Room EQ Curve

[Bryan Nemecek]

Vote for your favorite Room Voicing Curve.

1. Academy Curve
2. X-Curve
3. No Curve at all!

Interesting article I read caused me to open this thread...
http://www.hometheaterhifi.com/volum...es-6-2002.html

"In the film sound industry an X curve is also known as the wide-range curve and conforms to ISO Bulletin 2969, which specifies for pink noise, at the listening position in a dubbing situation or two-thirds of the way back in a theater, to be flat to 2 kHz, rolling off 3-dB/oct after that. The small-room X curve is designed to be used in rooms with less than 150 cubic meters, or 5,300 cubic feet. This standard specifies flat response to 2 kHz, and then rolling off at a 1.5 dB/oct rate. Some people use a modified small-room curve, starting the roll-off at 4 kHz, with a 3 dB/oct rate. " -RANE Pro Audio Reference http://www.rane.com/par-x.html

[Sonnie]

B-Dogg... we lost this poll in the host transfer so you may want to start if over. We found the thread in the wrong place, but the poll part was lost. You can start a new on if you wish and we'll delete this thread here. I don't think you can add a poll to it now.

Sorry for the problems.

[Bryan Nemecek]

Sonnie wrote:

B-Dogg... we lost this poll in the host transfer so you may want to start if over. We found the thread in the wrong place, but the poll part was lost. You can start a new on if you wish and we'll delete this thread here. I don't think you can add a poll to it now.

Sorry for the problems.

No Worries-- With only 2 votes in it, I doubt anyone will miss it..and we all know things happens...

BTW: Did I get your take on this EQ room curve thing, yet?? And if you are the 'other' vote that voted for the NO EQ curve, then how did you 'voice' your listening postion??

[Sonnie]

I don't think I voted because I had not had the time to actually read the article yet... I seem to have so much going on lately I'm missing a lot of good reading probably.

I wonder how this compares to Wayne's sticky thread on house curves... have you read it yet?

[Wayne A. Pflughaupt]

Hey B-dogg,

Regarding this quote from the article:

If you could get your hand on the X-Curve table, one corollary would stick out for you: As the rooms get smaller, less and less of a roll-off is defined, because as we said, smaller rooms have less of the reverb which the X-Curve addresses.
By the time we shrink a room down to typical home theater size, we can say that no X-Curve compensation is needed, much to the contrary of popular opinion.

I’ve noticed that the X-curve calls for flatter response with a smaller room, and that’s always been a puzzler to me. Most home audio buffs who’ve measured their systems will tell you that flat response sounds bad. And my personal experience measuring rooms both big and small have led me to just the opposite conclusion, that large rooms need flatter response than smaller rooms. The reasoning is that highs attenuate over distance, and therefore need a boost in a big room, because generally the speakers are further from you than they are in small rooms.

Brian Florian, who wrote the article, also noted the following:

The measurement of EQ is done using wideband pink noise excitation through the speaker. The larger the room, the longer and greater the reverberation buildup over time, resulting from this steady-state signal. If we measure EQ on a fixed bandwidth basis, like full octaves or third octaves, the reverb which tends to be stronger at low frequencies will tend to make the SPL read louder there than at the higher frequencies where it is better absorbed.

In other words, he’s supporting the theory that big rooms need a high end EQ boost because highs are more readily absorbed than lows.

However he also says:

Home theaters are usually more reverberant than studios, cinemas, and dubbing stages, sustaining high frequency energy much longer, despite their small size.

This might seem to be contradictory but it’s really not. Absorption is the key, I think. What’s inferred, but not specifically stated in the first quote, is that if the highs weren’t absorbed, they’d show up in the room readings as much as the lows. Obviously that would result in flatter measured response.

This got me to thinking about something I’d never considered before, that the large rooms I’ve measured – churches, clubs, etc. - have been pretty “live.” I.e., not dampened much at all. Therefore I can see that it makes sense that a movie theater’s ideal curve would run contrary to my experiences, since they are heavily dampened. However, from discussions I’ve had with Terry Montcliff, an expert in these matters, theaters don’t often need to EQ for the X-curve. I expect this is because all the dampening attenuates the highs naturally. That, and the fact that theaters use compression horn drivers like those use in other professional sound applications, which typically start falling out by 10-12 kHz or so.

So - looks like I need to make some revisions to my house curve article!

However, I think Mr. Florian shot himself in the foot when he said “By the time we shrink a room down to typical home theater size, we can say that no X-Curve compensation is needed.” In other words, he’s saying flat response is the ticket. But he also noted, “The speakers [in a home theaters] are much brighter than properly set up theater arrays,” because most home speakers extend out to 16 kHz or higher.

The reduced dampening in a home theater compared to a movie theater, coupled with speakers that have greater high frequency output, adds up to much more high frequency energy at home. Which means we’re back to having flat response, which as noted, sounds bad to most people. So any way you cut it, a room curve is needed.

As to the exact curve that’s needed – X, Academy, etc., Mr. Florian summed it up quite nicely:

While the X-Curve puts all the commercial facilities on the same page, there's no real way to account for different reverb characteristics, since even rooms with identical Rt60 measurements can still sound different due to a different spectrum of absorption. How do they finally decide the room is right or not after EQ adjustments have been performed if X-curve can still allow for some subjective variability? The answer is, listen to it with familiar reference material. Does the system sound right, bright, or dull? If it is one of the latter two, further adjustment of EQ, acoustics, or other properties may be necessary.

Regards,
Wayne

[Ayreonaut]

Here's the nearfield response of my mains, the DALI IKON 6. The built in curve sounds completely natural to me in my small room.



Here's my subwoofer response (at four locations.) I tried several approaches and settled on a 6dB rise (in addition to the crossover slope) from 80 Hz down to 30. With less curve it lacked authority. With more it was overpowering. To me, in my room, this curve sounded just right.