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Adjusting Room sound using material damping methods (not DSP)

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  • Thanks for the article. I wonder how much the owner had spent in that room in order to let his speaker to sound good.

    I feel very lucky my Harbeths do not need such room to sound half good. :P
    "Bath with Music"

    Comment


    • 1951 BBC studio design

      Originally posted by A.S. View Post
      From my archives, I attach an easy to follow approach to the design of a (BBC) studio. Even though this was published in 1951 (nearly sixty years ago) nothing has changed in the world of acoustics...
      Where can I find the link for that article?

      Sebastien

      Comment


      • Modern building construction challenge (P3ESR room integration)

        Since our move earlier this year I've battled with a thin midrange, the first time this has been an issue in any previous iteration of our system as the components are usually selected for midrange quality above all else.

        For many years I've been happy with small Magneplanars but all good things come to an end and about the time the Maggies finally died I first encoutered Harbeths in the the form of the original HL-P3 - my first brush with natural, unfatiguing sound in a "box" speaker.

        So shortly before the move my beloved Quad 33/303 was sold to help fund a pair of P3ESRs, and the combination of new speakers, stop-gap amplifier, and new room has really had me going.

        The first step was to eliminate the P3ESRs as a source of the problem by trying them in other' systems (Audio Research and Luxman electronics - both wonderful matches but way way out of my price league).

        Although I have since moved onto a more competent amplifier (albeit still somewhat lean sounding in comparison with the above-mentioned Audio Research setup), the room has turned out to be the main culprit.

        AS recently posted a PDF of the seminal Shorter paper. The perceived frequency response in our living room is something like the top curve in Fig 1. (p3).

        Shorter writes "if a progressive decline in response with increasing frequency is followed by an increase, the upper frequency range will be heard to stand out in unnatural relief, even though the response may nowhere rise above the mid-band level. It should be noted that this type of frequency characteristic modifies the spectrum of the reproduced sound in a way not experienced when listening to natural sounds. Progressive attenuation with increasing frequency is an everyday occurrence - it is experienced, for example, when listening to sound that has travelled round a corner - but, apart from a few isolated cases of specular reflection, selective reinforcement of the upper frequency range does not appear nature."

        Now to the room - it probably represents typical modern construction in the UK, with the interior surfaces being plasterboard over cinderblock. It is a hard flat surface that makes a distinct "tack" when rapped with the knuckles. It's not solidly attached to the cinder blocks, and can even be provoked into booming (hard to believe with mini-monitor bass).

        The smallish size of the room (about 3.5 x 4.5m) and hard surface make it prone to flutter echo, so the room ends up giving reinforcement to the top and bottom ends of the frequency range - and hence the "hole in the middle".

        I suspect earlier iterations of the Harbeth mini-monitor may be more tolerant of this setting on account of their LS3/5a style "presence bump" which has a "double whammy" effect of filling the hole and doing so at a lower SPL so that more of the HF reflections fall below the threshold of audibility (but that's a guess!). I also wonder whether the improved bass of the P3ESRs is actually counter productive in this setting.

        Sorting out the room is a work in progress, the owner of the property wouldn't permit some quick fixes like heavy curtains. (The P3ESR measurements published by Stereophile have been very useful, by the way).

        Oddly enough the best speaker positioning (so far) follows rules that worked with the Maggies,
        • a clear wall behind the speakers (more midrange energy than HF escapes to the rear of the speakers)
        • tweeters point at the shoulders of the listening position, at ear level (avoid the suckout that occurs when ears are above tweeter level)
        • slight backward tilt to the speakers (HF reflections don't go back and forth forever)


        In this room it is quite important to point the speakers almost at the listener's head as this also seems to result in fewer reflections bouncing back and forth between the front and back walls. This is counter to what I'd normally do, listening a bit off-axis to reduce the amount of direct HF energy.

        Reluctantly I've come to the conclusion that proper room treatment is going to be needed - but as it's a normal living room the challenge will be to find something that is discreet, inexpensive, and effective.

        This has been quite an essay but hopefully it will be of use to other P3ESR owners (and hopefully there will also be some useful suggestions that come in response to it).

        Comment


        • Discrete, inexpensive room treatment

          Originally posted by honmanm View Post
          ... I've come to the conclusion that proper room treatment is going to be needed - but as it's a normal living room the challenge will be to find something that is discreet, inexpensive, and effective.
          I face the same challenge so any suggestions are welcome.

          Sebastien

          Comment


          • Thwe new User Guide that will be supplied with our speakers adds some more information about room treatment. We will make a version available here on line shortly.

