cutting down from 8 ohm to 4 ohm

terteliu · 7th May 2011, 08:29 PM

I would like to cut down from 8 Ohm to 4 ohm, an the reason would be:

My amplifier is technics A800 mk2, and the current speakers are visaton starlet, a project that I've recently done, with the help from previsious posts.

Booth speakers have 7.2 ohm measured with a digital multimeter (not eight like the original project, i've done the crossover slighty different)

I think that cuting to near 4 ohm, would not damage the amplifier, and the speakers would sound louder on this same amplifier.

The problem is that I've calculated on a paper several times the resistence, adding the crossover components resistance, and my value should be close to 2 ohm, not 7.2 with is measured.

My thinking was to lower the resistance by changing the mid from 8 ohm to a 4 ohm driver, based on the fact that in all 4 ohm systems, presented in visaton site, the bass and high frequences drivers have 8 ohm, and they use two 8 ohm mid in parale, after the crossover.

Why is not three 8 ohm speakers in paralel, have a total resistance of 2 ohm? What is the piece that is missing from my judgement?

DF96 · 7th May 2011, 08:44 PM

A digital multimeter measures DC resistance. This is not the same as AC impedance, although for a typical loudspeaker they may be in the same region for part of the audio spectrum.

cliffforrest · 7th May 2011, 08:51 PM

"Why is not three 8 ohm speakers in paralel, have a total resistance of 2 ohm? What is the piece that is missing from my judgement?"

As DF says, there is a difference between DC resistance with a meter and the driver's IMPEDANCE over the frequency range of interest.

You may also be trying to be too precise! (8R)/3 = 2R6 by calculation. In the world of speakers and crossovers that is really quite close to 2R.

Unless I misunderstand your point ... It is a safe bet that your English is better than my Romanian!

terteliu · 7th May 2011, 09:06 PM

LOL, only now I see that I compared two completely different things.

If I change the mid from 8 ohm to 4 ohm, the power over it would be double, and the bass and mid will have half. Isn't it?
I thing I will change the amplifier.

DF96 · 7th May 2011, 10:15 PM

I am no speaker expert, but I know enough to realise that any change will have knock-on effects. Simply changing a driver from 8R to 4R means a redesign of the whole thing.

terteliu · 10th May 2011, 08:14 AM

I've changed the amplifier, problem solved, thanks

7th May 2011, 08:29 PM	#1
terteliu diyAudio Member Join Date: Mar 2011 Location: Bucharest	cutting down from 8 ohm to 4 ohm I would like to cut down from 8 Ohm to 4 ohm, an the reason would be: My amplifier is technics A800 mk2, and the current speakers are visaton starlet, a project that I've recently done, with the help from previsious posts. Booth speakers have 7.2 ohm measured with a digital multimeter (not eight like the original project, i've done the crossover slighty different) I think that cuting to near 4 ohm, would not damage the amplifier, and the speakers would sound louder on this same amplifier. The problem is that I've calculated on a paper several times the resistence, adding the crossover components resistance, and my value should be close to 2 ohm, not 7.2 with is measured. My thinking was to lower the resistance by changing the mid from 8 ohm to a 4 ohm driver, based on the fact that in all 4 ohm systems, presented in visaton site, the bass and high frequences drivers have 8 ohm, and they use two 8 ohm mid in parale, after the crossover. Why is not three 8 ohm speakers in paralel, have a total resistance of 2 ohm? What is the piece that is missing from my judgement?

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7th May 2011, 08:44 PM	#2
DF96 diyAudio Member Join Date: May 2007	A digital multimeter measures DC resistance. This is not the same as AC impedance, although for a typical loudspeaker they may be in the same region for part of the audio spectrum.

7th May 2011, 08:51 PM	#3
cliffforrest diyAudio Member Join Date: Sep 2004 Location: UK	"Why is not three 8 ohm speakers in paralel, have a total resistance of 2 ohm? What is the piece that is missing from my judgement?" As DF says, there is a difference between DC resistance with a meter and the driver's IMPEDANCE over the frequency range of interest. You may also be trying to be too precise! (8R)/3 = 2R6 by calculation. In the world of speakers and crossovers that is really quite close to 2R. Unless I misunderstand your point ... It is a safe bet that your English is better than my Romanian!

7th May 2011, 09:06 PM	#4
terteliu diyAudio Member Join Date: Mar 2011 Location: Bucharest	LOL, only now I see that I compared two completely different things. If I change the mid from 8 ohm to 4 ohm, the power over it would be double, and the bass and mid will have half. Isn't it? I thing I will change the amplifier.

7th May 2011, 10:15 PM	#5
DF96 diyAudio Member Join Date: May 2007	I am no speaker expert, but I know enough to realise that any change will have knock-on effects. Simply changing a driver from 8R to 4R means a redesign of the whole thing.

10th May 2011, 08:14 AM	#6
terteliu diyAudio Member Join Date: Mar 2011 Location: Bucharest	I've changed the amplifier, problem solved, thanks

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