Perfect Subwoofer Location

Discussion in 'Archived Threads 2001-2004' started by Chris Tsutsui, Oct 15, 2002.

  1. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    By a combined method of calculations and trial and error, I've found an excellent position for my subwoofer resulting in a +/- 4.5 decibels in one of the smallest HT rooms on the forum.
    Dimensions 10'x11'x8 feet.
    With the help of a few acoustic panels, an SPL meter, and my graph worksheet it was very easy to come up with what phase, crossover, level, position did to actual room response.
    Feel free to visit my site for a full page of graphs as well as my updated room mode and graphing worksheet (Microsoft Excel needed).
    BTW, I'm not affiliated with any pop ups or banners.
    There you will find that there are 3 graphs to a chart so you can easily compare what each adjustment did to the response. You can also see how I made the acoustic panels. (Later I'm gonna take the panels out and see if it changes the response.)
    Some interesting statistics/tips:
    1. To reduce a peak or null, try moving the subwoofer away from the wall (axial mode) causing it.
    2. When I added a 2nd identical subwoofer to the adjacent corner it produced an extra 5-6 decibels over using a single sub in the left corner or right corner. Also, Phase needed adjustment so the subs don't cancel out any bass the mains play.
    3. My crossover adjustment barely altered frequencies below 40hz and above 200hz, while significantly altering frequencies between 60-140hz. So basically, if your problems are with deep bass, then don't touch the crossover.
    4. Moving the subwoofer around in the corner (equal distance to each wall) is wasting your time as the difference is small. However, moving a subwoofer along an adjacent wall starting from the corner can make a significant difference.
    Just to think, a few weeks ago with my single tempest and no panels I had a response that was +/- 7 decibels and the bass was rather boomy with certain notes.
    The setup:
    DIY GR-Research AV3 set to small powered by Rotel
    DIY Dual Tempest Adire alignments (Pyramid) 214L tuned to 15.4hz (Response goes down to 16hz at 100db) each powered by 250W Parts Express Plate amps.
    DIY 4" thick acoustic panels with a 7" fiberglass + 1" polyester layer suspended in air by wires with 6" spacing between panel and drywall.
     
  2. mark rush

    mark rush Stunt Coordinator

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    Thanks for the info Chris I will check out your site
    Mark
     
  3. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    I'll mention a few more things:

    1. Though a subwoofer crossover is set to 80hz, there's still a good deal of audible noise at higher frequencies output through the subwoofer. This is due to the roll off and overlapping of frequencies at the crossover point. I found this to be a severe weakness in running a single subwoofer as it made the soundstage off balance and deeper voices sounded off center towards the single sub location. Using dual subwoofers in opposite corners on the front wall corrected the stage as when both woofers are playing mono simulataneously (with mains off) the stage is front and center with what frequencies the subs play.

    2. The way I checked my subwoofer for leaks was I ran a sine sweep and listened very carefully. It was at 145hz when I noticed a distorting noise located near the driver. It turned out that one of the drivers wasn't screwed in air tight and this caused a resonance at 145hz. So a tip of advice is to check for leaks using sine sweeps because distortion happens at different frequencies.

    3. If you plan on using two subwoofers with PE plate amps, running a Y-splitter or adapter is the ONLY way to go. When I daisy chained the amps, it totally disrupted the phase which needed fine adjustment. It also caused a severe signal loss at 20hz and below due to the 20-20khz pre-amp outputs. Not to mention the 2nd daisy chained subwoofer played more high frequencies and distortion than the first which was immediatly noticeable.

    4. If using an analog HTPC, I turn off the CD output on my sound card which greatly reduces the amount of THD (Hiss) noise from my speakers. The same thing happens when you unplug the sound card's digital wire from the CD rom. I always turn off the CD output when watching a DVD or playing MP3s.
     
  4. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    This was my first double post (EVER)
    I guess it happens to the best of us. [​IMG]
     
  5. Chris Brown

    Chris Brown Stunt Coordinator

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    Glad to see i'm not the only one stuck using a Monitor as the primary Display device in the bedroom. Have to say though, they are sharp as hell!
     
  6. Kevin C Brown

    Kevin C Brown Producer

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    Good info!
     
  7. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    What I want is a program that estimates the best position of the speakers and listener position in 3D space for the best response. This way everyone doesn't have to use the trial and error method...
    Chris B.,
    I prefer a monitor over a 27" tube television unless a lot of people have to watch. (My HT is designed for one or 2 person enjoyment and used with 80% music, hence the 4.1 and no center channel)
    I do agree in that the picture quality is spine tingling though.
    Stats:
    Cornerstone P1460
    Shadow Mask CRT, .22mm dot pitch, capable of 1600x1200 @ 100hz
    The monitor I use is a factory direct only model I got from http://www.bigmonitors.com/. It was Cnets #1 pick for best 19" CRT. Went for about $450 if I remember correctly, the first one had a minor cosmetic pixel discoloration that Cornerstone replaced free and payed for both way shipping. (Advanced replacement 5 year warranty) [​IMG]
    It is a shadow mask CRT so the colors may not be as vibrant as aperture grille monitors but the geometry and picture is perfect.
     
  8. Casey H

    Casey H Stunt Coordinator

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    Chris,
    Just an addition to your problems daisy chaining with the PE amps. I just finished 2 Sonos for Myself and my Father-In-Law and are using the AVA250's. I had the same problem daisy chaining with the higher frequencies and distorting. It was the first time he was listening to it and I was playing the T-Rex on JP. To say the least I was very embarrassed (it sounded like schit! So I ran the input straight to his amp only and it cleaned right up! Strange deal!
    Just FYI... Casey
    Edit* added the fact I daisy chained the AVA250's [​IMG]
     
  9. Chu Gai

    Chu Gai Lead Actor

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    You do nice work Chris...I'm impressed!
     

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