350 WPC into 150 MAX

[mike c]

what i don't like about bridging commercial amps is that you are stuck to powering 8ohm speakers - i don't know tech stuff about amps, but what if that speakers is nominal 8ohms but dips to 4 ohmms and below?

wouldn't the stereo amp used as stereo be better for that speaker than a bridged amp?

of course, if stato wants unlimited power at whatever load - i would recommend the Yamaha Pro Amps

 

[stato]

That is another interesting point Mike. I probably dont need all that power most of the time but was just something I have wanted to try ( bridged mono X2 ) but I definately dont want to go that way if it will not give me good sound. I have used one RB981 on my Jamo E875 fronts for years now and I think they are 4ohm so now I am getting some 8 ohm speakers it si the time to try it I suppose. The single Rotel has done everything asked of it with the Jamos fine as far as I hear but just want to make sure I look after my 60's when they come and also get out of them exactly what they have to offer.

 

[poutanen]

of course, if stato wants unlimited power at whatever load - i would recommend the Yamaha Pro Amps

+1

I've run the behringer A500 bridged into 4 ohms (a pair of SW118 subs daisy chained), and it ran fine the entire time, despite being rated for 8 ohms when bridged.

Those Yammy's are beasts...

 

[stato]

If Rotel advise the RB981 will only run 8ohm speakers in bridged mode would they not be capable of doing so? If not it seems to defeat the purpose of having the ability to bridge them.... Am I missing something here? Does what Mike say come into play here?

 

[poutanen]

If Rotel advise the RB981 will only run 8ohm speakers in bridged mode would they not be capable of doing so? If not it seems to defeat the purpose of having the ability to bridge them.... Am I missing something here? Does what Mike say come into play here?

Mike's talking about the difference between the listed impedance and actual impedance. I'm not 100% on the subject, but this is the basics (as far as I know)...

Every speaker has an impedance curve, and sometimes that curve may have dips lower than the listed impedance on the speakers spec sheet. If your amp isn't stable at those impedances, you could run into problems...

Typically a pro-audio amp will run stable at much lower impedances than a consumer/home audio amp like the rotel. As far as the rotels running the specific speakers you want them to run in bridged mono, I can't say for sure...

 

[mike c]

stato, you'll be fine bridging the rotels. i was just wondering how much you'll be spending for the second amp, it would actually be possible to spend the same amount of money on a pro amp but with more power.

i've used a bridged RMB1066 myself, i also have a 1077 and 1075 amp (note, the 1075 is running studio 100's)

 

[stato]

I already have one which my wife bought me years ago. I dont want to get rid of it BECAUSE she bought it for me and that is so unheard of. I got another SH for 200.00 so I thought I would give it a go. Just wish those 60's were here now...by the way that is some serious gear you have there,, does the 1075 bi wire your 100's or 130w is plenty?

 

[mike c]

130w is plenty

i don't believe in bi-wire or bi-amping (which i tried with the 1077's)

 

[stato]

Perhaps I underestimated what I already have. Thanks very much all for your help..

 

[fmw]

what i don't like about bridging commercial amps is that you are stuck to powering 8ohm speakers - i don't know tech stuff about amps, but what if that speakers is nominal 8ohms but dips to 4 ohmms and below?

The problem with bridging is that doing so makes the outputs see half the nominal impedance. 8 ohm speakers become 4 ohm, 4 ohm speakers become 2 ohm etc. The reason the manufacturers recommend against bridging the amps into 4 ohm speakers is that they aren't stable enough at full power to deal with a 2 ohm nominal load. Normally, they will be fine somewhere below full power.

Also note that all speakers, regardless of nominal impedance rating actually have a range of impedances over the frequency spectrum. So all speakers have dips. You should deal with nominal impedances not minimum impedances when dealing with these interface issues.

wouldn't the stereo amp used as stereo be better for that speaker than a bridged amp?

Every time in my opinion.

of course, if stato wants unlimited power at whatever load - i would recommend the Yamaha Pro Amps

At a reasonable load at least. There are some pro audio amps that will deliver full power into a short circuit but they can get pretty expensive. The Yamahas are practical, nice looking and they have heat activated fans so you don't have to listen to fans while you listen to music.

 

[annunaki]

annunaki said what I was about to add. But also...

When the signal clips it looks like DC to the speaker causing the cone to go all the way out at full power and all the way in at full power. A speaker is better adapted to handle short durations of higher power (thus their peak rating) then it is to handle full power at longer steady state durations (DC). High power DC can burn out a speaker very quick, and that is why generally speakers blow due to lack of power rather than too much. Obviously use your head with the volume knob regardless, but you will actually have more room for error with more power.

I generally use this rule of thumb:

Take your speakers IEC (program wattage), double it ... and then multiply by .8 and 1.25 to find a range.

