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New Generation "High Powered" MI Level Speakers

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Reggie Kendrick:

--- Quote from: john manson on February 06, 2011, 07:39:51 PM ---What does "MI" stand for?

--- End quote ---

It's not the sexiest acronym but here you go:  http://www.livesoundint.com/lab/lab/messages/archive4/5478.html

Bob Leonard:

--- Quote from: Brad Weber on February 05, 2011, 08:46:39 AM ---I agree with Paul's response, it all depends on what you are trying to do.  Having an amp rated equal to or even less than the RMS rating of the speaker may be absolutely fine and provide plenty of headroom unless you try to get more out of that combination than it can support.  There is no magic that happens by using an amp rated at 1.5 to 2 times the continuous power rating of the speaker, that is simply a general guideline to have a reasonable balance of maximum output and reliability.  Maybe the simplest way to put it is that it is the use that defines what power is needed or appropriate and a speaker power rating does not define what power a speaker needs but rather what power it can handle.

There are two aspects of speaker power ratings that are commonly overlooked.  One is that typically only the continuous power rating of a speaker is actually measured.  The peak rating is assumed calculated based on that measurement and the crest factor of the test signal while the Program rating is just a number somewhere between those two, typically midway between them.  The other aspect is that nothing says the speaker performance stays the same all the way up to the ratings, there could be variations in frequency response or other changes prior to there being some form of failure.  This is one reason why people sometimes may subjectively feel that a certain speaker sounds better with more power, but it also is not inherently a positive nor is it reflected in specifications.

People sometimes seem to get too caught up in power values that probably don't matter as much as they think.  For example, being worried that the Program rating of the speaker is 1,200W and you only have a 1,000W to power it, a 0.8dB difference that probably no one would notice.

To the comment "Does it really mean that a DJ could take a PLX 3402 and let it rip on either of these cabinents constantly in "clip" or "peak" and never burn up anything?   I mean, that's what the RMS figures suggest right?", the short answer is no, that is not what it means.  The long term or continuous (not RMS, there is no such things as RMS Watts) rating is simply the power the speaker could handle for a specific period of time with a specific test signal.  Clipping is not part of the rating.

--- End quote ---

Not sure if you may have missed this part of my statement.
 
"2 x 800 watts = 1600 watts. 1.5 can be substituted for 2, and an amplifer which provides 800 watts may work fine depending on the application and as long as the amplifier does not clip."

Clipping, when an amplifier will reach at least twice it's rated output power, is a very real and common reason for driver failure, usually the compression drivers first.
 
You are correct in stateing that the term RMS when used today is innacurate. An RMS rating would depend on a purely resistive load and speakers of any type are not a purely resistive load. I'll amend my old school statement to read "manufacturers long term power rating".
 
In a general context without measurement and analysis of the application I'll stand by my time proven rule of thumb and add that for the novice this rule is in most cases the safest method to use for sizing an amplifier.
 
I'll state that because regardless of the amplifier size, a person who fails to recognize the limits of their speakers and system can and will destroy drivers regardless of amplifier size, and will destroy those drivers more often with an amplifier rated much lower than most manufacturers recommend. And that manufacturers recommendation will almost always be 2x the long term power rating. I have rarely met the person looking for less power for their cabinets, at least not in my 45 years of working with sound.

John Roberts {JR}:

--- Quote from: Bob Leonard on February 07, 2011, 03:20:01 AM ---
Not sure if you may have missed this part of my statement.
 
"2 x 800 watts = 1600 watts. 1.5 can be substituted for 2, and an amplifer which provides 800 watts may work fine depending on the application and as long as the amplifier does not clip."

Clipping, when an amplifier will reach at least twice it's rated output power, is a very real and common reason for driver failure, usually the compression drivers first.
 
You are correct in stateing that the term RMS when used today is innacurate. An RMS rating would depend on a purely resistive load and speakers of any type are not a purely resistive load. I'll amend my old school statement to read "manufacturers long term power rating".
 
In a general context without measurement and analysis of the application I'll stand by my time proven rule of thumb and add that for the novice this rule is in most cases the safest method to use for sizing an amplifier.
 
I'll state that because regardless of the amplifier size, a person who fails to recognize the limits of their speakers and system can and will destroy drivers regardless of amplifier size, and will destroy those drivers more often with an amplifier rated much lower than most manufacturers recommend. And that manufacturers recommendation will almost always be 2x the long term power rating. I have rarely met the person looking for less power for their cabinets, at least not in my 45 years of working with sound.

--- End quote ---

This is the first time we had this discussion since re-skinning this forum.

It is true that an amplifier clipped so hard it turns a sine wave into a square wave will put out roughly 2x it's clean sine wave power. IMO more important is the simpler explanation. Amplifiers clip because the operator turns up the gain too high. This "too high" gain increases all of the signal, not just the peaks that may be clipped. It is this higher average power that overheats the voice coil.

This topic has been beat to death, but not completely to death.

Sizing power amps to loudspeakers is not neat. To get useful peak output we routinely connect them to amplifiers that can fry them long term. The operator must use some discretion.

This is a little like car engines. To be able to get up to cruising speed quickly and safely we put in bigger motors than we need to just barely reach speed limits. That's why we have speedometers and temperature gauges. A stock passenger car driven at full throttle for too long, like on a race track, could overheat and fail. Just like a loudspeaker driven too hard. 

JR
 

Geoff Doane:

--- Quote from: Bob Leonard on February 07, 2011, 03:20:01 AM --- 
You are correct in stateing that the term RMS when used today is innacurate. An RMS rating would depend on a purely resistive load and speakers of any type are not a purely resistive load. I'll amend my old school statement to read "manufacturers long term power rating".
 
--- End quote ---

At the risk of being pedantic, I think Brad was correct when he said "There is no such thing as RMS watts".  I remember an instructor telling us the same thing in tech school, 30-odd years ago.  The term has been appropriated by marketers to mean "continuous average sine wave power", or something like that, although I do admit that "RMS" does roll off the tongue more easily.

All the rest of that stuff, I'm in agreement with.  People would blow up fewer speakers if they listened to the speakers, could recognize the sound of speakers reaching their limits, and actually cared about not blowing them up. ::)

GTD

Bennett Prescott:
Here is an article I wrote on this very subject. The rules of thumb from 20 years ago still apply, but you can extract much more performance from a loudspeaker by using RMS limiting, which is now widely available.

http://www.bennettprescott.com/downloads/LoudspeakerFundamentals.pdf

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