[matevana]

It occurred to me that often H & U Frames are constructed as a foundation to an OB system (both structurally and musically) and matched to a suitable top baffle with either full range or multi-way drivers. The top baffle can sit on top of the carrier for simplicity, be partially isolated with the use of a damping mount, or fully isolated by employing a bridge.

In any case I wanted to investigate the use of an existing product that might greatly simplify construction. I also wanted it to have a finished appearance and not require a full shop of power tools to build.

This project makes use of the eco-friendly "Way Basics" series of furniture cubes as a starting point (Amazon, Target, etc.) They are made of compressed recycled paper and are fairly dense, light weight, and hopefully non resonant. They have a decorative outer layer in a variety of finishes and sizes. To build a suitable H or U Frame, one should only need to add cleats to support the baffle, and the baffle itself. The particular photos below are part of my test project with these materials. This is the smallest of the three cubes available in a natural (cedar) finish. This project will use two 10" woofers for the bass section with each cube supporting a single driver. It should be noted that the smallest cube will house most 8" and 10" drivers; the largest cube will accommodate most 12" drivers.

Since the cubes are prefab, they go together in about 10 minutes using locator pegs and pre attached 3M adhesive strips. I used clear adhesive caulk and wood screws to mount the cleats and baffles. They are surprisingly stable and acoustically dead when complete. (knock test). They are also finished on all sides, which works well with a visually exposed H frame configuration. 

Here's some pics so far to illustrate the concept. As soon as the drivers come in (Usher 10" model 1001B) I will cut the baffles and show the finished product and begin testing the acceptability of the materials. The thought of not having to veneer a project is pretty cool. 

[JohnR]

Neat idea 

[matevana]

In sourcing suitable baffle material for the project, I came across this Rubbermaid finished MDF shelving available in big box stores. It happens to come in an exact 11.75" width which is just what is needed for the small Way Basics cube. This would mean only 1 cut for the baffle height. The finish also compliments the cube. It is about 5/8" thick so two baffles could be doubled-up if need be.

[matevana]

Baffle test fit. Will be glued and screwed to cleats once the drivers arrive.

Front:




Rear:

[matevana]

Drivers mounted. I'm happy with the look of the H-Bombs having invested only about an hour of my time per enclosure. They occupy less than one cubic foot, small enough for any bedroom or perhaps even living room. Now for some driver break-in and eventually critical listening. I will pair these with the top half of the Hestia-SL's for evaluation. 

[ArthurDent]

Slick idea, nice execution. Let us know how they sound.   

[matevana]

Initial Testing:

Conventional wisdom states that cabinet material should be dense, heavy and well braced. All materials have one or more frequencies where they enter resonance and start vibrating. The higher the mass of the material, the higher the SPL is needed to excite vibration.

The baffle itself is made of MDF with a decorative foil finish. MDF is desirable as a baffle material since it is dense and resistant to warping. But an entire H-Frame made of MDF will have a common resonance point (or points) and vibration will be easily transferred (and magnified) from the baffle to the frame.

My prior attempt at reducing this transference of energy included a mock-up frame made of carpet underlayment with a conventional MDF baffle suspended in the center. While the sound-deadening underlayment was far from an ideal frame material, it definitely did help confine the mechanical energy to the baffle itself. I then discovered that keeping the baffle small, perhaps just slightly larger than the drivers diameter, helped reduce vibrational distortion to non measurable levels at reasonable SPL's, for most program material.

The Mini H-Bomb concept makes use of compressed paper as a frame material, with a conventional MDF baffle suspended by pliable latex adhesive. Additionally the baffle size has been kept as small as possible, to make it more difficult to excite the panel at any given frequency.

In the first three days of testing with various low frequency sweeps the results have been very positive. The compressed paper frame seems to result in shorter decay times for vibrational energy. Whether this is a factor of two materials with different resonant points, the paper's ability to dampen vibration coming off the baffle, or the pliable coupling between the two, I do not know. It seems reasonable to me that it may be a combination of factors. So much so that I constructed an all MDF version of the same dimensions to compare.

The advantages of the compressed paper frame appear to be: a natural damping property similar to the previously tested foam underlayment but with superior properties for frame fabrication; dense yet light weight (the frame and baffle combined weigh 12 lbs); available to the DIY community in the form of prefab "cubes". So far the only negative properties I have observed are in the somewhat soft nature of the frame material.  The decorative foil finish is prone to "dents" when pressure is applied.   

