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In-floor subwoofers - 8x8" drivers each, highest WAF factor

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  • In-floor subwoofers - 8x8" drivers each, highest WAF factor

    In-floor subwoofers - 8x8" drivers each, highest WAF factor, lowest THD

    I built in-floor sealed subwoofers consisting of 8 x 8" drivers each (Dayton Audio DCS 205-4). Those were the only 8" drivers which I found to fit in the subfloor cavity with a box built around them. Each sub has the cone surface area of 2 x 15" subs and 1 x 15" sub displacement. The drivers were not the reference type but I had to compromise since they were the only ones which would fit. The whole build was designed around the subfloor cavity restriction.
    The purpose of the subs was to use them below 40Hz. The box size gives each driver Qtc=0.9, Vb=5 Ltr, , Fb=82Hz .
    When the house was still renovated and did not have the drywall installed yet I tested them both with 120Hz x-over at full displacement and they played really loud - I would say around 120dB at 120Hz. The garage floor concrete slab was shaking .
    Each subwoofer has 2 boxes - the first one is the "drivers head", the second box is the "cavity box". Assembled total length is 10.5ft, height 9.25", width 14".
    The subwoofer boxes are bolted together and have a removable cover for bolts access. They were installed in the basement ceiling - between the floor joists. The boxes are separated from the floor structure and don't transfer vibrations to the house. The drivers are mounted opposed to each other to cancel any vibrations too. The boxes are suspended by multiple metal straps (like a swing cradle). For safety there are aircraft cables spun across the bottom too (not tensioned, slightly loose and taped to the boxes to prevent rattling).
    The subwoofer ports are covered with the same covers used for the heating ducts in the house and you can't tell that they are there.
    When there was no furniture in the house yet you could feel the floor bending from the air pressure whenever the subs played.
    Now when I have them set up below 40Hz they are enough for movie playing. For this open floor plan and the music levels I enjoy occasionally though I would need 4x that displacement. That's why there is another project on the go for few years already - but that's another topic altogether

    Here are the in-floor subwoofer design drawings..
    I'm using Crown XLS 2500 to power both subs. You can use Crown XLS 1500 too. Plenty of power to drive them both to Xmax.
    The combined cone surface per sub equals 21" sub. The excursion is 8mm only though. Displacement equals 15" sub each subwoofer box.


    The main design goals here are: 1. Cancel out all subwoofer drivers vibrations by opposing them in pairs; 2. Decouple the subwoofer boxes from the house framing so no direct vibration gets transferred to the walls, floor and nearby rooms.
    The sound effect is generated by the subwoofers pressure alone. After certain sound level you start feeling it in the floor. Whenever a massive flying object in the movie hits the ground it feels like it landed right in front of you.
    Again it's a main floor room with basement floor below and although I doubled up all the floor joists to make it stiffer the floor is still responsive.
    Last edited by Will P; 04-03-2020, 12:20 AM.
    When they don't make what you need - DIY;
    Listening Position - Standing, 20 feet back

  • #2
    .. more pics..
    When they don't make what you need - DIY;
    Listening Position - Standing, 20 feet back

    Comment


    • #3
      .. some more pics ..
      When they don't make what you need - DIY;
      Listening Position - Standing, 20 feet back

      Comment


      • #4
        .. and some more pics ..
        When they don't make what you need - DIY;
        Listening Position - Standing, 20 feet back

        Comment


        • #5
          .. and again some more pics ..
          When they don't make what you need - DIY;
          Listening Position - Standing, 20 feet back

          Comment


          • #6
            .. and here are the construction drawings ...
            Attached Files
            When they don't make what you need - DIY;
            Listening Position - Standing, 20 feet back

            Comment


            • #7
              This is fantastic, and something I've wanted to do for a long time. My friend Monte Kay turned me on to the idea, only he was going to build his into his ceiling (no basement where he lives). I have a full basement below our family room, and used to have dual IB subs in there, but the rear wave traveled way too much and could be heard everywhere. I was contemplating dual 8's in each enclosure (two total), but never thought to go this big.

