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

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  • Chris Roemer
    replied
    What you saw couldn't have been configured like THIS. If they were oop there'd be no bass.

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  • Nasteski
    replied
    What is the wiring config on these? I saw an interesting video of a bloke who did a similar thing though he wired the opposing woofers out of phase, is that what you've done here?

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  • insperationaudio
    replied
    Great idea! I would have not thought to hide the subs in such a fashion. Design and install while the house is under construction, very smart planning, and execution. I have a 4ft. crawl space under 100 yr. old house, its do-able in my situation also! I am thinking more in the way of 4 x 12" woofers rather than the 8 per. Koodoos to you!

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  • Steve Lee
    replied
    Yeah baby!



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  • Will P
    replied
    You can definitely feel the air flow coming out of the vents. I placed the tower speakers so they stay on top of the vent covers otherwise the covers would rattle.

    I measured the THD with the vent covers in place. Surprisingly the pressure drop around the vents did not create significant distortion.

    No chaffing sound is coming from the vent covers for those test levels.



    I did not measure the excursion of the drivers but it seemed around 0.8 Xmax. The subs are capable of around 6-8dB more before hitting the Xmech. The sound quality remains almost the same until it hits the Xmech.


    The main strengths of that system are:

    1. VERY VERY LOW THD - around 1% from 8Hz - 37Hz.

    2. The subs are totally out of view and wife really happy about that.



    OMG, I still can't believe those numbers given whatever the average mass market subs THD measurements are (10% and up).

    I did the readings few times over just to make sure. Than I pulled out the RatShack meter and its SPL reading was +/-1dB from the REW readings - so the UMIC was OK.


    The bass sound is Clean and Detailed - no matter if the music is playing at 100dB or 70dB - you can always hear the bass standing out especially when the sub sound starts/stops.

    It sounds effortless, quick, clean, with authority, no lingering after the sound is gone.











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  • Steve Lee
    replied
    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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  • Will P
    replied
    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

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  • Steve Lee
    replied
    This is outrageous!

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

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  • Will P
    replied
    More measurements

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  • Will P
    replied
    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.

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  • Will P
    replied
    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

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  • badman
    replied
    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.

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  • Will P
    replied

    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.

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  • christianb
    replied
    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/

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  • Will P
    replied
    .. and here are the construction drawings ...
    Attached Files

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