2ohms-4ohms- 8ohms?

Powered mixer specs say:

XXXXX watts @ 2 ohms
XXXX watts @ 4 ohms
XXX watts @ 8 ohms

The more ohms the speakers are, the less watts the mixer puts out. My Peavey TLS5 speakers are 8 ohms.

Peavey says anywhere between 150 to 300 watts are required for my speakers. The only powered mixer that reaches the 300 watt top end in stereo is the Mackie 808s. It is 600 watts per side 2 ohms and 300 watts per side at 8 ohms.

Anyone here understand all of this @#$@#$!$#@#@?

Anyone knows of any 2 ohms speakers?

It's a simple application of Ohm's law. Watts = (Voltage x Voltage)/Resistance. So an amplifier with 40V rms output will deliver 200 watts into 8 ohms, 400 watts into 4 ohms and 800 watts into 2 ohms, all things being equal (which they usually aren't). Generally speaking, you won't find 2 ohm speakers. This rating is meant for two 4 ohm speakers in parallel.

Bryan

An ohm is a unit of measure of the resistance of an electric circuit.
A watt is a unit of electric power.

So if you are in your swimming pool and you try to kick your girlfriend in the butt and knock her down it will take a lot more power in your leg to do it than if you done the same thing on the deck of the pool. Therefore it takes a lot more power under water to get the same reaction than it does in air because there is more resistance. So it is with your speakers. A speaker of 8 ohms has much more resistance than a speaker of 4 ohms. Therefor it takes more power to get the same noise out of a speaker of less resistance. There are formulas that will give you precise answers of watts, ohms and all that if you are really interested. Just keep in mind, if your going to punch a guy in the nose, better check your watts of power in your biceps against his ohms of resistance to your watts of power.

Taken from the wisdom of Grandpa Doug. I know Uncle Dave could do a better job of explaining, but after all, I’m getting old and he aint married to Ruthie.

How about the yogi with the 2 ohm mantra of resistance: ohm - ohm

Scott

Good one Scott

I hope I can remember my physics well enough:

Watts = Voltage x Current or
= Current x Resistance(or Impedance) x Current

Buy powered speakers--it's all done for you.
You'll get amps that are tailor-made for the speakers.
DonM

yes Don.....and less to carry....

You did a fine job of explaining it Doug ! As for being married....oogh(shudder)... That word is only a few pages away from the "K" word in my book of freights !
Too soon to even joke about that stuff!

and Don ....... The Mackie advertises a 450 watt powerhouse in their cabinet, when actually, it only produces full power at 4 OHMs ! The cabinet is loaded with 8 ohm speakers ! It's not quite a lie, but it ain't no 450 watts either. Now we have to read lables for carb content as well as speaker inpedance !

Yes UD, but are those 8 ohm speakers in parallel? If so then you'll get the 450 watts (assuming they're truthful). And I must be doing something wrong. Still happily married after 33 years and looking forward to another 33.

Bryan

P.S. Book of freights?? Do you drive a truck in your spare time?

Hey guys,

Which Mackie speaker are we talking about here?

Must not be the SRM450's since they are bi-amplified using a 300 Watt RMS amp for the bass and a 100 Watt RMS amp for the mid/hi.

http://www.mackie.com/products/srm450/index.html

Just trying to get on the same page as you guys here.

mike

[This message has been edited by msutliff (edited 08-20-2003).]

Mike is certainly right about the specs on the SRM450's. Mackie doesn't claim these are 450 watt speakers, although some may think that based on the model number. And they are indeed bi-amped, which allows them to use an active cross-over network.

In designing an integrated amp/speaker package such as the 450's, you'd better believe that the amps and speakers are matched for best overall performance. They've got a limited volume, a limited ability to dissipate heat and they've got to strive for the best overall performance given all the variables they have to work with and the design compromises that have to be made. And based on what I've heard and what others have said about the Mackies, I think they've done a darn good job.
Paul C.

The inside scoop on the SRM450's from a Mackie tech is that the power amp can indeed, produce 300 watts for the lows, but NOT at the current ohm load. I love the sound of the 450's, but they were far from perfect. The overheating was a constant threat in high output situations or when used on their sides.
Anyway - that's thw way it was told to me from a Mackie insider.
I doubt that they are optimized for the full 300 watts,..... just like the EV sxa100's - rated at $350 watts? Naw. These are made up peak numbers I think.

