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The professional way to evaluate loudspeakers?

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  • The professional way to evaluate loudspeakers?

    This thread concerns itself with how previous researchers have set about evaluating loudspeakers. It covers the recognised defects of loudspeakers known as 'coloration', their measured objective characteristics and the design of and results from listening panels. It commences with the historical perspetive of public hifi denonstrations from over fifty years so.

  • #2
    First steps - a consideration of how humans judge sound

    Rather than dive into the complexities of the ear, which are not necessarily relevant at this stage because they apply to all listeners regardless of race creed or colour (we assume) I'd like to make an opening statement. It is this ....

    Most humans can tolerate an extremely low quality of sound. We know this because during the 78 and medium wave (AM) radio era, despite the serious technical limitations of 78s and AM radio, certain listeners believed that what they heard closely mimicked the live sound.
    And that was pre-pop music, so those that experienced live sound were very familiar with the concert hall experience (of classical music) and yet, these listeners allowed themselves to believe in the accuracy of reproduced sound when we, by today's perspective, find AM radio of laughably low quality. So the definition of "high fidelity" is not fixed. It varies generation to generation depending upon many factors, and those factors are not immediately obvious. The fidelity baseline cannot be re-set by the public's exposure to the day's best quality reproduction equipment because so few would be able to afford it and therefore actually hear it. It cannot be due to opinion leadership (in the media) because audio magazines are a very small niche in publishing. No, the appreciation of "fidelity" sound seems to be innate, variable with time and exposure and highly personal.

    Not a good basis for an industry to move forward satisfying such a vaguely specified consumer preference.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK


    • #3
      EMI defines 'high fidelity' over fifty years ago ...

      Thanks to the general archives of the late Raymond Cooke OBE that his widow passed to me and are incorporated into mine, I am able to illustrate my point about the shifting sands that define "high fidelity" from generation to generation. It's interesting to step back to the mid 1950s to a leaflet "The pursuit of High Fidelity" issued by EMI who were a major force in recording, audio equipment manufacture and record production.

      To quote the leaflet ....'No longer is it [high fidelity] a mysterious cult practised only by the technically initiated ...'. EMI set about defining high fidelity from a perspective of engineers and consumers fifty years ago. Do we recognise their definition, and presumably the definition the public then accepted, today? It's interesting to see the term monitoring loudspeaker in the leaflet, this implying a loudspeaker of particular ability, special, a professional tool rather than one which might satisfy the home listener.

      With the the pursuit of really high fidelity sound being a very small minority interest by today's public, next I'd like to show you just how strong the appetite was amongst the ordinary (middle class) public was half a century ago, a few years before the first stereo recording was released. Today, with attendance at western hifi shows in marked decline, can you believe that public demonstrations of high fidelity mono sound held by equipment manufacturers in live-v-reproduced performances could easily fill the largest theatres to capacity and beyond - upwards of three thousand curious listeners, seated, all eyes and ears on the stage. Believe it!

      P.S. EMI brochure page corrected and new improved JPEG2000 image quality.
      Attached Files
      Alan A. Shaw
      Designer, owner
      Harbeth Audio UK


      • #4
        Public hifi demonstrations in 1957 ....

        Attached I have scanned two reports of the public hifi on-stage demonstration given by Gilbert Briggs (of Wharfedale fame), ably assisted on-stage by R.E. Cooke (KEF) and Peter Walker (QUAD). Interesting how these three competitors were able to cooperate in public.

        The sheer audacity of taking-on such a logistical challenge of filling a public hall with reproduced sound and introducing real live instruments to permit the public to make an A-B comparison must have been a logistical nightmare. Would such a demonstration be undertaken even today in the digital era, when the recording chain is virtually perfect (even if the loudspeakers aren't)? And if not, why not? Has fidelity progressed or not? Or is the issue something to do with public expectations?

        I have a few more write-ups covering these public demonstrations from Raymond's archive, but as I often find with these older more accessible papers, a few re-readings uncovers a wealth of interesting comments and observations, each one of which could be an entire discussion here. There are certainly several golden lines in these papers. Note Peter Walker's comment on page 1 about 'chromium-plated larger than life hi-fi'. Having read the report, can you analyse just how the stage management conspired - as the presenters probably well knew - to give an outcome which both entertained, thrilled and simultaneously deceived the public?

        The demonstration in question was performed exactly two weeks before my birthday.
        Attached Files
        Alan A. Shaw
        Designer, owner
        Harbeth Audio UK


        • #5
          Even longer ago - 'The Festival of Sound 1954'

          An even deeper trawl of my archives (again, the section bequeathed by Raymond E. Cooke of KEF) takes us to the public demonstrations of loudspeakers in 1954.