[MarvinTheMartian]

Another option worth checking out .......
EXPEDIT Shelving unit, birch effect $19.99

http://www.ikea.com/us/en/catalog/products/30265126

Shawn

[kc8apf]

The EXPEDIT is made out of particle board.  Even with those extra thick panel, it won't have much strength.

[MarvinTheMartian]

Probably stiffer than ...
http://www.waybasics.com/zboard

Shawn

[kc8apf]

That's cute.  Basically extra-thick corrugated cardboard.  Should be similar in strength to compressed paper boards.  I would skip their "super-strong" adhesive-only construction technique though.

[matevana]

Yes. Similar to my tests with carpet padding, the Way Basics zboard product was being tested for its properties as a frame. Unlike conventional boxes which are subject to high internal pressures, I am suggesting that H and U frames can benefit from softer materials with a higher absorption coefficient, and where the resonance point is different from that of the baffle itself.

[MarvinTheMartian]

You maybe on to something "dampening".
I did the knuckle test on an Ikea LACK top and it sings!!
Even though the Ikea paper honeycomb sandwich structure may be stiffer / stronger it has no dampening factor whatsoever.
In either case most of the H rigidity would be from the central "-" driver MDF plate.
It would be interesting to attach an accelerometer to the center of a front edge to measure the natural panel resonance in both cases.
 
Shawn

[matevana]

An accelerometer is an interesting idea I didn't think of Shawn. I may have access to one at work. I had planned on taking near field distortion measuremens with the same driver in both the hard and soft frames. Cabinet vibration should easily be picked up as a distortion artifact at the system resonance. I can tell plainly just by listening that the zboard has fewer and less objectionable points than particle board, at least in this application.

[MarvinTheMartian]

The thick Ikea panels are not solid particle board, otherwise they would be way too heavy to $hip.
These 1-2" thick panels are constructed from a paper honeycomb core sandwiched between two framed 1/8" hardboard panels.

http://en.wikipedia.org/wiki/File:CompositeSandwich.png

If either style frame panel resonance is within the low pass frequency range, it's bad news.
Ikea  rigid undamped would ring like crazy. ( fixable with damping ie. floor tiles ? )
Zboard more flexible but damped would soak up energy (and we all know how much excess bass OB has).

On the bright side both options are under 20 bucks : )  Shawn
 

[matevana]

That's good feedback. It would be great if someone would be willing to test the Ikea cube. They look substantial and are larger than the Way Basics products, so theoretically could house even larger diameter drivers. Depending on the wall thickness (I'm guessing 1.5") they should accommodate up to a 12" driver. The largest Way Basics cube will also house a 12" woofer, but will cost more.

My power amps are housed in a glass faced cabinet, made from the same IKEA series (Besta Vara); it is surprisingly well made for the cost.

Ed

[mix4fix]

Those are nice. I wish I could have a pair.

Question: I assumed the 3M tape was to help it stay together. Why is there tape on the exposed back?

[matevana]

Good observation! The Cube comes with 3M tape pre-attached to several of the sides for easy assembly. It normally gets a cardboard backer that keeps the cube from racking when it's being used for it's intended purpose (a storage cube). Since the backer isn't used here, it's just a matter of peeling off the tape on the back when you're done. I originally left it on because I was contemplating using bullnose on one side of the cube, but eventually decided against it. 

BTW, in our case the baffle itself prevents the cube from racking and shores-up the entire system nicely. As you guessed, I ended up using the tape as a "clamp" to hold the cube together while the sealant cured.

[jonnoshore]

They do the Ikea ones in Europe too which is nice £12 for a bass cube is not too bad to trial OB bass... inner measurements are ~34cm if I estimate correctly...

http://www.ikea.com/gb/en/catalog/products/30265126/?query=302.651.26

Not sure the other cubes are available in Europe and are a little small for my 12" drivers Emmience Beta's

[matevana]

Let us know if you try the IKEA cubes. Now that the drivers are mostly broken-in, I can report that the Way Basics cubes do a fairly good job of dampening vibrations below 120Hz as compared to the comparable MDF frame. The Usher drivers continue to impress for use in OB. This is the third time I have worked with them (models 8955, 8137A and 1001B) and motor noise is simply not an issue. This is NOT true for many of the "better" drivers out there, even those specifically designed for sub woofer duties. Motor noise emanating from the back of an open-back cabinet can be horrible, no mater how low the drivers distortion characteristics are reported to be.