If UD's "inside scoop" is true, then I'd agree that it's bordering on false advertising to claim you have a 300 watt RMS power amp when the speaker impedance will never allow the amp to deliver that level of power. Most non-integrated amps have their electrical output ratings tied to the load (speaker) impedance, which is the correct way to spec. an amp. If Mackie has done otherwise, then shame on them.

While I have personally not owned the Mackie 450's I have heard about the overheating problem and that it does indeed create a limitation under certain operating situaitons. Engineering always involves compromises and trade-offs and good engineering can minimize the "bad" and maximize the "good."

Re the heat dissipation problem, some of the manufacturers of powered speakers are using fans to help with cooling and others are using the air movement created by the low frequency speaker to aid in cooling.

Cooling is certainly an issue at high power levels, especially given the compact nature of the newer powered speaker ssemblies. But so is sound quality and maybe, as is the case with keyboards, (there is no perfect keyboard, as echoed many times on this Forum) so too there may be no perfect powered speaker.
Paul C.

Frank,
I concur with your formula. As per some of my technical training: P=EI. Power (in watts) = Voltage X Current.
Starkeeper

You know Dave, truth is for the most part, shaded, and sometimes hard to believe if not. In real life shaded truth sells better than pure white truth in merchandizing, including all areas, from products to religion. With merchandise, sometimes truth aggravates people and they try to defend what they want to believe. In religion when truth is brought forth they will try to do in the purveyor of it as evidenced over the past millenniums, from the prophets to Mr. King. Even the guy who said the world was not flat but round, got it in the neck. True religion? Which is worse? Truth is always truth but will not always be very popular. Round and round she goes and where she stops nobody knows.

Just thinking, Grandpa Doug

It looks like some writers in this thread think the output of speaker-cabinets depends on the impedance (Z) of the speakers ?!

The lower the Z, the higher the audio-power.... but be careful please !!

The optimum match between an amp and speaker is when they both have the same impedance. Current amps are able to auto-adjust within limits, but there ARE limits. (max.speaker Z and min.speaker Z)
When users keep lowering the speaker impedance often amps get damaged because the power-supplies and other components get overheated.

There are 400W speakers with 4 Ohm Z, but also 400W speakers with 8 Ohms. The amp used for the 2nd one has the double output voltage.

Roel

I'd like to ask Brickboo a question.

Yo Brickboo,

Are you gettin' anything out of all this?

mike

PS. I did get a kick out of the swimming pool analogy, Grandpa Doug.

Nice discussion.

Here is another very important issue to think about: in order to get more volume (that is at a certain level) you need a lot more watts to achieve a audible difference.

300 watts or 400 watts don't make much of an audible difference at all. Try it if you don't believe me.

Or try this: turn up your volume knob on your KB very slowly to about 2/3. You'll a here a noticeable difference in volume with each increment.
Then turn it up all the way. Not much difference.

Regarding the overheating problem: I own 3 Mackie SRM450, 2 for the audience, 1 as a monitor.
We just had an outdoor gig at a french festival. It was very hot and we played at a good volume. No overheating noted.
The Mackies are clean and loud.
As far as I remember, Uncle Dave is the only one who had that problem in the past, with a speaker that was placed on the floor.
Corect me if I'm wrong.

I still give the Mackies 2 thumbs up
But of course only with the 9000Pro

Eric

You're wrong Eric.
Donny had the troube more than once, and I was at an outdoor show and saw it in action again. The heatsinks need to be redesigned, or the amp must be made more efficient.

I know they sound good, but I can't take another chance till I see improvement. Today my setup is the JBL Eon10s(G2) with the G2 sub...run by a DBX Drive Rack. I love the flexibility and the sound so far.

I had the mackie 450'scut out on my [embarrasing I might add] on stage more then a few times when laid down as desined due to the horizontal heat fin positioning, but it also happened when on poles also. This is a big problem. I have now installed fans inside my Barbettas Sona 32c's that eliminate this proble entirely...seems Mackie should take the hint also in future designs if any.

