Up2Stream Amp: PSU influence to Power output (Watt) ?

In my current project I am combining the Up2Stream AMP v4 with a vintage 2-way speaker. The speakers specifications are:

  • Output = 15 Watt RMS
  • Output = 20 Watt Peak/Music
  • Impedance = 4Ω

These are the specifications I found for the Up2Stream AMP v4 (Stereo mode):

  • 12v power input = max 10W at 8Ω / 20W at 4Ω <<< choosen
  • 15v power input = 2x 15W at 8Ω
  • 21v power input = 2x 50W at 4Ω
  • 24v power input = max 30W at 8Ω / 50W at 4Ω

So, I found it logical to choose a 12v (5A) power supply, because this matches exactly the limits of the speaker.

My findings

  • When connecting PSU + Up2Stream AMP + speakerbox I found that the output volume was quite low.
  • As I had a 24v (6A) PSU available, I connected this one to the Up2Stream AMP. Result: the output volume levels are almost the same as with the 12v PSU.

My question
I expected to have recognizable higher output volume with the 24v PSU, but that didn’t happen.

Anyone has an explanation?

Hi Ernst,

When you are saying “a higher output volume”, this is called SPL (sound pressure level) By doubling the amplifier power doesn’t double the SPL.
I’m sure that someone more experienced than I can explain this better, or can elaborate, but this is what I know.

A speaker’s sensitivity rating is stated as db @1W/1M (SPL) this is, with one watt of power measured at a distance of one meter from the speaker (speaker sensitivity is measured in an anechoic chamber) a more efficient speaker will have a higher number and a less efficient speaker will have a lower number.
So in real terms, say for example you have a speaker with a sensitivity of 90dB @ 1W/1M and the speaker has a power handling capacity of up to 100W. If that speaker is powered with 1W of power, it will generate 90dB when measured at a distance of 1M, if you double that power to 2W the SPL measurement will only increase to 93dB and if you increase the power to 10W then the SPL measurement will increase to 100dB.

There are lots of SPL calculators online which will demonstrate this to you.
Example Peak SPL Calculator

Investigate the speakers that you are using and determine the sensitivity of them, they may be low?

Hope this helps a little?

1 Like

Interesting feedback @Steve1, thanks!

So far I haven’t been aware that the sensitivity of a speaker also plays a role. What you say about that seems possible in case of these speakers.

The speakers are from 1969, I just looked up the sensitivity and it says: “4 Watts (DIN 45 500)”. So not measured in dB. But I presume that is rather low.

Maybe you can comment on this?

I just had a read of DIN 455500, with regards to speakers it appears to relate to frequency response, or from the standard drawing shown an ‘ideal’ frequency response from 50Hz to 12.5kHz, so doesn’t really tell us much.
I’m guessing that the 4W relates to the power applied when the frequency response was measured.

Is there a manufacturer’s name on the enclosures?

I just found another website that may be of interest to you: https://geoffthegreygeek.com/understanding-speaker-sensitivity/

Thanks @Steve1.

Yes, I only could find this indication of speaker sensitivity. Which isn’t the typical description of sensitivity, as you mentioned.

Sure, the speaker in this case is a Bang and Olufsen, BeoVox 1200.

I’m reading a lot, but not getting too far. This thread on diyAudio is of some interest. Speaker Sensitivity Interpretation? | diyAudio