          "... Mr. Briggs quickly cut through the undergrowth of "hi fi" to get at the roots of good sound reproduction ....". Do we agree with that full quote?

          Also interesting to see the use of 'neon lamps arranged to strike in ascending order as the power increased from 3 to 60W...'. 60W to fill a theatre - doesn't that put into perspective the simply lunatic amount of power claimed to be necessary in an ordinary domestic room.

          Incidentally, now that we have standardised on Acrobat 9 for PDF creation, I have been able to strike a better balance between file size and image resolution. Even so, this PDF is about 1MB - the original scanned documents were over 6MB.
          Attached Files
          Alan A. Shaw
          Designer, owner
          Harbeth Audio UK


          • #6
            Public demonstration of loiudspeakers in USA ....

            At about the same time as Briggs was filling halls in the UK with his loudspeaker demonstrations, our American cousins were enjoying the same show, but on an even larger scale. Attached is Brigg's Wharfedale loudspeaker travelling show at the Carnegie Hall in 1955. Interesting reading.

            Anyway, the point I have wanted to make across these posts is that the public demonstration of hifi is not a new idea, and you'll have read for yourself that even with the crude equipment and loudspeakers of half a century ago, either the public willingly allowed themselves to be duped, or they truly couldn't hear the difference between live and reproduced sound. Or maybe both. Or that's how it seems on the face of it. But we can apply what we now know about how the ear works to untangle the euphoria and arrive at a much more objective assessment of those demonstrations. A couple of clues .... programme selection, distance and acoustics.

            I've done my bit ... over to you. Thread opened. I'm going to take a back seat and watch the discussion but please keep on-topic. We are discussing loudspeaker evaluation, nothing else. And there are many nuggets to be teased out of the papers I've provided that really should be fully explored before contributing other data. In fact, there is enough in just those papers from the 1950s to write a thesis on the subject of speaker evaluation! Beware! This thread is Moderated!

            P.S. CLUE!! One tell-tale comment in the Briggs-at-Liverpool PDF (a few posts ago) I fervently disagree with - you may be able to find a post I made a year or two ago about a listening panel that I sat in on, and which inspired me to purchased a speaker I'd listened to, on the way home, only to be disappointed.
            Attached Files
            Alan A. Shaw
            Designer, owner
            Harbeth Audio UK


            • #7
              Summary of the 50s public demos

              The papers presented in this topic is surely causing some discomfort to our long held believe by so called audiophiles ( mostly from non technical background) about sound reproduction. A few examples:-

              1) 30 and 60Watts amplifiers were more than adequate to fill a 3000 capacity hall! Just how efficient were these speakers?

              2) Audience couldn't tell the difference between recorded sound and live performance!

              3) Two speakers arranged side by side..and they say you shouldn't do that because of comb effect. Well... 3000 people didn't notice that!

              4) Curiously, the writer prefers colouration because it gave him warmth..

              What is really bugging me right now is if the original recording were recorded in a hall with 1.5 second reverberation time, then how come the audience couldn't tell the difference when the recording was played in another 1.5 second RT hall?

              I have read the articles several times but still unable to say if the said articles talked about recorded sound or the monitoring loudspeaker characteristics?


              • #8
                'Stereo not viable for home use!'

                I noticed a fantastic statement by Walter Beaver in the 'Briggs at Liverpool' piece:

                I have a rooted objection to stereophony and a conviction that it is not, and never can be, a successful medium for domestic sound reproduction
                That just about wraps it up for stereo then!


                • #9
                  Observation about the validity of the public demo

                  One thing that's noteworthy about these demonstrations is that they take place in extremely large spaces, far far larger than any domestic listening environment would possibly be. They also involved equipment which, however crude by modern standards, which I assume would be vastly more powerful and sophisticated than any home equipment available at the time.

                  Two things follow from this (actually probably more than two, but two is what occurs to me at the moment):

                  1. The acoustic space is nothing at all like the domestic acoustic space.

                  2. The reproduction equipment is nothing at all like domestic reproduction equipment.

                  The consequence would be (I would think) that the average listener would have had no frame of reference for what he/she was hearing, no way to compare the reproduced sound in the hall to the more familiar reproduced sound of domestic hi fi of the day. Lacking that frame of reference, I can understand that making the "reproduced v. live" distinction would have seemed very difficult, almost impossible. Though I imagine that more sophisticated listeners (e.g. the demonstrators) would easily have been able to do so.


