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Loudspeakers - help !

shermans
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Registered: 07-09-2007

Loudspeakers - help !

I really do not know what I am doing.  I use my pc to play music through an external, quality hi-fi system which has a pair of good quality speakers attached.
A couple of years ago, I found some old car radio speakers which I decided to hook up in parallel to the hi-fi speakers, and run them into the kitchen.  The hi-fi amplifier controls the volume, so it is the same level on all four speakers.
So far so good.  However, one of the car radio speakers has started to rattle badly.  Now I do not know if that is due to old age or due to damage - I do not play music particularly loud, but maybe the kids did when I was out, but they are not admitting it.
Anyway, I want to get some new ones but I am in a complete fog about the technical detail.  If I am listening seriously, then I would do so through the hi-fi speakers.  The kitchen ones are more for background listening.
They should not be big and I have been looking on E-bay for some, and seen several which look as if theyt are suitable.  But what I do not know is how many Ohms to go for.  What about RMS and power ?  What about Db which I am told is the most important.  And cross-over ?  Woofers and tweeters ? And then I have seen 100v / 8 Ohm switches Huh?  I wish I had never started, because I am so confused.
Can anyone offer some simple, sensible advice as to what I need just to be able to listen to some music without damaging anything ? Embarrassed
Thanks.
10 REPLIES
Moderator
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Registered: 14-04-2007

Re: Loudspeakers - help !

Your Hi-Fi system manual or the back of your current Hi-Fi speaker should tell you what RMS output power the amplifier is per channel. It should also tell you what the best loading is, that is Ohms per channel.
You are then looking for a set of speakers rated accordingly. For example if the amplifier is 50 watts RMS into 8ohm per channel then you are looking for speakers rated at greater than or equal to 50 watts RMS and 8 ohm.
Db is not something to be considering as it comes as standard with the setup.
The crossover is built into the speaker and not seen by the user....forget that.
Woofers are the drive units that reproduce the 'bass' (low frequency) sounds, the tweeter reproduces higher frequencies, the treble sounds.
Good speakers have at least one of each in the box.
100 volt speakers are the sort usually found in so called Tannoy systems and not suitable for domestic Hi-Fi.
Speakers are very much a personal choice and listening before buying is a good idea....more difficult in your case I appreciate.

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Plusnet Alumni (retired) orbrey
Plusnet Alumni (retired)
Posts: 10,540
Registered: 18-07-2007

Re: Loudspeakers - help !

if it's just for listening in the kitchen and you aren't too fussed about the quality I'd consider getting a cheap pair of bookshelf speakers second hand. If you also pick up a speaker switch box - you should be able to get one from somewhere like maplins for a tenner or so - you shouldn't need to worry about impedance or anything like that either.
Well worth checking ebay, local forums/gumtree online in your area, local papers or even for sale boards in supermarkets and what have you.
Hope that helps,
VileReynard
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Re: Loudspeakers - help !

Since your 8 ohm speakers are in parallel, your amplifier sees a notional 4 ohms.
This shouldn't matter - I ran 100W/channel into two pairs of 50W speakers (separate rooms) for years.
I used a mains switch in the speaker cable to be able to switch one pair off when they weren't required - this might cause damage!
Try to get speakers of roughly the same sensitivity.

shermans
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Registered: 07-09-2007

Re: Loudspeakers - help !

Thanks guys
All I can find is 45 Watts per channel and 8 Ohms on the hi-fi.
I have found that most of thge speakers I would like (ceiling speakers) are only 4 Ohms.  Will that matter providing I keep the music at adult level, not teenager lvel ?  I can obviously get an impedance switch to control the volume on the extension speakers, but previously the volume was fairly equal, so if I do not have to do so, I would prefer not to as finding somewhere suitable to instal it would be difficult.
Community Veteran
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Re: Loudspeakers - help !

When I looked into this in days of yore (I built my own Warfedale Unit 5 speakers - about 4 feet high with a 12"base speaker if I remember correctly) I think that one effect of using a lower resistance speaker was that the bass needed to be cut back otherwise everything vibrated.
However with a modern compact speaker with piddly little domes I can't see that being a problem
Moderator
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Re: Loudspeakers - help !

The PA rig I drove as a roadie had 1Kw for the mids / highs and 2 Kw for the bass bins but that's probably overkill here. Lips are sealed

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VileReynard
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Re: Loudspeakers - help !

It's ages since I "did hi-fi" - but don't all car systems tend to go for 4 ohm speakers - possibly due to being limited by the 12V supply?

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Re: Loudspeakers - help !

1 Megawatt into 4 ohms per channel according to the stuff that parks outside my office window occasionally Angry

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Community Veteran
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Registered: 02-10-2008

Re: Loudspeakers - help !

Many hifi amplifiers now have facilities for two sets of speakers - does yours ?.
Denzil
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Registered: 31-07-2007

Re: Loudspeakers - help !

Car speakers are usually 4 ohms. Your amplifier might be OK with that, but it depends how it was designed. It would be better to use domestic 8 ohm speakers, as they will put less stress on the amplifier. The power handling doesn't really matter in most cases. You are never likely to use anywhere near all 45W. Cheap  amplifiers can damage speakers through distortion and clipping at high volume levels before they get to the rated power. By the sounds of it you are not going to go that loud anyway.
Two sets of 8 ohm speakers on the same terminals will look like a 4 ohm load to the amplifier. Most amps will be happy with that, but it would be better still if the amp has two sets of speaker terminals, usually marked A and B, with a switch on the front to select between them, although you might not be able to get both at once that way.