Lighter than air

January 4, 2023
 by Paul McGowan

Here’s something crazy. The mass of the FR30 and FR20’s tweeter and midrange diaphragms is less than the air being moved.

Compare that with the heavier mass of even the world’s best diamond-encrusted tweeter, and, at least for me, I experience a moment’s pause.

A pause for two reasons. First, I never thought about air having mass. Second, if all that’s true, what does it mean for the sound of heavier-than-air tweeter and midrange technologies? Are their outputs colored by that extra mass?

Of course, the aspen tweeters and midranges are not the only drivers that are lower in mass than the air they move. Most well designed planar or electrostatic drivers have extremely low mass diaphragms, some falling into the same category as the Chris Brunhaver-designed aspen drivers.

I wonder how much of the natural, open, and uncolored upper-end extension of the aspen speakers is due to this head-scratching fact and how much is due to other factors like crossover design, etc. Even the very best exotic metal dome tweeters and midranges sound colored to me.

After focusing the past 40 years of listening to the top end through low-mass planar and ribbon designs, I suppose I’ve answered my own question.

Still, I wonder.

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48 comments on “Lighter than air”

  1. Agree Paul, the speed and immediacy of the planar-electrostatic-ribbon diaphragms are ideal for reproducing the top 6 octaves!

    The excellent upper bandwidth clarity, tonality, and timbre of the custom RAAL tweeters in my stand monitors I attribute to their extremely low pure aluminum ribbon mass of less then 1/100th of a gram. They are very fast, have no overhang and the transient attack/decay sonics are very natural and real!

  2. Now that’s a kick-arse (ass) observation Paul.
    I’d say that the extremely low mass of the planar magnetic ‘Teonex’ diaphragm material that CB uses in the tweeters & the mid-range drivers has a helluvalot
    to do with the very pleasing & extremely close to ‘tonally accurate sound’
    coming from the FR20’s & FR30’s.
    The crossovers could have been made with ultimate-grade caps & resistors
    & no iron core inductors in them, but you can’t have everything…or as they
    say in the industry, “Everything has to be built to a price”.
    Regardless, they are obviously very fine loudspeakers.
    Maybe, for an extra charge, customers could request ultra-high-grade cross-
    overs, employing Duelund caps & Mundorf resistors…at least for the FR30’s.
    😀

    1. No one ever mentions V-Caps capacitors. Chris VenHaus came up with this design which is unbelievably expensive on a per unit basis. Nevertheless, I hear that their selling but I have no idea who is buying.

  3. A plasma tweeters is a more more extreme approach concerning the minimizing of driver mass/inertia. But the big challenge is always to get both drivers midrange driver and tweeter having most different mass values to move perfectly synchronized in the crossover range! 🙂

    1. Didn’t Nelson Pass create a plasma speaker quite a while back? I think he had to take them off the market because the Ozone that they created was making everyone sick.

      1. Actually you can buy loudspeakers with plasma tweeter from two German companies: Lansche Audio and Acapella Audio Arts. No problems here with ozone. This “problem” was solved already some 40 years ago! 🙂

  4. When it comes to speakers the term ‘coloured’ has negative connotations. Yet thinking back to yesterday’s post, when the recording engineer picks their chosen method, in its own way, they could be considered to be colouring the sound. If you view yesterday’s post as a question, how do we like our piano recording, I think the answer was clear, naturally and without any exaggerated effects. It could also be said that the mixing and mastering engineer’s create their own shades of colour, so good or bad it just depends what shade you like.

    In recent comments about speakers wasn’t it said that highly neutral studio monitors were not generally suited to a home audio system, a warmer and therefore coloured speaker being frequently preferred. I just feel there’s some slightly mixed messages here.

    Also, worth remembering in any conversation about audio, hot air is the lightest. 😉

    1. Hi Please allow me to give some comments on the expresión”air moved”
      Actually it should no be be any air moving understanding air moving as a current of air
      What happens is air compressed and uncompressed
      It means the driver produce a compression in the air, true a compression is air molecules are more close each other and it means higher pressure The pressure is an statics way of measuring the energy of the chocks between partículas per square meter or cm
      The energy the drivers delivers to the air makes the pressure increase
      If all the energy transmitted were used to create air movements, no increase in pressure and then no sonic wave
      Probably and difficult to affirm it might be a very limited, very small, micro mm current of air. So yes particles of air have mass, but increases of pressure is not an air movement, although it is increase of kinetics energy of particles moving in a chaotic way producing pressure
      The drivers shall produce increase in density and pressure and not air speed at all
      The example of waves created by plasma it is a good example of the fenomena of sound waves

      Hope this physical comment on fluid mechanics help.

        1. From Chris Brunhaver.

          Well, it’s a little complicated and relates to radiation impedance. I’ve attached a paper on the subject.

