Anechoic Speaker Testing Room

[LCRLive]

Hi, Vic here... so i want to be able to setup an anechoic testing room going here in my front office in brampton for being able to create proper FRD files. These files are for my crossover guy to help me design a crossover for a tall 6-way speaker set idea for a special sound room powered by rack amps in a hybrid active/passive setup.

So for the testing, I can put the room into anechoic mode, at least i hope i can with these stacks for foam strips i can pile into tall towers... basically all these extremely firm 6 X 24 inch polyester foam offcuts - the results of the stacks being about 6 inches thick and can pile all the way up.. i can do this all around the room in a few lanes and only lose about 9 inches of the footprint if i do a basic wall treatment behind these on the wall first, pile those strips in front, and then with some large 8 foot tall acoustic panels leaning on them on the front side to keep them in place from tipping over into the room. Will also bass trap two corners with a full triangle fill behind corner fabric panel covers.

But i was wondering if this treatment is enough going all the way around to be able to make everything extremely flat in a dead way for the room response to be used as a valid anechoic testing room? the room has large storefront windows and hollow drywall, each of which will be covered with that first inch or more layer of paneling of extreme firm foam first, and am hoping that the windows and hollow drywall behind all the stacks of extreme density foam to each 'helmholtz out' some different bass frequencies depending on their resonances, hopefully with some good luck to cancel stuff out, but I am not counting on it hence the very thick treatment regardless. I just hope to get lucky there. Ceiling is ceiling tiles drop ceiling [will replace with new acoustic ceiling tiles i found... ] but with tons of the same type of extreme polyester foam up above the tiles there on top of them creating some low frequency trapping. hopefully Modally this room does not sound bad at all there doesnt appear to be any major audible modal buildup other than basic reflection issues untreated.

room is 107 tall (but about double if the ceiling tiles don't really 'count'. above the ceiling tiles is a bunch of the same foam.
the length is 172 and width is 124 and there is an angled notch in the corner with the 90 degree sides being about 55 x 55 removed out of the room with that angle.

My question is is it possible to do accurate FRD files in such a room for both the close and 1M measurements? I'll certainly run some sweeps through the room to see what the plots look like. but will go all out like this only if you guys think its worth to even set this thing up to begin with.

And as i was saying, i guess when i remove the stacks. im trying to create some very uniquely shaped speakers for this room when the room is converted to being used for the sound listening (and healing) experience.

The rest of the room would be the bean bags for the 3 sitting positions with only the center beanbag getting the most optimized stereo listening experience. The stacks of 6 x 24 x 1,5 extreme density foam strips I have no shortage of for piling everywhere as I get them every month and I sell them. I have huge piles of this stuff so I may as well use them for something when I am not selling them.

Do any of you think its possible to get a proper testing room before I go for all this? Because its hard to get FRD files for alot of speaker brands. And even then i wouldn't trust them as I would want to make my own because with some of these brands you simply never know how well they were tested and where.

 

[John Mulcahy]

You would probably get better results measuring outside, weather and noise permitting.

 

[LCRLive]

You would probably get better results measuring outside, weather and noise permitting.

I see... just would rather try to avoid what interference the ground may impart there. But what if i create a grille platform 1.5 foot tall with some minimal framing and mostly just wiring as the mesh and below that i can put a bunch of foam in there and i can go up to 1.5 foot tall platform. with 1,5 foot worth of foam in there... then any mic stand would come from the side on some other decoupled platform from iso acoustic.

As for testing the actual woofers, do people test them open baffle? or is there some major deep testing enclosures optimized per woofer requirements with some sort of very thick acoustical treatment in the enclosure?

I just hate the thought of open baffle anything. so flubby loosy goosy on the midbass, if any midbass at all. but then again maybe percieved 'tightness' 'focus' and timbral characteristics like grainy vs 'creamy' subntleties may not matter matter that much for testing i figure. I am still very new to this speaker testing stuff. But coming from the car audio world, one will very rarely meet audible expectations that a graph will show them. Ive seen flattest as possible read outs in build planning and their speakers still sounded lifeless! But then again that is car audio and it could have been a number of things causing issues.

I've started putting piles on the window ledges. It's all stacks of 6 inch x 24 x 1.5 x 2 sandwich double off-cuts. But obviously I will go all the way to the top and also go for one or two more rows in front on the ground then the 8 foot panels in front. And same in front of the drywalls and some sort of 8-ich minimum baffles in front of the angled door/

 

[John Mulcahy]

It is very difficult to create an anechoic space. Stacks of foam will be much more reflective than you might expect, anechoic chambers generally use very deep wedges. The bigger the space the better. This thread has comprehensive information on making quasi-anechoic measurements. Here is another thread that may have some useful info on testing speakers to try and replicate anechoic conditions without a chamber or a Klippel NFS.