[sdiy] speaker fun against summer silence

[Dave Krooshof]

>Hi Martin,
>
>Czech Martin wrote:
>
>>  btw.: what is usually used for guitar amp mic pick up?
>>  I guess magnetic coil? Shure something?
>>
>
>http://www.shure.com/microphones/models/sm57.asp
>
>HTH, Michael.

yep, that's the one.

Take care of this:
A sm57 is a cardioid microphone.
Basically, that means this:
It's deaf on the rear, and more sensitive on the front end.
But there's another issue with cardiods, and it's called "proximity effect"
which translates into: the closer you get the more lows you get.
(This also happens with the unboxed speakers. I'll get back to that.)

The funny thing is: this only happens on the front, on axis, the proximity
effect does not occur at the side.
So the angle the mic has, is a the cheapest and the best EQ's for the mic.
So if you want to record the amp/speaker very close and without the
pumping bass, then you hold the mic in a 90 degree angle for a "flat" response.
The sunny side of that is, that you won't need a mic stand: Simply tie the
wire to the handgrip of the amp, and let the mic hang in front of the speaker.
(So this is not a lazy habbit, is has a good reason!)


more on this:

The   no enclosure=no bass   issue is actually a matter of short circuiting
in the air. Wavelengths that are longer then half of the width of the speaker
get cancelled out. Unless you are so close that you tap out the sound before
it has managed to find it's way around the speaker.
Thus, speakers have a proximity effect.

You'll get more bass when you widen the speaker.
So you do not need the enclosure so much, you need a ~infinately wide speaker.
The cheapest way is to mount a small speaker in a large wooden plate.
______________/\_____________


This is actually related to the sm57 mic. The holes around the side are
the openings to the back side of the mic's membrane.
If you close the holes with tape, it becomes an omni, and the proximity
effect disappears. (and since the handgrip has a tuned resonance,
the mic is likely to feedback on that frequency (low impedance!)).

To be precise:
An unmounted speaker has a figure 8 pattern. (silent on the sides)
An enclosed speaker is more or less a omni (if small enough)
an bass reflex makes a cardioid speaker, sort of (more silent at the back)


-- 
--

groets,

_          >^v<        _

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