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Since its inception ten years ago, the Harbeth User Group's ambition has been to create a lasting knowledge archive. Knowledge is based on facts and observations. Knowledge is timeless. Knowledge is human independent and replicatable. However, we live in new world where thanks to social media, 'facts' have become flexible and personal. HUG operates in that real world.

HUG has two approaches to contributor's Posts. If you have, like us, a scientific mind and are curious about how the ear works, how it can lead us to make the right - and wrong - decisions, and about the technical ins and outs of audio equipment, how it's designed and what choices the designer makes, then the factual area of HUG is for you. The objective methods of comparing audio equipment under controlled conditions has been thoroughly examined here on HUG and elsewhere and can be easily understood and tried with negligible technical knowledge.

Alternatively, if you just like chatting about audio and subjectivity rules for you, then the Subjective Soundings sub-forum is you. If upon examination we think that Posts are better suited to one sub-forum than than the other, they will be redirected during Moderation, which is applied throughout the site.

Questions and Posts about, for example, 'does amplifier A sounds better than amplifier B' or 'which speaker stands or cables are best' are suitable for the Subjective Soundings area.

The Moderators' decision is final in all matters regarding what appears here. That said, very few Posts are rejected. HUG Moderation individually spell and layout checks Posts for clarity but due to the workload, Posts in the Subjective Soundings area, from Oct. 2016 will not be. We regret that but we are unable to accept Posts that present what we consider to be free advertising for products that Harbeth does not make.

That's it! Enjoy!

{Updated Nov. 2016A}
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Adjusting Room sound using material damping methods (not DSP)

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  • Re: A really good listening room - how to make

    Originally posted by davidlovel View Post
    ...I assume that your "discussion in New York" was at the AES meeting...
    No, most definitely not the Audio Engineering Society which was (apparently) running at about the same time in New York.

    As the maths alone tells you nothing about how a speaker sounds I'm afraid that as a humble speaker designer I do not have the intellect, imagination or patience to wade through impenetrable maths of the type that is the AES these past years to be no further forward in subjective evaluation. Harwood was the last really great writer - but the greatest of all was, of course, Michael Faraday - my personal hero. He brought science to the ordinary man through his public lectures.

    No, my training session was outside AES and is here.

    I have more to comment on this later. It was remarkable not for what we covered, but what we didn't.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

    Comment


    • Re: Side-wall reflection

      Originally posted by davidlovel View Post
      Not sure if you have read my recent post on this thread, Alan:
      http://www.harbeth.co.uk/usergroup/s...=6182#poststop
      I am sure it is very subjective but evidence of the potential value of the first side-wall reflection has been around for a few years.
      David
      Talking about side-wall reflections - Sam, the Harbeth agent in Malaysia, set up a pair of SHL5 in a small room, about 4.5m X 7m. The speakers are placed on the short wall. One of the side wall has a big glass window looking out to the outer room. A rather think foam is placed over it. The concrete wall on the other side is not treated. Sam did it that way on purpose to make the room 'alive'.

      I was impressed by the demo. In fact Harbeth was the first speaker I auditioned after I decided to look for an alternative to my 12 weeks old speakers. I was so impressed that I placed the order for a pair of C7 and a P3ES2 right away. There is a magical quality in Harbeth that lead to an instant recognition that I don't have to look any further.

      Anyway back to the side-wall reflection. The 'live' factor was impressive indeed - but I was troubled by a discordance band around the high overtones of the human voice. It was a very narrow band of frequencies, but I find it jarring and disconcerting, almost like two slightly out of tune instruments playing together. It lead me to think that the reflected voice is causing a destructive interference around that particular frequency band.

      I pointed it out the Sam, but he was not the least troubled by it - so I am wondering whether my perception is correct.

      Comment


      • Re: Side-wall reflection

        Hi,

        Please read my PM to you.

        Thanks

        Comment


        • Re: The acoustical design of a studio

          Originally posted by A.S. View Post
          I've just returned from a conference in New York, during which we (briefly) discussed room acoustics. I know that I've said here that 'all echoes are bad in the listening room' but it seems that this may not be completely true. Current thinking is that some echoes, those which closely follow the music (in time) and decay evenly may fuse together with the music in the brain and suggest a bigger sound stage. The key to making this work is to keep the reflective surfaces near to the speakers (hence the reflections follow the notes very quickly) in a relatively small room.

