Acoustic Treatments and General Mayhem

Now that I have skin on my hands again and it doesn’t hurt to type this—
Proper acoustic treatment is vital in studio and performance spaces to avoid echoes that will prove destructive to audio quality. Sometimes it’s done right. Sometimes it’s done wrong. To me it’s utter black magic but I know what works for the most part.

The first thing you want to look out for is stray sound entering your studio space. This may be trickier to do unless you’re constructing a studio from scratch. The methods I’ve seen used to great success are either adding insulation batting inside walls as they’re being built, or using cinder block walls to enclose the space instead of hollow. Either way, avoiding the use of walls shared with noisy things like air conditioning units or bathroom plumbing are very good ideas. Don’t use the other side of the wall pictured here if you can avoid it 😉

The second stage in acoustic treatment is to manage reflections within the space. Any hard flat surface within the studio may cause echoes which can become unpleasant and generally make your recordings sound like you’re standing in the shower.

The typical method of dealing with this is to put up some kind of sound absorbing material on the walls. A number of criteria should be considered when selecting your sound absorbing material:

  • Cost
  • Durability
  • Acoustic performance
  • Fire retardant properties

Materials I’ve seen used:

  • Carpet. Can be obtained anywhere, extremely cheap and actually very durable, since it’s made to be walked on. Works pretty well, but double check that all materials you are using will meet fire code standards for use on a wall. (Carpets may only be rated for proper fire retardant action when installed on a floor, as the flame spread dynamics are a hell of a lot different. Consult the manufacturer and/or their documentation before use.)
    You can glue and/or staple it to the wall or even use the self adhesive carpet tiles that peel and stick.

    CAN BE CLEANED. This is a big advantage. Over time, airborne contaminants will settle on the wall material and should ideally be removable. I’ve found that in an old studio with textile walls, allergens will gather and cause some people to get sniffly if not removed. Your mileage may vary, but I’ve found that the ideal maintenance interval to vacuum the walls is about 2-6 months. That’s all it takes, actually – just use a vacuum cleaner with a hose and an upholstery attachment and suck the dust out. More major junk may be dealt with using carpet shampoo and a wet/dry vac.

  • Cloth and Fiberglass. I’ve seen this one in a couple of older studios and it works very well. Small wooden strips were attached to the wall followed by fiberglass batting being installed between them, with a fairly open weave upholstery cloth used to cover it all up. The cloth is finally secured by tacking a small wooden moulding to the wooden strips below it.

    Performance is very good. Flame resistance will be identical to that of the upholstery fabric used. Durability isn’t as good; wheeled chairs, furniture, irresponsibly sharp spiked leather gauntlets (of course I say this from experience), and other things can tear the fabric. Repair is easy though.

    You can also buy prefabricated panels using these materials, or build your own. How to Build Your Own Acoustic Panels

    DIY acoustic panels – from article on acousticsfreq.com

    Cleaning: Can be surface cleaned. I’ve always just used a vacuum – with a HEPA filter just in case glass fibres are released through the surface fabric as you’re sucking the schmutz off. When I’ve done it, I have never noticed glass fibers visible in the vacuum as I cleaned it out – just lots of fine dust and pollen!!

  • Foam. This is a very common acoustic treatment material and I kind of wish it wasn’t. Performance is good, yes, but durability is totally in the dumper. When it’s new, it’s easy to tear up, especially when…. SOMEONE… decides to get creative and try to hang decorations from it. By the way, don’t cover your acoustic treatments with posters, because the essentially airtight paper of the poster will just form a really nice REFLECTOR, completely defeating the treatment. Some materials have fire retardant ratings, check with the manufacturer.
    A really swank looking example of Auralex SonoFlat foam installation from their website, with corner diffusers and wall and ceiling panels.

    When it gets old, some foams will just crumble and disintegrate horribly, especially if touched.

    Cleaning: …. maaaaaaybe. If you’re lucky.

    Shop-Vac 9018000 soft bristle brush. Horsehair vacuum brushes work fine too. BE GENTLE!!

    I’ve had okay luck with vacuuming the surface of Auralex StudioFoam products using a soft bristle brush. Work slowly and gently going along the ridges. In one studio I started doing this and the foam turned from dingy gray to its original burgundy red— I didn’t even know that was the color it was supposed to be! Yeeeechhhhh.

    I wouldn’t even try this at all on the type of sound insulation where it has alternating deep, thin vertical and horizontal ridges.

Now here’s where I talk about strange things.

