# First reflections and front wall treatment...



## Digital_Chris (Apr 7, 2011)

Hey there! I'd like to start off by saying that I'm a bit relieved already even before I post my questions. This forum seems to be a bit easier on the brain when it comes to suggesting room treatment specifically. I'm not going to mention names but other users on other forums are WAY to technical to say the least and it's just complete overload on my brain and makes me want to do this to my theater... :hsd: and just give up, no lie.. 

:rant::alright, rant over: :whistling:

Ok, here are a couple questions to start and tomorrow I can post pics of my specific setup 

First reflections and mirror trick. Is there any type of speaker/room design that *wouldn't* benefit from first reflection treatment? If there is not, then I would think the mirror trick is a very easy way to show where panels need to be, no? I know ETC is the tool of the gods to some and I agree, it does what it's supposed to, but the ETC tool *is* going to tell me that I have destructive reflections coming from the side walls right where the mirror tells me, right? If so, then why do some of these guru's say that even before placing first reflection treatments, I need to implement ETC into my measuring right away? I figure ETC will come in handy for getting those pesky reflections that I'm not anticipating, but not as the first tool I need to use :dontknow:

2nd question on first reflections, how much wall above and below ear height should the panels cover? I've seen 2x4 panels placed on walls all the time but not sure how high or how low they are placed or if it even matters. I guess I'm asking beacuse I can make my panels any size but don't want to over treat the room, so I'm just curious what the general rule of :T is.

Oh boy, I'm making this too long, no one will want to read this :doh:

I'll stop for now and continue tomorrow with more questions and some picturtes to help address the concerns... :wave:


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## Jetjones (Jan 29, 2012)

It has been my understanding that you do not need to just go blindly treating your room. You first need to measure your rooms frequency responce to see where your problem areas are at. There are ways to interprit the results of the measurements by doing a little simple math. I can not explain this with much detail, because honestly, I don't know much about it.

I am sure you will get answers to your questions that say you need to do (x) or  ect...from people that make a living selling this stuff. I would take those recommendations with a grain of salt. 

Bottom line is that you might either, a) make the sound worse, b) waist time and money on something that does not make a difference, c) make a latteral move, d) screw up your sound stage, or possiblity you could improve the SQ. Until you measure your room, you wont know what to do. It is totally pointless to add this stuff blindly.


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## bpape (Sep 14, 2006)

ETC is a powerful tool certainly. That said, you're correct in knowing that you almost certainly will hae problems from your reflection points and that thin panels aren't going to address all of them. You also know that some broadband bass control is going to be required in your room to bring the overall decay time in line. 

If you do those 2 things, while not a 100% solution, it will take you a long way toward a MUCH better sounding room. So, if you don't want to get into all of the technicalities, sure, you can do the things you KNOW you are going to need to do and leave it at that.

Bryan


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## Digital_Chris (Apr 7, 2011)

Thank you guys for your responses. Let me apologize though. I always makes posts like this forgetting the fact that you guys don't know what I've gone though already. I always leave out key points and somehow my posts are still uber long :heehee:

I also didn't mean to make it sound like I'm planning to blindly place treatments all over the room, but I wasn't under the original impression that it took such work and thought to cover the first reflection spots that will almost indefinitely need to be covered.

I have done lots of measurements to know that I definitely need more bass trapping, my 2 rear corner superchunks weren't as huge a help as I expected. I have no wall treatment yet because I'm in the process of modifying my wall panels to accept thicker broadband absorption. I'm now able to do 3" thick panels for those reflections, just curious about a few details on them. But like I guessed earlier, almost every room will need broadband treatment at those first reflections points, correct? And that I don't need ETC to tell me that. I was trying to keep this process simple but other users draw it out to the max, almost like it's either perfection or it will sound like garbage, sounds a bit :coocoo: to me.

So, how much of the surrounding area of the first reflection point per seat needs to be covered? Do I need to/should I make them 4' in length? Should I cover all seats first reflection points? I'd be afraid of them making the room too dead. Am I over thinking this? 

Now onto the front wall. Thicker absorbtion is better, but I'm going to say 2" minimum, correct? What about when my speakers are flush mounted into the wall, can the fiberglass protrude past the speaker? Below are a few shots of around my room. The rear wall is another area that will be difficult to adress, this is where I hope to get some ideas for treatment back there. Excuse the blurriness, manual focus in low light wasn't working out well 




























*Screen mount...*















































As you can see, the room is on the small side (18 x 10.5 x 7ish) so bass is going to be hard to tame especially with this 33hz peak at my reat seats...










