Watts and ohms

Powered Speaker

Just one question is left about the JBL EON P15 G1 Speaker. The seller told me that it doesn’t matter how much ohms the speaker is because it’s a powered speaker. Normally an amp. 200 W 8 ohm gives much more and heavy power than 200 W and 4 ohm. But because it’s a powered speaker you can compare the powered mixer (4 ohm: 300W + 100W) with an amp with seperated speakers 300W + 100W 8 ohm because the ohm has a lesser bad influence on the power because of a direct link. Is that true? ???

I hope so…

Those JBL speakers are self powered (they have an amplifier in them) so you don’t need to worry about what impedance (ohms) rating they are - it’s irrelevant.

You need to drive them with a line-level signal - NOT the speaker output from a powered mixer or amplifier (otherwise KABOOM!).

HTH


Mark

200W is 200W no matter what the load impedance. But most amplifiers are effectively voltage sources, not current sources, so the lower the impedance of the load, the more current and therefore more power is delivered. So an amp rated at 200W into 8 ohm will deliver more power into 4 ohm. (If the amp is a perfect voltage source, it will be twice the power). But a tube amp needs to be matched to its load otherwise nasty things start happening. Solid state amps are much less choosy about load impedance, but even so it’s best to go with the recommended load.

With a powered speaker, the amp and speaker will be matched (hopefully), so you don’t have to worry about what is going on inside the amp/speaker combination, all you’re concerned with is input level and impedance, and how loud the noise coming out is.

Hope that helps.

what is important here is the sound pressure level (SPL) that you get for a given electric power dissipated by the speakers

generally speaking , powered speakers have a good matching between the build-in amplifiers and the speakers.

Quote (Gizmo @ April 19 2006,12:02)
So an amp rated at 200W into 8 ohm will deliver more power into 4 ohm.

Don't understand you. which one gives more power?

electricity rule : P= U²/R

if U stays the same (as it normally does) , then you will get twice electric power in 4 ohms than in 8 ohms

An amp produces a voltage. Power is voltage squared divided by impedance. (that’s amp short for amplifier, not amp short for Ampere).

So if an amp is putting 200W into 8ohms, that means it’s producing 40V (RMS, but ignore that).

So if you hang a 4 Ohm speaker onto that amp instead, the power will now be: (40 x 40) / 4 = 400W.

But the amp is being asked to produce twice as much current, and it might or might not be capable of doing that.

But as everyone says, it doesn’t matter with your powered speaker. You put line level in, and out comes SPL, you don’t have to worry about how the amp is matched to the speaker.

Quote (clevermind @ April 19 2006,12:03)
what is important here is the sound pressure level (SPL) that you get for a given electric power dissipated by the speakers

generally speaking , powered speakers have a good matching between the build-in amplifiers and the speakers.

Bingo! Clevermind wins the prize. :)

Watts, shmatts. They mean absolutely nothing unless you’re buying amp and speaker separately. In a powered speaker, it’s a useless spec. All you should really care about, other than sound quality, is HOW LOUD ARE THEY? And loudness is measured in dB SPL (Sound Pressure Level, in decibels), measured at one meter from the speaker, when fed a 1 watt signal. This is a standard spec. For these speakers, I think it’s a whopping 129dB or something like that – pretty darn loud enough for most of us pikers.

For more info, see How LOUD will it be?, a post on the n-Track Wiki.

Quote (maria @ April 19 2006,12:11)
Quote (Gizmo @ April 19 2006,12:02)
So an amp rated at 200W into 8 ohm will deliver more power into 4 ohm.

Don’t understand you. which one gives more power?

Just for the heck of it, and you might care someday:

200W going into a 4 ohm speakerwill be louder than the same 200W going into an 8 ohm speaker. The 4 ohm speaker presents less resistance (ohmage) to the amp’s current, so it’s louder.

There be the Pikers’ Explanation. :;):

But as was said, you don’t care about that just now. :)
Quote (learjeff @ April 19 2006,18:58)
For these speakers, I think it's a whopping 129dB or something like that

Well I found out that the speakers are from a different type: JBL EON 15PAK . According to Jimbob's answer in the topic "good speakers" they're around 3 DB lesser? Can that be right?
Or does anybody know these 15PAK and is suitable for vocals in a rockband?

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200W going into a 4 ohm speakerwill be louder than the same 200W going into an 8 ohm speaker. The 4 ohm speaker presents less resistance (ohmage) to the amp’s current, so it’s louder.

Just for the record: no, you’ve missed the point again.
Please re-read clevermind, gizmo and learjeff’s posts above.
It would be right to say that the same amp would be louder connected to a 4 ohm speaker than to an 8 ohm speaker. But that would be because the amp would be delivering (up to two times) more current (and therefore: power) to 4 ohms. That is, if it doesn’t blow a fuse or melts first.

Re: 3 db less sound pressure: That is no big difference. If Learjeffs figure of 129dB is correct, 126dB will still easily damage you ears within minutes. :)

EDIT: To lecture a bit more about watts and SPL-dBs:
Many people think that twice the power means twice the perceived loudness . It doesn’t. To get two times as loud you need ~10 times the electric power (because your ears are microphones with a logarithmic response curve). Meaning 30W is still half the loudness of 300W. And 3W still 25%. Go figure.

