4 ohms pseakers on a 8 ohms amplifier ?

[NullMind]

i was lookign to buy a set of B&W 600i to use with my RVD-8090RDS amp., but the speakers are 4 ohms, and the amp is 8 . can that be a problem ? will the speakers work ?

[Scott_Mac]

It is fine, fear not.... they'll just be a more stubborn load.

[indolent]

The speakers will be a harder load to drive and will try to draw more current. This should not be a problem - the ohm rating is always nominal and can be more or less over the musical range.

Your amp will most likely run a bit hotter and if running really loud its possible you could cause the protection circuit to trip if the load is too much - but this is equally true of any speakers.

[Dankeech]

Sure this doesn't sound like a good idea.

The amp is likely to run hot, if you don't have circuit protection you could fry it, and it different volumes and frequencies, the impedence of your speakers will not stay stable so you'll probably find the speaker impedence drops quite a bit below 4ohm at some points.

This sounds like a bad idea, just my opinion. i'm no electrical eng etc though.

hth.

Dan.

[Helicon]

If a speaker tries to draw more current from an amplifier that can't provide it, you could be heading for all sorts of troubles. It's ok if you play them at low/average volumes, but when the going gets tough, something will let go. You'll need an amp nearer the £1k mark to start drive 4ohms properly.

If your car is capable of 0-60 in 7 seconds with a top speed of 120mph, it's physically not capable of doing 0-60 in 4 seconds, and forcing it to do more than 120mph.....

Just an analogy to try and get the point across

[Steve Zodiac]

If your amp is, as you say, rated for 8 ohm speakers; then 8 ohms is the rating of speakers that you should attach.

If the amp could safely take 4 ohm speakers, then the manufacturer would certainly state this somewhere in the specification, because it is an additional selling point.

You'll certainly get sound out of the 4 ohm speakers with your amp, but for how long is another matter!

[Scott_Mac]

Blimey, did no-one check the actual amp before the panic!

It's fine, i used to own one and it briefly ran my Dynaudio Audience 40's! It is actually rated at 6ohms IIRC (and 100W per channel at that) it will run 4 ohm speakers perfectly well and yes it may run a little warmer, but it runs hot anyway and i certainly noticed no discernable difference in heat.

[Steve Zodiac]

Originally Posted by Scott_Mac

Blimey, did no-one check the actual amp before the panic.

Yes, the original poster and owner of the amplifier did! He said the amplifier was rated at 8 ohms.

I also did a quick search and could only find references to using 8 ohm speakers with this amplifier.

[Bee-Man]

The speakers are rated 100W at 4 ohms...

You need to ensure the amp is rated sufficiently higher if you play for music for any decent period of time....not as big a deal for home theatre.

Will the playability be affected. Not a stitch....

This amp is 100W rated at 8 ohms....I would give it a go.

[av-phile]

If the amp's recommended minimum load is 8 ohms, I would strongly suggest you follow that. Ofcourse you can still hear your favoruite materials with such a mismatch. But while you can listen at low volumes, the current draw will still result in inordinate heat dissipation and could even trigger the portection circuit at peak transients. I know some HT set-ups that momentarly lose sound at explostions or loud moments because of the protection circuit engaging momentarily.

OTH, if you're using a subwoofer and has set the receiver's speaker settings to SMALL, this can alleviate the situation. Because low frequencies eat up around 60% of the current, diverting these to a powered subwoofer can free up your main amp to handle less current demanding mids and highs and so can be relatively cooler and taxing at 4 ohm loads. But this is still no gurantee the protection circuit will not engagne at sudden loud burst in some passages.

[NullMind]

i've decided to skip on them, just not worth the risk

thanks everybody

[eureeka]

I'm sorry to hear you've decided to 'skip on them'. I fear you have been yet another 'victim' of scare mongering.
In many cases, a speaker which has a specification of 4 ohms is quoting the nominal load presented to the amplifier.
To understand this better we must invisage a speaker whose minimum impedance is 4 ohms (this is normally at the fundamental resonance of the drive unit in an enclosure).
The impedance then usually rises with frequency (if we exclude cross over componants).
e.g

For a 2 way bookshelf bass reflex speaker (Tweeter, Midrange/Bass and port) with a frequency response of say 60Hz - 18Khz (+/- 3dB), the minimum impedance of 4 ohms would be measured at around 80Hz (the theoretical fundamental frequency of the midrange/bass drive unit).
There will then be a rise in impedance verses frequency (due to the inductance properties of the voice coil). For a midrange/bass driver the maximum impedance could be 100's of ohms depending on where the designer wishes to cross over to the tweeter. Typically though, the average impedance of a 4 ohm system will be around 6 ohms (60Hz-3Khz) then 6 ohms to 10 ohms (3Khz-18Khz) including the cross over.
Yes an amplifier will get slightly warmer when driving a lower load at high volume levels but that is simple ohms law. What we have to look out for here is whether the amplifier driving the system is capable of delivering enough current to sustain high transient signals at the fundamental frequency of the speaker.
These days even the cheapest of amplifiers have built in protection circuits to guard against such eventuallities, but more often than not it is these cheap circuits that cause us the most problems and we often mistake the activation of these circuits as 'clipping'. A well designed (normally found in the upper end of many of our budgets) amplifier will have a protection circuit that is 'stealth' and goes un-noticed when we crank that volume up a bit too much.

[russ.will]

Well said and good first post.

This question crops up regularly and the basics behind it are nearly always misunderstood. An eight ohm speaker is probably only 8ohms once or twice in it's frequency range.

My old Kefs varied between 3.4 and 22ohms depending on the frequency, yet they were still quoted as an 8ohm speaker.

The Original ATC SCM10, a small standmount was an 8ohm speaker, yet a 200w Mark Levinson power and could easily be made to clip driving them.

It's a nominal figuer and is only of any real importance if the speakers sensitivity/efficiency is low. The 600i is quoted as 88dB/w. This is fine. If you're totally lacking power then something in the 91-93dB/w range would be good. The ATCs above were 84dB/w and as such were a complete slayer of amplifiers.

The B&W 600s will be fine. As with all speaker/amplifier combos, use your ears. If it's starting to sound strained, then it probably is, so turn it down. Simple common sense. If you want headbanger volumes then search out some more efficient speakers.

Russell

[eureeka]

Thanks Russ.
I have been watching these forums for many years but untill now I have never really found the need to join in.
Instead of watching I might get a little bit more pro-active.

[vigman]

I've just changed my old beloved 1970 Audiotronic LA4000 amp for a new Marantz PM4000.

The old system ran with B&W 600i speakers and sounded superb. When I connected up the new amp, I was really annoyed at the muddy sound produced. I checked all the obvious things, like +/- connections and then rang B&W. They say the speakers are rated as 4 Ohm and the Marantz amp speaker outputs are 8-16 Ohm. B&W said the Marantz would cut out on the protection circuity if there was a bad mismatch.

However, the 4 Ohm B&W 600i speakers sound terrible on the Marantz....has anyone else experience of this and/or advice, please?

TIA

Vigman (Jon)