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The best 'speakers are the width of a human head - discuss

Discussion in 'audio' started by Robert, Nov 29, 2020.

  1. HansW

    HansW pfm Member


    Interesting thread. Although I agree with most of what you are stating Tony, I think the qouted statement above is wrong. The amount of reflected sound in proportion to the direct sound should be affected very much by the dispersion. The arrival time of the reflected sound should be exactly the same if the speakers and listener is in the same position. Dispersion does not affect the speed of sound. If smaller speakers mean sitting closer to them, as you suggest the second paragraf, the time delay will increase, but this is not an effect of dispersion.

    Best regards

    Mr Pig and tuga like this.
  2. Tony L

    Tony L Administrator

    Dispersion does not effect the ‘speed of sound’, which is obviously a scientific constant, but it does clearly impact the available routes of the sound to the ear, and therefore the speed of post-delay the brain has to deal with. With a highly directional speaker, say a horn or ESL 57, hardly any sound in the smaller wavelengths (mid & treble) hits the side-walls, floor, ceiling etc until after it has first hit the listener’s ears and later bounced off the back wall and back into the room. Maybe easier to get this point across if we consider an omnidirectional speaker that splashes sound out in all dimensions, the time delay from direct and reflected sound becomes hugely blurred as effectively it is arriving not at one time but many different ones, and many of them are far closer to the original signal. FWIW I’m not knocking omnis, many love them, and I can understand why, though I do view them as an effect and absolutely not what is heard in the recording studio.

    A wide dispersion box speaker is kind of a middle-ground allowing a lot of treble and mid energy out to the side, up, down etc which will inevitably hit the listener long before say a horn speaker or ESL located in the same position.

    As ever with hi-fi it is a compromise/personal choice thing, e.g. I always set a system up for a hot-seat and don’t really care about filling a room. As such having a distinct lack of treble off-axis (as Tannoys etc do) is really no issue to me as I’m just not sitting there. As long as I’m not getting the real ‘head in a vice’ thing where a speaker is beaming so acutely you can’t move a few inches without losing top end I’m happy (57s can certainly do this, Tannoys to a lesser extent).

    PS As stated above I consider LS3/5A type nearfield mini-monitors as their own thing and largely excluded as typically you are listening to them in such a tiny listening triangle of just a metre or two well away from any walls. Again you get the direct sound far further ahead of the room splash, so same effect regardless of dispersion, though I’d not enjoy them in a room without a good thick carpet. I am increasingly convinced this is why my favourite speakers are either horns, panels or mini-monitors, and also why I hate typical hi-fi speakers in typically sparsely furnished rooms (my rooms are deliberately very well damped, I do not like adding random reverb to a recording with the room!).
  3. tuga

    tuga Legal Alien

  4. tuga

    tuga Legal Alien

    Also relevant to this discussion is the horizontal directivity characteristics of different speaker topologies:

    Dutch & Dutch 8C (wave-guided cardioid narrow baffle box with rear woofers)

    Kef Blade 2 (wave-guided coax narrow baffle box with side woofers)

    PSB T3 (wave-guided narrow baffle box)

    Sonus Faber Stradivari (650mm wide baffle box)

    Jamo R907 (open baffle dipole)

    Gradient Helsinki 1.5 (wave-guided open baffle dipole)

    Quad ESL-2805 (planar dipole)

    MartinLogan Montis (planar dipole above 300Hz)

    Avantgarde Uno Nano (horns above 350Hz)

    MBL Radialstrahler 101E Mk.II (omni)

    PhilofCas and RJohan like this.
  5. tuga

    tuga Legal Alien

    Interesting to see that it is possible to achieve constant directivity characteristics with different topologies.
  6. RJohan

    RJohan pfm Member

    I actually buys the 'same size as the human head theory' as long as it's just that we reproduces, the human voice. It should give (roughly) the same dispersion characteristics as the human head. BUT only if that human vioice is reproduced by ONE speaker! If it's two speakers reproducing a mono voice it all falls apart. The reflected sound from the room will not mimic that of a single mono voice, or any other musical instrument.

