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Guitar speaker magnet influence on close dynamic mic?

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Guitar speaker magnet influence on close dynamic mic?

PostPosted: Thu Dec 03, 2020 1:05 pm
by Wonks
Just one of those thoughts that keeps floating round my head and won't go away, so I thought I'd air it here.

I've seen reports of people disliking neo/neodymium guitar drivers for recording with as they've struggled to get a good sound compared with the more common ceramic and alnico magnet drivers. I've got both the normal and neo versions of the Celestion Creamback in different amps and cabs, and to me, the neo sounds really nice (as well as being considerably lighter).

So, given that neodymium magnets are far stronger than the other magnet types for a given size of magnet, is there any possibility that sticking an SM57 right against the grill cloth a couple of inches away from the end of such a magnet might be having an effect on the mic itself, maybe akin to a small DC voltage providing an offset in the diaphragm position?

I don't have a gauss meter, otherwise I'd have tried to compare field strengths myself.

I can only look at bass speaker info to get an idea of comparative field strengths between similar power drivers, as you don't get the T+S parameters given for guitar speakers (I know Celestion don't bother measuring them, I did once ask). And the BI for equivalent power rated speakers of the same size does have the Neo speakers with a greater BI value, between 10% to 100% greater.

But I have no idea if that has any real world influence on a fairly close mic, as the flux patterns and inverse square laws also come into it.

So just wondering if anyone's seen any testing into it, or is any influence going to be so negligible at even 2"-3" that the initial observation is purely down to the producer's sound preference?

Re: Guitar speaker magnet influence on close dynamic mic?

PostPosted: Thu Dec 03, 2020 3:22 pm
by James Perrett
Isn't the main advantage of Neodymium that you don't need so much of it to produce the same magnetic field? I would have thought that the manufacturers wouldn't use more than needed to produce the required field so the actual field strength would be similar for the different types.

The diaphragm of a mic isn't magnetic so all that a change in field would give you is a change in shape of the field around the microphone coil which may result in a little distortion. However, I would have thought that the effect would be minute as the microphone diaphragm moves very little.

Re: Guitar speaker magnet influence on close dynamic mic?

PostPosted: Thu Dec 03, 2020 3:32 pm
by Wonks
Very true, which is why I tried to compare the BI value as I thought they would be the same/similar, but the neos do appear to have a stronger flux, at least on the bass speakers. But maybe there are other design variations to counter that within the driver construction itself.

Noted and accepted about the dynamic mic construction, so no offsetting of position, which leaves magnetic field influence as the only possible influence.

As you were.

Re: Guitar speaker magnet influence on close dynamic mic?

PostPosted: Thu Dec 03, 2020 4:14 pm
by Tomás Mulcahy
Very interesting question I never thought about it! I would comply with James' assertions, but I would still like to see measurements/ data. We have some people here who research this kind of stuff, maybe one of them is looking for a study topic. I'll put it to the group. Don't expect a result soon though ;)

Re: Guitar speaker magnet influence on close dynamic mic?

PostPosted: Thu Dec 03, 2020 5:12 pm
by Wonks
I'd suggest all it takes at first is a gauss meter stuck in front of a neo and non-neo speaker next to the grille and see if there's any significant difference in readings. If there is, then it could be worth having a closer look.

Re: Guitar speaker magnet influence on close dynamic mic?

PostPosted: Thu Dec 03, 2020 5:56 pm
by Sam Spoons
Pure guesswork but I suspect the magnetic flux at the speaker grill will fall into a relatively narrow range and that Neo speakers won't all be at one end of the range. The logic is that a certain flux (along with the rest of the design) will contribute to a certain sound and many Neo speakers are built to sound as close to the 'original' Ceramic or Alnico speakers so will have similar flux density just in a lighter chassis. I wonder if the Neo version is more efficient? Interested to see if any of that turns out to the case.