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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. lambdastorm
    Danny did mention the box being purely resistive, so I guess its a resistor array that raises the overall impedance from .04 ohms to a more reasonable 4 ohms. The transformer you mentioned sounds more like an impedance matching transformer which, in theory, doesn’t consume any power itself.
  2. lambdastorm
    Believe me most speaker amps will run into trouble powering such a difficult load. I used to experiment on impedance matching and when I run a 0.05 ohm resistor between the positive end of the amp’s binding post and the negative end, most amps straight up go into protection and the only amp that doesn’t fries itself. A resistor box is pretty much the only viable solution though it does have its drawbacks.
    Last edited: Jan 11, 2019
  3. lambdastorm
    FYI to raise the impedance of a planar headphone, a designer can either print thicker conductive traces or make longer traces. This technique however is not applicable to ribbon headphones as neither of the two on the market (RAAL and if that DIY design on Alibaba counts, Allen) employ serpentine traces, making the effective impedance almost zero. If you plug the headphone directly into an amp, the amp would most likely recognize it as a short.
  4. SilverEars
    Difficulty is not due to being hard to drive.

    What we are stating, it's not hard to drive in a sense that the headphone is not sensitive enough (like HE-6 for example), but the headphone load being so tiny.

    If an amp has as small output impedance or smaller (comparatively to the headphone, if it's flate impedance response), it will drive it easily without going to protection mode. But, that's difficult to find an amp with .05 ohm output impedance.

    But due to such a high sensitivity, you don't need gobs of power to burn through the adapter as long as the amp's output impedance is very minor and comparable scale to the .05 ohms.
    Last edited: Jan 11, 2019
  5. lambdastorm
    That’s exactly what I said. The amp likely has a higher output impedance than the impedance of the headphone making the damping factor around or even below one. In most circumstances an amp recognizes such tiny impedance as a short.
  6. SilverEars
    It's due to that box being required with speaker amp that puts a certain power requirement I think.

    Question. What impedance speaker taps is that box compatable with? What if you had amp with 2ohm taps?
  7. lambdastorm
    4 ohms I think. In theory if you are to hook that thing up a 2ohm tap you would be fine, but don’t quote me on that....
  8. Zhanming057
    Perfectly fine. The taps are just optimized for the load and power ratings so there may be SQ differences between different taps.
  9. Aleksandar R.
    Hello everyone!

    Thank you for the attention you're giving to our headphones!

    I see that we weren't quick enough with publishing the specs in detail, so naturally, a lot of guessing is going on. Sorry about that.

    Here's an excerpt from the white paper we're preparing right now, that will be published at our new website in a few days;
    I hope this will explain a lot of things and why some decisions are made:

    Unique Demands Of True Ribbons as Headphone Drivers

    1) True ribbons have very low resistance. Typically from 0.015 to 0.08 Ohms. SR1a ribbon is 0.018 ohms, or practically, a short-circuit.

    Impedance matching transformers can be used to transform the ribbon impedance to a higher value, say, 32 Ohms for use with conventional amplifiers. But...

    2) Transformers are big and heavy, in other words, you can't wear them on your head. They would have to be on the table, with a 10-foot cable going to the headphones.

    3) A cable that would not be too heavy, and acceptably flexible, would not have less than 0.15 Ohms per channel at 10 feet. That means the cable would have at least 10 times the resistance of the ribbon driver itself!

    4) While the transformer will convert 0.15 Ohms + 0.018 Ohms into 32 Ohms, and the headphone output will work just fine, there wouldn’t be enough power to compensate for the resistive loss of 10dB or tenfold of power! Only 1/10th of your headphone amp power will be developed at the ribbon, 9/10ths will just heat up the cable.

    5) That is a 10dB loss of volume, so we can forget using the headphone outputs on CD and DVD players, computers, iPods...whatever! Simply, not enough juice!

    6) If we try to compensate by increasing the ribbon efficiency, it would require 3 times stronger magnetic induction at the ribbon, which is about tenfold in weight increase to about a pound on each ear!

    7) So, do you prefer wearing 2 pounds of transformers or 2 pounds magnets on your head? Well, neither, preferably! Or, how about using 2 pounds of cabling that will have no significant resistive loss? That, especially, is out of the question!

    8) Just the 3uH inductance of a normal 10-foot cable will destroy the highs completely when terminated by 0.018 Ohms. Decreasing cable resistance to 0.018 would render all cabling useless, as far as HF response is concerned, as the physically possible inductance is not low enough. Simply, for cabling not to become a problem, cables must be terminated with loads that are greater than 2-3 Ohms.

