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post #1 of 23 Old 03-20-2014, 09:30 AM - Thread Starter
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I very much understand a lot of people use double thick baffles; some even triple. The question I keep coming up with is "what math drives this". Is it purely to provide strength for holding the heavy drivers? Because if you say it is to "increase resonance", why not make the back double thick or the sides double thick? Or..is more more aesthetics. I've done quite a bit of searching...but I keep only coming up with "conventional wisdom" statements/assertion.

Looking for a discussion here.

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post #2 of 23 Old 03-20-2014, 09:48 AM
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The main reason for a double thick baffle is to make it adequately stiff, as it's more difficult to stiffen a baffle with panel to panel bracing than the other panels.

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post #3 of 23 Old 03-20-2014, 10:19 AM
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I think a lot of people also do it so they can recess the drivers and still have plenty of material left for the screws. (If that makes sense.)
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post #4 of 23 Old 03-20-2014, 11:08 AM
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Originally Posted by Trepidati0n View Post

Because if you say it is to "increase resonance", why not make the back double thick or the sides double thick?

I'd say it's to decrease resonance. smile.gif

Resonance is easier to introduce when connected directly to a 40lb vibrating object. If that is sufficiently controlled, there is no reason to have to go to extreme measures with the rest of the cab.

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post #5 of 23 Old 03-20-2014, 12:02 PM - Thread Starter
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Originally Posted by bass addict View Post

I'd say it's to decrease resonance. smile.gif

Resonance is easier to introduce when connected directly to a 40lb vibrating object. If that is sufficiently controlled, there is no reason to have to go to extreme measures with the rest of the cab.

I meant to say increasing resonant frequency. Increasing or decreasing resonance is ambiguous. The term "adequately stiff" is about ambiguous as saying "sufficiently loud". I know there is a lot of knowledge here...just trying to figure this out. Nearly every aspect of subwoofer cabinet design is modeled fairly well. The tools used here along with the knowledge match up really well. But this is one aspect I just don't see anything other than "this is the way we've always done it and it works".

So, let me make a statement and tell me where i'm wrong. in many cases...even modest bracing in a subwoofer cabinet raises the resonant frequency outside of the danger zone (well outside of 1/4 wavelength even). Therefore, the only reason to have a thick baffle is to increase stiffness caused by the hole made for the subwoofer so it doesn't flex during large displacement.

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post #6 of 23 Old 03-20-2014, 12:06 PM
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Originally Posted by Trepidati0n View Post

Therefore, the only reason to have a thick baffle is to increase stiffness caused by the hole made for the subwoofer so it doesn't flex during large displacement.

And that is good enough for me. smile.gif

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post #7 of 23 Old 03-20-2014, 12:37 PM - Thread Starter
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Originally Posted by bass addict View Post

And that is good enough for me. smile.gif

So, I should have a 1.5" thick baffle for a 4" woofer? Why don't I need a 6" baffle for a 18" woofer? Why not a 1' thick baffle for the SI 24"?

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post #8 of 23 Old 03-20-2014, 12:57 PM
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Quote:
Originally Posted by Trepidati0n View Post

So, I should have a 1.5" thick baffle for a 4" woofer? Why don't I need a 6" baffle for a 18" woofer? Why not a 1' thick baffle for the SI 24"?

Let's over analyze this some more.

You don't want to go with a db then don't. Why debate it all day. Why stop there, why is my oven square; maybe it should be round.

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post #9 of 23 Old 03-20-2014, 01:05 PM
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Just double up the baffle and brace wherever possible. Don't over think it.

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post #10 of 23 Old 03-20-2014, 02:15 PM - Thread Starter
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Originally Posted by bass addict View Post

Let's over analyze this some more.

You don't want to go with a db then don't. Why debate it all day. Why stop there, why is my oven square; maybe it should be round.

Doing something because somebody told you to do it just doesn't make sense to me. Not even in the slightest. Has anybody here built a 4 cubic foot sub with a single and double baffle and heard a defined difference or even a measured difference? Seriously...any data, even one point would be helpful.
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Originally Posted by jpmst3 View Post

Just double up the baffle and brace wherever possible. Don't over think it.

How am I over thinking. Put it this way. Lets say I have a 1/4 watt resistors on a schematic page which has a maximum of 24volts possible. With impunity , I can say any resistor above 2300 ohms doesn't require analysis. Analyzing a resistor above 2300 ohm would be "over-thinking it". But what I keep reading is "we put in these really big wattage resistors because we don't know the maximum voltage on the page...and so far it has worked...do that and don't over think it".

There is so much knowledge is this forum (and others) which is based upon modelling, building, and measuring with a solid touch of experience. However, it seems like this topic is lacking and I keep wondering why.

