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Below; another diagram of measured absorbtion from that thesis for MSc at KTH. Setup: The same 70 mm high sealed wooden frame, 10,5 m², on the floor. Slats 70x16 mm on top of the frame with 4 mm gaps in between, below the slats the filling: A) 70 mm glasswool (”Glasull”); B) 50 mm rockwool...

A helmholtz / slat absorber with narrow depth, like 10 cm / 4", can show good absorbtion performance in the lower frequencies if made correctly. I posted the diagram below on a Swedish forum yesterday. It has been posted on the Gearslutz forum before by the acoustician Jens Eklund. The diagram...

A table top of perforated metal or stretched metal will work fine, as long as the perforation is large enough, say above 30% or so. A post I made on another forum: https://gearspace.com/board/showpost.php?p=15523832&postcount=16 (Check the link within that link) A crash course...

I had Ohm's law from 7th year at school, so 13-14 years old (compulsory school starting when you turn 7 years old in Sweden). I was a bit surprised some years later when I was an exchange student in Georgia, USA and took science class for all 3 semesters as a 12 th grade senior (age 17-18). What...

Those circular absorbers may be called bass traps in the advertisement but are they ...? I guess my Italian is about as good as your Swedish, but I couldn't find any specification / detailed test report from a reputable laboratory for them. If one reads acoustic books (like Cox' and D'Antonios'...

If one is on a tight budget, I wouldn't buy ready made costly absorbers or panels. -After all, the common types are nothing more than glass or rockwool, put in a frame and dressed up with some fabric. (Basotect, a melamine foam from BASF is an exception from those but costly if you want...

I agree with that, a diffuse field is impossible in any normal sized room, which is the reason I didn't write RT60. Decay time varies with frequency and low frequncies cannot be diffuse in any normal sized room. I don't agree with your remark in the posted diagram though, about "noise in the...

My ETCs are quite similar. What I have noticed though, is that when the Schröder Integral curve start to rise above the straight line (around -30 to -40 dB), it is because of bass mode frequencies are lingering for a longer time at the place of the microphone. If I move the microphone towards...

Get some large paper board / paper and draw up angles in 15 degrees increments. Put a Lazy Susan in the very center of the paper with the speaker on top of it. Ikea's "Snudda" isn't that expensive. https://www.ikea.com/us/en/p/snudda-lazy-susan-solid-wood-90074483/

(My bolding). No, not really. One must consider the mass / area unit, as well as the geometry of the foot (its form factor). A circular disc shows different values compared to a rectangular one, even if the “flat area” is the same, -the area along the circumference x thickness is different for...

To reach a natural resonance frequency of 20 Hz, a foot of solid rubber and hardness of, say 60 Shore A, needs to be compressed about 6-7 mm ( = a lot !!!). It will then start to isolate / not transmit speaker vibrations from 20 x root (2) Hz and upwards (>28,2 Hz). At its resonance frequency it...