Question for Acoustics Experts for Audiophile cinema room

I see no difference in treatment strategies between two channel audio and movie surround sound. Movies have music too! So do concert DVDs. Some people will tell you that a two channel room should be more live sounding than a home theater, but I disagree with that advice. In all cases, you want to hear what the producers intended, with minimum contribution from the room.

--Ethan

If you plan to document your build, then this is the place to do it. I would suggest you start your build thread now. The advice you can obtain, especially during planning/design phase is invaluable.

I've made several adjustments on my build based-upon feedback received. In particular there were several issues with treating HVAC and stairwell wall that I was able to address based upon the great feedback from everyone.

Sounds like you will be building a theater vs. a dedicated listening room. IMO opinion, there is no reason why you can't design a theater to achieve both excellent stereo imaging and home theater emersive experience.

Ultimately, the differences in "taste" will amount to one sweet spot (stereo) vs. all seats being very good. IMO I go for all seats being good or very good. I want others to enjoy the experience with me. For room of you size, you could get two really nice sounding rows of seating.

There are some threads discussing room treatments and / or you could explore some books. I like Toole's "Sound Reproduction" or Everest's "Master Acoustics of Acoustics".

Comments on Sound Engineering:

Yes good sound engineers/room designers exist that will take into consideration your goals. If go to the pros, be prepared to spend $$. Also make sure they come to your room for infield verification (i.e. Real-time analysis). Get references too or you could be wasting your $$.

Ultimately, all spaces require verification to determine a room's performance. If you have time and inclination, you can teach yourself how to do this with your own calibrated mic and RTA software. May be a good long-term investment both educationally as well as getting some new toys.

Hope this helps. Please post your build thread!

Ethan, You don't think there is a difference in having just 2-3 speakers in a listening room to having 8-10 speakers for a 7.1 system. I am not an expert but I would think it just common sense to think there are going to be so many more points that the sound can bounce off of in a dedicated HT room compared to just 2-3 speakers in a dedicated listening room.

Like I said, I am in no expert but really interested in your thoughts on this.

Same number/size/configuration of surfaces. Same resonances and standing waves. At least, with a bass-managed system, you have more freedom to place the woofers properly.

SLC is home to me.

Ethan and Kal's viewpoints not withstanding there are significant differences between multi-channel play back and two-channel which will equate to acoustic strategies in the room. That is not to say multi-channel means no stereo imaging. While movies may have music, the difference is not between music and movie sound tracks (except that movie sound engineers at least attempt to mix to a standard we can duplicate); but, between multi-channel and two-channel playback requirements.

Have fun.

True, but a 2-speaker set-up is making more use of the room as a surround processor than a 7.1-speaker layout does.

I understand your dilemma. I gave up on two-channel playback years ago when ambiance extraction processors started do a better job than any room I could design. That coupled with having been on the mix side of things, I just cannot stand the problems inherent in even a good two-channel recording.

Yes, there may be more surfaces that need treatment, depending on where the speakers are, and where they face in relation to where you and others sit. I was just addressing the common, but incorrect IMO, opinion that two-channel music somehow benefits from untamed reflections off nearby surfaces.

--Ethan

Define "untamed".

Unfortunate but true.

I went through the same process about 6 years ago and have upgraded a couple of times since then. My room is smaller 20 X 15 X 9 I planned and then planned some more, taking in everything I could based on this site, WSR etc. I also wanted to optimize for 2 channel but had a 7.1 channel set up with a 103 inch screen. Lots of lessons learned lots of tweaking etc. I even bought an RTA to make sure the room had as flat of a response as possible.
Hear is the one thing that caught me off guard.
My cuurent L/C/R are Usher Mini Dancer 2 DMD's. but the same happend with my original speakers which were Energy Veritas 2.8's. When you position the L/R perfectly for 2 channel sound they have to be pulled out far enough from the back and side walls that they block the screen except for those sitting directly in front. So I had to compromize by having them far enough back that they did not interfere with the screen but not perfect for 2 channel. Not a big issue for a monitor speaker but when they weigh over 100 pounds each you can't keep moving them around.
Remember that when you buy your L/C/R.

Easy: Reflections that arrive within 20 milliseconds of the direct sound, and are louder than 15 dB below the direct sound. In a really wide room you might be able to get away without absorbing those reflections, or maybe diffusion would be nice. But in "normal" size rooms less than 20 or 25 feet wide, I'd use absorption at the side-wall (and ceiling) reflection points every time. Of course that's just my opinion. Others are welcome to compare both ways, and do what they think sounds best.

