Qms upgrade

Posted In: Lambda Drivers


  • Member
    nicknoack on #695

    Hi,

    We would like to test 2 of the AV15X in a 220 cubic meter room,
    but please can you let us know whether it is possible to
    change the Voice coil former to Nomex, Kapton or Glassfibre
    to get a higher Qms? We are currently using the Focal 15″
    and their high Qms (>10) make plucked bass sound extremely
    tuneful and fast. I think we can live with the reduced power
    handling, as the amps they will be on are anyway only 250Wrms.
    Also, are the specs on your store for the 2x2ohms in series?

    Best regards,
    Nicolas Noack


    Participant
    stryke on #7418

    Hi Nicolas,

    I don’t see any Focal with high Qms. Most seem to be much lower than the AV woofers. Which model are you using?

    This is possible for a different former, but would require a minimum of 10pcs to order a custom coil to do this. In reality you will hear very little if any difference regardless. The woofer Q is dominated by Qes. The system Q is going to be dominated by the enclosure. The biggest issue in accurate reproduction is not Qms, but in keeping parameters linear as the driver begins to move. This is what makes the Lambda motor so special. It keeps Le the same and keeps the flux from modulating. When this happens, the issues in the time domain that “muddy” the sound are virtually eliminated. The “speed” of bass is strictly determined by inductance as well. There has been a discussion going on about the Lambda drivers over on diyaudio lately which I have gone into some detail about.

    http://www.diyaudio.com/forums/multi-way/163914-who-has-overtaken-lambdacoustics-some-user-tell-best-bass-i-have-ever-heard.html

    If you’re looking at bass guitar, keep in mind the frequency range required. B0 is going to be right around 32hz as the low point with fundamentals extending up to about 343hz. The attack/pick is in the 700-1000hz range. Snap/string noises at 2.5Khz with harmonics to 4KHz range. For plucked bass to sound accurate you need to cover all of this properly.

    That all said, If you plan to have only 250W per driver then the AV15 is probably isn’t the best choice anyway. You will never be able to come close to the limits of the driver with only 250W. Looking at something like the TD15X or the TD18H+ is likely going to be the best option. I believe we do have a kapton former coil we can use for the TD15X even if you want to go that route. You will get much more efficiency and even lower inductance with either of the drivers vs the AV woofers, which is ideal for music reproduction. Depending on the usage of the system, the TD15M could also be an option. It is used in some extremely high end bass guitar cabinets for a customer. It can play flat on axis to over 4KHz, covering the entire bass guitar range with a single point source. Is this for a music only system or is there some home theater use also?

    John


    Member
    nicknoack on #7419

    Hi John,
    no such Luck off the shelf. Had to gut it and have it rewound onto
    kapton locally. Softer foam surround and kapton => Qms increased to 10.

    It makes sense what you say about muddy bass being
    mostly due to high Le, after all this puts on the most
    brakes onto the rise time. But Martin Colloms clearly
    states the higher the Qms, the lower the mechanical
    hysterisis, and the cleaner the bass at lower levels.

    The Td woofers all are -6dB or more @20Hz in our 8cuft
    encl. So that is why we are looking at the AV15x for
    -3@20. With room boundary lift might be even better.
    Are your specs for the 2x2ohm in series AV15X-D3?
    Anyway, no way to attempt edge wound alu wire locally.
    So will just order two AV-15X for now.

    Thx for the link to Diyaudio. Your Td6s are very Interesting.
    Best rgds,
    Nick


    Member
    simon5 on #7420

    Hello Mr. Noack,

    Did you measure room gain in your room ? I guess it’s around 11m x 10m x 2m or so ? Room gain should still start at around 80 Hz, which will give you between 4 and 6 dB of gain at 20 Hz. I don’t know if you have many openings in that room and the kind of walls you have on the other hand. You could measure it, that would be the best way, but not possible for most people.

    You could also use passive radiators to raise LF response.

    Specs are measured with the coils in series, or the Z would be at 1 ohm, Re slightly below 1 ohm, sensivity @ 2.83V would increase by 6 dB, and BL would decrease by half. On the other hand, that means nothing, because it will simulate the same, same power input will give same sound output at whatever frequency you choose, but it may help to better match your amplifier output impedance.


    Member
    nicknoack on #7421

    Hi Jon,
    even though walls are all concrete, ceiling is lossy.
    So far got another friend to also take 2.
    Hope I can make up an order for 10 units by next week
    for the low Qms version AV15X.
    Simulates excellently by the way in a closed box too.
    The more gradual slope of a 220 liter closed box might
    even suit the room better, but only ears can tell.

    regards
    Nick

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