Loading ...
Sorry, an error occurred while loading the content.

Happy New Year

Expand Messages
  • regtas43
    Happy New Year,Everybody. I look forward to another year of lively exchange of audio ideas. Have a happy and safe New Year s celebration. REG
    Message 1 of 36 , Dec 31, 2007
    • 0 Attachment
      Happy New Year,Everybody.

      I look forward to another year of lively exchange of audio ideas.
      Have a happy and safe New Year's celebration.

      REG
    • Hans-Martin
      Thank you, Ted Great stuff- takes years to work through... ;-) Regards Hans-Martin ... interesting, the technique ... directional microphone. ... materials.
      Message 36 of 36 , Jan 5, 2008
      • 0 Attachment
        Thank you, Ted
        Great stuff- takes years to work through... ;-)
        Regards Hans-Martin
        >
        > Yes, free is good!
        >
        > Here's something on the original topic that Hans Martin may find
        interesting, the technique
        > used by the BBC to measure cabinet resonance energy using a
        directional microphone.
        > Details are included also on the physical properties of various wood
        materials. This is BBC
        > R&D report 1977/3 by Harwood and Mathews available free here
        > http://www.bbc.co.uk/rd/pubs/reports/rpt60s_70to96.pdf
        >
        > Among conclusions reached was that cabinet structural resonances,
        being unavoidable, were
        > found to be manageable by ensuring the Q factor of the panels in
        question was the lowest
        > that could be achieved, this was based on the observation that small
        amplitude but sharp Q
        > panel vibrations from "rigid" panels were more objectionable than
        low Q vibration from
        > thinner less rigid panels augmented with damping material. One can
        think of this as the
        > difference between the "ping" of a thick panel compared with the
        "thud" of a thinner but
        > damped one. Damping material for panels was a major contribution to
        BBC speaker design.
        > One of their criteria was the portability of speaker boxes by sound
        engineers. Lightness was
        > a valued property.
        >
        > Ted
        >
        >
        > On 3 Jan 2008 at 22:13, Richard Tuck wrote:
        >
        > > http://www.ebu.ch/en/technical/trev/trev_home.html
        > >
        > > Hi Ted
        > >
        > > Another source of interesting stuff is EBU Technical Review - open
        and free.
        > >
        > > Richard
        > >
        > > -----Original Message-----
        > > From: regsaudioforum@yahoogroups.com
        [mailto:regsaudioforum@yahoogroups.com]
        > > On Behalf Of Ted Rook
        > > Sent: 03 January 2008 04:24
        > > To: regsaudioforum@yahoogroups.com
        > > Subject: Re: [regsaudioforum] Re: My first New Years project -
        speakerstands
        > > measurement
        > >
        > > The material available online for self education is a fantastic
        resource.
        > > The AES electronic library costs about $150 a year I think and covers
        > > everything back to the 1950s and tubes.
        > > When the articles are written by experts in the field it doesn't
        matter so
        > > much about them not being rigorously peer-reviewed because the
        author is
        > > probably the best qualified reviewer, and audio is such a small
        industry
        > > there are probably not enough qualified independant reviewers to
        keep up
        > > with the demand.
        > >
        > > It doesn't take long to get to recognize authors names that crop up in
        > > references to begin to get a handle on who is who. I strongly
        recommend the
        > > AES resource to anyone here, only a minority of material is
        technically
        > > dense and obscure, much is immediately approachable.
        > > In the same way the BBC publication archive is a gold mine not
        because it is
        > > peer reviewed, it wasn't, but because the stuff was written by
        people who
        > > knew their subject well.
        > >
        > > So pay no attention to Robert being cynical, join AES at
        www.aes.org and
        > > visit Auntie BBC at
        http://www.bbc.co.uk/rd/pubs/archive/index.shtml and
        > > enjoy quality audio technical material.
        > >
        > > Of course some of the AES material is commercial, audio is thriving
        > > business, that's not a problem, it's the information that counts.
        > >
        > > Ted
        > >
        > >
        > > On 3 Jan 2008 at 3:25, regtas43 wrote:
        > >
        > > > I assessing these papers, it is important to note that what is
        being
        > > > discussed(eg by Paul K, mmay he rest in peace) is NOT the Doppler
        > > > distortion from vibration of the whole speaker but rather Doppler
        > > > distortion arising from asking a single driver to exhibit large
        > > > excursions to reproduce a low tone while also reproducing a much
        > > > higher tone.
        > > > This could conceivably be an issue with a speaker like the Spendor
        > > > SP1/2 which covers a lot of frequency range--at times its driver is
        > > > producing 50 Hz at volume and 1.5kHz at the same time.
        > > >
        > > > However, experience suggests that this is not really a serious
        issue
        > > > compared to other kinds of distortion at least under oridnary
        > > > circumstances of music.(You can produce an audible effect with test
        > > > tones at high level, I think).