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post #11 of 23 Old 03-20-2014, 03:10 PM
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Originally Posted by Trepidati0n View Post

Doing something because somebody told you to do it just doesn't make sense to me. Not even in the slightest.

My dad told me not to piss on the electric fence when I was younger. Guess I should have tried it out for myself just for the experience. cool.gif

As much analyzing as you've done you could have built three baffles by now. smile.gif

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post #12 of 23 Old 03-20-2014, 03:27 PM
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Should I even bring up the fact that I used 3 baffles? 2 because everyone else was doing it and 1 because I wanted to flush mount the sub and was too lazy to try and router it out? biggrin.gif

I am going to go with the fact that this monster weights about 50lbs, that coupled with the force from all the bass I am putting through it, might put a strain on a single 3/4" piece of mdf. Maybe if the baffle was facing up and the speaker just sat there it wouldnt be a pick problem but with the speaker on the front I can see it coming loose after some time.
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post #13 of 23 Old 03-20-2014, 03:33 PM
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Originally Posted by cessna1466u View Post

Should I even bring up the fact that I used 3 baffles? 2 because everyone else was doing it and 1 because I wanted to flush mount the sub and was too lazy to try and router it out? biggrin.gif

I am going to go with the fact that this monster weights about 50lbs, that coupled with the force from all the bass I am putting through it, might put a strain on a single 3/4" piece of mdf. Maybe if the baffle was facing up and the speaker just sat there it wouldnt be a pick problem but with the speaker on the front I can see it coming loose after some time.

I ran a triple on my two behind the screen. I got lazy on this last one and only did two. I'm such a slacker.

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post #14 of 23 Old 03-20-2014, 03:33 PM
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Quote:
Originally Posted by Trepidati0n View Post

Doing something because somebody told you to do it just doesn't make sense to me. Not even in the slightest. Has anybody here built a 4 cubic foot sub with a single and double baffle and heard a defined difference or even a measured difference? Seriously...any data, even one point would be helpful.
How am I over thinking. Put it this way. Lets say I have a 1/4 watt resistors on a schematic page which has a maximum of 24volts possible. With impunity , I can say any resistor above 2300 ohms doesn't require analysis. Analyzing a resistor above 2300 ohm would be "over-thinking it". But what I keep reading is "we put in these really big wattage resistors because we don't know the maximum voltage on the page...and so far it has worked...do that and don't over think it".

There is so much knowledge is this forum (and others) which is based upon modelling, building, and measuring with a solid touch of experience. However, it seems like this topic is lacking and I keep wondering why.

Well, I guess that's because the differences between a 1.5" thick and 2.25" baffle (double or triple based on 3/4" ply) depends on how large the baffle is, how much input power, motor strength, frequencies being reproduced, etc. etc.
The bottom line is it is infinite. If there is a 1% difference between and double and triple on a 20" cube then why not keep splitting that difference in half forever.
Of course there is a difference, but your ear would not be able to detect it.

Why not run 1 awg speaker wire and on an on. You maybe reading way to much into it is all. There is nothing wrong with that.
Why not build the enclosure out of concrete or 1" plate steel...

There is a law of diminishing returns is all and it comes on quick.

It just isn't worth worrying about in my opinion.
I get it, you want data and analysis.

Every design and build is about compromise. There just isn't any point in going beyond triple at max, double is the best compromise for most.

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post #15 of 23 Old 03-20-2014, 03:38 PM
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Originally Posted by bass addict View Post

I ran a triple on my two behind the screen. I got lazy on this last one and only did two. I'm such a slacker.

I saw your post about the speakers behind your seating. Looking forward to seeing that finished. I love "out of the" enclosures. Have been looking for ideas about how to make my mains and center different than just a rectangle box. Thinking I might need to make a smaller version of your behind the chairs box to put behind my couch under a sofa table the wife wants to put there. Maybe 2 12" subs just to fill some of the back. Got one of those straight jackets in XL I can borrow?biggrin.gif
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post #16 of 23 Old 03-20-2014, 03:48 PM
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Originally Posted by Trepidati0n View Post

Has anybody here built a 4 cubic foot sub with a single and double baffle and heard a defined difference or even a measured difference?

Yes.

My 3/4" thick baffle (no flush recess) was also braced front to back with 2x2 hardwood at 4 out of 8 mounting locations and was a dual opposed design. The baffles were 18 x 18". Three of the four baffls have now failed. But that's a separate issue. Before they failed, they would flex, resonate, and make all kinds of noises. I never would have thought it would be a problem. When your bass is very clean, you hear everything.
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post #17 of 23 Old 03-20-2014, 07:40 PM
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Quote:
Originally Posted by Trepidati0n View Post

Therefore, the only reason to have a thick baffle is to increase stiffness caused by the hole made for the subwoofer so it doesn't flex during large displacement.

