Just wondering how much is too much. Decided to go and build a pair of single sealed boxed for 2 DA ultimax 15's. Started with some old 15 "hatchback" style boxes I had laying around, removed the carpeting, cut the tops open and added about 12" to the hight of them to give me about 3.11 cu/ft internal. I've been cutting and attaching MDF panels over the existing ones via contact cement and a ton of pre-drilling and screwing from the inside, they're ending up kindof a compound/trapaziod type shape. So far the fron baffle is going to be 2 1/4" thick, side panels are 2", top/back/bottom are 1 1/2". (All panels are bonded/screwed layers of 3/4" and 1/2" MDF). So far the one box weighs almoast 100lbs without the front baffle or driver. My thought process was to build it so thick there wouldn't be a need for internal bracing. But this is my first build and I'm beginning to wonder if all of the extra effort is worth anything or if I've been overlooking something. Defenitaly want to get the first box right before I start building the duplicate next year. Constructive critisizm is welcome.
Overbuilding is Fun
Zach,
Western NY, the old stomping grounds!
I also did my first ported alignment build with layers of plywood and MDF, way back in the 90's. Search this forum for plywood versus MDF for subwoofers, plywood is better, you want stiff for subwoofers, dense for upper bass and midrange.
Right now I would suggest you check out the Loudspeaker Design Cookbook by Vance Dickeson:
Loudspeaker Design Cookbook 7th Edition Book
It is chock-full of info, for example the various kinds of enclosure bracing and how it can raise panel resonances up and out of subwoofer range.
BTW, the fabulous cats in this very forum can, if you ask them nicely, simulate to a high approximation how your sub will perform given the parameters and the enclosure volume.
Paul FX
Zach,
Western NY, the old stomping grounds!
I also did my first ported alignment build with layers of plywood and MDF, way back in the 90's. Search this forum for plywood versus MDF for subwoofers, plywood is better, you want stiff for subwoofers, dense for upper bass and midrange.
Right now I would suggest you check out the Loudspeaker Design Cookbook by Vance Dickeson:
Loudspeaker Design Cookbook 7th Edition Book
It is chock-full of info, for example the various kinds of enclosure bracing and how it can raise panel resonances up and out of subwoofer range.
BTW, the fabulous cats in this very forum can, if you ask them nicely, simulate to a high approximation how your sub will perform given the parameters and the enclosure volume.
Paul FX
If you really want to overbuild you should be using some PL glue and braces for sure. For building tips if you've got some time check out BillFitzmaurice.com forums (Tuba and Titan Pro Sound ... as an example). The forums show a lot of builds and have advice that will get you going in the right direction even though your build will be different than Bills plans.
Grant.
Thanks, very cool. Yes, they will be sub's. I defenitaly needed something to get me pionted in the right direction before I was too far ahead in the build. I'll check out the read. 3/4 ply can easily be incorperated without affecting the final finishing. It is fun, so many design options.
Awsome, I have some reaserch to do. Thank you, I'm new to forums and can't tell If my last reply went through or not. 3/4 ply could easilly be incorporated. This will help get me better guided before I build any further and end up having to undo/redo something.
You are quite welcome.
Once you get going this hobby/desire/what ever you want to call it is addictive. We constantly want to undo/redo/do new. To build it then stop would only be fun for a very short while.
I used 3/4 ply on my last build (tapped horn) with braces and PL glue. It worked out well
Enjoy.
Grant.
Grant,
If you want a cabinet that is easy to knock apart undo/redo/do-over, PL glue is a good choice, you can often save every piece.
If you want a cabinet to last for a lifetime of high power and road abuse, yellow carpenter's glue like Titebond II is a better choice, but if you try to knock it apart, the plys will fail before the glue.
Art
Thanks for the heads up Art. To knock apart the PL cabinet takes ply off as well with the amount I use.
I hope things are going well for you.
Grant.
Attachments
The pl glue will work good for mock up. When they're fully assembled and routed they can't move at all though. They're getting bondo'd, sanded/primed, then spray boothed with a couple coats of black, some maple in-lays, then some clear laquer. I was worried any panel movement might crack the laquer over time wich is another reason I made the box so thick, wishful thinking I guess. They're for my home setup, mostly for music and some movies. Deffenitaly going to incorperat some internal bracing now after reveiwing some other builds.
When you say the volume is over 3 cubic feet, is that based on internal dimensions or external? It sounds like they are trapezoids which makes estimating volume more difficult.
