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Ortho headphones based on Planar speakers

Discussion in 'Currawong' started by currawong, Apr 23, 2010.
  1. Currawong Contributor
    I will let this craziness explain itself. I believe someone also posted a separate thread where people were asking for pictures of it on the maker's head.


    Originally Posted by marcan /img/forum/go_quote.gif
    About ten years ago, Monsoon Audio put on the computer market nice little speakers. Based on the flat planar technology, the sound was incredible for these little speakers and for a decent price (100 $ for the MM-702).
    Being instantly hooked by the sound, I bought several models: two MM-702 and one MM-2000.

    Unfortunately, Monsoon Audio is now bankrupt since several years and the only way to find those is sometimes on ebay.
    The soundstage was amazing and medium was particularly refined and detailed. I haven’t heard this kind of medium on electro dynamic loudspeakers (I used to work as audio engineer/mixer). The only drawback was in the bass department. The flat panel didn’t go below 200 hz and the subwoofer couldn’t decently fill the gap up there. The low mid was also a little thin. Also they were very directive, meaning you had a small sweet spot but because there were little room reflections, the sweet spot was really… sweet.[​IMG]
    I was so in love with the sound that I often ended sandwiched between them…[​IMG]
    The first think I noticed was that the low mid issue disappeared. Obviously the limitation in the low department was partly due to the sound cancellation between the front and the rear of the speakers. Being bored to place the speakers manually around my head and based on the previous observation (about sound cancelation), I started to think about making headphones based on the flat panel satellite of the monsoon speakers.

    The construction
    Original Monsoon flat panel speaker

    The main goals were:
    1. Accurately place them on my ears
    2. Avoid sound cancelation between the front and the rear of the panel

    I’m usually not a pro at building anything (any amplifier I have done when I was young blew out instantly), but when sound is in question I can be very persistent.
    So I grab what I had around me (toilet paper and adhesive tape) and start the work.
    As you can see, I didn’t really care about the esthetic aspect of the beast, just the sound…
    A juicy headphone amp was required, so I used my Grace Design Model 901 which is quite generous.
    Grace Design Model 901

    The beast (probably funnier than beautiful)
    I know this is April 1rst and it will probably make you laugh but it’s real.
    Don't ask me to show it on my head, I look like a fool [​IMG]

    The sound
    The sound is wonderful. The lush, the separation, the details, the speed, the transient, the image, the soundstage are gorgeous and aren’t even comparable to other traditional headphones (I’d like to listen to ortho’s tho).
    I can hear that some dynamic compression is going on (all amp, speakers and headphones do compress the dynamic anyway).
    You have a gentle roll off below 80 hz, so the two last octave are recessed and therefore it lakes impact. Otherwise, the bass above 80 hz are very clean and warm especially bass notes.
    Mediums are breathtaking. From low mid till high mid, everything is well balanced, defined and consistent. Voices are unbeleiveble: Close your eyes and the singer is just in front of you. No dicussion here. All the little details (breath, mouth, fingers on the strings, room, little noise, ...) and transient are fabulous. You can’t miss it.
    Trebles are lightning, lush, fruity and detailed, never sibilant. A slight roll off start around 14 khz but nothing annoying (especially with the aggressive mix/mastering nowadays) and probably better than the vast majority of headphones anyway. Actually, it isn’t more than -3 db at 17.5 khz, my personal limit.

    The comfort
    Not really. Especially for someone who hasn’t the same head size. [​IMG]

    None. Recycling!

    The most noticeable drawback is the limited frequency response. It starts to very gently roll off below 80 hz and above 14 khz.

    For the top end, I tried some equalization but these headphones are so sensitive that I couldn’t find any equalizer, even pro/high end equalizer, that didn’t jeopardize the overall sound. I also tried to upsample the DAC, it opened a bit the top end but again I could hear the upsampling artefact. Finally, I preferred to keep it simple and forgot about the equalizer and the upsampling.

    In the bass and sub bass department, it was more annoying. So I decided to solve this with an old idea: Add a subwoofer in the equation.
    Headphones are interesting because they can deliver a phase and time consistent sound at a fairly loud level. Loudspeakers can’t do that mainly because of the room reflections and because you need several drivers in order to deliver a sufficient acoustic pressure. Several drivers means that you need a crossover that will destroy the phase consistency of the sound.
    Now, headphones have a drawback: the physical impact of the sound is limited. Actually, sounds below 200 hz start to be felt by the body and below 50 hz are mainly felt. Therefore, the idea to add the subwoofer.
    Thanks to my Motu ultralite which has eight analog output and inside foobar (with the crossover dsp), I time aligned the subwoofer (a velodyne CHT-15) with my monsoon based headphones.
    Velodyne CHT-15

    Time alignment in Foobar Crossover dsp (subwoofer is channel 4 and headphones are channels 5-6

    I disabled the low pass filter on the subwoofer and the dsp (letting the natural roll off of the subwoofer and avoiding phase issue), checked the phase, blended to taste and voilà.
    Both layered pretty nicely. I have now bass extension and physical impact with my DIY ortho planar headphones.

    It’s sound heaven now! [​IMG]
    Comments and suggestions are welcome!

    ZGLISZCZ likes this.
  2. Pricklely Peete Contributor
    An interesting footnote to the defunct Monsoon companies excellent speakers (the full size ones were really good) is the fact that they licensed the planar panel design from Bruce Thigpen the designer behind my current reference speakers, the ET LFT-VIIIB's.

    Hi. Really good idea and something that also keeps me wonder. Usually small planar and ribbon speakers are used as a tweeter but planar headphones have amazing low extensions and actually are much smaller. So is It possible to make headphones with Great low extension Using small planar tweeters? Anyone tried that maybe?
  4. rgonzale
    I was thinking this would be a cool way to build a DIY planar headphone, and am glad someone's already laid the groundwork!

    Regarding the limited low frequency response of the Monsoon speakers when used conventionally, this is related to the width of the speaker: at frequencies whose wavelength is longer than the dimensions of the panel you will start getting cancellation from the rear of the panel. That's part of the reason full-range planar speakers are huge. With an 8" wide panel cancellation will start happening below about 1-2 kHz. The designer can compensate a little using resonance and/or EQ, but that probably only buys you an extra octave. I would guess that the Monsoon design requires the subwoofer to cover a good part of the upper bass and lower midrange to avoid a hole in the response.

    Now, if you put your ears very close to a planar speaker, the rear-cancellation issue mostly goes away. In this case the distance from the near surface to your ear is much less than the distance sound from the rear has to travel to diffract around the edges and reach your ear, so due to the 1/(x^2) nature of sound pressure there is almost no cancellation effect. So you should be able to get pretty deep bass from a small planar speaker used in a headphone configuration.

    However I'm a bit concerned with what appears to be a closed-back design on this headphone design. (Are the rear protrusions some kind of cavity or is this part of the Monsoon speaker itself?) Based on the surface area of the planar diaphragm, a huge rear enclosure (on the order of a cubic foot I would guess) would be required to avoid an acoustic suspension design with a very high f3 (low frequency limit). Moreover you're likely getting early reflections from the enclosure which are partially cancelling the bass.
  5. rgonzale
  6. canthearyou

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