# first reflection concerns



## corock (Sep 7, 2009)

I'm trying to figure out how big of a screen I can fit in my HT.
How far from the side wall should I keep the front speakers to avoid first reflection issues. Acoustic panels can be used to assist in this area. The speakers are Sig 8's.


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## bpape (Sep 14, 2006)

Regardless of where they are in relation to the side walls, you'll still have reflections that will need to be addressed. Every speaker is different - though for the most part, it's good to have a minimum of 2' to the side wall if at all possible.

Bryan


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## corock (Sep 7, 2009)

This is the first time I've had speakers anywhere near the side wall and had to think about first reflection so excuse my ignorance. I have to balance the compromises in my room, so how serious are the consequences of having the speakers close to the wall, like 10 or 12 inches close.


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## bpape (Sep 14, 2006)

Not a problem at all - just trying to clarify that reflections are always a concern regardless of placement.

Having speakers close to a boundary like that will change their bass response characteristics. This is a function of what is called SBIR which is the interference caused by the spherical radiation pattern of larger bass waves coming off of a close surface and blending with the direct sound. Some interfere positively (you'll get a peak in response). Some interfere negatively (you'll get a dip in response) Where the interference occurs is a direct function of the distance from the driver to the wall boundary.

Bryan


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## corock (Sep 7, 2009)

Thanks Bryan,
Since Sig 8's have four 7" bass drivers and ported front and rear I assume having them close to the wall is going to cause some issues. I'll keep them as far away as possible, but if I do end up inside 2' will a 2" panel still be fine for the first reflection or should I go to 4".

btw, I'm reading your stickys now and as many posts as I can to get educated.


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## bpape (Sep 14, 2006)

I'd probably go with something like our 242 panel on the side which is 2" with a 1.5" gap built in. It will perform similarly to a solid 4" panel. Not quite but pretty close.

You'll also want to look at something thicker in the front corners since the rear ports will be effectively firing right into them if there's any toe in at all.

Bryan


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## bbieger (Sep 15, 2009)

Bryan is definitely the most knowledgeable on this issue but for whatever it is worth. My Polk rti 8's are 18" from each wall and room sweeps don't show that many abnormalities. That said, my back wall is completely covered with 2" rock wool, I have floor to ceiling corner bass traps and one set of 2"x 2x4' acoustic panels placed at the first reflection point.


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## bpape (Sep 14, 2006)

Right. Every room and speaker combination is different. 2' was a general rule of thumb ballpark.

Sometimes, the abnormalities can cancel out other problems. 

Bryan


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## corock (Sep 7, 2009)

I've only done measurements for subs in the past. I assume the procedure for mains would be similar. Take rew measurements, find the problem frequencies, then start moving things and treating the room to correct them.


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