        > > >
        > > > Second point: The journal of the AES is not, to my mind, really a
        > > > legitimate scientific journal, not with any consistency.
        > > > Surprisingly many of the articles are about some form of supposedly
        > > > significant distortion that the author's soon to be released
        procuct
        > > > gets rid of. A lot of it is just unpaid advertising to the
        trade, peer
        > > > reviewed only in the sense that someone else read it, not that they
        > > > checked the conclusions themselves or even worried too much
        about the
        > > > methodology.
        > > >
        > > > I apologize if I sound cynical. But anyone who has read a lot of
        the
        > > > Journal--and at some point I read through almost all of its back
        > > > issues(hours and hours in the UCLA Engineering Math Science
        Library),
        > > > the conclusion is inescapable: Caveat lector.
        > > > It is not so much that the stuff is wrong, but audio is about the
        > > > relative importance of things, and that is seldom really analyzed.
        > > >
        > > > On top of this, let me reiterate that NO ONE not even Paul K claims
        > > > that the vibration of a large heavy speaker as a whole is enough to
        > > > introduce Doppler. To the extent that anything the low frequency
        > > > driver does would cause trouble, it would be generating unwanted
        > > > harmonics and so on and just plain noise by causing the speaker
        > > > cabinet to flex unduly and uncontrollably.
        > > >
        > > > Incidentally, at some point Magnepan tried and experiment where
        they
        > > > suspended a pair of their speakers on chains, so that they were
        > > > totally free to move essentially. No one could tell the sound made
        > > > that way from the sound when they were spiked to the floor.
        > > >
        > > > One really ought to keep that experiment in mind.
        > > >
        > > > Attaching the speaker rigidly to something is far more likely to
        cause
        > > > the rigid something to emit noise in a region of hearing
        sensitivity
        > > > than it is to help anything.
        > > > That is the point of my rugs and wooden stands: they do not emit
        any
        > > > sound to speak of. And if they did it would not he hard edged.
        > > >
        > > > A lot of what seems intuitively clear is wrong.
        > > >
        > > > REG
        > > >
        > > >
        > > >
        > > >
        > > >
        > > >
        > > > --- In regsaudioforum@yahoogroups.com, "Ted Rook" <rooknrol@>
        > > > wrote:
        > > > >
        > > > > Richard, by chance I read some AES papers on this recently and
        > > > they described it as a non-
        > > > > issue. For example Harwood (of BBC and Harbeth) wrote an AES paper
        > > > in 1972 with the
        > > > > following conclusion
        > > > >
        > > > > "Estimates have been made of the Doppler distortion produced by
        > > > recent high-quality
        > > > > loudspeaker designs, and these figures have been compared with
        > > > critical data
        > > > > obtained for reproducing machines (meaning LP playback and tape
        > > > playback wow
        > > > > and flutter). In all cases the Doppler distortion has been shown
        > > > to be inaudible in the
        > > > > loudspeakers concerned. As far as is known,this is the first time
        > > > a real assessment of
        > > > > actual loudspeakers has been made, and at least in these cases,
        > > > has at long last shown
        > > > > the real degree of importance of this particular form of
        > > > distortion. Design criteria
        > > > > have been drawn up relating the minimum sound level in a room of
        > > > 2000 fta before
        > > > > Doppler distortion is audible on program; the actual diameter of
        > > > radiator, and the
        > > > > cutoff frequency."
        > > > >
        > > > > Harwood's paper details Loudspeaker Distortion with Low-Frequency
        > > > > Signals JAES Volume 20 Number 9 pp. 718-728; November 1972 Three
        > > > differing
        > > > > forms of distortion, which are associated with low-frequency
        > > > signals in loudspeakers,
        > > > > are investigated. It is shown that distortion due to the Doppler
        > > > effect can be compared
        > > > > with that due to wow and flutter in recording machines, and
        > > > subjective data obtained
        > > > > for this purpose can be applied to loudspeakers. Generalized
        > > > design limits for
        > > > > loudspeakers are calculated. In loudspeakers designed to reproduce
        > > > low frequencies,
        > > > > the voice coil is made longer than the magnetic field. At low
        > > > frequencies, when the
        > > > > amplitude of vibration of the cone exceeds the difference in
        > > > length, it is shown that
        > > > > instead of the peaks of the waveform being clipped, expansion of
        > > > the input-output
        > > > > curve takes place. This effect, with its associated distortion,
        > > > can be compensated by
        > > > > employing an appropriate nonlinear suspension, and thus a much
        > > > greater useful
        > > > > output can be obtained than by using a linear suspension. Finally,
        > > > a vented cabinet is
        > > > > often used to reduce the magnitude of the undesirable effects
        > > > previously mentioned
        > > > > as well as to extend the bass response. However, a vented cabinet
        > > > is a resonant
        > > > > system and high sound pressures and particle velocities are
        > > > produced in the vent.
