Hi, everybody!
I've used MDF for years for subwoofer enclosures (as I'm sure many of you have), and I've never had any problems or complaints.
But I recently found a thread with folks talking about how porous MDF is... and how it's advisable to 'seal' the interior surfaces to prevent 'micro-leaking.'
Does anyone have any information or insight into this?
Is it a good idea to seal not only your seams but also the WALLS of your MDF enclosure?
If you do seal your MDF walls, what do you do it with?
Are there any downsides to a PERFECTLY sealed enclosure (I've heard that there can be--but that's a whole other thread, I'm sure.)?
I don't know... what do you think?
Thanks!
I've used MDF for years for subwoofer enclosures (as I'm sure many of you have), and I've never had any problems or complaints.
But I recently found a thread with folks talking about how porous MDF is... and how it's advisable to 'seal' the interior surfaces to prevent 'micro-leaking.'
Does anyone have any information or insight into this?
Is it a good idea to seal not only your seams but also the WALLS of your MDF enclosure?
If you do seal your MDF walls, what do you do it with?
Are there any downsides to a PERFECTLY sealed enclosure (I've heard that there can be--but that's a whole other thread, I'm sure.)?
I don't know... what do you think?
Thanks!
MDF is more likely to absorb moisture over time.
So depending on location or region it could be a issue.
So sealing to protect from moisture would make more sense.
micro leaking sounds like internet BS to me.
Having seen amazing wood work skills
and incredible horrible wood work skills
the actual box joints are more likely to leak.
or a enclosure with plate amps.
Its more likely to have leakage or whistles from plate amps.
having seen a few newer videos of car stereo installs
it seems to be a trend with that camp.
what they use....not sure
So depending on location or region it could be a issue.
So sealing to protect from moisture would make more sense.
micro leaking sounds like internet BS to me.
Having seen amazing wood work skills
and incredible horrible wood work skills
the actual box joints are more likely to leak.
or a enclosure with plate amps.
Its more likely to have leakage or whistles from plate amps.
having seen a few newer videos of car stereo installs
it seems to be a trend with that camp.
what they use....not sure
Yeah, Dragon... 'Internet BS' was my first instinct, too... but there are some smart folks here with a lot of experience, so I thought I'd see what others had to say.
Absolutely... I imagine that the air loss from one note with a less-than-perfect seam would exceed a lifetime's loss from 'micro-leaking' through the walls.
Thanks for your input!
I have always use sanding sealer, shellac-based “Seal Coat” to seal MDF, both exterior and interior sides of the panels, but especially roundovers. The “micro leaking” is a bit much but moisture absorption is real. I seal inner joints with sikaflex sealant as this is what is done in pro audio enclosures to prevent air leaks.
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Ah... very interesting, Brinkman. Since you're more knowledgeable about this than I, what do you think about using polyurethane (I ask because I have a can of it handy)? Thanks!
Yes, as long as it is not self-leveling that should work.
Just lay a bead then smooth it into the corner by running a gloved finger down the seam.
I used to seal MDF with oil-based primer but got sick of the roundovers and edges sopping up paint more aggressively than the sides. Now I just use shellac (universal binder) and move on to painting or veneering.
Just lay a bead then smooth it into the corner by running a gloved finger down the seam.
I used to seal MDF with oil-based primer but got sick of the roundovers and edges sopping up paint more aggressively than the sides. Now I just use shellac (universal binder) and move on to painting or veneering.
Will MDF do for a 200 PSI compressed oxygen tank?
No, you will quickly lose pressure.
Will micro-losses affect box tuning, frequency response, damping, etc.?
Most emphatic NO!!!
No, you will quickly lose pressure.
Will micro-losses affect box tuning, frequency response, damping, etc.?
Most emphatic NO!!!
I wonder if sealing the surface of MDF will increase the acoustic Q factor of the box, resulting in more resonant energy being stored instead of being dissipated at the box surface.
