DIY but exceptionally high end semi portable HA system made with pro recording studio equipment

Discussion in 'High End Audio' started by jhisted421, Aug 18, 2005.

  1. jhisted421

    jhisted421 Guest

    I have been trying to help my father who is suffering age related
    hearing loss (very typical.. no high end left)... and he has used an
    NHS dispensed HA (He lives in the UK), with some success; but it leaves
    him unable to make out speech often on broadcast TV. (I should say he
    listens to the TV via some Spendor BC1s and Quad amps as obviously
    conventional TVs are "un-listenable to" even by non HA users).

    Anyway; I have a good scientific background, and understand a fair bit
    about the physics of sound, and its reproduction, and also the biology
    of the ear, and electronics and computing. (I read maths at Oxford). I
    used to be involved in recording classical music, so have a passion for
    audio clarity. It strikes me that all hearing aids that I have so far
    seen, seem to be battling to squeeze as much battery life, oh yes-and
    quality ;) out of components that are essentially too small to do the
    job. As Scotty said "Ye canny change the laws of physics".

    When producing semi-pro classical recordings, I worked out a long time
    ago, that to achieve "acceptable" sensitivity from microphones, you
    need 1 inch or so diameter condenser capsules. Anything less produces
    horrible dictaphone type results. (OK I exaggerate.. but it's not far
    off.). So: If one sticks to the premise that the device has to fit
    invisibly within the ear; you are forever handicapped in the design
    possibilities.

    Now for my father, I have 2 DIY tasks in mind: (1) to concoct a
    headphone style listening device for watching TV: He doesn't care
    what's connected or the size... no one will see him!
    (2) Closely following on the heels of this one... It struck me that if
    we could pair a fairly unobtrusive in-ear; sound isolating earphone (At
    the mo. the etymotic Er4s appear sadly the best one can do; though they
    leave a lot to be desired), and perhaps use something like some AKG 414
    mics that one sits on the seat in front during a concert; plugged into
    a battery powered mic. pre amp that is of high quality (so few are);
    and suitable "processing" box. In a restaurant one could stick the mics
    on the table, having the obvious advantage in the noisy restaurant
    environment of simply harnessing the inverse square law; to separate
    the person talking; from background hubbub, by putting the microphone
    nearer to them, than would be possible with all in one -within the ear
    solutions. In both circumstances I feel it should be easy to surpass
    the quality achievable with a hearing aid; at the expense of having to
    be happy to lug some equipment with one, that is only semi-portable.

    For these two very special circumstances; which hearing aids are just
    not optimised for; his pleasure could be improved significantly;
    judging by our experiments so far.

    Before anyone says: I know one can never regain what's lost in terms of
    his ability to perceive; but as long as one pours the highest quality
    stimuli achievable into his ear canals; one should be able to maximise
    the best of a bad starting situation. As an aside- my father has never
    really been interested in hifi, but his ability to pinpoint the
    "quality" hifi components recently as we started to play with this idea
    within seconds is uncanny; in A-B comparisons when asked to. Just
    because he has impaired hearing; doesn't mean he can't use what's left:
    and he himself has observed; surely we should try and maximise the
    quality of every component in the chain.

    When I recently put my father under a pair of "listenable to"
    headphones (AKG electret K340s, which retailed for approx. =A3150 UK 10
    years or so ago, as I remember), fed from his DVD player; his eyes lit
    up. Simply delivering good quality reproduced sound, allowed his
    admittedly now poor hearing, the best chance of extracting enough
    information for him to tell what is going on. He hasn't given the
    headphones back, preferring them to his dispensed hearing aid.

    I am wondering whether it is worth going the whole hog, and getting
    some serious Stax ear speakers (e.g. the 4040s or gulp the 007s); and
    couple them with some kind of DSP/ filter box; that would normally live
    in a recording studio; and suitably calibrate the boxes, to give both
    mutli band compression, clipping/limitting function, and frequency
    filtering to try and compensate for the shape of the sensitivity of his
    hearing.

    It is notable that a good friend of his, who is a retired GP (so an
    intelligent; thoughtful chap); is thoroughly fed up having got through
    3 or so really expensive "digital" hearing aids, (I think one cost many
    thousands of pounds) with similar results-just ending in frustration.
    He similarly noted that good hi-fi; seemed to help him more; and this
    was before trying anything clever with filters etc., for this special
    application of sitting at home in the lounge.

    I feel quite strongly; that none of the signal processing systems I've
    read about in commercial hearing aids seem to do offer any more than
    the basic kind of functionality that I imagined existed 20 years ago
    (but obviously didn't). None of the function appears difficult to buy
    in completely configurable guise, if you're happy with a big box i.e. a
    piece of recording studio 19 inch rack equipment. Indeed if you proceed
    down this route I suspect one should be able to maintain significantly
    better sound quality, if bolted together from off the shelf studio bits
    of equipment, and being prepared to spend a lot of time carefully
    calibrating everything to my father's hearing characteristics.
    Conventional hearing aids seem to be hampered by apparently quite low
    end audio components.

    Etymotic for example, trumpet their products as being pretty
    audiophile, with some justification. However, I own their top end ear
    phones (ER4s) (sold for listening to music they are not HAs) which many
    rave as being "the ultimate hi fi ear phones"-- well they strike me as
    "just about ok"; but they are anything but great; when compared to say
    sitting in front of a decent pair of electrostatic speakers or hi end
    Stax ear speakers, both of which I always think are good starting
    points, as audio references.

    We are willing to throw money at the problem: the aim here is to
    maximise quality. Has anybody else gone down the same route; and if so;
    have any suggestions of particular pieces of kit I should put into my
    hypothetical audio chain? Has anyone specifically got any suggestions
    for studio equipment that is appropriate for the signal processing
    stages?

    I can't believe I'm the first to try this... any suggestions/
    observations from those who've been here before?

    Sorry this is such a long post, but I would truly value any feedback
    any one has to offer.

    Jonathan Histed
     
    jhisted421, Aug 18, 2005
    #1
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  2. jhisted421

    outsor Guest

    I would suggest an inexpensive electret pzm type mic as having the best
    overall performance parameters as to reach and intelligibility. I'm not
    convinced the gear needs to be expensive, just that it have enough
    headroom to handle frequency shaping and the ability to comperess the
    final signal. When I was a child hearing aids were box affairs that were
    carried on a belt with an earpiece going from it and the mic was in the
    box, did I mention it was tube powered. Chip amps that fit in a radio the
    size of a pack of cards are common and could do the job nicely with some
    sensitive headphones which are often in the 90 + db range. Doing the
    frequency shaping using dsp in the research stage would be good with the
    final assembly done using the amp chip with a compression ic and a
    network. It might be useful to consider telephone technology where years
    of research went into finding the amount of compression and frequency
    shaping that provides the best intelligibility. I fear your presumption
    about hifi gear and best intelligibility are two mostly unrelated factors
    with divergent goals.
     
    outsor, Aug 19, 2005
    #2
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