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Multi-Way Conventional loudspeakers with crossovers

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Old 11th September 2012, 09:16 PM   #11
tvrgeek is offline tvrgeek  United States
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Ker,
I think the age old answer to that one is " it depends". I use different materials for different size boxes. There is no right answer.

Mondog,
Some ideas there. Your last idea is quite appropriate for room size absorbers, but I don't think that scales to the inside of a 15L box. A bit of visualation is in order. Think about how the different frequencies will radiate from the back of a driver. Logically, the further the effective distance is before a reflective surface, the longer the path so the lower the frequency that is absorbed.

Sreten,
Kind of confused on the vented box. It is not as easy as stuff and measure like a sealed box. Just like sealed boxes, I have seen everything from bare walls to full blocks of foam, light stuffing and tight stuffing. Years ago, a gradient stuffing was all the rage.

So, lots to think about. If I am staying in the stuffing topic, I need to find a driver that the frame is not a bigger problem than the box. That probably means a "decent" driver so I don't have one on the shelf. It probably should be a reasonably wide band driver so I can see if there is a point where it no longer matters. ( an octave above the crossover would be a rule of thumb I bet. I should get the paid version of ARTA so I can save charts. Printing and holding to the light works fine, but not easy to post. Side note, I am finding ARTA so much easier to use that I have not bothered with Sound Easy at all.

I have a couple of woodworking ideas. The first is how to get MDF sealed so finishes don't sink into the seams. I have tried a lot of things; all fail, even though some took a year or so. I have not ventured into non-regular shapes yet. I have had skill issues with angle repeatability on the saw so I just bought a digital tilt gauge. I have an idea for box that is basically the intersection of two ellipses. Not sure how to make it, but the result would only have simple curves so it could be veinered. I already concluded a 3/4 radius edge is a lot better than a 1/2 inch. I don't know what a flat angle as is used frequently does. As so much as the fit of the tweeter in the baffle is measurable, I have a feeling it is not as good as expected.

Another subject on which I have only seen subjective testing is decoupling the drivers from the baffle. Never seen a method that I actually believe achieves this in the first place.

A trend here. I only have interest in things that apply to something that fits into my rooms. That translates into a box-ish shape of bookshelf size. I have no room for floor standers anywhere. Even my subs are all under two cubic foot.
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Old 12th September 2012, 11:30 AM   #12
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KEF used to do effective driver decoupling. their simple sytem for wmaller woofers used rubber grommets at the holes and soft foam tape arount the perimeter. There was a sleave inside the grommet that prevented over tightening. Acelerometer tests on the cabinet showed a big difference in cabinet vibration when issolation was used.

I think a practical stuffing test would be useful. Just drill a hole in the corner of an unstuffed cabinet and insert a probe microphone. You will see all the standing waves based on the cabinet dimensions. Trial absorption samples will have varying effects on reduction of the various resonances. The test can be done on a sealed box yet give good info for a vented box, i.e. what materials work well as a lining rather than as total stuffing.

David S.
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Old 12th September 2012, 01:59 PM   #13
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Quote:
Originally Posted by tvrgeek View Post
A trend here. I only have interest in things that apply to something that fits into my rooms. That translates into a box-ish shape of bookshelf size. I have no room for floor standers anywhere. Even my subs are all under two cubic foot.

Give some consideration to researching high'ish efficiency speakers with controlled directivity. There are many positive comments on the value of greater dynamics and improved low level musical details.

There are many Econowave designs based upon the low cost SEOS-12 waveguide and 10" or 12" midbass that could be sized to fit into your room and mate well with your stereo 100Hz woofers.

Plastic SEOS DIY Sound Group

You could also purchase a high'ish efficiency dome tweeter like the small SB29RDNC-4 rated 94db/watt and mate it to a high'ish efficiency 8" pro audio. Cabinet edge diffraction could also be part of your research: large radius edges; Avalon ISIS truncated pyramid; B&W 801 sphere+tapered_tube; etc...
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Old 12th September 2012, 08:49 PM   #14
tvrgeek is offline tvrgeek  United States
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Thinking out loud.
If I can go by The Edge, the largest refraction problem is the lowest one and it is greatly effected by the driver placement. With small cabinets and large, relative, woofers, there is not much room to play with that. Kind of forces you to do what you can with the crossover.

Subjectively, I noticed a big difference between the front baffle edges being radiused and all 12. That should not be hard to quantify.
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Old 16th September 2012, 02:53 PM   #15
tvrgeek is offline tvrgeek  United States
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After much contemplation, I am testing MDF sealing and finish materials and will be finishing the subs I built many years ago for higher WAF. They are just black plywood on the outside. I am going to build them into Chinese type chests to make them look like just part of the decor. They have all the sound I need, now to raise the WAF. NOt exciting.
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Old 16th September 2012, 03:40 PM   #16
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Default Re: sealing MDF edges.

I dont know if you've tried this, or if it has been suggested already, so bear with me. Try a 1:2 mix of PVA and any old emulsion paint. I have used this method to prime a number of times, and topcoating with regular spray cans. It takes a few coats and alot of sanding, but its miles better than car primer which i tried and became frustrated with. I have also used just regular spirit based varnish, thinned in the normal way. That finish looked rather good considering the lack of grain.
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Last edited by mondogenerator; 16th September 2012 at 03:44 PM.
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Old 17th September 2012, 12:44 AM   #17
tvrgeek is offline tvrgeek  United States
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PVA and latex paint. Never heard of that. I'll give it a try. Old style sanding sealer and auto lacquer primer look good to start, but after time, the seams sink in and show. I have tried fiberglass resin with mixed results. My first test is comparing auto spot putty with elmers wood filler in the seams. Spot putty seems better when fresh.

I like plain old auto lacquer primer, it is the base I am having so much trouble with. Most of my primer problems are my cheap gun. It is a HVLP that only works with HP. I should buy a old style gun. Not having a booth causes me much trouble.
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