Impedance matching - how important?

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floydbloke

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#73082 8-Dec-2010 20:26

My Philips 5500D all-in-one home theatre unit has gone kaput.

I'm thinking of replacing it with an AV receiver, with a view to eventually acquire a 3D player an TV.

I'm also intending, for now at least, to keep the existing speakers. I'm not exactly a purist or audiophile and to me they sound good enough.

Obviously one thing I'd need to keep in mind is the power rating, the output of the amp will likely exceed what the speakers are rated at, I'll make sure I don't turn it up too loud.

My question is around impedance matching. The speakers are 4ohm and the one amp whose specs I've checked out is 8. Is this likely to cause any issues? Distortion, cut-outs, or anything like that.

Did Eric Clapton really think she looked wonderful...or was it after the 15th outfit she tried on and he just wanted to get to the party and get a drink?

floydbloke

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#414958 9-Dec-2010 12:25

After trying the lazy-man's way first by asking here I thought I'd better go and do some research myself.

Came across this:
http://www.the-home-cinema-guide.com/speaker-impedance-matching.html

Based on that I think I'll risk it. I can put up with a little distortion and I figure that the ouput power of the amp is likely to exceed the power rating of the speakers substantially. Also, I won't be turning it up particualrly loud so risk of overloading the amp is minimal.

Did Eric Clapton really think she looked wonderful...or was it after the 15th outfit she tried on and he just wanted to get to the party and get a drink?

xarqi

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#414962 9-Dec-2010 12:30

Edit: (Ha! I was typing as you were posting)

No replies, huh?
I'll take a swing at it then. This way, if I write something stupid, those who are in the know will descend on the thread to correct it!

Ideally, you should get an amplifier that is rated for the impedance of the speakers. Any amp can safely drive any speakers with higher than its rated impedance, with some loss of volume.

Problems can potentially arise where an amp is called upon to drive speakers with lower than its specified impedance rating. This is the situation you are in.

What happens there is that the lower impedance results in higher current flow, and that results in greater heat being generated in the amp. This in turn may either trip a thermal overload mechanism in the amp (a good thing), or reduce it to a smouldering pile of molten slag in the charred ruins of your house (not so good).

That said, this overheating will occur to a much greater extent when the amp is called upon to deliver high power levels to the mismatched speakers (i.e. when the volume is turned up high). If you don't do that, you may be perfectly safe, but it's your call.

Me, I'd look to have proper matching. Being somewhat "old school" perhaps, I'd be looking for 8 ohm speakers rather than an amp that could drive 4 ohm speakers.

Dunnersfella

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#415177 9-Dec-2010 18:08

As a 'heads up'...
I'm picking you have a passive sub woofer as part of your Philips system? By that, I mean that it won't have a seprate power supply you need to plug into the wall.
If so, you should know that a new AVR will require a powered sub.
So you'll need to buy a new sub.
And, for the record, you'll find entry level Yamaha speakers etc, that come as 5.1 packs... that include a sub (well more of a powered bass speaker) for around $400 - $500. Meaning buying a new sub would ALMOST be a false economy. Why not buy a new 5.1 setup than just a subwoofer?

Having said that, ultimately, a sub from the likes of Velodyne would be a very nice addition :-)

floydbloke

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#415219 9-Dec-2010 19:41

Many thanks for the good advice. Re-thinking my options now.

Did Eric Clapton really think she looked wonderful...or was it after the 15th outfit she tried on and he just wanted to get to the party and get a drink?

Jaxson

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#415378 10-Dec-2010 08:37

floydbloke: the ouput power of the amp is likely to exceed the power rating of the speakers substantially.

Yeah the risk it part makes me laugh a bit, so please video it at least to share with the group if it all goes south in a hurry.

As Dunnersfulla says, your home theatre in a box unit won't have a powered sub, so you'll be spending and risking a bit on a receiver and then probably a sub just for the sake of the existing speakers. For the cost of a receiver alone you could buy some complete home theatre in a box systems so might really be worth the upgrade.

Typically you want to pair higher power rated speakers with a receiver, not necessarily the same rated value. All hell breaks loose current wise (as xarqi alluded to) when a speaker reaches it's maximum travel (clips) so the idea is to ensure this doesn't happen. So point is "power output of the amp is likely to exceed the speakers" is not really a good thing.

Dunnersfella

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#415405 10-Dec-2010 09:48

I'd suggest that there would be some better solutions than just a home theatre in a box replacement...
Look for some of the end-of-line amps - they may not be 3D compliant or feature full iPod integration - but they'll work just fine.
Then pair it with a good deal on speakers (whether it's satellites, or a floor stander / stand mount combo) and you could surprise yourself price wise.

Flick the choices you have up on the site, and we can give you the run down if you like.

elldizzle

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#415804 11-Dec-2010 10:19

Jb-HI-FI is always a great place to start when looking for entry level receivers and 5.1 speaker combo's.....

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Dunnersfella

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#415833 11-Dec-2010 11:54

Actually, I just looked at your original post, and you've stipulated that you're looking to end up with a 3D player + TV...
So make sure the new amp you buy is capable of carrying the 3D video signal and HD lossless audio via HDMI. If you listen to quite a bit of music, get floor standers up front... if budget allows.

richms

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#415889 11-Dec-2010 15:27

The philips speakers will probably be a nasty one way design or non matched crossover, with matching correction before the amplifier in the dead unit. (mum got a philips cheap stereo with flybys that has decorative tweeters, so I have zero trust in them having real tweeters on them)

Chances are that you will hook it up to an amp with a flat response and it will sound something like a speakerphone as you dont have the equalization needed to correct the speakers response.

4 ohms is prettymuch the norm for speakers, since it means that for any given input voltage they get twice the power so can fudge the sensitivity figure up by 3dB - any amp that doesnt do 4 ohms is in my opinion somewhat suspect.. Some will only 2 8 ohms if you use both the A and B terminals on them since they are just in parallel, but thats of no concern to you unless you want to hang a second pair of front speakers off the amp.

Richard rich.ms

floydbloke

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#416092 12-Dec-2010 11:26

Thanks all for the good tips.

Budget is a factor, hence my intention to re-use the original speakers. Although it was an all-in-one package set-up, it certainly wasn't cheap cheap.
I guess I need to look for an amp that will allow me to select 4ohm speakers and for future-proofing have HDMI 1.4 support. That still leaves me with the sub-woofer issue though.
Alternatively, I might do nothing for a while and have a big spend-up in about 18 months time including amp, speakers, 3D TV and player. That also gives me a chance to see where the whole 3D TV and movie thing is going in NZ (if anywhere) and re-evaluate.

Did Eric Clapton really think she looked wonderful...or was it after the 15th outfit she tried on and he just wanted to get to the party and get a drink?

elldizzle

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#416108 12-Dec-2010 12:15

Sounds like a good plan to me. Imo it's always best to wait and get something you really want and can afford. Than to rush into getting something, then regret it in the long run..