NOTE WELL: Emphasis is on compare both ways, not just blindly follow what I or anyone else says in a web forum. When someone asks if they'll benefit from absorption there, I suggest hanging doubled-up bath towels at the reflection points. It's not as good as real acoustic panels, but it will show you right away if it's going in the right direction.

--Ethan

This explains the principles, and the free ModeCalc program lets you experiment with different dimensions to see how the (theoretical) response will be affected:

Graphical Mode Calculator

Somewhere between 19 and 21 feet long looks pretty good.

--Ethan

[quote]I'd like to know if there is a good optimum dimension for the length of the room since I have flexibility in that area - After the walls are up and soundproofing in I estimate the room will be 14'8 wide x 8'5 high by xx length. [quote]

Well, not really. You're dealing with what is acoustically a small room. No matter what dimensions you pick, you're going to have modal response issues. Those issues will need resolution regardless of what frequencies they are. Furthermore, you're about to find out a "good" room can be as much as 6" different than a "bad" room. Think you'll ever move your head 3" one way or the other while watching a movie?

I know some people that use a entirely separate 2 channel system in their theater rooms just for music reporduction. I helped them, and we deduced the treatments on the room were the same for either setup.

It is pretty understood with one system, you really can't have both optimized. But on the room? If it's a nasty reflection in any given room causing a null or spike or whatever that you can see on the graph it should be delt with.



Now for myself? I have a really good theater for audio, I purchased a Marantz AVR quite a number of year ago now and I call them both good. Most of the time? If I am listing to music with no video associated with it, I am doing it in my living room where the room stinks. A bit of a bummer, as my theater slays my living room on audio quality.

In the end, you are not going to minimize anything in a room of that size by making small changes in dimensions. Get the room size to meet your seating, screen size and other functional requirements. Further, all room mode calculators are fundamentally wrong since wall impedance isn't taken into account. You could be fretting (even if you don't play a guitar) over a problem that isn't.

^^^ Best advice ever, especially about room mode calculators. But they're still useful for avoiding obvious problems, even if the absolute frequencies are not 100 percent accurate.

--Ethan

^^^^

Depends on how you want to make things look. If you want the treatment to be hidden, best to incorporate that into the design from the start.

I may have missed it, but I don't see any discussion regarding noise control, which may have bearing on your final interior room dimensions. This will determine your dynamic range, resolution and distraction possibilities.

There will always be compromises in a room, it's unavoidable. It's a matter of understanding the pro and cons and prioritizing them. Low frequencies are a major problem from a noise control and a sound quality point of view. Optimum room dimensions will play a significant role in sound quality. Most people consider bass tonality the biggest characteristic of the room. Dimensions and speaker/listener positions within the room will have the biggest impact on low frequency tonality.

You will still need acoustic treatments to further smooth out room modes, first order reflections and reverberation times. You want to control reverberation times in a linear fashion. That window will be the same regardless of the room being used for 7.1 or 2 channel playback. However, you should address the first order reflection points for each speaker, on each surface via appropriate diffusion or absorption.

Be cautious regarding the use of an RTA. They can tell you a little about the performance of the electronics in the room, but are not used to characterize the room itself.

There you go. Here's a suggestion. Draw a rectangle showing the largest possible size of your room. Inside that rectangle, draw seats, rows. Now, draw lines 3' out from each seating row on the sides ... at least that behind the back row (5' is better). Now, from the center of the front row draw two lines toward the front of the room tha will form a 45 degree angle from the front center seat. From the end seats on the front row, draw a straight line to the front of the room. Where your two straight lines intersect your two angled lines from the center seat, draw a line between these two points. There you have your screen width and distance to the screen from the front row. Allow approximately three feet of space behind the screen.

Ok, now you have working dimensions to use to begin determining actual room dimensions, room entry, platform locations, where you can install equipment (not in the room). In other words, you have defined your maximum and minimum dimensions available, so play in that sand box. For your walls, ceiling consider that your finished wall surfaces willl be 5" to 6" inside your framing. You can now tweak ... screen aspect vs seating distance, 3D or not 3D, speaker locations, your preferences and so forth.

 

Example.pdf 11.49609375k . file

That is really good info to get a better idea or screen size and distance, as well where seats should be from the wall. Thank you.