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Adjusting Room sound using material damping methods (not DSP)

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  • #91
    Re: The best from your room [size, positioning furnishing, construction, temperature]

    Yes, I fully understand. It's all about absorbing energy.

    A trick that can show you where best to place the wall absorbers ... seated in your listening hot spot in a darkened room ask an assistant to hold a mirror on the side wall somewhere between your seat and the speakers. Shine a torch at the mirror and according to the angle-of-incident theory (just like snooker or squash) where the light beam hits the mirror it will reflect off at the same angle. Adjust the position of the mirror forwards/backwards until the light beam strikes the speaker. That is the shortest path that the reflected sound wave can travel from the speaker to the side wall to your ear. Put most of your wall absorber at that place and you'll achieve maximum absorption for minimum surface area of treatment.

    As for the LPs - their jackets are hard and will reflect but the small air gap between them will help absorb. So, they'll help absorb but in a frequency selective way. And of course, because only one side wall is treated, it will skew the stereo image a little (but humans are good at mentally correcting for that).

    Books, especially with the spines inwards (difficult to know what they are then!) are better, but with the spines outwards, much more reflective. Heavy curtains or drapes - spaced away from the wall - are best of all. If they are on tracks then they can be slid into the listening position or put back in the corners for normal domestic life.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

    Comment


    • #92
      Reducing noise in a hospital

      Here is a video showing how the treatment of the walls and other simple sound deadening solutions improved the environment in a nursing home. Of particular interest is the treatment of the walls with what looks like BASF's Basotect melamine fireproof panels. I used these in our listening room and they are an excellent sonic solution. The material comprises of millions of microscopic 'pores' and dust settles in these pores and cannot be completely removed not even by vacuum. Note that the ones they are handling in the video seem to be covered in a (washable?) cloth. Basotect can be cut/shaped to any size.
      Alan A. Shaw
      Designer, owner
      Harbeth Audio UK

      Comment


      • #93
        Need advice on setup in small room

        Hi Alan,

        I would appreciate some advice on setting up my new P3-ES2s in a small room. Room size and possible layouts are shown in the diagram below. I've bought the speakers but haven't set them up yet.



        My original intent was to go with option 2, but the Harbeth dealer I bought from said that this option would lead to sound bouncing off between walls B and C, negatively affecting the quality of music. The other alternative would be option 1, where there is more room to move the couch further or closer to the speakers. My concern there is that the right speaker is too close to wall B, although I don't know what impact that would have on the sound. There are curtains along wall A, and bookshelves along Wall C. Unfortunately I can't test both configurations as that would necessitate a lot of furniture movement, and the wife wouldn't like that.

        Any opinions would be much appreciated, thanks!

        Comment


        • #94
          Re: Need advice on setup in small room

          That's an excellent drawing which makes is so much easier for us to understand your set-up. I encourage others to make a similar drawing when they enquire about room layouts - even a scan of a hand drawing really helps us to give best advice.

          OK. I see your problem. In the real-world, neither Option 1 nor Option 2 are ideal. I also fully appreciate the domestic practicalities of dragging the furniture around in your room to experiment with the sound, and how that would irritate a wife. It certainly would irritate mine. Frankly, I think that you have to put domestic bliss before the last degrees of sonic perfection. You also have to consider the visual symmetry of the room; even if one Option gives a better sound than the other if it makes the room look visually unbalanced or markedly asymmetric it will disturb your listening pleasure because you just won't feel comfortable sitting in there. Agree?

          So - judging from your drawings, I suggest that you're really obliged to go with Option 2 regardless of whether or not Option 1 sounds better (or not) because Option 2 looks neater and more visually appealing. The question is - how will it sound? I note that you say you have bookshelves along wall C and curtains along wall A. Both are definitely worthwhile, although the books would soak up even more if the spines are against the wall - but totally impractical as you wouldn't be able to read their titles!*

          You don't say how far you can bring the P3s into the room from wall B, but judging from the fact that the wall A is 2.8m then I suppose that the maximum distance from the wall can't be more than about 0.5m. It may even sound better with the speakers closer to the wall - it's one of those things that you'll have to experiment with yourself; at least moving a pair of P3s around is a much easier prospect than moving the furnishings.

