Over on the fullrange driver forum someone mentioned an oddball 8" 45ohm full range driver. Being about 92 db/w ( based on 6.8v into the 45 ohms ) Even one pair of 6as7's should be able to drive the heck out of that a 45ohm driver. https://mcbrideloudspeaker.com/images/specs/8C5Z45.pdf
I am curious why there are commercial driver units with 45 ohm? a new trend 
?
Regarding the OTL, yes possible, and the low damping factor may not even be a problem (maybe even better, thinking about the good match of transconductance amplifier with FR drivers) - still, quite an effort to build it to eventually drive a speaker that doesnt even show a Frequency response in the datasheet.
?Regarding the OTL, yes possible, and the low damping factor may not even be a problem (maybe even better, thinking about the good match of transconductance amplifier with FR drivers) - still, quite an effort to build it to eventually drive a speaker that doesnt even show a Frequency response in the datasheet.
That suggests they are designed to run off a 100V distribution network - but without the need for a drop down transformer at the end. Clever idea, but it doesn't bode well for their potential quality as this is usually a low grade application.Curious specifications
Mona
Looking at those small magnets doesn't inspire confidence either.
Shoog
Or… it could be a typo. It makes much more sense if you substitute "4.5 Ω" as the specification. Normally, 8 Ω drivers are always less in DC resistance measure than their dynamic impedance. By how much? I've measured 'em over the years as lower than 1 Ω to just under 8 Ω. A friend reported measuring one at over 10 Ω, but I think his meter was full of crackerjacks.
Never underestimate the ability of foreign manufacturers to drop a character here or there. Remarkable how often it happens.
GoatGuy
Never underestimate the ability of foreign manufacturers to drop a character here or there. Remarkable how often it happens.
GoatGuy
> why there are commercial driver units with 45 ohm?
Standard impedance for intercom speakers (which also served as microphones) was 45 Ohms. This allow use of smaller wire over longer runs, and also got the microphone output voltage conveniently high (or not so inconveniently low).
And Quam was the major supplier.
Intercoms were almost all 4-inch. Maybe there was a 8-inch for factory application. As most Quam cones and coils may be mix-matched, it is easy to suppose an 8-inch with the 45r coil.
That speaker is what I would call a "ceiling speaker" for classrooms and supermarkets. If someone really has found good sound in it, good for them.
> pair of 6as7's should be able to drive the heck out of that a 45ohm
Better than 8 Ohms, obviously. But speakers are few-Ohms, tubes are hundreds of Ohms. Tube loads should normally be thousands of Ohms for good power transfer. 6080/6AS7 is around 300 Ohms over most of its range. A 45r/345r circuit puts 13% of power input to the 45r load, a shameful efficiency. (Transformer to give decent impedance does 25%-55%.)
But you can get a Watt this way, and that Quam 8-inch doesn't need (or tolerate) huge power. It can be enjoyable music.
Standard impedance for intercom speakers (which also served as microphones) was 45 Ohms. This allow use of smaller wire over longer runs, and also got the microphone output voltage conveniently high (or not so inconveniently low).
And Quam was the major supplier.
Intercoms were almost all 4-inch. Maybe there was a 8-inch for factory application. As most Quam cones and coils may be mix-matched, it is easy to suppose an 8-inch with the 45r coil.
That speaker is what I would call a "ceiling speaker" for classrooms and supermarkets. If someone really has found good sound in it, good for them.
> pair of 6as7's should be able to drive the heck out of that a 45ohm
Better than 8 Ohms, obviously. But speakers are few-Ohms, tubes are hundreds of Ohms. Tube loads should normally be thousands of Ohms for good power transfer. 6080/6AS7 is around 300 Ohms over most of its range. A 45r/345r circuit puts 13% of power input to the 45r load, a shameful efficiency. (Transformer to give decent impedance does 25%-55%.)
But you can get a Watt this way, and that Quam 8-inch doesn't need (or tolerate) huge power. It can be enjoyable music.
100V on 45Ω
P=V^2/R=10000/45=222W
Mona
100v line is not 100v signal, but 100vdc "carrier" between master and slave transformers.
No, Z45 in the model name 8C5Z45 indicate the speaker nominal impedance, so it is 45 ohms.
The purpose of a 100V line is to reduce restistive losses in the cable. As such it increases the voltage which reduces the current (the element of the signal which causes the losses). Mostly they use standard speakers which need the voltage to be brought back to normal levels which usually involves a cheap transformer. 100V line driving amps put out a signal at the required 100V level.
Shoog
Shoog
OK, I stand corrected. But the original question was why the speaker was also marked 8 Ω. Can't have it both ways. That's all.
GoatGuy
But were they “supposedly 8 Ω” impedance speakers? I can understand if they had higher impedance at 32 Ω of DC resistance.
Higher impedance speakers optimize use of smaller wire (leads) and PCBoard traces. They also match with smaller amperage output transistors which however work at higher voltages. It is a design decision mostly. “What's cheap(est) that more-or-less accomplishes the job, well enough that people will comment at the store that the sound is 'Big' ”
Just saying. For 99% of the TELEVISION buyers, high fidelity wasn't the objective. Powerful was. And lowest cost. Y'know?
GoatGuy
Higher impedance speakers optimize use of smaller wire (leads) and PCBoard traces. They also match with smaller amperage output transistors which however work at higher voltages. It is a design decision mostly. “What's cheap(est) that more-or-less accomplishes the job, well enough that people will comment at the store that the sound is 'Big' ”
Just saying. For 99% of the TELEVISION buyers, high fidelity wasn't the objective. Powerful was. And lowest cost. Y'know?
GoatGuy
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> why the speaker was also marked 8 Ω
Because transcribing speaker specs is dull tedious work, and mistakes happen.
There is no doubt that Quam can make you a 45r speaker. I remember it from decades back, and it is shown in this PDF. Several models come either 8 or 45, same power rating, same magnet. Just skinny wire.
> Never underestimate the ability of foreign manufacturers to...
Quam is long-time USA, and apparently still makes the stuff(!!) in Chicago IL USA. That may be "foreign" to some of us, true.
Because transcribing speaker specs is dull tedious work, and mistakes happen.
There is no doubt that Quam can make you a 45r speaker. I remember it from decades back, and it is shown in this PDF. Several models come either 8 or 45, same power rating, same magnet. Just skinny wire.
> Never underestimate the ability of foreign manufacturers to...
Quam is long-time USA, and apparently still makes the stuff(!!) in Chicago IL USA. That may be "foreign" to some of us, true.
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