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Material for new frame

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Posted on October 31, 2021 at 17:02:06
SteveJewels
Audiophile

Posts: 244
Location: OH
Joined: August 11, 2018
 Now that the new midrange/tweeter plan is coalescing I am again thinking about upgrading the panels for the bass and midbase.

I have access to someone that can drive a router well and is willing to carve up something for me. Is MDF a worthy upgrade or are their better choices?

While I am messing with them I will have a go a Razoring too.

Thanks!

 

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RE: "Is MDF a worthy upgrade"? ..., posted on October 31, 2021 at 19:13:39
andyr
Manufacturer

Posts: 12550
Location: Melbourne
Joined: September 2, 2000
 Why do you think MDF is an "upgrade" - the stock Maggie frames are made from it?

Hardwood is the common material used in place of the MDF, by people wanting to upgrade their Maggies. Alternatively, if your friend can do it ... you might like to try carving up solid aluminium sheet. (AIUI, tools for wood can be used on aluminium.)

Andy

 

RE: "Is MDF a worthy upgrade"? ..., posted on October 31, 2021 at 19:38:01
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008



Real wood.....and don't forget that TECHNICALLY.....Balsa is also a hardwood, is a Natural Composit.

Various densitites in the wood have distributed resonant modes.

Some other materials may be better than the stock (cheap) MDF.

I'd look into PlyBoo.....Bamboo Plywood. Extremely dense in the Neopoltian. comes in 4' x 6; sheets and is kind of $$$

I've heard suggestions for Corian and Silstone. Both synthetics.

I'd AVOID both MDF which is available in several different densities AND excess bracing in the form of bridgework.

Clever design triumphs over brute force EVERY time.

Image shows a proposal for triangulated and ADJUSTIBLE bracing in a Phi ratio mounting.....This is not my final design but shows how my thoughts progressed....
Too much is never enough

 

RE: Material for new frame, posted on October 31, 2021 at 19:45:51
Joe Schmo
Audiophile

Posts: 518
Location: Palm Beach
Joined: April 21, 2008
 I'd second what Andy said. Most of us used hardwood to build DIY frames and were very pleased with the sonic results and aesthetics. MDF is a horrible material to work with in a typical DIY workshop when compared to hardwood too.
-Joe

They're not that big!

 

RE: Material for new frame, posted on October 31, 2021 at 20:00:59
hahax@verizon.net
Audiophile

Posts: 4309
Location: New Jersey
Joined: March 22, 2006
 Panzerholzwood from Germany. I think it's available in Canada. It's expensive but super strong and heavy and well damped.

 

RE: Material for new frame, posted on October 31, 2021 at 20:18:10
emailtim
Audiophile

Posts: 5483
Joined: July 2, 2017
 For narrow midrange/ribbon line array baffles, aluminum would provide the required rigidity while not requiring artificial baffle width growth.

Danny Richie used aluminum for his top of the line NEO3/NEO10 line arrays. I think he is currently experimenting with some composite materials.

MDF could be used for prototyping.
.

2022/03/30 Historical Records CENSORED

 

RE: Material for new frame, posted on October 31, 2021 at 22:43:02
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 man, I HATE Aluminum.......

Wood is a natural composite, so what IS he experimenting with?

Ingenious design would also provide the desired rigidity, without recourse to metals.......
Too much is never enough

 

RE: Material for new frame, posted on October 31, 2021 at 23:49:20
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 I'd see if I could get Iso no Ki which is a Japanese wood traditionally used in the making of Bokken.
This is basically a wooden Samuri Sword used for practice and realself defenese.

The woodis harder and finer grained than either the Red Oak or White Oak which is also used for this purpose.

I have zero idea how to source this here in the states, but would love a sample to have a look at.
Too much is never enough

 

RE: Material for new frame, posted on November 1, 2021 at 00:53:49
emailtim
Audiophile

Posts: 5483
Joined: July 2, 2017
 Here is the original NEO10/NEO3 in an CNC'd aluminum frame.



I don't know the name of the composite material he is testing now.

I think this set was made out of the composite material.






.

2022/03/30 Historical Records CENSORED

 

RE: Material for new frame, posted on November 1, 2021 at 03:44:30
SteveJewels
Audiophile

Posts: 244
Location: OH
Joined: August 11, 2018
 Thanks for all the great responses!

I had considered and dismissed aluminum. From my experience with plates on electrodynamic vibration tables (think 25,000 lbf) substituting aluminum for magnesium invariably results in problems with ringing. However, using 80/20 would result in a thin frame that is relatively light and still rigid with no concerns of changing shape due to humidity. If it has a ringing problem it may be possible to damp it with Dynamat.

My friends shop is pretty well equipped, table saw, planer, router etc. He makes butcher block for himself but I would not ask him to do that. He would be able to make frames from hardwood. I like oak so that is an attractive choice.

An 8' X 24" X 1.75" piece of butcher block like what would be used for a countertop would be enough to make frames for both sides. There is a countertop place nearby, perhaps they have seconds. They would have Corian too.