    About Tonys idea about phase response and LS3/5a vs JR149. LS3/5a has the tweeter mounted quite a bit forward of the woofer. So they SHOULD have different phase response.

    In a recent thread I went on about my theory that wide dispersion speakers and omnis works because they gives many reflected sounds from the walls which results in a diffuse reflected sound field that helps the ear/brain with the localisation of the direct sound. As long as the reflected sound reach the ears with a long enough delay, as pointed out by the pics tuga has posted.
  7. tuga

    tuga Legal Alien

    This is true for live sound sources but not for stereo. This is so because with stereo over a pair of speakers both recorded direct sound and recorded ambience cues come from the same location in your room (one or both speakers).


    This is of course only relevant with recordings of live music performed in a natural acoustic environment (most classic, hardly anything else).

    With stereo what gives localization cues are differences in level (and phase) between the signal that is feeding the two sources/speakers. The two speakers create the illusion of phantom images located on or between them and in the plane form by the speakers or behing it. In a studio mix the acoustic guitar is picked up by a mono microphone and the signal is then pan-potted to its intended/imagined position, a bit like using the balance control in an amplifier.
    Stereo over a pair of speakers doesn't provide vertical localization information.

    In regard to reproduction of stereo recordings, reflected sound increases the sense of immersiveness or envelopment but hinders the localisation of phantom sources.
  8. tuga

    tuga Legal Alien

    With "real" stereo recordings (as opposed to studio mixes) the soundstage is expected to be restricted to the space in-between the speakers:


    Side-wall reflections produce an artifact which is perceived as wider soundstage and phantom images and more envelopment.
    The downsides are the overlaying of one's listening room acoustics over the recorded ambience cues and loss of phantom image sharpness.

    The way several sources are distributed over the space between the speakers varies depending on the mic technique used, as can be observed using this visualiser by changing the "Microphone system" (middle left):
  9. RJohan

    RJohan pfm Member

    I was a bit unclear. Many reflected sounds from the walls result in a diffuse sound field that in itself is hard to hear the direction from. Few reflected sounds from the walls (to be extreme, think just one from the side wall) is not diffuse and as such is easy to hear the direction of. Few reflected sounds will, as you say, hinder the localisation of phantom sources. Not, my idea, it comes from famous speaker designer Stig Carlsson.
  10. IVELIN

    IVELIN pfm Member

    It's worth mentioning that the sound wave generated by a speaker is a semi-sphere (talking only about the forward movement of the cone) and the wavefield goes in all directions of the semi-sphere. If you add reflectors, refractors, diffractors that wavefield will constantly change direction and there will be constructive/distructive interference. In the diagrams above all this is represented by rays and gives false impression for a one-directional/linear propagation of the sound wave. In other words, the diagram with the orange rfz is not entirely true because does not represent all raypaths.
  11. Tony L

    Tony L Administrator

    Physically they are both wrong, as any flat baffle is wrong. Hence many speakers having a tilted baffle like a Spica TC50, SBL etc as you want the tweeter and the bass-mid dust-cap (or phase plug) in vertical alignment assuming the crossover isn’t doing too much odd stuff.

    The thing that interests me in the 149 vs 3/5A comparison is what exactly the BBC did to electrically time align the LS3/5A as its mid band is extraordinarily good. I have read many comments that phase alignment was part of the brief, but I don’t know how they achieved it. Looking at the speaker suggests they started from quite an odd place given the tweeter is substantially ahead of the B110 dust-cap! My electronics knowledge just isn’t sufficient at this stage to pick apart the crossover differences. Crossovers certainly make or break phase and timing, different order filters shifting phase by different amounts etc, and in far more bizarre ways than simple inversion. I know that the LS3/5A tweeter and bass unit are wired in opposite phase (as say are Tannoys to align the compression horn that is quite a distance behind the cone), but there will be a lot of additional phase angle stuff going on as well, it is always far more complex/flawed than it first appears. Multi-way speakers are by nature hugely flawed things. There is a reason say a Quad ESL 63 sounds so, so different to any multi-driver box, and it certainly isn’t all the box!
  12. Robert

