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Raal Ribbon Headphones - SRH1A

Discussion in 'High-end Audio Forum' started by once, Oct 7, 2018.
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  1. Torq
    They handle EQ very well ... and since there are no cups etc. there are no screwy resonances or other issues at work to complicate matters at other frequencies. I initially ran my SR1a with the same kind of EQ profile, though as I progressed to better amplification that became less necessary.
     
    Darthpool and Zhanming057 like this.
  2. Thenewguy007
    Can't wait to hear it!
     
    nishan99 likes this.
  3. samuraivoodoo
    Are there any flaws with the SRH1A? My worry is it does what sometimes other summit systems do, that they are phenomenal technical achievements but miss out on the music part.
     
    Last edited: Sep 27, 2019
  4. Scgorg
    Every headphone has flaws, compared to the "ideal" headphone (if such a thing were to exist) it has extremely high distortion, especially third order (this is typical of RAAL speaker ribbons below 2KHz, though the SR1A has quite good distortion characteristics down into the lower midrange). The headphone rolls off, if ever how slightly, it has max SPL limitations compared to most dynamic, planar and electrostatic systems. It has a 2KHz peak that some people find tolerable and others do not. Other than this there is of course the power requirements, but that is to be expected.

    In short, high THD, 2KHz peak, some limitations in bass (both max SPL and extension).

    Distortion on the bass on SR1A varies between 10-20% (depending on volume) which might be audible seeing as much of it is 3rd order. If you want to test your own sensitivity to distortion then Klippel has tests that are supposed to be used for gauging loudspeaker driver and headphone performance. I can hear down to about -25dB consistently depending on the music played, which is about 5% distortion. Klippels test has the whole signal distorted, however. Humans can't perceive distortion in the bass as well as we can perceive distortion in the midrange and treble, so while 10-20% is quite high it should not be a very big concern seeing as that is only bass distortion.

    Most of all it is important to understand that practically every loudspeaker/driver is inherently limited by physics as for how good of a response it can create. The driver is always, no matter what, the limiting factor in high fidelity playback because their linearity and distortion is always orders of magnitude worse than any DAC or amplifier. The only exceptions to this rule are plasma drivers (but they have a whole slew of other issues). The SR1A is a feat of engineering and one of the few headphones to break the mold these past few years (in my opinion).
     
    nishan99, Thenewguy007 and Tugbars like this.
  5. Bertel
    Can you please share some evidence for this? So far I have only read about mostly the absence of distortion, and that is my impression as well when listening to the SR1as.
     
  6. Bertel
    Thanks for sharing, very interesting!
    Yes please, if possible that would be extremely valuable.
     
  7. hrklg01 Contributor
    Distortions of the SRH1A:

    Hello,
    I want to mention a few things about distortions of the SRH1 ribbon driver.
    As I'm most likely the oldest driver developer in this forum I want to share some may be interesting information with you:
    1) :
    distortions are audible of course, but we have to differentiate between harmonic- and non-harmonic distortions.
    Whereas non-harmonic distortions are audible very much (typically called often as Rub&Buzz), harmonic distortions are audible differently. 3rd harmonics - also called as symmetric distortion, are more audible than 2nd harmonics - non-symmetric distortions. A good example are Violins - they have more than 30% 2nd harmonics, but when played well, it sound great.
    2) :
    A ribbon driver works in the so called drum-skin mode. This means that the effective membrane (ribbon) surface is changing during movement. The higher the excursion the smaller the effective surface is.
    As this is true for both movement directions (+ and -) of ribbon, the effect generate a symmetric harmonic distortion. Yes, it's audible.
    But Raal did really a very good job in designing the membrane (ribbon) as it's not a simple ribbon, but it's designed so, that the both ends of it, are more flexible than the middle part of the ribbon. Clever design!
    Therefore at least to me, it's a very good compromise.
    3) dynamic drivers are working mostly in piston mode (at least it should be if designed correctly). However, the magnet system is difficult to get a symmetric force in both direction. Therefore harmonic non-symmetric distortions are mostly more present than the symmetric ones.
    This is why, a dynamic driver has (when offering the same excursion and effective membrane surface = same SPL at same frequency) has less audible distortions.
    Best regards,
    Heinz
     
    nishan99, skypillow, pavi and 14 others like this.
  8. Aleksandar R.
    Hello Heinz and everyone!

    Heinz, it's a pleasure to read you here!

    Here are my measurements of SR1a distortion, 2nd and 3rd harmonics at 100dB and 90dB.

    SR1a dist 90dB.JPG SR1a dist 100dB.JPG


    You can see markers with frequency and distortion in % of 2nd and 3rd harmonic.
    Measurements are done in steady-state, after the settlement of the diaphragm.

    Sure, it measures quite high, but it's not a big deal audibly and I'll explain why.

    This is not unlike what speakers would do at high SPL, but speaker's distortion doesn't rise so monotonically as SR1a's distortion and that is very important for distortion audibility. Speakers "clip" much harder, so to speak, but still way softer than amplifiers.
    For example, imagine these numbers in an amplifier. It would be terrible to listen to, only because it would do that too abruptly to stay unnoticed.

