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Discussion Starter · #1 ·
I thought I understood the power needed to drive a speaker, but now I'm not so sure. If a speaker is rated 100 to 250 Watts, does it make any sense to get an amp that can deliver 300Watt/channel? I know that it's good to have some headroom, but this seems to go beyond the capability of the speaker. This probably has been explained before but I guess it's hasn't really sunk into my head. I do understand about the sensitiviy of a speaker and the doubling of power to get +3Db increase so I'm hoping that someone has the patience to regurgitate the information about the power range of a speaker one more time. :scratch:

Thanks

Bob
 

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Speaker wattage ratings are typically “program material” and as such have little to do an amplifier’s rating, which is typically RMS continuous.

The amp’s power rating isn’t that important, especially since virtually no one runs their amps wide open anyway. All that matters is how hard you drive the speakers with it. You can use a 500 watt amp with a cheesy HTIB speaker, if you keep the volume the same or lower as it would be with the cheap HTIB amp.

Regards,
Wayne
 

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Discussion Starter · #3 ·
Wayne,

Thank you for your response. So for example, if I'm driving a 4 ohm speaker with an amp that can deliver 300 Watt into 4ohms, I wouldn't gain anything by going to an amp that can deliver 400 watts into 4 ohm (in regards to headroom) outside of the electronic characteristics of the amp (perhaps less distortion or a slightly different sound). Is that correct?

Bob
 

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So for example, if I'm driving a 4 ohm speaker with an amp that can deliver 300 Watt into 4ohms, I wouldn't gain anything by going to an amp that can deliver 400 watts into 4 ohm (in regards to headroom)
The question really is, do you need the extra headroom? You’d only need it if you were topping out the 300-watt amp.

Of course here you get to the whole “upgrading your amp” situation. You know the rule of thumb for that, right? I.e., you need to double the power to get any significant improvement in headroom – which is something like an additional 3 dB if I recall... I think going from a 300 to a 400 watt amp would get you probably 1 dB or so extra headroom. But hey, that might all you need to stay out of clipping!

Regards,
Wayne
 

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Does the amp you are using now have power meters or at least a clip LED? If the LED never lights and your volume level is as loud as you ever want to go with your speakers then you dont need to worry. Obviously the bass frequencies will put your amp through the best test so play a movie or audio track and see how it preforms.
I you have no indication of where the amps power output is at then use your ears and listen, distortion is usually easy to hear and thats a sign your amp is about to clip or already doing so.
 

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I you have no indication of where the amps power output is at then use your ears and listen, distortion is usually easy to hear and thats a sign your amp is about to clip or already doing so.
Generally the above should work well. Make sure that you have good speakers. With some "best bang for the bucks" speakers, I feel that cone breakup often happens before clipping. Good speakers have stiff cones that prevent cone breakup and they usually use better materials like high tech ceramics, metal or specially made composite. Cone breakup can be mistaken for clipping. I had a pair of speakers that suffer from cone breakup at modest volume level (70-80dB from listening position).

For an explanation of cone breakup you can just google or visit the Polk website.

Here's some pics of cone breakup from Polk Audio(scroll down to the bottom):
http://www.polkaudio.com/education/tech_article.php?id=25

Good speakers are as important as having an amp that can drive the speakers. If your amp provides ample dynamic range, it behooves you to match the amp with good speakers that have ample dynamic range too.
 

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Bob 99

I would worry more about characteristics then wattage, which usually not 100% accurate, depending how the company rates it.

I go by sensitivity, impudence and if the list it the Voltage.

If I see a speaker rated at

4-8ohms
2.35v
89dB Sensitivity

I know my amp neets to have enough current to drive them at that.
 
G

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I thought I understood the power needed to drive a speaker, but now I'm not so sure. If a speaker is rated 100 to 250 Watts, does it make any sense to get an amp that can deliver 300Watt/channel? I know that it's good to have some headroom, but this seems to go beyond the capability of the speaker. This probably has been explained before but I guess it's hasn't really sunk into my head. I do understand about the sensitiviy of a speaker and the doubling of power to get +3Db increase so I'm hoping that someone has the patience to regurgitate the information about the power range of a speaker one more time. :scratch:

Thanks

Bob
It's important to understand what happens when an amplifier "clips".
"Clipping" is when a 200 watt amplifier, for example, is asked to deliver 201 watts. (this is a bit of an exaggeration, but you get the point)
Harmonic distortion generated by the amplifier suddenly, and VERY dramatically, increases at this point.
This excess energy (harmonic distortion) is biased toward the high frequency spectrum and will usually burn out even the most robust tweeter pretty quickly.
The tweeters in a "250 watt speaker" will usually burn out pretty quickly with fifty watts of energy concentrated within its passband. This is because tweeters are primarily intended to reproduce harmonics, which constitute a very small proportion of the overall program material. Woofers and midrange drivers handle fundamentals and harmonics and are much more robustly constructed.

An ideal amplifier for any given system would be one that is never driven close to the point of clipping.
The solution is to use an amplifier that exceeds your needs by a comfortable margin.
This varies significantly depending on the sensitivity and impedance of the loudspeakers.

The first indication that you are exceeding the wattage rating of a loudspeaker will usually be the sound of the woofer voice coil hitting its stops. (a very loud CRACK! no damage usually occurs, except to your nerves)
The first indication that you're running your amplifier significantly beyond the clipping point on a regular basis will usually be silence from your tweeter(s). They make nice paper weights, but are usually too large for a keychain or watch fob.

Here's a basic scale for calculating wattage relative to 1 watt:
1 watt = +0db
2 watts = +3db
10 watts = +10db
20 watts = +13db
100 watts = +20db
200 watts = +23db
1000 watts = +30db

Some general rules of thumb, subject to debate:

+1db is the smallest perceivable change in SPL.
+3db is somewhat louder.
+6db is significantly louder
+10db is "twice as loud"

a 100 watt amplifier is somewhat louder than a 50 watt amplifier.
a 200 watt amplifier is significantly louder than 50 watt amplifier. (nice upgrade!)
a 1000 watt amplifier is twice as loud as a 100 watt amplifier. (nice electric bill!)

Multiply your current amplifier power by 4 to achieve a truly worthwhile upgrade in headroom.(+6db)
 

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Discussion Starter · #11 ·
snickelfritz,

Thanks for your very excellent explanation. I think I'm finally starting to understand some of this.

Bob
 

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Check out this "SPL Calculator" to see what your system can do, and what you might expect from a new amp. LINK

Dolby Digital reference level is supposed to peak at 105 dB at the listening position. (115 dB for LFE)
 

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Of course you must take any calculation with a grain of salt.
How did the manufacturers rate the power handling or output?

For example:
My speakers have a sensitivity or 91.5 dB.
The manual says recommended amp power is 25-150 watts.
But the maximum SPL for the speakers is 111 dB.
So the speakers can really only handle 90 watts before they hit their limits.
A 115 watt receiver would seem to provide more than enough amplification to drive the speakers to their limits.

But are these measurements peak, average, broadband, real program material, or some thing else?
In the end it's just an estimate.
 

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Discussion Starter · #14 ·
Naut,

Thanks for the link. That's a pretty interesting calculator. :T

Also, I think you are quite correct about measurements. There's a lot of wiggle room for manufacturers to provide dubious specs. I would hope that the better names would be a little more honest in their specs.

Bob
 
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