            Comment


            • Rooms - cannot ever be perfect so cease worrying and enjoy the music

              That would be much appreciated, HUG-1, many thanks.

              @honmanm, I have a similar experience to you, though in a slightly different way. I have P3ES2s in a small room, constructed from plaster board fixed to block walls. The room gives a bloom in response in the mid-bass, somewhere around the low cello range. I've taken to simply ignoring the effect; I don't let it bother me. I went to a live concert recently. The live sound is so massively different from reproduced sound at home anyway, that I've come to accept the shortcomings of the latter. Once I got my mind round to this, I found it very liberating and enjoy music at home all the more for it.

              Seek perfection in your room by all means, but don't look too hard!

              Best wishes, Ben
              Ben from UK. Harbeth Super HL5 owner.

              Comment


              • Better room damping

                honmann - it's interesting to see someone going from Maggies to Harbeths. For a while I was only interested in "non-traditional" speakers - Maggies, Ohm, Vandersteen... Harbeths are the first "box" speaker that I've heard (that's not a $Million) that disappears and doesn't sound like a box.

                I'm starting phase II of a renovation in my apartment, and had to move a bunch of things into my living room/kitchen area while the work is being done in another room. The room is now significantly more damped, and although not set up optimally, my P3ESRs are sounding better! My living space reminds of a control room now :0

                Good luck with your room treatments!

                Comment


                • Room treatment - summary

                  Originally posted by honmanm View Post
                  Sorting out the room is a work in progress, the owner of the property wouldn't permit some quick fixes like heavy curtains. (The P3ESR measurements published by Stereophile have been very useful, by the way).

                  Reluctantly I've come to the conclusion that proper room treatment is going to be needed - but as it's a normal living room the challenge will be to find something that is discreet, inexpensive, and effective.

                  This has been quite an essay but hopefully it will be of use to other P3ESR owners (and hopefully there will also be some useful suggestions that come in response to it).
                  Hi,

                  I would like to share with you on my recent journey to set my listening room... and how it had been a gruesome but enriching one... :-) What I have gone through might be of help to you, I hope.... or at least you could try out with... if you look at the pictures section, you may find pictures to my previous room and current room.

                  I do agree with you that proper room treatment is needed if we wish to enjoy our music to the best possible without the room affecting us... and something discreet, so as the living room still look like a living room... but that is truly tough challenge. I am fortunate to have my "serious" listening in a room and "casual" listening in the living room.

                  Experiences in my listening room set up:
                  - basically... all the materials I used initially in this room, are from my previous room... same curtain, same pictures from my old room... The photographed pictures printed on coarse paper helped my fluttering echo in my old room, but it did not help in my new room... :-(
                  - So I went around to look for economically price canvas painting... these assisted my in fluttering echo treatment
                  - I also learnt from a friend recently when he demoed to me, how his room curtain assisted him in fluttering echo, where he has them on both rear and sides of speakers... and also, for rear sides, how he uses nice carpets hung on walls to assist that...
                  Both the above materials, you could place around to treat it as a decor and at the same time... room treat the place

                  But in my journey to this new room of mine... the bass bloom was the trickiest! It went to the extend that I gave up all "powered" power cords, to tame the amps and source down... that cuts the bloom to some extend... BUT Cello or Double bass pieces still gets the problem....
                  - Then I replace away my tube amps, as they have a less control bass or ... what we call they do not have tight bass.... Transistor amps works better in the room... there goes... the amps and new amps came on board... :-( sad but a happy upgrade too :-)
                  - How was the bloom eventually solved? This is classic... as I would marked in my learning journey... I had Sonex placed everywhere I could... front of speakers, rear of speakers, side of speakers... and even took mattresses and pillows to fill the rear of the speaker's space.... BUT none assisted, I even home trial a China made bass trap (works in the owners's shop but not my room...).
                  And where did it assist...? The sonex was placed behind the curtains you see in my picture? Stand upright with the absorbing side facing the room, somewhere off middle of the room near to the right speakers. That killed the bloom!

