REW analysis, need for room treatment?

[Ruato]

Hi all,

I have been building my first "real" home theater. It is a 5.1.4 system (Q Acoustics 3000i series) with Denon X3600H as the AVR. I also did some REW measurements with the following results (please, see the attached images). The measurements have been done with Denon room correction enabled.

About the room and the measurements:
- Concrete all around (floor, 3 walls and the ceiling).
- Left side is open to the dining room and to other parts of the apartment.
- Right side is almost fully covered with windows.
- Measurements: width 18ft, length 11.5ft, height 9ft.
- No room treatment done yet. However, I have considered getting some attenuation material/panels to the back wall.
- MLP is about 2.25ft from the back wall.
- There is a very noticeable echo if one, for example, claps his hands.
- The background noice level is very high as I live in the city centre. Almost 60dB.
- As written in the images, I have boosted subwoofer by 5.5dB to compensate the "human ear attenuation" of low frequency voices.

Some questions regarding the attached measurements:
- In general, how does the SPL and Waterfall measurements look like?
- There is quite a large dip around 2k, does it cause issues?
- In your opinion, would attenuation panels on the back wall help producing considerably better audio?
- The bass response seems quite OK compared to the rest of the frequency spectrum? Or would you consider some room treatment to make it even better?

Any help and comments are very much appreciated, thank you!

Kind regards,
Kari

 

[Marc Lombardi]

If this is with room correction applied it would be interesting to see measurements with room correction turned off. Seems like very wide peaks and nulls in the response especially that wide 2KHz null and (assuming nominal 88db) the bass is up 10db! The waterfall does show considerable background noise. Does Denon room correction work full range or just on the bass?

 

[Tommyjr]

I'm a bit if a novice, but from my understanding, room treatments will help significantly with sound localization and speech intelligibility more than affecting your frequency response. Adding some room absorption is highly recommended in a concrete room. On YouTube look up home theater gurus and absorption. It's a great tutorial explaining how to do it properly. Start with that, then do new measurements. From there you could get into equalization using minidsp.

 

[Marc Lombardi]

Yes room treatments will help a lot: Bass traps in corners, some absorption at first reflection points side walls and ceiling, possibly some absorption or diffusion center of the front and back walls. What concerns me is that huge null at 2KHz .... have to track that down because it's unusual to have an acoustic cause for something like that.

 

[linearphase]

Yeah that is pretty awful response but some of it could be measurement error. Where is the measurement mic relative to the speaker and listening position? The huge dip in the 2 KHz region looks like the woofer and tweeter are out of phase acoustically. This could be due to the mic being at an extreme angle relative to the woofer tweeter axis such that the path length from the woofer to the mic is 6” different than the path length of the tweeter to the mic OR the system came from the factory wired backward.

It is also possible the Denon EQ messed this up. In order to get correlation between Denon EQ and REW it is important to have the mics in very close physical proximity. Probably within 1” is good enough.

I would turn the Denon corrections all off and repeat the measurements. Place the REW mic at the listening position where the ears would normally be. Then repeat the REW measurements. Show a display of 20-20KHz at 5dB per vertical division to start.

With that much concrete you are going to have real problems. I would start by putting a large area rug on the floor that covers as much of the floor as possible. To judge the effects of sidewall treatment you can use large moving blankets hung on the walls at a point roughly half way between the speakers and the MLP?
The ceiling and other untreated wall wil also likely require attenuation. The bass boost should be reduced about 2-3 dB.