crtexcnndrm99 Posted July 26, 2021 Posted July 26, 2021 51 minutes ago, Pasic007 said: Also made 2 new bass traps. 3x 75mm polyester inside enclosure 19mm pine with 12mm plywood back. I can place 4kg mass loaded vinyl on front to get better effect but will experiment at later time. I actually place one behind curtains and it made big difference. This was going to be the lid but I just left it behind curtain. Nice! That’s what I was thinking to do - where’d you get the polyester batting? If using the standard insulation type you couldn’t leave it without the cloth covering it..
EHT007 Posted July 26, 2021 Author Posted July 26, 2021 2 minutes ago, crtexcnndrm99 said: Nice! That’s what I was thinking to do - where’d you get the polyester batting? If using the standard insulation type you couldn’t leave it without the cloth covering it.. Yeah I think this is just polyester, no nasties. Bradford polymax acoustic. https://www.insulwest.com.au/
crtexcnndrm99 Posted July 26, 2021 Posted July 26, 2021 2 minutes ago, Pasic007 said: Yeah I think this is just polyester, no nasties. Bradford polymax acoustic. https://www.insulwest.com.au/ Perfect. Found at Bunnings 1
EHT007 Posted July 27, 2021 Author Posted July 27, 2021 Here is a pic a posted on another thread. Im tempted to try drill it out for 45hz. I think another 51mm hole would get me there. Blue line is with HR in place. Definitely need a second HR. 1
EHT007 Posted July 27, 2021 Author Posted July 27, 2021 (edited) So im going to try build LIMP trap with 4kg membrane this is to make the box more compact as the corner is limited with available space. I've drawn up a Jig to assist me with precision, and visual appearance bolts in-line.. Going to 3d print 4 of these bad boys. Edited July 27, 2021 by Pasic007 grammaaaaa 1
EHT007 Posted July 29, 2021 Author Posted July 29, 2021 (edited) Yay Weekend. I've got few different ideas, i want to try tackle the 61hz peak. I might make two membrane type absorbers one for 45hz and the other for 61hz. Here is a Giff of before and after measurement is with Left + Right + Sub . Presets Time Range 300ms SPL Scale 100 top 50 bottom, Left 15 right 300hz Smoothing 1/48 Edited July 29, 2021 by Pasic007 1
EHT007 Posted August 1, 2021 Author Posted August 1, 2021 Membrane absorber. Silicone the front panel with membrane. Mass loaded vinyl is *****, when you try to pull and staple by your self. Second one I've done was much easier I put no more nails over the frame and placed it down on vinyl with 60kg of weigh on top. Seems to have worked ok. 1
EHT007 Posted August 1, 2021 Author Posted August 1, 2021 (edited) Another change to Helmholtz was addition of polyurethane foam in the ports! I found publication on scientific report that was published recently and they talk about addition of polyurethane around neck of the ports increase bandwidth by large amount. The resonator did demonstrate much wider bandwidth when striking the box, however it was very little change to Frequency response. What I have observed was the decay RT30 was much smoother!! Reference: https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.nature.com/articles/s41598-019-49222-w&ved=2ahUKEwjA2-_9rY_yAhWDj-YKHTM3DTQQFjAAegQIAxAC&usg=AOvVaw08_OGCbzdnj8L1m0l3P1P9 Edited August 1, 2021 by EHT007 2
EHT007 Posted August 2, 2021 Author Posted August 2, 2021 Made these up for side reflections. Hard work when you got manflu. 3
EHT007 Posted August 2, 2021 Author Posted August 2, 2021 22 minutes ago, TDX said: Mate you changed ID? Yeah. Get more views. Jks haha Pasic is my last name. Though I'd try be little more anonymous. 1
frednork Posted August 2, 2021 Posted August 2, 2021 On 01/08/2021 at 5:56 PM, EHT007 said: Membrane absorber. Silicone the front panel with membrane. Mass loaded vinyl is *****, when you try to pull and staple by your self. Second one I've done was much easier I put no more nails over the frame and placed it down on vinyl with 60kg of weigh on top. Seems to have worked ok. Interested in the measurements on this. Which calculator did you use?