    Robert Tapehead

    One of the very few 'speakers ever produced which can reproduce a recognisable square wave :)
  13. tuga

    tuga Legal Alien

    If I'm not mistaken, with passive filters one'll have to use first-order filters on top of physical alignment in order to achieve time-coincidence

    Spica TC-60, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth). souce

    This raises other problems (directivity, resonances) and requires a head-vice.
    Here are a couple of Linkwitz's comments on phase linearity:

    Sound reproduction is about creating an auditory illusion.

    When the recorded sound is of real instruments or voices there is a familiar, live reference in our auditory memory.

    The illusion of hearing a realistic reproduction is destroyed by distortion that is added anywhere in the signal chain from microphone to loudspeaker, but the speaker is by far the biggest culprit.

    Every designer focuses on the on-axis frequency response as if it were the all determining distortion parameter.

    Sometimes great attention is paid to the phase response in an attempt to preserve waveform fidelity, which at best can only be achieved for a single listening point in space.

    Ignored usually, though of much greater importance, is resonance in drivers and cabinets and the slow release of stored energy that goes with it.

    Furthermore, the uniformity and flatness of the off-axis frequency response which we hear via room reverberation and reflections is rarely a design goal.

    You can check the naturalness of the timbre by listening from another room.

    Does it sound like a loudspeaker is playing?

    The imbalance in the speaker's power response between low and high frequencies destroys the illusion


    Now, a first-order crossover can be made phase-perfect at one point in space, but I feel quite strongly that you cannot just look at a speaker's performance at one single point in space.

    The off-axis response is also very important to a speaker's overall performance in a real room, because the radiation in these other directions will add, through reflected and reverberant interactions, to what you hear.

    Typically, we don't listen to speakers outdoors or in anechoic chambers.

    One can achieve time-coincidence with a flat baffle using a DSP crossover (f.e. Kii Three, D&D 8c).

    Dutch & Dutch 8C, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth). source
  14. tuga

    tuga Legal Alien

    For comparison the time-coherent step response of an Harbeth P3ESR and the mess of a Klipschorn AK6:

    Harbeth P3ESR, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth). source

    Klipsch Klipschorn AK6, step response on tweeter axis at 50" (5ms time window, 30kHz bandwidth). source

    In the time domain, as with the Auditorium 23 horn-loaded loudspeaker, the Klipschorn's step response (fig.8) is complicated. The problem with a loudspeaker using horn-loaded drive-units but with the horn openings in the same plane is that the outputs of the drive-units arrive at the microphone or the listener's ears at different times, due to the different lengths of the horns. While all three drive-units are connected in positive acoustic polarity, the tweeter's output—the upward-moving spike at 4ms in fig.8—arrives first at the microphone. The output of the midrange unit doesn't arrive at the microphone for another 1.5ms, while the woofer's output is too late to be shown in this graph. (Separate measurements of each drive-unit indicate that the woofer's output arrives 6ms after the midrange unit's.) Does this matter? In theory, even the woofer's output is within the hearing system's tolerance for different arrival times (footnote 2).
  15. Colin L

    Colin L High-tech low-life

    The ear can localise a sound when the reflected sound arrives at the ear more than 15 milli-seconds after the direct sound. its called the precedence effect.
    It's why true omni's like MBL's need to operate have space between the side and front walls and the speakers.
    Because of this the sound-field generated by my 101's is wide and deep and seems baffling given they are radiating sound 360 deg.
  16. tuga

    tuga Legal Alien

    Actually what I meant is that any reflection which arrives too close in time (<20ms) to the direct sound is perceived as direct sound (see Haas or precedence effect) and if it is coming from anywhere other than the speakers will make the images fuzzier (edit: see @Colin L 's post above). This is why narrow directivity speakers produces phantom images which are a lot sharper and their location better defined than wide directivity speakers and omnis.
    Which one you go for is a matter of taste in presentation but one could claim that narrow directivity and/or treated early reflections (broaband absorption or deflection) will produce a more accurate transduction of the recorded signal.
  17. tuga

    tuga Legal Alien

    Toole mentions Carlsson and omnis in his book Sound Reproduction:

    In the early 1980s I visited Stig Carlsson in Stockholm.
    He and his not-quite-omnidirectional loudspeakers had a following in Europe.
    These “ortho-directional (OD)” designs aimed at creating an active reflected sound field in rooms and, with the directional asymmetry, attempted to stabilize the stereo image over a larger listening area.
    I heard several existing and developmental models and all had varying degrees of success, depending greatly on the recording.
    All of them generated an active reflected sound field that solved the interaural crosstalk coloration.
    The randomized sounds arriving at the ears softened the images, which made movements of them less obvious.
    Steady-state room curves were quite smooth and flat.
    Readers may recall my own experience with an almost omnidirectional loudspeaker shown in Figures 7.19 and 7.20.
    If the reflected sounds are abundant and timbrally matched to the direct sounds, the subjective effects can be pleasant indeed.

    Personally I would rather listen to the (direct sound coming off) speakers than the sound of our family's sitting room.
    Bang and Olufsen cleverly allows the user to choose between a Narrow mode, a Wide mode and an Omni mode in the Beolab 90s.
  18. Yank

    Yank Bulbous Also Tapered

    I have a lot of experience with the Spica, a friend's shop sold them. It uses a sloped baffle to achieve physical alignment with the drivers, which means the listening axis is ~30 degrees off the driver axis. So when it sounds right in the listening chair, the top end of the midrange driver is spewing out excess 1K - 3K over the listener's head. It's one of those speakers that sounds good in the designated listening spot and not so good if you're in the next room.

    I'm a big fan of the "how's it sound in the next room" test...

    Still, the little TC-50 had a lot of "rightness" about it. What it lacked was detail and power.

    Also, it used the rather fragile Audax HD100D25 fabric dome tweeter with a first order network (and an LCR @ FAR), good thing they had replaceable diaphragms. The network on the woofer was 4th order (acoustic).
    TimF and tuga like this.
  19. Colin L

    Colin L High-tech low-life

    Having listen to box speakers all my life, personally I prefer listening to a good omni. When done right it doesn't sound like you are listening to your room and if you haven't heard it you won't understand. Some think that Omni's means vague and reverby sound and imaging but it's absolutely not the case.

    From the Fremer review...
    "No box above the bottom octaves and a 360° radiating pattern should produce imaging and soundstaging superior to that of any boxed or planar speaker, and once the speakers had been placed properly, the 101E Mk.IIs did just that, reproducing with eerie verisimilitude recordings of large orchestras as well as of small ensembles in intimate settings, such as a superb-sounding reissue of Johnny Hartman's I Just Dropped By to Say Hello (LP, Impulse!/ORG 176). The sound was intimate and properly sized, and produced Hartman's baritone with a natural warmth free of congestion or bloat.

    Going back to some of the live Carnegie Hall tracks I listened to for my 2004 review reinforced the 101E Mk.IIs' astonishing spatial abilities. The speakers' presentation of physical instruments and musicians in space required no suspension of disbelief—the holographically three-dimensional picture was just there. The Weavers' Reunion at Carnegie Hall 1963 (single-sided 45rpm LPs, Vanguard/Classic 2150) was reproduced with the singers arrayed holographically across the stage. The images of Ronnie Gilbert's and Pete Seeger's voices and the glistening acoustic guitars were as convincingly portrayed as I've heard them here, including the toe-tapping, the wooden stage floor, and the airy, open space. Lights out and you're there!"
    TimF and camverton like this.
  20. Purité Audio

    Purité Audio Trade: Purite Audio

    B&O advise selecting omni for parties and non critical listening, although you could argue the 90’s aren’t true omni’s.
    ‘Narrow’ is really superb, I would very much like a pair.

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