I think the dB of the 15Pak are around 110. But I’m not sure. Can’t find that much info on internet of the 15PAK. The seller told they were 1,5 years old but I think that was not true. Just in holland I can’t find one or 2 links when I google the 15PAK …

When I search JBL I find only 2 types of powered 15" EONs:

1) EON 15 G2 - 300+100W - rated maxSPL=129dB (@1m)
2) EON 15 P1 - 130+50W - rated maxSPL=127dB (@1m)

The P1 is the older version of the two.
So if you were told you were buying the G2 and got the P1, you’ve been hustled.
That said, if undamaged, they’ll probably still be fine for your band.
The difference in loudness is minimal anyway.

Quote (maria @ April 19 2006,11:34)
Just one question is left about the JBL EON P15 G1 Speaker.

I think she got what she was told. Everything else (watts etc) point to it being the Original EON. Now don’t get confused on the EONs. In the 15s there have only ever been two models… the originals and the G2s. The Originals are the PAK, or P1, or G1. Depending on what site you look at (Musiciansfriend, American Musical, etc.) they all call the same thing something slightly different depending on if they bundle a speaker stand with it etc… but it is the same speaker and it is plenty for a rock band in reasonable sized clubs. They are not loud enough to fill a whole soccer stadium, but for most everything they will be plenty. Really.

This is only one example where marketing hype and advertising tend to screw up universal constants. A watt is a watt is a watt… no matter watt. :D However, amps and speakers have been marketed in a such a way for so long, the Average Joe always thinks more is better no matter watt. :) Even if you are edgumacated enough to go into a mega-store and ask questions about SPL etc… chances are the freckle-faced snot nosed kid ain’t gonna have a clue.

It stinks but that’s the way it is I suppose…

D – more constants! Less hype!

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A watt is a watt


one can speak of peak power (instantaneous max power) or RMS power (continuous power, the only value that matters)

The formula used to compare two power levels is 10log(P1/P2) where P1 is the first power level and P2 is the second. When voltage levels are compared it is 20log(V1/V2) where V1 is the first voltage and V2 is the second.

These formulas are actually equivalent since doubling the voltage quadruples the power into the same load (P=E^2/R) due to the square in the voltage term. So doubling the power is achieved by increasing the voltage by a factor of aboput 1.41 (the square root of 2). Doubling voltage is 6 dB, doubling power is 3 dB. Adding decibles is the same as multiplying their linear equivalents and subtracting decibles is the same as dividing their linear equivalents. So doubling power once results in a 3 dB increase in power (increasing voltage by 1.141X) and a second 3dB increase (doubling power again) results in a total increase of 6 dB (3+3) which is 4X (2X2) the power and twice the voltage.

Hansje is right. The reason that a 200W amplifier typically sounds louder working into a 4 ohm load rather than an 8 ohm load is that it is delivering more power and loudspeakers are essentially “transformers” which transform input electrical power into output acoustic power. Not all speakers have the same efficiency and furthermore not all amplifiers can continue to deliver the increase in current that a low-impedance load would require at the maximum output voltage so reducing load impedance does not produce a “free lunch” in terms of increased output.

Many pro amplifiers can deliver more power into loads as low as 2 ohms so paralleling speakers (which reduces the load impedance seen by the amplifier) can provide usable increases in acoustic power, just don’t expect miracles. Typically the increase in maximum amplifier power is not linear and clipping will begin at a lower output voltage, eventually reaching a point of diminishing returns.

Jim

Quote (clevermind @ April 20 2006,12:42)
A watt is a watt


one can speak of peak power (instantaneous max power) or RMS power (continuous power, the only value that matters)
EXACTLY! That's what I meant by less hype... more constants. When lay people don't even know what "watt" really means, you really confuse the crap out of 'em with peak power and RMS and all that techie speak. All they really wanna know is "How loud will it get?" Prime example, my son thinks he just HAS to have a full stack and at least a 200 watt amp head for his guitar rig. I sez "What? You guys gonna play football stadiums with no PA?" "No dad it will just sound better!" HA! Marketing BS! My little 2x12 combo amp which I run with a pair of output tubes pulled (with impedance selector set properly of course... don't wanna burn up an expensive output tranny...) still has enough volume to make your ears bleed if you set the master volume above "3". We're now talkin' about slightly less than 25 watts max. Of course IF he gets a 200 watt stack he'll just have to run it at ridiculous volumes (because he can) and then wonder why he's going deaf...

Sorry... can you tell I'm having issues with my teenager who just KNOWS he's smarter than the OLD man? :D

D

What cracks me up are the cheapo amps rated at 8 zilliuon watts… peak. So for 1/4 of a second on a sunny day in June it will gie you that muich power. If an amp does not specify it’s RMS output, I won’t even look at it as I see only showing peak wattage as hype and a way to hide poor performance.

As for the kids with the zillion watt guitar amps… there is truth to differences in wattages sounding different. It is not a volume difference, but a “How soon before a can really saturate the power tubes” difference. I know some guys who get 200 watt amps for jazz just for the stupid amount of head room and I know guys who get 15 watt amps so they can absolutely saturate the snot out of the power tubes.