                  In my living room... the C7s, each have diffusing at their rear and partial sides... where my customized TV and equipment rack is, I have asked the carpenter to have strips of wood strips... in high and low height.... to help diffuse the sound sound wave around the speaker. It works, and no major bloom. Now that my room problems are resolved... I am working on my living room now... :-)

                  From the above... in summary...
                  Try using curtains, canvas oil paintings, paper drawings... to help your room fluttering issue and still decor the room :-), but please note (as you would already know)... different cloth thickness gives a different effect.
                  Try absorptive materials for your bloom issues, try all areas in your room and see where helps... it can be at the most un-thought of location... if you need to use sponge/foams... see how you can hide it behind strategic areas, using the curtain to hide them? OR some other forms... or look for ... Chinese "curtain"? You know... those... emm... wood panel pieces that can be folded? And once you stretch them open.. it becomes a "wall", this can break sound waves... and some comes with porous matetrials, you can hide your foams behind them... so you do not see the foams but a nicely decorated panel :-)
                  Try carpets... hung on walls... it helps, right in the middle, it helps lots in imaging... sides or "funny" corners, it helps bloom issues too...
                  Try your cables first... if you are using "hi end" cables, now is time to dig out all your old basic cables... try reverting all power cables and RCA cables... all to basic first. From here... see if cables are your issues... (btw: all my cables are back to basic, normal belden power cables, normal belden RCA cables) and system is sounding great in this match in this room. You will be surprised cables that works for your past room but not in the new room... that happens to me! :-)
                  Try speaker placement.... fluttering issues and bloom can be cured with this too... use the basic position... if it does not work... then try using they most unknown or untried angles... and tune from those angles to the best... for you and your room (only try unorthodox speaker placement method... if all traditional methods, does not work...)

                  I hope you can understand my writing... and the information will be of some help to you :-)

                  Comment


                  • Pillows behind speakers

                    Thanks, that's a lot of useful pointers.

                    One thing that has helped - at least while Mrs H is on holiday - is to put pillows on top/behind the speakers. I hadn't expected it to help, but it has reduced both flutter echo and bass bloom.

                    Comment


                    • DIY (portable, removable) room treatment for little money

                      The basic truth of high fidelity sound reproduction in the home is that the acoustic signature of the listening room is the final link the the reproduction chain.

                      In fact, starting from the microphone, we have the acoustic signature of the recording studio picked-up by that microphone, delivered to the loudspeaker and then played over the speakers in the listening room. But if we think about it, the loudspeaker cabinets themselves are miniature rooms. So in truth we have the acoustic signature of the studio overlaid by the acoustic signature of the speakers and finally overlaid with the acoustic signature of the listening room.

                      Put crudely: we have the acoustics of the studio (a box) reproduced over the loudspeaker (a box) in the listening room (another box). We can take this one step further: consider that we are reproducing a wooden instrument such as a cello or even piano: now we have the instrument (a box) in the studio (a box) reproduced over the loudspeaker (a box) in the listening room (a box).

                      A box in a box in a box in a box. No surprise then that each box will have a modifying effect on the preceding signal.

                      The characteristics of the instrument are as intended by the maker, resonances and all. The loudspeaker designer (presumably) controls the contribution of the speaker box, so that leaves the recording studio and the listening room as the biggest variables, and the ones which benefit from some acoustic treatment with the sole objective of minimising their contribution to the reproduction chain. We at home have no influence over the studio (or hall) that the recording was made in, so that leaves only the listening room as within our capability to modify. Some rooms can be inexpensively treated; others can't. Let's look at them.

                      To be continued .....
                      Alan A. Shaw
                      Designer, owner
                      Harbeth Audio UK

                      Comment


                      • Keep going!

                        Interesting! Keep going.
                        Ben from UK. Harbeth Super HL5 owner.

                        Comment


                        • Different types of listening room construction

                          OK thanks!

                          Right: the listening room at home. Let's completely ignore any sort of physical bricks-and-mortar reconstruction. Forget it. My wife wouldn't permit it and I don't think yours would either. That's for millionaires to build. If we ordinary listeners are going to demolish walls then we are going to let ourselves into all sorts of issues about structural integrity and local govt. planning approval. No, all we can do is light-weight surface treatment, because anything too heavy could pull the wall down.

                          So with that as our starting point let's have a look at the sort of situations we encounter in typical listening rooms (in no particular order).
                          1. Listening room built over or under a cavity (a garage, a basement or an apartment adjacent/above/below)
                          2. Listening room with relatively hard but flexible (plaster board) sheets walls nailed onto timber uprights
                          3. Listening room with brick walls or concrete walls
                          4. Listening room with no walls at all -listening in a field

                          Turning to 4) if we do literally take our speakers outside we'd appreciate just how dominant the listening room's sonic signature is, yet we can generally 'hear through' the room and normally enjoy music. I can give an example of just how much the room contributes if we make a recording of an orchestra in a concert hall and then transport the orchestra to an anechoic chamber and re-record them there. Same orchestra, same instruments, same microphones; the only difference is the complete absence of echoes in the anechoic chamber. So the difference between these recordings is solely that of the contribution of the room.

