Impedance and tone

[J M Fahey]

Higher Impedance means more turns of lighter guage wire - so lighter coil...maybe / maybe not.

Please let me clear this; obviously with Math:
for a given winding length, thinner wire means less copper, but you can put more turns in same space, so on first sight it "looks" like it might even out.
But turns-per-inch is a linear function (it depends on diameter), while weight-per-inch is exponential (it depends on the square of diameter).

A practical example:
we have a coil with, say, 100 turns and it weighs 2 grams.
Now we halve diameter, and of course, now can fit 200 turns.
One turn will have same length as before, diameter will be half, section will be 1/4 and of course, weight will also be 1/4 as before.

So we have twice as many turns as before , twice the wire length, but 1/4 the weight-per-turn, so 2X(turns)/4X(w.p.t.)=1/2 original weight = 1 gram .

Putting it another way: VC resistance varies with the *cube* of wire diameter
As in: half diameter means 2X as many turns and 4X as much resistance per turn=2X x 4X=8X=2^3=2 cubed.

Remember I design and make my own voice coils, both for own use and servicing, so this is "everyday stuff" for me.

When I started on this job I thought I would need tons of different wire sizes; later I noticed a few sizes let me duplicate a lot of commercial coils.

My last project is cloning (really I'm designing it on my own, rather than mindless copying) the weird Ampeg 32 ohms 10" woofer ..... and I'm finding it *much* easier than the "monster" I imagined.

I originally thought it might need a 4 layer coil for such a high impedance but no, it came out to be a very reasonable 2 layer one.

Which matches what I hear; a 4 layer coil is muddy (that's why it's used in those horrible car woofers) while the old Ampeg 8x10" (I'm trying to catch the '69 to '72 "Alnico sound") were bright and punchy.

[Steve Conner]

JM, you forgot to take into account that the thinner wire also allows you to fit more layers of wire into the magnet system gap. If you increased the layers as the wire got thinner, you would find that the voice coil weight (and hence Qms, Qes, BL product and so on) remained constant as the impedance changed.

I would expect speakers to be made this way, with the voice coil of the 16 ohm version using more layers of thinner wire so it weighs roughly the same as the 8 and 4 ohm ones, but I have no idea if this is true in practice. If the 16 ohm coil needed 1.2 layers that would obviously be a problem.

If the voice coil is the heaviest part of the assembly, then the reduction in weight due to using less wire than you can cram into the gap will cancel out the loss of motor strength due to having less amp-turns than you can cram in. The efficiency will stay the same and the speaker will get brighter sounding as the lighter voice coil (and shorter RL time constant) improves HF response.

If the voice coil is not the heaviest part then the efficiency will start to fall as you fill the gap less, because you have less amp-turns to push a mass that didn't decrease in proportion. The HF response will still get better, and that may make the speaker sound louder anyway (insert Fletcher-Munson waffle here)

[Leo_Gnardo]

Gingertube's post # lucky 13 - finally, the voice of reason for multi speaker cabs. Thank you Ian! My ears agree.

[J M Fahey]

JM, you forgot to take into account that the thinner wire also allows you to fit more layers of wire into the magnet system gap.

No, I didn't forget, truth is 2 layer coils are the norm in speakers, as simple as that.

4 layer coils are so bad, that they are only "acceptable" in the Car Audio world (or maybe in a home theater subwoofer)

In fact, a few super tweeters go the other way, and use a single layer coil.

What you say applies to transformers, which have static coils, of course, and have *huge* multi-layer windings.

Mass and inertia is not a problem there.

Note: we are talking round wire coils; edgewound ribbon is of course single layer.
And EV "Force" speakers half-cheated: they use ribbon wire, not (standing on)edgewound but the *much* easier "parallel-to-axis" wound ...and use 2 layers

[jazbo8]

Damping factor is Zload/Zsource so, as jazbo stated, it is backwards. Damping factor increases as the SOURCE impedance decreases, not the speaker impedance. Or if the speaker impedance increases and the source impedance remains constant.
So if we are using impedance taps to match impedance, damping should remain the same. It would only change if we mismatch impedances (different speaker impedances, same OT tap).
On top of all that, better damping is opposite of bass response. From the same wikipedia entry: "A lower damping factor helps to greatly enhance the bass response of the loudspeaker". So tighter bass is not the same as "more" bass.

Fryette definitely has it backwards, here is a quote from KOC wrt to mis-matched impedance:

A nominal 8-ohm load may reflect 4k to the plates of the output tubes with a given transformer. The amp might be designed to produce its maximum power into this load, with a designed frequency response. This is the "power bandwidth". If we change the load to 16-ohms, the reflected load doubles and the frequency response shifts upward. We lose bass but have a brighter sound, and also lose power. If we change to a 4-ohm load, the reflected impedance drops to 2k, into which the tubes produce less power, and the bandwidth is again narrowed. from here.