 is supposed to be). Why?

I think I will bridge and just go from there.

Unbridged but clipping means you're probably getting power compression or the failsafe in the amp is reducing power.

A basement isn't the place to be objective about what's going on max output wise.

I know my BP102 loaded 20" T39 cabs with a limit of 35V go louder than I wish to push them, ie I've not taken them to the limiter max and they will do around 130dB. 3012lf loaded cabs can go 6dB louder at max than the BP102's. Loud is loud!

If you have the ability to RTA then repeat your test outdoors. I wouldn't be surprised if there is only a couple of dB difference in between bridged and unbridged in reality.

Also, repeat your test after you have turned off the Peakx limiters on the amp (read your manual) for unbridged. And see if the results are much the same then.

Still it's your gear and your money, so do what you will.

Where are you measuring the voltage on each test?

I can see a scenario where one amplifier input is getting very low signal and one input is getting high signal.

On the channel where the input signal is low, the amplifier won't put out nearly the 50 volts, however if your voltage meter is hooked to the opposite channel (the one with high input signal) that could very well be showing 50V.

Just a thought.

Grant - are you a DJ or do you use the PA for live sound?

Ryan A wrote:Where are you measuring the voltage on each test?

I can see a scenario where one amplifier input is getting very low signal and one input is getting high signal.

On the channel where the input signal is low, the amplifier won't put out nearly the 50 volts, however if your voltage meter is hooked to the opposite channel (the one with high input signal) that could very well be showing 50V.

Just a thought.

I thought of that also. I am simply swapping the output from the DSP to the input on the amp. That carries the exact same input signal level.

yigba wrote:Here's where I can't wrap my head around it.

Your filter set points are messed up.

yigba wrote: ...set the BSS DSP crossover to 45HZ lo pass and 100 HZ high pass...

Flip'em around the other way. 45 for the high pass. 100 for the low pass.

*edit* for grammar

yigba wrote:Grant - are you a DJ or do you use the PA for live sound?

I do both of those options...

Also, with a kick drum, there are a lot of factors in play, most prevalent is your kick drum micing technique and processing

I suspect the reason it sounds so full when bridged is because you are slamming the limiter, making a big fat blocky "over compressed" kick drum.

you may also be clipping the input stage of the amp.

to Reiterate, 100 hz LOPASS, 45hz Hipass. you should never be using a single t39 for PA use (use a pair).

Go download some kick drum samples and play them through your t39s.

I run two bridged XLS1500s to power my 4 T39s. Limited, of course. Hit 'em hard with no problem. Good headroom and they run just fine.

Something is off...check what Radian said. My T30s have only been past 40 volts a couple of times and that was uncomfortably loud to me. I'd say 50 volts should be more than just loud and full...it should curl your toenails.

It sounds to me like the limiter isn't a brickwall type, and is letting the transient attack of the kick drum to pass, hence the clipping when it isn't bridged. Once you run bridge, the amp has sufficient headroom to try and reproduce the initial attack before clamping down.

This isn't good. You need a faster attack setting for the limiter.

Radian wrote:
Flip'em around the other way. 45 for the high pass. 100 for the low pass.

*edit* for grammar

Sorry - that is what I have - I wrote it backwards.

yigba wrote:Sorry - that is what I have - I wrote it backwards.

Seeing that you are using an outboard DSP ahead of the power amp, have you then double-checked to make sure that any of the PureBand features in the XLS are completely defeated? If not, you could be inadvertently cascading filters.