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Thread: Sierra-2 Bass, Subwoofers, Acoustical Treatment

  1. #11
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    Default Re: Sierra-2 Bass, Subwoofers, Acoustical Treatment


  2. #12
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    Default Re: Sierra-2 Bass, Subwoofers, Acoustical Treatment

    Quote Originally Posted by Beave View Post
    Optimal in what sense? In terms of response smoothness?

    Do you have a link that explains this in greater detail?

    I've seen analysis that recommends corner placement instead of midwall placement. According to the analysis (was it Welti?), corner placement has better efficiency with only minimal reduction in response smoothness.
    Yes, it was Todd Welti's research:

    https://www.harman.com/sites/default...multsubs_0.pdf

    Basically he ran computer simulations (using Matlab) to see what would happen as you increase the number of subwoofers in a sealed rectangular room. He was assuming that you place the subs all at floor level and they are all placed in reasonable locations. What he was trying to measure along the way is how the standing waves in the room will be reduced with either placement or an increase in the number of subwoofers. The way that he measured the standing waves was by looking at the Max Minus Min, Max Minus Average and Standard Deviation all in dB's over multiple seats. As these figures get smaller the standing waves in those seats get reduced and your bass is more even from one seat to the next.

    Basically what he did with one subwoofer was run the simulation for the sub in one location and then slowly move it around and then pick out the location that was optimal (in reducing the standing waves over multiple seats using the three different ways of measuring it). Then he did it for two subwoofers, three subwoofers and four subwoofers. In the attached plot you will see the effects of the standing waves in the seats as you go from 1 sub to 2 to 3 to 4 (here https://drive.google.com/drive/folde...Jb?usp=sharing ). Surprisingly, either 2 or 4 subwoofers is best and 2 subs is actually really close to what you get with 4 subs, at half the cost (because in most cases one should be using identical subs).

    Afterwards, he also did actual in room measurements of some of the positions to compare with that of the simulations that he ran to determine how close the two were. It turned out that they were actually quite close, so you can look at either the in room measurements or the simulations with confidence that they are both accurate. To sum up he found that either placing 2 subs at the midpoint of opposing walls or 4 subs at the midpoints of opposing walls was best. Going from 2 to 4 was only slightly better. He also suggested as an alternative to 4 subs at the midpoint of each wall, to place them all in a separate corner. This gives up a slight bit of the reduction in the standing waves (close to that of 2 subs at the midpoint of opposing walls), but gives you a lot more output. See the other attached figure for figures of these configurations ( https://drive.google.com/drive/folde...Jb?usp=sharing ). Again, you can keep adding more and more subwoofers and you might reduce the standing waves a slight bit more, but it really doesn't make sense with the extra additional cost.
    Last edited by N Boros; 01-17-2018 at 09:32 AM.

  3. #13
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    Default Re: Sierra-2 Bass, Subwoofers, Acoustical Treatment

    Quote Originally Posted by jjackkrash View Post
    Dr. Toole was discussing this very thing in a thread on AVS and also indicated that corner placement has much better efficiency with only minimal reduction in response smoothness, even though midwall placement generally does get you the smoothest response.
    Pulling figures from the Welti paper (here https://drive.google.com/drive/folde...RR?usp=sharing ), I guess I disagree. The midpoint of opposing wall placement has a Standard Deviation of about 1.3 dB, Max Minus Min of 4.6 dB and a Max Minus Average of 2.3 dB. Going with the opposing corner placement has a Standard Deviation of about 2.6 dB, Max Minus Min of 13.1 dB and a Max Minus Average of 5.6 dB. That seems pretty big to me. But, maybe his idea of minimal is different than mine. Or more likely, maybe I don't have the context of what he was saying.

    If Dr. Toole was referring to configuration number 4 from pages 19 and 20 of the paper, where the subs in the front to corners of the room, then things get even worse. This configuration would have a Standard Deviation of about 4 dB, Max Minus Min of 21 dB and a Max Minus Average of 7 dB. If it were me, I would stick with the midpoint of opposing walls, if at all possible. It's not the end of the world if that isn't possible, but it does seem drastically better than either of the corner placement configurations mentioned.
    Last edited by N Boros; 01-17-2018 at 12:20 PM.

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