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Thread: Ways of producing rear fill and speaker placement

  1. #1
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    Aug 2010

    Ways of producing rear fill and speaker placement

    I've been toying with this idea for awhile now since Adam lent me a copy of Floyd Toole's Sound Reproduction book.

    The book does an excellent job of explaining surround fill in a few different ways, and the one that has caught my eye (or ear) is using rear channels to deliver a significantly delayed version of the front channels. Now, based on what I have read from the chapter it appears that he is proposing NOT modifying the signal to an L-R or R-L which would just create ambiance, but instead to just play the original full range signal, but with a delay of 10+ ms (I extrapolated that delay from the example of a 21ft room with approx 20ms of delay used).

    Here's where it gets interesting for car use in my mind from an installation and driver selection standpoint. In the books example the speaker placement for the surround drivers are behind and to the left and right of the listener (think standard home 5.1 speaker placement). In a car (at least mine) this would be more than likely the B-Pillar, which actually would stick the driver directly to the left and right of my head (mid sized vehicle). Therefore other alternative locations need to be looked at, simp,y due to location and distance.

    Rear doors, C-Pillars slight canted toward the front of the car or rear deck? All these options pose some serious compromises it seems ( audio causing compromises). The biggest issue is driver selection would seem to point to which location to try. Also, how much are we trying to recreate with this methodology? Would a couple of widebanders work, or should a tweeter be added in for good measure? Should we look at a more specific FR to reproduce? Since we are significantly delaying the signal do we need to really worry about other reflections such as glass, interior panels etc? What kind of sensitivity do we need as well?

    My idea is a pair of 2" or so widebanders in each of the c-pillars slightly canted forward and approximately head height. This to me seems to get me positionly the closest to the example Toole shows, while keeping the installation the least obtrusive. A larger driver set would have to go on the rear deck which means most likely reflecting off the rear window.


  2. #2
    Devil's Advocate Adam_MSS's Avatar
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    Aug 2010
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    In thinking about the same concepts, an discussing some rear speaker ideas with Earl Geddes, I started leaning toward a larger nearly full range pro-audio driver. I looked at a couple B&C 6" drivers that seemed to fit the bill (B&C 6NDL44 6-1/2" Neodymium Woofer 294-647). For larger drivers I think the rear deck could be viable. In general we're talking about creating a sense of space by mimicing diatant reflections with digital delay. That makes me somewhat less concerned with reflections. I thought about angling them up and out a bit so they'd be aiming toward the top outside corner of the rear window (sedan).

    I've also considered an aura whisper or something similar for use in B pillars. I just struggle with getting the left and right speakers to sound similar at considerably different output levels (assuming the near speaker would be at much lower volume as it's mere inches from the ear).

    I hadn't previously considered the smaller drivers in the c-pillar, but it could work. I think it has more potential than the b-pillar option. I just wonder how much bandwidth we need to cover and where that leads us in terms of driver selection.
    You don't use science to show that you're right, you use science to become right. - R.Munroe

    The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. - W.L.Bragg

  3. #3
    Founding Member
    Join Date
    Aug 2010
    Sounds like we are on the same page on the concept stages here.

    The b-pillar is just a bad idea. I taped up some tweeters I had sitting around to just get an idea of was less than 5 inches from my ear...way too close.

    My only concern with the rear deck at least in my case is volume and spacing. My car doesn't have rear deck drivers so I would have to cut metal and I don't like that idea at all.

    You're totally right on trying to figure out the bandwidth we need. I have been looking for some more info on that today and so far it's looking like the more bandwidth the better. That makes your full range driver selection make more sense over my idea of the whispers, but stupid space limitations might rule it out in my case.


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