                          Recording in a normal concert hall, a so called 'wet' recording:

                          [Clip #1]

                          Recording in an anechoic chamber, a so called 'dry' recording:

                          [Clip #2]

                          And here is a recording in the Boston Symphony Hall - a very wet recording:

                          [Clip #3]

                          The Boston Hall recording, an extreme case, highlights the problem of a very long reverberation time (Rt) in a room: the clarity of the individual notes is lost because the reverberation washes-over and smears the new notes. This is what happens when the Rt of a large room becomes several seconds long. But we have related problems in the listening room at home, even although the room is proportionately much smaller, and the reverberation time is proportionately smaller too and the listener is much closer to the source. So that a seemingly innocuous echo off nearby walls can be sonically significance, even though our listening room is a tiny fraction of the hall or studio.

                          Recently I was asked to reinstate the 1951 Wireless World reprint which I now attach. Before we move on again, I think it would definitely be worth skimming through, and in particular looking at the graph I've annotated on the first page. Can you see how it relates to this business of echoes? Other places I've annotated in red - these are really the core of the room treatment issue.

                          BTW; the words absorption coefficient (p.p. 357) sound horribly complicated. It's nothing more than a number, as a fraction of 1.0 (= 100%), indicating (in this case) the effectiveness of a material and its sonic absorption potential at any given frequency. In other words, the 'goodness' of the surface at absorbing sound. I suppose only a vacuum would have perfect absorption and therefore a coefficient of 1.0.

                          The graph on p.p.357 says that even at the most absorptive frequency for any material, no material has an absorption coefficient above about 0.75, that of thick curtain at about 1500Hz. That implies that 0.25 (or 25%) of the energy hitting the thick curtain bounces off at that frequency. At the bottom of the graph you can see that bare plaster has an absorption coefficient of about 0.02 right across the frequency band. That implies that 98% of the sound that hits a plaster wall bounces off it - an acoustic disaster. Hence, untreated, undamped plaster lined rooms have (in round numbers) walls that are almost 100% perfectly acoustically reflective. From that point we can conclude that the untreated plaster room will have a dominant influence on the sound field in the room and will impact markedly to the character of sound perceived at the listener's ears because of the way that sound will bounce continuously around the room, losing only about 2% of its energy each time it impacts and bounce off a wall. Starting with a sound at 100% energy, even after five wall-to-wall bounces that's 100%- 2% -2% -2% -2% - 2% = 90% still available to continue bouncing around, long after the note has ceased.

                          Hopefully by now we can see how completely absurd the idea of placing little bells around the room to 'damp' the room is.
                          Attached Files
                          Alan A. Shaw
                          Designer, owner
                          Harbeth Audio UK

                          Comment


                          • Dry recordings - sound best?

                            Originally posted by A.S. View Post
                            .....
                            The Boston Hall recording, an extreme case, highlights the problem of a very long reverberation time (Rt) in a room: the clarity of the individual notes is lost because the reverberation washes-over and smears the new notes.....
                            I really need help, here. Why is that the "Recording in an anechoic chamber, a so called 'dry' recording" sample sounds better to me than the "normal concert hall" and louder than the latter. I am using in-built sound card and headphone. If I can't get this right then I don't know what I have been listening all these years.

                            ST

                            Comment


                            • Absorption coefficient - more thoughts ...

                              I've had a look for more information in my archives to illustrate just how effective any material is at absorbing sound that falls on it.

                              In my previous post I stated that ...

                              BTW; the words absorption coefficient (p.p. 357) sound horribly complicated. It's nothing more than a number, as a fraction of 1.0 (= 100%), indicating (in this case) the effectiveness of a material and its sonic absorption potential at any given frequency. In other words, the 'goodness' of the surface at absorbing sound. I suppose only a vacuum would have perfect absorption and therefore a coefficient of 1.0.
                              However, I am not certain that this is a completely accurate statement. In the attached BBC Research Dept. paper BBC Absorption Coefficients 1992-03 there is an overview of the various methods that could be used to measure absorption. The BBC method is one of several alternatives (such as the ISO method) and as with most acoustic matters there is no absolute and many alternatives approaches.

                              Ignoring all the minute detail, you will see that many absorption coefficient graphs are scaled from 0 to a number greater than 1.0 (typically 0-1.5) with some of the measurement points exceeding 1.0 (or 100%). I am unable to explain this, since according to my previous post, a coefficient of 1.0 (100%) would surely represent total absorption, so a number greater than 1.0 would seemingly not be possible. If the measurements were comparative, with one data set normalised then a figure greater than 1.0 (100%) would be possible comparatively. So I'm mystified - can anyone explain this?

