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Have you concidered these kind of s-frames? I was planning to build a dipole bass stand for my speakers and wanted to make the "box" as narrow as possible so I designed these. These frames probably suffer from resonances above 150 Hz but for subwoofer they probably are ok.
 

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Charles,

If you mean a combination of both closed box and U-frame, I already tried that, with dissapointing results. My objective was to cancel out harmonic distortion by using a compound construction with a U-frame. Below noted pictures illustrate this.

11658.jpg


11659.jpg


The net result was worse than the U-frame or a simple closed box with both woofers operating out of phase. Actually Tony knows about these experiments already as we live close to one another and he's seen previous W-frame, U-frame etc. experiments of mine, as I have seen and heard his 21" uber-subs.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com

Ps. sorry Tony for hijacking your thread, does that mean you'll be keeping the UcD amplifier now :D
 
SSassen said:
Something tells me I've seen that amplifier before? See below url, spot the differences!


Thanks to Sander for lending me his amp!


But yes, I've noticed the same in the compound construction I've built recently, it is logical as both woofers move out of phase so there's no pressure build up inside the box. I however found it to sound 'boxy' nonetheless.

http://www.hardwareanalysis.com/content/image/11711/

Best regards,

Sander Sassen
http://www.hardwareanalysis.com

Both drivers are in phase and the cabinet has two seperate volumes, both drivers go inwards or outwards the same.
 
I should have been more specific:

There are two possibilities:

a) Combine dipole and closed box such that you get a cardioid radiation.

b) Use the dipole in a position where it works best. Put the closed one in a corner. Cross them over such that you get the best combined performance.

Regards

Charles
 
DIAR said:
Have you concidered these kind of s-frames? I was planning to build a dipole bass stand for my speakers and wanted to make the "box" as narrow as possible so I designed these. These frames probably suffer from resonances above 150 Hz but for subwoofer they propably are ok.

I guess this would work the same as a W-frame of a Ri-pole, except for that the cabinet is a different shape.
 
I have a couple more theories why the your particular ripole design contributes toward a more boxy sound. In general I have found that the boxy sound (from any speaker) arises from boxes which are not braced sufficiently. This is really true of horns. I have Hedlund Horns which sounded like a hammer beating a pillow without sufficient bracing. I see several contributing factors to why your boxes may fall into this category.

First, it seems that you are using some sort of MDF. While MDF is great for deadening and thus preventing resonances which otherwise arise from the material, it is not as stiff as other materials. To have a very sharp bass sound, W-dipoles would require very stiff surfaces. To accomplish this with MDF, your various panels would best be doubled in thickness. I built my W-baffle out of 3/4 inch 13 ply birch plywood. This is very stiff stuff. Addiitonally, the baffles on which the drivers are mounted are 1 1/2 inch thick.

My W-dipoles use 18 inch drivers which require smaller panels than your 21 inch drivers which would stress the panels more and allowing them to flex more. I recall that Linkwitz uses 1/2 inch birch with his W-dipoles using 12 inch drivers. I used 3/4 inch for my 18s. Perhaps you should use 1 inch or 1 1/2 inch material.

By cutting holes in your panels, it weakens the panels further from resisting the pressure sources of the drivers.

I did a knuckle rap test. All points of my boxes resonate at frequencies above the crossover point for my drivers which helps to convince me that I would not have cabinet flexure which is too great.

The ripole boxes subjects the panels to greater pressure and are likely to flex more by virtue of their narrower width.

Even considering the points I make here, my boxes still vibrate quite a bit when really pushed with loud bass passages, thus my boxes would benefit further from additional thickness for some panels. I don't think that I would gain too much, but doubling all the 3/4 inch panels in my W-dipoles would likely improve the bass slam a finite amount.

Retsel
 
Hi Retsel,

Thanks for the input. My enclosures are built from 22mm mdf (1"=25,4mm). I agree that the sturdyness of the boxes could be better. The various boxes are all experimental prototypes and all have the same general "fault" of being not thick enough. I am sure that the boxiness would have been less if I had made them thicker and added some extra bracing, but at least this way I can compare the relative characters.
 
phase_accurate said:



That would make it a cardioid like this one (i.e. case a):

http://www.wvier.de/texte/UniPol.pdf

Regards

Charles

Your wish is my command......... :D

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The best of both worlds. :cool:
 
nice sub ... wish it was mine but the woman in the house is saying no :bawling: but the drives looks very nice :cool:

but can i use one of the 12" or 15" with and diy ribbon, crossover around 1khz in a cabinet like the linkwitz orion or something... im not sure what i should go after because my speakers stand in corners
 
wuffer, you can put an open baffle dipole in a corner as seen in Linkwitz site, but its not so good for the midrange. I've seen a corner dipole woofer under a oris horn which seemed an appropriate combination. Or you could use a sealed monopole 12" for mids and above on top of a corner dipole. 3 way makes sense to me for this kind of setup, with a sub below 40 Hz if desired.
 
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