Enclosure Vent Holes and Shielding

[Jdansti]

I plan to use this metal enclosure from an HDTV converter for some
effect circuits. Could the vent holes and other 1/4" holes cause a problem with shielding?

[bonaventura]

IIRC the shielding may have holes provided that it is significantly smaller than the wavelength. if that condition is satisfied the (holed) shield would be as if continuous.

at 20kHz wavelength is abt 15000mtr,so i think you are still ok.

maybe somebody can chime in?

[Earthscum]

I would have power issues... something like that calls for extensive backlighting. 

[ashcat_lt]

Nevermind

[Jdansti]

IIRC the shielding may have holes provided that it is significantly smaller than the wavelength. if that condition is satisfied the (holed) shield would be as if continuous.

at 20kHz wavelength is abt 15000mtr,so i think you are still ok.

maybe somebody can chime in?

Thanks. If I understand correctly the 20kHz frequency (from the guitar signal) moving through the circuit has a wavelength of 15 km, so the enclosure holes have to be < 15 km.  As you infered, that's pretty large.  It seems though that this would apply if we're concerned about the pedal interfering with something outside of the box.

If I want to keep something outside of the box from interfering with the pedal, the holes would have to be small enough to prevent the wavelength of the other device from getting to the circuit inside the box.

If I consider an outside 60Hz interference, the holes can be as large as 5,000km! US cellular frequencies are 800-1700mHz, which have wavelengths of 18-37cm. 

Wikipedia defines radio waves as 3kHz-300GHz, which would be wavelengths of 100km down to 0.001cm.

After doing more research, I find that there are other criteria to consider but haven't found a straight forward rule of thumb.

[Earthscum]

You could always (if you want to retain the holes) use a finer mesh screen on the inside, as long as you can couple it to the enclosure effectively.

[artifus]

You could always (if you want to retain the holes) use a finer mesh screen on the inside, as long as you can couple it to the enclosure effectively.

splatter guards for frying pans can had very cheaply from a dollar store/pound shop, are conductive, easily cut with scissors and shaped. can also be used as a pop shield on mics.

[amptramp]

If it didn't have a problem with HDTV frequencies, it won't have a problem with audio.  With a slot antenna array like this, imagine the magnetic field inducing voltages on either side of each "V" shaped slot.  The voltages on either side act as the antenna.  But even if you have a large field at audio frequencies, the induced electric field is too small for anything to be noticed.  Now if you have digital logic internally or something that could be upset by an external field, just follow earthscum's advice and add an internal screen - but make sure the screen makes good electrical contact at each crossover point of the wire and to the box or you could get rectifying junctions that promote radio reception.

[Jdansti]

Great ideas guys and good point Rob. Thx!