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Re: Crown xti4000 vs. Itech 4000
Posted: Fri Jun 11, 2010 11:04 am
by jcmbowman
guitarkeys.com wrote:JCbowman,
You stated that the 3015lf T48 can be limited at 60v. I just want to check my math to make sure I am setting up my limiting correctly.
That would be limiting (1) at 360watts: 10 Ohm x 360 watts = 3600 > sqrt = 60 v
To limit (2) in parallel at max would be: 5 Ohm x 900 watts = 4500 > sqrt = 67 v
To limit (2) in parallel at 400 watts would be: 5 Ohm x 800 watts = 4000 > sqrt = 64 v
Didn't know you were going to have a math test today! But seriously, I just want to protect my investment. I limit at 400 using a 80 hz sine wave. If I did my match right and you have reasons for limiting at 360 watts, please share so that I don't blow anything up. Don't know if it makes a difference, but my system is used for live music.
Jamie
I don't worry about the math, I just feed a sine wave within the passband to the amp, hook up my multi-meter to the amp's output and set the limiter to 60 Volts.
The 60 Volt figure is not based on the RMS wattage rating of the driver - it is based on the maximum displacement of the driver within the speaker cabinet. It's a calculation that Bill came up with to prevent driver over-excursion.
The nice thing about basing your limiting off the measured voltage is that you can add as many cabinets as your amplifier can handle in parallel and the voltage will not change.
Re: Crown xti4000 vs. Itech 4000
Posted: Fri Jun 11, 2010 1:20 pm
by guitarkeys.com
You mean I did all that math for nothing!!!
Thanks for bringing that important point to my attention, I see that in the plans now. Looks like I need to do a little reading in the difference between driver excursion and watts. At a guess, I think it would depend on the frequency used to test as 80 volts at 1K is much different than 80 volts at 30 Hz (mechanically speaking) when it comes to reproducing the tone.
Thanks,
Jamie
Re: Crown xti4000 vs. Itech 4000
Posted: Fri Jun 11, 2010 1:24 pm
by sine143
yeah, all of the rules are kinda altered here. They are horns, which changes the impedance, which changes the realistic powerhandling, All of which changes the overall output, and finally, we cant hear them when they are screaming at us, which is why we have to limit as per the plans.
Re: Crown xti4000 vs. Itech 4000
Posted: Mon Jun 14, 2010 1:33 am
by AntonZ
guitarkeys.com wrote:You mean I did all that math for nothing!!!
Thanks for bringing that important point to my attention, I see that in the plans now. Looks like I need to do a little reading in the difference between driver excursion and watts. At a guess, I think it would depend on the frequency used to test as 80 volts at 1K is much different than 80 volts at 30 Hz (mechanically speaking) when it comes to reproducing the tone.
Bill takes that into account. He knows at what frequency a particular cab reaches max excursion. The max volts in the plans are based on that figure. The frequency for max excursion will be quite different between say a 3015LF loaded T48 and a S2010 Jack 1x10. But as long as you follow the max voltage in the plans for both cabs and set limiters accordingly, you don't need to worry about frequencies when limiting. Bill has done that for us.
Re: Crown xti4000 vs. Itech 4000
Posted: Sat Jul 10, 2010 10:31 pm
by macrotechsoundman
To answer the question of the differences between the IT4000 and the XTi4000 : The Itech has a lot more DSP power, particularly the HD/Omnidrive model, the IT is a BCA amp (it loves inductive loads), IT4000 is going to be more efficient, it has a PFC power supply, the peak voltage output is going to be around 160 volts, the limiters and compressors are a lot more sophisticated. All said the XTi4000 is a pretty good amp, but the IT4000 is a definite step up. I have seen the IT 8000 put out 196 volt peaks into either 8 or 4 ohm loads, it just lowers it's shoulders and pushes harder with the 4 ohm load.
