Increased power handling on the W3-871s? - diyAudio
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Old 18th October 2004, 05:22 AM   #1
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Default Increased power handling on the W3-871s?

Seeing how the W3-871s only has a 15w RMS rating when run full-range, I was wondering what you guys think the RMS could be bumped up to if it was crossed over higher, say at 150-200hz, or maybe if it was crossed at 2000hz and used as a tweeter? The reason I ask is because it seems to average 87-88db above 150hz, and if I were to use them to run above the 150-200hz mark, and run a sub with them, how much output could I expect? I'm also curious how much more output I could expect from them if I use them as a tweeter paired with a woofer in a 2-way and crossed them over at like 1.5khz to 2.5khz? Would like to get the sensitivites to match up as best I could.

Any information or links or anything at all is greatly appreciated!
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Old 18th October 2004, 05:36 AM   #2
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Default depends...

If the power rating is entirely thermally derived, it probably doesnt matter what the freq is that you drive the unit with, it will have a similar heating effect and with enough power will ultimately fry the voicecoil, we are talking power here after all, 15w is 15w at 100hz or 10khz.

If the power rating takes into account the excursion expected at the low end of the freq range, by raising the crossover freq you may be able to get significantly more output. Of course this means you have no idea what the actual thermal power limit is...

...though you can probably make a good guess by considering the length, diameter and former material of the voicecoil.

Someone with experience of the driver will probably be able to give you a 'real world' number.

Good luck

Stuart
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Old 18th October 2004, 12:50 PM   #3
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Thanks for the good start, Stuart!
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Old 18th October 2004, 01:24 PM   #4
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Power requirements of a driver closely mimic the 3dB/octave roll off rate of pink noise, so for each octave above Fs you place the HP filter you effectively double power handling.
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Old 18th October 2004, 01:45 PM   #5
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Quote:
Originally posted by BillFitzmaurice
Power requirements of a driver closely mimic the 3dB/octave roll off rate of pink noise, so for each octave above Fs you place the HP filter you effectively double power handling.
Yep, I've done this. If you get the HP above 500Hz it will be able to handle most anything. I'm using it with a woofer rated at 90 watts and it works fine.
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Old 18th October 2004, 02:51 PM   #6
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Default question...

Bill,

Please correct me if I'm wrong, If I understand your answer correctly I think you are saying the fraction of the total power 'given' to the high freq driver diminishes as the low end is removed, but it's actual power handling doesn't change does it? i.e. this TB driver, despite a 15w thermal rating could be used in a system designed for 200w, if it's crossed over high enough, because it will only ever see 15w or lower...but if one were to clip a big amp hard and long enough to drive 20w into the VC, sayanara...

Stuart
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Old 18th October 2004, 03:45 PM   #7
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What actually happens is as you go up the spectum the amount of power being put into the driver by the amp decreases by approximately 3dB per octave, so while the actual power dissipation ability of the driver is unchanged the amount of power being fed to it by the amp changes with the HP frequency. This used to cause a lot of confusion vis a vis tweeters, which once were generally rated by the actual power they could dissipate. and thus appeared to have very low capabilities. For instance, it was once common to see tweeters rated at 5 watts. Nowadays 100 watt ratings are common, but that is with a specified crossover frequency and slope.

As an example, a tweeter rated at 100 watts with a 5kHz 2nd order crossover in all likelyhood can only handle 5 watts broadband, but in a 100 watt signal the amount of power contained from 5kHz and up when filtered at 12dB/octave is only 5 watts.
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Old 18th October 2004, 07:10 PM   #8
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I think I digested all that

So in all actuality the numbers pretty much stay the same if you apply them in this sense:

1w - 87db
2w - 90db
4w - 93db
8w - 96db
16w - 99db

So if I were to run this driver full-range with 16w of power (close enough to the 15w RMS) and it had a perfectly flat response curve, it would output 99db all across the band, correct? If I were to cross it over at 3khz, and the amp running it was a 16w amp, it would only take 1-2w for it to achieve 99db at 3khz and up, correct? Even though the amp was trying to put out all 16w, the crossover was only letting the speaker take a fraction of that.

If that's not the case, I'll be more than happy to punch myself a few times for you frustrated guys!
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Old 18th October 2004, 09:19 PM   #9
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That's close enough to it to suffice.
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