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unsafe8989
02-24-2012, 11:56 PM
Ok so my question is why do Guitar amps sound loud at like 20 watts rms when DJ cabs need 800 watts rms.

fueledbymusic
02-25-2012, 12:00 AM
Cause the speakers are usually close to your ears..... I think

Al Poulin
02-25-2012, 12:10 AM
Guitar amplifiers/speakers reproduce a more limited range of frequencies - most of which being mids. Hi and mid frequencies need very little power to produce plenty of sound - it is the low frequencies that take the most power to reproduce. For example, in a typical powered speaker - say a 650 watt powered speaker - it is normal to see 550 watts going to the woofer with only 100 going to the horn. My YX15Ps (for example) only have 20 watts going to the horns and 180 to the woofers. Low frequency reproduction simply requires a much bigger amount of power than mids and highs - and the lower you go in frequency, the more speaker and power is required.

Another good example is a megaphone like this one :

http://www.apexelectronics.com/category/Other_Accessories/product/Mega2/

Only 15 watts and it can be heard up to 1300 feet. Do you think it is is putting out any deep bass? Of course not. It's output is completely focused on mid (vocal) frequencies.


Al

unsafe8989
02-25-2012, 12:12 AM
Cause the speakers are usually close to your ears..... I think

Its about 20 feet away and sounds nice?

unsafe8989
02-25-2012, 12:13 AM
But im mostly speaking here for bass it sounds great at such distance.

Bill Fitzmaurice
02-25-2012, 09:09 AM
Power requirements double for each octave lowering of response. The power bandwidth for guitar starts at 200Hz, with peak output at 400-800hz.

unsafe8989
02-25-2012, 12:22 PM
Power requirements double for each octave lowering of response. The power bandwidth for guitar starts at 200Hz, with peak output at 400-800hz.

Ohh ok I see.

djscrizzle
02-26-2012, 04:22 AM
Also take into account that certain speakers have higher sensitivity than others. Many "DJ" speakers are typically between 85-99dB, 1watt measured at 1 meter. (3.3ft)

PA (paging) horn speakers typically have 103dB 1W/1M as a minimum sensitivity, and certain Atlas compression drivers get 115dB 1W/1M sensitivity, with ridiculously high SPLs (155dB @ 1M) when taken to full power of 150-200 watts.

Bill Fitzmaurice
02-26-2012, 09:24 AM
certain Atlas compression drivers get 115dB 1W/1M sensitivity, with ridiculously high SPLs (155dB @ 1M) when taken to full power of 150-200 watts.200 watts results in an increase of 23dB, and that's calculated; real world results are more like 20dB. Going from 115dB to 155dB would take 10,000 watts calculated, 20,000 watts minimum real world.

Windows 95
02-26-2012, 10:30 AM
Plus the threshold of pain is about 120 dB or 130 dB.
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/intens.html


OSHA Workplace Standards
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/deaf.html#c5

Incognito
02-26-2012, 11:16 AM
Plus the threshold of pain is about 120 dB or 130 dB.
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/intens.html


OSHA Workplace Standards
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/deaf.html#c5
With a drop off in SPL at every doubling of distance, it's the listening position you need to keep an eye on so the speakers SPL potential can be higher then this without ill effect depending on it's distance in cross reference to the listening position.

djscrizzle
02-26-2012, 11:15 PM
200 watts results in an increase of 23dB, and that's calculated; real world results are more like 20dB. Going from 115dB to 155dB would take 10,000 watts calculated, 20,000 watts minimum real world.

I TOTALLY fat-fingered that one! I really meant that 135dB is not unheard of at a metre out front of some Atlas speakers, assuming a single driver. IIRC, it's a 2-3 dB bump when you add in a manifold and additional drivers for each horn.

Budzak
02-27-2012, 05:04 AM
Al's response pretty much covered everything you need to know.

It's easy to make a speaker loud over a narrow band of (mid to high) frequencies (especially those that the human ear is already sensitive to). It's even easier when you're allowed to add all sorts of distortion to 'color' the signal.

A PA cab is, to an extent, "doing it all": Covering a wide range, from the lows to the highs, and (in theory) minimizing distortion.

Try playing a CD through a guitar amp. Likely it's going to sound like ass. But hey, it'll be loud-at-20-watts ass.

For another angle on things, go look at the size and wattage needed for good electric bass amps/cabs. There's an area where things get really power hungry.

unsafe8989
02-27-2012, 10:42 AM
Ok Thank you.