Hi Chester
If the only access you have is through the speaker cutout, this limits your options quite a bit.
One possibility is to glue some stiffening pieces across the panel. In some tests I did recently I used a piece of MDF 25mm thick and around 50mm wide and about 300mm long. The size that you will need will depend on the size of the enclosure. The stiffeners are mounted so that the 25mm dimension is in contact with the speaker wall. If you have enough access you could use a piece of allthread rod between stiffening pieces on opposite walls and tighten these up so that the rods is pushing the walls of the enclosure out. Steel is quite stiff, so a rod of say 10mm will provide much stiffening as a 25mm wood dowel.
If the volume of the enclosure is already fairly small and it is ported, then adding bracing may affect the tuning of the speaker. If this is the case, it may be better to use steel stiffeners, as they will provide much more stiffening for their volume.
If the walls are quite thin, then damping may be an easier option. There are various stick-on panels available (usually for car panel noise reduction) that you can use.
Mick
If the only access you have is through the speaker cutout, this limits your options quite a bit.
One possibility is to glue some stiffening pieces across the panel. In some tests I did recently I used a piece of MDF 25mm thick and around 50mm wide and about 300mm long. The size that you will need will depend on the size of the enclosure. The stiffeners are mounted so that the 25mm dimension is in contact with the speaker wall. If you have enough access you could use a piece of allthread rod between stiffening pieces on opposite walls and tighten these up so that the rods is pushing the walls of the enclosure out. Steel is quite stiff, so a rod of say 10mm will provide much stiffening as a 25mm wood dowel.
If the volume of the enclosure is already fairly small and it is ported, then adding bracing may affect the tuning of the speaker. If this is the case, it may be better to use steel stiffeners, as they will provide much more stiffening for their volume.
If the walls are quite thin, then damping may be an easier option. There are various stick-on panels available (usually for car panel noise reduction) that you can use.
Mick
Assuming the speaker cutoff is close to either the top or the bottom of the baffle, you should not have too much trouble adding braces.
It has been shown that while just about any bracing helps to stiffen a box, the best way to brace is along the vertical dimension. That is, a box that is two feet high by a foot wide by a foot deep should be braced with two foot long braces running top to bottom on the inside. One foot long horizontal braces are not nearly as effective. This has been studied in an article in the Journal of The Audio Engineering Society.
I have not tried MDF as a bracing material-which is not to say that it is not effective-but I noticed that many speaker builders like to use hard wood if it is convenient. I have toyed with the idea of getting angle iron cut for this purpose, but I have not done this, nor have I heard of anyone who has.
While angle iron would seem to increase the possbility of ringing, I would think that tendency would be suppressed when it is tightly glued to the side of an MDF box. Something about two things of different densities suppressing each other's resonances, or something. I would like to hear from any DIY'er who has tried it, or knows of anyone who has. The advantage would be an extremely stiff brace while taking up almost no interior space.
Anyway, it is just a theory on my part, so I cannot recommend it. So the only thing I can recommend it-whatever material you use, brace the long dimension, not the short.
If your box is small, like .75 cu ft, and built with 3/4" , (18mm) MDF, you might not need bracing. Smaller boxes are intrinsically rigid by their nature. You can even get by without bracing in larger boxes than that, though I would recommend bracing in a box 1 cu foot or above.
It has been shown that while just about any bracing helps to stiffen a box, the best way to brace is along the vertical dimension. That is, a box that is two feet high by a foot wide by a foot deep should be braced with two foot long braces running top to bottom on the inside. One foot long horizontal braces are not nearly as effective. This has been studied in an article in the Journal of The Audio Engineering Society.
I have not tried MDF as a bracing material-which is not to say that it is not effective-but I noticed that many speaker builders like to use hard wood if it is convenient. I have toyed with the idea of getting angle iron cut for this purpose, but I have not done this, nor have I heard of anyone who has.
While angle iron would seem to increase the possbility of ringing, I would think that tendency would be suppressed when it is tightly glued to the side of an MDF box. Something about two things of different densities suppressing each other's resonances, or something. I would like to hear from any DIY'er who has tried it, or knows of anyone who has. The advantage would be an extremely stiff brace while taking up almost no interior space.
Anyway, it is just a theory on my part, so I cannot recommend it. So the only thing I can recommend it-whatever material you use, brace the long dimension, not the short.
