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PostPosted: Thu Jan 10, 2019 10:08 am 
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Joined: Tue Mar 25, 2008 3:31 am
Posts: 63
Location: Cork Ireland
Somebody, I think probably Ethan, way way back proposed that a MiniTrap between the Front Wall and Speaker would eliminate the SBIR. If I may FWIR.
At some stage I tried it and found it to make the FWIR worse, but that may have been a particular rather than general situation.

In case I do actually get to test this I will hypothesise on an actual current scenario.
Neumann KH310, almost touching the Front Wall in a ProSumer CR. My White Room.
These are Horizontal speakers with the Woofers inside. This perhaps place the woofers closer to the FW than some other designs with deeper cabs. So my Woofers are at 30cm from the FW. So using an online Calc ......143 Hz FWIR Dip.
Insert 10cm Fibre Trap, FWIR Dip drops to 107Hz. Bobgolds.com suggests absorption at about 0.7 for a 705 100mm panel. But acousticmodelling.com can come up with Alpha as low as 0.2 around 100Hz depending on the angle of incidence, GFR, etc.
So...... what angle of incidence should we presume? Related question, what surface area of the Front Wall do we think is bouncing the wavefront back at high level? Lastly how big is our 1.2 x 0.6 Meter panel relative to the surface area of the source and or the bounce patch?

Anyone done a test one this?

DD


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PostPosted: Thu Jan 10, 2019 1:03 pm 
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Joined: Wed Jun 15, 2016 7:52 am
Posts: 63
Location: San Antonio, Texas USA
Hi Dan, thats a really good question. Its a 10' wavelength, so you would need a substantial surface area i would think. I know what the popular answer at GS would be, but I also know that Stuart has done so for quite some time. I too would be interestrd in seeing a before and after test.


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PostPosted: Fri Jan 11, 2019 5:43 am 
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Location: Santiago, Chile
Quote:
I too would be interestrd in seeing a before and after test.
I'll see if I can find something in my library of REW data from many studios... But to be honest, the majority of my clients end up soffit-mounting their speakers, so it just isn't an issue at all for them. The issue then becomes SBIR from the rear wall, which is a lot tougher to fix... and insulation alone isn't much use for that.

But 4" of 701 or 703 should have a decent effect on front-wall SBIR for speakers up against the wall. And as regards to size: I generally suggest at least three times the width of the speaker (more if possible), and from well below the level of the desk, up to about a meter above the desk, at least (and more if possible). That puts it well within the wavelength of the baffle step response mid point, ensuring that it has a good chance of seeing those frequencies, in addition to doing nice things for SBIR.

Also, Dan, I'm pretty sure you already have this, from Neumann themselves, but if not, then it's an interesting addition to your library...

http://www.neumann-kh-line.com/klein-hu ... on_v02.pdf

- Stuart -

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PostPosted: Fri Jan 18, 2019 11:24 am 
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Joined: Tue Mar 25, 2008 3:31 am
Posts: 63
Location: Cork Ireland
A quick test.
Blue is the Speaker almost touching the Wall.
Green is 80mm Gap between Speaker and Wall.
Red is a 80mm MiniTrap between Speaker and Wall.
Attachment:
80mm.jpg


DD


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PostPosted: Fri Jan 18, 2019 4:50 pm 
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Joined: Wed Feb 01, 2017 6:03 pm
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Location: St. Albert, Alberta, Canada
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Red is a 80mm MiniTrap between Speaker and Wall.

It seems to be doing the job.

I'd suggest (and like to see the results from) using 4" 703.

How big is your MiniTrap?

Greg

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PostPosted: Sat Jan 19, 2019 8:26 am 
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Joined: Tue Mar 25, 2008 3:31 am
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Location: Cork Ireland
I think you must be reading or interpreting opposite. The Red graph is the worst to my eye. The MiniTrap is an old one so just 705, 80mm thick.
OC products are in effect not available in Ireland and afaik the EU.
DD


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