Is there any advantage to or disqualifying reason not to make two separate panels for the bass and mid bass panels? (T-IVa's)

I have trapezoid shaped panels for midrange (RD75's) and tweeters. It is solid wood of some sort and quite heavy. I am not using the midrange panels from the T-IVa's.

 

RE: Material for new frame, posted on November 1, 2021 at 08:39:28
emailtim
Audiophile

Posts: 5483
Joined: July 2, 2017
"... Is there any advantage to or disqualifying reason not to make two separate panels for the bass and mid bass panels? (T-IVa's) ..."

The shorter the wavelength of the drivers, the closer you want the center-to-center drivers located to minimize the off-axis variance issues over the XO region.

That being said, the bass drivers can distort the midrange if on the same baffle, thus the Tympani and 30.7 multi-baffle designs.
.

2022/03/30 Historical Records CENSORED

 

RE: Material for new frame, posted on November 1, 2021 at 17:01:19
SteveJewels
Audiophile

Posts: 244
Location: OH
Joined: August 11, 2018
 Dupe

 

RE: Material for new frame, posted on November 2, 2021 at 01:20:20
Roger Gustavsson
Audiophile

Posts: 2058
Location: Huskvarna
Joined: February 12, 2010
 Hollow aluminium profiles filled with blasting sand for damping is better than a solid material.

 

RE: Material for new frame, posted on November 2, 2021 at 01:43:11
SteveJewels
Audiophile

Posts: 244
Location: OH
Joined: August 11, 2018
 Thank you for the reply @emailtim but I'm not sure I follow you.

I am asking about the two bass panels that are joined together in T-IVa's.

I'm wondering if there is an advantage to keep them together or a reason not to separate them.

The mid and tweeter will be in their own box.

 

RE: Material for new frame, posted on November 2, 2021 at 12:40:17
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Wood has distributed modes, too......the 'rings' are of different densities / growths.......

I will FREELY admit to not wanting anything to do with aluminum. No fatigue strength, either.

What problem is a filled hollow aluminum structure meant to solve?
Too much is never enough

 

RE: Material for new frame, posted on November 2, 2021 at 12:45:58
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008



By trapazoid....do you mean something like THIS?

Showing general shape and the rear bracing (part of it) as seen from the front.....
Too much is never enough

 

What problem is a filled hollow aluminum structure meant to solve?, posted on November 2, 2021 at 13:51:31
Roger Gustavsson
Audiophile

Posts: 2058
Location: Huskvarna
Joined: February 12, 2010
 I recommend reading:

https://tinyurl.com/dc7n9rkw
https://tinyurl.com/h7yxx8uf
https://tinyurl.com/cputuabm
https://tinyurl.com/4jp9xkyw
https://tinyurl.com/uu6a4mdr
https://tinyurl.com/nyfhs3zk

 

RE: Material for new frame, posted on November 2, 2021 at 17:13:57
SteveJewels
Audiophile

Posts: 244
Location: OH
Joined: August 11, 2018
 @pictureguy Trapezoid like this.





 

RE: What problem is a filled hollow aluminum structure meant to solve?, posted on November 2, 2021 at 17:18:54
SteveJewels
Audiophile

Posts: 244
Location: OH
Joined: August 11, 2018
 Great links @Roger Gustavsson Thank you!

 

RE: What problem is a filled hollow aluminum structure meant to solve?, posted on November 2, 2021 at 19:18:03
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 RG....
I just read thru the first 4 of 6 URLs.....
I might be permitted a REPHRASE? What problems does this method solve which would not be or could not be addressed by other means?
I agree that rigidity is a good design goal. but I'm less than willing to admit in the 'Build a Bridge' solution. Laminates of differing properties offer opportunites for simple damping and proper choice OF those materials also can be very rigid in practice.

I am quite certain that these goals can be reached by means other than brute force...

Don't count real wood out, just yet. From a materials standpoint, it is very near a composite with differeing modes of resonance. This in effect Self Cancels. I have suggested a couple alternatives, one of which I woud love to test. PLYBOO, is a form of Bamboo Plywood. This is considered an Engineered Material and had both high density and high rigidity.
It is available in several 'orientations' of strand AND you can also now get it as Dimensional Lumber.
This is an excetional opportunity.....

I had sent off for samples some time ago and the Strand version called 'Neopolitan' is the densest by far of all the samples I acquired. Each sample was ABOUT 4" x 4" and 3/4" thick.

Too much is never enough

 

Tubing Test:, posted on November 2, 2021 at 21:42:24
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Many people like 'mass loading' of tubes.

I start with the idea that wall thickness to Prevent what's called a 'soda straw' break should be at some minimum. Maybe 1/50 the diameter? Something along those lines. So for a bicycle wher you need a certain amount of rigidity to, just as a goal, MIMIC a decent mild steel tubing you need a greater diameter of aluminum.....In this case a 6061 alloy is Very common. This drives wall thickness, up, too. The result? While Aluminum weighs about 1/3 LESS than steel, the net savings for an equivelent aluminum structure is MUCH less. I've seen this with aluminim wheels for big rigs and aluminum trailers, also for big rigs. You DO save some weight but not 1/3. And also? You must deal with fatigue limits, which should NOT BE the case with a frame for Panel Speakers where it is never stressed anywhere NEAR its tensile limits.

