use 2 ohm speakers

[bitemeboat]

Can I use 2 ohm speakers with dynaco stereo 70?


The speakers are an 8 ohm speaker and a 4 ohm speaker in parallel in a custom built cabinet. That would be approximately 2.67 ohms(32 ohms divided by 12)

[TheGimp]

I suspect it is a bad idea for the reasons that (1) it will reflect a much lower plate load to the tubes, resulting in higher distortion, (2) possibly excessive loading, (3) it will result in odd sharing of the power to the speakers with 1/3 to the 8 ohm and 2/3 to the 4 ohm one at nominal impedance.

What are the two speakers in parallel, and why?

[atmasphere]

I would work to raise the impedance. You will be loading the power tubes are barely more than half of what they are expecting (~1500 ohms instead of 3000) so they will not make power and they will make a lot of distortion.

If you set the speaker up at 16 ohms, or 12, you will have lot easier time of making power, and the amp will make less distortion. Going to higher impedance in the speaker is a very easy way of making it seem more transparent for this reason, and it almost does not matter what kind of amp is driving it!

[DougL]

I suspect you have an 8 ohm tweeter and a 4 ohm woofer with a simple crossover, correct? One of The crossover's job is to prevent a 2 ohm load from being seen by the amplifier. My answer is to try the 4 ohm taps.

HTH

Doug

[tinitus]

Originally Posted by DougL

I suspect you have an 8 ohm tweeter and a 4 ohm woofer with a simple crossover, correct?
Doug

Or the opposite
Many new tweeters are 4ohm
If so, all you need is a series resistor for tweeter attenuation

On many 2ways you get 5-6 ohm(8ohm nominal)

A few modern output trafos are made with a single 6ohm tap

[bitemeboat]

I actually have a diy speaker with a alpair 6 4 ohm full range speaker,and an 8 ohm woofer.

[atmasphere]

Originally Posted by bitemeboat

I actually have a diy speaker with a alpair 6 4 ohm full range speaker,and an 8 ohm woofer.

So, what do you mean by that? You have a pair of 6" 4 ohm speakers, or do you have six 4 ohm speakers? Sorry but your text above is ambiguous.

[bitemeboat]

I am sorry. the speaker is an alpair 6. It is 4 ohms. I also have an 8 ohm woofer.
2 speakers per enclosure. 1 is a 4 ohm full range driver, and the other is an 8 ohm woofer.

[tinitus]

No problem
As Doug said, you need a crossover
Drivers will not be in paralel the way you think
cap and inductor causes impedance rise

And You may need some BSC compensation
A small series resistor on your alpair6 might be part of that
5-6 ohm is realistic

But I dont know if fullrange forum is the right place to teach about crosssovers
But you cant just paralel the two drivers
You would get severe phase issues

[atmasphere]

Yes, I would cross over the drivers, probably about 300Hz or more, so that the fullrange unit has no excursion to deal with. Then it will be more transparent. That way your impedance would be 8 ohms to 300Hz, then going to 4 or 5 ohms above that. The ST-70 will have no problem dealing with that at all.