# Bass traps effect on bipole surrounds



## marty1 (Jun 29, 2010)

Okay it's been quite some time since I've had a look at any potential improvements to my home cinema. Not that I am unhappy in any way it's just as a tweaker I am always looking to squeeze every last ounce of improvement from my system just for the fun of it  I would love to hear your ideas on the following questions not just the main thread question which I will get to.

I have treated most of the room, tritraps in the front corners, sound absorbers along one side wall but not on the opposite wall as I have windows there so not much choice there really, just relying on a combo of blinds and curtains, how bad does this effect the balance?

Nothing on the ceiling as it will probably look a bit too much in a home cinema/living room and I am not really sure just how much positive impact it will have on the sound as I am worried that with all the absorption I have already it may deaden the room too much?

I have 3 bass traps along the rear wall about 1 foot behind the listening couch. Now to my main question.

I have to my left and right bipole surround speakers which fire towards the rear wall and to the front of the room, I sit in between the 2 tweeters, like you would with a dipole speaker when you sit in the null area, not ideal with a bipole I know as you are ideally supposed to have them placed slightly behind your listening position but I cannot really move the couch any further forward or move the bipoles further back as they are already only 2 feet from the rear wall.

What I would like to know is if I put tritraps in the rear corners is this going to have a negative impact on the surround sound? I would have thought it would as the tweeters firing at the rear wall would essentially reflect the sound off of those back corners filling up the rear soundstage, If I put tritraps there would they not deaden the rear soundstage?

I would interested to know your thoughts on this and how would anyone deal with rear wall room treatment if, like myself, you are using bipoles/dipoles and are close to the rear wall.

Marty


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## hjones4841 (Jan 21, 2009)

Well, I don't have bipole surrounds, so no real world experience. My thoughts are that the rear absorption may have an impact on rear imaging since there would be some attenuation. However, if you place the absorption out of the "line of fire" of the bipoles, then the attenuation should be less. 

To find the line of fire, use the mirror trick that you likely used when placing the absorption on the side walls - sit backwards in the main listening position chair and have someone move a mirror along the rear wall. When you can see the surrounds, then that is not the place for the absorption.

3 bass traps were not enough for me. I ended up with 5 of the GIK Monster Traps in my 12x20x8 room. What is the thickness of your bass traps and how big are they? Note that 6" thick is about the minimum for bass traps to be effective.

I think it would be helpful to post a sketch of your room with chair and speaker positions and the current locations of the absorption.


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## marty1 (Jun 29, 2010)

I have 3 Monster traps on the back wall.

If I was to put tri traps in the rear corners I would literally have hardly any bare wall left.

If you look behind the back corners of the couch there is about 2 feet between each corner on the Monster traps, sorry if it's a bit blurry.

My main listening position is next to my wife, busy on her phone as always 

Marty


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## eclipse911t (Jan 8, 2013)

My initial impression is that you are already absorbing some of the first reflections of the rear firing tweeter and any further impact on the surrounds would be very minimal and heavily outweighed by the positive impact of trapping.


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## bpape (Sep 14, 2006)

You can get the Scatter Plate option on the Tri Traps for the rear to couple bass control with scattering.

Bryan


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## marty1 (Jun 29, 2010)

Would that be a similar case to a diffuser in terms of you need to have a fair distance to have any effect, I would be about 2 feet from them?

Marty


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## bpape (Sep 14, 2006)

Don't need quite as far and it looks like you'd be farther than that measured diagonally.


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## marty1 (Jun 29, 2010)

How would i mount these in the corners?


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## bpape (Sep 14, 2006)

They just sit on the floor.


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## marty1 (Jun 29, 2010)

Just one or would I need to stack a few on top of eachother to go up to and above ear height?

Or am i misunderstanding their purpose  

Marty


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## bpape (Sep 14, 2006)

Just one each side. That also helps avoid part of the problem. Primary goal is to get the bottom end decay time under control.


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## marty1 (Jun 29, 2010)

Thanks Bryan, When i get back to my laptop i will have a look at these panels, would they need to be straddled across each corner like a tri trap placement.

Marty


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## bpape (Sep 14, 2006)

I was recommending the Tri Traps - but with the Scatter Plate option.

Bryan


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## Prof. (Oct 20, 2006)

I have a similar situation where the side surrounds are only about 2'6" forward from the back wall..
I built corner bass traps that extend up to just under the height of the surrounds..That worked well for me..
The only difference I have is one rear wall panel 5' x 5' and that has reflective facing..


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## marty1 (Jun 29, 2010)

Prof. said:


> I have a similar situation where the side surrounds are only about 2'6" forward from the back wall..
> I built corner bass traps that extend up to just under the height of the surrounds..That worked well for me..
> The only difference I have is one rear wall panel 5' x 5' and that has reflective facing..


That's a great suggestion Thanks, the only trouble is in the corner next to me I have my av equipment which is not moveable, this would mean that I could only fit a tritrap with height dimensions about 2 feet, this will go from ear height to the level of the bipoles tweeter......actually, will it still have a positive effect on the bass control considering it does not touch the floor?

In regards to your rear wall panel does that mean you only have diffusion on the rear wall, no bass traps? 



bpape said:


> I was recommending the Tri Traps - but with the Scatter Plate option.
> 
> Bryan


Ahh now I get it Thanks Bryan :T

So will the scatter plate be effective being right next to the firing line of the bipole, there won't be any rear soundstage loss?

