# The ideal amount of (good) reflections



## maikeldepotter (Jan 10, 2008)

We all know that too much sound reflection destroys the sound image. While getting rid of ALL reflections (like in a anechoic chamber) will makes the room sound 'dead'. Obviously we need SOME sound reflections in our room in order to achieve the optimal sound experience. What would be the 'normal' or 'ideal' amount of dB increase caused by room reflections in the ideal Home Theater? 

Let's assume the SPL of a front speaker standing free outside (no reflective surfaces nearby) measures 70 dB at 2 meter distance using pink noise at volume setting -20. What would the same measurement produce with the speaker standing in a well designed home theater: 73? (total reflection SPL equals the direct SPL), higher? lower?

Is there some rough indication to give, without going into detail about bad (early) reflections and good (late and diffuse) reflections? Lets assume for the sake of this argument that the design of the HT gets rid of the bad, and keeps the good. So, how much of these good reflections you would like to have measured in dB per speaker?

Anyone?


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## salvasol (Oct 31, 2006)

This will be interesting ... most of us just deal with early reflections (I think to save $$$) :yes:


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## tonyvdb (Sep 5, 2007)

The question here is what frequency range do you want reflections in and how much I am not even sure if you can really get an answer to this. A so called dead room is great for recordings (studio) but even in these situations there will still be reflections of some sort.


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## Bob_99 (May 8, 2006)

I would strongly recommend reading:

Sound Reproduction : The Acoustics and Psychoacoustics of Loudspeakers and Rooms
by Floyd Toole

Excellent book that answers the question that you are asking. I'd tell you the answer but to be honest, I think that I need to re-read it at least one more time before I can think that I understand it. What I like about the book is that, unlike others that give you a lot of math, the author explains things in english and backs it up with references to research that has been done.

Bob


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## PT800 (Feb 19, 2008)

For starters, the bigger the distance between the speakers and walls the better. You'll still have reflections, but not to the point that they muddle the sound, as you would get when a speaker is right next to a side wall. Floyd Toole mentions this in the Harman White Papers, and probably in his book.
With a large space around the speakers you can do away with wall treatments, provided the room is normal, have thick drapes, carpet, padded seats, not too many windows, no hard wood floors.


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## maikeldepotter (Jan 10, 2008)

Bob_99 said:


> I would strongly recommend reading:
> 
> Sound Reproduction : The Acoustics and Psychoacoustics of Loudspeakers and Rooms
> by Floyd Toole
> ...



Well, the coincidence is that I just recieved this book a week ago. I agree, it is well written and I can start reading at any page and find understandable and relevant information. With quite a a lot of myth busting from my perspective! Recommended. :T


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## maikeldepotter (Jan 10, 2008)

PT800 said:


> For starters, the bigger the distance between the speakers and walls the better. You'll still have reflections, but not to the point that they muddle the sound, as you would get when a speaker is right next to a side wall. Floyd Toole mentions this in the Harman White Papers, and probably in his book.
> With a large space around the speakers you can do away with wall treatments, provided the room is normal, have thick drapes, carpet, padded seats, not too many windows, no hard wood floors.


Then wall treatment definitely will improve my sound, and the current absence of it might just be responsible for the 4 dB SPL difference between fronts and center. I already did a quick experiment with putting two pillows at the first reflection points of the fronts on the front wall. It seemed that the singers' voice gained in warmt and depth, more natural sounding. I haven't yet checked what this does with the SPL of pink noise at calibration level. To be continued...


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## maikeldepotter (Jan 10, 2008)

OK, I did my measurements. :nerd:

The 4 dB difference between the Dynaudio Contour S 1.4 (fronts) and the Contour S C (center) stays the same no matter the distance from the speaker. And, putting pillows at the closest first reflection point of the fronts does not change the SPL to a measurable degree. 

I will get back to the book and do some further reading...


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## PT800 (Feb 19, 2008)

maikeldepotter said:


> OK, I did my measurements. :nerd:
> 
> The 4 dB difference between the Dynaudio Contour S 1.4 (fronts) and the Contour S C (center) stays the same no matter the distance from the speaker. And, putting pillows at the closest first reflection point of the fronts does not change the SPL to a measurable degree.
> 
> I will get back to the book and do some further reading...


The SPL I don't think will really change. The problem with early reflections is the late arrival of the signal to the seated position. Or if the speaker is very close to the wall the reflection will bouce back into the cone, thus producing a muddled sound. Now its true that sub frequencies gain from wall boundry.


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