Speakers - 4 ohm / 8 ohm

[Magistrate]

Can someone tell me in simple terms which speaker would be better (presuming they were the same in all other ways) a 4 ohm speaker or an 8 ohm speaker? I don't get the difference.

My amp can output both 4 or 8 ohm (switch on the back), so should I look at speakers which are 4 or 8 ohms?

Thanks in advance.

[Funk]

When talking about ohms, you're talking about the resistance a speaker presents to an amp. If an amp puts out 100w into an 8 ohm load, it will have to put 200w into a 4 ohm load to achieve the same level of output, but the resistance will vary depending on frequencies, dropping as low as 2 ohms in some cases. A 4 ohm speaker will be trickier to drive than an 8 ohm one.

The speaker will also have a rating measured in db/w/m. For example, a speaker with a rating of 92db/w/m will produce an output of 92db at a distance of 1 metre given 1 watt of input. The higher this number is, the easier a speaker is to drive.

To be frank, it's not something that's likely to be especially taxing on most amps these days; most speakers are 4-8 ohm and will be easily driven by something with a modicum of grunt (50-100w per channel). What power delivers more than outright volume is control over the speaker when the load the speaker presents becomes trickier (eg. the resistance varies with frequency) along with lower distortion.

I'm sure there will be others along with more detailed explanations, but this is my layman's understanding of it.

[Some Gump]

In real trivial terms:

An amp has to work "harder" to drive a 4 ohm load than 8. Therefore for most people, 8 ohm speakers are the better bet purely on the basis of heat. Most "seperates" kit is designed round 8 ohm. However, this advice flies out of the window for:

High end kit.
Subwoofers.
Car audio.

Out of interest, what amp is it?

[Magistrate]

Some Gump said:

Out of interest, what amp is it?

See my previous post last month here. Still to buy some, but gotta get some soon!!

[Some Gump]

Ahh, that's covered by "high end kit" then!

Cheaper amps are often miles away from the theoretical doubling of power from 8 ohm to 2.. Your valves may well do exactly that - valve designs normally have current capacity through the roof!

Bearing in mind your amp, IMO sensetivity is the only stat to worry about - 88 db/w/m or more (ideally 90+) would be good. Other than that, all down to your ears!

[Funk]

Interesting! Valve amps don't normally have the same level of grunt; I'd be looking for some sensitive speakers with an 8 ohm load if it were me. You've been given some good advice in that thread. As per the specs, the amp will put 45w into an 8 ohm load.

You'll have to accept that with a move to 'stand-mount' speakers (I hate the term 'bookshelf'!) you'll sacrifice some of the bottom end. It's possible to get some speakers that are capable of astonishing levels of output with relative ease though. I have a pair of Celestion A2 floor-standing speakers that are 8 ohm and 90db sensitivity which for a large speaker is pretty good. They sound wonderful too, even with a modest amp (I'm running a Cyrus 8vs2 after ditching all my Naim gear).

[Magistrate]

Some Gump said:

Ahh, that's covered by "high end kit" then!

Cheaper amps are often miles away from the theoretical doubling of power from 8 ohm to 2.. Your valves may well do exactly that - valve designs normally have current capacity through the roof!

Bearing in mind your amp, IMO sensetivity is the only stat to worry about - 88 db/w/m or more (ideally 90+) would be good. Other than that, all down to your ears!

Cheers, so it doesn't make any difference this switch which changes things from 4 to 8 ohms?

[Some Gump]

Mag,

It will, but with valves I'm not exactly sure what effect it will have =(
On digital (class d or pulse width modulation) amps, you tell the amp what the load is as this effects the treble / bass balance; on solid state amps, some have this switch but a lot of that is to avoid blowing the amp..

Someone cleverer will be along shortly to sort you out - my background is in high end solid state home cinema - never seen a valve 5.1 setup, and don't want to give duff advice =)

[Funk]

You'll need to set it to the correct rating for the speakers you eventually buy, that's all. It will be fine handling either option though, but as SG points out (as did I), you'd do well to look at reasonably sensitive speakers.


