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The right power for your speakers


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6 replies to this topic

#1 of 7 OFFLINE   Ottawa

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Posted April 05 2011 - 04:23 PM

I've spent weeks now trying to figure out which power amp to buy.  How many channels...How much RMS power output per channel and all the other valuable information one needs to make an informed decision.  Though it seems that I forgot one thing.  My Speakers!!!



How much power can my speakers really take?  The two or three amplifiers I am debating between put out 150 w @ 8 ohms ACD FTC up to 325 @ 8 ohms ACD (all channels driven).  Ok...so they're nice amps.  Probably will blow my mind.  But will they blow my speakers?



For speakers, I have Paradigm Studio 60s (fronts), Studio CC-690 (centre) and Studio 20s (rear).  So 5 channels.  But these speakers have a "Suitable Amplifier Power Range" from 15 to 300 Watts depending on the speaker.



I've ready many of the old threads regarding power ratings for speakers to amps, but they all seem to be specific to certain cases.  My goal here is to learn more about the dangers of over powering speakers.  Learning what I should set my limits to when purchasing an amp given my speaker power ratings and whatever else that might apply to this topic.



Thanks!

Kevin



#2 of 7 OFFLINE   Ed Moxley

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Posted April 06 2011 - 01:01 AM

The Paradigms should be able to handle any of those amps. I'm wondering why you're buying an amp? Do you have a pre/pro setup, and you're replacing the amp part? Or is this an external amp you're adding to a receiver? Your receiver has pre-outs, right? With the speakers being 8 ohms, they shouldn't need an amp to drive them, unless you're just wanting one.


Most of my life I've heard that power doesn't blow speakers. Distortion does.

Maybe someone who knows more about the technical aspects of speakers will chime in.

Good luck!


Samsung HL61A750 (LED DLP)            Onkyo TX-SR805
Oppo BDP-83 Blu ray                                  Polk Audio LSi9
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#3 of 7 OFFLINE   Ottawa

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Posted April 06 2011 - 01:06 AM

Hi Ed,


Thanks for the reply.  I've decided to sell my Yamaha RX-V3900 and go with separates.  I'll likely stil be running my speakers @ 8 ohs with my new amp.  And yes, I am also getting myself a pre/pro.  I'm thinking of going with either the Arcam FMJ AV888 or the Integra DHC-80.2.  I think I'll get a good deal more from my speakers with this setup.


So, what have I learned...Distortion causes damage, not power.  What about clipping?


Kevin



#4 of 7 OFFLINE   Ed Moxley

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Posted April 06 2011 - 04:16 AM

I don't know. I've heard of clipping, but have never heard clipping personally. I've heard it can do damage, but don't know what kind of damage. It may damage electronic parts rather than blow the speaker. When I think of blowing a speaker, I'm thinking it damages the actual driver itself, and not messing with the electronics of it. You and/or others may use a different definition of it. Again, maybe someone with more info will chime in. Sorry I'm not more help with this subject.


Samsung HL61A750 (LED DLP)            Onkyo TX-SR805
Oppo BDP-83 Blu ray                                  Polk Audio LSi9
Polk Audio LSiC                                  Sony SS-MB100H
SVS PC12-NSD (Sub)                       ...

#5 of 7 OFFLINE   Robert_J

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Posted April 06 2011 - 06:11 AM

The distortion you hear is clipping.


There are only two types of speaker failures - 1.  Thermal - things get too hot and melt.  2.  Mechanical - You push the driver beyond it's limits and parts fail.


Thermal failure is caused by either too much power and/or too little cooling.  Any speaker can take bursts of power 2 or 3 times what the RMS rating is.  That's because the RMS rating is how much continuous power the speaker can take for 1 hour (or 2 or 3) before things start to fail.  They use a sine wave or pink noise to figure this out.  Movies go from loud to quiet to loud and give the speaker internals time to cool down before each blast.  Music is less forgiving since there is a more constant signal.  Finally, clipping does help speed up the thermal meltdown of speakers.  When a signal is clipped, it will push the driver out to a point and stop while still sending power through the driver.  Heat is building but there is no motion to aid in cooling.  This only happens for a split second but it is repeated over and over and over several hundred or thousands of times per second.  It adds up and adds up fast.  Usually the first thing to go is the epoxy that holds the voice coil windings to the former.  They come loose like a slinky and your speaker stops moving.  The amp is still pushing power but with no more movement, things really get hot and start to smoke.  Sooner or later, one of the small wires will burn through and shut down the process.


Mechanical failure is another has nothing to do with heat.  For example, a sub can take 500w while mounted in a sealed box.  Remove the driver from the box and send it a 10hz tone and it will reach its physical excursion limits well under 500w.  The spider and or surround will tear.  The voice coil may jump out of the gap which can lead to it hanging on the pole piece.  Most common is the driver "bottoming out".  That's when the voice coil hits the back plate.  Lightly doesn't hurt.  Slam into the back plate and it is like you stepping on an aluminum can.  The voice coil will deform and start to rub the pole piece.  Usually the coil will rub the gap.  Once the insulation is rubbed from the wires, you will have a direct short.  That will send your amp into protection or worse, burn it up.


In the following video at 23 seconds you can hear the coil bottom out slightly.  As a disclaimer, I know the guy in the video and that sub is one we built together out of spare parts.  It is designed to work well in large, sealed boxes or infinite baffle.





#6 of 7 OFFLINE   gene c

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Posted April 06 2011 - 01:52 PM

What a great explanation! But you need to put that disclaimer "Don't try this at home!" in there somewhere before the video.


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#7 of 7 OFFLINE   Robert_J

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Posted April 07 2011 - 03:48 AM



Originally Posted by gene c 

What a great explanation! But you need to put that disclaimer "Don't try this at home!" in there somewhere before the video.

If you are posting "sub porn" as it is commonly described then you probably know what you are doing.  You are basically showing off how much excursion your driver has.  In the case above, that one is moving about 25mm in each direction.  That is about all it can mechanically do with that combination of parts.  Use a deeper motor, basket with a higher and larger spider landing and the driver will have much more excursion.  In the video below, that sub is moving about 35mm in each direction.  I'm working on building some subs that are pushing the 40mm range.  And that's all for this topic because I've really taken this thread off track.