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

[David Rieben]

Hi Phil,

Wow! I didn't actually expect someone to try this out but
I guess the myth is now confirmed! ;^)) Thanks for putting
the myth to the test and reporting the results. Sounds like
a theme for Mythbusters :^)

David Rieben


----- Original Message ----- 
From: <FIFTYGUY at aol.com>
To: <tesla at pupman.com>
Sent: Wednesday, January 02, 2008 5:48 PM
Subject: 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 at comcast.net writes:
>
>>BTW, does anyone recall the Bose 901 series speakers? They were  pretty
> popular back in the
>>1980's.
>
>
> 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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