From: info@turneraudio.com.au   
      
   Phil mentioned....   
      
   > ** The AR9 was first sold in 1978 and used two 12 inch woofers, same ones    
   > used in the AR11 released in 1977.    
   ** AR constantly refer to the above woofers as being 12 inch.    
   But they are closer to 11 inch, in reality.    
   I remember now there was something odd about the woofers in a friend's    
   AR11s.    
   The impedance curve of the AR11 was so wild I drew it out and kept a copy -    
   here is a listing:    
      
   DC       =    4.2 ohms    
   10Hz    =    5 ohms    
   32Hz    =  30 ohms    
   100Hz  =    4 ohms    
   500Hz  =   10 ohms    
   1kHz     =   4 ohms    
   2kHz     =   2.5 ohms    
   5kHz     =   2 ohms    
   10kHz   =   2 ohms    
   12kHz   =   2 ohms    
   20kHz   =   3 ohms    
   50kHz   =   8 ohms    
      
   BTW:    
   The low figures above 2kHz are because the 4ohm dome mid and 4ohm dome    
   tweeter are operating in parallel.    
   The owner was originally using twin wire he got from Tandy / Radio Shack (    
   14x0.14 stuff ) -  so each run was about 1.5 ohms resistance, plus about 2.5    
   ohms of inductance at 15kHz.    
   So I made him up some leads using "Tocord" ( aka Mogami cable)  with near    
   zero inductance and about 0.2 ohms resistance.   
   His mouth dropped open when he heard the difference.   
   ..  Phil   
      
   Before completely re-forming the pair of AR9 I was given to fix, I did manage   
   to get one working as it may have worked when new by swapping out working   
   mid/HF drivers so that enough working drivers were in the same box. I found   
   the acoustic response    
   response using the middle position of mid-HF level switches was anything but   
   flat and extremely poor by my standards. I don't recall any HF dips to 2 ohms   
   as you state exists above 2kHz, but I do recall the 3.6 ohm woofers were   
   connected in parallel and    
   had a second order filter so that the current through L&C plus current   
   speakers summed to Z < 2 ohms, and potential amp killers.    
      
   I didn't like the switches, or the wire wrap type of connections typical of   
   cheap junk. I figured prevention of future problems was needed, and they could   
   be made to have a minimum Z of just over 4 ohms, and thus be drivable by the   
   customers 200W ARC    
   monoblocs. So the bass speakers were connected in series to raise Z, and a   
   damped second order LC filter used with a bar cored L to avoid Rw losses in   
   the L. Bass speakers were atrociously insensitive, and the acoustic levels   
   above 150Hz had to be all    
   tailored to be flat, and equal to the level of bass at 80Hz, so this allowed   
   resistance networks to drive the mid/treble units. The owner had given me a   
   pair of supposed replacement lower midrange drivers from AR, and I thought   
   they looked badly made,    
   like a cheap Chinese POS, and these were remarkably sensitive. Considerable   
   series R was used. The new X-over networks were mounted on new boards with all   
   soldered joints and losses in speaker cables due to their resistance or   
   inductance ceased to be a    
   problem - any cable could be used OK, as long at it was at least dual core   
   mains flex rated for 5Amps, and say 3M long, max. I've also made speaker   
   cables using two cat5 blue covered cables to form a twisted pair and the 8   
   conductors in each cable are    
   all soldered to a banana plug on each end. I made 3 pairs, each 6M long to get   
   from a power amp to 3 stacked pairs of ESL57, each had been fully re-membraned   
   by John Hall in Melbourne. I didn't bother measuring those cables, but I   
   thought they'd be fine,    
   and sound OK.    
      
   I've got all the info on what I did to those AR9 speakers buried in a pile of   
   papers a foot high which I doubt I'll ever get around to publishing. IMHO, it   
   is very easy to make a better pair of speakers than the AR9.    
   Patrick Turner.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)