[werd]

I am just curious as to what people's opinions are on partnering up amplifiers to speakers. What the ratio is between power delivered and speaker rated power should be. My tastes are 2/1 (twice the rated amp power over speakers rated power). For eg. my 4b is rated at 300 watts per channel and my AZ's are rated at 200 watts into 6 ohms. Dont be afraid to be technical if u think it makes your point.

[Phil A]

Much depends on the efficiency (and other characteristics) of your speakers, the volume and attributes of your listening space, and what type of music you listen to and how loud you like it.  In the main system, I have Thiel 3.7s that like power.  The 14BSST is what I use.  I had Thiel 7.2s before that and before the 14BSST, I briefly used the 6BSST (with the 7.2s) and before that a Proceed HPA amp with lots of power.  The main room is very large and opens into other spaces.  The B&Ws I have in the basement are not as power hungry and easier to drive.  It is also a large room and I currently have a NAD 2100 for the center channel so I don't overload the amps in the receiver on a demanding movie soundtrack.  The Thiel SCS2s in the bedroom are 4 ohms but not a horrible load.  I use an old Adcom 555 to drive them (the amp is not deep and fits behind the LCD - I wouldn't mind a used Bryston 3BST, SST or 2BSST at some point) so I don't tax the receiver.  At 325W into 4 ohms in an avg. size room it is plenty of power.  I tend to err on the side of a little too much.  With many people into home theater and the new lossless audio formats for Blu-Ray, there may be many people who may get surprised on their system limitations.  People who are into audio more vs. home theater tend to be a bit more aware of the potential problems.

[niels]

Speaker ratings has no value whatsoever, dont even look at them.
Its fine to use a Bryston 28B on a pair of 60 watt speakers. On the other hand its not wise to use a 70 watt surround amplifier on a pair of 300 watt speakers if you tend to play loud, the treble units might blow because of clipping from the amp.

[werd]

Speaker ratings has no value whatsoever, dont even look at them.
Its fine to use a Bryston 28B on a pair of 60 watt speakers. On the other hand its not wise to use a 70 watt surround amplifier on a pair of 300 watt speakers if you tend to play loud, the treble units might blow because of clipping from the amp.

I actually agree with u whole heartedly but i think the analogy of the 28b on a 70 watts is stretching it. I think the voice coils would soon over heat even with the most subtle transients. But none the less its drive the point home nicely.

[SF]

Hi Werd;

I run a 14BST 600 wpc into B&W 804S 200 unclipped power rating. Based on some measurements that I had done on the speakers and the amp, I posted a thread couple of weeks ago http://www.audiocircle.com/index.php?topic=65177.0 . James and Chris responded to the thread, and from the numbers that they gave me, I have concluded that to be able to run my B&W804S properly, I will need much greater power than the 14BST offers. The text of some of that exchange is quoted below. So faced with the decision to upgrade the 804s or the 14B, I would have to chose the latter, because the 14B can not fully drive the 804s without the amp clipping, and that is at a theoretical 3:1 power ratio! So my suggestion would be at least 4:1 or higher. Please see the numbers below -- I was very surprised.

Hope this helps.





From CWR
Hi Shafie;
 
A volume control generally works a logarithmic taper with 10% of the final Voltage value reached at 50% rotation, so a small adjustment at low volume may only make a difference of a few tens of miiliVolts.  At volumes over 12:00 or 1:00 on the control, however, it can make a difference of several Volts. 

Another thing to keep in mind is that the Voltmeter is broadly measuring the average Voltage at the output terminals of the amplifier.  Generally, there is a substantial difference, 10-20dB, between average and peak levels in recorded music.  Even a 10dB difference is over a factor of 3 in Voltage, and 20dB is a factor of 10.  Thus, if you are measuring roughly 10-12 Volts average, the peaks could be between 35-120Volts! 

Keep in mind also that power is calculated as the square of the output Voltage, divided by the speaker impedance.  Thus, a doubling of Voltage means a quadrupling of power, and a multiplication of 10 in Voltage means a factor of 100 in power!  If you see the red clipping LEDs flashing that means you are reaching over 600 Watts on peaks, (in fact, on musical peaks, it would be well over 750 watts). 

In general, a rotation of one 'clock position' on the control, (from 11:00 to 12:00, say), may give you a 6dB increase in volume.  That means a quadrupling of power, so multiplying 4X4X4X4X4X4X4 eventually becomes a LOT of power, even if you start at a few milliWatts at lower levels.
 
I hope the above is helpful, but please let me know if you have any other questions.  Thanks for choosing Bryston!
 
Sincerely,
Chris Russell
Bryston Ltd.

Dear Chris and James;

Thank you for your responses. Now my measurements make sense. The numbers have important implications. The 804S is rated at 200W unclipped. If transients are 10-20 dB higher than average, that would suggest, taking the more conservative 10dB rating, that unclipped reproduction requires 9x200 Watts = 1800 Watts. That implies that my 14B ST is likely to clip before I even come close to the 200W unclipped program of the 804s. They say you can never have too much power and this certainly proves it. To do it the other way, for unclipped signal, the average power usage, with 10dB head-room for dynamics, would be 600Watts / 9= 66 Watts! If at 12 O'clock I'm at 10% voltage, that would 10% x (SQRT(600Watts x 8 ohms)) = 7 Vmean or 6 Watts. At 1:00, double voltage and quadruple power, it would be 24 Watts, at 2:00 it would be 100 Watts. This would be past the 66Watts + appropriate head room for transients (taking the 10 dB conservative increase for transients). According to these calculations, anything past 2:00 clock would put the Amp into clipping range -- way before my 200 Watt speakers give up. Now, if you want full head room for proper representation of transients using 20dB rating, that translates to (20dB = 100-fold power increase) 600 Watts / 100 = 6W! That is the power at 10%Vmax, which is accomplished at 12:00 clock. So for my amp/speaker combination, going past the 12:00 clock my lead to compression of transients and unfaithful reproduction of dynamic music. This is very important information, and it shows that to fully utilize my current speakers, I have a long way to go in terms of power (somewhat surprising that the 600 wpc amp would clip before the speakers would). That means 28BSST(2) before I even think of the 500W B&W802Ds, which theoretically could never achieve their full potential with any available Amp design!

Alright, this was a very valuable exercise.

Again, let me thank you both for taking the time to respond with hard numbers to crunch. I appreciate it vey much -- another reason to love Bryston.

Best regards,

Shafie