          By implication, large untreated rooms will have a longer decay and unless this decay is really even across the spectrum and fast (unlikely) then there will be some confusion in the brain as to the direct and reflected sound. Under those conditions I hold my original statement that 'all echoes are bad'.
          Although I am not an expert in room acoustics, I can offer some thoughts based on my experience. Echoes are caused by reflection of sound off the walls of the room and will be present in any listening environment. To eliminate echoes completely, all wall surfaces including the floor and ceiling can be covered with absorptive material which will render the room to be acoustically dead. There will be no reverberation at all. An acoustically dead room is not conducive for proper listening since all life and dynamics will be sucked out from the system. Personally I have not experienced listening in an acoustically dead room before but I can imagine how a system would sound like in one.

          Speakers will always sound different in different rooms irrespective of the electronics that are used. I have listened to the SHL5 in 4 different rooms and all of them produced a different kind of presentation. Generally a smaller room will give a more focused sound, more precise imaging and better bass definition while the bigger room yield a "bigger" and life sound but reduced bass impact and tautness. It is difficult to say which is good or which is less preferred as each has their own merits. One thing I discovered is the Harbeth does not require a lot of treatments to sound good. In fact I am not using any absorption in my pretty big listening room now and love the organic and life-like sound in the room. I have 8 pieces of 2'x2' diffusors on one side of the wall though and they brought an appreciable difference, although not as huge as when compared to when they were in the smaller dedicated room.

          Comment


          • Re: The acoustical design of a studio

            Originally posted by A.S. View Post
            By implication, large untreated rooms will have a longer decay and unless this decay is really even across the spectrum and fast (unlikely) then there will be some confusion in the brain as to the direct and reflected sound. Under those conditions I hold my original statement that 'all echoes are bad'.
            I believe that artificial echo may be added during the mixing stage. I have listened to many voice books. Some recordings seems more 'roomy' than others, and I believe that these are artificially added 'special effects'. I also vaguely remembered playing with voice recording software that allow me to add various effects to the recordings. I have to say, I find these special effects quite pleasing.

            My Denon AVR and my car CD player both contain setting for various simulation modes, like Jazz Club, Rock Arena. I think it is a set of equalizer profile and echoing effect. They make marked differences to the reproduced sound, but I have never been bothered to play around with them though.

            Comment


            • Panel Absorber

              The winter is long and I'm going to start a new DIY project for a panel absorber. The reason for that is to get rid of room resonances / bass problem below 100 Hz. My other DIY panels that I have placed in all four corners improve the acoustics very well, but seem to have almost no effect at very deep frequencies. (and that's no wonder).

              I also have some electronics to beat the bass, but I want to try to solve as much as possible "mechanical" before the computer does the rest. Maybe it's even possible to go without any electronic filtering later...

              Before buying something commercial like this:
              http://www.mbakustik.de/main.php?tar...sorber&lang=en
              I want to try how far I can move myself.

              The theory is pretty clear and a good description how we find the final formular is here:
              http://dogbreath.de/misc/PlaneAbsorberResonance.pdf
              Everything ends up with the mass of the panel and the depth of the box as parameters. Quite surprising!

              The question is: Has anybody of you done this already? What is your experience? Is it worth to give it a try?

              Thanks. Any thoughts welcome!
              T.W.

              Comment


              • Re: Panel Absorber

                I've constructed many panels for dealing with mid and high frequencies but not attempted low frequency absorbers. From what you've shown and what I've read elsewhere, the construction is relatively easy and I reckon could even be incorporated into a cupboard or bookcase etc. for a neater effect.

                Fortunately my current demo room has walls which are plasterboard over a wooden frame, filled with 6-9 inches of fibreglass. The floor is ceramic tiles over concrete and the resultant sound is clean and tight.

                Good luck with your endeavours and keep us up to date with your progress.

                Comment


                • Re: Panel Absorber

                  As noted, putting a thin absorptive skin (foam or similar) in contact with and on the surfece of, say, a wall has no effect whatsoever at low frequencies. None. Complete waste of effort. A surface treatment will only effect the upper frequencies.

                  We covered relatively thin surface treatment boxes here and they do work in the higher frequencies effectively. As you say, for LF absorption you need to suck-out those frequencies by absorbing their very considerable energy by causing a (relatively heavy) membrane to flex at those frequencies. The flexing converts the acoustic energy into heat, and so it disappears as a sonic problem.

                  Back in 1951 (and I'm sure before that) the design and tuning of these membrane absorbers was well understood and the de facto standard for BBC control rooms and studios. Look here. I think it shows exactly the same concept of a mass of air in a box covered with a flexible skin. As we well know in quality audio, all the fundamentals were thoroughly understood fifty plus years ago.
                  Alan A. Shaw
                  Designer, owner
                  Harbeth Audio UK

                  Comment


                  • Re: Panel Absorber

                    hifi dave's room is probably a huge panel absorber. But that's nothing that I can (and want) to build at home. The funny thing about the bass absorption is that you find tons of products state are meant to deal even with deep frequencies, but I still wonder if this works.

