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A good question for DIY experts in design...

Discussion in 'Home Theater Projects' started by ClaudeL, Nov 9, 2006.

  1. ClaudeL

    ClaudeL Well-Known Member

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    When you make some braces in your subwoofer box, does this matter HOW they are and HOW they are placed? In a certain way, Im pretty sure that yes. However... in order to not compromise at all maximum output, are there any rules to follow in order to avoid any loss in output?

    For example, does a lot of braces can limit more ouput because of air passage restriction than a sub with just a few braces? Or does it really less matter than port placement, where you have to really pay attention to not place them too much near a wall of the enclosure or near the driver. Is it possible to loose for example one dB because you doesn't allow enough airspace in the braces and/or between the braces?

    Lots of questions to be answered, I hope that you know in general what I want to ask [​IMG]

    Thank you in advance!

    P.S.: If you can explain more with physics laws and things, I would be really interested as this would reinforce more your theory!
     
  2. Andrew Pratt

    Andrew Pratt Well-Known Member

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    It won't matter so long as the net internal volume remains true to the design you're following. The only caveat I can think of is if you put a brace too near the port opening as that might tweak the tune a little but that's likely not something you'd do anyway.
     
  3. Chris Tsutsui

    Chris Tsutsui Well-Known Member

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    I suppose the air passage within a box can be altered to an "extreme" to fundamentally represent a transmission line. Basically, the back wave of the subwoofer would be altered by the "braces".

    Holes in a solid box brace may act as a sort of "filter" of acoustic energy. "Compartments" would perhaps act like a duct for sound propagation. (Like a car muffler)

    I wouldn't use too thick of a brace where a hole in the brace could act as a "port", and I would use either large holes or a lot of holes and you will reduce the effect of the braces.

    I think that in most cases it is counter productive and too complicated to make braces/compartments that will affect the output.

    It is probably easier to adjust the signal with an EQ to compensate for a resonance that poses a problem.

    Then I guess the only other problem that occurs during bracing is putting a brace that restricts air flow near the driver (or vent) cause more air turbulence and maybe creating more work for the woofer.
     
  4. ClaudeL

    ClaudeL Well-Known Member

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    Allirght! This is mostly what I was thinking. By reading those 2 answers, this makes me think about something. I would really appreciate others to comments on this as I think that I may be wrong.

    Suppose that the end of a port is too near a wall of the enclosure or near the back of the woofer. This can restrict maximum SPL. But what are the effects of this SPL reduction? A bit less airflow through the ports or the woofer working harder for the same input voltage. So to make it brief, what Im thinking is that in order to have sound pressure reduction at a certain input voltage, something must CHANGE in the system... be it the woofer excursion, or the amount of airflow. Why would we have a change in SPL if nothing in the system change at all. Im thinking about a chemistry law... "nothing is lost, nothing is created, everything is transformed".

    So whatever there are 5 braces, or 2 braces, if they are not near the sources of output in a vented system (woofer + ports), SPL accross all the frequency response of the system should be the same at a certain input voltage if you take in consideration that adding braces reduce the internal volume (you just have to raise the box dimensions).

    What do you think about this all? I try to see all of this in a physics way, but despite having doing physics in college, Im not yet an engineer and I may skip some theories in wave propagations.
     

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