# Speaker impedance and amplifier **URL:** \ **Category:** Factual Questions\ **Created:** [April 3, 2015, 10:45pm UTC](https://boards.straightdope.com/t/speaker-impedance-and-amplifier/716756 "2015-04-03T22:45:20Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![K364](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k364/32/5_2.png) [@K364](https://boards.straightdope.com/u/K364)\ **Post date:** [April 3, 2015, 10:45pm UTC](https://boards.straightdope.com/t/speaker-impedance-and-amplifier/716756/1 "2015-04-03T22:45:20Z")
My little blue-ray home theater 5.1 blew up and I bought a new home theater receiver thinking I could re-use the old speakers and sub-woofer. The specs on the receiver says that it supports speakers in the “Normal 6-16 ohm impedance range”. I checked the old speakers and they say 3 ohms impedance. Do I need to get new speakers? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [April 4, 2015, 1:09am UTC](https://boards.straightdope.com/t/speaker-impedance-and-amplifier/716756/2 "2015-04-04T01:09:53Z")
3 ohms is pretty low. You could add a 3 ohm resistor in series with each speaker, and that would protect your amp, but it would cut your maximum volume by half. I’d probably buy new speakers. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 4, 2015, 1:25am UTC](https://boards.straightdope.com/t/speaker-impedance-and-amplifier/716756/3 "2015-04-04T01:25:16Z")
> [@beowulff](#): > > 3 ohms is pretty low. > You could add a 3 ohm resistor in series with each speaker, and that would protect your amp, but it would cut your maximum volume by half. > > I’d probably buy new speakers. it would also change the frequency response of the speakers since you’ve set up a voltage divider and the speaker’s impedance is not flat across the frequency spectrum. adding too much resistance in series will make the amplifier look like a current source, and the speaker’s frequency response will be influenced by its impedance curve. > [@K364](#): > > My little blue-ray home theater 5.1 blew up and I bought a new home theater receiver thinking I could re-use the old speakers and sub-woofer. > > The specs on the receiver says that it supports speakers in the “Normal 6-16 ohm impedance range”. I checked the old speakers and they say 3 ohms impedance. > > Do I need to get new speakers? you probably should. most A/V receivers are built and rated for “8 ohm” speakers. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [April 5, 2015, 2:26pm UTC](https://boards.straightdope.com/t/speaker-impedance-and-amplifier/716756/4 "2015-04-05T14:26:28Z")
> [@K364](#): > > I checked the old speakers and they say 3 ohms impedance. A nominal impedance of 3 Ω is pretty low for a speaker. Most speakers are 6 Ω to 8 Ω. Speakers that have a nominal impedance ≤4 Ω tend to be “high-end” (i.e. expensive). Am curious what type of speakers you have. I know you’ve already purchased a new amp. But if your speakers are indeed high-end/expensive, I would get an amp that can safely drive these speakers (i.e. an amp that can drive speakers with an impedance of 2 Ω). After all, the performance of the _speakers_ are what determine the overall performance of your system, not the amp. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 5, 2015, 2:52pm UTC](https://boards.straightdope.com/t/speaker-impedance-and-amplifier/716756/5 "2015-04-05T14:52:27Z")
How sure are you that the “3” ohms you read off the tiny embossed black print on the back of the black plastic speaker by flashlight light while teetering on a ladder isn’t actually “8” ohms? ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 5, 2015, 3:18pm UTC](https://boards.straightdope.com/t/speaker-impedance-and-amplifier/716756/6 "2015-04-05T15:18:37Z")
> [@LSLGuy](#): > > How sure are you that the “3” ohms you read off the tiny embossed black print on the back of the black plastic speaker by flashlight light while teetering on a ladder isn’t actually “8” ohms? those “Home Theater in a Box” (HTiaB) systems are known to use Class-D amplifiers and have lower impedance speakers so they can have a higher power rating without needing a big and expensive power supply inside the amplifier.