        > > > > These are liable to give rise to distortion from the inherent
        > > > nonlinearity in the air and
        > > > > from turbulence at the orifice and in the pipe. Existing data ae
        > > > used to estimate the
        > > > > sound levels which may be generated in a typical listening room
        > > > before distortions
        > > > > from any of these causes are audible. It is also shown that this
        > > > form of distortion is
        > > > > not a troublesome factor in the design of studio monitoring
        > > > loudspeakers. Author:
        > > > > Harwood, H.D. Download now (1.2 MB)
        > > > >
        > > > >
        > > > > Klipsch however writing in 1970 titled a paper to Audio magazine
        > > > on the same subject "The
        > > > > mud factor" perhaps wanting to tout the advantages of horn loading
        > > > and the smaller cone
        > > > > displacement.
        > > > >
        > > > > Then there is Roy Allison ten years later:
        > > > > The Audibility of Doppler Distortion in Loudspeakers Although
        > > > Doppler
        > > > > distortion in loudspeakers has been often viewed with alarm since
        > > > Beers and Belar
        > > > > described it in 1943, the question of its significance in music
        > > > reproduction has not yet
        > > > > been answered. In this study the audibility of Doppler distortion
        > > > in simple direct
        > > > > radiators is investigated theoretically (by analogy to tape-
        > > > machine flutter and by
        > > > > analysis of blind listening-room acoustic effects), and
        > > > experimentally (by double-
        > > > > blind listening tests). The analysis predicts Doppler inaudibility
        > > > for any practical
        > > > > cone velocity, and the experimental results provide confirming
        > > > evidence. Preprint
        > > > > Number: 1844 Convention: 70 (September 1981) Authors: Allison,
        > > > Roy; Villchur,
        > > > > Edgar Download now (1012 KB)
        > > > >
        > > > > Quite a lively debate.
        > > > >
        > > > > Ted
        > > > >
        > > > >
        > > > >
        > > > > On 2 Jan 2008 at 17:22, Richard Tuck wrote:
        > > > >
        > > > > >
        > > > > > Presumably people are worried about Doppler distortion?
        > > > > >
        > > > > > Is this a real issue Robert?
        > > > > >
        > > > > > Richard
        > > > > >
        > > > > >
        > > > > >
        > > > > > From: regsaudioforum@yahoogroups.com
        > > > [mailto:regsaudioforum@yahoogroups.com] On
        > > > > > Behalf Of Tom Mallin
        > > > > > Sent: 02 January 2008 15:57
        > > > > > To: regsaudioforum@yahoogroups.com
        > > > > > Subject: Re: [regsaudioforum] My first New Years project -
        > > > speakerstands measurement
        > > > > > I agree than ordinary elastomers like a sheet of sorbothane or
        > > > BluTac will not provide any audio-
        > > > > > frequency isolation of speaker from stand. But shifting the
        > > > frequency of the vibration downward
        > > > > > might be beneficial unless, as you speculate, this could
        > > > modulate the higher frequencies.
        > > > > >
        > > > > > My experience also tells me that hard interfaces like cones or
        > > > spikes produce higher frequency
        > > > > > vibrations in the speaker, since such interfaces have a high
        > > > frequency resonance. Thus, a bit of
        > > > > > brightness is typically added to the sound. Some listeners
        > > > interpret this as additional detail or
        > > > > > clarity.
        > > > > >
        > > > > > I suggest trying three other things:
        > > > > >
        > > > > > (1) Some feet under the speaker which allow the speaker to
        > > > wobble back and forth when touched
        > > > > > at a low enough frequency that you can count the cycles
        > > > visually. This low-frequency resonant
        > > > > > suspension might act like and spring and thus as a high-pass
        > > > filter preventing a significant amount
        > > > > > of vibration at audio frequencies of 20 Hz and above.
        > > > > >
        > > > > > (2) Symposium Rollerblocks or equivalent. These provide
        > > > isolation by having a lateral resonant
        > > > > > frequency below the audio range. Thus, when the cabinet is
        > > > induced to move by back and forth
        > > > > > cone movements, the effect of such movements may be filtered by
        > > > the Rollerblocks to some
        > > > > > extent. Much may depend on how undamped the movement is. To work
        > > > properly, the hard
        > > > > > rollerball should contact a very hard smooth surface, such as
        > > > steel, so as not to be damped by the
        > > > > > ball's indenting the surface it contacts. The Rollerblocks come
        > > > with little metal plates which can
        > > > > > be attached to the surface contacted by the rollerball
        > > > (typically the speaker's bottom).
