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Lbjefferies7 wrote:

Very good.  Raal 70-20XR...interesting.

Oh, yes, the 70-20XR is very interesting. I did not have this driver but Alex allowed me to experimented with some elements of it’s design in context on my “Water Drop” tweeter and it was quite remarkable. I end up do not use those “elements of it’s design” with “Water Drop” as my tweeter has different objectives but in context of the 2-way MiniMe the 70-20XR’s “elements of it’s design” shell show themselves vey very positively.

Lbjefferies7 wrote:

Where are you planning to cross these over?

You have no idea how loaded this question. The crossover point with the MiniMe is not a tactical question but actually the very strategic question of the entire speaker, let me to explain why. The woofers that I use are fairly bizarre – they are what made me to think about the MiniMe. They have diaphragms made with reinforced fabric, the outer suspension is rubber. However, the reinforced fabric is semi-soft in the similar elasticity as the outer suspension. So, it is not a piston motion (like in foolish ceramic drivers) but rather motions with a lot of break ups – the right motion in my books. But then is the kink of the driver- the dust cap. The dust cap is inverted dome of aluminum and it the way how it placed makes the dust cap as the literally keystone of the diaphragm resonance. It is sort of the resonance’s lighting rod – if you see the driver then you understand why I got enthusiastic about it. Now, the woofer goes up, let say to 4K-5K and the dust cap begin to ring. The similar effect to JBL LE8 that also has metal dust cap. Here is where I will be playing with my woofer – to tune by ears the dust cap’s resonances. You see, that dust cap ring in a very measured dosage is in fact very good (in context of these speakers) as it works like the “Oops-resonator”. I will damp the dust cap by painting the driver with volcanic ash (no speaker white cones in my home!!!). That will extend the safe operation of the driver for 500-1000Hz up but the primary tuning tool for me will be the crossover point. So, I will be searching for crossover point by just listening the Oopses with witch the woofer’s dust cap will resonate – where it will become too much Oops then I will cross right there… Well, here is the question: how the woofer’s dust cap will behave if I have 6-8 woofers per channel and the excursion of each woofer is substantially minimized? I have no answer now but I think I will found another 2K of response. Then we have the HF’s cancelation coming from the line-array configuration… It will eat the HF but will it each the dust cap Oops-resonances with the same appetite? I have no answer now… How the “not eaten” residues of the HF woofer resonances will be “subjectively friendly” to the distortions of the 70-20XR tweeter’s lower knee? I have no answer at this point. I need to found the woofers, to build the box to screw the array of the woofers and the tweeter in and start to run the crossover point up and down, to hear how it will work all together. I have no planning to cross at a specific point I will cross it wherever it will be, I anticipate that it will be somewhere between 2K and 6K, most likely a second order.

Lbjefferies7 wrote:

I remember the discussion about the internal balloon.  That is a very good idea and this may be the perfect opportunity to try it.  It will also be interesting opportunity to work on enclosure damping methods.  Being made of steel, they will probably make all kinds of noise without some help.  I have used frequency sweeps and a stethoscope to find the resonant modes in enclosures and strategically damped them out.  It worked out very well.  Today, I thought of something that may be worth trying.  With a steel enclosure, you might try glueing (silicone glue would be perfect) some hockey pucks over the most resonant areas.  It should work, they are easily removed if it doesn't, and best of all, hockey pucks cost 99¢ each.

Hm, in interesting idea – to offset the box resonances by targeted mass-damping – sort of rotationally balance a car’s wheel by adding mass on one side. I think it might work with light enclosures. I do not think it will work with heavy and stiff enclosure as I am planning to do. As you understand from my previous paragraph it will be a lot of active resonances radiated out of this speaker, so I presume that the enclosure resonances will be a least of my problem. I do not decided with steel finally. I know that I am not willing to do anything myself with enclosure. I will design it (after I know how many woofer I will be able to fish out), get a quote for my machinist and then see what other material are available. It will not be 1” of wood but a few mm of something very strong- steel, aluminum or architecture plastic (Perhaps the material-savvy Jessie could advise something). Anyhow I will try to keep the dimension of the baffle as little as possible….

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