              Do you notice any problem having the outlet be so small for so many drivers? This FAQ, from the IB cult site, says you want it as big as possible, and at least 50% the size of the drivers' area. See #15:

              http://www.ibsubwoofers.com/

              Comment


              • #8

                This project: It's built on compromises. The major restriction was the size of the cavity available (14in x 9in between the floor joists). The sub box couldn't be longer than 10' since the back reflection would go below Xover 60Hz).
                That determined the size of the outlet opening too. You are absolutely right that ideally the opening should be at least x2 driver cone area in order to reduce compression and air speed (turbulence).
                The outlet opening is the size of an 8" driver cone area. My thought was that if I kept the drivers excursion low (for more linearity, lower distortion) I could get 12" driver equivalent of displacement from those 8" x8 drivers for critical listening (music) and at Xmax I could get the equivalent of 15" driver displacement.
                The in-floor subwoofer was an opportunity too good to pass - house in construction and basement ceiling open. That was my "Plan B" as far as subfoofers on the main floor went - it was there if for whatever reason I got stuck with having only my tower speakers allowed there (WAF).
                The main floor room is 20' x 35' and those subs are good for "below reference" listening level only. If you keep the dialogue around and below 70dB then the subs can keep up with whatever LF material comes their way.
                I designed them with Fb=65Hz, higher than the X-over 40Hz so they always stay in the linear range of driver behavior. They are EQ from 40Hz down to 20Hz (similar to Bag End subs). The bass is clean and detailed.
                For that size room I do need x4 the subs driver displacement though.

                There is a new project going on for the last 3 years: Open Baffle Line Array (L/R) in the same living room.
                Speakers: Dayton Audio RSS265HO-4 (x32; infrasubs, L/R Line Array), Dayton Audio RSS265HF-8 (x32; woofer subs, L/R Line Array), Dayton Audio RS100T-8 (x48; mids, L/R Line Array); Dayton Audio AMT PRO-4 (x20; tweeters, L/R Line Array); Dayton Audio DCS205-4 (x16; in-floor subs); PSB CW383 (x4; surrounds);
                Amplifiers: Behringer NU4-6000 (x6) - infrasubs and subs amps; Crown XLS 1500 (x4); Crown XLS 2500; Crown XTi4002;
                Total power: 36kW
                I just have to find the time to put them together.
                Last edited by Will P; 04-02-2020, 01:22 PM.
                When they don't make what you need - DIY;
                Listening Position - Standing, 20 feet back

                Comment


                • #9
                  It's a cool build but I'd have mounted several smaller systems in different locations- that not only allows the manifold to be larger relative to cone size but also will smooth response.

                  Comment


                  • #10
                    I wanted to use all 8 bays between the floor joist for separate subs but my better half approved of 2. Which I was very happy with
                    When they don't make what you need - DIY;
                    Listening Position - Standing, 20 feet back

                    Comment


                    • #11
                      Today I did some THD measurements of the in-floor subs using REW and calibrated UMIC. The readings were taken in the Listening Position which is 12ft away from either sub.

                      The room is open concept, 45ft deep, 28ft wide, 10ft ceilings. Open to both basement and second floor through stairs. No treatments on walls, lots of hard surfaces, very little furniture, lots of windows. There is a horizontal bass trap in the back upper corner.


                      The normal listening level peak is 105dB Pink Noise (2Hz-20Hz noise spectrum) in Listening Position.

                      That is the max level before LF starts rattling the windows, patio door, floor, walls.

                      Any louder than that and it gets too much LF and the room can not take it.



                      There is no EQ on the subs.

                      The subs are xovered at 40Hz.

                      The subs were drawing no more than 400W each side (-20dB LED on CROWN XLS1500 is solid on; -10dB LED never came on; subs drivers wired for 8 Ohm)


                      I measured THD starting with the Noise Floor and then continued with the 8Hz - 37Hz band.



                      I knew the subs were clean sounding even before I started.

                      The THD measurements really surprised me though. THD% was around 1% anywhere in the 8Hz-37Hz band.

                      That is a mid-bass driver THD territory, not a subwoofer THD territory.



                      That shows the advantages of using multiple smaller subs vs one single sub even when the displacement is equal.

                      Some of the advantages are increased sensitivity (add extra +3dB each time number of subs is doubled; here that means 9dB more sensitivity - which means the total power for all 8 subs is 1/8 of the power needed for 1 large sub if big and small driver sensitivities are equal), reduced thermal compression (the 1/8 power is further dived between the individual drivers - in my case that's about 40W/driver; heat dissipation is a lot easier when the heat load is spread out to multiple drivers) , reduced THD.
                      When they don't make what you need - DIY;
                      Listening Position - Standing, 20 feet back

                      Comment


                      • #12
                        More measurements
                        When they don't make what you need - DIY;
                        Listening Position - Standing, 20 feet back

                        Comment


                        • #13
                          This is outrageous!

                          Is all of the WOOF! getting out of that little floor vent?

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                          • #14
                            Yes, the subs were the only ones playing during the measurements. All the other amps were turned off (main tower speakers, Surr L/R, Rear L/R)
                            Attached Files
                            When they don't make what you need - DIY;
                            Listening Position - Standing, 20 feet back

                            Comment


                            • #15
                              Wow!

                              I'd really like to see a DP (Differential Pressure) reading across that floor vent and also the room pressure at peak.

                              Does it pop your ears?

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