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Voltage/Thermal Limiting

wabbit

wabbit

Nov 26, 2003
656
8
61
Toronto, Ontario, Canada eh?
#1
Howdy all. I have just purchased a new Crown Amp to drive my AccuGroove Whappo Jr. and 210L speaker cabinets. I can communicate with the amp using HiQnet System Architect 3.0. I am at the point where I am setting things using LevelMAX and it is asking me for the Threshold Voltage (RMS), the Thermal Voltage and the Thermal Response Time (sec) for each of my speaker cabinets.

My problem is that AccuGroove is no longer with us so I have no idea what to set these limits at. This amp puts out a ton of power and the last thing I want to do is fry my cabinets.

Does anyone have the slightest idea of what these settings might be or how to determine them?

Thanks in advance for any help you can provide. Peace out and cheers!
 
#3
I'm pretty sure the speakers are OEM. I bought the two cabs brand new and never changed the speakers. I've never actually pulled the speakers out to check what brand they are but I guess that's a good place to start.

To calculate the Voltage limit, it wouldn't just be as simple as taking the square root of the Power rating of the cab times its Impedance would it?

V = sqrrt (P x R)
= sqrrt (800W x 4 ohm)
= 56.57 V
 
#5
The practical limits on the power you can feed a cab aren't actually that simple. They vary with frequency, and it isn't a smooth gradient. The power rating is kind of made up. You want to put the limit before the speaker cab break itself by moving too far, which is a different place to where it breaks from overheating.
 
#6
That's what cab manufacturers would have you belive with their 1kHz cab power handling lies.

If you figure on half the thermal power in the low frequencies before farting you might be closer to the truth.

What's the new amp? The limitng you're talking about sounds a bit more swept up than an XTI. Has it got EQ and passbands like an XTI? You can do a lot to limit farting with EQ and shelving. Can it tailor the power output to the frequencies?
 
#8
Back in the old days, we used what's known as a "volume knob," and we listened to our gear, and if the cab made a sound known technically as "farting out," we'd back down the "volume knob." Set.

:D
 
#9
JimmyM said:
Back in the old days, we used what's known as a "volume knob," and we listened to our gear, and if the cab made a sound known technically as "farting out," we'd back down the "volume knob." Set.

:D
Click to expand...

Wise advice indeed Jimmy lol. I will definitely be keeping my ears open and get a feel for how loud I can push this puppy. I am indeed blessed to have a guitarist that uses a small Tech 21 amp that is basically a small stage monitor. The only one in the band I need to be louder than is the drummer. He's an animal and really beats the crap out of his kit. I love that guy even if he is a big lug. :p

Before I bought the new Crown amp, I was running the same cabs through an SVT4-PRO and although it was quite loud, it was also a friggin' boat anchor. Now that I'm getting on in years, I wanted to go light but powerful. I have that now in spades. The preamp I'm using is an AxeFX II.
 
#10
Axe-FX! Now that's a digital emulator that sounds like it could actually work. Not played one but it gets rave reviews. Pretty light on bass emulations, though. Still, sounds like a rig that kills.
 
#11
wabbit said:
To calculate the Voltage limit, it wouldn't just be as simple as taking the square root of the Power rating of the cab times its Impedance would it?
Click to expand...
No, because the driver thermal limit is moot. What counts is the displacement limit, which you can only know by using modeling software inputting the driver parameters and cab dimensions. Unfortunately of all the companies out there only Barefaced Bass even acknowledges that displacement even exists, let alone providing you with displacement specs.
 
#12
So I'm basically left with leaving the settings at the default then it seems. The LimitMAX software used to have a spot where you could enter the power rating and impedance of the cabs attached to its outputs but I can't seem to locate this. Maybe they took it out of this version of the software. I dunno.

I guess I'll just have to be really careful when really pushing the amp and as Jimmy mentioned, keep my ears open.
 
#14
Well just as a reminder, just as many people took that same volume knob and didn't listen and blew their cabs ;) Me, I think you're all crazy and everyone just needs to turn the heck down!
 
#15
JimmyM said:
Axe-FX! Now that's a digital emulator that sounds like it could actually work. Not played one but it gets rave reviews. Pretty light on bass emulations, though. Still, sounds like a rig that kills.
Click to expand...

I've only had the AxeFX II for a couple weeks now and I've barely scratched the surface of its capabilities which are vast indeed. There is a definite shortage of bass amp emulations but the classic SVT emulation is really excellent. The effects are really fantastic and no cables or batteries to worry about. I bought the MFC-101 midi foot controller for it and thus, the only cable I have coming from my amp is a CAT5 cable which has two-way communication and phantom power for the MFC. I've also gone wireless which really frees up my area of cables. I love it and the rig sounds effin amazing. Monster rig indeed.
 
#19
BassmanPaul said:
You got a day job don't you!! :D
Click to expand...

lol yes indeed I do.

Just remembered that I started this thread awhile ago and have since had a chance to work with the rig for a bit.

Does anyone have experience with the I-Tech series of amps? Oddly enough, the amp doesn't seem loud enough actually. For 2500W going into each cabinet, it should be ridiculously loud but there seems to be some limiting happening behind the scenes. The output scale goes from -100 to 0. For band practice and some of the larger gigs, I have to set it around -9 just to hear myself over the drums. I figure at this setting, I should be breaking windows and ear drums.

I am going to read through the manuals again but was wondering if someone has some tips like now and stuff. Immediate gratification and all that rot whut?
 
#20
wabbit said:
lol yes indeed I do.

Just remembered that I started this thread awhile ago and have since had a chance to work with the rig for a bit.

Does anyone have experience with the I-Tech series of amps? Oddly enough, the amp doesn't seem loud enough actually. For 2500W a side going into each cabinet, it should be ridiculously loud but there seems to be some limiting happening behind the scenes. The output scale goes from -100 to 0. For band practice and some of the larger gigs, I have to set it around -9 just to hear myself over the drums. I figure at this setting, I should be breaking windows and ear drums.

I am going to read through the manuals again but was wondering if someone has some tips like now and stuff. Immediate gratification and all that rot whut?
Click to expand...

What are you driving the power amp with, and what is the amps input sensitivity?
 

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