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Room acoustics - a little tip

Discussion in 'audio' started by 2ManyBoxes, Dec 4, 2019.

  1. 2ManyBoxes

    2ManyBoxes pfm Member

    This is a story about room acoustics.

    Years ago I used to run Naim SBLs and I now run SL2s. It's only when I got the SBLs that I started thinking about room acoustics because there was a big treble problem, which could be too sharp. I tried all sorts of acoustic panels and mucked about with trying to get diffusion behind my head. None of this really cracked it.

    One evening I tried a very simple thing. Whilst playing a track that had the treble problem in spadefuls, I cupped my hand over each ear in turn. I noticed that the treble problem was much stronger on the right hand side, even though the lead singer who was producing most of the problem was stationed in the middle.

    I then looked at what was in the same plane as my ears and the tweeters on the right-hand side. On that side I've got four cubes of record storage in two stacks. The top edge of the top cube is level with my ears and the tweeters. Because the sound will bounce off a surface at the same angle that it came in at I could roughly work out what shape and size of triangle would have my ears at the bottom corner, the tweeters at the top corner and have the right angle of reflection. That gave me a point that was on the edge of one of the record cubes.

    I then simply twisted that cube through about 15 to 20 degrees so that the treble would hit the bookcase behind my head. There was now no point on that edge that would directly reflect the treble to my ears.

    Bingo, problem solved. I can now wick the volume up more because I'm not limited by the treble problem. If anything the room sounds a bit over damped because of all the acoustic foam I've put in over the years in the wrong places, I'll have to try removing some of it, but I'm just enjoying the music.

    It seems to me that the interaction between your room and your kit needs careful consideration, particularly in the plane between your head and the tweeters and particularly if your kit produces a lot of treble. Hard surfaces at the wrong angle can be a nightmare.

    You might ask why didn't I just ditch the SBLs? The answer is that otherwise they sounded absolutely bloody brilliant, a massive jump up from the Linn Keilidhs I'd had before.
    Mr Pig, mikemusic, ToTo Man and 6 others like this.
  2. mikemusic

    mikemusic pfm Member

    I've got to try a blanket or similar on the wooden fronted Ladderax cabinets directly behind me.
    Short term for a comparison.
    Longer term if it works needs thought
  3. stevec67

    stevec67 pfm Member

    I did similar with a bookcase that damped a very hard room. It was long and thin, with tiled floor and 3 unplastered stone walls. No curtains, this was in France. Sounded like a cave to start, but a rug on the floor and records and books at the reflection points on the side walls calmed it down.
    ian123running likes this.
  4. 2ManyBoxes

    2ManyBoxes pfm Member

    Putting the cubes of records on the right-hand wall at the first reflection point was exactly what I did as well. Unfortunately the wood of the cube walls is at exactly the same height as my ears and the tweeters :rolleyes:

    I can't tell you how much I've spent trying to sort this problem but going from SBLs to SL2s was just part of it...
  5. 2ManyBoxes

    2ManyBoxes pfm Member

    Someone posted that the classic acoustic room should have absorption in front of you and diffusion behind you. Commercial diffusors are pretty expensive for what they are (I bet IKEA could crank them out for £10 apiece). I've got a bookcase with a load of books of different dimensions behind my head. I've also scattered some 1:43 scale model cars and assorted knickknacks on the shelves to further break things up, although this didn't do much TBH.
  6. mikemusic

    mikemusic pfm Member

    I'll give the blanket a go when the boss is out next
    A start at least
  7. 2ManyBoxes

    2ManyBoxes pfm Member

    Diffusion is about pinging lots of reflections but in different directions. So it is lots of hard surfaces but at different angles. There seems to be a relationship that I don't understand between the wavelength of the sound and the length of the element of the diffusor element. So the diffusor should have lots of different lengths as well as angles. This is the idea behind the 'skyscraper' diffusers.

    There's a website which gives a recipe for making one out of different lengths of wood and then gluing them all together on a base board. I've just been too ill / lazy to get a round to it...

    I predict that a blanket behind your head will sound muffled and lifeless. See what you think :)
  8. Mike Reed

    Mike Reed pfm Member

    Welcome back and hope you're fully up and running now. It's been a long time since I bought that HiCap from the boot of your car in a lay-by on the A1. No Naim left at this end now, though.:)
  9. 2ManyBoxes

    2ManyBoxes pfm Member

    Mike, I'm afraid that my illness isn't curable by anything other than complete replacement of the organ in question for a new one, which they still haven't managed to develop yet :rolleyes: Still, there are much much worse health problems and essentially it only means that I can't travel very far and I have the diet of a monk stuck up a mountain.

    Another reason I've not posted much is that since I got the SL2s I've attained a near audio nirvana :) The treble problem meant that I had to spend the first track fiddling with the volume so that the treble wasn't too bad but it's loud enough to hear the bass. That's not a problem any more.