A while back I was in the studio of The Jeff Adams Show and as soon as I walked in, I saw his wall panels and couldn’t believe my eyes. They’re wood! They did not contribute to any unpleasant echoes, yet had a little bit of a warm reverberation. You can see one in this picture:
I didn’t get a closeup picture of the panels when I was there, but they did not have a smooth planar surface. The different planks are overlapped forming a convoluted surface, which would contribute to diffusion instead of a clean surface reflection. Notice the mic he’s holding here – that’s a Heil PR 40 cardioid dynamic that is just INSANELY sensitive. You’d almost think it’s a condenser (I mean— it kind of even looks like one). The Heil PR 40 is NOT forgiving to bad room acoustics. It proves that these funky wooden wall panels work perfectly as an acoustic treatment!
In contrast, the Electro-Voice RE20 that’s used at close proximity by a lot of radio jocks couldn’t care less what your room acoustics are like as long as you aren’t in an all glass aquarium or something.

The same soft vacuum brush cleaning I mentioned above will work if they ever start to gather dust. Since he’s doing video on the same set, avoiding lighting glare is definitely a plus – they’re not shiny in any way.

Now, you may have a sick curiosity and wonder what the first sentence of this post is all about. Well…. I had to displace some very old carpet on a wall at work to hide a cable behind it, and I don’t know if it was the 20+ years of old crud built up in the carpet, the glue that held it to the wall, or a likely combination of both, but something caused a very bad reaction on the skin on my hands that caused it to blister, crack, and weep as if it had been severely burned.

If you’re really curious, I have a picture of the results here. Content warning: extremely gross. There’s good reason I put /nope/ in the URL. It’s mostly healed now and all that remains is a little redness. That week sucked, man.

Tilt-A-Whirl Video Heads.

I was digging around in the… uh… museum… here at work and found a whole box of worn out video head drums. Some of them had a very interesting feature to them— piezoelectric tracking.

The head can be shifted up and down on a piezo bender.

Why is this here, you may ask? Well, here’s the reason—

Normally, when you play a tape in a helical scan transport like this, the video heads trace an arc across the tape as the drum spins. This arc more or less perfectly matches the way the video frames/fields are recorded across the tape *as it moves* at normal operating speed.

Purpose of the fixed heads and other gribbles on this drum will be read out of a dusty old service manual some day when I’m not fighting the migraine from hell.

But what about when you are NOT at normal operating speed? The tracking angle will not be correct, and the picture “tears” as the head runs across the boundaries between fields.

Enter the piezoelectric tracking mechanism. By applying a sawtooth waveform synchronized with the head drum’s rotation, Sony was able to cause the head to perfectly track a video field beyond angle differences caused by different tape speeds. Thus, when you grab the jog/shuttle dial on one of the decks employing this system and start moving around, or settle down on a still frame (don’t do this too long!), the picture remains clear.

The Sony J-1 Betacam/SX compact player I use at my desk doesn’t have this, and the picture tears when you mess with the speed or pause on Betacam SP (analog) tapes. On BetaSeX tapes, as my coworker calls them, the digitized frame data seems to land in a RAM buffer somewhere and you can still frame or slow down. The tape transport speed and drum rotation speed in Betacam SX mode are much different, and the angle error doesn’t cause as much of an impairment.

I recall seeing a high voltage warning on or near the head drum inside these decks. Not just for show. It’s about 200 volts!
A much more thoughtful description of the dynamic tracking system and better view of the heads and benders may be found here:

http://dexterslab2013.blogspot.com/2016/05/sony-betacam-dynamic-tracking.html

Two Giga Hertz Super Bowl

Breaking news near Downtown Miami! Okay, we’re good here, just tell the live truck to send us a signal on one of our ENG channels to the downtown repeater aaaaaaand… BLITHERFART!!! WHAT IS THAT?! Our truck’s signal gets smashed, and there are No Excuses On ‘Da Bowl!

image

Someone else’s live truck is feeding a tape from hours earlier on the day. Spin the receiver around a bit and it’s clear that they’re aimed at the same receiver site or thereabouts. The station responsible has a receiver up there too, I believe.

image

Okay, so let’s see. How many people had to FAIL to accomplish this?

1. The studio ENG operator. The studio ENG operator would have been the one responsible for directing the truck to use this channel; or, they would have been able to tell the truck, hey, change channel, we ain’t down with O P C. (Other People’s Channels)

2. The truck’s crew. They should have also known better.

They continued to send the footage from tape for a couple minutes then just sent black for a while after that before *finally* coming down….. after any hope of us getting our shot waned. Fortunately, the story turned out to be a total non-event. But still, FAILURE.