So for 150 watt speakers:

150 * 2 = 300 ... then *0.8 = 240 and *1.25 = 375

So for those speakers I would shoot for an amp that has between 240 and 375 watts per channel.

Also note that power supplies generally get better as the amplifier has more power. This is important because current is what we can control from the wall.

Actually most speakers fry when the amplifier clips because it will typically output 2x the rms rating at .1% thd. So in essence, a 100 watt amplifier outputs 200 watts when fully clipped. If a speaker handles 100 watts rms, this is a big issue even when "half-clipped" the amplifier may be doing in upwards of 150 rms. This is what typically kills the speaker. Too much average power over time. The amplifier tends to lose control over the speaker and can yield damaging effects on the speaker's suspension or voice coil to boot.

 

[stato]

annunaki going by what you have said then I would be better served to have amplification above what my speakers are rated so I have more headroom to control the speakers when driven harder?

 

[jamie2112]

Isn't that the same thing I stated a few pages ago?

 

[stato]

Jamie2112 I am just a bit confused as you have said that more power will serve me better and mike has said that 130w is enough to run his 100's. I am also concerned that if I run 2 amps bridged that they will not perform as well as one when dealing with loads lower than 8ohms but then if they cant why would Rotel offer this feature on their amps?

 

[mike c]

stato,

i thought you have already purchased the second amp? try them bridged, since the 60's are 8ohm speakers, they should run fine. and if you have subs to crossover your speakers with, the less power they need.

i did say that 130w was enough, but having more power doesn't hurt either, i opted not to mention this but i have another theater that has lots and lots of watts per speaker. actually, to be specific: they're currently 360wpc BRIDGED at 8ohms. but i am now in the process of replacing them with big wattage but 4ohm stable amps. e.g. 450wpc at 8ohms, 650wpc at 4ohms OR 250wpc at 8ohms, 310wpc at 4ohms.

oh and one more thing, i do not and cannot hear a difference between all these amps. i just like playing with them, but do feel my 2nd most wasted purchase ever was the Rotel RMB1077. (second only to the eD subwoofers)

i have the following:
Rotel RMB1066
Rotel RMB1075
Rotel RMB1077
Behringer A500 x 4
Behringer EP2500 x 2
Yamaha P2500S

 

[stato]

thanks Mike. I have the amp but I am waiting until mid November to get my 60's. I am just working out what is best for them and to try and get the best sound out of them as I possibly can. Compared with some kit around here I know mine is way down the scale but the 60's represent a major investment on my behalf in sonic bliss and I dont want to trash them. This will be the start of an upgrade that I hope will see me (and the MASTER OF MAJOR INVESTMENTS ) happy for a long time before I am allowed to have another crack at it. I will try bridging the 981's and see what its like when the 60's arrive and then I will go from there. I will have a sub as well as I have also purchased a DSP3200 which I hope will go down a treat compared to what I have now.

 

[annunaki]

annunaki going by what you have said then I would be better served to have amplification above what my speakers are rated so I have more headroom to control the speakers when driven harder?

I would agree to this for most sensible users.

It allows for the cleanest, most dynamic output at higher output levels.

Grossly overpowering speakers can cause issues as well. However, that is not usually a problem.

 

[MidnightSensi]

Actually most speakers fry when the amplifier clips because it will typically output 2x the rms rating at .1% thd. So in essence, a 100 watt amplifier outputs 200 watts when fully clipped. If a speaker handles 100 watts rms, this is a big issue even when "half-clipped" the amplifier may be doing in upwards of 150 rms. This is what typically kills the speaker. Too much average power over time. The amplifier tends to lose control over the speaker and can yield damaging effects on the speaker's suspension or voice coil to boot.

We are saying the same thing. Your rms when the signal looks like DC goes up by whatever the integrals difference of a square-like versus a sine wave is....which is nearly double.

 

[annunaki]

We are saying the same thing. Your rms when the signal looks like DC goes up by whatever the integrals difference of a square-like versus a sine wave is....which is nearly double.

The issue here is that the speaker never sees DC. It is simply a clipped wave form on an oscilliscope. The amplifier outputs an A/C signal and cannot output D/C unless there is a problem with it. The output is much higher regardless. I digress though, as we are essentialy saying the same thing.

 

[MidnightSensi]

The issue here is that the speaker never sees DC. It is simply a clipped wave form on an oscilliscope. The amplifier outputs an A/C signal and cannot output D/C unless there is a problem with it. The output is much higher regardless. I digress though, as we are essentialy saying the same thing.

Only we ARE SAYING THE SAME THING

We are saying the same thing. Your rms when the signal looks like DC goes up by whatever the integrals difference of a square-like versus a sine wave is....which is nearly double.

I was just trying to make it super easy to visualize. Trying, I failed big time haha.