• Audio

  Building an audio amplifier for 2.5 ohm speakers

  Posted by Kyson Lin on February 14, 2017 at 6:36 am

  Hello!
  I am trying to dug out of my box o’ stuff a pair of seemingly decent 2.5ohm bookshelf speakers recently. I wired them to an old mp3 player I have and while they sound good at low volumes, I get lots of distortion at high volume. Given that they are only 2.5ohm, I’m assuming that this is because they are trying to draw more current than the poor mp3 player can produce.
  Rather than buying one (or new speakers for that matter), I’d like to try and build an amplifier for these speakers. I was looking at using an IC such as the TDA7294 but like all of these chips, the advised load impedance is 4 ohms. It doesn’t specifically state anywhere that the absolute minimum is 4-8 ohms, but has anyone had any experience with this sort of thing? Will it still work at a lower load impedance if I just make sure that the volume is limited? If not, will I be able to use this IC if I chuck a big 2 ohm power resistor in series (as much of a waste of electricity as that is)?
  I’ll probably get some anyway to play with but I am a poor student and I would prefer not to blow up several $12 chips.
  Any advice or suggest will be great helpful ! Thanks a lot !

  Richard Crowley replied 9 years, 6 months ago 2 Members · 1 Reply
• 1 Reply

• 

  Richard Crowley

  February 15, 2017 at 4:29 am

  How do you know that the speakers are 2.5 ohm? As you note, that is an extraordinarily low impedance.
  What speakers? Make and model.
  What is the nameplate rating for impedance? for power?

  What kind of speakers are they? What were they designed to be driven from?
  If they really are 2.5 ohm, then they are extremely odd-ball

  Remember that measuring speakers with a DC ohm-meter is not valid. It wouldn’t be unusual to measure 2.5 ohms DC resistance on a 4 ohm speaker.

  Since we know almost nothing about the speakers, we don’t know whether throwing 2 to 4 ohm resistors in series might be a reasonable work-around or not. And we don’t know what the power handling or sensitivity of the speakers are, either.

  I agree with you that putting such a very low impedance load on a chip amplifier like the TDA7294 is not advisable.

  ———————————————————————————
  Recording audio without metering and monitoring is exactly like framing and focusing without looking at the viewfinder.

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