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Re: [TCML] Speakers - was: Terry filters (speaker/motor load modeling)

In a message dated 1/2/08 4:32:35 P.M. Eastern Standard Time,  
drieben@xxxxxxxxxxx writes:

>BTW, does anyone recall the Bose 901 series speakers? They were  pretty 
popular back in the 

I currently own two pairs of 901s, one  pair is still in use as the front 
stereo channels of our main surround-sound  system. I've experimented with 
several 901's of various vintages over the  years.
>I assume that they were the standard 8 ohm impedance type  

901's are anything but "standard". In later  versions Bose developed their 
own unique "woofer" for this application. Like  some Tesla Coilers, Bose used 
edge-wound ribbon instead of round wire to make  a more compact voice coil 
assembly. The ribbon edges are on the inside and  outside of the coil, not the top 
and bottom as we wind it for a TC. Not that  strange, other manufacturers have 
done the same, and some even use *hexagonal*  cross-section magnet wire to 
more efficiently pack the wire into the limited  space in the magnet gap.
    IIRC, all 9 of the identical "woofers" in  the original 901 were all 
connected in series. I also remember in later  versions there was a 
series/parallel connection. A lot of tweaking and  technology went into the later versions.
>and it seems like I heard someone say that as part of Bose's  advertisement 
campaign for these
>speakers that they actually connected  the input leads of a Bose 901 
directly to

>a 120 volt outlet and the speaker did not blow. 
    I've seen a lot of the advertising for the  901's, even the original 
magazine reviews from the late '60's when they first  came out, and never saw 
anything like that. Believe me, it would've stuck in  my mind!
    They *did* originally spec them at "unlimited  power handling in 
non-commercial applications", but much later changed it to  something specific and 
quite reasonable. The later versions were much tougher,  anyhow. I *can* say I've 
never seen a blown 901. Like many older speakers,  especially of the 
mid-70's, they tended to dry-rot and fall apart (Bose even  had a trade-in upgrade 
program going for original owners).
>Assuming the 8 ohms to be the correct resistance that the 120  volts, 60 Hz 
AC saw, that means 
>that the speaker would have been processing 1875 volt-amps (not  sure what 
the power factor

>would be in this situation) of sound power! 
    That's no big deal. I drive my 901's with an  older Carver TFM-45, rated 
at 375W/channel continuous indefinite, 750/channel  for a few seconds, and 
I've measured it as much higher on the peaks. Carver  had some interesting 
designs that used power supply transformers with a lot of  leakage inductance to 
store energy, instead of big filter caps on the DC bus  (although the TFM-45 has 
pretty big caps, and Carver amplifiers are another  story unto themselves...). 
I once plugged the speaker leads from my TFM-45  into an uncooked hotdog, and 
at full output the hotdog began smoking as it  made music...
    During the heyday of the 901's, there weren't too  many affordable amps 
that were capable of putting out enough clean power to  blow them. But the 
901's were very inefficient speakers, so it took a lot of  power through them to 
get them as loud as most other speakers. Another  tradeoff...
    People (myself included) would take 901's, turn  them around, and use 
them as PA/sound reinforcement speakers. Bose eventually  introduced the 802's, 
which were basically 901's turned around without the 9th  driver on the 
backside. So they were very tough.
>Sorry to get a little OT here, but has anyone else heard this  "story"?

    Well, now that I typed all this, I figured we might  as well find out. 
I'm just dumb enough to try something like this, and in a  position to do so:
    I just took a single 901 speaker, Series V, 1983  vintage, downstairs to 
the garage. Donned safety goggles and *earmuffs*. I  plugged it directly into 
the wall. No ballast, no variac, no switch, no nothing!  Twice in a row for 
five seconds each time. No smoke, no smell, and a good clean  60 Hz sound with 
no indications of clipping. Lights dimmed very significantly.  VERY loud. My 
wife upstairs said it vibrated the whole house.
-Phil LaBudde

Center for the Advanced Study of Ballistic  Improbabilities

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