          As far as the air load goes, there’s a resistive and reactive component to it. The resistive component that easiest to imagine a vibrating plate carrying with it a mass of air. The reactive component to the inertial properties of the air (and that mass reacting to the vibrating diaphragm).

          Without getting into the math of everything (getting out my Baranek acoustics book), with our planar drivers, this air mass is greater than the diaphragm mass and that is not the case with cone or dome drivers.

          Because the air load is a lot more than the diaphragm, we have an interesting benefit where the viscosity of the air itself provides a lot of damping to the diaphragm and so planars over most of their range are an inherently a damped system and “stop” very quickly (without ringing or delayed resonances).

          Here is a link to the paper Chris suggests: https://www.psaudio.com/wp-content/uploads/2023/01/Publication3436.pdf

          1. Physics, is the foundation of electronics and electro mechanics. Today’s post has turned out to be much more complex than most of us realized.

            I think I’ll go listen to some music to relax my body, mind and soul and let the Speaker Design Master Chris do all of the calculations and possess the knowledge necessary to create his masterpieces.

            “In Chris I Trust”.

          2. Paul, Thank you. I had thought about the initial post quite a bit and did conclude it was likely a vibrating mass of air. The post now provides clarity on the benefit of having lower mass than this volume of vibrating air. I still do not understand how the volume of vibrating air is estimated or measured but that is probably beyond the scope of this blog

  5. All correct, but two things to mention:

    Podszus Görlich chassis convince in sound by being extremely light also below midrange, as everyone knows who heard e.g. a Zellaton speaker.

    And Martin Logan electrostatic foils, although probably comparably light as the FR’s midrange, sound colored to my ears and imprint a certain, if anyway fascinating, sound to the top end of every recording.

    Anyway, not sure if I could ever enjoy metal domes or metal inverted domes after listening to planars, textile domes, ribbons, Magnetostat tweeters or AMT for all my Hifi life.

    So light = uncolored combines often, but seemingly not always.

    1. I’ve been listening to Maggies for over 20 years now and I am still thrilled by the speed and transparency that they produce at such a reasonable price. Anyone listen to the LRS+? For $995 +$200 additional for their new stands, anyone who listens to jazz, blues or anything but hard rock or orchestral music dynamics should certainly appreciate the SQ at such a rock bottom price.

  6. I thought that it was power to weight ratio that actually mattered. And a planar has a big gap where the magnetism occurs to allow the movement of the diaphragm which is in the middle of the gap. But a classic dome driver has its voice coil in a smaller gap. And the width of the gap is super significant in the amount of magnetic flux which is the motor for a tweeter. So it seems that the dome driver weighs more but is heavier than the planar tweeter. Which has the higher power to rate ratio is a question I don’t know. And listening doesn’t give me a clue since there are also other factors in the ‘sound’ of both driver formats such as break up characteristics. Speakers are such interesting devices.

    1. Hahax,

      I was thinking the same regarding Effects of efficiency. Also horn loaded tweeters move even more air than open dome tweeters for equivalent diaphragm mass. So I would question any direct, or strong relationship based on masses of the diaphragm to mass of air being moved ratio.

  7. The coloring of sound…. The mass of air…. The crossover design….

    Is it possible that the judging of colored sound may be influenced by the mass of preference and bias?

    Paul, I suppose you did answer your question. Maybe not scientifically why, but with 40+ years of preference.

  8. Please, which volume of air? That which has the same volume as the material of which the moving part of the driver is made? That which is some fixed distance infront of the driver? (The volume in the room?!)

  9. Dear Paul,

    The Infinity IRS V introduced me to high-end audio. Since then I have enjoyed magnetic planar (Magnepan MG-IIIA) and then electrostatic (Martin Logan Monolith, Monolith III and Prodigy) and soon ribbon (Gryphon Pendragon) loudspeakers. So obviously I share many of your preferences in loudspeaker topology.

    The challenge for planar loudspeakers (whether pure or hybrid crossing over to cones for around 100Hz and below) tends to be generating sufficient dynamics and impact and convincing corporeal body in the 100Hz to 500Hz region.

  10. Paul, I admit to not remembering much from Physics class, but if the mid and tweeter are lighter than the surrounding air, doesn’t that require extra force to move them?

    Also, what is the volume of air being measured? How far from the surfaces of the devices?

  11. Heh heh heh.. I believe you did answer your own question Paul.

    I’ve heard that folks that know about planer speakers have made that claim before and got laughed out of the listening room.

  12. I recent years I’ve had Quad electrostatics (ESL82) and Radio X1 with their famous quasi-ribbon tweeter. Also a pair of planar headphones. My main speakers use standard drivers. Just different ways of doing things, not really fact, more a matter of personal preference.

