Rob Zombie Test~

[TNRabbit 370]

Interesting~  pulled from Club Polk:  http://www.polkaudio.com/forums/showthread.php?t=97431

 

The Rob Zombie Spec

 

One specification you will not see on any amplifier specification chart is the Rob Zombie test. The Rob Zombie test is something our engineers (we call them ‘lab rats’) cooked up. It seems for whatever reason to be the most effective way to test a power amp... In this case we take a worst combination of low impedance (within the IEC spec) and reactive (phase shifted) impedance and find the meanest music we can. This simulates the worst case operating conditions an amplifier may see in the field.

 

It is important that the speaker has a large heavy voicecoil to remain cool and keep the impedance low over time. We play Rob Zombie’s ‘Hillbilly Deluxe’ CD, Track 6 ‘Demonoid Phenomenon’ and see how long it takes for the amp to trip its internal protection or shut down. Demonoid, it seems, shuts down amps faster than white noise, Whitesnake, pink noise, Pink Floyd or Metallica. (With the rare exception of the one amp that shut down during an extended ‘Celine Dion’ test ... but we think that might have been a suicide.)

 

As odd as this test sounds, we used a Bruel and Kjaer 2304 audio analyzer to investigate amplitude distribution and found that the toughest music was Rob Zombie (harder on your power system than typical AM radio source material) in terms of punishing an amplifier. This program material spends the most time at an amplitude that we've found overheats amplifiers. It is an opportunity to drive the amp in a real world application, in less than the ideal circumstances of a laboratory and test equipment. It forces the amplifier to play real music source program material (not theoretical source material) into an impedance shifting / phase shifting speaker load. This is a test of the real world capabilities of the amplifier, in conditions you could easily see in a nightclub, a rave or a rock concert ... not a design lab.

 

We always run this test, among others on our products, and occasionally competitive products, just to see where we stand. We have seen competitive amplifiers with impressive specifications not pass the Rob Zombie test either in the lab, or in a nightclub.

 

The truth is, current trends in music like super low bass synths and massive samples now commonly used can be far more punishing than popular program music was in the past. A good amplifier has to have the ability to cope with whatever source material you choose to use, even if it is Rob Zombie.

 

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[RichP714 3,151]

Here it is for anyone that wants to try this test.

 

http://thecarversite.com/yetanotherforum/userfiles/06 Rob Zombie - Demonoid Phenomenon.wav

 

It seems to be an extreme case of the modern trend of using compression in recordings.

 

 

You can see by the screen grab that this track is recorded 'hot' that is, the average level is way up there, meaning the peaks would clip, so they have to compress them.

 

Typical music has a peak to average ratio of 20dB, so in a well recorded track, the average level shold be -20db, allowing uncompressed peaks to reach 'all bits on' at 0db.

 

In a compressed track, you get average levels above -20dB (typically 12 to 15dB); makes the music 'sound' louder, but is eventually fatiguing, as there are limited dynamics.

 

This track has an overall average level of -9.8dB; it overall sounds about twice as loud as it would if it had been recorded well.

 

Some sections of the track have a peak to average ratio of only 6dB, which is crazy.

 

If it's a stress test, it seems to be because of the compressed recording rather than the musical content.