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Author Topic: subwoofer eq approach  (Read 4659 times)

John Chiara

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Re: subwoofer eq approach
« Reply #10 on: September 05, 2014, 03:57:04 pm »

Maxxbass?
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boburtz

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Re: subwoofer eq approach
« Reply #11 on: September 05, 2014, 04:11:47 pm »

  A 69 volt sine wave (or music with only 3 dB crest factor) measuring 69 volts RMS has twice the average power as the (old) AES pink noise signal with 6 dB crest factor having 69 volt peaks.
The specs say the QRX218 is rated at 1200 watts rms, with 4800 watt peaks. I am under the impression that the test waves have a 6dB crest factor, with the rms power being 600 watts per driver, or 69 volts into the cabinet, with 138 volt peaks. Your commentary is the reason why I have initiated this thread, because I know there are things that I don't know, and experimenting to the point of failure is an expensive proposition. However, I'm still not following your rationale on why the continuous rated power is going to damage the driver. I am not second guessing your knowledge, I would just like to understand better how you arrived at your conclusion.

EDIT:
After putting in some more thought, I think I understand what you are saying, which is, and please correct me if I'm wrong, that the thermal power rating that EV plublishes for the evx was determined through the utilization of a sine wave with 6dB crests, which has a lower average power than today's modern music or even a tone generator's 3dB crest sine wave. I got confused with your term "peaks" and EV's term "peaks" essentially describing two different things. Your term describes the crest of the long term sine wave, their term describes a momentary 6dB spike in addition to the sine wave.  I can see how a driver that is thermally rated for a 6dB crest sine wave would overheat when a 3dB sine wave was put into it at the same power rating. Peak spikes notwithstanding. Thanks Art, this is the type of info that I was looking for.
« Last Edit: September 05, 2014, 04:55:37 pm by boburtz »
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Art Welter

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Re: subwoofer eq approach
« Reply #12 on: September 05, 2014, 05:14:05 pm »

The specs say the QRX218 is rated at 1200 watts rms, with 4800 watt peaks.
 
I'm still not following your rationale on why the continuous rated power is going to damage the driver.
Bo,

The cabinet is not rated at 1200 watts "RMS", it is rated at 1200 watts using the AES2-1984/ANSI S4-1984 signal using a 6 dB crest factor.

RMS , or root-mean-square, is a measure of the average power level of a signal. The RMS level is representative of the heating capacity of the signal.
Peak is a measure of the maximum level that a signal attains.
For a sine wave, the peak level is 3 dB above the RMS level. For music, the peak level can easily be in the range of 10 to 15 dB above the RMS level, or as low as a sine wave for low frequencies in EDM (electronic dance music).

The pink-noise output of AES2-1984/ANSI S4-1984  has a peak to RMS ratio of voltages of  2:1, or 6 dB, half the average power of a sine wave.

Look at the current draw of your PLX 380 amplifier at various output levels, 1/8 power is 12 dB crest factor pink noise, about the equivalent of fairly compressed music, 1/3 power is 6 dB crest factor, Full Power Sine Wave is 3 dB crest factor, like we see in some LF EDM. Note the BTUs and current, around 80% of that power is being dissipated through the speaker, only 3% or so actually makes sound, the vast majority just makes heat.

New speaker designs have improved heat management and excursion by a factor of three or more compared to the EVX 180B, designed in a kinder, gentler era (late 1980's), when the most compressed EDM you could find had more than double the crest factor of today's droning stuff.

Sold the last of the EVXs off years back, I no longer can get behind my EV ad from 1990. There have been a lot of changes in 24 years, EV has not kept up  :'(.


Art



« Last Edit: September 05, 2014, 05:20:39 pm by Art Welter »
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