From: info@turneraudio.com.au   
      
   I said..... > My reply is :- What has this got to do with the idea of stacked   
   Quad ESL57    
   > for hi-fi?    
      
   Mr Allison replied with ....   
      
   ** It's the mad ohms load thing again !!!!!!    
      
   No amplifier Quad ever made would "drive" a 1ohm load  -  or a 2 ohm for    
   that matter.    
      
   But it does not matter.    
      
   Yes, but many people gat all mixed up and cornfeused because they lack any   
   skills to think about grey. Black is fine, so is white, but grey? No way.   
   They need to be spoon fed with care. Quad ESL57 do present an amp with Z < 2   
   ohms at HF, but then Z > 32 ohms at LF, and Z "average" is between say 32 and   
   2 ohns and dependant on frequency, In fact, the load value average between 1   
   mili sec and the next    
   changes depending on the hundreds of harmonics in the music and how they   
   combine to cause a much varying load between one small time period and the   
   next.    
      
   If one uses a 1 ohm series R between speaker and an amp with Rout = 0.01 ohm,   
   then the source resistance driving the speaker = 1 ohm.   
      
   This is about the same as for Quad-II. If the amp is set for 2Vrms into ESL57,   
   then power at LF where Z = 32 ohms = 0.125 Watts. At 18kHz, the Z = 2 ohms   
   approx, and Vo has become 1.33Vrms and Po = 0.88 Watts. The Quad-II works OK.   
   But what does this tell anyone about power and speaker sensitivity?   
   In the above sampe case, perhaps it takes 0.125W to produce LF SPL = 70dB, (   
   just guessing ). The same SPL at 18kHz requires 0.88W, ie, 7.1 times the LF   
   power. Luckily, the amount of HF power needed for most music between say 7kHz   
   and 20kHz is far less    
   than for LF, so for those puzzled by what doesn't matter, maybe there's the   
   answer. Many ppl just don't get it though, and never ever will.    
      
   Speakers with low Z at LF present a much worse problem for amps than ESL57,   
   which are in fact "easy to drive". Maybe old AR9 were real horrors. They had a   
   pair of 3.4 ohm 11" bass woofers in parallel. These had world's lowest   
   sensitivity and required    
   high power to gety good bass, and very low amp Rout becaise at 120Hz they were   
   less than 2 ohms. I found connection of woofers in series and with totally   
   revised X-over, you could get Z to be less likely to fry amplifiers.   
      
   Patrick Turner.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)