And of course major, what looks to be like SBIR issues, above 80hz? This is where I'm not sure if my screen border, lip on the bottom of the LCR cabs, position between speakers and sub, etc, is causing interference. I'm going to treat the complete wall behind the screen with 2"-3" absorbtion but like my earlier question, can the fiberglass protrude past the LCR's without screwing up the projected sound?

Last note before I end another lengthy post, the distance from inside edge of screen border to the edge of the left speaker cabinet is 4 3/8" and from the bottom inside edge of the screen border to the woofer is 2". The front of the LCR baffle is about 1" away from the wall and the screen sticks out just over 2" from the wall, so there is an inch between LCR baffle and screen material.

I'll end this here for now, I will add more later


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## zheka (Jun 11, 2010)

Looks very impressive!
It's a shame that you flush mounted the mains because you pretty much lost all the advantages that waveguides give you in terms of wide uniform coverage and reflection control. 
Is there any way you could try how it sounds with L/R toed in at 45 degrees?

http://libinst.com/PublicArticles/Setup of WG Speakers.pdf

Also, it is unlikely you could tame the 30Hz mode with any room treatment. EQ is your only option ther IMHO. 
As to the rest of the curve, you coul probably get good result with one or, better yet, two more small subs anywhere in the room away from the front stage.
Are you familiar with Geddes multi sub technique?


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## Digital_Chris (Apr 7, 2011)

I did try toe-ing them in a bit but didn't notice any difference in the way it sounded. Why does flush mounting the speakers affect the way they sound, other than the reflections off the wall they are mounted on? I would guess no difference if those reflections are dealt with.

And yes, I am familiar with the Gedded approach, thank you for mentioning that. This is actually how I took care of the huge dip in the first place. I temporarily placed my table tuba in the back and it helped. Not sure how much another or bigger sub will help but...

Here are my before and after graphs for both rows, this is after the table tuba and a little EQ...

Front Center before sub...










Front Center after sub...










Overlayed...










Rear Center before sub...










Rear Center after sub...










Overlayed...











So, as you can see, it definitely helped, how much more after another or bigger sub(s) are implemented, not sure :dontknow:


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## zheka (Jun 11, 2010)

The FR looks much better with the tuba! 



Digital_Chris said:


> I did try toe-ing them in a bit but didn't notice any difference in the way it sounded. Why does flush mounting the speakers affect the way they sound, other than the reflections off the wall they are mounted on? I would guess no difference if those reflections are dealt with.


The problem is not so much the flush monting but the lack of toe in
My understanding that controlled directivity speakers are supposed to be toed in much further than conventional ones. Pi speakers guys and Earl Geddes recommend 45 degrees , Waslo suggests pointing the speakers to the side seats of the front row.
The problem is not only unwanted reflections but also significant narrowing of the sweet spot. Please take a look at Waslo's paper when you have a chance.



Digital_Chris said:


> And yes, I am familiar with the Gedded approach, thank you for mentioning that. This is actually how I took care of the huge dip in the first place. I temporarily placed my table tuba in the back and it helped. Not sure how much another or bigger sub will help but...


I do not think bigger sub is needed but another smaller one may prove beneficial especially if you can control its bandwidth and phase/delay.


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## Digital_Chris (Apr 7, 2011)

Thanks! I think I will ask the guru's over at Audiokarma about toe-in with these cabs, they seem to be the specialists on these. I will also ask them about the flush mounting in general 

I might be able to pick up a couple of Dayton 12's from another member that include a Dayton plate amp for each, that way I should have multiple adjustments for them and maybe that will get me even closer to flatter response


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## zheka (Jun 11, 2010)

Digital_Chris said:


> Thanks! I think I will ask the guru's over at Audiokarma about toe-in with these cabs, they seem to be the specialists on these. I will also ask them about the flush mounting in general
> 
> I might be able to pick up a couple of Dayton 12's from another member that include a Dayton plate amp for each, that way I should have multiple adjustments for them and maybe that will get me even closer to flatter response


It's going to be an awesome theater. I wish I was as thorough when I was building mine.
Good luck!

btw, do you use REW's RTA feature at all when dialing in the subs?


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## Digital_Chris (Apr 7, 2011)

Don't EVER wish that! Haha, it's painful! :doh:

I have not used RTA yet, I'm not sure what it's for, I guess I will have to read up on it


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## zheka (Jun 11, 2010)

Digital_Chris said:


> I have not used RTA yet, I'm not sure what it's for, I guess I will have to read up on it


Real Time Analyzer. 
Among other things you can use to watch real time the effect of the changes you are making to the sub position, volume or LPF settings,etc. 

two important things that may not be clear from the documentation:

1. use one of the RTA modes, not spectrum
2. use Pink PN test signal in signal generator.


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## Digital_Chris (Apr 7, 2011)

Ooooh, cool, I just checked that out. Neat tool!


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