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Viable method for raising cabinet resonance further than would otherwise be possible using only two very common items!

mike7877

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I really enjoyed the two pairs of branded speakers I have right now when I brought them home. The first pair for a while longer than the second, though they both ended up disappointing me eventually (and for the same reason!)

I won't waste too much time building up to what you obviously already know this thread is about from the title - cabinet resonance. Resonances in the upper bass and lower midrange in particular were Pair 1's problem.

Pair 1 would get excited with the right snare at medium to medium-high levels (upper bass/lower midrange range),
Pair 2 was "better" in that its problems didn't show up until higher frequencies. Not better because it took significantly less than the snare energy of Pair 1 to start muddying up vocals just 250-400Hz higher. The resonance was remarkably low Q (excitable from more than just 383Hz and 534Hz, 370 and 562 were almost as problematic, and all the frequencies in between, plus many surrounding, though they were slightly less so....

I thought to myself "what to do, what to do?!", sans quotes.

First I'll tell you what I didn't do - what I didn't do, was change cabinet volume - I didn't want to throw off the tuning of either pair, but especially Pair 1 was important to not muck with. They're 2.5 ways with midbass drivers in separate compartments, each compartment sized and tuned to create a larger, more sophisticated sound than one typically expects from compact floorstanders, even in their price range. They extend effortlessly to below 40Hz, and, if a room they're in interacts with their sound in unfortunate ways, they are uniquely adaptable - the chamber tuned lower is ported to the front to allow for good dispersion in tighter places (compact, remember?). And if you're getting punched too hard in the chest with every kick, all you have to do is shove your bung in a hole (or 2!). I think I've said enough to explain why I don't want to change the volume of Pair 1 now.

Pair 2 is kind of funny in that its structure is made of constrained-layer-damped boards specifically designed to damp resonances. Multi-layer construction with some layers made of rubber or something... I can't remember anymore. Anyway, it is remarkably effective... right up to the point it starts being remarkably ineffective. What a problem for a sealed design! They definitely aren't short on bass or extension... and I really enjoy its quality and control. But with Q just a bit below 1, I can't imagine I can take too much of the (already limited) space away from the woofer and keep everything I like the way I like it

The enclosures! Pair 1 and Pair 2...
Pair 1 made from (what I can tell) really dense, knot free hardwood boards 0.75" to 1.5" thick, randomized and glued in parallel.
Pair 2 made from that exotic stuff...

What I did was
1.) Got some long bolts and some really long nuts...
2.) Screwed one bolt (with lock-tight applied) into a long nut about 1"
3.) Screwed bolt 2 onto the other side of the long nut so that I had an adjustable-length metal rod.
4.) I screwed bolt 2 in enough to get the expandable metal rod inside the cabinet, placed the rod width wise in a good "lower cabinet resonance" spot, grabbed my two pairs of vice grips, and used one to hold the long nut in place, while I twisted the [free] bolt on the right, to expand my rod.
5.) When the rod was wide enough to reach each side of the cabinet, I made sure it was in the right place (there's a ratio or something stupid), and then
6.) I held the long nut in place with my vice grips to prevent it from moving, while I further expanded the rod by spinning the bolt on the right in the counter-clockwise direction. You really have to yank on it so that the compressive force placed on the rod by the enclosure is enough to keep the bolt from tightening itself over time from the vibrations of music.
7.) If you fail, your rod will shrink and fall down.
8.) Technically, you could use lock-tight on both bolts, but what if you want to remove it some day in the future without cutting up your hands again, but 4x worseq?

Note: You must understand torsion, and your muscles, and exactly where your hands are in that really cramped 7.75" wide box, because if you screw anything up, you're punching hard wood and sharp metal really hard, while awkwardly holding tools. It'll hurt!)


So that's what I did to my speakers. with 12mm bolts. It's been years since, and the resonances are still gone and nothing rattles around when I move my speakers. I haven't noticed any bulging, either.
This is with maybe MDF+rubber of 0.75 to 1.5" thick, and wood of 0.75" to 1.5" thick.
I usually keep my speakers between 30 and 40% humidity. For a couple weeks a year thing deteriorate to the point that they see 52-54% (relevant? Irrelevant? I'm sure if you live in 90% humidity and try this with 1/2" LDF junkers, they might just blow apart lol)


I recommend everyone do what I described above to their speakers if they have resonance problems and their speakers are made of thick, medium to medium high-quality boards.

Unless there are compelling reasons not to. I hope from this thread we'll find out if there are!


I haven't noticed any bulging!
 
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If you are looking for something to internally push against the 2 opposing speaker cabinet walls, maybe something like this is easier?

And here are a wide selection of threadlockers for all different types of applications, from high strength to removable/adjustable ones.
 