                    So the panel absorber is probably better - at least in theory. Ok, everything is related to the mass and the volume that gives a resonant frequency. Damping inside without touching the membrane changes the characteristic and makes the curve flatter and expands it.

                    But what about the size? Let's say that we have two M40s in the room that create the bass. Since the room doesn't add any energy we have to "eat" parts of the energy that the speakers produce. Giving the size of the membrane and the excursion of the membrane there is a volume of air that we can calculate with. Since the panel doesn't really move if would have to be quite large to eat all of this energy. (But we don't really want to do this :-)

                    - Are two panels of 1 square meter a good starting point or too small?
                    - How do I measure the resonant frequency / characteristic if the panel is done? Microphone inside and some pink noise?
                    - Does the size ratio of a panel matter. The paper I mentioned says: 1:1 to 1:1.5, 1:1.7

                    T.W.

                    Comment


                    • Re: Panel Absorber

                      If I were you, I'd print out, carefully study and run a highlighter over key points in that 1951 studio design paper I mentioned here. In my experience, there is more wisdom, more pragmatism and more elegance in the way our grandfather's generation solved (acoustic) problems than any of the modern papers. I selected that paper with care - it really does give you lots of answers ... and just quickly looking at it your questions 1 and 3 are really answered by Fig. 12 and the Worked Example.

                      In short, you are wasting your time with a couple of 1m2 absorbers.
                      Alan A. Shaw
                      Designer, owner
                      Harbeth Audio UK

                      Comment


                      • Re: Panel Absorber

                        Originally posted by A.S. View Post
                        If I were you, I'd print out, carefully study and run a highlighter over key points in that 1951 studio design paper I mentioned here. In my experience, there is more wisdom, more pragmatism and more elegance in the way our grandfather's generation solved (acoustic) problems than any of the modern papers. I selected that paper with care - it really does give you lots of answers ... and just quickly looking at it your questions 1 and 3 are really answered by Fig. 12 and the Worked Example.

                        In short, you are wasting your time with a couple of 1m2 absorbers.
                        Yes, you are right. I looked at the paper again and everything makes sense to me. They first analyse the room, come up with a target of what to achieve and then build the stuff. That's an engineer's approach. The figures you mentioned are very detailed and it should be possible even for me to adopt some of the ideas for my own "project". I'm probably not able to and don't want to re-design and the entire room, but after doing some homework I hope to come up with an idea what to build. One constraint will be that everything has to moveable and doesn't look too ugly.

                        I will start doing some measurement to find out what I have in my room. From calculations I know my trouble frequencies but have never really verifed this with a measurement. I also have no idea about reverberation time yet. My DIY panels that I mentioned helped to make this better and speech sounds quite good. They also helped to remove the echo from clapping but I have no idea what actual values I have.

                        I recently started with SynRTA to look what response I have in my room and what the electronics are doing. But I have just been playing and one challenge was to tell my Vista notebook to accept the M-Audio Transit soundcard and also to use it. With the newest drivers from M-Audio SynRTA also seems to run under Vista (although they recommend XP) and the results look quite reasonable.

                        Many people publish these nice looking waterfall diagrams. What software do you use for those and RT measurement? I downloaded the RoomEQWizard from Home theatre shack and I'm about to have this also running.

                        I'll keep posting my findings here...

                        T.W.

                        Comment


                        • Re: Panel Absorber

                          Alan,

                          That 1951 paper you mention has been taken down temporarily, can you repost it?

                          Comment


                          • Re: Panel Absorber

                            Ok, this must have been one of those huge PDFs that couldn't be taken from the old version of the HUG to the new. I'll put it on my list of jobs to do. (I think I'll have to split the PDF).
                            Alan A. Shaw
                            Designer, owner
                            Harbeth Audio UK

                            Comment


                            • Re: Panel Absorber

                              It is worth reading what is probably one of the most wide ranging (and free!) documents on the whole subject of acoustic room treatment, as seen from a BBC perspective.
                              I think this probable answers 90% of questions on this subject (except where to get the money to do acoustics properly :-) )

                              http://downloads.bbc.co.uk/rd/pubs/a...icpractice.pdf

                              Derek

                              Comment


                              • Building a Reference Grade Listening Room - This is an interesting article of how one of the best listening room is created!

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