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MG Midget and Sprite Technical - Speaker matching

If replacing speakers - 'cos the cones in the old ones are damaged - is it important to match the same output as the originals?
The old speakers are marked as 15W 4 ohms. I have some good new ones but they are 60W and 2 ohms. On a trial hook up they seem to work well, but what is the effect of the changes? Will it damage the radio/CD unit?

Guy
Guy Weller

2 Ohms is a bit low and depending on the set may mean it puts through too much current.

I guess it would be a problem if you had four speakers (two per channel)and turned it up quite load.

If only two speakers in total probably not too much of a problem!

eddie
Eddie Cairns

Just don't max out the amp, the flat line will do your speakers in, otherwise just go with it.
Brad (Sprite IV 1380)

Guy you could really do to know the output of your CD/Amp

This will be expressed such as 20W @ 4ohms

If yours is expressed as that it will mean that if you load your CD with speakers of only 2 ohms then effectively your amp will be able to diliver twice the power say 40W

If this is enough to overload the amp then you will soon hear it as distortion and will soon turn down the power anyway

From the speakers point of view the situation is the same

The same rules apply, when the speakers are overloaded then you will hear the distortion and turn it down.

Use them and if they are distorting at the volume levels you require then buy some higher powered stuff.
Bob Turbo Midget England

OK,
So the lower ohms on the new speakers means that it needs less power from the amp to work them. And conversely they will overload and distort if the amp is turned up too high?

And the fact that the speakers are 60W compared to the original 15W doesn't come into it? I thought that the higher Wattage meant that they would handle more power although that isn't the objective.

I will check on the car next time I see it and see if it has more than the two door speakers, and what output the amp is rated at.

Thanks.

Guy Weller

They will handle more power guy, but how did your old speakers perform

Lets not get too technical so as you rightly say when you hear distortion, that will be that. Extended periods will cause damage.
Bob Turbo Midget England

Not played with this sort of thing for a while but I seem to remember that amps have a minimum speaker impedance (ohms) that they are designed for. If you go lower than that you're partially shorting the amp out & will force more current through the output stage of the amp, possibly leading to it overheating. Think the rule of thumb was that it is no problem to have higher impedance speakers, but not lower.
However if you put them in series, their impedances add, and in parallel they divide. So 2x 2ohm speakers in series = 4 ohms load on the amp, 2x 2ohm speakers in parallel = 1ohm load on the amp.
Having said that if you keep the levels low, I think you'll get away with it, but an open top midget isn't the quietest environment...
As others have said, if you hear distortion, change the speakers! I don't think you'll damage the speakers but you could damage the amp in your radio.
-Craig
C Robertson

>>If yours is expressed as that it will mean that if you load your CD with speakers of only 2 ohms then effectively your amp will be able to diliver twice the power say 40W


This would be the case if the output stage of the amp had no internal resistance (which it has)... I'd expect no more than (guess) 10% more power using 2 Ohm speakers.

But you will have more sound-pressure for a given volume level on the pot, until the amp begins to saturate/distort excessively. (Assumes of course that the speakers produce the same sound-pressure for power in, i.e. they are equally efficient.)

But as stated above/below, if you use them with discretion there will be no problem.

A 60W speaker can handle more power in than a 15W speaker (assuming they are both rated RMS power rather than 'peak' or 'music' power, which are rather meaningless). Given the same power-in, and assuming equal efficiency, they will both be as loud. But remember you need 10X sound-pressure to make a noise twice as loud (as the ear has a logarithmic response).

Didn't mean to make post this long...!

A
Anthony Cutler

Thanks for the replies but this is getting too technical for me! Bob had it about right when he said if the speakers distort when turned up loud, then turn the volume down again. I can cope with that!

It isn't on a Spridget, and it isn't my car. The old speakers were damaged - tears in the paper part of the cone in one and the other one was buzzing at quite low volumes. But we do have these spare speakers. They seem to work OK so I just wanted to know if there was likely to be a long term problem.

If low impedance speakers are likely to damage the amp unit, would adding a resistor to the circuit somewhere help?
Guy Weller

Good explanation here if you're interested enough.

http://www.prestonelectronics.com/audio/Impedance.htm
Jordan Gibson

How did I know Ant would not be able to resist the full tech job!! LOL well done Ant nice one!!
Robert (Bob) Midget Turbo

But, darn it, after reading pretty much the whole site linked above (Preston Electronics, which is really well written, by the way), I couldn't find the answer to Guy's question, and now I am intrigued about it too because I CAN'T remember from my school days:

Is adding a resistor in series with a speaker ok to make the 2ohm speakers look like 4ohms to his amplifier, or will that cause another problem?

I mean, sure, electrically it makes sense (series 2ohm + 2ohm = 4ohm), but I think I am missing something. Maybe it is the necessary current capacity of the resistor (need, like a 50W resistor = a very large resistor, and a lot of heat)? Or, would using a resistor in series change the efficiency of the speakers so that the volume becomes really low)?


Norm
Norm Kerr

Adding a 2 Ohm resistor will make the amp see the right load. But... you're now dissipating the amp's power into the speaker and the resistor (which will make no sound); plus you will need to use a resistor that can take the same pwoer as the speaker...

... so I wouldn't bother with the resistor; and as Bob says, be careful to make sure you're not driving the amp into distortion, and it should be ok.

A
Anthony Cutler

Fitted them today. And one can turn the volume up to almost unbearably loud without any apparent audible distortion to the sound - except the volume that is!

At "normal" listening volumes they seem fine and much clearer than the old speakers ever were.

Thanks for the advice. That Preston Electronics site is particularly clear. Thanks Jordan.

Guy
Guy Weller

Guy
You are welcome to try my method regarding speakers.

(1)Fit one very loud exhaust
(2)wind window down
(3)throw stereo and speakers out of window

Enjoy that exhaust note
Rob Newt

(1)Fit one very loud exhaust
(2)wind window down
(3)throw stereo and speakers out of window

Robert...Do you mean like in this video...LOL

http://www.youtube.com/watch?v=5BaR1Kc62Pk


Prop

Prop

Thats what you call a musical note Prop, Mine does not sound quite like that.
Rob Newt

The best bit is the car is French and is playing the National anthem!!!! :

Robert (Bob) Midget Turbo

This thread was discussed between 03/02/2010 and 07/02/2010

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