DB and Ohms..
 

Can someone explain DB rating and ohm rating in Lehmans terms?

So I just bought some Focal 1038be and they are rated at 93db which is “efficient” and 8ohm nominal impedance.

In Layman's term, the higher the dB rating, the less power it takes to make the speaker reproduce sound from the amplifier at a certain sound pressure level, expressed as "SPL".

So a 93dB rating means that the speaker will produce 93dB SPL for each 1 watt from the amplifier when measured 1 meter away from the speaker.

(If the rating is expressed as 93dB/1W/1M and not 93dB/2.83V/1M axial as that is a bit misleading.)

The difference in sensitivity quickly becomes relevant with higher levels of playback and/or big rooms and distance from the speaker.

So to listen twice as loud, we need four times the power from the amplifier. Twice as loud is only 6dB more in SPL terms... So it eats up amplifier power very quickly.


The nominal ohms in the speaker's expressed DC resistance and AC reactance. Basically, you want lower impedance for solid state amps (but not too low for most, so around 4 ohms is good) and you want the 6 ohms or higher, more like 8 ohms for tube amplifiers since they like that better.

Typically the nominal impedance means the speaker impedance shall not drop below the 80% of that number. So an 8 ohm speaker will be 6.4 ohms over the frequency range of the speaker (-10dB points at most).

This is as simple as I can explain it. There is much more to it if you want to know and I can provide some links.

Thank you!

So with my McIntosh MC402 I am currently using the 8ohm taps, should I switch to the 4 ohm taps for these Focals?

It will not hurt anything if you try but I think you are good with 8 ohms. An 8 ohm "nominal" speaker, by the international standard, shall remain at 80% of the nominal or 6.4 ohms in the frequency range it can reproduce (down to -10db points at extremes). Also one needs to keep in mind the impedance will also rise drastically and especially around the lower octaves/bass frequencies of a typical speaker.

Switching taps from 8 ohms to 4 for example will yield a slightly louder output to the speaker overall and sometimes the slight increase in loudness is interpreted as a "better sounding tap" when in reality it would take a careful listening and evaluation of the overall response of the speaker across the whole frequency spectrum. The bass articulation, the midrange changes as well as even the slight effect it may have on the upper end of the spectrum or the "highs".

I suggest you play your favorite music and pay attention to the overall presentation. Whichever tap brings you closer to music or puts a bigger smile on your face is your tap. It doesn't have to be technically right, it just has to be right for your ears. :music:

Exactly. :thumbsup:

Excellent, thank you very much for the explanation.

I can’t damage the amp or the speakers by running the 4ohm taps? It appears McIntosh engineered the amp to run the same wattage at 8, 4, and 2 ohms.

No you will not. The autoformer in the MC402 maximizes power transfer between the amplification output stages and your speaker as the typical solid state amplifier will typically be half as powerful going into 8 ohms as it is into 4 but not with the McIntosh autoformer. So the McIntosh is comfortable driving a 2 ohm load as it is an 8 ohm.

Great explanation Serge!

To the OP, when you change taps from 8 to 4 ohms you will need to increase the preamp volume 3 dB to compensate for the output level difference. A lot of people don’t do this and think the 4 ohm tap sounds worse.

It’s fun to experiment with this to see which taps work best for your speakers.

You have a very nice speaker. :thumbsup:

The Focal 1038be has a nominal impedance of 8 ohms. I would definitely stick with the 8 ohm impedance which is the impedance Mac would recommend.

Many folks like to take a speaker rated at 4 ohms and use the 8 ohm tap. Mac does not recommend doing this because with an inefficient speaker, it can over stress the amp and decrease its longevity. When you take a 4 ohm speaker and use the 8 ohm tap you create a larger more dynamic amp at the expense of longevity.

Best

Charles