My BFD experience..... again! (EQ'ing the sub in the new HT room)

Discussion in 'Speakers & Subwoofers' started by Sonnie Parker, Jan 22, 2004.

  1. Sonnie Parker

    Sonnie Parker Second Unit

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    Well it was two years ago yesterday that I finalized our BFD settings for our Velodyne HGS-15 sub. Yesterday I started again. Of course this time it's for our new HT room, Cedar Creek Cinema.

    It was obvious when I took my first measurements that I didn't build the perfect anechoic room. I thought it would be somewhat better than our great room which is where our HT has always been up until now.

    It was really good that I had my BFD Comprehensive Setup Guide for reference since it had been 2 years since I last setup my BFD and I had almost forgotten how to use it. Ahhh but it came back to me ever so easily and it took me only 7 measurements to get it right.

    Here's a graph showing the before and after:

    [​IMG]


    It worked out pretty good... the smoothest response I've been able to get thus far in my BFD experiences.

    I decided my best bet was to attempt somewhat of a house curve being that I had such a dip at 40hz. I knew I would probably never get that area boosted enough to completely level out the response although I was surprised at how well the boost worked. I know you are wondering why did I boost when it's not a great idea to do so. With my previous setup I had a more serious dip (or room null) and there was a very noticeable strain put on the sub amp when I boosted the null frequency. Playing that sinewave back with the boosted frequency caused a racket that I didn't think my sub was liking too well. Another tidbit was that no matter how much boost I put into the null area I couldn't get the response line to smooth out... there was still a null (a 15db boost only actually increased the null by a couple db). In the new HT room it is different (I can't explain the physics part of it but I would think it has something to do with the room and no openings). Boosting the dip in the new HT room did not cause any adverse sounds... I could not notice any additional strain on the amp as it sounded smooth and normal when testing the boosted area. The response line smoothed out fairly well this time. Thus I left it boosted.

    I used up all 12 filters in one channel to get as smooth of a response as possible. I started with 4 filters and adjusted and added as needed.

    Here's the before and after measurements along with the filter settings I used:

    [​IMG]

    [​IMG]

    I post this info because sometimes it helps to be able to see what filters are used to get a better idea of what other BFD owners can try.

    Notice the narrow bandwidths I'm using. It is important to use narrower bandwidths for cutting peaks especially if you are working near a dip. On 25hz, 28hz, and 31.5hz I used narrow bw's so that I would not be fighting the boost I gave 40hz. 5/60 on 28hz was cutting it close as it would still have some small effect on 40hz but not enough to hurt.

    Many of the small filters I inserted were really not a "dire necessity" (wasn't that from Jungle Book?). I filtered frequencies such as 20/25/44/71 just to get a few decibels smoothed out although they probably would not be that noticeable for sub performance. They were more to make the line look prettier. Had I really needed another more serious filter I could have eliminated any of those. I could go on and on and keep adjusting more but provided this sounds okay there'll really be no need.

    I could have also cut 20hz-28hz a little more and brought them down to 85db but then I like the house curve sound for movies and this give me that little extra umphhh for the extreme low end. There's nothing like the "feel" of bass. This sub toys with 16hz like it's nothing during the test measurements. It's a great witness for those that want a sub that can play flawlessly down low.

    So... the BFD does work... those that have it sitting in the closet or still in the box... it's time to get it out and lets get that sub response smoothed out.
     
  2. David Judah

    David Judah Screenwriter

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    I'm going to have to redo my sub too here pretty soon, so your setup guide will come in handy since it's been so long since I've messed with the BFD. It looks like a very nice curve. I'm really suprised about the major boost not straining the amp.

    Have you A/B'd with it in the chain and on bypass with music to make sure you're not compromising overall dynamics higher up? The reason I ask is because it's easy to miss initially if you're concentrating on the lower frequencies--it's happened to me when I was trying to get the graph to look pretty.[​IMG] If you find it does, it should be fixable with a different placement, but of course, then you have to start all over.

    If it works though it works; that's all that matters--theory be damned! [​IMG]

    DJ
     
  3. Sonnie Parker

    Sonnie Parker Second Unit

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    Thanks DJ... I'm not much on music. I'm 99% movies but have purchased 2 DVD-Audio disks and 1 SACD. I purchased them mainly to say I had them and to get a feel for what multi music was like. Thus far I've not noticed any problems from the boost. I think if it had been in the 20-30hz range I'd been asking a little much from the amp. At 40hz it's borderline area. I was surprised too as well that the amp isn't struggling any but I really cranked it up on the 40hz sinewave for about 5 seconds and I couldn't notice any strain. Then I tried full band pink noise and didn't notice any odd sounds although it was hard to figure out what was what with loud pink noise. I'm gonna keep my ears open to what's happening though. We do have several concert DVD's that may tell me a different story once I get around to watching and listening to them.
     

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