Thinkin' Outside the Box

[slhijb]

I'm in the planning stages of a 3-way, two-box (TM upper & W Lower box) diy speaker project. A couple questions for the group.

1. Has anyone used 1/2" thick (comes in 4' X 8') sheets of Hardipanel in building speaker boxes? Hardipanel is fiber cement siding panels that can be cut the same as plywood. Their hardness, rigidity and density appear excellent, they are readily available and fairly inexpensive. I'm thinking of using them glued together (on the inside of the box) with 1/2" or 3/4" MDF as the outside layer. Good idea?

2. I read somewhere that isolating the mid-range from the tweeter (within same upper box) will reduce the effects of resonance & vibration from the M on the T. Is this a sound concept?

3. Finally, is supporting the mid-range and woofer magnets with internal bracing (resting of felt damping) to reduce vibration a good idea?

slhijb

[nunayafb]

1. hardipanel never used it. If it is hard it will a very high resonant freq and this is good. However, if it is not well damped like many hard surfaces, it will transmit vibrations easily to the other layers. In a roundabout way your are planning "constrained layer damping" and some reading on those words will guide you as to whether you use this material.

2. Based on the laws of physics, yes the M will vibrate the T. But you have to ask at what freq. will the motor structure of the tweeter transmit vibes, at what amplitude, and since the tweeter cone is mounted on a suspension which is damped how much will transmit to the cone and be reradiated out. I cant offer you much for an answer other than I would imagine all of these forces are trivial and not near any resonant f's and the resulting output is negligable.
Even better, you are building two speakers so if you can manage a removable rear baffle you can listen to them each way and prove it to yourself.

3. Im of the school of thought that you should minimize the driver to enclosure contact to minimize the transmission of vibes. This means no to your Q, and in addition what I do is mount the drivers on a fabric ring so that the frame does not touch the wood. Also, there are T-nuts out there that have the nut isolated from the t-nut frame via rubber insulators, Im trying to find those again. The end result is a floating driver with minimized vibration transmission to the enclosure.

[Nuuk]

Has anyone used 1/2" thick (comes in 4' X 8') sheets of Hardipanel in building speaker boxes?

It's called something different over here but it has been used for speaker building for some years. It is particularlry good for subs!

One commercial manufacturer uses it for their TL speakers, and having heard those speakers, I can confirm that the box adds an absolute minimum (if anything) to the sound!

[slhijb]

nunayafb, thanks so much for the response. It really helps. The Hardipanels look like they have great promise, but in the interest of keeping this project as simple as possible I may hold off on them for a future project.

I will take your advice on the M & T separation mounting and will do some software speaker modeling and actual sound checking to see if there is an audiable difference.

Also, am taking your advice on the possible vibration to the box resulting from bracing the woofer & M magnets with felt liner. It seemed to me that the possible result in increase vibration may offset any benefits from the added support.
Thanks again, this newbee really appreciates your taking the time to help.
Jim