Multiple pickups and mids

[AttitudeCastle]

Hey guys!

It seems pretty common knowledge, and I've noticed in practise, that when using basses with more than one pickup, when using more than one the mids drop.

And the further the pickups are apart the more the mids are decreased.

Can someone explain why this is? Or is it all urban myth?

The more scientific the better! I have a solid grasp on physics for a non degree holder of the public and love to read up on this stuff.

Just curious really,

AC

[winterfire666]

great question, i too would be very interested.

[Prime_BASS]

I don't know the science but question yourself, why when adding a bass pickup(neck) and treble(bridge) you get get more mids?

I think Alex at barefaced goes over this over on his website though.

[LukeFRC]

[quote name='Prime_BASS' timestamp='1341856941' post='1725249']
I don't know the science but question yourself, why when adding a bass pickup(neck) and treble(bridge) you get get more mids?

I think Alex at barefaced goes over this over on his website though.
[/quote]

you don't. each pickup has an amount of bass and an amount of treble- with both on you get [u]less[/u] mids than with just one or the other. Hence the scooped sound of a jazz bass- and the further apart the pickups the more scooped the signal..... but for the life of me I can't remember why, I think it has to do with the aperture of the pickup.... but can't remember

[Machines]

Alex Claber wrote an article on this in a recentish BGM issue.

[bremen]

barefacedbass.com/bgm-columns.htm

Edited July 9, 2012 by bremen

[chrismuzz]

[quote name='bremen' timestamp='1341864080' post='1725408']
barefacedbass.com/bgm-columns.htm
[/quote]

Cheers for that, theres some really interesting stuff on here!

[dannybuoy]

'Tis to do wth phase cancellation: [url="http://barefacedbass.com/uploads/BGM61%20Dec2010.pdf"]http://barefacedbass.com/uploads/BGM61%20Dec2010.pdf[/url]

[AttitudeCastle]

Ah thanks guys!

Haven't been on the Barefaced website for a while now, and can't keep up with BGM!

The '69er has given me too much GAS

[iiipopes]

It's not "phase cancellation" or "comb filtering." It's a function of[i][b] inductance[/b][/i], measured in an electronic value called, "Henry" (no relation to the houses of Normandy, Plantagenet, Lancaster or Tudor).

What's happening is (oversimplified) when you put two coils in parallel, you decrease the amount of overall inductance the circuit has. The practical effect is that the less inductance, the less mids. For those of you who play electric guitar, you will recall that a humbucker wired in parallel has a brighter, thinner tone than it does in series wiring, or with a single coil. Conversely, the more inductance, whether by two coils in series (typical humbucker, and stock P-bass wiring), or by overwinding a single coil, the inductance goes up, the treble goes down, and the mid resonance increases.

Here's the math:

[url="http://www.electronics-tutorials.ws/inductor/parallel-inductors.html"]http://www.electroni...-inductors.html[/url]

Now, one way to get around part of that is what Rickenbacker does: add a capacitor inline to one of the pickups. I personally have a .01 microfarad capacitor inline to my jazz bridge pickup. This does roll off the bass a little out of this pickup, but 1) it's so near the bridge there's not much real bass content anyway; and 2) what comb filtering there is from having two pickups is reduced where it matters, on the lowest fundamental, giving me a more solid bottom end, and 3) adding the capacitance in line adds another whole 'nuther kettle of fish, because a guitar or bass pickup induces an alternating current, so you get into reactance, set forth as "Z" in the math equations.

Edited July 9, 2012 by iiipopes

[LawrenceH]

[quote name='iiipopes' timestamp='1341875308' post='1725658']
It's not "phase cancellation" or "comb filtering." It's a function of[i][b] inductance[/b][/i]
[/quote]

The resonant peak of the tuned circuit is important especially for the upper mids, but comb filtering due to phase cancellations IS also important - if you move two pickups further apart the inductance remains pretty constant but the comb filter pattern changes as the OP talks about (scoop freq gets deeper) and this is really audible.

There is/was a handy calculator that easily lets you visualise the comb filtering effect of pickup positions etc here http://www.till.com/articles/PickupResponseDemo/
But I think it's pretty old and sadly isn't working on my browser currently - if anyone can get it working it's great and you can see the first lowmid-scoop shift as you move the pickups apart.

[LawrenceH]

Also worth noting that you can effectively separate the effects of changing capacitance/inductance from those of the phase cancellations if you have a pre-amp that buffers each pickup separately before the blend.

[Conan]

What about Ricks when you have a separate output for each pickup? Do they still scoop the mids?

[muttley]

[quote name='LawrenceH' timestamp='1341876568' post='1725668']
The resonant peak
[/quote]

<pedant mode on>It's [i]resonance[/i], not resonant. The peak isn't resonant, but indicates the frequency at which resonance occurs.

Same with resonan[u]ce[/u] frequency.</pedant mode>

If I had a pound for every time I saw or heard that common error I'd have enough for a new bass . Add in the "is it 3dB or 6dB" confusion and I'd have enough to retire .

[Cosmo Valdemar]

[quote name='Conan' timestamp='1342007730' post='1727862']
What about Ricks when you have a separate output for each pickup? Do they still scoop the mids?
[/quote]

Not if you are using the Rick-O-Sound feature, which essentially runs each pickup individually to separate amps.
Ricks don't actually have separate outputs for each pickup, but rather a mono and stereo output.

[Conan]

[quote name='Cosmo Valdemar' timestamp='1342010893' post='1727955']
Not if you are using the Rick-O-Sound feature, which essentially runs each pickup individually to separate amps.
Ricks don't actually have separate outputs for each pickup, but rather a mono and stereo output.
[/quote]

Not sure I understand. This post seems contradictory... The stereo output essentially splits the signal, one from each pickup then? So if you put them both into one twin channel amp and then into two stacked cabs, would the mids still be scooped?

I'm confusing myself now!

[LawrenceH]

[quote name='muttley' timestamp='1342008299' post='1727875']
<pedant mode on>It's [i]resonance [/i]</pedant mode>
[/quote]

Thanks, I will be sure to hit myself with a birch rod for besmirching our glorious language of course then I'd have to kill myself for insisting on saying 'tone' instead of 'timbre'!

[quote name='Conan' timestamp='1342013167' post='1728043']
Not sure I understand. This post seems contradictory... The stereo output essentially splits the signal, one from each pickup then? So if you put them both into one twin channel amp and then into two stacked cabs, would the mids still be scooped?

I'm confusing myself now!
[/quote]

With separate inputs you will not get the inductance change that alters the circuit tuning but you should still get the comb filtering effect, though this could be potentially further complicated if the channels introduce different phase shifts in the signal, which they will do e.g. with different EQ settings.

[muttley]

[quote name='LawrenceH' timestamp='1341877246' post='1725672'] Also worth noting that you can effectively separate the effects of changing capacitance/inductance from those of the phase cancellations if you have a pre-amp that buffers each pickup separately before the blend. [/quote]

Presumably the same could be said of a pre-amp that doesn't buffer before the blend? If the input impedance of the pre-amp is of the order of megohms then a few henries difference plus or minus isn't going to have much of an effect within the audible range.