@mike7877 , do you have a picture that shows what you did?
 
If you are looking for something to internally push against the 2 opposing speaker cabinet walls, maybe something like this is easier?

And here are a wide selection of threadlockers for all different types of applications, from high strength to removable/adjustable ones.
"Log in to view Product Detail" :(

I'm not looking, it's done now and has been for a while. I made this thread more for people know that they can pretty easily fix their cabinet resonance problems for cheap with just a simple adjustable length rod (or two or three or four...) made of two 12mm x your required length bolts, and an oddly long nut. And a little bit of muscle (and maybe a bruise and a couple of hand cuts if you're not well trained to make swift, large, accurate adjustments using vice grips in each hand! (with the force required on one directly dependent on the other). Did I mention "in an enclosed space less than 9x9x9 inches with no visibility, with both hands entering through a hole with a 5.5 inch diameter at an inconvenient height for you"? Oh... Now I did!
Sounds convoluted, but this is what's needed to expand the rod against the inside of the box. You need to simultaneously hold the nut in place so the rod is perpendicular to the side walls, while loosening the free bolt to expand the rod and secure it. Once secured, each degree you turn that bolt in the counterclockwise direction to further expand the rod, it takes more force. This force, is always greater than the force it's generating to hold itself in position, and you have to counter ALL of it (nothing more, nothing less), and it must be done in the correct direction, or else your effort will not further expand the rod to increase pressure and push up cabinet resonance! Once the difference in force and direction between hands is great enough to dislodge the rod, ALL of the stored energy in both hands is released in the form of a couple of punches to the inside of the box (including the corners of those 0.75x0.75x2" blocks they glued in the vertical corners every 5 inches for added stability (for all hey helped... lmao)

That explanation was unnecessary, but an accurate depiction of what must be done. It's difficult for some people to visualize written descriptions... Hopefully that's not you because I can't draw!



Along with how to install the expanding rod, in the OP I report how my speakers, which I modified a few years ago now, have fared since their modification. Set up as they are, obviously a LOT of outward pressure has been placed at points on the inside of the outer walls of my speaker cabinets. Very happy to report (for my sake too lol) that there is still no visible sign of outward bowing.

Also noteworthy, is, as far as I can tell, everything is as tight as the tightest it's ever been (or pretty close), because the resonance is still way up where it can't be excited (in a disruptive way) with loud music of any genre.


If you've come across or thought of something easier to use as an expanding rod than what I suggested (two 12mm bolts and a massive nut all screwed together and expanded with vice grips), you're welcome to use it instead. I think it's better to use what's been tried though. If you really want to keep it in place, you can use lock-tight on both bolts. Just remember this doesn't make it so you can use any less force to expand the rod during installation. Regarding maximum force, if you're using 12mm bolts and strengthening 0.75 to 1.5" MDF or plywood, you're likely going to be limited by your own strength, especially considering the work needs to be done inside a speaker box, which will range from roughly 6"x6" internally, to 11" x 11". UNLESS...
Unless you're bracing a cabinet from the top down with multiple rods. 2 rods? Go a little easy. 3 rods? a little more easy. If you hear creaking (past the couple light ones at the beginning, which is your loose box being finessed into a structurally sound speaker cabinet.


If anyone is thinking of using dowels or a 1x2, cutting to size, and then jamming it in, I HIGHLY suggest you don't.
Yes, it might seem easy, but every time you jar the cabinet like that, you could be causing a new problem that needs to be fixed. To get a good fit, you're likely going to have to try many times which is more jarring. If the box is MDF (which it probably is), all these attempts will scratch away the surface particles, effectively widening the gap, but in an unpredictable way (ie. depending on where exactly the dowel ends up installed, it may no longer be long enough to exert the pressure you desire/require...)
If you use a dowel too thick and it's too long, you may split your box apart as you try to mash it into place.
If you use a dowel too thin, it will not be able to exert enough outward pressure, and its contact area with the MDF may be too small, slowly denting it over time, with pressure decreasing as it happens. Equilibrium will eventually be reached, the dowel still secure, but the box will sound like it's not there.


Keep expectations in line with reality: When you tighten your creaky loose box this way, yes, its resonance increases to a frequency which implies its weight increased from 30 to 55lbs, and its internal volume decreased from 34L to 20L. Since this isn't true, neither is this statement
"My box is so strong, it can take anything now!"
Your box is no stronger than it was before its operation. In fact, if it can survive a 6 foot drop without breaking right now, that means it could survive a 7.5 foot drop before.

Using sticky tack to secure your speakers to their stands, instead of those drawer stoppers, is a good idea.
Also some weight in the stands might help.
 
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@mike7877 , do you have a picture that shows what you did?

