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Quality In-Walls

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  • Quality In-Walls

    For christmas my mom wants a new set of in-walls to replace their current old ones (6" poly cone, 1" fabric dome). Don't have a specific budget, but probably $500ish for the pair would be the expected range.

    The plan is to use the largest DIY in-wall kit, in order to allow for the largest woofers possible. The plan is to simply increase the current hole size from the existing pair, and drop these in. They listen to about 98% of their music from the current in-walls so a top quality replacement would be a huge upgrade. They are driven off of an older Kenwood AVR in the basement HT room, as "B" speakers, and have a local transformer-type volume dial.

    For woofers, I've been looking around a lot for 8-inchers that look okay for IB use. Where they are installed isn't really a massive airspace, but a step in the corner of a slanted ceiling. There's a picture below, I'm modelling with a very large sealed box rather than as true IB. I've been looking for woofers with as low a resonant frequency as possible, and a Qts of 0.4-0.5, if I should be looking for something else someone please say so. My current choice is the HiVI M8a, with an fs of 30Hz and Qts of 0.43. Anyone know of a better 8" woofer for IB use? I've used the M8N in another project before and loved the sound, coincidentally the M8a looks to have good specs for IB use.

    I'm not as sure on a choice for the tweeter. Definately will need the best off-axis response as possible, so should I just be looking at domes? Right now I'm considering the Dayton RS28a for it's low crossover capability.

    Another thing I'm worried about really is the off-axis response, since the speaker locations are by the ceiling, maybe 10ft+ high. The room is pretty large, maybe 30-35' x 10-12'.

    I'm also thinking about painting the speaker baffles to match the paint in the room, since I'm concerned about the grills not clearing the woofer surrounds completely. So a tweet with a removable baffle would be nice so I could paint that, too. Another reason the RS28a is looking so tempting.

    Due to location restraints, putting together a sealed in-wall enclosure is out of the question. Where a sealed Qtc .707 box would handle 20W (for the M8a), the IB config would only handle 20W with a 2nd order HPF at fs, and that loses a solid 1dB for most of the bass range compared to the Qtc .707. The only problem is, as I mentioned before, I'm not sure that I could fab an in-wall enclosure for these. So the best suited 8" driver for IB may be the best bet. With no HPF they will handle close to 10W, which I think will be plenty considering they don't turn up the volume loud often (if ever) and mostly listen to classical and jazz.

    The cut-out locations:

    So far I think I have a design pegged. Modelled using raw .frd info from the drivers, the HiVi M8a and the Dayton RS28a. Both are aluminum and should match voices nicely, I'm thinking.

    I worked up an xover based on the actual physical layout, and an off-axis listening location @ 4m away and 2m down. Kinda taking advantage of the fact that the sitting/listening area and the location of the speakers is pretty well set in stone.

    physical layout for modelling:

    The model achieves 2nd-order roll-off for the LPF at 1300Hz (actual filter is below 1kHz or so), 4th order roll-off in the HPF at 1300Hz, series L-pad resistance of 2 ohms, and includes a series LCR notch at the woofer's breakup mode (2khz). Impedance stays above 6 ohms, which is desirable. This comes to about 10 components per crossover and puts the total price under $400.

    Theoretical response is within +/-2dB and I'm not sure much could be done to improve it? Further off-axis response and power response look pretty great also. Actual on-axis response is strong in the high end and less flat, but I don't see anyone climbing on a ladder to listen to these at that level. Phase on the model does wrap like crazy but I'm not too concerned about that.

    Does anyone see any problems with this design or approach? I feel pretty satisfied with it and am ready to order parts any day now. Since I've heard the Bagby software is pretty accurate, I'm kinda banking on that for designing around off-axis response.

    Any comments or suggestions would be highly appreciated.
    Last edited by fusseli; 12-19-2010, 08:05 PM.

  • #2
    Re: Quality In-Walls

    There's a crossover out there for a Modula MT in-wall speaker which should work great for your purposes.


    • #3
      Re: Quality In-Walls

      Put this in the main forum please. This is supposed to be a gallery of finished projects.
      R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
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      • #4
        Re: Quality In-Walls

        Originally posted by spasticteapot
        There's a crossover out there for a Modula MT in-wall speaker which should work great for your purposes.
        Due to the constraints of the placement of the speakers, I really don't want to drop in someon else's canned design. The way I see it that'd produce no better off-axis results then buying some big-brand in-wall. Also, the RS180 has an fs that's 10Hz higher than the M8a-- which would have worse IB power handling.

        Originally posted by Pete Schumacher ® View Post
        Put this in the main forum please. This is supposed to be a gallery of finished projects.
        Sorry I don't know how to move the thread. In a week or two, it will be a finished project though Buying parts and will start construction in the next few days.

        Did some more tweaking and I think I'm happy with it. Kinda taking a gamble at designing for off-axis performance. According to the exact spacing and orientation I've layed out, 4m away and 2m down the response is looking pretty good! I'm going to call this a wrap and order parts in the next few days. The xover is achieving roll-offs of 4th-order Butterworth on the woofer (via 2nd-order LPF + notch @ cone breakup), and 4th-order Linkwitz-Riley for the tweet (both @ 1200Hz). I'd call it an 8 Ohm "nominal" load. Theoretical FR looks to be +/-1dB (~2dB max deviation) now in this "finallized" design, with reference level of 86dB. No baffle step added since it's in-wall.

