Best practices for fastening speaker parts

[Salt]

Using first a Fostner driller for outer diameter of collar type RAMPA and afterwards inner diameter drill will flatten a hump by srewing in the Muffe

 

[DCDK]

There was an interesting discussion on a German HiFi Forum about virtual volume and damping:

Dämmmaterial für maximale virtuelle Volumenvergrößerung?

I wanted to try Isover TP-1 + Visaton Polyestervlies for sealing on my next build.

 

[Rick Sykora]

Well I found JB Weld Wood Restore in 16 oz bottle for $14. Have had good experience with their epoxies, so seems a decent value and only 2-4 hours to cure. Have to fix the wood before I make another attempt.

 

[Head_Unit]

I will immediately start the development of a refrigerated loudspeaker that uses snow as insulation!

@Rick Sykora could you do a test with snow inside the enclosure?

More seriously a big thanks for a very interesting thread. The shifts in port output due to some amount of "making the box appear bigger" stuffing effect? Or what do y'all think is up with that? C-Note is not physically big, could the internal linings be rerouting airflow internally and changing the apparent tuning? And the somewhat steeper cutoff at the lowest frequencies seen in post 57 and others, what's up with that?

Another parallel topic would be the usefulness of various stuffings on sealed boxes for purpose of increasing the apparent acoustic volume. (And also damping internal waves re-radiating back out the cone). If you or someone does a thread like that it would be really cool; the only such I know of is the chapter in Vance Dickason's Loudspeaker Cookbook which while great is long in the tooth by now (I haven't read the much more expensive 8th edition yet).

 

[Rick Sykora]

Well I found JB Weld Wood Restore in 16 oz bottle for $14. Have had good experience with their epoxies, so seems a decent value and only 2-4 hours to cure. Have to fix the wood before I make another attempt.

It worked! Once the Wood Restore dried, I drilled larger holes for the black speaker screws I use for drivers and they hold tight without stripping. For added measure, I have applied wood epoxy to the new holes as well.

Going to forgo nutserts for now as the require much larger holes than my driver screws.

 

[Head_Unit]

The sealed use case is simpler and not sure much could be done beyond what Dickason and others have. For sealed designs, I think the most interesting recent aspect is applying the Linkwitz transform. Not sure how bounded it is, but seems much easier than constantly changing out internal damping materials. That said, their application is not mutually exclusive either.

If you're implying I need to get off my butt and dig through my garage to find his book and re-read it...GUILTY!!!
I always thought the Linkwitz Transform was cute but imperfect, given that it's based on canceling simulation polynomial terms and that the polynomial (i.e. rolloff characteristics per the math of Benson/Thiele/Small) changes with drive level. Not sure how big a problem that is, heck room correction has the same "problem"...

 

[Rick Sykora]

Ok, new test speaker is ready for more testing.

Do not have any additional damping material to test but plan to test combinations and different quantities of the some of them. Plan to buy some of the Sonic Barrier Blue eventually but others may follow depending on requests. As with fiberglass, am open to testing special cases but nothing that needs to be attached or glued together. Felt strips were more trouble to remove than I thought as tacky glue did not stay tacky.

 

[Roland68]

I've tried all manner of thread-in and drive-in threaded inserts and they all have shortcomings when it comes to insertion in MDF. On the flat, they create a hump because the threads displace material, and it has to go somewhere. On the edge, they tend to split the material. To make it viable, I think one would need to have a tap that mimics the exterior threads of insert.
The method I show is best I've found at not creating more problems and I suspect stronger than you might guess. If I had a strain gauge, I could test to failure. What I'll do is rig up a weight bearing test as I've put an insert in both ends of the material

Yes, but is the back and would require gluing wood blocks in each corner though.

You need special thread inserts for MDF and wood that cut their own thread without splitting the MDF or wood. The thread on these thread inserts is interrupted and tapers.

Alternatively, for example with prototypes, you can insert sections of m3-m8 threaded rods on the front side. To do this, drill the hole about 0.5-1.0mm smaller and about 15-30mm deep. The threaded rods are then simply screwed in with a cordless screwdriver. It holds rock solid. For the other side you can use normal or sleeve nuts, which are also available as countersunk nuts. It couldn't be more stable and precise and not only does it look professional.

For gluing MDF and plywood I can recommend waterproof laminate and joint glue. It sticks better than most much more expensive wood glues, if you break a bond apart you tear pieces out of the materials. It also penetrates deeper.
Apply a thin layer of glue to the hole before inserting threaded inserts or threaded rods. It does not glue the threads to the MDF/wood, but rather clamps the threads more tightly than without the glue. It is then almost impossible to remove it without damaging it.

