# Effect of early reflections



## atomik (Apr 8, 2009)

Hi there !

I've made some measurement today. I just want to see the effect of the first reflections on my desk.

So I mesure on axis at 1 meter the response with REW with and without some foam on my desk (I have only 2 pieces of 25cm² polyeurethan foam 2cm thick...).

Here the result where we can see some comb filtering (green is WITH foam and purple without):









How do you get rid of these early reflection in studio ? (because there is mixing table between the monitor and you...)

Thanks


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## bpape (Sep 14, 2006)

Most pro studios have their board there and it slants down from the front toward the engineer. The monitors are normally on the bridge or on stands so they're not so close to the surface either.

Bryan


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## DragonMusic (Apr 6, 2009)

atomik said:


> How do you get rid of these early reflection in studio ? (because there is mixing table between the monitor and you...)


I prefer my monitors on stands behind the desk to avoid some early reflections. How is your setup?


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## atomik (Apr 8, 2009)

I think a photo would give you an idea of my setup. My goal is not to have a studio but just an Hi-Fi setup.

Whan I made the measure I measure only the left channel with the two foam in front of the left speaker.

The bass-traps make in fact very little effect. It just decrease a "null" at 150-160Hz (I'll put shots later)

Thanks


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## bpape (Sep 14, 2006)

The desktop coupled with the low ceiling will definitely give you some issues. Any chance of pulling the desk a bit forward to get farther away from the slanted ceiling?

Bryan


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## atomik (Apr 8, 2009)

Yes it's possible  How far ? try and see with REW ?

What is the problem with that ? Multiple reflexion in the bass ? (as the event is on the back of the loudspeaker ?)


Thanks

N.B: I think I will love this forum :sn: Very fast response :R


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## bpape (Sep 14, 2006)

You will get boundary interactions in the bass as you saw in your plots from any surface that's close to the woofer due to uneven room gain and cancellations. Right now, you have 3 surfaces that are relatively close, and the desktop coupled with the angled ceiling is acting like a horn. 

Not sure how much space you have to pull things out or where your head is in relation to the room length but I'd like to see maybe another foot at a minimum depending.

Bryan


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## atomik (Apr 8, 2009)

Ok thanks. I haven't think about the horn...


I'll try moving the desk (fortunatly I've put wheels under my desk) when I have time and plot some results here.


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## atomik (Apr 8, 2009)

Here some graphs I made during my free time. Note that measurement were done at 3 days interval so the volume is not exactly the same...

blue is speaker 30cm from wall and purple about 10cm




























Between 100 and 200Hz holes reduce in size (dont' know if it's the correct work..correct me if not).
The holes at 5KHz and about 15Khz are present in the two configuration.

I will do more precise measurement when I have time.

Do you think some foam behind the monitors could have some benefit ?

Thanks


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## bpape (Sep 14, 2006)

The foam would have to be VERY thick to have much impact in the bass region. 2" of OC703 or equivalent would work just fine though.

The 5k and 15k are not something you can normally deal with via treatments. Usually, you're working with 300Hz down in terms of frequency response. High frequency things like that are usually either of axis anomalies with the speakers or something actually resonating in the room like glass table tops, TV screens, windows, vases, etc.

Bryan


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## atomik (Apr 8, 2009)

After a long time....I decide to treat my room with fiber glass (like OC703).

I can have this: http://www.isover.be/sonebel_110_fr.html but doesn't have specifications...

I'm going to make panels like this (10 cm thick): http://www.basstraps.net/DIY-BASS-TRAPS-MADE-EASY.pdf

So the question is: Where to put the panels ? I think one in each corner and two behind my speakers ?

Thanks for help


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