                              Regardless of a complete understanding of the data, what I think we can safely conclude from these two reports is that:
                              1. Sound absorption is not equal across the audio spectrum for an given material (i.e. the absorption curve curve usually has a slope up or down and often a peak)
                              2. Some materials are generally more absorptive than others i.e. their curves are drawn higher up the chart = a higher absorption coefficient on average across the audio band

                              We can use this observation that not all absorbers have exactly the same characteristics to our advantage in damping the room.

                              >
                              Attached Files
                              Alan A. Shaw
                              Designer, owner
                              Harbeth Audio UK

                              Comment


                              • Dry or wet acoustic - the producer's choice?

                                Originally posted by STHLS5 View Post
                                I really need help, here. Why is that the "Recording in an anechoic chamber, a so called 'dry' recording" sample sounds better to me than the "normal concert hall" and louder than the latter. I am using in-built sound card and headphone. If I can't get this right then I don't know what I have been listening all these years. ST
                                It's snowing heavily outside now so a perfect time to follow this up.

                                OK, the first thing to say is that if you are here on the Harbeth User Group and you are a Harbeth user then it is unlikely that you have been chasing the wrong high fidelity goal! So let's step back and see if I can improve my explanation. Let's sidestep the discussion about room treatment for a moment and just think about what we are trying to achieve with our hi-fi hobby.

                                I think we are all aiming at recreating what the microphones picked-up at the recording venue with as little 'corruption' as possible over our speakers in our own listening rooms. If the microphones were of poor quality, or the recording environment (studio or hall) had characteristics that became embedded in the recording we can't blame our speaker or equipment for that. All we can do is try and faithfully reproduce what is on the recording at home. Let's assume that the recording engineer is wise enough to use good quality microphones, and let's assume that the performers are trained experienced professionals, adequately rehearsed and can play well. What variables are available to the producer now? Two: the selection of the venue, and the position of the microphones in that venue.

                                Let's assume that the producer visualises the promotion of the recording venue on the CD cover "Recorded live at XYZ hall!" as part of his marketing strategy on the basis that if the consumer recognises the hall (e.g. The Royal Albert Hall) he is more likely to buy the disc, then in fact we are down to just one variable within his control: where to position the microphones. And that depends upon what sort of experience he is attempting to recreate in the listener's room on playback. After all, recording is an art form and as with all art, there is the duality of intention and perception.

                                Let's imagine that the producer was not in fact the final decision maker in this creative chain. He in turn reports to a record company senior business manager, the executive producer, he being the man who actually finances the project and as the financier, has the final say over the entire process. And he says that according to feedback from the market (reviews of similar performances, similar recordings; sales records of his and competitor releases etc. etc.) his marketing dept. is telling him that there is a shift towards younger consumers. He explaines that market research shows that those consumers rarely if ever attended a live concert and that the record company considered that the most marketable recording now was one not aiming at capturing the 'concert hall experience' (since that experience was completely alien to the new-generation CD buyer) but something "more contemporary". He asks the producer if a more intimate sound could be captured, adding "... more like what the CD buyer would hear if he was in the third row .... not the fifteenth.... a dryer sound ...". Can you see where this is leading? Can you see how the producer then leans on the humble recording engineer to give him the sound that HQ want?

                                So what can the recording engineer do to oblige his two bosses? Since technology does not (yet) allow a wet, reverberant recording to be dried-out by removing the reverberation, the engineer has to find a way of reducing the amount of reverberation collected by the microphones. And he has three basic possibilities:
                                • Move the microphones closer to the performers so the reverberation, whilst still present, is drowned out by the louder direct sound from the instruments and/or
                                • Change the microphones to more directional ones so that they concentrate on collecting the direct sound from the instruments and are less sensitive to the reverberation which is still there and/or
                                • Shield the microphones from the reverberation by erecting absorptive screens to soak-up the reverberation before it reaches the microphone (i.e. move towards an anechoic recording)

                                In reality, he'd probably use a combination of all three attacks on the problem to dry-out the sound. But whatever strategy he takes he is aiming at the same objective: removing or reducing or controlling the contribution of the room (the hall or studio) relative to the direct sound from the performers. And listening at home at the back end of the reproduction chain, we face exactly the same problem of controlling the room's contribution to what we hear.
                                Alan A. Shaw
                                Designer, owner
                                Harbeth Audio UK

                                Comment

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