  13. Two words.
    Oskar Heil.
    Brilliant mind.
    Chemistry, physics, mathematics AND audio.
    Guys like this make me realize that the extent of my entire cranial capacity is one fish two fish red fish blue fish.
    On a good day.
    Ribbons at home, Heils at work. Does the Heil AMT sound as good as a true ribbon? Too close to choose, but part of the magic while listening to the AMT is pondering in awe just how the ff..f…firehydrant someone came up with this whole concept.
    The first time curiosity compelled me to read about and understand how the AMT works, my brain immediately morphed into Foghorn Leghorn after a large wooden mallet strike to the head: doiy..doiy…Doiyyy

    See pik listen. Listen pik listen.

    1. Thanks for posting that comment pikpen. The Heil Air Motion Transformer was a revolutionary design.

      Foghorn Leghorn would certainly appreciate your plug son.

  14. Paul, If you do no think air has mass then try riding a bicycle at speeds that are 18 – 20 mph. You will quickly discover that air has mass, because at those speeds about 80% of the work you are doing riding that bike is pushing the air out of your way!

    The biggest problem with dome tweeters is dome breakup. I think a better name would be dome flexing ( the dome does not actually breakup into pieces, it just flexes when different parts of the dome travel at different velocities ). You want the dome’s motion to remain pistonic ( the entire dome moves as one ). It is this dome flexing that some people hear and thus do not like dome tweeters.

    There are ways to reduce this problem of dome flexing. You can make the dome smaller. This raises the frequency response of the tweeter, thus the mid-range must handle higher frequencies and thus you usually need a mid-bass and low-bass woofers. Another approach ( used by Magico whose speakers I use ) is to use a beryllium dome with a thin diamond coating. This combination has been shown to remain pistonic better than any other dome tweeter materials.

    I personally find that whether one prefers dome tweeters or ribbon tweeters is a matter of what one is accustom to.

  15. In general it is a misunderstanding about the sound waves physically
    Sound waves are not moving air volumes at all.
    Drivers transmit energy to air partículas increasing its energy an cresting pressure
    In the physical equation of air in movement you have three terms : pressure due to altitude(constant in our case) , a second term measured with speed elevated to 2 , which is the term of the speed of the air , or energy due to speed of the air, and the third term is energy due to pressure of the air
    In the air waves only the last one is present: cero air speed and constant pressure due to the altitude(statics pressure equal in our cases)
    Bernoulli equation applied to air.
    Equally sound waves in water does not produce any volumen of water to move

  16. Adding more
    Inertia of the driver is a problem that must be solved by the motor moving the driver
    Driver diagfram pushing air molecules shall be rigid enough not to flex with resistance(pressure) given by air , and as well big enough to transmit instantaly its energy to air molecules creating the pressure which from that instant is transmitted to air at sound speed to the rest as sound waves.
    IG might be of interest to study the influence of air temperature inside the speaker box to help and give more efficiency to the driver work.
    According to temperature speed of sound change …. Think about

    1. Yes, of course, the tweeter dome material is strong enough not to be deformed by the air alone ( although at very impact high velocities the air does become “harder” ). The tweeter dome is restrained around it outer edge so that the dome actually creates a pressure signal in the air rather than the air just sliding around the dome. At high frequencies it is the combination of the dome being driven in and out and the restraining seal at the edge that can cause flexing.

  17. There are many factors besides low mass that go into a great speaker driver and there are many great midranges and tweeters out there by choice that do not use planar or ribbon drivers.

      1. With the aid of computer technology those break up modes are pushed beyond the audible range. I happen to like a dome or inverted dome tweeters and conventional midrange drivers. Even in my headphones. They also do unique things or every manufacturer of expensive speakers would not use them in their cost no object applications. Even inexpensive dynamic drivers can sound quite good.

      2. I see it the same, but this would be another great discussion:

        What role plays superior singular technology in an overall design?

        On the one hand a big role, on the other hand we’d all probably prefer a lot of certain superior overall designs with inferior singular technology (like what tweeter is used) to other overall designs with superior singular technology used. Just because the main magic lies in the overall design.

        Surely everyone using the best singular technology states that also his overall design is the best…but in fact that’s rarely the case.

    1. This directionability makes them more room compatible in difficult rooms, yes, but, speaking e.g of AMT ribbons, where I have most current experience…they sound dynamic, fast, resolved, extended and natural and most of it more so than conventional domes. Conventional ones in comparison sound less refined, less smooth, less clean and less natural due to more colorations and distortion I guess. But this is valid for most ribbons and planars, just not all of them sound dynamic.

      1. Ok. 😀

        I’ve had ribbons in some form for the last 30-40 years. So I have a preference or bias that way.

        I‘ve also had horn and conventional drivers that sound really freakin’ good.

        Nothing is perfect and one persons idea of most correct for all probably isn’t …

  18. Perhaps this is why I have kept my Infinity Ref 4.5 speakers with EMITT and EMIM drivers for over 40 years. Changing all my front end components several times over and adding room treatments has kept me very satisfied.

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