# Acoustic Ramp?



## Owen Bartley (Oct 18, 2006)

I ran across this while I was browsing around learning a little about diffusers, and was curious because I haven't seen something like it before.

















It seems to be a QRD with a twist... instead of being a uniform rectangular shape, with wells of several different but consistent depths, it is wedge shaped, with different wells of _varying_ depths. The backs of the wells are angled, and the depth increases as the fins get wider at the base of the wedge. The amount of the depth increase depends on the angle of the board at the back of the well.

I can see how standard diffusers are built using calculations for wavelength, etc... and am wondering if this would effectively "cover more ground" by handling different frequencies along the varying depth wells, or if it would just make a mess of the sound waves.

Just curious as it was new to me and I don't even have a remote idea of how you would make the calculations for this added complexity. Googling "acoustic ramp" (now that I know what it is called) gives some more info, but it doesn't seem very common. Has anyone tried one?


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## bpape (Sep 14, 2006)

QRD's work on more of a sliding scale with a definite upper and lower boundary where they stop scattering. There are formulas for the relationship between well width and well depth that should be obeyed. Depth determines how low, width determines up high. If it were that easy, we'd all make them 12" deep and 1/8" wide wells for more range coverage but that doesn't work well and breaks a lot of rules.

My guess is that these definitely break some rules in the shallow end of the diffuser.

Add in that these have 8 wells - not a prime number. Also the symmetric nature of it would negate the ability to properly mount 2 next to each other without a repeating pattern that would cause comb filtering.

It's probably better than a flat wall and covers a decent range, I'd just be suspect of the lobing and how smooth the dispersion pattern is in space and time.

Bryan


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## robbo266317 (Sep 22, 2008)

I have never heard of it either. 
I do like the look of it and also wonder if it would work.

I haven't done any room treatment yet in the new house for reasons too numerous to mention.
However I did notice when running Audyssey that I have some flutter echo present.

Building one of these would not cost a lot. I might give it a go.

As Bryan mentions, it may need some tweeking to improve the design.


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## Owen Bartley (Oct 18, 2006)

Thanks for the quick reply, Bryan! I kind of thought there was something strange going on there, so I'll stick to my research in the traditional style.

I thought I'd sneak in and edit another question into my original post, but you were too fast for me. I also wanted to ask about these "poly fuser" types, which I think would more closely follow traditional rules, but add some vertical dispersion?


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## bpape (Sep 14, 2006)

That looks kind of interesting. A nice way to extend the high frequency absorption without breaking the rules. But it's a incredibly difficult to build though....

Bryan


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## Owen Bartley (Oct 18, 2006)

Do you think that following the usual instructions for a standard 1D QRD, but curving the pieces instead of leaving them flat would still be effective in the calculated frequency range, plus give you the benefit of some vertical dispersion?

How does the curve extend the high frequency absorption, is it the variance in depth, or the curved surface? Just trying to wrap my head around this stuff.

It would definitely be more of a pain to build.


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## bpape (Sep 14, 2006)

The standard QRD has a definite upper and lower limit. The curve when implemented as above, extends the high frequency limit, though in a perpendicular dimension significantly to how the QRD would scatter. There would be no variable depth cavities as they follow around the arc together. Having variable depths like the ramp would again, break some of the important design rules if too varied.

Bryan


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## Owen Bartley (Oct 18, 2006)

Interesting. Thanks Bryan. I feel like some of these concepts are juuuuuust out of reach, and I need to do more reading to fully grasp them, even though they may be pretty basic once you get the hang of things. I'm most of the way through the MHA, although I've set it down for a few months now so I might need to backtrack a bit, and I've done a lot of reading online about acoustics and treatment. It's a very interesting subject, and can get amazingly complex pretty fast.


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