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MTM Design

Discussion in 'DIY Projects' started by Zing, Aug 28, 2010.

  1. Zing

    Zing Retired Admin Famous

    If someone were to build a 2-way MTM speaker, would these drivers be an outstanding combination?

    Morel EW536
    [​IMG]


    Morel ET448
    [​IMG]


    I'm thinking the 5" driver is the right size to make an awesome midrange speaker but, because it's technically a woofer, it low frequency perfomance should greatly surpass any midrange-only driver.
     
  2. Flint

    Flint "Do you know who I am?" Superstar

    You have to ask yourself what your goals are for the speaker.

    If the midrange drive is expected to have great output below 100Hz, then using a driver designed for woofer duties is a must. But, doing so will inhibit midrage performance when compared to a proper midrange driver.

    if you are comfortable with the mid woofer to only operate to 100Hz, or so, then a proper midrange is more likely to give you the best midrange performance.

    Keep in mind that with any small two way speaker, if the mid-woofers are operating well below 80hz, there will be a high likelihood of experiencing audibly high THD and doppler distortion - which I would try to avoid.

    A better solution would be to build that speaker with a proper midrange driver and then add a bass speaker to make the system a three-way solution. I did it, PaulyT did it, and most high end speakers do it.
     
  3. Zing

    Zing Retired Admin Famous

    Can you describe the drawbacks of using a woofer for midrange duties?
     
  4. Flint

    Flint "Do you know who I am?" Superstar

    First off, the terms do not inherent reflect a driver's ideal application.

    Terms like "Woofer", "Mid-Woofer", and "Midrange" are really just guideline words used to differentiate one driver from another. One company's "woofer" could very well be another company's "midrange".

    That said -

    In general, woofers are intended specifically to not have any crossover applied to the bottom end of their operating range. That doesn't every driver referred to as a woofer can reproduce 40hz with power, but it does mean their power handling and input operating range can be well below 40Hz without destroying the woofer during use.

    In order to get those characteristics, woofers tend to have larger voice coils, longer peak to peak excursion capabilities, and looser suspensions. This makes them capable of handling lots of bass energy without harsh distortion, but it also reduces their finer capabilities at the top end of their spectrum.

    A midrange and most mid-woofers do not have the ability to absorb tons of bass energy without harsh THD or potentially failing. They tend to have short peak to peak excursion limits, potentially underhung voice coils (limiting their throw), and lower power handling. They also tend to have tighter suspensions.

    The difference in sound can be heard in the midrange detail, differences in THD characteristics, and "resolution". A good midrange driver will have very low THD in the 500Hz to 5kHz range, even at high SPLs while a good woofer will have a lower THD below 400Hz. The inverse of that is that a good midrange could have higher THD below 400Hz and a good woofer will have higher THD above 500Hz.

    Then you could get into the electrical issues that impact performance, things like reactance at different frequencies, the Fs, and other qualities make one more suited for the most realistic midrange performance at that price point versus the most realistic bass peformance for the size and price.

    When the SPLs are over 90dB, then you need to consider bass causing THD in the midrange as well as doppler distortion. A true midrange with a crossover at or above 200Hz will inherently have lower THD and doppler distortion in its operating range than an equivilent woofer with no crossover at or around 200Hz. Attemping to move a cone around at 60Hz at real world listening levels just gets in the way of that very same cone attempting to produce very realistic sound in the 1kHz to 3kHz range.

    So, my advice is all about getting the cleanest output at real world listening levels, improving peak performance, and reducing all forms of distortion.
     
  5. Zing

    Zing Retired Admin Famous

    If the goal is to get the cleanest possible sound and have each driver specifically chosen for its maximum performance within its given range, what - if any - advantage is there to doubling up on drivers?

    In other words, if a traditional (T-M-W) 3-way design would meet or exceed those goals, what would be gained by designing a W-M-T-M-W speaker?
     
  6. Flint

    Flint "Do you know who I am?" Superstar

    One driver, alone, can have clean, dynamic, accurate output in its operating range, but then you have to take acoustics into account for how that physical audio wave reaches your ears. One driver requires a baffle, and the shape of that baffle and where the driver is placed on that baffle can help or hurt the sound. That's just for one driver.

    If you ignore large planer speakers (which have their own set of issues) - One driver cannot really operate from 20Hz to 20,000Hz at realistic listening levels with acceptable distortions. Thus two or three drivers have to be used - each operating in a specific audible range (hence W-M-T configs). Once you start mating a midrange to a woofer, and a tweeter to a midrange, you are forced to deal with more acoustic issues - specifically two drivers operating within the same frequency range over a significant portion of the audible spectrum.

    As humans we are extremely perceptive of what we hear in the 800hz to 5kHz range, which is where most tweeters have their crossovers tuned to mate with midrange drivers. Having two drivers attempting to "crossover" in that range inherently has flaws, and many remedies are available to reduce the impact of those flaws - one being the use of two midrange drivers flanking the tweeter. This gives the listener the perception that all of the sound coming from the MTM speakers is coming directly from the center of the tweeter (assuming it is setup correctly). This improves perceived accuracy, detail, and coherency. Likewise, when combined with a good D'Appolito configuration, the in room dispersion characteristics of the MTM will be such that reflections off the floor, coffee table, ceiling, and anything else between the speakers as the listener are reduced. This improves the in-room performance.

    The need for two woofers flanking the MTM is less of a requirement since the effects of point source perception is reduced at lower frequencies.
     
  7. Zing

    Zing Retired Admin Famous

    Interesting. That puts me right back to where I was originally. And that was thinking I'd like to build a speaker, similar in design, like this one.


    [​IMG]
     
  8. DIYer

    DIYer Well-Known Member Famous

    Before I got into tube amp and horn speaker, I was contemplating 3 way speaker with 2" - 3" mid range tweeter/woofer, super tweeter and woofer which would have crossover points set above and below mid range. You could look into that, Zing.
     
  9. Zing

    Zing Retired Admin Famous

    Huh?

    A 2 or 3 inch midrange, a tweeter/woofer, a super tweeter and a woofer? Is that what you said? And do you mean a coaxial driver when you say "tweeter/woofer"?
     
  10. DIYer

    DIYer Well-Known Member Famous

    No, I said 2" - 3" mid range tweeter/woofer, super tweeter and woofer. These are what I meant by mid range tweeter/woofer.
     
  11. malsackj

    malsackj Well-Known Member

    When looking at this are you looking at the design of the crossovers?

    Active?

    Passive?

    Active like Pual and Flint has advantages, but costs more 6 amps for stereo pair. Passive has compromises. Becuase the High pass is a single crossover it will change the time domain of the signal. When you combine a High pass and low pass for the midrange it will double the time domain fo the signal. from 0 to 90 low pass and 90 to 180 for high pass. So the tweeter will be running at 90 degrees the midranger will be 180 degrees and the woofer with out a low pass is at 0 or with a low pass running at 90 degrees.

    Some of the actives will have time delays to allow for adjusting the alignment and requires time and testing to align.

    with a passive in a simple off the self crossover you will see by my DIY on SaV for little EV the tested patern of the crossover. Paul has posted his also on the Altec active crossover.
     

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