[jeffreybehr]

Another member of our little community made some observations about power required for 5As and 7s.  I indicated I had a 'power' indicator and would check my system tonite.

Conditions. 
1. V'steen 5As.
2. Monarchy SE-160 poweramps.  These are rated at 160 Watts per chassis into 8 Ohms and 320 into 4 Ohms.
3. Bass amps unplugged. 
4. No other poweramps turned on. 
5. Level meter is a Phonic Audio Assistant 2, no frequency weighting, set to full band and to indicate peak level.  It was parked on my chest about a foot ahead of my ears in my usual listening position. 
6. My normal system setup but only 2 channels. 
7. Set the listening level first and then repeated the track several times to observe 'power' level. 
8. Power indicator is an Audio Technology 510.  It reads, of course, only Voltage, and references that to the Voltage required for 25 Watts, 50 Watts, or 100 Watts into 4 or 8 or 16 Ohms.  It's calibrated for peak indication with enough peak holding that the LED can be seen to illuminate.


At 80dBSPL at the listening position, the power indicator displayed 9dB below 25 Watts into 8 Ohms.  As you may be able to see in the pic, the steps are a rather course 3dB in this area, so this is just an estimate.  9dB below 25 Watts is about 3 Watts.

I then increased the level to get 90dB at the listening position; this is quite loud and I was wearing hearing protectors.  The indicator then showed 1dB over 25 Watts, or 32 Watts.  Interesting that 10dB higher listening level required almost exactly 10dB more power, so the about-3-Watt reading appears to be fairly accurate.

BTW my listening-room volume is about 3200CF, somewhat larger than average.

[zybar]

Thanks Jeffery.

George

[avahifi]

Amplifier power ratings are a very misleading and non-intuitive specification.

Power equals voltage squared divided by load resistance.  Thus power goes up with the square of the voltage swing.  This is an exponential function, not a linear function as one would expect in looking at the power numbers alone.

One hears loudness differences much more closely related to voltage swing capability rather than by power capability.

For example an amplifier that swings 40 volts RMS into an 8 ohm load would have a 200 watt power rating.  An amplifier that swings 50 volts RMS into an 8 ohm load would have a 312.5 watt power rating.  If you looked at the power rating differences between these two amps, you might assume, "oh wow, the second amp is 50 percent more powerful, just what I need."  However if you look at the two ratings more realistically, you would compare the 40 volt swing of the first amp to the 50 volt swing of the second amp and realize that you were really only getting about 20 percent more useable output.  Not the good deal you thought it was.   

Certainly don't agonize between amplifier rated only a few watts apart in power, their voltage swing capabilities will be quite minor as will their loudness capability.

Of course this is assuming all other things are equal, and of course they are not. 

Regards,

Frank Van Alstine

[mgalusha]

I still have a pair of 2Ci's, may have to hook them up and see how much power then need in relation to my current speakers. I recently treated myself to a Fluke 289 which will happily record the levels and report average and peak voltages. I've had the 2Ci's for a long long time, just can't bring myself to put them out to pasture.

[jeffreybehr]

Frank, you're so right, and that's why it's useful to compare differences of power outputs in deciBels.

We 'all' know that 3dB is double or half power and 2 - 3dB is about the smallest difference that many of us can hear.  How, then, do some of us get so worked up at the thought of buying a 'bigger' amp, say 200 Watts instead of our 150-Watt amp, so we can listen at higher levels?  One reason is that few of us ever bother to express those kinds of differences in deciBels.  If we did on the above example, we'd know that 200 over 150 Watts is an increase of only 1.25dB.  Huh?  ONE-odd dB?  It's FIFTY Watts!!!!!!!!!!!  Yes but only 1.25dB, probably not audible, other things being equal (which, I agree, they virtually never are).

Neither of us is proposing that having more power is seldom useful, but being thoughtful about this sort of thing would save lots of us money.

[7x57]

Vandersteens are a bit power hungry. Even the Vandersteen Premier Dealer that I bought my 2Ci's from back in 1991 said they took at least 100W of high current amp to wake them up. He was right. I ran them thru a 200W amp.

After 20 years of service, the 2Ci woofers finally started rattling. I replaced them with a pair of VMPS RM-1 speakers with TWO 8" woofers per side, plus a 10" PR, and haven't looked back. Sensitivity is 3 dB higher, plus the MUCH better midrange goes from 280 Hz to 7kHz-10kHz depending on listening angle. Replaced the 200W amp with a lower powered 120W Conrad-Johnson amp and actually have a bit more dynamic range.

I am going to replace the 2Ci woofers with Vifa P21 woofers (built now by ScanSpeak) since they have a few dB more sensitivity than the Vandy woofers, which are Vifa P21 based, slightly modified.  Probably cost new a bit less than the Vandy rebuilds of the old 2Ci woofers. I value the sensitivity more than the bass extension. The VMPS RM-1 goes deeper and louder at the same power level as the 2Ci, so I am trying to at least get the 2Ci at the same sensitivity level, though one 8" woofer will never match two 8" woofers of similar quality at headbanging levels.

I will eventually replace the original RM-1 woofers with American built woofers that beat the Scandinavian woofer of the 2Ci for less money. Below 100 Hz, this American woofer will soundly beat ScanSpeak Revelator woofers that cost over $300 each, for under $60 delivered.

While frequency spread was very good in my Vandy 2Ci speakers, the VMPS RM-1 can equal it in frequency range, can soundly defeat it in the frequency range of the midrange, gives 3 dB more efficiency, goes higher and lower without compression (measured, not just a subjective assessment), and can play louder withput hardening up and losing focus. Too bad Brian Cheney died back in 2012 and VMPS is no longer in business. However, in Vandy Model 2 vs. VMPS RM-1, the RM-1 wins in spite of the fact it never had anywhere near the sales figures. It showed up around year 2000 where it had a serious late start but could take advantage of a state-of-the-art balanced push-pull neodymium magnet ribbon midrange designed by Bruce Thigpen of Eminent Technology. No cone midrange can equal that midrange. It beats them in every parameter, including playing loud enough (and still clean) that the cops are called on you to tone thing sdown. Been there and done that.