BS indeed! One need only take a tour of a PB manufacturing plant or just look at its MOE (stiffness) spec to confirm whether or not a subwoofer can generate enough pressure. That said, large cabs with no bracing can 'breathe' with thinner panels and/or absolute lowest quality of PB (a form of pressure loss), so in some cases guess we could call it a half truth.
Depends on what the sealer is, though anything that stiffens it will raise its resonant frequency, a good thing for LF cabs, but the downside is that we're adding mass, so a 'robbing Peter to pay Paul' scenario with maybe no audible net gain.
Can you point to that thread where it is discussed, I would like to have a look at it.
I don't have any hard core scientific facts, but here are my thoughts.
Regarding the "leakiness" it depends on what is being implied here, if it pertains to a leak-through through the enclosure walls then that effect on itself is probably minuscule and gets mishmashed and swamped by other non-ideal qualities such as non-perfectly rigid enclosures which gives way for the pressure changes, resonances etc..
Regarding the seems it depends how they are made, if glued then that is the last place where any leakiness of concern is happening.
On the other hand, porous enclosure materials such as non-processed wood and processed such as MDF and other types of fiber boards, concrete molds etc. have some near surface boundary effects which could be best likened to the Dielectric Absorption phenomenon found in capacitors which resembles a cascade of RC filters, which in turn lowers the Q slightly, this effect smears out the sound pressure variations inside the enclosure.
One can reduce the effect by painting the whole inside of the enclosure with nearly any kind of paint, a typical white wall paint painted onto the surface with a paintbrush works very well to seal off the porous surface and is what I have used.
Now whether it sounds better or worse is a subjective matter, IMO the difference is there but not very profound, from an acoustical point of view as far as I can see there is no real negative concerns regarding sealing the enclosures inner surface, but worth a try, it's after all DIY and the wall paint is quite a low expense factor, a sealed surface enclosure IMO requires a bit more dampening material though.
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Small holes in a speaker box are not a problem. The resonance of the panels is, MDF or whatever. There are some luminants that reduce the Q of those panels because the layers rub together to absorb the flexing energy.
BS they do not need to leak at all, thats like saying automotive suspension air bags need to leak... its air suspension it works by compressing and decompressing a volume of air.
Whether a negligible amount that possibly could leak due to mdf bleeding air through its surface has any effect it would need to be substantially bad... poor cutting technique and not enough glue yeah maybe
Your way of addressing me disappoints, all the more so because you are wrong.
A totally sealed enclosure with airtight drivers will become in effect a barometer. Hence the need for at least enough leakiness to even out atmospheric pressure differences.
Sorry mate didnt mean to be rude, Humble apologies 😳
I understand what you are meaning by barometric pressure, the sort of temperatures most enclosures would be subjected too would be of negligible effect.
You probably could indeed use it as a barometer and be able to measure(acoustically)a very slight difference but probably not enough to hear it in real life, car audio would probably have the most effect given the biggest temp swings
I understand what you are meaning by barometric pressure, the sort of temperatures most enclosures would be subjected too would be of negligible effect.
You probably could indeed use it as a barometer and be able to measure(acoustically)a very slight difference but probably not enough to hear it in real life, car audio would probably have the most effect given the biggest temp swings
Thanks Harry.
Thermal variation actually would induce even larger pressure variations, read woofers popping out or in, than atmospheric variations. Assume a range of temperatures of 50 K, between minus 10 and plus 40 degrees C. Delta P would be almost 20%. No Xmax is large enough and drivers would be destroyed.
Please thank your superior being of choice for tiny holes.
Thermal variation actually would induce even larger pressure variations, read woofers popping out or in, than atmospheric variations. Assume a range of temperatures of 50 K, between minus 10 and plus 40 degrees C. Delta P would be almost 20%. No Xmax is large enough and drivers would be destroyed.
Please thank your superior being of choice for tiny holes.