Adventures in Room Correction

On thursday the measurement microphone for my Behringer DEQ arrived, but due to the bakeoff I didn't get a chance to play with it.

Still I've just been playing with the measurement and room correction capabilities of the DEQ.

Interesting...

Does it solve the significant room issues I've been contending with?

Surprisingly, yes. Yes it does.

It's not perfect, but it does manage some very credible improvements. By killing off some of the low-end room boom interactions, there's a lot of bass detail that was previously masked coming through. The whole thing sounds much cleaner now, without dropping into the "clinical" that many people have accused room eq of (although I did deliberately limit its eq range, which may account for that).

It is also showing me exactly what the characteristic problems of my room are, and consequently I can use that information to come up with a targeted acoustic correction, rather than stabbing in the dark.

But if the room EQ is so good, why not just use that?

The room EQ works well. However, I find that the DEQ itself kills the life from the music somewhat, even with no processing being applied, just passing digital through. I suspect that this is to do with the clocking of the DEQ, and that could easily be improved. However, I'm also not a fan of the bright orange display that can't be turned off, and for long term use I would rather just have transport to DAC to Amp (and eventually transport to amp).

However, I think the DEQ is valuable as a measurement tool, and for those with room problems that can't be treated acoustically (rented places, SWMBO, etc), it may present a good solution. It would be interesting to hear the effects of clocking it.

 

Sounds interesting, Isaac. Any ideas how one would hook up an EQ to an AV receiver? I'm tempted to get a cheap one and have a play myself.

 

With an AV receiver, the best way would be optical into the DEQ, optical out to the AVR (there's no coax, only AES/EBU (which I'm using) and optical).

The point about the DEQ is that it's digital domain, and can measure via a mic. It's not worth getting a simple eq with sliders (much as the DEQ is without a mic).

 

to what extent is 'room correction' a once-off matter, or is modification required on different types of music? If its the former, what is to stop 'circulation' of EQ equipment?

 

Well, if you were to circulate your EQ equipment, your own system would no longer be equalised.

 

If you use the equipment to understand what your room is doing, and fix it acoustically, nothing at all.

 

It is essentially a one off. I don't know how the piece of kit in question works (almost certainly the same way), but room treatment uses a Maximum Length Sequence (MLS) which is a kind of pseudo random modified white noise type thing based on prime number sequences. You play an MLS into the room, and record the response with a mic. The computer then 'deconvolves' the recorded MLS with the original MLS which leaves you with the impulse response. When you view the impulse in the frequency domain, you are viewing the room frequency response.
You then apply room treatment accordingly to try to flatten the response as much as possible (without making it totally dead which is a horrible condition to listen to music in). So if your going to physically treat the room, you can pass the same piece of kit round.
The eq may not be the best thing to test the room for permanent treatment though, depends on how many octave bands it has. Aurora, winMLS etc. and a mic would (possibly) be more accurate.

 

That is a way of doing it. The DEQ simply uses pink noise which it then eqs and remeasures until the output is as flat as possible.

 

pink noise, white noise, MLS its all the same method in the end.

 

Thanks Isaac for the reply. Think I'd have to give it some serious thought - the DEQ idea sounds good, but they aren't cheap. A bit pricy for me to 'just have a play' with.

 

Well yes, but surely that's rather easier said than done if you want results even vaguely comparable to what you can achieve with the likes of the digital equalisation we're talking about here.

 

Indeed. But the correction has its own pitfalls as I suggested.

 

The main downfall of DEQ is that it is only good if you always sit in the same place. Outside of the spot in the room you set up the EQ to correct, the sound can be even worse than without it. Physical acoustic treatment can improve everywhere in the room.

In my experience, DEQ is best for knocking out strong room modes, and acoustic treatment is best to tighten up everything, bring more detail and control; basically improve the sound. Acoustic treatment will help room modes, but probably not as much as a DEQ if you have just one or two very strong ones.

I use A LOT of acoustic treatment but I would still miss my DEQ.

 

Thats not true at all. You just use tuned dampers which have been around far longer than digital correction.

 

To get as large a difference from acoustic treatment as you can from a DEQ at a single given frequency.. lets say a 6db change (The Behringer DEQ can do up too + or - 15db) you would need quite a lot of 'tuned dampers' (thinking Helmholtz resonators?) and they are also extremely large for low frequencies.

So yes, you are right that it can be done by room treatment, but I don't think corrective EQ can be beat for just cutting down a few spot frequencies as simply and effectively.

Most of the time it has to be said that a room will present enough problems across the range that it is worth using broadband room treatment though.

cheers,

 

They aren't that big, they're a couple of feet square, half a foot deep. You only need a few at the main modes of resonance.
What do you mean by broadband treatment? You use different things at different frequencies. The room isn't flat in the first place so how can you broadband treat it? You use resonators (as you say, basically helmholtz) to control modes, then you move into absorption, then stick some diffusion in to control HF.

 

A broadband trap is something like the Auralex LENRD or VENUS. They are thick foam systems that have the depth to have some effect at low frequencies that 2"-4" foam tiles will not. They continue to have absorbtion all the way up the frequency range.

Broadband traps can be very effective (I've used them in treating a room at work). They kill a lot of the energy out of standing waves and flatten out peaks and dips. However, they're only effective down to around 125Hz or so. Below that (at likely room node fundamental frequencies) you need narrowband absorbers.

 

Which is basically what I said. Have you used them without diffusion?

 

Broadband traps aren't resonators. They're simply deeper chunks of foam.

There's no diffusion in the room (which was EXTREMELY lively prior to treatment). There is a significant amount of HF absorbtion (35mm foam tiles), along with a few other tricks and treatments. The work on the room isn't finished yet, as I'm going to do some targeted narrow band stuff, but there's some higher priority projects on the go at the moment.

 

No I didn't say broadband traps were resonators I said you can't use them to control modes.