Donny, are your fans specifically(produced/sold by Barbetta) to fit inside the Sona32c's? How difficult was it to install? If they're not Barbetta authorized fans, is there any risk of voiding the Sona32c warranty? Also curious if by any chanace the current Sona32s now come with cooling fans. - Scott

Scott,

The Sona-32-Cs now come with large, quiet computer fans suspended inside the cabinets, another vent near the top, and unless you place your ear against the vent, you cannot hear them running. As for the older models, they were not equipped with fans and they only had a single vent. The fans in Donny's were installed by me, along with a second vent. The fans will not void the warrenty, and since their installation, he has not experienced a single overheating problem, even when playing outdoors on the hottest day of the year.

I had a first hand look at the Mackies several weeks ago, and even with the volume turned down and the speaker on a pole, the heat sink got pretty warm. It's a poor design at best. The Mackies were among my considerations when I was shopping for lighter, powered speakers. When turned up, the heat sink became too hot to touch. That's the reason I ruled them out and went with the Barbettas.

Cheers,

Gary

[This message has been edited by travlin'easy (edited 08-20-2003).]

Roel, you are correct with regard to matching speaker impedance to the amplifier, but only with tube amps. Doesn't apply to the constant voltage type of solid state amp in use today which has zero output impedance (in theory). The limiting factor is the current that the output stages are able to supply. Most designers cut corners to save money, especially if you don't really need the performance. This is why you don't get double the output when going from 4 ohms to 2 ohms. The current limiters take over at high outputs to protect the output transistors.

Bryan

Dave, Donny,

do you guys think it might be a combination of humidity and heat?
Here in CA we have very dry heat.

Eric

I'm going back to laying brick.

[This message has been edited by brickboo (edited 08-20-2003).]

[This message has been edited by brickboo (edited 08-20-2003).]

I did that today--can't say it was much fun. Only had to put 140 pavers into the sidewalk in 94 degree heat with 80 percent humidity. Boo, if you lived closer, you would have got the job.

Cheers,

Gary

eric......no chance ....when you push them ther cut off...only once did it happen outside in the shade under a tent...the other times it was on stage inside.

watts @ 2 ohms
watts @ 4 ohms
watts @ 8 ohms

Just remember the ohms load of speaker to amplifier is not constant. The ohms load varies with frequency. Even a 8 ohm speaker load to amplifier can drop below 2 ohms or upto 16 ohms at a certain frequency.

It is foolish to run lower ohm speakers just to obtain a higher output volume than the Amplifier maker suggests.

Graham UK

Graham

While that's a good point and something to watch, not all speakers are created equal. My speakers have a flat impedance of 8 ohms, dropping to 6 ohms above 5000Hz due to the tweeter (where there's not much output anyway). And they're resistive at all frequencies except at resonance in the woofer. You pays your money and takes your choice.

Bryan

Hi guys long time no see, or hear

Did you consider the Carvin PA800c, I just bought one and its great, it has 3 amps built in, Left, right, and mono monitor,
333 watts a channel into a 4 ohm load, which is great for small to medium gigs http://www.carvin.com/cgi-bin/Isearch.exe?PAGE=mdetail&CFG=2&P2=pa800c&P1=MXP comes with fx and a case too http://www.carvin.com/images/product/PA800C1.jpg

Frankie,

It's great that you are enjoying the amp. However, in light of this discussion, I want to point out that it only produces 200W per side using regular, 8 Ohm speakers. To get the rated 333W per side, you need to use two speakers in parallel per channel, or buy special speakers (BTW of the four suggested package deals, only one lists 4 Ohm speakers, the others are all 8 Ohm).

Regards,
Alex

True but to get a difference in volume of 3dB ( which is what most people can concieve as a little bit louder) you need to double the power, so from 200 watts to 400 watts seems a big jump for a very little amount of increase, but if you add another pair of speakers you will have 4 speakers being pushed at 166 watts which will be much more than a 3 db increase,

I was just in the same market and this seemed to be the best set-up for me anyway, its better to add speakers than to ad amplifier power for most situations

Later dudes