acg Posted September 16, 2023 Author Posted September 16, 2023 (edited) Busy with the ceiling VPR's right now @frednork, but yes, looks like EBU is my jam. Looks like that part of the standard is based on that aforementioned research. Edited September 16, 2023 by acg 1
acg Posted September 17, 2023 Author Posted September 17, 2023 So, I did this today... ...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): 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. 2
playdough Posted September 17, 2023 Posted September 17, 2023 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 ?
acg Posted September 18, 2023 Author Posted September 18, 2023 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. 1
playdough Posted September 18, 2023 Posted September 18, 2023 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
davewantsmoore Posted February 2, 2024 Posted February 2, 2024 (edited) 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 February 2, 2024 by davewantsmoore
acg Posted February 6, 2024 Author Posted February 6, 2024 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.
Silent Screamer Posted February 10, 2024 Posted February 10, 2024 My imagination, or are these things breeding? I thought there were originally 5 or 6 stacked together. 1
almikel Posted February 27, 2024 Posted February 27, 2024 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
acg Posted October 5, 2024 Author Posted October 5, 2024 (edited) It's been a while. Am back to audio after playing with other interests for a while and today decided to finally get in and properly investigate the proposed midbass channel. For catchup, my system has a big broad suckout 60-100Hz and am about 10dB down in general below that. Walking around with an SPL meter while playing sines of the problem frequencies helped me identify where they were loudest and hence gave me an idea where the midbass channels need to be located. My weird ceiling shape seems to be wreaking havoc with these bass frequencies and they cannot be driven from anywhere in the front half of the room or anywhere that I would prefer. Today, I bolted one of my favourite paper cone 15" woofers into a roughshod sealed box and re-tried all my prefered spots and they were just rubbish. Did little to nothing at all for the frequency response. Then I put it in the first of the candidate locations at the back of the room, hidden inside one of my bass traps and still in a physically time-alignable position and this is what happened... Sweet mother of Jesus! Purple is without midbass channel - Green is with midbass channel. No smoothing has been applied. If you do the maths, prior to adding the midbass channel 70Hz was just 1.5% of the volume it was supposed to be, now with one little paper 15" driver in the right spot 70Hz is 50% down. I have three pairs of the Vitavox 15"ers and always planned to at least parallel a pair if not the trio, so I should be able to get that green line another 6dB or more higher, thus with the 100% of the required volume. Plus, it is easy to adjust the line level filters at the input to the six channel amplifier to raise or lower the channel gain to suit. The beauty of this location for the midbass channel is that it is hidden inside an existing bass trap and I can knock up the roughest, most ugly yet functional boxes and not have to waste time finishing them for any kind of aesthetics. Fingers crossed that the frequency response holds up when the drivers are paralleled and the low pass filter is applied but if so the frequency response down to 35Hz may just be +/- 3dB which is a extraordinary considering all my EQ is analogue (room treatment, filters etc.) which means my records will be on the same playing field as my digital sources which has been the goal from day one. There are a few options for 30Hz and below, including another bass channel or perhaps even messing with the filters into the six channel amplifier, but that will be the final step in room tuning. Edited October 5, 2024 by acg 4
andyr Posted October 5, 2024 Posted October 5, 2024 With respect - I suggest we need to see the graph up to 20kHz - you stopping at 205Hz doesn't really give us enough info to judge whether or not it's a good overall FR. But it's certainly not the 'classic' sloping down towards the right FR!
acg Posted October 5, 2024 Author Posted October 5, 2024 @andyrPurpose of the post above is about change of bass performance with addition of midbass channel. Frequency above 400Hz will not be greatly altered by this channel, and at the moment the new channel is unfiltered (i.e. no low pass) so it is definitely increasing SPL up to about 4kHz right now. Tomorrow I will play with some filters and perhaps knock up some boxes for paralleled woofers. See below for the higher frequency portion of the response at the listening position. Note that there are in effect five slopes from 400Hz and up...these are achieved by twiddling some knobs on the six channel amplifier to tailor the sound to my preference so all are valid. There are also other knobs to twiddle that change the sound (valve bias) but not the frequency response in any meaningful way on a graph such as below. Will add a couple of dB to the gain of the midrange channel (3.2kHz to 7kHz) to make it all nice and straight, but that is a job for another day. 1
andyr Posted October 5, 2024 Posted October 5, 2024 2 hours ago, acg said: @andyrPurpose of the post above is about change of bass performance with addition of midbass channel. Frequency above 400Hz will not be greatly altered by this channel, and at the moment the new channel is unfiltered (i.e. no low pass) so it is definitely increasing SPL up to about 4kHz right now. Tomorrow I will play with some filters and perhaps knock up some boxes for paralleled woofers. See below for the higher frequency portion of the response at the listening position. Note that there are in effect five slopes from 400Hz and up...these are achieved by twiddling some knobs on the six channel amplifier to tailor the sound to my preference so all are valid. There are also other knobs to twiddle that change the sound (valve bias) but not the frequency response in any meaningful way on a graph such as below. Will add a couple of dB to the gain of the midrange channel (3.2kHz to 7kHz) to make it all nice and straight, but that is a job for another day. I still reckon your roll-off towards higher frequencies (from 2.5K to 8K) is still too extreme - even at the top-most graph.
Red MacKay Posted October 5, 2024 Posted October 5, 2024 I heard it last week - it certainly wasn't extreme then! It certainly pulled every recording apart.
acg Posted October 5, 2024 Author Posted October 5, 2024 1 hour ago, andyr said: I still reckon your roll-off towards higher frequencies (from 2.5K to 8K) is still too extreme - even at the top-most graph. It might be if I had all the bass happening, but I don't presently, and will do in relatively short order. Then I will twiddle a few knobs and flatten out that curve...maybe...if it needs it. What you don't see in that SPL vs Hz graph is how controlled the bass modes are in my room due to all the VPR's. The waterfall shows even decay from 20Hz to 20kHz without major deviation or ringing and as a result I don't think I'll need as "flat" a house curve as someone in a more lively, uncontrolled and reverberant space as I won't need the treble so loud to cut through so much muddy, textureless bass. Not really sure how we got to talking about mid and upper frequency response when I came on to talk about bass, but there you go...forums. 1
acg Posted October 5, 2024 Author Posted October 5, 2024 27 minutes ago, Red MacKay said: I heard it last week - it certainly wasn't extreme then! It certainly pulled every recording apart. Was good to meet you Red. We will have to set aside more time when next you are up this way. 1
acg Posted October 9, 2024 Author Posted October 9, 2024 (edited) Moment of truth...does it fit? Got a Depeche Mode concert cranking on youtube and just shuffled the first midbass box upstairs. For scale, that horn beside it is 1m or 40" diameter. Midbass consists of three Vitavox K15/40 drivers each side. My wife stole my ute to take my daughter horseriding in NSW over the long weekend so I was left with a normal car sans towball to source lumber to build the boxes and I was unable to source MDF in anything thicker than 16mm, so I paid the iron price and built the boxes using 18mm hardwood. They are as rough made but only took a day each to cut/glue screw and wire and will go into existing bass traps never to be seen again. The paralleled trio of drivers should hopefully provide a tad of headroom so I can be inventive with the crossover filter. Fingers crossed. Will get this first fellow into its bass trap tonight, the second perhaps over the weekend and then the 12m long speaker wires should turn up next week so it can all be hooked up. Will have to see how much room there is to isolate these boxes from the floor. It makes a huuuge difference to soundproofing downstairs if the floor is not directly excited by the speakers, and all other speakers are isolated from the floor, so this one will also be one way or another. Edited October 9, 2024 by acg 1
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