Weird question about impedance

[revans]

Okay this is either really stupid or not, but probably the former methinks.

I'm putting together some speakers which I want to have an impedance of 4 ohms. Now I only want one speakers per stereo channel so I'm limited to using 4 ohm speakers, which is annoying.

However, I know that you can use two 8 ohm speakers wired in parallel to reduce the overall resistance to 4 ohms. Using this method Would it be possible to wire an 8 ohm resistor in parallel with one 8 ohm loudspeaker to reduce the resistance to 4 ohms without having to use two speakers? Just an idea.

[sreten]

Hi,

It is possible but completely pointless, there is no reason at all
why the 4 ohms load would be better than 8, in fact it is worse.

4 ohm speakers are common in MTM form, less so 2.5way TMM.

http://www.eldamar.net/audio/RS150MTM/

http://www.zaphaudio.com/BAMTM.html

/sreten.

[SY]

With the resistor in place, your amp will work harder and the speaker will play no louder. All you will have done is generate heat for no return in sound.

Understand a piece of reality: there's no such thing as a "4 ohm driver." This is purely an invention of marketing departments. The impedance of any speaker varies wildly with frequency- your "4 ohm" speaker might have an impedance of 50 ohms at resonance, 3 ohms at DC, 20 ohms at the high treble.

[revans]

So supposed "4 ohm" speakers will not be any better with my amp6-basic than "8 ohm speakers"?

[janneman]

4 ohms speaker will, generally speaking, have an average impedance lower than 8 ohms speakers. It does not mean they will play louder, that depends on a lot of other things like sensitivity and the type of enclosure. But the 4 ohms does load the amp more. So, if you have 8 ohms speakers, there's no reason to change them for 4 ohms unless you have a specific type of 4 ohm speakers that does what you want and the 8 ohms doesn't.


Jan Didden

[Buckapound]

Your Amp 6 will sound perfectly lovely with 8-ohm speakers.

Using two 8-ohm speakers in parallel will give you more sound, but obviously this adds to cost, size and complexity.

Hook that amp up to some borrowed 8-ohm speakers and you'll see how great the sound is. No point in going out of your way to get 4-ohm drivers. If you're concerned the tiny amp won't play loudly enough, it might be worth looking at the driver's efficiency, though. I can't recall the figure (3 dB = 2x power?), but just a few dB increase in efficiency is like having a much more powerful amp.

--Buckapound

[sreten]

Originally posted by revans

So supposed "4 ohm" speakers will not be any better
with my amp6-basic than "8 ohm speakers"?

Hi,

Real 4 ohm speakers will match better as the extra power drawn
is used in one fashion or another, e.g. in a MTM with 8ohm drivers
it drives the extra driver.

If you have a 8ohm MT that is say 84dB/W (2.83V - 8ohm), if you
use the same drivers for a MTM you get 90dB/W (2.83V - 4 ohm).

The reality is its actually 90dB per 2 watts as its 4 ohms but this
is still 3dB per real watt higher than the MT, box is twice the size.

Power output:
2 x 9 watts (4 ohms @ 0.04% THD+N),
2 x 15 watts (4 ohms @ 10% THD+N),
2 x 10 watts (8 ohms @ 10% THD+N)

The implied suspicion is that its around 6 watts into 8 ohms clean.
If you add an 8 ohm parallel resistor it goes down to 4.5 watts.

So making 8 ohm speakers 4 ohms with a resistor will draw more
power, 9 watts, but you will only use half, 4.5 watts. So you in
fact makes things worse, not better, and tax the power supply.

If you are using batteries 8 ohm loading is the better choice.

/sreten.

[Mooly]

Originally posted by SY
With the resistor in place, your amp will work harder and the speaker will play no louder. All you will have done is generate heat for no return in sound.

Understand a piece of reality: there's no such thing as a "4 ohm driver." This is purely an invention of marketing departments. The impedance of any speaker varies wildly with frequency- your "4 ohm" speaker might have an impedance of 50 ohms at resonance, 3 ohms at DC, 20 ohms at the high treble.

Quite so, my B&W's are called 8 ohm speakers yet the manufacturer freely admits in the brochures "Impedance minima 3 Ohms" How on earth you can call that a nominal 8 ohms is beyond me --maybe it's over a very tiny frequency range.

[myhrrhleine]

Originally posted by Mooly

Quite so, my B&W's are called 8 ohm speakers yet the manufacturer freely admits in the brochures "Impedance minima 3 Ohms" How on earth you can call that a nominal 8 ohms is beyond me --maybe it's over a very tiny frequency range.

Such is the meaning of the word.
▸ nominal: adjective: being such in name only

[Mooly]

You going to tell 'em or me