EHT007 Posted August 2, 2021 Author Posted August 2, 2021 3 hours ago, frednork said: Interested in the measurements on this. Which calculator did you use? Few different ones but they are just a guide it's not until you test it your self that you know exactly what the resonance frequency is. http://www.acousticmodelling.com/multi.php And http://www.mh-audio.nl/Calculator.html Attached is a pic of what I was supposed to get. And pic of me thumping it recorded with RTA. 2
EHT007 Posted August 2, 2021 Author Posted August 2, 2021 Here is the two identical volume Membrane absorbers, one vinyl it's very tight and other has bit more slack (orange) . 1
EHT007 Posted August 5, 2021 Author Posted August 5, 2021 (edited) I picked up some more plaster trim from bunnings to help hold polyester in frame. I initially bough these for different purpose. Looks neat. Very easy to install just cut to length and staple. It's cheap around 5$ for 2.4m Edited August 5, 2021 by EHT007 2
frednork Posted August 6, 2021 Posted August 6, 2021 On 01/08/2021 at 5:56 PM, EHT007 said: Membrane absorber. Silicone the front panel with membrane. Mass loaded vinyl is *****, when you try to pull and staple by your self. Second one I've done was much easier I put no more nails over the frame and placed it down on vinyl with 60kg of weigh on top. Seems to have worked ok. These look very interesting, Did you figure out a way to tune them to what you want and have you done any before/after with these great work!!
EHT007 Posted August 6, 2021 Author Posted August 6, 2021 19 minutes ago, frednork said: These look very interesting, Did you figure out a way to tune them to what you want and have you done any before/after with these great work!! From my understanding it depends on the depth of the cabinet. Also the tightness of membrane seems to have sort of effect. It would be quicker for me to make new Membrane than try tune the old one. I ended up reshuffling the placement of all the treatments. This gave me whole different frequency response! What I have observed is say your MVL absorber is tuned for 50hz and you place it in 50hz spot with highest velocity this works really well! But let's say you don't have issue with 50hz. You find new spot for MVL absorber where there isn't much 50hz velocity and the Membrane will still absorb other frequency to a degree. I found that placing it in one corner has managed to drop some 115hz peaks I was getting. So in summary you just move around the treatment you have to get the desired effect. I bought those 10$ bunnings dolly makes placement very easy.
frednork Posted August 6, 2021 Posted August 6, 2021 5 minutes ago, EHT007 said: From my understanding it depends on the depth of the cabinet. Also the tightness of membrane seems to have sort of effect. It would be quicker for me to make new Membrane than try tune the old one. I ended up reshuffling the placement of all the treatments. This gave me whole different frequency response! What I have observed is say your MVL absorber is tuned for 50hz and you place it in 50hz spot with highest velocity this works really well! But let's say you don't have issue with 50hz. You find new spot for MVL absorber where there isn't much 50hz velocity and the Membrane will still absorb other frequency to a degree. I found that placing it in one corner has managed to drop some 115hz peaks I was getting. So in summary you just move around the treatment you have to get the desired effect. I bought those 10$ bunnings dolly makes placement very easy. Ok, cool. so do you know how much dB impact it has at say 50Hz with a trap tuned at 50. The theory suggests it is significant
EHT007 Posted August 6, 2021 Author Posted August 6, 2021 30 minutes ago, frednork said: Ok, cool. so do you know how much dB impact it has at say 50Hz with a trap tuned at 50. The theory suggests it is significant From memory I've seen 9db drop in my case. It's pretty substantial.
frednork Posted August 6, 2021 Posted August 6, 2021 1 minute ago, EHT007 said: From memory I've seen 9db drop in my case. It's pretty substantial. If that is real that is phenomenal!!
EHT007 Posted August 6, 2021 Author Posted August 6, 2021 (edited) 2 hours ago, frednork said: If that is real that is phenomenal!! Ya that was with 300L resanator. But do note that bandwidth is fairly narrow, I'm trying to recall my spreadsheet think it was like 3-4hz wide. (Measure 3db down from peak). Foam in ports has made that wider, but at the cost of lower peak. Edited August 6, 2021 by EHT007
frednork Posted August 6, 2021 Posted August 6, 2021 1 minute ago, EHT007 said: Ya that was with 300L resanator. But do note that bandwidth is fairly narrow, I'm trying to recall my spreadsheet think it was like 3-4hz wide. Foam in ports has made that wider, but at the cost of lower peak. So is that with vinyl or w/o? Am particularly interested in the limp mass traps
EHT007 Posted August 6, 2021 Author Posted August 6, 2021 Just now, frednork said: So is that with vinyl or w/o? Am particularly interested in the limp mass traps That was no Vinyl. I haven't tested the effectiveness of LIMPs. But I had to place them in opposite ends of the room as two place behind L and R speaker was too much. One sits rear left corner now and the other front right. I'll probably do some more tests when I decide to make diffuser. I'll take all treatment out and test one by one.
frednork Posted August 6, 2021 Posted August 6, 2021 Ok, thanks, It should still make a significant difference even in any corner if my understanding of theory is right
EHT007 Posted August 6, 2021 Author Posted August 6, 2021 6 minutes ago, frednork said: Ok, thanks, It should still make a significant difference even in any corner if my understanding of theory is right I've got 7 corners, open on two sides with main space 450mm sunken . Not your typical rectangular room 1
Recommended Posts