        Used the PCD box modeller to extract min phase of the woofer, and used the raw phase data of the tweet. Both reference z-axis are left at 0.0, since both were measured at 1m by the manufacturers (Hopefully!!). Shifting reference planes for either driver by 10mm does change the FR, but doesn't seem to make a deal-breaking impact. I'm crossing my fingers that my assumptions are correct.

        Resistances added for 20ga Jantzen inductors:

        Also decided to add a 1st-order passive HPF @ 26Hz to protect over excursion at low frequencies, since these won't be used with a sub. This should make the M8a's handle 15W full-bandwidth, and 30W+ above 40Hz. Should be plenty loud for jazz/classical they'll be getting.
        Last edited by fusseli; 12-28-2010, 07:04 PM.


        • #5
          Re: Quality In-Walls

          Now having second thoughts on a passive infrasonic filter.... may go ahead without them and see how they handle without one. They should still handle up to 4-5W full bandwidth without it, still being good for the low 90s in SPL. That very may well be plenty loud-- need to test and see.

          Hesitant on using cheap electrolytics to pull it off, and a infrasonic @ 25Hz is ~800uF worth of cap.


          • #6
            Re: Quality In-Walls

            Parts came in and I've started construction. Took actual measurements of the baffles and had to make some small changes. Also going to be bottom mounting the drivers so that the grills attach properly. Would have been nice if the description for the IMS-812 was more clear on a few things.

            The real final layout, after simulating each possible configuration. There's hardly enough room on the baffles for both drivers so there really aren't many options:

            Starting to figure out crossover placement and driver mounting. PE wasn't lying when they said the largest woofer size possible is 8", just so happens that the [beautiful!] M8a's are 8.5" in diameter, which can be seen below.

            To make the woofers fit on the baffle, some modification is required... good thing I just got this handy Craftsman contraption that's dremel meets sawzall!

            Woofers fit now, will probably seal up the rough gap with some caulk upon final assembly.

            Tomorrow I'll be cutting holes and painting the baffles. Probably going to come up with some out of the box idea to get all the xover parts to fit/mount.

            After changing the orientation, the xover isn't perfect anymore but oh well. Closer to +/-1.5dB theoretical now with a <3dB swing around the crossover point. Here's the schematic:


            • #7
              Re: Quality In-Walls


              • #8
                Re: Quality In-Walls

                Uh oh!

                Forgot to mirror those baffles!:eek:

                I like the paint on the faceplate idea, though!

                You go your way, I'll go mine. I don't care if we get there on time.

                ~Pink Floyd


                • #9
                  Re: Quality In-Walls

                  To be honest I screwed up the baffles in more ways than one, and don't have time to order fresh ones so I just went along with it. My rotozip circle cutter was producing sub-par circles, I put the woofers on the wrong side of the baffles, among other things :o The grills hide 99% of the screw-ups though so I'm not too worried.

                  Only big hiccup was needing extra long screws to attach the baffles to the mounting bracket in the wall. The PE kit must assume you're not using thicker than 5/8" drywall, in my case I'm using 1x4 blocking on either side where the hardware sandwiches onto the wall. The six supplied screws were way too short, so I just used some 4" ones instead. I'd guess the finished product here to be ~10lbs, which is pretty heavy especially compared to what they are replacing.

                  The grills are fairly transparant even after being painted, plenty dark enough to hide the imperfections though! They are heavy and metal, not light flimsy plastic like the former ones. It took some pretty serious convincing to get the grills on once the baffles were torqued down, so it's safe to say they aren't going anywhere...

                  First, the old:

                  DVC? o.O

                  Now, the new:

                  Silicone & zip-ties, and a wide angle bracket. Hardly enough room for all of the xover components. I considered putting the entire xover on a seperate board to sit in the wall, but decided not to.

                  They sound pretty nice before any breaking in. Acoustic and jazz is particularly articulate and detailed. Bass is improved over the former cheap in-walls but not as strong as I was hoping, crossing my fingers that it will fill in a little over time. I really want to take some REW measurements but I can't really due to the AVR and room being across the house from eachother. I may try and setup a computer to record and average a spectrum and just play a pink noise disc...

                  Power handling seems to be excellent. With my zune on the input, these speakers can max out the AVR and produce 104dB+ (radioshack meter)distortion free. Off of the dvd changer via optical, the AVR seems to start clipping before max volume. No bass demanding music I've played so far has made the M8a's bottom-out.


                  • #10
                    Re: Quality In-Walls

                    Dude, you do great work!!


                    • #11
                      Re: Quality In-Walls

                      Holy snap! I remember buying one of those 6" DVC SpeakerCraft midwoofs from eBay for use in some sort of bandpass shoebox-something. Do you know a model number on the original SpeakerCraft speakers? Also, I'd like to figure out why those drivers have dual voice coils in a two-way.
                      Best Regards,

                      Rory Buszka

                      Taterworks Audio

                      "The work of the individual still remains the spark which moves mankind ahead, even more than teamwork." - Igor I. Sikorsky

                      If it works, but you don't know why it works, then you haven't done any engineering.


                      • #12
                        Re: Quality In-Walls

                        Those were Sonacraft S3000's, and I have no idea why they'd be DVC hahah.