SPL basic understanding and speaker placement

[CinemaDK]

Hi everyone, I am taking my first shot at REW measuring and optimization. Been reading and analyzing away for hours, but I have to admit it´s a more difficult journey than expected :-) I do not yet have the experience or trained ears, so I am relying a lot on measurements here in the beginning.

Setup:
Processer: Denon AVR-X4000 in Direct Stereo mode
Amp: Crown XLS 1002
Speaker (LCR): Dali 6006
Room: 3 x 4,5m with lots of hard wall surfaces
Carpet + Acoustic ceiling

I have done 3 simple 20-20KHz measurements of Left speaker only. But this is a home cinema setup, so I have some limitations when it comes to speaker placement, as the they will end up in front of the screen if I move them to "perfect" positions.

I thought I would start with focus on SPL measurements, which has lead to some basic questions:

1. If I got it right, the "goal" is end up as close as possible to a straigh curve around the baseline (75db here), perhaps slightly downgoing - Harmann)?
   
   
2. My understanding is that room modes affect the SPL curve? Like when the sound from another speaker and/or a reflection of a specific frequency hits the mic after the direct sound, that energy gets "added on top" of the direct sound in the SPL?
   
   
3. I have peaks at 100-120Hz, 1500-1800Hz and 7-8KHz.
   So to work on that, I need to look at speaker placement and reflections?
   
   If yes, it's a bit of a "chicken and egg" thing, as acoustic panels needs to be move around with the speakers.
   
   
4. I have a dip at 350-1000Hz. Not sure how to fix dimps (without EQ).
   
   Can this be done with adjusting speaker placement alone or can reflections also cause dips?
   I have read about soundwaves equaling each other out, but that part I didnt quite get yet :-) Also not sure if it is relevant when I am measuring on one speaker alone.
   
   
   Now to the actual changes I tried. I started out with the speakers all out in the corners (Measurement 1/Blue). First adjustment attempt was to move them further away from the back wall according to basic recommendations + to make room for bass-traps in the future.That actually seemed to improve the center feeling from a listening perspective.
   
   
5. Looking at my SPL measurements, moving the speakers further away from the back wall (Measurement 1/Blue -> 2/Orange) just made things worse in the low frequencies (but maybe my sub will fix that, not part of the measuring right now).
   From 300-1000Hz it seems like things just got worse (measurement 2/Orange & 3/Red compared to 1/Blue). 1-2KHz and 6-8Hz improved a bit.
   
   My speakers are ported on the backside for tweeter and middle tone, and in the front for Bass, so maybe they belong/work fine in the corner(?).
   Should I start over with speaker placement trying to get back closer to the 75db curve?
   
   
6. Measurement 4/Green is with an acoustic panel on the left side first reflection points. That seemed to lower the entire SPL level from 250Hz-10KHz. Is that consistent with the fact that it has removed reflections from SPL?

 

[JStewart]

Welcome to the forum!
You’ve got a lot of good questions there, but may I start with a somewhat higher view?
For your left and right mains you are looking for where they image best and have a pleasing soundstage depth and width. Having the frequency response of the pair matched as best as possible is more important here. This is why you’ll read about symmetrical placement. Use your ears first, measure after. The microphone doesn’t hear the same way your ears and brain do.
Placement options will, of course, be limited by practical considerations, such as not placing them in front of a screen, size of the room, seating location, etc.
It’s extremely rare that the best place for the mains is the same as the best place for low frequency response.
For imaging the equilateral triangle is as good a place to start as any. And since this is also a home theater setup you won’t want to stray too far from Dolby’s speaker placement recommendations.

Surround Sound Speaker Setup Guides

Browse our step-by-step home theater surround sound speaker setup guides. From placement to room considerations, discover how to get amazing Dolby sound.

www.dolby.com

Dealing with low frequency smoothness will be dealt with subwoofer placement first, then equalization. Multiple subwoofers can also be highly beneficial if the goal is similar low frequency response for multiple seats.