          * Books, especially when the open pages face the sound source (the speakers), really do soak up sound. Have you walked in a wheat, rice, maize (corn) or similar tall grain field just before harvest time and shouted at the top of your voice? It's like being in an anechoic chamber - the grain ears and stems are exceptionally good at trapping sound. One of the best ways to reduce road traffic noise is to put a cereal crop field between housing and the road; the attenuation of sound by the field is almost total - until harvest day!
          Alan A. Shaw
          Designer, owner
          Harbeth Audio UK

          Comment


          • #95
            Re: Need advice on setup in small room

            Originally posted by A.S. View Post
            That's an excellent drawing which makes is so much easier for us to understand your set-up. I encourage others to make a similar drawing when they enquire about room layouts - even a scan of a hand drawing really helps us to give best advice.
            Thanks for the quick reply Alan!

            Its sad that neither option is ideal but that's real life. I could move the speakers to a much larger living room, but then I won't have the freedom to listen to what I want, anytime I want. Cest La Vie!

            Comment


            • #96
              Re: Need advice on setup in small room

              Yes, I think that it is absolutely vital that we remember (as I do at the design stage) that we're making real value speakers used by real people in real rooms, not by a few rich folks under absolutely perfect conditions.

              I attach a picture of me during a listening session during the development of the C7ES3 as I make adjustments to the crossover. As you can see, the development room was literally a small unused bedroom at home and the speakers are in a very non-ideal situation close to the wall and near to the door.

              My strongly held opinion is this: if I can design Harbeth speakers sound good in such an imperfect environment they will sound fabulous given a little more air in a bigger, better room. We design for the least fortunate listener, listening in the smallest, hardest acoustic environment to be 100% sure that everyone can enjoy the Harbeth sound in their own home.
              Attached Files
              Alan A. Shaw
              Designer, owner
              Harbeth Audio UK

              Comment


              • #97
                Bass traps

                I plan to upgrade my system with new speakers, possibly M40.1s. I feel, though, that the present acoustics of my listening room will not do credit to these speakers, so I will try to make some improvements. The easy bit will be to use absorbers to kill off the first reflections. To clean up the bass, I could need bass traps, but hesitate to litter the corners of my room with such bulky items.
                I have, however, an interesting option (at least so I think). I could actually make holes in the sidewalls in my front corners, holes that open up to attics running alongside the room. These attics have a triangular shape 1,5 times 1,5 metres and some 15 metres long. They are heavily damped on one surface with 200 mm Rock Wool (roof thermal insulation). The holes in the walls could be quite large, 1 times 1 metre, or larger. The idea behind this is, of course, to allow the high pressures caused by standing waves to dissipate into the attics. Since ALL standing waves in a room have pressure maximas in the corners, I imagine that this just might be a very efficient bass trap arrangement. The holes would be covered with fabric.

                Unfortunately I am not an acoustic engineer, so I would be very happy if somebody out there has experimented with similar arrangements and would be willing to share his/her experiences. Good ideas are also extremely welcome. Tips on literature that could be useful are also very welcome of course.

                Thanks
                Forberg

                Comment


                • #98
                  Bass traps, room treatment or room reconstruction

                  I plan to upgrade my system with new speakers, possibly M40.1s. I feel, though, that the present acoustics of my listening room will not do credit to these speakers, so I will try to make some improvements. The easy bit will be to use absorbers to kill off the first reflections. To clean up the bass, I could need bass traps, but hesitate to litter the corners of my room with such bulky items.
                  I have, however, an interesting option (at least so I think). I could actually make holes in the sidewalls in my front corners, holes that open up to attics running alongside the room. These attics have a triangular shape 1,5 times 1,5 metres and some 15 metres long. They are heavily damped on one surface with 200 mm Rock Wool (roof thermal insulation). The holes in the walls could be quite large, 1 times 1 metre, or larger. The idea behind this is, of course, to allow the high pressures caused by standing waves to dissipate into the attics. Since ALL standing waves in a room have pressure maximas in the corners, I imagine that this just might be a very efficient bass trap arrangement. The holes would be covered with fabric.

                  Unfortunately I am not an acoustic engineer, so I would be very happy if somebody out there has experimented with similar arrangements and would be willing to share his/her experiences. Good ideas are also extremely welcome. Tips on literature that could be useful are also very welcome of course.