    The thing here is that I have used a progressive compliance to hang the ribbon. The more excursion the signal demands, the tighter the suspension will get, as there was no other way to control the excessive excursion and achieve high enough SPL. Basically, there is a change in resonant frequency as SPL is increased.

    The key to understand what's happening here is to watch the resonant frequency change and remember that below that frequency, the output drops at 12dB/oct slope.
    You can see the sharp dip in dist.measurements at about 28Hz at 90dB (the resonant frequency at 90dB) and at 100dB, you will see a less sharp dip (the Q-factor got reduced), showing that the resonant frequency has risen to 41-42Hz. That's what a progressive suspension does.

    Above the resonant frequency, the distortion peaks at ~9% at 100dB and ~7.5% at 90dB and that is not bad at all for a completely open design.
    Below the resonant frequency, the output drops at 12dB/oct., so it's normal to measure higher distortion % at 20Hz because the output has dropped (because the resonant frequency has risen), but audibly, it doesn't attract much attention to itself, as the total distortion output remains low.

    The main objective here was to have the distortion to smoothly increase with SPL and smoothly decrease as we go higher in frequency, as in my experience with speakers, those are the things that make it inobtrusive, if not downright inaudible in bass.

    In mid-high range, things are much more demanding and while the same rules about smooth distortion progression apply, the allowable numbers are much, much lower and the graphs reflect that this was the goal.

    All in all, what counts here is the distortion above 40Hz, where we have a good output at high SPL, not what happens below the -3 point of the frequency response. The numbers there are very much speaker-like, so they are nothing out of the ordinary. The lack of artifacts that are unrelated to music is very important.

    Also, a very important thing about distortion audibility in transducers is a very clean impulse response.
    No generated harmonics or any other artifacts should last longer than the signal that caused them. There shouldn't be distortion harmonics that can "ride" on top of ridges in spectral decay, dying out much later than the signal...due to time domain issues, same distortion percentage is not comparable between different transducers, as in some, the harmonics last longer than the cause, but that sort of discussion is for another time...

    Cheers,

    Alex
     
  9. hrklg01 Contributor
    Hello Alex,
    Very well explained! :)
    The non-linearity of spring force of the membrane (ribbon in this case) is very important for open systems to avoid too early clipping. I do not see another way to design it today.
    And yes - the impulse response is the most important factor for the driver!
    Best regards,
    Heinz
     
  10. Scgorg
    That is incredibly interesting Aleksandar and Heinz. You say the resonant frequency changes depending on SPL due to the variable compliance of the driver, my question is simply: what will be the lowest and what will be the highest typical resonant frequency found in the SR1A? I believe I've read before that it is 36Hz (before the knowledge of progressive compliance was known to me). In your measurements you show 28Hz at 90dB and 41Hz at 100dB, will it be even lower at quieter listening volumes or will the driver hit a limit for how low its resonant frequency can go?

    Does this also mean that due to the natural roll off the ribbon experiences below resonance frequency that when playing at 100dB the higher resonance frequency keeps the Xmax in check? So it is harder for the driver to start going into extremely high distortion because the driver is more limited due to its natural roll off compared to a lower volume where it can handle such excursion?

    A bonus question for Heinz since we are talking about fully open designs: does K1000 and MySphere have similar non-linear compliance and changes in f0? Or does this not apply due to the fact that the driver is working pistonically?
     
    Last edited: Sep 28, 2019
    Zhanming057 likes this.
  11. hrklg01 Contributor
    Hello Scgorg,
    The data of the SR1A only Aleksander can give.
    The K1000 does not have much of the non-linearity (a little bit it has too). This fact caused many "claims" from users because when the K1000 is driven hard, it starts immediate to clip awful loud.
    This fact and the request from guys here in the forum to reduce this effect, drove me also to implement more non-linearity into the MYSPHERE.
    Best regards, Heinz
     
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  12. Aleksandar R.
    Hello Heinz,

    I'm glad you like the approach, thank you!

    Well, my opinion is that with low resonant frequency drivers, like yours and mine, progressive compliance is much better than acoustical resistance. We don't HAVE to use it in quantities that will compress the dynamics in midrange. Just a little bit, enough to control the resonant peak at LF. Actually, because you have high (BL^2)/Re product, I see that you're using amplifier damping factor and that is a great solution to further reduce the use of acoustical resistance and retain the dynamics.

    Cheers,

    Alex
     
  13. Aleksandar R.
    All great things are alike in some ways. Our headphones are like LSD! (WHAT!?) I mean Limited Slip Differential that will ease you into sliding, not snap you into slide like open diff. and you end up in the gutter :)
     
    skypillow likes this.
  14. Aleksandar R.
    Hello Scgorg,
    The set I measured is already broken in, so the res. freq is lower than in a new set, but it doesn't get much lower with lower SPL, just 1-2 Hz, not more.

    Correct, the Xmax is kept in check by tighter suspension with greater excursion. Your conclusion about roll-off / SPL / distortion relationship is also correct.
    I mean, that was the idea and the goal, but because of physical limitations I can't manufacture the driver that will ideally follow this idea, but to some extent it does and I'm happy with the final result.
     
    Bertel and Scgorg like this.
  15. Articnoise
    Wow, I can’t remember ever seeing as high level of distortion on a HP.
     
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