Edit: this is a better link to Dolby speaker setup guides

Dolby Atmos Speaker Setup Guides

Browse our wide-range of Dolby Atmos speaker step-by-step setup guides to find the best speaker placement and configuration for your home theater.

www.dolby.com

 

[CinemaDK]

Welcome to the forum!

Thanks JSteward for taking the time to reply.

You’ve got a lot of good questions there, but may I start with a somewhat higher view?
For your left and right mains you are looking for where they image best and have a pleasing soundstage depth and width. Having the frequency response of the pair matched as best as possible is more important here. This is why you’ll read about symmetrical placement. Use your ears first, measure after. The microphone doesn’t hear the same way your ears and brain do.

I understand, and this did all start out because I felt the sound was a bit "muddy" and stereo perspective was off. But I have little experience within this area and no good reference point, as I have never listened to a calibrated and "great" setup, so it can be difficult to decide when it can be improved :-) Especially when you only make small improvements at a time.

So I was hoping that if I started out by following all core best-practices and make some improvements based on measurements afterwards, then I would improve the sound stage so much that I could actually hear the different myself.

Placement options will, of course, be limited by practical considerations, such as not placing them in front of a screen, size of the room, seating location, etc.
It’s extremely rare that the best place for the mains is the same as the best place for low frequency response.
For imaging the equilateral triangle is as good a place to start as any. And since this is also a home theater setup you won’t want to stray too far from Dolby’s speaker placement recommendations.

Those are the exact Dolby guides I started out with, but the guides i read back when I started, but they do not include anything about basic speaker placement in relation to walls and reflections as such.

So I started reading up on different forums and tried calculating speaker placement using several best practices for stereo speaker placement (equilateral triangle, 1/3 and 38% distance to back wall, 8:5 ratio between back and side wall and a few others) and found a real good place where the speakers sounded better than I have ever experienced before. Once the euphoria settled - I noticed that I couldn't see all of the projector screen :-)
So for this room it´s too late, the screen and listening position is fixed now, lesson learned. So now I will try to optimize as much as I can within the limitations I have, and then use all this knowledge for the next setup (which is probably 1-2 years out). Also when I look at most cinema setups, the perfect location for Left and Right are often not possible, like if you have your speakers behind the screen they cannot be in a circle, so I am not aiming for perfection in the stereo setup.

First I implemented a few "cheap improvement suggestions", like moving the speakers of the carpet floor to a concrete slab + spikes. I also built an acoustic panel for testing (that will be a different post).
Now my plan is to start out by optimizing the stereo placement of Left and Right speakers, then use those as base on placing the rest of the speakers according to Dolby recommendations.
Also I thought it best to start out simple with 1-2 speakers while learning about these things to not get overwhelmed by 7 more channels.

Dealing with low frequency smoothness will be dealt with subwoofer placement first, then equalization. Multiple subwoofers can also be highly beneficial if the goal is similar low frequency response for multiple seats.

Right now I dont have the equipment for adjusting frequencies for each individual channel. As I understand, this is what Audyssey tries to fix later in the calibration process.

But I fully understand that Audyssey cannot do magic, so the better conditions I can give it before it takes over, the better the end result will be.

 

[JStewart]

You’ve done some good homework and everything is as you say.

Attempting to distill your issues down I get the following:

1. Muddy sound.
Some of this will be related to the large boost at approx 110Hz. It will require Eq to fix it. I’d like to think audyssey can handle it.

2. Stereo perspective off.
Run a sweep of your left and right speakers after placing in the best of the practical spots. See where they differ. If they differ high enough in frequency that acoustic panels can help, great. Of course this also assumes one can locate where the panel(s) should go. Lower frequencies will best be handled by eq and the lowest with a well placed sub or subs.

Your room is on the smaller side as you likely know. In general reflections will be stronger and the room will have influence to a higher frequency.

Here’s a link to a build thread for a smaller room like yours that should have some useful information as to what can work:

Tower Cinema (9.1.6 in 12x12 room)

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