Goodbye HF reflections..Hello to my 703C desk

[Torea]

This is awesome! I was thinking of doing the same thing down the road. Very cool =)

[Hannes_F]

It might be of interest that for TV studios I have read they make the news presenter's desk from a steel grid with fabric on it in order to make it acoustically transparent.

[SAC]

Be careful with the assumptions...

A value of TI upwards of 10,000 should be the goal in choosing a perforated sheet intended for an acoustically transparent facing material. This would lead to an attenuation no greater than one decibel (dB) at a frequency of 10 kHz, and at lower frequencies, the attenuation decreases rapidly: in other words the sheet is essentially acoustically transparent over the entire frequency range of importance.

However, it is not essential to insist on very high Transparency Index. For relatively high values of TI, the transparency is not spoiled very rapidly with decreasing values of TI: with TI as low as 5000, the attenuation is only 1.5 dB, and with TI = 2000, the loss is only 2.5 dB.

Therefore, there is no harm in shopping around among the readily available perforated materials to find one whose TI lies between, say 2000 and 20,000. Any value within this range will yield acceptably high sound transparency for most sound absorption applications.

The value of TI increases as the hole size and the number of holes per sq in increases and as the thickness of the sheet and the distance between holes decreases. For values of TI less than 2000, the sound transparency diminishes rapidly, and the perforated metal blocks the passage of sound.


TI = nd^2/ta^2 = 0.04 P/pi ta^2

where:
n = number of perforations per sq in;
d = perforation diameter (in);
t = sheet thickness (in);
a = shortest distance between holes

a = b – d, where
b = on-center hole spacing (in);
P = percent (not fractional) open area of sheet.


Generally speaking, perforated sheets with small holes close together give the greatest transparency.

EX1:
A perforated sheet of 26 gauge steel with 0.023-in. holes on 0.054-in. staggered centers
TI = nd2/ta2 = [396 x (0.023)^2/0.0184 x (0.03)^2 = 12,650
The sound attenuation at 10 kHz is only 0.9 dB.

EX2:
16 gauge steel, but with 7/64" holes on 3/16" staggered centers.
TI = [32.7 x (0.109)^2/(0.0625) x (0.0785)^2] = 1009.
Even with a percent open area greater than 30%, the 10 kHz-attenuation has increased to 3.3 dB.

EX3:
16 gauge steel sheet, with 0.066" holes on 0.125"staggered centers.
TI = [73.6 x (0.066)^2/0.0625 x (0.059)^2] = 1474;
But notice that the 10-kHz-attenuation has increased to 2.9 dB, much more than the attenuation of Example 1, despite the fact that the open area for this example is 53% greater than in the earlier case!

From Schultz, Acoustical Uses for Perforated Metals.

And still the best, easiest and least expensive solution: minimize the surface area of the desk.Period.

[localhost127]

Originally Posted by dft3670

The design is very simple. I used a panel of faced 703C rigid fiberglass

you're using oc703 with FRK (faced)? is the faced side on the bottom?

[takman]

your monitors ( computer screens) are so far away, how can you look at them and not go blind?