                  • #10
                    Placement of the microphone defines 'recording Rt' more than hall's reverb time

                    Originally posted by STHLS5 View Post
                    What is really bugging me right now is if the original recording were recorded in a hall with 1.5 second reverberation time, then how come the audience couldn't tell the difference when the recording was played in another 1.5 second RT hall?
                    It does say

                    The oboe and violin solos were specially recorded in the studios of Hollick and Taylor, Birmingham, and the acoustics of the hall enabled very close matching between live and recorded to be achieved
                    Hollick and Taylor were (are) quite a small company with fairly modest studios compared to the London behemoths. Although the RT of their studio may well have been 1.5 seconds, it would nonetheless have been a far smaller room than the hall used for playback, with very different reverberation characteristics.

                    The standard for reverberation time measurement is called RT60, which is the time taken from interruption of the sound source until the residual reverberation has dropped to 60dB below the level of the original sound.

                    With any recording, the subjective amount of reverberation on that recording is broadly dependent on the proximity of the microphone to the sound source. If the microphone is close enough to the source, the recording will be as near "dead" as makes no difference. Placement of microphones for optimum results is probably the single most important aspect of the art of recording.


                    • #11
                      Interesting isn't it how the careful scrutiny of just one reported fact from a 50+ year old paper can yield a whole sub-plot.


                      • #12
                        Can't be hall reverb alone

                        I've thought about this some more.

                        It seems to me that hall reverb alone can't explain the inability to distinguish between live and recorded sound, since in the test it's common to both. But I wonder if it's having the effect of masking the noise that would otherwise be apparent in the recorded sound.

                        What I mean is this. Both live and recorded sound are going through the same loudspeakers and amplifiers, so the sonic contribution of both is neutral: whatever distortion and noise these add is added equally to the live and the tape feeds. Same with the room reverb. What should be distinctive, however, is the tape noise from the reproduced feed - unless that noise is being masked and hidden by a greater "noise", however subjectively sonically benign. Doesn't that have to be the sound of the hall itself, that is hiding the tape hiss and other artefacts of reproduction?


                        • #13
                          The monitors' characteristic & small rooms

                          Originally posted by Pluto View Post
                          ......Although the RT of their studio may well have been 1.5 seconds, it would nonetheless have been a far smaller room than the hall used for playback, with very different reverberation characteristic....]
                          Almost all recording studios RT is between 1.2 to 1.5 second. Let's leave aside the fact 3000 or more so accepted the recording sound to be as good as live recording for now and focus one what character of loudspeakers that professionals look for.

                          The articles talked about recording and adjusting the microphones to have a flat frequency response as possible. If my reading is correct, the speakers had limited high frequencies, and also the lows. Except where at one stage they used a special speaker to emphasize the highs.

                          On another note, at one point where the writer indicated about playback in small room where, I quote " one can get away with murder..." seemed to be incorrect. Isn't a bad recording is more revealing in a dead room than one like the hall here with 1 second RT?


                          {Moderator's comment: I think that the 'murder in small rooms' may have been the very comment that Alan strongly disagreed with .... strongly suggest that you hunt for the clues he has already given you in his old posts here .........}


                          • #14
                            Murder in a small room - more thoughts

                            Originally posted by Moderator View Post
                            I think that the 'murder in small rooms' may have been the very comment that Alan strongly disagreed with .... strongly suggest that you hunt for the clues he has already given you in his old posts here .........}
                            I have to say that I did not understand the bit in the article that went...

                            If you want to sort out the wheat from the chaff in a search for good recordings, the best way is to listen to them in a good concert hall. The reason is a very simple one: you can get away with murder in a small room, but any sort of dirty work is exposed in the concert hall
                            Obviously there is no way we can query this claim with the author but, if anything, the converse is true! I wonder if something was accidentally misquoted, mistyped, misheard or simply missed. The relationship between a loudspeaker and the listener is not entirely unlike that of the sound source and microphone, in that the closer you are to the loudspeaker, the more you hear of the loudspeaker (direct sound) while hearing proportionately less of the room (indirect sound).

                            So unless the author is implying that the typical room of that time was acoustically truly awful (unlikely because there were probably rather more soft furnishings, and other clutter to create sonic diffusion, in many rooms back then than there are today) or that the typical domestic loudspeaker of that era was poor (more likely but non sequitur as I assume the author is talking about Gilbert Briggs' then state-of-the-art speakers, whatever room they are used in).

                            I short, I really cannot comprehend the "get away with murder in a small room" statement.


                            • #15
                              Edison's audio demonstrations ....

                              Another view regarding Live-vs-Recorded from Dr. Sean Olive (of Harman International):