Remote Trucks - Acoustics

[Larry Elliott]

Our firm in New Zealand has been asked to give some advice to a local OB company on the setup of their sound rooms in OB trucks. Clearly, these are never going to comply with the ITU/AES standards for regular surround sound rooms but I am wondering what compromises are deemed acceptable.

An initial survey indicates the main problem to be excessive background noise levels. But compromised monitor location is also a problem.

Look forward to your comments.

Larry Elliott

[huub]

In our new trucks we put all things noisy out of the audio room, which is helpful..
The placement of surround speakers is always a bit problematic, I would show pictures of our solution, but I'm on holiday for the next 3 weeks.. (In lovely ny, ny now )

[huub]

How's the project going larry?

[Larry Elliott]

Have made measurements - so many early reflections that it is almost impossible to “align” the 5 speakers to have the correct time relationship. The centre speaker is too close - they are testing some mid Freq absorption on the rear wall which is making a bit of an improvement. Noise is terrible about 55dBA with Aircon on. Our view is this is the major problem.

[Remoteness]

Ah, the trials and tribulations of designing a proper mobile unit.

[jayfrigo]

Originally Posted by Larry Elliott

Have made measurements - so many early reflections that it is almost impossible to “align” the 5 speakers to have the correct time relationship. The centre speaker is too close - they are testing some mid Freq absorption on the rear wall which is making a bit of an improvement. Noise is terrible about 55dBA with Aircon on. Our view is this is the major problem.

Having been involved in a couple of truck builds (along with a host of other acoustics jobs), I can attest to the fact that truck acoustics are difficult to make excellent unless you have a big truck and a big budget. For most small to mid-level trucks, the air conditioning can indeed be a problem, and the only way to improve it is to cover the usual suspects:

Test multiple units to find the quietest possible, and get it as far away from the listening position as you can.

If you have room, duct the air and put the unit over another compartment; you may need multiple units, and, as with studios, may need to slow the fans, and have the ducts get larger as they progress, but that goes back to available room and budget. Wide, slim ducts are available that work well for limited space situations in mobile units.

And lastly, mount units with proper vibration isolation, and baffle them.

As for the position of the center speaker, that's the easiest fix. It's a good idea to have some kind of speaker processor like an xta or Lake for a truck, in which case you simply delay the center speaker to align it with the rest. You also can use this processor for crossover, safety limiting, corrective EQ etc. I wouldn't put my signal through a processor like this in a mastering room, but what truck will ever have the acoustics of Bob Ludwig's Gateway Mastering? The processor in a truck is definitely a good idea.

Also regarding truck acoustics, treating the early reflection points the same as in a control room applies, and do your best to include some bass trapping somewhere. The environment of a truck is far less than ideal for low frequency performance, and if you have space, trap it well. If you don't have much space, you can still trap a bit behind the front speaker baffle wall, perhaps in a cavity like the one that goes above the cab in many trucks, and you can superchunk corners, including some roof/wall intersections if possible. Remember to consider door openings and headroom when laying them out.

[Ethan Winer]

Originally Posted by jayfrigo

treating the early reflection points the same as in a control room applies

Exactly.

The environment of a truck is far less than ideal for low frequency performance

Yes, but the good news is truck walls are much less rigid and dense than typical building construction, so bass tends to pass to the outside rather than reflect back into the room. Especially the very low frequencies. But you're correct that bass trapping is still needed.

--Ethan