Any other reason for using 4 ohms version of driver other than power ?

[thinker10]

Aside from more power.

Would they sound quite same ?

I am asking since some KIT are available sometime in both version.


Thank You

[Kent Smith]

I can't think of any other reasons. But I can come up with reasons to stay with 8 Ohms!

1. Ohmic losses of interconnects and cables have more effect on 4 Ohm loads.

2. Amplifier distortion increases at lower impedances.

[LightwaveDude]

Not to take over the thread, but what advantages do lower impedance speakers have?

I know they will draw more power, but does that mean more output? I thought I heard somewhere, maybe from an uninformed place, that efficiency of the driver is independant from the impedance rating... so doesn't that mean at the most a 4 ohm driver would only produce 3 db more output than the same 8 ohm driver because the power is double. That seems to be very little gain.

Is this correct?

[Tenson]

Sounds about right. It is a small gain, but then the same goes for getting an amp with double the power. People still do it.

I am going to get a 4Ohm driver for my bass woofers as it means I can get 500watts far more easily. At peak levels, 3dB more headroom makes a noticeable difference as things are not pushed as hard.

[redunzelizer]

There even is a chance of having real bad luck with 4 ohm version in comparison to the "same" driver in 8 ohms.

1.) Look at the "Force Factor" B*L
a 4 ohm coil will have to have thicker wire (for lowered resistance), at the same time less windings fit into the gap of the motor. Common solution with many driver designs is: make the wire "a bit thicker" and at the same time apply fewer coil windings.

Bummer, you just lowered the B*L for a given motor design, so your amp will draw more current, but that current will interact lesser with the given magnet. Power efficiency increase anyone? *Might* happen, but might *not* happen, or even be lowered. Look at the data most carefully.

2.) Resulting from 1.) with that changing B*L:
your Thiele-Small params will differ. Sometimes this would even make an exchange of 8/4 ohm speakers within a given, serious enclosure design impossible, often unreasonable at least.


3.) Slightly differing mechanical properties:
the 4 ohm coil compared to the corresponding 8 ohm coil version sometimes show tiny but nasty differences in former height, winding height (X-max) and joints/glueing and soldering or connection wires. Many drive manufacturers, in case they offer two impedance versions of one driver model will have to buy from existing supplies. Thus the 8 and 4 ohms coils used not always will be intentionally built for true interchangabilty. Many are close, even closest, but most still not equal.

These differences often show in a shift of break-up nodes, both in frequency and magnitude. Again a close look at the data or picky measurements can show if the manufacturer of your choice did his homeworx.

4.) When using multiple drivers of one type in an array or some beefed up multi-woofer design, you will be more happy with driving two high impedance drivers in parallel, than with two low impedance drivers in serial configuration.

The risk of serial operation (with woofers) is that in general one is loaded *slightly* different from the other, thus you cannot any more rely on a 1:1 voltage divider. Even worse, in case one of the two (serial) drivers is somewhat blocked or hindered, it's impedance peaks will lower (and/or shift) and the other one will get way more than half the power, up to almost full power at it's own resonance impedance peaks. Solutions like these call for 8/12/16 ohms

5.) Most amps don't like delivering current at all. They don't like high voltage slew either, but in case of low frequencies, any amp will have decades of timing-reserve providing a high output voiltage. Do your amp (and your ears) a favor and balance the impedance of your speakers just as high that your amp won't start yelling at you alltoo soon...

regards

[Pbassred]

Tension,
I sort of did that, but the main benefit was getting more efficient/better sounding drivers (from "something" chinese to Eminence). 3db more nasty is just that.

I agree with your thinking, but I don't think that I would have bothered installing 4ohm in new cabs. With 8ohm you do have the option of hooking up to a 2nd cab if needs be.

[Tenson]

huh? The driver I happen to want is 4 Ohm so I will use that! The fact I can get the power more easily is just a bonus.

[noah katz]

"At peak levels, 3dB more headroom makes a noticeable difference as things are not pushed as hard."

The amp and speaker are both pushed 3 dB harder, but it beats clipping the amp.

[Salas]

max spl of the speakers remains the same. Its a matter of system economics. For fidelity I prefer 8 Ohm. They always sound faster.

[LightwaveDude]

Originally posted by salas
max spl of the speakers remains the same. Its a matter of system economics. For fidelity I prefer 8 Ohm. They always sound faster.

If the driver is half the impedance and only recieving half the power, how is the max SPL of the system the same?