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In wall RS MTM's

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  • In wall RS MTM's

    After starting my theater room ~2 years ago I can finally consider the room "finished" with the installation of the surround back in walls. I still have plans for an acoustic transparent screen and some more subs but I am claiming victory over the project .

    The drivers used are a RS28A tweeter and a pair of RS150-8's. I actually meant to order the RS28F's but... whoops!

    I know CJD has a design out there which I am sure is great but I have all the equipment to measure and I enjoy the process. As these are my back surrounds they don't need to be amazing or perfectly flat either and I went with a little simpler crossover.

    I ended up at the following crossover:
    20u cap
    .22mh ind

    30u cap

    This gave me LR4 slopes at ~ 1750hz
    Click image for larger version

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    Reverse null:
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    The data was measured in the box but not in-wall so I did not try to correct for baffle step.

    If I had it to do over again I would pick a different tweeter. Not because it cannot handle the job but because it just barely has the sensitivity to keep up with the RS150's. You will notice a hump in the response at 10k. I could have flattened it out in the crossover but that would have reduced the overall sensitivity of the design too much for my taste. The result of having to let the tweeter run with no padding is a pretty low impedance at high frequencies. I will let my receiver eq out that hump (Pioneer 1222k).

    Click image for larger version

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    The dip in the woofer resonance is what happens when you try to measure impedance of an MTM in box. I should have measured the impedance and the frequency response of the woofers in parallel instead of individually! The nasty wiggle's are box resonances before I added any stuffing.

    Response/distortion of measured speaker at low-ish volume:
    Click image for larger version

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    Distortion at high volume:
    Click image for larger version

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    In way of tools I used:
    HolmImpuse for frequency response.
    Arta LIMP for impedance.
    Arta for distortion analysis.
    WinPCD for crossover work.

    During this project I also managed to fry my sound card when testing my amplifier (output, input? does it really matter?? yes!! ha!). So I picked up an Xonar U7 external sound card. It worked very well for measurement.

    And on to some construction photos:

    These things are not light weight so after cutting the hole in the wall I attached some plywood strips to the studs so I could use screws to attach the cabinet both at the top and the bottom.

    The box is 1/2 ply but it is well braced. This wall is actually my roof so I had plenty of depth to work with (2x10's) but I did not want to give up that 1/4 inch!

    The baffle is cherry and maple. I hope it darkens with age as there is no UV in this blacked out theater room to speed the process!

    Thanks for reading!

  • #2
    Re: In wall RS MTM's

    A picture of the back of the room with the newly installed RS surround back's and the in-soffit RS surrounds:


    • #3
      Re: In wall RS MTM's

      Originally posted by eyekode View Post
      A picture of the back of the room with the newly installed RS surround back's and the in-soffit RS surrounds:

      Cool room, man! :D


      • #4
        Re: In wall RS MTM's

        Thanks! It was worth it. The family loves movie night!!