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Spin the free bolt to change length to fit, as well as increase outward force placed on left/right panels of enclosure. (left/right in description, can be any direction)!
 
I did something like this but by using threaded rod and two dowels which you can twist counter rotation. Two hands inside a 5" woofer hole. The all metal is probably better though taking up less space.
 
I did something like this but by using threaded rod and two dowels which you can twist counter rotation. Two hands inside a 5" woofer hole. The all metal is probably better though taking up less space.

Did you use your bare hands for tightening? What diameter dowel?
 
"Log in to view Product Detail" :(
Interesting, the McMaster-Carr web site never asked me to log in. Probably some geofencing that they employed.

What I was suggesting are turnbuckles. Turnbuckles have two threaded rods/fasteners at their ends, one with a left-hand thread and the other with a right-hand thread. If you restrain the rods/fasteners from rotating, either by friction or other means, turning the turnbuckle body will extend or retract the assembly. Left-hand to right-hand hex threaded adapters will also do the same job. You can find a good selection of left-hand and right-hand threaded fasteners at McMaster-Carr or your local industrial fastener suppliers to work with these adapters.

McMaster-Carr.png
94280A115_Left-Hand to Right-Hand Female Hex Thread AdapterX.png
 
Did you use your bare hands for tightening? What diameter dowel?
Bare hands and the dowel was quite thick 2nd hand stuff. Glued them after. Was a bit of a hackjob though.

Be sure to tap on the turnbuckles to see if they ring and need damping material.

Another option may be cld braces. Two pieces , the end glued on opposite sides, lay parallel on each other with damping / glue in between. Used this on an already quite solid cabinet. Did help somewhat I guess . Too much space taken is an issue though if retrofitting; need to use stiff but small volume material
IMG_20231024_070818.jpg
 
Bare hands and the dowel was quite thick 2nd hand stuff. Glued them after. Was a bit of a hackjob though.

Be sure to tap on the turnbuckles to see if they ring and need damping material.

Another option may be cld braces. Two pieces , the end glued on opposite sides, lay parallel on each other with damping / glue in between. Used this on an already quite solid cabinet. Did help somewhat I guess . Too much space taken is an issue though if retrofitting; need to use stiff but small volume material
View attachment 320795

Very nice, I like the adjustable dowel way too. I'd go with no smaller than 3/8", preferably 1/2" to 5/8"
I don't understand the thing you turn on the end though... does the dowel go into it and get threaded on its way in?

I don't quite get your picture - is that two bolts glued together lengthwise? I think that'd be fhard to get right... What about two slices of 1/2" plywood glued to a really thin strip of rubber, with one longer on one side, the other longer on the opposite side? It seems like gluing bolts together would be difficult, and if they touched through the glue anywhere...
 
Very nice, I like the adjustable dowel way too. I'd go with no smaller than 3/8", preferably 1/2" to 5/8"
I don't understand the thing you turn on the end though... does the dowel go into it and get threaded on its way in?

I don't quite get your picture - is that two bolts glued together lengthwise? I think that'd be fhard to get right... What about two slices of 1/2" plywood glued to a really thin strip of rubber, with one longer on one side, the other longer on the opposite side? It seems like gluing bolts together would be difficult, and if they touched through the glue anywhere...
It's not bolts; that was just to show the glued end. It's kind of an all at once job . Both pieces glued to opposing sidewall with damping in the middle at the same time. There may be better ways
 
It's not bolts; that was just to show the glued end. It's kind of an all at once job . Both pieces glued to opposing sidewall with damping in the middle at the same time. There may be better ways

I don't know how tension affects a constrained layer - I have a feeling that if there was enough, the stretching it could cause would change its behaviour, make it act like something similar but harder. Or like a thinner layer. I could be wrong, it's just a thought. I don't think damping on the cross tension rods matters too much, because usually one side of the box will resonate at a different frequency than the other. So even if one side resonates and that makes it through the rod, it's not going to come through loud on the other side. The rod should be pushing all resonances so high that they don't get excited anymore anyway.

I'm confused on one thing - how did you get it into the box? Did it go in during assembly, or?


I'm surprised manufacturers don't use tension bars/rods in their designs. They could use less materials and save so much on shipping
 
This is all very interesting. If a box is made from factory without enough internal bracing, this is a good solution.
My Sonus Faber Venere speakers have beautiful curved walls, but they are made by Kerfing three-quarter inch MDF with multiple half inch deep slots so that the MDF bends. When Danny Richie modified some of the lower model in the same line he filled the kerfs with a kind of plastic wood. I have thought that was a great idea for me to do too. But surprisingly on his tests and my own using REW the waterfall graphs are quite good for these boxes and they don’t show any major resonances. But the idea of only 1/4 inch of material essentially forming the skin and the essential total thickness of the cabinet irks me.
 
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