Speaker connection precaution

[Diver300]

No, you won't get the power, you'll only get a quarter of it, and you don't have much to start with - which was why I didn't suggest series connection.

Don't worry about Audioguru's paranoia, series connection really makes VERY little difference in practice, although it's best with identical speakers.

But as I said, no power that way.

If the amplifier puts out the same voltage into 4 Ohms and 8 Ohms, putting two 4 Ohm speakers in series will give a quarter of the power per speaker, so half the overall power. That is a 3 dB reduction in the sound.

 

[Nigel Goodwin]

If the amplifier puts out the same voltage into 4 Ohms and 8 Ohms, putting two 4 Ohm speakers in series will give a quarter of the power per speaker, so half the overall power. That is a 3 dB reduction in the sound.

Give it a try, it will sound a lot less loud, and it's a puny amp in the first place. 3dB is supposedly the minimum change you can notice, but in practice the volume drop is considerable.

 

[audioguru]

Why is that?
Typically a 4 ohm speaker will output more power since the max peak output voltage of a solid-state amp usually doesn't vary that much with load.

The datasheet shows that with a low power supply of 7V the clipping begins into an 8 ohm speaker at 2.2W but with a 4 ohm speaker the clipping begins at 4W.
With a 12V supply, the clipping begins at 7W into 8 ohms or 11W into 4 ohms.
With a 15V supply, the clipping begins at 11W into 8 ohms or 9W into 4 ohms.

I guess at high current the output Mosfets heating and on-resistance increase.
EDIT: Ohms numbers have been corrected.

 

[tympany]

Looking at the datasheet, it seems like a bit of a job fitting a heat sink. I assumed I'd just be able to use some heat transfer compound with mechanical pressure to hold it in place.

I might just buy a more powerful amp, without these cautions, and be careful not to turn it up too loud!

 

[Nigel Goodwin]

Looking at the datasheet, it seems like a bit of a job fitting a heat sink. I assumed I'd just be able to use some heat transfer compound with mechanical pressure to hold it in place.

I might just buy a more powerful amp, without these cautions, and be careful not to turn it up too loud!

If you're wanting to run two 4 ohm speakers in parallel, then you need to ensure it can drive 2 ohm loads.