Power Hungry Speakers

[Westy56]

I just got some really power hungry 4 ohm speakers.

Each of my amps can put 150 watts per channel into a 4 ohm load.
I can bridge them to get 200 watts, but the load has to be 16 ohms.

Will installing a 12 ohm (wattage ?) resistor in series with the speaker still allow me to achieve 50 more watts?
I'm not sure if the speakers will be safe.


Thank you


Steve

 

[Markw]

Maybe, but that resistor will absorb 75% of the power.

Net Gain? Negative 100 watts

 

[Westy56]

I think I'm a little confused. Please excuse my ignorance.

Just to be clear, I have two amps. Each one is capable of putting out 200 watts into a 16 ohm load.

My question is whether or not the 4 ohm speaker will perform the same with a 12 ohm resistor in series.
I think the amp will still see a 16 ohm load and produce up to 200 watts of clean power.


Steve

 

[Markw]

Here's a little math primer.

Keep in mind it's not what the amp sees as a load that's important to you, it's how much power the speaker winds up with.

You have two loads, connected in series on that amp.

1) The first load is 4 (four) ohms.

2) The other load is 12 (twelve) ohms

3) This gives you that magic total of 16 (sixteen) ohms.

Remember, the power (watts) will be divided proportionally between these two loads.

That boils down to:

4) 4/16 of the power to the first load and...

5) the remaining 12/16 of the power for the other load.

Simplifying that, it boils down to:

6) 1/4 of the power to the first load and...

7) 3/4 of the power for the second load.

Taking into account that you expect a maximum of 200 (two hundred) watts by bridging that amp, that means:

8) The first load (the speaker) will be using 1/4 of that 200 watts, or 50 watts, to generate sound.

9) The second load (the resistor) will be dissipating 3/4 of that 200 watts, or 150 watts, as heat.

So, you say the speaker is now getting 150 watts? You can do the rest of the math.

 

[NOHDjunkie]

I think I'm a little confused. Please excuse my ignorance.

Just to be clear, I have two amps. Each one is capable of putting out 200 watts into a 16 ohm load.

My question is whether or not the 4 ohm speaker will perform the same with a 12 ohm resistor in series.
I think the amp will still see a 16 ohm load and produce up to 200 watts of clean power.


Steve

first, what are the speakers and what is their sensitivity rating?

Second, markw is right. The resistor will just "absorb" a significant amount of power and dissipate it as heat.

Speakers are not resistors. They operate over a wide range that is frequency dependent. Your 4 ohm speakers probably operate anywhere from 2-3 ohms up to many tens or hundreds of ohms over their frequency range.

Look at a speaker impedance curve/graph to illustrate.

 

[Westy56]

Second, markw is right. The resistor will just "absorb" a significant amount of power and dissipate it as heat.

Speakers are not resistors. They operate over a wide range that is frequency dependent. Your 4 ohm speakers probably operate anywhere from 2-3 ohms up to many tens or hundreds of ohms over their frequency range.

Look at a speaker impedance curve/graph to illustrate.

That's what was out of my minds limited knowledge base...

They're magnepan12qr's.

I have them out on the patio now giving them some breathing room.
100-150 watt peaks are very loud. I guess I needed to let the speakers have some room.

Thanks for setting me on the right path.


Steve

 

[kirk57]

if you are saying you have 2 identical 150 wpc amps (into 4 ohms) then what you want to do is biamp. that way you can use both amps full power. it is a great way to upgrade the sound of Magnepans.

 

[Westy56]

if you are saying you have 2 identical 150 wpc amps (into 4 ohms) then what you want to do is biamp. that way you can use both amps full power. it is a great way to upgrade the sound of Magnepans.

Now were talking.:yes:

It will be nice using what I have to improve the setup.

Great advice.:thmbsp: Thank you.


