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Speaker OHM's

post #1 of 34
Thread Starter 
Hello, I have a question about speakers. If the speakers are 3 OHM and I have a Sony STR-K740P receiver which I think is rated at 8 OHM. Will this hurt the speakers or the receiver? This is for my parents surround sound system that I threw together. Just average use, not turn up too loud or anything?

Thank you,
Robert Smith
post #2 of 34
Correct expression is speaker impedance (makes you sound less of a noob) and as that AVR doesn't show a rating for speakers that low, I'd suggest don't use them together. It *might* work OK, but there is the potential to damage the receiver.
post #3 of 34
Thread Starter 
Ok, Thanks! How about using them with an Onkyo system which can be either 4 ohms or 6 ohms.
post #4 of 34
The general rule of thumb IMO is dont go below rated. Of course, thats the safest way.
Though sometimes with impedance rise it will work. If you see magic smoke, its not our fault
post #5 of 34
this is not my area of expertise, but why wouldn't wiring a 4 ohm resistor in line (series) with the speaker not work. it should bring the total resistance up to about 7 ohms, which will be fine for your amplifier. they only cost a couple bucks and then you wouldn't have to worry about it.
post #6 of 34
oh and parts express has a whole schlock of resistors for $0.39 a piece.
post #7 of 34
Quote:
Originally Posted by LTD02 View Post

this is not my area of expertise, but why wouldn't wiring a 4 ohm resistor in line (series) with the speaker not work. it should bring the total resistance up to about 7 ohms, which will be fine for your amplifier. they only cost a couple bucks and then you wouldn't have to worry about it.

It will make the load safe but it will dissipate half your output power as heat.
post #8 of 34
Quote:
Originally Posted by LTD02 View Post

oh and parts express has a whole schlock of resistors for $0.39 a piece.

As long as they are non-inductive and can handle a few dozen watts, sure.
post #9 of 34
Why are you getting 3 ohm speakers anyways? You would need a robuts separates amp for that.
post #10 of 34
Quote:
Originally Posted by moparbob7 View Post

... Just average use, not turn up too loud or anything?

This is the key piece; you'll be fine. There are no issues with real speakers when amps are run significantly below their rated power.

Here are a couple Audioholics links if you'd like to learn why from someone who knows what he's talking about, not just repeating it.
http://www.audioholics.com/education...ector-switch-1
and, even more to the point
http://www.audioholics.com/education...r-or-amplifier

Specifically addressing Onkyos (I have a 707), the 4ohm mode limits power to 35W/ch. The spec sheet says it can deilver 240W/1 ch @ 4 ohms, so I run mine (3ohm MTMs) in 6ohm mode and don't worry about it. The cooling fan has never turned on.

Have fun,
Frank
post #11 of 34
Quote:
Originally Posted by Eternal Velocity View Post

Why are you getting 3 ohm speakers anyways? You would need a robuts separates amp for that.

may be B&W speakers
post #12 of 34
Thread Starter 
Just looking at Samsung speaker sets that from the HT-C550 system. Found the set for $25. Just looking for something cheap.

166 WATTS WITH 3 OHM IMPEDANCE
* 2 FRONT (PS-FC550) SPEAKERS
* 2 REAR (PS-RC550) SPEAKERS
* 1 CENTER (PS-CC550) SPEAKER
post #13 of 34
thanks kal.

most speakers blow 97% of their power into heat anyways and he said his folks won't be blasting the tunes anyways.

http://www.parts-express.com/pe/psho...tnumber=004-20

get four-five of these per speaker.

wire them in parallel and then in series with your speaker.
.
.
..................../ -------resistor--------\\
.................. / -------resistor--------\\
.amp + -----/..................................\\--------- + speaker
..................\\ -------resistor--------/
................... \\ -------resistor--------/
.
.
.amp - ---------------------------------------- - speaker
.
.
this will give you a 5 ohm increase and 40 watts of power (which is more than your folks will be using).

$4 per speaker and you are good to go.
post #14 of 34
Quote:
Originally Posted by LTD02 View Post

thanks kal.

most speakers blow 97% of their power into heat anyways and he said his folks won't be blasting the tunes anyways.

http://www.parts-express.com/pe/psho...tnumber=004-20

get four-five of these per speaker.

wire them in parallel and then in series with your speaker.
.
.
..................../ -------resistor--------\\
.................. / -------resistor--------\\
.amp + -----/..................................\\--------- + speaker
..................\\ -------resistor--------/
................... \\ -------resistor--------/
.
.
.amp - ---------------------------------------- - speaker
.
.
this will give you a 5 ohm increase and 40 watts of power (which is more than your folks will be using).