Marty


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## Prof. (Oct 20, 2006)

marty1 said:


> That's a great suggestion Thanks, the only trouble is in the corner next to me I have my av equipment which is not moveable, this would mean that I could only fit a tritrap with height dimensions about 2 feet, this will go from ear height to the level of the bipoles tweeter......actually, will it still have a positive effect on the bass control considering it does not touch the floor?
> 
> In regards to your rear wall panel does that mean you only have diffusion on the rear wall, no bass traps?


A 2' high bass trap above your equipment rack is not going to do very much for you..Ideally the trap should be on the floor and at least 4' tall..
Is there no way of moving the equip. rack to the sidewall? How is it mounted now?
My rear wall panel is both absorber and reflector..It has 4" thick fibreglass faced with a 2ml. sheet of Mylar..


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## marty1 (Jun 29, 2010)

The are on an equipment stand which is moveable but the trouble is the speaker cables to my mains go under the floor all the way to the front of the room, I have 2 issues if I want to move the equipment to the side wall:

1. The speaker cables will not stretch that far
2. I would have to move the couch away from the side wall in order to get to the av equipment, that means the sweet spot I have spent so long calibrating and eq'ing will be lost, literally if I move 2 feet from my position I get a noticeable bass energy loss :sad:

I could slide the equipment behind the couch but it's the same predicament, bass energy loss and having to start REW all over again :gulp:

Marty


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## Prof. (Oct 20, 2006)

I had the same problem with my equipment rack..My room is only 10' wide and just 13' long from the screenwall to the back wall, which didn't give me any room for the rack..so I put it in the room adjacent to the theatre..
That allowed me then to have 24" wide bass traps in the corners of the back wall..
If it's at all possible to move the rack next door, you can always extend your speaker cables..


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## marty1 (Jun 29, 2010)

There is no room next to my room, just a small hallway with some stairs 

I will see if I can position the couch differently, I can then move the rack either next to or behind listening position. Sadly it means I will have to start all over again in terms of eq'ing :gulp:

Just had another thought, I have read quite often that diffusion is best for the rear wall but I think Bryan recommended Monster Traps only as the listening position was too close to have any real effect for diffusion. If that is the case wouldn't the scatter plate on the tri traps have very little effect?

If they are effective from a close range then would it be better for me to get scatter plates put on all of my Monster traps on that rear wall? I want to get as much treatment as possible but I am always concerned that I may make the room too dead, I am not sure how to tell if it is too dead at all.

Marty


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## bpape (Sep 14, 2006)

You would want 3' minimum to the scatter plates, 4 or more is better. 

Bryan


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## marty1 (Jun 29, 2010)

Thanks Bryan, thats good to know.

With the current setup its worth doing scatter plates on the tritraps but not the monsters behind me as they're only about a foot from my head.

Ideally if I could move the couch forward is it better to have the scatter plates on all the bass traps or not?

Marty


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## bpape (Sep 14, 2006)

Do them on the Tri Traps to help keep the surround field a bit more lively and make it sound bigger. The Monsters you'd have to move so far, not sure you'd be in a decent place for bass control, though the back row isn't real good right now. Just not sure what it would do to the front row.


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## marty1 (Jun 29, 2010)

Actually the seating position has quite an even response as is, IIRC moving the couch forward gives me a huge null around 50hz which sucks out some of the punch


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## marty1 (Jun 29, 2010)

Okay I've moved my couch forward a bit so I am now just slightly over 3ft away from the rear wall monster traps.

There is now room to fit some tritraps  

So just to check, I should go with tritraps with scatterplates attached. Will it be more benificial to have scatter plates attached to all 3 of my rear wall monster traps too, just wondering if it would be better for bipole reflections to have diffusion there?

Marty


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## bpape (Sep 14, 2006)

3' really isn't enough to let the scattering work right unfortunately so while maybe on the Tri Traps, likely not on the Monsters.

If you want extended bass control but not the reduction in mids/highs on them, I would use the Range Limiter membrane.


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## marty1 (Jun 29, 2010)

bpape said:


> 3' really isn't enough to let the scattering work right unfortunately so while maybe on the Tri Traps, likely not on the Monsters.
> 
> If you want extended bass control but not the reduction in mids/highs on them, I would use the Range Limiter membrane.


The tritraps would still be about the same distance as my monsters, well at least the one to my left is so is it even worth it on the tritraps?

I am on my phone at the moment so I will have a proper look later but does the range limiter membrane just attach to my existing monsters or is it an altogether different panel?

Marty


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## bpape (Sep 14, 2006)

It's a different product that's built in.


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## marty1 (Jun 29, 2010)

I will have a look at them on the website.

So in the meantime I gather that the scatterplates are not really going to add much to the rear soundstage (Monsters & Tritraps) from my current seated position right?

Marty


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## bpape (Sep 14, 2006)

I would think you might get away with them in the Tri Traps but not the Montsers.


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## marty1 (Jun 29, 2010)

Okay Thank You Bryan.

Is there a reason why it would work on the tris but not on the monsters, just out of curiousity?

Marty


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## bpape (Sep 14, 2006)

Well, the scattering I think will be OK in the corners wtih the reflective portion of the plate at an angle to you. Right behind you, those areas would be straight specular reflections for what is not absorbed/scattered.


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## marty1 (Jun 29, 2010)

Brilliant Thank You Bryan


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