Feel free to ask questions. I'll do my best to answer.


Friday, October 5, 2012

My Multi Sub Attempt

I have five subwoofers and a desire to test Dr. Geddes's approach to bass.  So I placed the subwoofers where they would fit into my room well completely unconcerned with acoustics.  Yea, not really his approach, but a have subs to burn.  Anyway, I graphed the effect of just the stereo speakers in five spots across my couch, then repeated the measurements adding one subwoofer at a time with all of them low passed at 80Hz, but no high pass on the mains.  No EQ is being used--currently I don't even own one.  Here's the results:

stereo speakers
stereo speakers with one sub

The difference between the stereo speakers and the stereo speakers with one sub added:

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That should say "-9dB".  Jimi's prophecy came true after all!

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"Well what about the time domain?"

Let's look at the center position without any subs verses all five subs in use:


I'll zoom in on the are of concern and make the graphs line up a little better.


Now here's a look at the time domain:


Doesn't look bad at all.  Looks like the only loss is in the financial domain. ;)







11 comments:

  1. Great blog, Dan, as usual!! I love reading these things when time allows me to be more scientific.

    I did a quick and dirty test for RecordingReview with a $150 Best Buy sub vs my Focal Sub6. The differences were BOOOORING. For about 1/12th the price the difference just wasn't large enough to warrant the expense. I have graphs coming in that upcoming article.

    Selling my single Focal and buying 5 of the Best Buy subs sounds like it would provide infinitely better bass response.

    Thanks!
    Brandon

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  2. Glad you liked it Brandon! You're welcome.

    One thing about cheap subs that may not show up in a quick listen are their annoyances... My cheap subs will turn off during quiet passages and then surge on with a vengeance and a pop when provoked! Never happened during music so far, but talk radio can drive me nuts. I just leave them off. Never happens with my nicer subs. You are probably only doing music with the ones in the studio, but I wouldn't be in too much haste to get rid of the Focal even if the audible differences are very minor. There could be any number of issues with cheap subs--or they could be very good. I'd just be sure b4 you get rid of the focal. I've also read reports of expensive subs having this same issue.

    My cheap subs actually do have some advantages as well--they actually play deeper and louder than the rest and use less power to do so!

    They are also much larger, lighter, plain, ugly, and the grills are very fragile... If I were to get rid of subs, they'd actually be the first to go.

    I don't want to discourage you, but I don't want you to do anything too rash either.

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  3. It looks very much like the fifth added sub took care of the 60hz null you had with no subs.

    I would be very curious to find out if the placement of the fifth sub was really all you needed.

    Any interest in doing a response chart with only the fifth sub in operation, leaving out subs one through four?

    Inquiring minds want to KNOW!!

    -Jack (in Austin)

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  4. I'd be most interested! Great idea. It will be a few days yet. I don't have any cable that will go that far

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  5. Even the fourth on for that matter.

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  6. Hi Dan, personally I feel that symmetrical placement of subs works better in rectangular rooms with predictable / easily understandable modal patterns.

    I've had very good results with four subs at the 25/75% of width points on the front and back walls. It is ABSOLUTELY critical to provide time delay capability for each sub pair relative to the mains. The rears HAVE to be delayed differently to the front otherwise you can't cancel the room mode.

    Normally the only modes you have to worry about are the axial ones and given that the multi-sub approach can only work in frequency range where the subs are playing then only the 1st-3rd modes (unless your room is miniature).

    With the symmetrical approach above you can cancel the 2nd length mode which normally rears it's ugly head in the sub range and minimize interaction with the width modes as the 25/75% locations are in the null for the 2nd width mode.

    With odd shaped rooms then good results can be had with fewer than 4/5 subs randomly placed if you have done your homework in terms of modeling placement. If you get your room into a boundary element model (BEM) then you can look at room mode distribution by placing a sub in a corner in the model. Once you have done this you can find locations for the subs that work well and then EQ to finish.

    Nyal Mellor / Acoustic Frontiers LLC

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  7. I've never done BEM, but I am willing to try anything. My room is "S" shaped .

    The 5th sub just died on me 2 days ago thanks to Willy Nelson. :) it's one of my 2 cheaper subs, but is sorely missed. In homage to another musical Willy--Willy "the Wimp", I'll bury him in a VW coffin, but that will be a different blogging.

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  8. Here's a better example of subwoofing: http://mehlau.net/audio/dual_nearfield_sub/
    Can be done cheaper and better than what I did for sure. I know where my system is moving too especially since a lost my one sub anyway.

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