Instead, I'd like to propose a means to increase RIGIDITY of a tube And a way to TEST, using materials you can easily get at a hardware store.

You'll need some 2" diameter PVC, schedule 40. You'll need CAPS for the ends and an EYEBOLT to go thru the pipe from which you can hand a weight. A straight edge and a 6" scale calibrated in 64s or better. And finally? EXPANDING FOAM.

The first test? Simply cap off a 3 foot length of PVC and weigh it down with a 10lb weight. MIght take MORE but not likely LESS to produce a measurable deflection. Hang the weighty from the HOOK in the middle. Than REPEAT with cured (let it sit for a day or so) expanding foam. this will test just how much MORE rigid the tube is. Use the same weight and means of measurement of deflection.

It might be possible to repeat again but using some kind of 'fill' mixed in with the expanding foam. Maybe some kind of steel shot. DO NOT USE LEAD. It is toxic and whoever inherits the frames will have NO IDEA what is in 'em......This would require some experiment to get the 'mix' right but will add mass and rigidity to the extent everthing 'sticks'....

It is possible that the PVC may not stick properly to the expanding foam. Than it'll get odd. An ACETONE wash to remove the mold release will fix this, I think. I glue PVC without 'primer' by that method and have never had a joint failure.

If this is successful, the technique could be applied to any tube.....

If this works, and I'm fairly certain it WILL, the technique could be applied to other layered materials. Which could than be cut to shape for frames or even speaker stands.....

Too much is never enough

 

RE: Material for new frame, posted on November 2, 2021 at 22:33:39
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 The image I linked / drew in Sketchup is ALSO a trapezoid.....

I think the 'round' top is a nice designer touch....
Too much is never enough

 

RE: Tubing Test:, posted on November 3, 2021 at 02:36:31
SteveJewels
Audiophile

Posts: 244
Location: OH
Joined: August 11, 2018
 @pictureguy

You are proposing to use foam fill PVC for a frame? Interesting.

"the technique could be applied to other layered materials. Which could than be cut to shape for frames or even speaker stands....."

What other material(s)/form did you have in mind?

 

RE: Tubing Test:, posted on November 3, 2021 at 11:19:04
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 All I'm saying is that IF rigidiity is the MAIN goal, there are easier ways to get it than building a BRIDGE.
I'm still noodeling thru OTHER choices. And you'll need a fabrication technique. High mass LOWERS resonant frequency which than has higher frequency harmonics. If you have a light AND rigid frame, you may be able to raise any resonance too high to matter or out of band. Distributed resonant nodes is KEY.

Remember Dual Turntables? My 12XX had a 2-piece platter. EACH piece rang like a bell. But they were at frequencies which 'cogged' in such a way as to cancel one another out. The TOTAL platter was quite inert.

For example? When I needed something GLUED together to Stay? It was a small piece so after glue-up I parked my CAR on it. With 'flatteners so the pressure was applied evenly.
I love Epoxy! And it ain't EVER coming apart.

Tooling up and running tests is important. For example? IF you decide to use a tubular frame rail?
Build a jig and route out a groove for the panel. Make the panel a snug fit. Clamp the OPPOSITE stiles together with the rails between.....
I"m out on a limb here, but you SHOULD be able to clamp the panel in the frame without drilling HOLES in the panel itself.

I'm still biased in favor of real wood or even PLYBOO. Trouble with Bamboo is the very HIGH silica content which is murder on tooling. Commercial speaker fabrication is a game of INCHES. The higher costs of Bamboo and enclosure construction may be a deal breaker. So the default MDF is used with either real wood veneers or that plastic stuff I'd be embarrassed to use as shelf liner.



Too much is never enough

 

RE: Material for new frame, posted on November 3, 2021 at 15:04:50
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Panzerholzwood is an ENGINEERED product. Just like or similar TO, my favorite, PLYBOO.

The aluminum in the comparison is a 6000 series alloy with no reference to any post-hardening, like T6 which makes a piece roughly the equal of mild steel tubing......
Too much is never enough

 

RE: Material for new frame:: MDF, posted on November 3, 2021 at 15:15:13
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Don't forget there are several different GRADES of MDF.

Some will go over 50lb per cubic foot...while water is over 60lb per cubic foot.

The MDF I used for my desktop just BARELY floats so I'll claim the weight as nearly 60lb per cubic foot.

I know the 4x8 @1" sheet of this stuff was VERY heavy. A test piece floated level with water so had just slightly less density.....

It is also tough enough that you can NOT even dent the edge with a firm fingernail... It appears to have been made from sawdust NOT chips.....Extremely fine grained and dense. and HARD....
Too much is never enough

 

RE: Material for new frame, posted on November 4, 2021 at 09:17:48
owkone
Audiophile

Posts: 53
Joined: April 9, 2015
 In my opinion the general considerations for frame material should be non-resonant to audible frequencies and its harmonics. It should also be dimensionally stable at all room temps and normal humidities. The frame would be covered up by the sock thus looks should be least important. I think high density outdoor grade MDF meets the requirements very nicely.

 

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