Steve

 

[NOHDjunkie]

Magnepan's are indeed power hungry. Recommended power is an amp that can deliver 200 WPC into an 8 ohm load and conversly 3-400 WPC into 4 ohms. High current amplification is the name of the game.

 

[dan-c]

Now were talking.:yes:

It will be nice using what I have to improve the setup.

Great advice.:thmbsp: Thank you.


Steve

I see what you mean, Steve

 

[NOHDjunkie]

Now were talking.:yes:

It will be nice using what I have to improve the setup.

Great advice.:thmbsp: Thank you.


Steve

The MG12's aren't biamp-able in stock form. It would require an xover mod.

 

[Westy56]

Right now were listening to a pretty steady 40wpc and its loud.
I just now found that they project from the rear. Oh, the possibilities.:drool:

Get them for a good price if you can swing it.

Steve

 

[NOHDjunkie]

the MG12's are 86db @2.83v (2 watts) @500hz efficient speakers.

so @ 40 watts is around 98db @500hz. so I would imagine you are listening to an overall level of 90db @ 40 watts at full spectrum freq range

Remember... Those peak meters on amps aren't perfectly accurate either.

There is no hard fast rule for amp power. It's up to the ear of the listener.

I can make my amp clip lights flash pretty easily on transients when cranking on my MGII's. 300wpc @4 ohms.

 

[whoaru99]

if you are saying you have 2 identical 150 wpc amps (into 4 ohms) then what you want to do is biamp. that way you can use both amps full power. it is a great way to upgrade the sound of Magnepans.

Now were talking.:yes:

It will be nice using what I have to improve the setup.

Great advice.:thmbsp: Thank you.


Steve

Too bad simple biamping really doesn't work that way with the power.

 

[JoeESP9]

Right now were listening to a pretty steady 40wpc and its loud.
I just now found that they project from the rear. Oh, the possibilities.:drool:

Get them for a good price if you can swing it.

Steve

Please forgive me for this post.

You bought a pair a Magneplanars not knowing they are dipolar radiators? I'm more than a little surprised. With all the threads about Maggy's on this and other forums and you didn't know sound comes out of both sides.

I can guess you don't know much about how to position them.
Suggestions for placement follow.
1. They must be well away from the wall behind them. Two to three feet minimum.
2. A good listening distance to start with is 1 1/2 times the distance between them.
3. While they (or any speaker) can be used in the near field. A distance of around 8 to 10 feet is a good place to start.
4. Toe them in so the center axis crosses a foot or so behind your head.
5. These are good places to start. I urge experimenting.

6. Placing them close to the wall behind them will kill the sound.

 

[Westy56]

Too bad simple biamping really doesn't work that way with the power.

I didn't give them a chance to be fully heard when I initially thought I needed more power.
150wpc will be plenty of power for my needs.

My audio guru and I are in the experimental stages of placement, etc.
She's being used for rear damping right now.awprint:

Steve

 

[NOHDjunkie]

From the placement you show in the pic....

the right speaker is next to a wall and the left is in the middle of the room. (1st pic)

Try putting them so that each is equidistant from the rear and side walls. Your imaging/reflections and boundary loading will be equal that way. (2nd pic)

The spacing and toe-in are dependent on the listening position.

 

[kirk57]

For Magnepans to image correctly, you need to have the dog lie in a straight line between the speakers. I thought this was common knowledge...

 

[PioneerGuy75]

Won't a 4 ohm load on a 16 ohm amp KILL the amp even with a 12 ohm resistor in series?

I have been looking for the thread titled "Why 4 ohm loads stress your amplifier" but cannot seem to find it.

 

[Markw]

Won't a 4 ohm load on a 16 ohm amp KILL the amp even with a 12 ohm resistor in series?

I have been looking for the thread titled "Why 4 ohm loads stress your amplifier" but cannot seem to find it.

The resistor becomes part of the load. With the 12 ohm resistor in series with the 4 ohm speaker, it presents a 16 (12 + 4) ohm load to the amplifer.