        > > > > >
        > > > > > (3) A piece of thick cut-pile carpeting under the whole
        speaker.
        > > > Such an interface may well
        > > > > > convert a substantial amount of vibration to heat by just
        > > > flexing the fibers. The surface area of the
        > > > > > carpet should be large so as to allow the fibers to be as
        > > > springy and uncompressed by the
        > > > > > speaker's weight as possible. In my experience, many floor
        > > > standing speakers sound their best
        > > > > > just floating atop such carpeting.
        > > > > >
        > > > > >
        > > > > > >>> hmartinburm@ 01/02/08 04:32AM >>>
        > > > > > My first audio project this year started yesterday to answer
        the
        > > > > > question how much does the speaker stand affect sound by
        > > > contributing
        > > > > > its own vibration.
        > > > > > I attached a magnetic cartridge to a microphone stand and
        let the
        > > > > > stylus touch one leg of the stand at half height + for
        > > > calibration the
        > > > > > front panel of the speaker cabinet at tweeter. As a
        reference the
        > > > > > signal output of the amp was the second trace on the screen A
        > > > > > microphone preamplifier was connected because the RIAA EQ is
        > > > not to
        > > > > > be applied. I used an oscilloscope to watch the result.
        > > > > > I compared 3 cases:
        > > > > > 1. speaker placed on stand top plate 2. speaker placed on 4
        metal
        > > > > > cone feet on stand top plate 3. speaker placed on 4 damper
        feet on
        > > > > > stand top plate
        > > > > >
        > > > > > On the screen I found
        > > > > > 1. same vibration amplitude on stand like on front panel 2.
        same
        > > > > > vibration amplitude but with varied frequency response 3. 12 dB
        > > > > > vibration amplitude difference between stand and front
        > > > panel,
        > > > > > this turned out being much more low level vibration at the
        > > > speaker
        > > > > > front than on the stand.
        > > > > > I had to adjust the 4 spiked feet of the stand to prevent the
        > > > stand
        > > > > > from rocking, it did not change the visible result.
        > > > > > I decided to postpone the project to make some digital recording
        > > > and
        > > > > > spectral analysis and use the mic input of TacT RCS to do
        > > > alternative
        > > > > > measurement.
        > > > > >
        > > > > > The first result is : There is much more low frequency vibration
        > > > on
        > > > > > the speaker if coupled with elastomer to the stand. The stand
        > > > will
        > > > > > vibrate slightly less.
        > > > > > Is this really desired ? If the tweeter vibrates with bass will
        > > > there
        > > > > > be audible modulation products in treble?
        > > > > >
        > > > > > ...to be continued...
        > > > > > Regards Hans-Martin
        > > > > >
        > > > > > > I look forward to another year of lively exchange of audio
        > > > ideas.
        > > > > > > Have a happy and safe New Year's celebration.
        > > > > > >
        > > > > > > REG
        > > > > > >
        > > > > >
        > > > > >
        > > > > >
        > > > > >
        > > > > >
        > > > > > Yahoo! Groups Links
        > > > > >
        > > > > >
        > > > > >
        > > > > >
        > > > >
        > > > >
        > > > >
        > > > > The following section of this message contains a file attachment
        > > > > prepared for transmission using the Internet MIME message format.
        > > > > If you are using Pegasus Mail, or any other MIME-compliant
        system,
        > > > > you should be able to save it or view it from within your mailer.
        > > > > If you cannot, please ask your system administrator for
        assistance.
        > > > >
        > > > > ---- File information -----------
        > > > > File: WPM$421F_1.PNG
        > > > > Date: 2 Jan 2008, 19:13
        > > > > Size: 1073 bytes.
        > > > > Type: Unknown
        > > > >
        > > > > The following section of this message contains a file attachment
        > > > > prepared for transmission using the Internet MIME message format.
        > > > > If you are using Pegasus Mail, or any other MIME-compliant
        system,
        > > > > you should be able to save it or view it from within your mailer.
        > > > > If you cannot, please ask your system administrator for
        assistance.
        > > > >
        > > > > ---- File information -----------
        > > > > File: WPM$421F_2.PNG
        > > > > Date: 2 Jan 2008, 19:13
        > > > > Size: 1073 bytes.
        > > > > Type: Unknown
        > > > >
        > > >
        > > >
        > > >
        > > >
        > > >
        > > > Yahoo! Groups Links
        > > >
        > > >
        > > >
        > > >
        > > >
        > >
        > >
        > >
        > >
        > >
        > >
        > > Yahoo! Groups Links
        > >
        > >
        > >
        > >
        > >
        > >
        > >
        > > Yahoo! Groups Links
        > >
        > >
        > >
        > >
        > >
        >
      Your message has been successfully submitted and would be delivered to recipients shortly.