DIY Acoustically Transparent screen - my journey

mhuk05

Well-known Member
I've not been able to test my potential acoustically transparent screen samples yet for acoustic attenuation as I've not been able to calibrate my sound card for REW (room EQ wizard) but here are a couple of photos of the samples over black cloth (top half of the photo is my normal non-AT screen). 3 grey, 5 white.

IMO the screenshots you often see are worthless where the sample is taped over an existing screen as you're not testing the screen samples the way you'll be using it as the screen behind will affect the results.

3 of the samples show too much weave but the other samples will be investigated further (and will have photos taken using a tripod but after a day spent moving a radiator I didn't have the will to do it properly...).

The prices varies from roughly £90 to £150 for 2400 x 1400mm

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The samples (woven samples, not lycra, although I do have some white lycra) are taped to the bottom of my screen so may not be perfectly flat/ in the same plane as the "big" screen.

Photos were taken at about 8ft. from the screen, ambient light from the projector, hand held, auto white balance in photoshop so please ignore any "off" white balance. More to follow soon.. once I've got the new rad fitted and can summon the strength to face REW again!

I had some promising samples from Silent Gliss but they refused to sell me any fabric.
 

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cossie

Active Member
I'm very interested in your results as I'm also looking for an AT screen. However I'm making it hard for myself as I want AT, in ceiling, high contrast (normal living room) and at a cost I can justify to SWMBO and hang onto my reproductive organs.
Could I ask a few questions, from whom did you get the materials, what did they supply and what type of installation are they supplied for?
 

mhuk05

Well-known Member
The samples are from blind companies found via Google, fabric is mainly Perspective White and grey/ steel. They're supplied as blinds so this will be a completely DIY venture for me - I'll be making a frame and mounting the fabric, although I may look at the practicality of using he blind rather than making a permanent frame if the fabric hangs flat enough.

Costs seem to vary from about £90 to £150 for 1400 x 2400mm blind (140cm width/ 240cm drop as it's cheaper 99% of the time than 140xm drop/ 240cm width). I don't have a sample of Seymour XD to compare/ test against.
 

celluloidzombie

Standard Member
Cheers mhuk05 , just the thread I've been waiting for. I've already made my frame and used some cheapo lycra , just so I had a screen . I've waiting for some spare cash (haha) and was looking at Seymore XD myself. Can't wait to read your results.
 

mhuk05

Well-known Member
Here's my REW graph, I'm not 100% convinced by testing methodolgy or the best way to show the graphs.

at%20fabric.png


I used the mic from my Anthem MRX "stuffed" into the back of hugger, with the mic stand placed about 1m from the speaker. I took measurements with the hugger only, then with the fabric sample taped to the front of the hugger.

hugger.jpg


At some frequencies the hugger (no fabric) is not the uppermost graph line, suggesting something in my test set-up is boosting frequencies, either because the hugger is a closed "device" or something else? Ideas, comments and suggestions much appreciated :)

Here's a more zoomed graph:

at-zoomed.png


Although there are differences the +- variation isn't very much and isn't consistently higher/ lower for one fabric - for example, the PS white Myblinds is "lower" at 2khz but "higher" at 3.5khz (I'm sure I could look up the proper terminology but I'm too tired.. frequency response?). The Maplins line is black polyester speaker fabric. I realise that the test methodology doesn't replicate the real-world usage of AT fabric (where the speaker is very close to the fabric and your ears are a few metres away from the screen) but the samples are too small to place over a speaker so this approached seemed the best compromise but open to suggestions for other ways of testing.

@celluloidzombie - JVC HD350 used in a dark room, no lights but yellow walls.
 

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picmalkin

Active Member
Cheers mhuk05 , just the thread I've been waiting for. I've already made my frame and used some cheapo lycra , just so I had a screen . I've waiting for some spare cash (haha) and was looking at Seymore XD myself. Can't wait to read your results.

Hi, can you provide some info on how you constructed your screen and possibly some pics please? Also very interested in this thread
 

picmalkin

Active Member
Hi, just thought I would add my thoughts. I have had a screen excellence screen with enlightor 4k fabric (which is a stretchy type of fabric) against a lot of the 'weave' type AT fabrics which are more rigid, so I do have a little experience. I am a big fan of the centre being in, what I consider to be, the right place that is afforded by AT screens. Failing that I go for a phantom centre setup with the ReactII I currently.

The issue, as I see it for AT fabrics acoustically is for them to attenuate the sound as little as possible, but also for them to do that in a way that is flat across the frequency spectrum - i.e. say -1.5db across the whole spectrum (have a look at how the AT screen manufacturers claim their materials perform as a guide) .

If they achieve this flat response, or close to this, it means that you don't need lots of eq to put right the issues caused by the fabric but can simply turn up the volume to compensate (this obviously ingnores discussion about general room acoustics and the need for eq anyway to improve audio quality as the room is always the biggest factor).

Materials that do this can then be tested for video performance.

I would suggest a graph which plots the differences between your control measurement and the fabrics to see what the 'effect' the fabric has on the signal. The flatter the better...
 

picmalkin

Active Member
p.s. the ultimate would be to create a good high, contrast / light rejecting screen which would allow the screen to be close to the speaker - i.e. weave based rather than micro perforated! sort of an AT ReactII or black diamond for video performance with the AT performance of enlightor 4K:D
 

mhuk05

Well-known Member
I would suggest a graph which plots the differences between your control measurement and the fabrics to see what the 'effect' the fabric has on the signal. The flatter the better...

That's what I'm trying to do/ show but I'm still learning how REW works, plus I need a test method that is consistent. I plan to try this out again tonight... :) and I'll try to remember to test the lycra as well.
 

mhuk05

Well-known Member
I'm much happier with my new testing setup and the results made more sense- the microphone-only measurement was typically, but not always, the highest graph line. But none of the fabrics were consistently worse or consistently better, the transmission loss varied according to the frequency. Measurements for white and steel of the same fabric varied quite a bit.

I took 3 microphone-only measurements and even those varied by a few dB at the same frequency so I'm thinking of taking 7 measurements for each fabric and work out the best way to take the mean reading at certain frequencies, probably the frequencies quoted in absorption coefficient tables.

To average the SPL readings I can convert each dB measurement to intensity (i = 10^(dB/10)), average the intensities and convert the average back to dB (dB = 10 log i)) for each fabric at a given frequency.. I need to remember my statistics work from college. Ahh!!

Graphs have 1/3rd smoothing applied.
 

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mhuk05

Well-known Member
Here's my data for the 6 At fabric samples plus a black sheet and Maplins polyester speaker material:

fabric-holmImpulse.PNG


I tested using HolmImpulse and these results have 1/12th octave smoothing. I took 3 measurements for each sample and the readings were consistent. The speaker was placed in the middle of the room at a height of 1.3m, and with acoustic foam on the table under the microphone and on the wall behind the microphone to help reduce room effects although looking at the measurements for 500hz and 1000hz I'm not sure this was entirely successful.

What's odd is that the same material in different colours gives significantly different results: the myblinds PS steel and white. And I forgot to test the lycra again!

My projector isn't set up at the moment but I'll try to do a more objective visual test soon.
 

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mhuk05

Well-known Member
Sorry for the late reply. Not yet, summer distracted me from this but I'm going to try some lycra first as it's only £10, compared to about £100 for the blind material in the same size.
 

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