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

Thu Jan 3 04:25:24 MST 2008

When I worked at a Hi-Fi store in Tampa years ago, there was a story about 
Joe Cerwinski (of Cerwin-Vega speakers) who reportedly showed up at the 
place with a woofer mounted in a box, and the speaker wire leading from the 
box had a 120 volt plug on the end. He was claimed to have walked in, 
announced "My speakers can take 1800 watts!" and plugged in the speaker to 
the wall for a moment, then took his speaker and walked out just as abruptly 
as he arrived (with everyone inside dazed, no doubt). Don't know how true it 
is, but I have heard the tale from more than one person.

Dave Goodfellow

----- Original Message ----- 
From: "David Rieben" <drieben at comcast.net>
To: "Tesla Coil Mailing List" <tesla at pupman.com>
Sent: Wednesday, January 02, 2008 11:44 PM
Subject: Re: [TCML] Speakers - was: Terry filters (speaker/motor load 
modeling)

> 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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