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Deep End DIY - My first speaker project


acg

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So, I did this today...

 

20230917_125947.thumb.jpg.5f33aedcaeb7d9f633c8fec0e332b933.jpg

 

...celing VPR's are up.  Not yet skinned.

 

The aim here is to try to tidy up the floor/ceiling interactions as much as possible.  That sloped ceiling at the back of the room is a massive reflector of sound down to the listening chair and I made a slightly different kind of VPR more suited to a diagonal installation than the type used for the walls.  I was hoping-against-hope that these fellas would sort out the octave wide SPL suckout centred on about 80Hz but running around the room with a microphone prior to installing these gave me enough information to dash my hopes.  Where I thought they might work really well based on floor-celing dimensions is from 100Hz through to perhaps 600Hz. 

 

Below are the measurements with the trapdoor closed (no smoothing):

 

CeilingVPRnotskinned.jpg.9154b6fdfdbcc71eae9473a4bd846165.jpg

 

So as you can see there has been a little bit of activity in that 80Hz suckout, some good, some not so good (don't you love how adding bass trapping is a two steps forward, one step backwards kind of endeavour!) but certainy not worthy of the effort to yeet about 200kg of steel onto the ceiling.  However, look at the change from 125Hz - 600Hz...very nice.  I'm not expecting perfect because I'm only treating half the ceiling and there is nothing but carpet happening for the corresponding footprint of floor.  The benefit may look a bit random in the graph above but when viewed separately the blue line is much more regular than the orange line.  That 200Hz-300Hz region is lower than I would like but perhaps I can help that with the next stage of room treatment.

 

What this graph does not show  (of course) is the change to decay times.  These ceiling VPR's have got the -60dB decay time to less than 500ms at all frequencies:  20Hz - 35Hz now sits in the range 350ms-500ms...job done and well worth the effort.  Last nights listening session included a lot of electronic music with a oodles of 20Hz-30Hz content...so loud but so clean!  Zero muddiness...beautiful.

 

So, next step is to skin these celiing VPR's.  The temptation here is to go with commercial absorption products so that I can experiment with absorption and diffusion in different locations.  Diffusion may be useful at the lateral extremes and perhaps right up near the ceiling peak.  The absorption panels will need to be doing something substantial at 200Hz and not fade away in the top couple of octaves.  Time to do a bit of research.

 

Then I need to attack that 80Hz octave wide suckout.  As evidenced by the graph above there is an element of ceiling/floor interaction happening there but I think it will be fixed by driving the bass from a second location.  Time to experiment.   

 

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11 minutes ago, acg said:

attack that 80Hz octave wide suckout

More subs are about the only way to fix that, if anything at all.

I have similar at 50Hz, much better after 12m2 of MLV Trapping, Strangely it is not an audible thing and my old 3rd octave real time Audio Control RTA doesn't pick it.

What will you skin the traps with ?

 

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23 hours ago, playdough said:

What will you skin the traps with ?

 

A soft faced absorber to get those top couple of octaves of absorption, but thick enough to get down to maybe 200Hz.  Am prefering not to have to build something from scratch so perhaps multiples of a Vicoustic or Artnovion panel, or maybe just three or four melamine or poly panels and be done with it.  Will need to be about 50mm thick and nothing but white for this application...there is enough other stuff in the room to draw ones attention and the last thing I need is another "statement" piece of room decor...sigh.

 

The melamine panels would be quicker, but the commercial 600mmx600mm panels would allow me to experiment with both absorption and diffusion on the ceiling.  Dunno.

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I had some very good results with fixing a clap echo down to 200hz showing some coefficient at lower frequencies (2.4m ceiling) , 2x  20mm layers of Polymax white , with a  cover layer of upholstery material. 40mm DAR Pine framing, glued and screwed, stapled the material round with air stapler. Covered 2 thirds of the ceiling area. Light and easy to fix.

 

Agree it has to be white. The material I used was a shade off white and yea even though only 40mm thin and looks darker do attract the eye a little, gives it purpose IMHO.

Your gable ceiling would be better than this flat 2.4m, terrible until treated 🙂

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  • 4 months later...
On 17/9/2023 at 4:04 PM, acg said:

Then I need to attack that 80Hz octave wide suckout. 

Can you show the SPL of each speaker separately on a chart for 0 to 600 Hz  !?

 

Perhaps start with just the L channels.... or just the right channels.

 

... and then later, move on to the opposite channel, and the combined (L and R) responses, if needed.

Edited by davewantsmoore
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On 02/02/2024 at 11:22 AM, davewantsmoore said:

Can you show the SPL of each speaker separately on a chart for 0 to 600 Hz  !?

 

Perhaps start with just the L channels.... or just the right channels.

 

... and then later, move on to the opposite channel, and the combined (L and R) responses, if needed.

 

Will do Dave.  May take a while...am currently preoccupied restoring my (now) vintage enduro bike and finishing the room acoustic treatment.  Very close on both, then I anticipate geting back to the final tuning of the horns.

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  • 3 weeks later...
On 18/09/2023 at 4:06 PM, acg said:

A soft faced absorber to get those top couple of octaves of absorption, but thick enough to get down to maybe 200Hz .... Will need to be about 50mm thick and nothing but white for this application...

Obviously if only using absorption, 50mm thick is too thin to be effective down to 200Hz even if appropriately air gapped.

@200Hz, max air particle velocity (wavelength/4) is 430mm from the boundary - which should be the mid point of your absorption...but you know all this already...

 

Mike

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