 

The station responsible called us and apologized so I won’t yell at them specifically here, but come on— don’t just grab someone else’s channel, and at least, not without asking nicely first! News happens, man!

Jimmy Jib Junk

Oh gee I wonder why your pan and tilt motors were losing torque?

(And I wonder who applied that much grease in there? Holy goobers.)

image
💦🎺 Spunk Trumpet 🎺💦

That’s the before…

image

And the after.

The motor is a Swiss made Maxon and has lots of life left in it, I just carefully de-melted-rubbered and degreased the pulley awaiting a new belt.

Sometimes high tech problems have low tech solutions.

Transmitting from the Troll Bowl

You know you’re doomed to be an RF person forever when you look at this…

image

… And just keep thinking “damn that’s cute”.

That’s a Troll auto tracking antenna system for broadcast microwave from a helicopter.

image

image

Swapped this corroded yackage out. So far, so good.

image
Hey News Desk, can you hear me now? Good.

image

image
Whose AM DA is this again? North of US 41, just west of 137 Ave...

image

I could never do this stuff regularly and am really hoping this project’s done. For a good long time. The Jet A fumes make me feel sick after a while of working around the bird or after being in the air a while. It’s not motion sickness; I literally just don’t get that… it’s the fumes. Yeeech. The weird part is when turbulence rocks the craft, it makes me feel better for a bit??

Can’t explain that one. Dammit I’m a broadcast engineer, not a doctor.

image
Good day, sir.

The whirlybird

We’ve had an ongoing issue at work with the helicopter’s MRC microwave transmitter powering down on us. The silly thing is really obtuse; the user interfaces won’t tell us after the fact why it happened. Don’t you love faults like that? It’s almost as great as on ham and other 2 way radio equipment where a high VSWR condition causes the transmitter to fold back its power output but not indicate to the user that this is happening. Come on man…

Anyway here’s the box.

image

image

The remote controller at bottom. The top unit is the N Systems antenna pod controller which allows aiming of the antenna or selection of which receive site to automatically aim at. The NSI antenna’s servos make a comically mad sound as the unit initializes on power up and they seek home position at full tilt.

image

The bird at roost.

The fault cannot be replicated on the ground; this has been tried several times with no success. Therefore the only way to figure this out…..

image

That’s Hollywood Beach down there.

image

image

I believe this is where parts of “Santa and the Ice Cream Bunny” were filmed, notably the fire truck driving through the dirt road and Tom Sawyer and Huckleberry Finn rafting down a waterway accompanied by “Old Man River” on kazoos.

I Am Not Making This Up. This film is fascinating as hell.

image

The A/V box. At right, radios and audio controls. At left, video switches, CCUs for a couple of small Toshiba cameras mounted in the helicopter interior.

Never photographed because I simply forgot: the FLIR pod ‘laptop’ controller. It’s a big chunky panel you actually just rest on your lap while using it, with a damn near fire hose sized cable coming out.

image

At about Atlantic Shores Boulevard.

image

Suspicious: this isn’t the RF cable for the MRC radio but was installed at the same time and is identical. To be replaced MoNday.

Part of the testing included putting a phone in there recording video of the transmitter front panel. What it revealed was just the unit going into standby and back. No informative messages. Meeehh!! I don’t know if these MRCs keep an internal log file like Nucomm radios do.

image

It Fell Out Of The Box Like That!

Really.

Seriously.

A refurb DirecTV Slimline receiver we had in service a while just up and died with no warning. It was opened up and showed no signs of trauma but I saw something everyone else missed….

Hmm. Let’s flip it and see what that is at the edge. It’s probably nothing at aaaaaaaaaaaaaa

Aaaaaaaaa
AAAAAAAAAAAWHATTHEAAAAAAAA

What.

A while back I found these units tended to burn the access card. This appears to be the fix – first, note how far heat would have to travel down those fingers to toast the card. Second, the card is actually heatsinked by a plate above the socket.

Front panel with mystery antenna. Also note the dual die IR LED next to the black lens IR receiver. This is probably used for the unit’s very user – friendly universal remote system.

The rectangles are touch button sensors.

RF filter and very big silkscreen note on where to find power.

The external converter.

Excuse me, I’m going to go wash my hands.

1 2 3