$4 per speaker and you are good to go.

Sure but do you think a newbie is capable of this?
post #15 of 34
Thread Starter 
Which is better 4 6 or 8 ohms? I have no idea what it is all about? I just buy speakers and go with a high watts...lol
post #16 of 34
Quote:
Originally Posted by moparbob7 View Post

Just looking at Samsung speaker sets that from the HT-C550 system. Found the set for $25. Just looking for something cheap.

166 WATTS WITH 3 OHM IMPEDANCE
* 2 FRONT (PS-FC550) SPEAKERS
* 2 REAR (PS-RC550) SPEAKERS
* 1 CENTER (PS-CC550) SPEAKER

Here's some advice: Do not buy speakers that have been excised from a HTiB. There is good reason that they are so cheap. Buy real speakers, even cheap ones from BB, that are intended to be sold separately.
post #17 of 34
Quote:
Originally Posted by moparbob7 View Post

Which is better 4 6 or 8 ohms? I have no idea what it is all about? I just buy speakers and go with a high watts...lol


Speakers don't even have watts.

As for which is better, it's hard to really say what I want to say.

All I'll say is that an 8 ohm speaker will give you the easiest time in matching with a receiver.
post #18 of 34
Thread Starter 
ummmm, what does 166 watts mean?
post #19 of 34
Quote:
Originally Posted by moparbob7 View Post

ummmm, what does 166 watts mean?

In this particular case, nothing.
post #20 of 34
Quote:
Originally Posted by Kal Rubinson View Post

In this particular case, nothing.

For the first time in a long time when reading something on the internet, I really did laugh out loud. Thanks Kal and moparbob
post #21 of 34
"Sure but do you think a newbie is capable of this?"

tying the end of four resistors together and putting that in line with the speaker?

i'm not really sure how it could it be any more simple.
post #22 of 34
Quote:
Originally Posted by LTD02 View Post

"Sure but do you think a newbie is capable of this?"

tying the end of four resistors together and putting that in line with the speaker?

i'm not really sure how it could it be any more simple.

You are more of an optimist than I am.
post #23 of 34
Quote:
Originally Posted by Kal Rubinson View Post

You are more of an optimist than I am.

Wow two LOL's in one day...
post #24 of 34
"You are more of an optimist than I am."

maybe it is too much. i was just trying to help. i'll bow out now.
post #25 of 34
Quote:
Originally Posted by LTD02 View Post

"You are more of an optimist than I am."

maybe it is too much. i was just trying to help. i'll bow out now.

We are all trying to help as well as enjoy ourselves, right?
post #26 of 34
Quote:
Originally Posted by LTD02 View Post

this is not my area of expertise, but why wouldn't wiring a 4 ohm resistor in line (series) with the speaker not work. it should bring the total resistance up to about 7 ohms, which will be fine for your amplifier. they only cost a couple bucks and then you wouldn't have to worry about it.

Xovers are typically designed expecting the amplifier to have an output impedance of basically zero. Add a 4R series resistor and the amp output Z effectively become 4R. This changes the frequency response, potentially xover points, and even if they are just a widerange single driver, the Fc and Qes of the system.

Go take a look at Steropile's measurements of SET amps and se what the high o/p Z does to the response.
post #27 of 34
Quote:
Originally Posted by moparbob7 View Post
ummmm, what does 166 watts mean?
The same could be asked about 3 ohms.
post #28 of 34
Quote:
Originally Posted by A9X-308 View Post
Xovers are typically designed expecting the amplifier to have an output impedance of basically zero. Add a 4R series resistor and the amp output Z effectively become 4R. This changes the frequency response, potentially xover points, and even if they are just a widerange single driver, the Fc and Qes of the system.

Go take a look at Steropile's measurements of SET amps and se what the high o/p Z does to the response.
You are correct, sir, but, in this case, such considerations are moot.
post #29 of 34
Quote:
Originally Posted by Kal Rubinson View Post

You are correct, sir, but, in this case, such considerations are moot.

I posted for LTD.
post #30 of 34
thanks for the correction alpha niner. like i said, this is not my area of expertise.

here is a theoretical question. what if he wired two speakers in series that gave a total of 8 ohm load. would that frequency response be the same as each speaker by itself? and if speakers wired in series sounded fine, would that be different from wiring 4 ohms of resistance in series with a single speaker?
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