Overbuilding boxes isn't a bad thing, but you can easily fall into a diminishing returns and at some point do more harm than good. You are trying to accomplish a few things with a box. One is simply to contain the backwave from the front wave of the driver, and as such, overly think boxes have a problem of transmitting sound out of the box. There is debate on how big a deal this is, and my read of the research and what I've been told is that its likely that the speaker transmits more sound out of the box via transmission through the panels than from transmission inside the box to out.
Another is to provide a loading or compression for the driver, which impacts its tuning. As such, the volume relative to speaker parameters become very important.
There is no such thing as making it so thick you don't need bracing. You simply can't make it thick and rigid enough to accomplish the same results as you would get with bracing. However, there is a lot of incorrect information out there on bracing. Bracing, in my opinion, should tie panels together at the mid points, not the edges. As such, I don't think a panel with a hole cut in it is a good brace. A windowpane is better, but I find you get equally good results with a simple stick of wood. Because you want something that is very strong and very stiff, I prefer a solid piece of hardwood for this. Earl Geddes turned me onto this and I think he was right on. You can get scraps of oak, poplar, etc. really easily, sometimes for free, and they really make among the best braces.
A simple way to understand the value of bracing is that you are trying to raise the resonant frequency of the panel to a point where its stiffness would now allow it to resonate, and its damping would essentially absorb it before it audibly degraded the sound. No box is 100% stiff with 100% damping. All boxes vibrate. If you add mass, like you are, all you are doing is lowering the resonance frequency of the box panels, making them a little stiffer, but likely adding little if any damping. As such you are really making things worse, not better. Now you have a huge mass to store that vibrational energy in at a frequency equal to that of the subwoofer's operating. Not what you want. You want the resonance frequency to fall outside of the operating range of the subwoofer, and breaking up the panels into stiffer smaller sections (i.e. adding bracing) does that.
As for overbuilding in terms of thick enclosures, lots of bracing, etc etc. This is what I can tell you from my own experience. First, I'm not a great woodworker. I used to have more tools than I do now, but I've never been very good at this stuff. I am a good scientist though. I've experimented with various construction techniques, measured using a WT3, accelerometer cabinet measurements, and Frequency measurements. I've almost never measured a variation in frequency. I rarely found a resonance I could detect in the impedance sweep (which implies its significant enough to be audible). I always can measure things with the accelerometer but never could correlate them with what I heard or measured in the frequency/time domain (i.e. a waterfall). In the latter, I literally took the raw data and attempted to correlate the data by normalizing the response of the output and then correlating its time domain data (variation from time 0) with that of the accelerometer. It was only slightly correlated once we are talking sub-100hz. I really think that what matters for subs is that the box is strong enough to handle the driver and of sufficient design to match the drivers parameters and meet your design goals. This means a double front baffle and minimal bracing is a good idea to keep it together, 4" thick baffles and side walls, tons of bracing, it just adds weight and wastes time and resources.
I suppose you could argue that a really beefy driver with very high output at very low frequencies in a light weight box could "walk" around the room, and that the mass helps keep it planted, but I've never experienced that. With some of the neo super subs and composites I'm sure its possible, but using MDF or plywood and any reasonable driver, I suspect it has enough mass to stay put.
My opinion is that these really crazy massive boxes just give people bragging rights, nothing of consequence to the sound. Most of the benefits of a vibration free box matter at much higher frequencies. For that, I use CLD, its far more efficient. Dr. Geddes is a big fan of CLD and I had a long conversation with him about CLD on subs, he seemed totally uninterested. I did some of my own experiments and found it didn't seem to matter. I assume that is why he was uninterested. Remember, you want the resonant frequency of the box to be outside the range of the sub, so that means low mass and high stiffness. What you have built is high mass and low stiffness. Which doesn't mean it sounds bad, I've done the same thing, and while folks around here schooled me on why it was bad, I didn't find the sub sounded bad. The primary reason seems to be that in my case I had high damping, so while it would resonate at too low a frequency, the time domain showed that it squashed the resonance very quickly. None the less, I wouldn't choose to build that way today.
Overbuilding boxes isn't a bad thing, but you can easily fall into a diminishing returns and at some point do more harm than good. You are trying to accomplish a few things with a box. One is simply to contain the backwave from the front wave of the driver, and as such, overly think boxes have a problem of transmitting sound out of the box. There is debate on how big a deal this is, and my read of the research and what I've been told is that its likely that the speaker transmits more sound out of the box via transmission through the panels than from transmission inside the box to out.
Another is to provide a loading or compression for the driver, which impacts its tuning. As such, the volume relative to speaker parameters become very important.
