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Old 24th September 2012, 02:47 PM   #1
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Default Power amp sizing for subwoofers?

Been trying to figure this out and have been doing a good bit of searching. I want to build a couple of ported subs for light PA use, will be run with a pro audio amp. The modeled design I have right now does not hit xmax with RMS power, and the xmech is plenty.

The pro audio guys say run double the RMS power of the subs, and set limiters for no clipping - amp is comfortable and sub gets clean power all the time.

People using the pro amps for HT say that power matching the RMS rating is fine, and a little bit of clipping at a bit above RMS levels is no big deal.

Can anyone point me in the right direction or give more advice?
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Old 24th September 2012, 04:45 PM   #2
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Old 24th September 2012, 05:01 PM   #3
NEO Dan is offline NEO Dan  United States
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Go with the PA recommendation for your PA setup.
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Old 24th September 2012, 06:37 PM   #4
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So, something like the Behringer inuke 6000dsp (1700w RMS 4 ohm x 2 both channels driven) could be a good match for Dayton audio 15" Ref HO's (800w RMS), in 2.5 cubes vented, tuned to 37hz? Seems pretty excessive to me.

http://forum.speakerplans.com/behrin...opic69202.html
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Old 24th September 2012, 07:00 PM   #5
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Originally Posted by turbodawg View Post
Been trying to figure this out and have been doing a good bit of searching. I want to build a couple of ported subs for light PA use, will be run with a pro audio amp. The modeled design I have right now does not hit xmax with RMS power, and the xmech is plenty.

The pro audio guys say run double the RMS power of the subs, and set limiters for no clipping - amp is comfortable and sub gets clean power all the time.

People using the pro amps for HT say that power matching the RMS rating is fine, and a little bit of clipping at a bit above RMS levels is no big deal.

Can anyone point me in the right direction or give more advice?
As long as you aren't tearing the speaker apart by exceeding Xmech, long term average power is what burns speakers up.

Average power can be very different for different types of music, heavily compressed sine wave like material can have 5-10 times the average LF power compared to say 1980's Steely Dan or the like. HT is generally about sound effects, which usually are fairly short, though there certainly are exceptions.

If you run double the RMS power and have limiters set for no clipping, there is still a very real potential of burning the voice coil if the amp is driven in to hard limiting, as is typical of a DJ mashing in to the red for long periods of EDM.

That said, most amps are capable of + 3 dB output when driven in to hard clipping, in the above scenario one can still burn a voice coil with a clipped amp rated at the speaker's RMS rating.

By the way, most speakers are rated using the AES standard, which uses compressed pink noise with a 6 dB crest factor (normal pink noise is around 12 dB crest factor, still less crest factor than "normal" music), which has only half the average power of a sine wave, which has a 3 dB crest factor.

Although I have tested (almost) all my woofers with sine waves at the AES rated wattage, it has been short term with resting periods between tests, so the average still is around the AES power rating or less. Some of the tests I have done not leaving enough time between tone bursts have resulted in burnt voice coils, and the amp was not clipping at all.

So the short answer about how much power is safe is "it depends".

Art Welter
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Old 24th September 2012, 07:08 PM   #6
NEO Dan is offline NEO Dan  United States
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That's not a PA woofer, and that amp has limiters so the level of excess is totally up to you.
It used to be the case that a PA woofers had short coils and Xmax with Xmech being 3x Xmax or more. So basically no mater what you did the driver ran out of force and the suspension could safely keep the driver from bottoming.
OTOH the HiFi subs with soft suspension and 30mm Xmax 40mm Xmech are exactly the opposite situation...
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Old 24th September 2012, 07:19 PM   #7
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Originally Posted by turbodawg View Post
So, something like the Behringer inuke 6000dsp (1700w RMS 4 ohm x 2 both channels driven) could be a good match for Dayton audio 15" Ref HO's (800w RMS), in 2.5 cubes vented, tuned to 37hz? Seems pretty excessive to me.

Behringer inuke NU6000 vs KAM KXD7200 bench tested - Speakerplans.com Forums - Page 1
See my post # 5, this is kind of a P.S.

Just looked at the Eminence Lab 12 specs, rated for 400 watts using the AES EIA 426 test signal (6 dB crest factor) and Parts Express wrongly label the speaker as 400 watts RMS, overstating its power by 3 dB.
Id expect the Dayton 15 Ref HO to be rated using the same AES EIA 426 test signal, be careful with an amp rated for 1700 watts, even at peak.

Art
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Old 24th September 2012, 08:15 PM   #8
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Originally Posted by weltersys View Post
See my post # 5, this is kind of a P.S.

Just looked at the Eminence Lab 12 specs, rated for 400 watts using the AES EIA 426 test signal (6 dB crest factor) and Parts Express wrongly label the speaker as 400 watts RMS, overstating its power by 3 dB.
Id expect the Dayton 15 Ref HO to be rated using the same AES EIA 426 test signal, be careful with an amp rated for 1700 watts, even at peak.

Art
Wow, thanks Art. Dayton gives 800w RMS on their spec sheet and web page. Given the claimed Mms of 380.6g and BL of 21.52, do you think they are rating the sub correctly for power? Seems like it should have a pretty large voice coil, and get some cooling from the aluminum cone?
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Old 24th September 2012, 08:29 PM   #9
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Originally Posted by turbodawg View Post
Wow, thanks Art. Dayton gives 800w RMS on their spec sheet and web page. Given the claimed Mms of 380.6g and BL of 21.52, do you think they are rating the sub correctly for power? Seems like it should have a pretty large voice coil, and get some cooling from the aluminum cone?
I would suspect the speaker is 800 watts AES 426, which would be 400 watts RMS.
Still, that would be 3 dB more power handling than the Lab 12, and I have not burned any Lab 12s using about 2000 peak watts.
That said, I also have never used my Lab 12s for long periods of EDM .

Art
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Old 24th September 2012, 09:16 PM   #10
DrDyna is offline DrDyna  United States
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You should probably note that clipping produces DC voltage, which is much more hazardous to a speaker than short sine wave power.

When in doubt, select a stronger amplifier, IMHO.
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