That would be me my answer.
Quote:
Originally Posted by Trepidati0n View Post

So, I should have a 1.5" thick baffle for a 4" woofer? Why don't I need a 6" baffle for a 18" woofer? Why not a 1' thick baffle for the SI 24"?

If the aim is to get the woofer/baffle mass/stiffness to give a minimum resonant freq, things need to be scale properly.

An important factor I haven't seen mentioned yet is how far the woofer hole is from the nearest sidewalls; the bending stiffness of a beam or plate decreases with the cube of the distance from a support, so a little makes a big difference.

Note that running a crossbrace to the back panel (ideally from the driver mounting holes) isn't as effective as you might think; you've added the stiffness of the back panel which for sure helps but you haven't nullified displacement completely like with a brace connecting identical panels subject to equal and opposite pressures.

A method that would give high stiffness is to extend braces from the driver mounting holes radially outward to a side, top, or bottom panel to benefit from their in-plane stiffness.

All of the above is one reason I like boxes barely wider than the driver with it mounted near one end so the driver loads can go directly into the sides and bottom (or top).

Three points define a plane so these stiff attach points solve the problem completely.

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post #18 of 23 Old 03-21-2014, 06:43 AM - Thread Starter
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Originally Posted by tuxedocivic View Post

Yes.

My 3/4" thick baffle (no flush recess) was also braced front to back with 2x2 hardwood at 4 out of 8 mounting locations and was a dual opposed design. The baffles were 18 x 18". Three of the four baffls have now failed. But that's a separate issue. Before they failed, they would flex, resonate, and make all kinds of noises. I never would have thought it would be a problem. When your bass is very clean, you hear everything.

Thanks. This is what I was looking for.
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I get it, you want data and analysis.

There was nothing until Tux's post. Everybody was saying double or triple and the only reason it appeared they said that is because that is what they have always done based upon what somebody else told them to do. Like I asked for...just one data point with a single layer baffle is enough to "stop over analyzing". Theory without measurement is just conjecture.

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post #19 of 23 Old 03-21-2014, 06:45 AM
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Originally Posted by Trepidati0n View Post

Thanks. This is what I was looking for.
There was nothing until Tux's post. Everybody was saying double or triple and the only reason it appeared they said that is because that is what they have always done based upon what somebody else told them to do. Like I asked for...just one data point with a single layer baffle is enough to "stop over analyzing". Theory without measurement is just conjecture.

I got ya.

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post #20 of 23 Old 03-21-2014, 07:41 AM
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Originally Posted by noah katz View Post


A method that would give high stiffness is to extend braces from the driver mounting holes radially outward to a side, top, or bottom panel to benefit from their in-plane stiffness.

 

whatcha talking about willis? (old TV show reference)

 

Seriously, can you provide a pic?  I'm one of those that a pic is worth a million words as I was never good at understanding the written word. 

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post #21 of 23 Old 03-21-2014, 09:31 AM
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whatcha talking about willis? (old TV show reference)

Seriously, can you provide a pic?  I'm one of those that a pic is worth a million words as I was never good at understanding the written word. 


The baffle braces here connect to the back, which is more effective than to the sides, top or bottom. That way at the points of contact the forces trying to push/pull the baffle in one direction are negated by the forces trying to push/pull the back in the opposite direction.

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post #22 of 23 Old 03-21-2014, 10:13 AM
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Quote:
Originally Posted by tuxedocivic View Post

My 3/4" thick baffle (no flush recess) was also braced front to back with 2x2 hardwood at 4 out of 8 mounting locations and was a dual opposed design. The baffles were 18 x 18". Three of the four baffls have now failed.

How did they fail?

If they buzzed from the get-go, sounds like a construction issue.
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In the above picture panel motion would be reduced a lot compared to no bracing, but isn't quite what I described.

To do that the two lower dowels near the driver would be extended (looks like they'd be about 1 x 6) to the upper slot port panel, and the upper dowels extended sideways, looks like about 1x6's again.

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post #23 of 23 Old 03-21-2014, 10:24 AM
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One eventually started to leak at one side of the woofer. One eventually started to pull apart from the enclosure (that lasted the longest and happened only a few weeks ago). And the other broke away from the braces. None happened immediately and all would have had superior holding power with a double baffle. The constant flexing destroyed them.

12" woofers on an 18 x 18" baffle. Had they been bigger, the forces would have been closer to the sides and maybe that would have worked better.
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