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Old 28th October 2009, 05:54 PM   #1
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Default How much headroom is needed

If I have a speaker that at a given crossover reaches full excursion at 10 watts. Does 20 watts provide some improvement in headroom? 40 watts? What is reasonable?
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Old 28th October 2009, 06:23 PM   #2
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depends on the frequency. As the audio frequency goes up the cone excursion goes down. If you are certain that the music you are listening to does not contain any low frequencies that will cause the maximum cone excursion than you can use a higher power amplifier. If you use a higher power amplifier and drive the speaker to beyond its max cone excursion rating the spls will not increase it will sound louder beacuse the higher frequencies will be louder but the distortion due to cone compression will increase dramatically. If you are asking about a midrange driver then you can move the crossover freq up an octave and this will again lower your cone movement. If you are talking about a tweeter, don't shoot me for this but many tweeters cannot sustain continuous sine wave signals at or near their rated power. I have blown many so called 30-40watt rms tweeters with as little as 5 watts rms sine testing. Most high frequency drivers fail because of too low rated power amplifiers being driven into clipping. Most people cannot tell when an amplifier just begins to clip. Clipping results in high frequency harmonics at high power levels and this is what destroys most tweeters. Most tweeters can handle high power for a relatively short period of time. The amount of energy in most music is very low at high frequencies compared to low frequencies. My basement system uses a tri amp configuration. I have never even come close to clipping with the midrange and treble 30 watt amplifiers but the 100 watt bass amp led display shows clipping very often especially when playing some Telarc disks. For your brain to perceive that music is twice as loud you need 10 times the power. Ears are logarithmic. At low sound levels you are probably using a few hundreths of watts.
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Old 28th October 2009, 06:37 PM   #3
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If you use an amplifier with a rated power of at least 2X the drivers rating and use self control you are better off than using an under powered amp and running the risk of clipping if you try and squeeze the last drops of juice from it.

My 2 cents.
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Old 28th October 2009, 06:52 PM   #4
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thanks. Let me be more specific. This is for a Dayton RS52, 2" dome crossed at 600 hz. It will reach full excursion at 10 watts.

Cal -So 20 watts is all that is required. Correct.
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Old 28th October 2009, 07:04 PM   #5
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It should handle more power input toward the top crossover point as excursion will be lower here. That said, there is generally less power in music as you go higher.

I also have the RS52 dome in my (currently being built) system. Where did you get the 10W at 600Hz excursion limit from? What crossover slope are you using?
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Old 28th October 2009, 07:25 PM   #6
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Correction, crossover is 500 Hz, not 600 Hz.

I used Unibox, w/an excursion of .75mm and someother data that Zaph had posted in another thread in the forum. No crossover, just where max excursion excursion is reach.

In actual use, I will be using an 18 db electronic crossover.
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Old 28th October 2009, 07:54 PM   #7
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Quote:
Originally Posted by multisync View Post
If you are talking about a tweeter, don't shoot me for this but many tweeters cannot sustain continuous sine wave signals at or near their rated power. I have blown many so called 30-40watt rms tweeters with as little as 5 watts rms sine testing. Most high frequency drivers fail because of too low rated power amplifiers being driven into clipping. Most people cannot tell when an amplifier just begins to clip. Clipping results in high frequency harmonics at high power levels and this is what destroys most tweeters. Most tweeters can handle high power for a relatively short period of time
Absolutely spot-on IMO.

Take a tweeter apart some time; you very soon realise that tweeter power ratings are 'music ratings' ie about as useful as 'PMPO' (reemember that?). In truth, no tweeter voice coil [apart - maybe- from some ribbon/magnetoplanar types] has enough thermal mass or radiating area or heatsink ability to withstand more than 3-5W RMS for any length of time.
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Old 28th October 2009, 09:53 PM   #8
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I found I was quite shocked at how badly amps cope with transients.

My first amp had about +/-40v rails and was poor with transients.
It clipped before I got any decent volume out of it.

I now work with 60 volts or better to get teh response i want.
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Old 29th October 2009, 12:22 PM   #9
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Just speaking from a headroom standpoint only and not destroying speeds from clipping or heat or over excursion. If my speakers max excursion is reached at 10 watts, and I will be judicious in the use of these 10 watts for said reasons. Will the amp produce those 10 watts faster, more agressively, more dynamically, if it has 40 watts to spare?

For example, let's say the speed limit is 60 miles per hour and lets assum you can not exceed that limit. And you have two cars, one has 100 hp and the other 500 hp. Even though the speed limit is 60 mph, those ride can be very different.
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Old 30th October 2009, 02:31 PM   #10
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Quote:
Originally Posted by mitchyz250f View Post
If I have a speaker that at a given crossover reaches full excursion at 10 watts. Does 20 watts provide some improvement in headroom? 40 watts? What is reasonable?
Hi,

First off, the size of you amp is not as important as how much actual power you send to the speaker. Believe it or not, I have seen more speakers blown by small amps that were pushed then by large amps that were just idling along.
At low frequencies, it is normal for the speaker cone to deflect a lot. But, control of the cone is also determined by the amplifier's damping factor. My 7 watt per channel 2A3 parallel SET tube amps make the cones in my test speakers deflect more then a 40 watt Proton D540. The reason is that the Proton has a damping factor several times as high as the zero feedback triode amp.
So actual power is not the only determining factor. There is also the frequency of the sound sent to the speaker, the damping factor of the amp and the mechanical damping of the speaker in combination with it's cabinet.

Headroom refers to the amount of extra power you have to accommodate peaks in demand from the music you are reproducing with an amplifier. Using the old Proton D540as an example, it is rated at 40 watts RMS into 8 ohms. But, Proton says the amp has a dynamic headroom equating to four times the amp's rated output for peak bursts of power up to 1 second.
A slightly larger amp that is not pushed to clipping is far better then a smaller amp that clips on peaks. This clipping and such is what can kill a speaker. Using a big amp (100 watts or more per channel) and playing it at 2 - 10 watts means you have a lot of dynamic headroom that is undistorted. The use of a large, powerful amp in this way is much kinder to your speakers.
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