Oh Stuart, you really know how to spoil the fun
Just kidding - you know how much I value your input!
I was expecting much worse, actually - going through your post it seems like I did at least some of the things right, it just wasn't very obvious from my post.
I'll try to make it more clear - please let me know if I understand you correctly (but don't be afraid to ruin my optimism, if it's needed
)
Then you didn't build the enclosure boxes correctly! You'll find it next to impossible to slide anything on Sorbothane...
Exactly! it was impossible to slide the speakers in, but after I covered the sorbothane pads with sheets of paper, it was possible - the paper got attached to the naturally sticky sorbothane and the speakers were sliding on the paper. I'm pretty sure I got the sorbothane deflection right - the results of the calculation were confirmed with actual measurements in place. For these REW measurements I used 2 rectangular pads of 50 duro sorbothane. Here's the calculation for one pad bearing half of the speaker weight:
Sorbothane_pads.png
The weight is 50lbs per speaker. To calculate the height of the box I took speaker height, added 2x height of the sorbothane pad and deduct 2x deflection. Same for the width.
I used two pads on the bottom and two pads on the top - after I found the balanced position on the bottom I glued them in and mirrored their exact position on the top with another two pads. I didn't worry about the sides just yet.
I really didn't want to leave the speakers permanently in the soffits just yet - I'm too afraid I'm gona scratch them when building things around them - that's why I'm looking for a way to slide them in and out.
For permanent installation I'm gonna use thin strips around the perimeter of the box, like you suggested in
this post.
Calculation for one strip/one side of the box/one speaker (perimeter + strategically placed small pads/offcuts from this strip):
Sorbothane_strip.png
By the way, your enclosure boxes don't seem to be massive enough. It looks like only one layer of MDF there: probably not enough, for those speakers
It's two layers of 22mm MDF (with the exception of bottom, where there's only one layer, that's screwed to another MDF in the soffit structure) - it feels pretty rigid (and heavy!).
... you have not calibrated your REW setup correctly, so your data isn't much use anyway. You should calibrate then repeat all the tests.
Hm, why do you think so? I did actually calibrate my measurement system: I'm using miniDSP UMIK usb measurement mic, which is natively recognised by REW software and it comes with it's own unique calibration file from manufacturer. It's possible I did something wrong, but the setup seemed pretty straightforward. Here are the setup/measurement steps I followed:
https://www.minidsp.com/applications/ac ... p-with-rew. With the exception of the desired sound level (75dB vs 80dB) it looks identical to your guide. I included the calibration file with the measurements below.
Birch ply? You used high density PLYWOOD for the hanger cores? Ummm!!!!! That's about TWICE the density you need, and much too rigid. You should be using Homasote for that. Homasote is a low density light-weight, soft fiber-board
You got me on this one
Thank you for your explanation! I was searching for Homasote, but it's not available around here... do you perhaps know of some substitute material? Would cork work? Or very lightweight soft thin plywood (balsa)?
...since you only posted the full-range frequency response graphs, which are not important at all for evaluating bass trap response...
...do the complete REW calibration procedure and the full "baseline - empty room" test with REW, exactly as outlined in the thread I linked above, with NO treatment at all in there: just the speakers, nothing else
By some lucky chance I do have measurements of the empty room, taken some time ago (calibrated for 75dB sound level, too):
Baseline_empty_room. It's not the same speakers, but I hope that it could still be usefull, given that we're solving 40dB hills and dips here, not 5db differences between speakers...
Here are the measurements of the speakers with soffit stuffed with insulation and hangers in place:
Soffit_hangers
And here is the measurement with insulation filled soffits but without hangers:
Soffit_without_hangers
Also, it looks like you have enough space to get one extra hanger in there: if you bring those four a little closer to each other, and slide them all over a bit, I think there's enough space to fit a fifth hanger in there. Highly recommended!
Will definitely do this when rebuilding the hangers. Thanks for the recommendation!
And finally: Are you sure your speakers are set at the correct height? They look rather low to me...
The acoustic axis of the speaker (center of the middle driver) is 125cm above the ground, as per your design - the picture is stiched from multiple shots so the perspective may be a little misleading...
Many thanks for your input, Stuart - I really appreciate it!
As you can probably feel, I'd REALLY hate to have to remove all the insulation, break the speaker boxes and start again
. But will do it, if absolutely necessary.
I'll definitely rebuild the hangers and post measurements then...
Thank you once again!
Martin