Although I do feel a little like I'm talking to myself here at the moment.

[Magistrate]

Funk said:

You'll need to set it to the correct rating for the speakers you eventually buy, that's all. It will be fine handling either option though, but as SG points out (as did I), you'd do well to look at reasonably sensitive speakers.


Although I do feel a little like I'm talking to myself here at the moment.

Thanks Funk.....sorry to be thick and ask again , but I can't see my original question has been answered......If I have 2 identical speakers but the only difference is the ohms, which one would be best 4 or 8 or would it make not a blind bit of difference? It's a hypothetical question, as I know the ohms rating is not the way to choose a speaker, but I'm just interested.

[TonyRPH]

Magistrate said:

Cheers, so it doesn't make any difference this switch which changes things from 4 to 8 ohms?

In the case of a valve amp, it can make a big difference.

Valve amps use transformers in the output stage, and the switch you refer to will match the impedance of the speaker (as near as possible) to the output tap of the transformer.

This will ensure optimum power transfer between amp and speaker.

[Funk]

Magistrate said:

Funk said:

You'll need to set it to the correct rating for the speakers you eventually buy, that's all. It will be fine handling either option though, but as SG points out (as did I), you'd do well to look at reasonably sensitive speakers.


Although I do feel a little like I'm talking to myself here at the moment.

Thanks Funk.....sorry to be thick and ask again , but I can't see my original question has been answered......If I have 2 identical speakers but the only difference is the ohms, which one would be best 4 or 8 or would it make not a blind bit of difference? It's a hypothetical question, as I know the ohms rating is not the way to choose a speaker, but I'm just interested.

Given that the amp has the facility to handle both, it won't matter. As per others' advice here, I would be looking more at the sensitivity of the speakers; don't worry about whether it's 4 or 8 ohm, but do ensure you set the amp correctly to whatever speakers you choose to use.

[doodlebug]

Funk said:

When talking about ohms, you're talking about the resistance a speaker presents to an amp. If an amp puts out 100w into an 8 ohm load, it will have to put 200w into a 4 ohm load to achieve the same level of output...

Not quite. If an amp puts out 100W into an 8 ohm load, all other things being equal, it will still only have to put 100W into a 4 ohm load to achieve the same output level.

Normally an amplifier rated at 100W into 8 ohms should be able to drive 200W into 4 ohms if it has been designed for that. A 4 ohm speaker will be capable of twice the sound level of an 8 ohm speaker with the same dB/W/m rating. The reason why car audio is invariably 4 ohms is because historically it was easier to get higher power with the limited supply voltage available.

However amplifiers with matching output transformers will not double the output power with halving of speaker impedance because the transformer ensures optimum power transfer to the speaker. So in your case, there will be no difference.

BTW, W is the correct abbreviation for watt.

[tobinen]

Thread resurrection! Rather than start a new post, hopefully this is relevant

I have an old car sub lying around and I am in the planning stages of choosing a home system

Can I use this sub: http://www.hertzaudiovideo.com/wp-content/uploads/...

With this AV receiver? http://www.eu.onkyo.com/downloads/3/1/3/5/9/ONKYO_...

I think I am OK with the resistance, but i am unsure if the amp assumes a powered sub.

Thanks

[OldSkoolRS]

That amp will require an active (powered) sub, which you would connect via the RCA/phono output on the amp. You could use an external power amp like an iNuke 1000/3000/6000 (depending on power requirements) as I do myself to drive 'passive' subs.

Might be cheaper/less hassle just to buy a decent used sub or maybe look up BK Electronics which are UK based direct sellers, well thought of on AVForums.

[tobinen]

OK thanks. I have bookmarked BK's site from another thread on here and certainly being considered. I can't sell this Hertz amp so I was trying to 'recycle'.