If your box is small, like .75 cu ft, and built with 3/4" , (18mm) MDF, you might not need bracing. Smaller boxes are intrinsically rigid by their nature. You can even get by without bracing in larger boxes than that, though I would recommend bracing in a box 1 cu foot or above.
damping might be easier and might do the job too.
hm. I think dampfing and stiffening the enclosure follow two different goals, doesn't it?
Damping helps against standing waves. They appear corresponding to the meassurements of the box.
Stiffening is good to supress resonances of the box's (is that the right genetiv contruction?) material or to move it into a harmless frequency range.
actually how does one know/tell when to add more bracing/damping to an enclosure..
standing waves will show a peak in your frequency response and in the impedance plot, too. You cann see it in the waterfall, either. For Example a height of 0,85m will have a peak around 400Hz.
The other thing it quite more difficult. Meassuring the cabinets oszillations needs a very expensive equipment. There is a thread about this here. Look some days back.
However, knocking against your enclosure is a quite simple and good test. It shouldn't sound like a bell
It should be acoustically dead.
Place your bracing in an asymmetrical way!
hm. I think dampfing and stiffening the enclosure follow two different goals, doesn't it?
Damping helps against standing waves. They appear corresponding to the meassurements of the box.
Stiffening is good to supress resonances of the box's (is that the right genetiv contruction?) material or to move it into a harmless frequency range.
actually how does one know/tell when to add more bracing/damping to an enclosure..
standing waves will show a peak in your frequency response and in the impedance plot, too. You cann see it in the waterfall, either. For Example a height of 0,85m will have a peak around 400Hz.
The other thing it quite more difficult. Meassuring the cabinets oszillations needs a very expensive equipment. There is a thread about this here. Look some days back.
However, knocking against your enclosure is a quite simple and good test. It shouldn't sound like a bell
It should be acoustically dead.Place your bracing in an asymmetrical way!
As long as the volume is taken to account and your arms are strong enough to carry the boxes
Too much bracing, maybe?
I think I may have a box with too much bracing. I built a pair of woofer boxes that are something like 18" x 24" x 36" internally.
At the time I was infatuated with the B&W matrix enclosure design, so that's what I attempted in my boxes. I put a matrix of internal walls, so that the internal cabinet was composed of many compartments. I spent hours cuting holes in the internal walls, and glueing and screwing the whole thing together. The result! I put the braces in the wrong places. So when I slid it across the floor of my garage, my 9 cubic foot, 1" thick walled enclosure started to ring like a bell at something like 400 Hz??
Unfortunately I was planing to cross over the woofer at 300 Hz, so this design was a disaster for that. I ended up using it as a pretty good sub woofer crossed over at 70Hz. Speaker building can be very humbling.
I think I may have a box with too much bracing. I built a pair of woofer boxes that are something like 18" x 24" x 36" internally.
At the time I was infatuated with the B&W matrix enclosure design, so that's what I attempted in my boxes. I put a matrix of internal walls, so that the internal cabinet was composed of many compartments. I spent hours cuting holes in the internal walls, and glueing and screwing the whole thing together. The result! I put the braces in the wrong places. So when I slid it across the floor of my garage, my 9 cubic foot, 1" thick walled enclosure started to ring like a bell at something like 400 Hz??
Unfortunately I was planing to cross over the woofer at 300 Hz, so this design was a disaster for that. I ended up using it as a pretty good sub woofer crossed over at 70Hz. Speaker building can be very humbling.
Okay, don't wanna start a new thread, so I am continuing an old one....
I am in the process of designing/building my speaker boxes...
the internal dimensions are 1150mm High.... 200 wide and 280 deep... I think... thats 64.4 litres, right? lol
anyway...
I am using an 8inch peerless 850136 woofer per box, and I was wondering how much bracing I need and where? Angle the bracing, right? and have it so it is fastened to all 4 sides.. (front, back and sides) or, should I do some fancy thingy? lol
just 2 braces...
or fancy thingy?? lol
I am in the process of designing/building my speaker boxes...
the internal dimensions are 1150mm High.... 200 wide and 280 deep... I think... thats 64.4 litres, right? lol
anyway...