    The SL2s are something else, in a different universe from the SBLs I had before.

    When I got my house rewired I put in a dedicated spur for the wall socket for the hifi. I changed the wall socket to a switchless Crabtree one and the house already has one of those big fuses for the power shower. Any other tips you've found?

    If you've moved away from Naim what did you move to?
  10. Mike Reed

    Mike Reed pfm Member

    It's not a spur; it's a radial (circuit). Sounds like you simply stuck a twin and earth cable (hopefully at least 6mm2) into an existing (domestic) consumer unit but not sure why you mentioned the shower fuse. Only 1 socket for all the hifi? Anyway, it's prob. better than the ring main. Full dedication as far as is poss. in a dwelling is having separate cables to a separate c.u. so no physical connection to your domestic rings.

    I first sold the 135s for E.A.R. 509 valved mono's but controlled by my 552. I then changed my enormous ProAc R4s for big Quad 2905 electrostatics. I finally sold my 552, Superline, Supercap etc and got the E.A.R. 912 pre. with onboard ph/stages. Then bought a Myryad h/phone amp and sold my Headline. Finally, a few months ago, sold my freshly serviced 01 and bought a cheap NAD tuner. Apart from the latter, which more or less equalled out, each step was quite a jump in s.q. and musical enjoyment. I am now utterly Naimless, and don't regret anything; not even, surprisingly, the 30 year journey. :).

    The SL2s have an enviable reputation. I did have SBLs for a time but found them rather cool in presentation; about the time I gravitated to ProAc Ref. floor-standers in the later nineties.
  11. Mr Pig

    Mr Pig ^'- -'^

    Well Keilidhs are fairly poor so there is that...

    You are absolutely right. Sonically, everything in the room matters. The question is what do you decide on first, the Hi-Fi equipment or the furniture? ;0)
  12. Si74

    Si74 pfm Member

    Diffusors to the rear, love to try them but since my couch sits a foot from the back wall, no chance of them working.As to the speakers, saying nowt.
  13. davidjt

    davidjt pfm Member

    If you search for 'comb filtering explained' on Youtube there are several videos - all grist to the mill.
  14. darrenyeats

    darrenyeats pfm Member

    I'd get away from the wall behind the listening position at almost any cost, at least 1 metre. Have you any room for manoeuvre?
  15. Mr Pig

    Mr Pig ^'- -'^

    There aren't hard and fast rules about this. My settee is up against a brick wall. I have a large drape on it and it's fine.

    I think there is a danger in overdoing this. If you go too crazy you can end up with a lifeless room.
  16. darrenyeats

    darrenyeats pfm Member

    Hi Mr Pig, I've done the drapes thing in younger years, and overdoing those can lead to a dead sound. I prefer to have less absorbing stuff and focus on firstly speaker and listener positioning, and second things like natural diffusion, or diffraction (with curved shapes).
  17. Mr Pig

    Mr Pig ^'- -'^

    Yes. I totally agree. It's a case of living in the room and only fixing problems if you can actually heard them My room is very 'live'. Even with the drape you can hear hand claps echo and it sounds good. Most of the items you naturally put in living rooms are very good sound diffusers. Chairs, plants etc. I reckon people with solid floors and minimalist rooms will have the biggest problems.
  18. Millennium

    Millennium pfm Member

    I acoustic foamed my main room but left a lot of gaps and it still sounds a little damped. Looks the part though!
  19. ToTo Man

    ToTo Man the band not the dog

    Treating a room with 'thin' absorption materials such as drapes, acoustic foam, throws, etc, can often suck the life out of a room as it leads to lopsided dampening. 400ms-500ms is a good reverb target to aim for (my listening room is verging on the deader side at 300ms), but even more important is to aim for a constant reverb time across all frequencies. This is impossible in practice as damping low frequency ringing is much harder to achieve as the frequency decreases, but IME if you can stave off the rise in low frequency decay times to below 100Hz then you will experience significant improvements in clarity and dynamics. A viable alternative to room treatment is moving your speakers and listening seat away from boundaries and into a nearfield arrangement to increase the direct sound and reduce the reflected sound.
  20. 2ManyBoxes

    2ManyBoxes pfm Member

    Also I think it's worth especially looking at the triangle formed by the tweeters, your ears and the first reflection point. If the first reflection point just happens to be on a hard reflective surface, no matter how small, then treble will bounce straight off it into your ears.

    One other little tip, more for domestic acceptability: I got some dark grey acoustic foam squares to dampen the walls a bit. They would have looked awful so I got some small canvases on a wood frame from an art shop and stuffed the foam up the back of them. I then got some pictures printed onto canvas and attached them to the frames with a staple gun. That worked OK in that it generally damped the room and looked OK. Amazingly I managed not to fire a staple into my leg - nasty things, staple guns.

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