There is no such thing as making it so thick you don't need bracing. You simply can't make it thick and rigid enough to accomplish the same results as you would get with bracing. However, there is a lot of incorrect information out there on bracing. Bracing, in my opinion, should tie panels together at the mid points, not the edges. As such, I don't think a panel with a hole cut in it is a good brace. A windowpane is better, but I find you get equally good results with a simple stick of wood. Because you want something that is very strong and very stiff, I prefer a solid piece of hardwood for this. Earl Geddes turned me onto this and I think he was right on. You can get scraps of oak, poplar, etc. really easily, sometimes for free, and they really make among the best braces.
A simple way to understand the value of bracing is that you are trying to raise the resonant frequency of the panel to a point where its stiffness would now allow it to resonate, and its damping would essentially absorb it before it audibly degraded the sound. No box is 100% stiff with 100% damping. All boxes vibrate. If you add mass, like you are, all you are doing is lowering the resonance frequency of the box panels, making them a little stiffer, but likely adding little if any damping. As such you are really making things worse, not better. Now you have a huge mass to store that vibrational energy in at a frequency equal to that of the subwoofer's operating. Not what you want. You want the resonance frequency to fall outside of the operating range of the subwoofer, and breaking up the panels into stiffer smaller sections (i.e. adding bracing) does that.
As for overbuilding in terms of thick enclosures, lots of bracing, etc etc. This is what I can tell you from my own experience. First, I'm not a great woodworker. I used to have more tools than I do now, but I've never been very good at this stuff. I am a good scientist though. I've experimented with various construction techniques, measured using a WT3, accelerometer cabinet measurements, and Frequency measurements. I've almost never measured a variation in frequency. I rarely found a resonance I could detect in the impedance sweep (which implies its significant enough to be audible). I always can measure things with the accelerometer but never could correlate them with what I heard or measured in the frequency/time domain (i.e. a waterfall). In the latter, I literally took the raw data and attempted to correlate the data by normalizing the response of the output and then correlating its time domain data (variation from time 0) with that of the accelerometer. It was only slightly correlated once we are talking sub-100hz. I really think that what matters for subs is that the box is strong enough to handle the driver and of sufficient design to match the drivers parameters and meet your design goals. This means a double front baffle and minimal bracing is a good idea to keep it together, 4" thick baffles and side walls, tons of bracing, it just adds weight and wastes time and resources.
I suppose you could argue that a really beefy driver with very high output at very low frequencies in a light weight box could "walk" around the room, and that the mass helps keep it planted, but I've never experienced that. With some of the neo super subs and composites I'm sure its possible, but using MDF or plywood and any reasonable driver, I suspect it has enough mass to stay put.
My opinion is that these really crazy massive boxes just give people bragging rights, nothing of consequence to the sound. Most of the benefits of a vibration free box matter at much higher frequencies. For that, I use CLD, its far more efficient. Dr. Geddes is a big fan of CLD and I had a long conversation with him about CLD on subs, he seemed totally uninterested. I did some of my own experiments and found it didn't seem to matter. I assume that is why he was uninterested. Remember, you want the resonant frequency of the box to be outside the range of the sub, so that means low mass and high stiffness. What you have built is high mass and low stiffness. Which doesn't mean it sounds bad, I've done the same thing, and while folks around here schooled me on why it was bad, I didn't find the sub sounded bad. The primary reason seems to be that in my case I had high damping, so while it would resonate at too low a frequency, the time domain showed that it squashed the resonance very quickly. None the less, I wouldn't choose to build that way today.
Yea, I had to break out the old high school geometry book lol. It is the internal, 3.11. Kind of another reason the front baffle is 2 1/4", so I could gain a small amount of internal volume out of the 15" hole while still being able to flush mount the driver. Dayton Aud recomends 3.1 for the 15" ultimax so I'll have to make it a little taller to make up for the volume the bracing displaces. Trying to stick close to their specs, not really sure how much small increments of change in the volume will effect the F3, something I should reaserch more probably lol. Planning is the most important step in any project. Thank you all for the help getting this right.
How?
I think I know what you mean, but it's a little bit confusing. Would you mind rephrasing / clarifying this bit?
I think he has increased BOTH.
The OP stated that the extra MDF is glued and screwed to the original MDF. This is a rigid join, so is essentially the same as doubling the thickness of the MDF.
I believe thickness x 2 = stiffness x 8 (thickness cubed), so the stiffness of his walls should be substantially increased.
I've made some $0 acoustic tiles by laminating layers of cardboard together. In this project, the increased stiffness as thickness increases was very obvious.
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