I am using an 8inch peerless 850136 woofer per box, and I was wondering how much bracing I need and where? Angle the bracing, right? and have it so it is fastened to all 4 sides.. (front, back and sides) or, should I do some fancy thingy? lol
just 2 braces...
or fancy thingy?? lol
http://www.geocities.com/adrian_mack/homepage.html
check out this guys 18 with its bracing.
notice the larger the box ,more bracing needed.
you cant have too much,and you want it uneven distances
how high will you operate your box?
check out this guys 18 with its bracing.
notice the larger the box ,more bracing needed.
you cant have too much,and you want it uneven distances
how high will you operate your box?
Skinny,
64L seems quite big for that woofer. What Q are you aiming for? Ported? ( tuning?)
I remember reading the following guidelines (one of Ray Alden's books?):
- if you have a rectangular panel, then better to run your brace longways and not widthways
- angle bracing? - I don't think that would provide as much rigidity as a perpendicular brace (eg. as each side flexes out, the perpendicular brace is providing maximum stiffness). However, an angle brace can help make different panels of different sizes therefore you don't 2 or more panels combining and resonating at the same frequency
- as you would using golden ratio type numbers for the box dimensions, so to the internal bracing spacing (such that you divide panels into golden ratio quantities)
as for the number of braces - not sure (that's really what you are probably after - not my mumbo jumbo. Maybe there is a "brace calculator" out on the net somewhere? (eg. brace position to "tune" a panel to a desired resonance frequency).
If you go overboard with braces - do take them into account with box volume (they do make a slight difference - about 8% when I made my sub box)
Reality?:
- with 1 x 6.5" woofer per box (< 5mm xmax?) - you aren't going to create huge pressure (further reduced if ported)
- 25mm is a good wall thickness to go for. Based on an MDF spec sheet I have, and my crude analogy - it will flex 35% less than 18mm MDF
- you will probably get better bass definition by having a heavy box that doesn't wobble
Dave.
64L seems quite big for that woofer. What Q are you aiming for? Ported? ( tuning?)
I remember reading the following guidelines (one of Ray Alden's books?):
- if you have a rectangular panel, then better to run your brace longways and not widthways
- angle bracing? - I don't think that would provide as much rigidity as a perpendicular brace (eg. as each side flexes out, the perpendicular brace is providing maximum stiffness). However, an angle brace can help make different panels of different sizes therefore you don't 2 or more panels combining and resonating at the same frequency
- as you would using golden ratio type numbers for the box dimensions, so to the internal bracing spacing (such that you divide panels into golden ratio quantities)
as for the number of braces - not sure (that's really what you are probably after - not my mumbo jumbo
. Maybe there is a "brace calculator" out on the net somewhere? (eg. brace position to "tune" a panel to a desired resonance frequency).If you go overboard with braces - do take them into account with box volume (they do make a slight difference - about 8% when I made my sub box)
Reality?:
- with 1 x 6.5" woofer per box (< 5mm xmax?) - you aren't going to create huge pressure (further reduced if ported)
- 25mm is a good wall thickness to go for. Based on an MDF spec sheet I have, and my crude analogy
- it will flex 35% less than 18mm MDF- you will probably get better bass definition by having a heavy box that doesn't wobble
Dave.
When I was trying to figure out if I wanted to add bracing to my last project I did the following sort of fun experiment. I don't recall where I learned about it.
I drove the woofer installed in the cabinet with my function generator feeding an amplifier. I layed the speaker on it's side on some carpet and sprinkled some table salt across the side facing up. With the tone playing at a moderate level, I changed the frequency of the generator. When a fundamental frequency of the cabinet structure is reached, the salt dances on the side of the box and shows the "mode shape" of the box that is being excited.
This was helpful in finding the first (lowest) resonant frequency of the structure. The test can be repeated after braces are added to see where the lowest mode as moved up to.
Unfortunately this method requires that the box be completed first.
I drove the woofer installed in the cabinet with my function generator feeding an amplifier. I layed the speaker on it's side on some carpet and sprinkled some table salt across the side facing up. With the tone playing at a moderate level, I changed the frequency of the generator. When a fundamental frequency of the cabinet structure is reached, the salt dances on the side of the box and shows the "mode shape" of the box that is being excited.
This was helpful in finding the first (lowest) resonant frequency of the structure. The test can be repeated after braces are added to see where the lowest mode as moved up to.
Unfortunately this method requires that the box be completed first.
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