amp power & driver sensitivity in multiamp setup

Something that is missed from this conversation:

The driver is measured in sensitivity, not efficiency. As a result the impedance must be taken into account; in this case it results in the efficiency being not quite so high. You can't exchange the two specs unless the impedance of the drive is 8 ohms. So this is going to make the situation worse.

Second, adding more drivers will not change the efficiency at all although it will affect sensitivity adversely if the drivers are in series. However this means little to a tube amps with no feedback!!

By putting the two drivers in series all that will happen is 1/2 the power will be dissipated by each driver, resulting in exactly the same output as if one driver were to be used, assuming the same amount of power in both cases.

Based on what I've seen so far, the 2A3 amp will likely be OK for the tweeter, but for midrange you will either need a more powerful amp or a more efficient driver. If the driver were to be about 105db you might do OK as that would be about the same as if the amp had 10x the power. However if you insist on an SET for that, well there just isn't one that can do that sort of power and no go over 20% so this problem will need some rethinking IMO.

Hi Al- got it. I really don't think so, although it would help the amplifier to have lower distortion. He would still need either greater power or a more efficient driver.

Its probably that if the amp has only one output and no taps, that the 5 ohm load would result in less output than the 16 ohm load.

If you use drivers that are 100 db 1 watt/1 meter (PHY?), then you have a chance with the 2A3 amp but I have my doubts about the type 45 amp- realistically they only make about 0.75 watts.

PHY is a French manufacturer too...

'Taps' are the outputs of an output transformer. A tap is a connection into the winding of the transformer that allows for a different impedance. Usually a tube amp has an output for 4 and 8 ohms, possibly also 16. If there is only one output, its probably for 8 ohms.

The 1040 or 1050 seem the best bet in 6.5" drivers; the 2520 or 2530 in teh 8" drivers. Now I suspect that the specs are not accurate- they may be efficiency specs rather than sensitivity as claimed. The reason for this is that the drivers I have mentioned here have the same sensitivity rating while having two different impedances, and the sensitivity rating does depend on impedance somewhat.

What I am getting at is if these driver selection represent the same driver but in two different impedances, the 16 ohm unit should have had a sensitivity rating of 3 db less. Now they are claiming that the 16 versions are 100db, if that is really true the efficiency would 103 db.

This is because efficiency is 1 watt/1 meter regardless of the impedance, while efficiency is 2.83V/1 meter. 2.83volts into 8 ohms is 1 watt, into 16 ohms its only 1/2 watt- a 3 db difference. You might want to contact them and see if they can shed some light on this.

At any rate if the drivers are 100 db then you have a good chance of using them as midrange drivers with your 2A3 amp.

Yes.

In the case of driving a 5 ohm driver, the output of the amp will be lower power and higher distortion. Since its a tweeter, this might not be much of an issue as there is little power that is needed for a tweeter.

The 16 ohm load will also result in reduced power and more distortion, but the loss in power won't be as much as in the 5 ohm case. Also, the distortion will come from the output transformer and really not that much from the power tube; its the other way around in the 5 ohm case.

Since efficiency and power is a big deal in this case I would go with the 8 ohm version of the driver (assumed to be 100db 1 watt 1 meter) if you have a choice. This will keep distortion down and power up.

The life of the power tubes are likely not going to be much different in either case.