Cabinet resonance minimising

[michael]

I am beginning construction of my new towers very soon and want to know what i can do to minimise if not eliminate cabinet vibration and resonance.
My ideas so far are as follows:
-Using combinations of different materials, MDF, Ply/marine ply, Chipboard.
-Lining with fibreglass (not batting, but the kind you rollon with epoxy that they use on boats, planes etc)
-lots of bracing, plenty of weight.

Please let me know how good these things are at taming the cabinet, im mainly after info on using the fibre glass though.
Thanks in advance guys.

[claudio]

Hello,
to minimize tower cabinet resonances, a Double Chamber Reflex system is an option. If interested check my site for DCR explanation and measures, with comparison to the reflex system.

regards

Claudio

[kingdaddy]

Using unconventional shapes like Polygons or Spheres work very well, deep cabinets are good they allow the back wave to dissipate before reflecting back to the driver cone, an egg shape with the driver loaded in the large end would ideal. I always use some Tar roof patch on the inside as well; this adds mass and dampens vibration very effectively.

[sreten]

Of your 3 options IMO only the third will work well.
IMO the first two will not work well at all.

sreten.

[SCD]

How I built my towers
This is the process I went through when I designing my tower cabinets. I had all kinds of things that were critical to getting a great project. The solution I came up with is a bit complicated but I think it worked quite well. I had some a beautiful Douglas fir lumber I wanted to use yet I also wanted to have high density and a internally a non-reflective cabinet. I also wanted to have non-parallel surfaces on the inside to reduce the effect of standing wave resonance. As these are tower cabinets there was going to be large areas that would be hard to keep rigid. I wanted to incorporate a stone base to provide stability and mass. This is a lot of difficulties to take on in a first speaker project.
After consulting with planet10 Dave I came up with the following design. The design it self is a little complicated. The trick was figuring out the critical path for production. I will get Dave to post the construction photographs and I will try to describe the process and some of the pit-falls to watch out for.
I chose to have the front and rear baffles overlay the side panels as the lumber has some real nice natural stain pattern that I wanted to wrap around the top of box. I started with a pair of 1x12x120” planks of vertical grain Douglas fir this became the sides and top. Another pair of 1x12x100” planks became the front and rear baffles. I squared up and planed the lumber, then cut ¾” MDF to the same width and laminated the MDF to the Fir with Tightbond 2 glue (you need a lot of clamps to do this). To reduce the working weight I then cut one of the 45’ inside angles for top corner joint on each cabinet. I left the top attached to one side panel to be cut latter. I then routed ¾” bracing channels into the side and rear pieces. I then rabbit cut the front and rear baffles to allow the MDF to be inset into the cabinet side panels.
So to summarize the side and top panels of each cabinet are from a single length of laminated fir and MDF with routed channels for bracing. The front and rear panels are the same yet the MDF has been rabbit cut so the MDF is inset by ¾” I did not put a vertical brace on the front panel (could be done).

