Speaker compatibility with AV systems?

[Lobster]

I have a 7.1 surround sound AV receiver, which was actually sold as a

5.1 system (ie speakers included; with the option of adding another pair of rear speakers). I already happen to have a pair of spare speakers from a previous home cinema box which I'm hoping to use, but I'm not sure whether they'll be OK or not, and/or whether I'll blow something up if I try...

The new receiver is an Onkyo TX-SR508; its speakers are labelled 120W 6 ohm. As far as I can tell, that's what the ideal type would be for my rear speakers, but the manual doesn't say much about it.

The old speakers are from a Sony DAV-S500 box; the speakers are just labelled 6 ohms, but the manual mentions that the box has an output of

40W RMS per channel.

What's going to happen if I press the old speakers into use? Will they go pop? Any thoughts appreciated.

(For reference, the Onkyo manual and datasheet are here:

or or df and the Sony manual is here:

Thanks!

[meow2222]

they'll be fine as long as you dont put more than 40w through them. That's assuming these are all rms watts, not some nonsense like pmpo watts.

NT

[John Rumm]

Unless you are a fan of turning everything up to 11, then you will be fine.

[Bert Coules]

They should be fine. I ran an almost identical 7.1 setup for years, only recently replacing the odd rears with new speakers the same make and model as the others. If I'm being completely honest with myself, the audible difference was very, very slight indeed.

[Brian Gaff]

Unlikely to go pop, but they may well be of a different sensitivity to the others in the system. I don't know enough about the Onkyo to know how versatile its gain controls are etc.

Brian

[Brian Gaff]

Besides you will hear problems well before you reach destructive levels as long as large instantaneous sounds like clicks or feedback are avoided. Brian

[RobertL]

Also you will need to check the phase; you can't always rely on the +/- convention being the same IME.

To check the phase, undo one LS cable conect a 1.5 battery onto the speaker the same way as the cable was (+ for +, - for -). Note which way the bass cone jumps. All the cones should respond in the same direction.

Robert

[Martin Brown]

Only if you wind the wick right up or play pure sine waves through them. Most likely you will blow the fuse in the lower rated speaker if you try to drive it too hard. 120W x 5 is already very loud!

Their power handling isn't as high as the new ones but all impedances of loudspeakers are all pretty nominal and frequency dependent. It would be a terrible design of power amplifier that was so tetchy as to misbehave with other nominal 6 ohm speakers. I'd expect 4 ohm and 8 ohm ones to work but not necessarily with matched output (which might be an issue if the old ones are radically different efficiencies to the new).

[Syd Rumpo]

RMS watts, whassat then? I know it's what many people use, but it's a rather nonsensical measurement. Continuous average power is the one.

That said, the advice is sound. (Geddit?)

Cheers

[george]

Why is it? Explain the reasoning.

[Syd Rumpo]

It would take more than a couple of minutes, but briefly, the RMS _voltage_ of a varying waveform, squared and divided by the load resistance gives you the long term (as in non-instantaneous) power. An RMS calculation using _power_ gives a value which is not useful as it doesn't represent the long term power (heating effect) and is waveshape dependant.

Google for RMS power and you'll find many better explanations, it's a well-known electronics canard.

Here's one...

Cheers

[Dave Plowman (News)]

Really? I've never come across any speaker which doesn't. Cone moves outwards with DC connected as marked.

[george]

Surely a speaker rated at xxRMS power is rated for continuous sine wave equivalent power.

[Syd Rumpo]

One would hope that a reputable manufacturer really means 'continuous average power' when they quote 'RMS power', but as the latter has little useful meaning there's plenty of wriggle room.

Being cynical, it makes me wonder why they often don't use the correct term.

Cheers

[Martin Brown]

No. It absolutely isn't and doing that for any length of time will destroy it at certain resonant frequencies much like the wine glass and the opera singer. The speaker coils will make a nasty grating sound after their mounting fails - perhaps OK for heavy metal bands.

It will tolerate a pure tone for a short while in music but at full power with a continuous sine wave you could easily do permanent damage in tens of seconds (and maybe quicker if you are unlucky).

Certain assumptions are made about the nature of music in the design of loudspeakers and one of them is that real instruments have harmonics and that notes have a finite duration.

[Dave Liquorice]

Nor me but why faff about with batteries and removing grills (if you can) to expose the woofer when your ears will tell you about phase problems.

[Dave Plowman (News)]

Can be more of a problem with surround systems. But likely doesn't much matter anyway. ;-)

[Dave Liquorice]

Might not be immediatly obvious with surround coding that uses phase like, Dolby Surround. But 5.1 should be 5 discrete, full bandwith, phase coherent, channels and the .1 LFE channel(*). I find out of phase speakers most unpleasant, the sound whacks me around or inside my head rather than being away from it.

(*) Debateable if this is required to be phase coherent with the 5 main channels as it should only be carrying LFE (Low Frequency Effects). The LFE signal ought not be mixed into the main channels. How ever what happens in the real world is another matter so it would be wise to have it phase coherent.

[Lobster]

On 19 Mar 2015, John Rumm grunted:

Thanks, all: the 7.1 system seems to be working well. The relative volume of the old and new speakers is fine, and to my not-particularly-discerning ear at least, I really can't see I'll gain anything by replacing the old speakers with matching ones.