Absorption Behind Speakers.

[DanDan]

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

[JasonFoi]

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.

[Soundman2020]

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 -

[DanDan]

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.

80mm.jpg

DD

[Gregwor]

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

[DanDan]

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

[JasonFoi]

To me it looks like the trap robbed a bit of LF reinforcement from the hard boundary, but it certainly filled in the nulls a bit at 190/220ish hz. Seems like a good option IMO. Certainly not what i expected given the strong opinions on the subject by a few at GS.

[DanDan]

Those Dips are a bit disturbing!. But this was a quick test using my talkback mic, not really at the mix position.
DPA 4090 though. That 190/220 dip is probably not representative of the real response. But do note it is with the speaker touching the Front Wall, not the trap. i.e. No Trap.
There are many Myths out there. Quite often they start valid. e.g. Many of the big old Hi Fi Speakers did sound better distant from the wall in the domestic environment. In the case here, it is likely that Ethan or somebody else did a test which showed benefit.
Or who knows? On page 228 or so of the MHOA there is a single Tub Helmholtz allegedly completely nuking a 47Hz mode.
Hard to believe it actually happened, and hard to believe that somebody faked it.
GS has followed the International trend towards Megalomania, Despots, Suppression of views.
One doesn't see Ethan, Me, John Brandt, etc. or even GIK, there any more.
DD

[JasonFoi]

Oddly, your pal Jens is absent lately too. Just Andre, Bert from studiotips, and ocassionally Stuart. Sadly, youve left a rather large void over there my friend. I wish more would migrate this way.

[Soundman2020]

and ocassionally Stuart.

When I have time, I drop in to see if I can help out, but I don't have much spare time to be following threads over there as well as over here.

I wish more would migrate this way.

Feel free to point them over here!

- Stuart -

[Skol303]

Oddly, your pal Jens is absent lately too. Just Andre, Bert from studiotips, and ocassionally Stuart. Sadly, youve left a rather large void over there my friend. I wish more would migrate this way.

Ditto! GS has become something of a ghost town of late. I still check in there, but far less frequently. Shame really, as it was a place of healthy discourse until

[DanDan]

GS has a good GUI and had great image handling. But the image handling was changed yonks ago and is now pretty poor with lots of question marks instead of images.
Due to popularity GS had a critical mass, a sort of 'gravity' I have met some truly great friends there, some world leading acousticians. If one has something to contribute it is nice to know that many may benefit, so an audience is desirable in that sense. However an audience also leads to grandstanding, Ego nonsense. Due to allowing anonymity, Trolls and Stalkers, and no real moderation at all, it is a dirty place. Nobody cleaning or taking out the thrash. Mods resent being asked to function.
It would be nice to get Andre, Bert, Rod, Glenn, Jeff, Ethan, etc. etc. over here.
I suggest the way to do that is tell them we are here and keep posting interesting things here.
Perhaps worth remembering that any time and effort spent there is time not spent here.
DD