Epoxy resin does not work particularly well on MDF unless you are working with a vacuum.

 

[Rick Sykora]

You need special thread inserts for MDF and wood that cut their own thread without splitting the MDF or wood. The thread on these thread inserts is interrupted and tapers.

Alternatively, for example with prototypes, you can insert sections of m3-m8 threaded rods on the front side. To do this, drill the hole about 0.5-1.0mm smaller and about 15-30mm deep. The threaded rods are then simply screwed in with a cordless screwdriver. It holds rock solid. For the other side you can use normal or sleeve nuts, which are also available as countersunk nuts. It couldn't be more stable and precise and not only does it look professional.

For gluing MDF and plywood I can recommend waterproof laminate and joint glue. It sticks better than most much more expensive wood glues, if you break a bond apart you tear pieces out of the materials. It also penetrates deeper.
Apply a thin layer of glue to the hole before inserting threaded inserts or threaded rods. It does not glue the threads to the MDF/wood, but rather clamps the threads more tightly than without the glue. It is then almost impossible to remove it without damaging it.

Epoxy resin does not work particularly well on MDF unless you are working with a vacuum.

View attachment 394037View attachment 394038View attachment 394039

Thanks, am good for now. As long as I can get several cycles, am good with occasionally repairing the screw holes.

The nutserts I have would not leave much MDF to hold them so if I use, will likely add some small blocks. Will see how the next round of tests go.

 

[Roland68]

Thanks, am good for now. As long as I can get several cycles, am good with occasionally repairing the screw holes.

The nutserts I have would not leave much MDF to hold them so if I use, will likely add some small blocks. Will see how the next round of tests go.

You can also use this glue to stabilize the threads in the wood, it lasts much longer.
Various tapping nuts are suitable for attaching drivers, and this also works very well afterwards. If you use burnished (black) machine screws, M3 screws are also sufficient for the largest chassis.

 

[carbidetooth]

You need special thread inserts for MDF and wood that cut their own thread without splitting the MDF or wood. The thread on these thread inserts is interrupted and tapers.

Alternatively, for example with prototypes, you can insert sections of m3-m8 threaded rods on the front side. To do this, drill the hole about 0.5-1.0mm smaller and about 15-30mm deep. The threaded rods are then simply screwed in with a cordless screwdriver. It holds rock solid. For the other side you can use normal or sleeve nuts, which are also available as countersunk nuts. It couldn't be more stable and precise and not only does it look professional.

For gluing MDF and plywood I can recommend waterproof laminate and joint glue. It sticks better than most much more expensive wood glues, if you break a bond apart you tear pieces out of the materials. It also penetrates deeper.
Apply a thin layer of glue to the hole before inserting threaded inserts or threaded rods. It does not glue the threads to the MDF/wood, but rather clamps the threads more tightly than without the glue. It is then almost impossible to remove it without damaging it.

Epoxy resin does not work particularly well on MDF unless you are working with a vacuum.

View attachment 394037View attachment 394038View attachment 394039

With all due respect, I don't find that info to be accurate. I've tried those inserts with little success. Both flanged and not. They will indeed displace material and split edges. I doubt they would work with the limited thickness we're talking about here. Have you actually installed them on an edge? The rest just doesn't apply to this situation.

 

[carbidetooth]

You piqued my interest, Rick. This epoxy takes 24hrs to cure, so we'll see how it works out. #6 insert, 1/4" hole, 1/2 material.View attachment 393645View attachment 393646

I tested to the limit of what I could without some additional compact weight. Here's my test rig:



I won't bother with the lead up, but that's 25lbs of lead shot hanging on a single epoxy-in insert on two edges with a #6 x 7/16 " screw. I originally started using this method for installing drivers, but this suggests more uses.

 

[Roland68]

With all due respect, I don't find that info to be accurate. I've tried those inserts with little success. Both flanged and not. They will indeed displace material and split edges. I doubt they would work with the limited thickness we're talking about here. Have you actually installed them on an edge? The rest just doesn't apply to this situation.

Yes, it is used millions of times in carpentry and industry. Hobbyists make mistakes by drilling holes that are too small. Well-intentioned, but it doesn't work. Take a look around the area of fastening technology.
In order not to split wood in the front area, the threads must be self-tapping and conical. And you need a little practice, ideally with a cordless screwdriver. Mistakes are, as I said, drilling holes that are too small, but also screwing them in too slowly.
For fastening speaker chassis, drive-in nuts are a much better choice.
I have been using this technique from furniture construction for over 30 years, also in the front area of 16 and 19 mm MDF and plywood.

Using epoxy resin on MDF doesn't help much, nor does the load test with weight. The bond with the epoxy will suddenly separate from the metal when screwed tight and tilted in the slightest way.
You should also expose your body to as little amines as possible.

