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In Reply to: RE: How to raise the total resistance of a speaker posted by saki70 on November 27, 2014 at 08:59:01
Saki,
"Is it possible to take a manufactured box speaker rated at 8 ohms and raise it to 10 , 12 , 14 or 16 ohms?"
My short answer is no. I don't know if you meant to restrict this to OTL amps, but I would answer your question a different way, and I think it is the other side of the coin of what Maxhifi said.
The Tanny Red is valued by tube guys, because it is 16ohms, which means it is three decibels more efficient, which means that your power requirement just got cut in half. Also the higher impedence load is easier for a vacuum tube to handle, so the two go together. People usually don't run SS into high imp. and they usually don't run tubes into low imp.
Jamie
Big speakers and little amps blew my mind!
Follow Ups:
Being a 16ohm speaker doesn't make the Red 3dB more efficient. There are other reasons, like sound quality, that make the Tannoys a popular speaker.
"Being a 16ohm speaker doesn't make the Red 3dB more efficient."
Can we agree that it is 16ohms and it is 3db more efficient?
"There are other reasons, like sound quality, that make the Tannoys a popular speaker."
That is true.
Big speakers and little amps blew my mind!
Basic efficiency and impedance are two independent characteristics.
"Basic efficiency and impedance are two independent characteristics. "
That's why they have two different words for them.
I'm in no mood to get in a debate about the efficiency gain of a 16ohm speaker that is run by a tube amp, as opposed to an 8ohm speaker. Google didn't bring the proof easily to hand.
You win.
Pardon me if I carry on my merry way.
Big speakers and little amps blew my mind!
...I just don't understand the basis of your claim regarding the relationship betw eff and impedance or what your "reference" for this claim might be. Kinda surprised Google wasn't too helpful. ;-)
I wish I had the technical answer for you, but I don't. Maybe someone who has a better technical background understands the argument will chime in.
As I understand it; using a tube amp, and all else being equal, a 16ohm driver will be 3db more efficient than an 8ohm driver.
People usually think in SS terms, where if you go from 8ohm to 4ohm, then you pick up power. But with tube amps it runs in the other direction. You pick up power as you increase impedence, up to a point where there is a dimishing rate of return, which is why you don't see 32ohm drivers. Although you once did see them when tubes were king.
Jamie
Big speakers and little amps blew my mind!
If you have a circuit with an output transformer with a 2.5K Primary and an 8 ohm secondary and another identical circuit with a 2.5K transformer with a 16 ohm secondary with each connected to an appropriate speaker load, the power output will be the same. You can stack the speakers in a number of ways and you can rephrase the question in any number of ways but your initial question on the HiEff board remains the same. You don't get 3dB magically.
There's no free lunch.
"There's no free lunch."
Yes, that's always seems to be the case.
"you can rephrase the question in any number of ways"
Once more into the breach;
Then why does a solid state amp put out more wattage the lower the speaker impedence? It's almost like a free lunch.
Big speakers and little amps blew my mind!
Watts is a measure of energy used and is a derivative/result of Ohm's Law. Current, voltage and resistance determine watts. This is ONE reason why great amplifiers are designed to produce "more than adequate" current - to deal with low resistance speakers.Just because an amp/speaker circuit can consume 8 billion watts driving a 2 ohm load doesn't mean that it's louder than an amp/speaker circuit which only consumes 1 billion watts into an 8 ohm load.
And let's not forget the speaker's reactive component.
:)
Edits: 12/01/14
...at a high level, the reason a solid state amp might appear to put out more power into lower impedances is that it tends to approximate an ideal voltage source. i.e. zero output impedance/infinite current delivery capability. So...if our voltage source amp can deliver say, 16W into 16ohms, that's 16V across the 16 ohm load. Drop the load to 8 ohms and the 16V remains constant so now we have 16^2/8=32W. Drop the load to 4 ohms and we get 64W and so on. Few amps have the output stage or PS beef to actually accomplish doubling of power when impedance is halved but the trend is present. As always, there are exceptions, notably the Mac SS amps with autoformer outputs. These tend to deliver the same power into any load that matches the tap impedance...just like a transformer coupled tube output stage.
Since this is a high level discussion, we'll avoid the issue of non-optimum primary to secondary coupling that occurs with most OPTs incorporating tapped secondarys when used with the lower impedance taps. I believe this is what gives rise to the impression that transformer coupled tube amps do better delivering power to high impedance loads.
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