                  Thanks
                  Forberg

                  Comment


                  • #99
                    Re: Bass traps

                    Hello,

                    ASC bass traps will work but they are quite pricey esp when you factor in freight cost from Oregon to Sweden. Also, the more traps, the better. I use a total of 14 in my listening room with the SHL5s.
                    I use bass traps for many years and they do wonders.
                    However since you are in Sweden, i suggest you look at the Lyngdorf room correction from Denmark. These are very very effective & I also use them.
                    Good luck.

                    Ferdinand

                    Comment


                    • Re: Bass traps

                      Hello Ferdinand,

                      You use 14 ASCs pluss a Lyngdorf?! I am sure all that stuff works, but I really hesitate to go down that road.
                      I think I?ll test the idea of using my attics a while longer, but thank you for your comment.

                      regards
                      Forberg

                      Comment


                      • Re: Bass traps

                        That is a really interesting idea and certainly would seem in principle to have vaildity.
                        I personally would consult an acoustician before knocking holes in my walls

                        Cheers
                        Andrew

                        Comment


                        • Re: Bass traps

                          I have used a Lyngdorf before and I did not find it that satisfactory.

                          Have you looked at Deqx HDP-3 before. It might be a better solution though I have not tried it out.

                          It also does speaker correction in addition to room correction.

                          Comment


                          • Mechanical problems & mechanical solutions

                            What would help here would be a dimensioned sketch (scanned, hand drawn?) of the room so we could see the layout clearly.

                            Derek and I hold dear an old saying from the wise men late of the BBC Research Dept. It applies right through speaker design and room acoustics in our experience and we daily work with these word very much at the front of our mind ...

                            "Solve mechanical (or acoustic) problems mechanically not electrically if at all possible".

                            In other words, no matter how fast, cheap or convenient to apply electronic EQ gizmos, it's far better to get to the root of the problem and solve the basic issue even though it involves cost, inconvenience and cosmetic considerations. An example of this is in DSP digital speaker correction within the speaker itself. These systems sound so horrible because the designer mistakenly believes that applying a layer of digital correction to a fundamentally flawed mechanical design will disguise the basic imperfections. It may measure well, but can leave a tell-tale sonic signature of a computer thrashing about overlaid onto the music - an unwelcome grittyness and glare which drives you mad. In a word these DSP-based speakers can sound extremely fatiguing.

                            No - solve the problem at root.
                            Alan A. Shaw
                            Designer, owner
                            Harbeth Audio UK

                            Comment


                            • Re: Bass traps

                              You have a point there, of course, but I?m afraid it might be darned difficult to find an acoustician who has real experience from an equivalent project. And of course it?s much more fun to do it yourself with help from the web.
                              It might seem a bit drastic to make holes in the walls, but they?re only 13 mm plaster sheets on wood frames, separating the listening room from the attics.The thermal insulation is attached to the outside of the attic triangle (the longest side) so the attics always have the same temperature as the listening room.

                              Comment


                              • Re: Bass traps

                                Originally posted by Forberg View Post
                                ... I?m afraid it might be darned difficult to find an acoustician ... and of course it?s much more fun to do it yourself with help from the web....
                                Yes. I absolutely agree! Much more fun to 'have a go' providing - and I stress this - that you do not expect an immediate miracle cure and accept that you are only at the stating point of the journey, not the end. If you keep that in mind then your expectations will be realistic and you won't be frustrated by the additional input of your time that may be needed, and maybe materials and money too.

                                Now, as it happens, I can recall a very similar concept of dividing a chamber into two with a layer of (felt) absorption between the two chambers. It was inside the BBC's LSU10 loudspeaker from about 1950. A speaker cabinet is of course exactly the same thing as listening room, but on a mucha smaller scale. The BBC's concept was patented, and being a BBC invention was well documented in the sort of simple language that we hobbyists can get our teeth into. Let me see if I can find the papers ...

                                Quote about LSU10 cabinet - "... Such (cabinet lagging) treatment is effective in suppressing high-frequency sound waves but does not sufficiently eliminate low-frequency vertical air-column resonance which occurs at about 120 Hz. This is suppressed by three ? inch layers of carpet loom felt stretched horizontally across the centre of the cabinet where the standing waves have maximum particle velocity. If a thin layer of absorbing material were attached directly to the walls the absorption would be low because particle velocity is a minimum close to a reflecting surface... "

                                See how that speaker cabinet and your twin-rooms can be considered analogous?
                                Alan A. Shaw
                                Designer, owner
                                Harbeth Audio UK

                                Comment

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