With assembly adhesives from industry or Bauhaus you will get a better and more durable bonding result.

The technology with threaded rods/threaded pins and sleeve nuts is much more durable and stable.

 

[carbidetooth]

Yes, it is used millions of times in carpentry and industry. Hobbyists make mistakes by drilling holes that are too small. Well-intentioned, but it doesn't work. Take a look around the area of fastening technology.
In order not to split wood in the front area, the threads must be self-tapping and conical. And you need a little practice, ideally with a cordless screwdriver. Mistakes are, as I said, drilling holes that are too small, but also screwing them in too slowly.
For fastening speaker chassis, drive-in nuts are a much better choice.
I have been using this technique from furniture construction for over 30 years, also in the front area of 16 and 19 mm MDF and plywood.

Using epoxy resin on MDF doesn't help much, nor does the load test with weight. The bond with the epoxy will suddenly separate from the metal when screwed tight and tilted in the slightest way.
You should also expose your body to as little amines as possible.

With assembly adhesives from industry or Bauhaus you will get a better and more durable bonding result.

The technology with threaded rods/threaded pins and sleeve nuts is much more durable and stable.

For clarity, this is the epoxy I'm using in this application. Various epoxy resin formulations are used in many industries here in the USA. Some of which I'm pretty familiar with.
https://www.systemthree.com/products/t-88-structural-epoxy-adhesive
As I understand shear and shear strength the rig I set up will put nearly 100% of applied weight in vertical shear between insert outer diameter and wall of drilled hole. Out of curiosity, I will rotate 90° and see what happens. If that survives, I'll use a torque wrench to help determine rotational shear force to failure. Stay tuned.

Rick, I apologize for zagging your thread, but while not directly relevant to your testing of cabinet damping, I think it might be useful to the community.

 

[Solveit]

Rick, I apologize for zagging your thread, but while not directly relevant to your testing of cabinet damping, I think it might be useful to the community.

Yes it's very useful for us who build speakers and I failed many times with speaker screws not gripping because of many unscrewing moments.
I use this now with some glue and it works pretty good even if it's a little to wide.

 

[Roland68]

Yes it's very useful for us who build speakers and I failed many times with speaker screws not gripping because of many unscrewing moments.
I use this now with some glue and it works pretty good even if it's a little to wide.

You can easily remove any annoying parts beforehand using a strong side cutter.

 

[Roland68]

For clarity, this is the epoxy I'm using in this application. Various epoxy resin formulations are used in many industries here in the USA. Some of which I'm pretty familiar with.
https://www.systemthree.com/products/t-88-structural-epoxy-adhesive
As I understand shear and shear strength the rig I set up will put nearly 100% of applied weight in vertical shear between insert outer diameter and wall of drilled hole. Out of curiosity, I will rotate 90° and see what happens. If that survives, I'll use a torque wrench to help determine rotational shear force to failure. Stay tuned.

Rick, I apologize for zagging your thread, but while not directly relevant to your testing of cabinet damping, I think it might be useful to the community.

Hey, this wasn't meant to be a competition, I just wanted to share some of my experience.
I work with a wide variety of industrial adhesives and resins, as well as with connection and joining technology. The materials used are everything from balsa wood to tungsten.
I learned how to work with epoxy resin at an aviation manufacturer, laminate, composite and making connections. But that was a long time ago.

What you are using is not a normal epoxy resin, but an adhesive that nevertheless achieves a high level of strength when it hardens and is very sensitive to shear forces, especially on thin bonding surfaces.
To avoid this, you would have to thicken the epoxy adhesive with cotton flakes, use larger holes, thread inserts with a rough surface, e.g. Rampa sleeves, press-in sleeves for plastic, or special ones for epoxy resin.

But as I said, with assembly adhesives from industry or from Bauhaus and press-in threads you can achieve an equivalent or better and more durable bonding result. It's also much quicker and easier, there's no risk of the MDF splitting and it can be used after just 30-60 minutes.

This is aimed at everyone here who works with epoxy resin or epoxy glue.
Please never use it in living spaces, especially not with children in the household, always ensure good ventilation, wear effective respiratory protection and gloves and avoid any skin contact.
I know what I'm talking about, if I had paid more attention to such things when I was younger, I might not have such severe restrictions today. These effects are often only noticed after many years or decades.

 

[Solveit]

You can easily remove any annoying parts beforehand using a strong side cutter.

Just what I have done.

 

[Rick Sykora]

Thanks for the fastener discussion!

I think it deserves its own thread, so will have these posts moved to a new thread. Please hold off any further posts until I get it established.

 

[Rick Sykora]

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