    The best way to drive True-Ribbon Earfield™ Monitor

    Clearly, there are no good ways to solve a true-ribbon drive problem with headphone outputs or even dedicated, and more powerful, headphone amplifiers. Current requirement and low resistance demand different approach.

    We could have gone with a solution to introduce a very specific amplifier that will drive the headphones, similarly to how electrostatic headphones need their own dedicated amplifiers, but we wanted much more popular and cost-effective solution.

    Fortunately, the solution offers itself. Since there’s already a 10:1 (or higher) ratio of cable to ribbon resistance, this means that the ribbon will not be controlled by amplifier damping. That was clear from the beginning of designing our headphones, so the ribbon excursion and damping control was done by passive means, using the aforementioned small amounts of acoustical resistance.

    So, since the amplifier damping factor plays no role and if the cables need to be terminated with more than 2 Ohms, then we can use a resistor of any convenient value that is connected in series to the headphones and their cable. As far as the ribbon is concerned, this will become a current-source operation mode.

    This type of drive will greatly attenuate the power that is developed across the ribbon. Let's see what the specs say:

    Ribbon resistance: 0.018 Ohms

    Sensitivity: 85 dB / 1 mW

    Power handling with bass-heavy tracks: 450 mW RMS

    Max SPL at 450 mW RMS(limited by ribbon excursion at LF): 111 dB

    To develop 450 mW of power at 0.018 Ohms load, we need 5 Amps RMS.

    Loudspeaker amplifiers can easily deliver 5 AmpsRMS current.

    A good example is a 100W / 8 Ohm (200 W / 4 Ohms) amp that is loaded by 5.6 Ohms. At that load, it will deliver 140W RMS and the Current will be 5 Amps RMS. There are many amplifiers like that out there.

    In the end, in musical peaks, we are burning 140 Watts at the resistor, just to properly load the amplifier, while developing only 0.45 Watts at the headphones. That is not an unfortunate circumstance. As the old adage goes: “all systems approach perfection when their efficiency approaches zero”. In reality, there truly is a benefit to this; resistive loading will bring the best out of the amplifier's sound capabilities and SR1a will allow it to be easily heard.

    With this approach, all we need now is a 100W loudspeaker amp that is connected to a 5.6 Ohms resistor, that is connected to the true-ribbon headphones...

    Amplifier Interface unit

    Supplied with SR1a headphones is an Amplifier Interface unit.

    It contains an array of small, large value resistors, which are paralleled in enough numbers to achieve 5.6 ohms of combined resistance and 140W of power dissipation with moderate temperature increase.

    Also, it contains a passive de-emphasize circuit that corrects for line-source/open baffle rising response.

    Together with the cable and headphones, the amplifier load will be ~6 Ohms.

    The amplifier connects to binding posts / banana plugs at the back, and at the front, the SR1a cable plugs in to a male 4-pin XLR connector. The connector gender is chosen to prevent the possibility of plugging SR1a into a conventional headphones amplifier and effectively short it, causing damage to both the amp and the headphones.

    The Amplifier Interface unit is air-cooled, so it should be kept on top and not covered.

    All the best,

    ineztia, KaiSc, ToroFiestaSol and 6 others like this.
  10. coinmaster
    Last edited: Jan 12, 2019
  11. coinmaster
    Whoops, double post sorry, can't delete the other one :frowning2:.

    You said
    Then you said
    Why the emphasis on LF power consumption? Is there a big dip in impedance @ low frequency? If so why is this?
    Last edited: Jan 12, 2019
  12. Aleksandar R.
    I meant to say that ribbons in general, (depending on length and width) have 0.015 to 0.08 Ohms. Not meant as that impedance varies in a single ribbon driver. It does not.

    As for power handling , as you go lower in frequency, the excursion rises, so when you run out of excursion capability, that is what determines the power handling.
    Nothing to do with thermal handling or impedance.
    Ribbon of this size would easily handle 200W if it was crossed at 3k, but with full range operation it is ~0.5 W to reach +/-3.75mm of excursion when you play Japanese drums.
    ToroFiestaSol likes this.
  13. wuwhere Contributor
    I'd love to listen to a pair. I already have an amp for it, an old Linn Klout, 80wpc @ 8ohms, 160 @ 4ohms. Its a little dark sounding.
    HoloSpice likes this.
  14. Thenewguy007
    Any chance you will be sending out review copies to publications?
    I'd love to hear opinions from some professionals.
    BreadMaster likes this.
  15. Aleksandar R.
    We sure will! In about 20 days from now, after we finish NAMM 2019.
    Thenewguy007 likes this.
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