Next I made an angled sled for my thickness planer. I took a piece of ¾” MDF that the same width as the table of the planer and about 2 feet long finished it with varathane sanded to 300 grit and applied 4 coats of carnuba wax (to reduce friction). I put a 1”x3/4” runner lengthwise on the bottom side of the sled on one extreme edge. This created a ¾’ in 12” slope across the bed of the planer. I put stop feet on the bottom to keep the sled in place on the planer bed. I then ran the side/top and rear panels through the planer on the sled to remove the MDF side of the panels. I stopped planing when the MDF was ~ 1/8” on one side and not planed at all on the other side.
Next I completed the 45’ inside cut and removed the top from the side panels. I then glued and screwed the vertical bracing into the side and rear panels. Then I taped off the edges and painted on three coats of slightly thinned glue on the inside of all the pieces. ( I could have used epoxy resin but I did not want to open a new can for this small project. As the glue absorbs in it has a similar effect to stiffening and hardening the panel). Then I dry fit the entire cabinet to make sure I did not make any mistakes. Yeah! it fits together. Next drill out the holes for the binding posts and screw in cup hooks to hold a piece of grill clothe to act as a support for the dacron stuffing at the correct location. Then glue up the sides and be real careful to keep it square with grain wrapping around the top and sides. Drill and route out the front baffle to accept the driver. Flare the MDF to the inside and set the driver into the front baffle by 1/8”. Glue the front and rear baffles to the sides. Flip over the cabinets and glue in the port vent baffle. Route the edges flush and chamfer to reduce bulky appearance. Sand to 220 grit with a random orbital sander. Finish with three coats of Varathane natural oil sanding to 220 grit between coats, then three coats of Varathane Satin Urethane sanding to 320 between coats. Use a sprayer if you can, thin the first coat with ten % lacquer thinner to help finish penetrate and flow. Wire and install binding posts, put in grill cloth stuffing holder.
Next I had a couple of pieces of granite cut to the cabinet width and length plus a 1” shoulder all around and 1” thick. I drilled the bottom of the stone to accept a ¾” x 3/8” plug for a screw in leg. Then through drill 3/16” holes to allow anchoring screws to pull the cabinet and base together. Epoxy the plastic leg plug into the drilled holes. Finish the stone with three coats of Websheen (Xylene based concrete floor sealer, finish). Flip cabinets onto top put a bead of silicone on bottom of edge side panels and use 3” #8 screws to pull the base and cabinet together. Allow the silicone to ooze out and dry. Razor knife the excess silicone off after it dries. Flip the cabinets over and line driver inset with felt (real skinny piece, use silicone as the adhesive) Install the drivers.
One final coate of floor paste wax with Carnuba to finish.
Tah dah

Enjoy

The pathway I described worked for me. There may be other ways to do this but I know this one worked.
The stone base was a nice touch but is not really needed.

Moderator's note: this post and the associated pictures that followed have been split off into their own thread

http://www.diyaudio.com/forums/showt...777#post327777

[kingdaddy]

Originally posted by sreten
Of your 3 options IMO only the third will work well.
IMO the first two will not work well at all.

sreten.

Does this mean that you don't think a rigid cabinet will reduce vibrations? If not surly a sphere or multi-sided tapered design will be more rigid than a box, also channeling the back-wave away from the driver into a terminus should reduce overall cabinet flexing and vibration no?

[sreten]

Originally posted by kingdaddy


Does this mean that you don't think a rigid cabinet will reduce vibrations? If not surly a sphere or multi-sided tapered design will be more rigid than a box, also channeling the back-wave away from the driver into a terminus should reduce overall cabinet flexing and vibration no?

referring to these 3 options :

-Using combinations of different materials, MDF, Ply/marine ply, Chipboard.
-Lining with fibreglass (not batting, but the kind you rollon with epoxy that they use on boats, planes etc)
-lots of bracing, plenty of weight.

sreten.

[SCD]

This topic has been explored before. You need to focus on the source of the vibration in the first place? I think standing wave resonance is the prime culprit. Therefore. non parralel rigid sides should help eliminate a huge part of this issue. Rigid so they do not "absorb" and reradiate later. Bracing is also good to reduce vibration.

[michael]

Thanks everyone for your replies so far. But what would the fibre glass do as i have access to it, either chopstrand mat or woven rovings. im sure this would increase strength alot but im wandering about sonicaly. Also i was planning on doing a standard shape so all parrallel sides, i dont want to try curves for my first project and especially not to towers, could i use non paralel sides inside the box, so have lots of sloping pieces of wood to minimise these standing waves. My idea is to have like lots of door-stop shaped pieces of wood going up the sides inside the box, either all in the same way or alternating with the opposite side. tell me what ya think.

[planet10]

Originally posted by michael
either chopstrand mat or woven rovings. im sure this would increase strength alot

Fiberglass resin itself has an effect on the panel stiffness (you would ideally do it inside and out.Bonding fiberglass roving inside (and outside would be good too) makes a big difference. Jonathan Carr commented on how effective this can be.

dave