using a mike at listening position to time align mid-bass and tweeter

[TimboinOz]

These are old but good 2-way spheres using a LP less 8 inch which rolls off by itself pretty cleanly from 3.3K, it has a damping R of wire and an RC network across it for Z-rise, the VC diam. is 38mm.

The big 35MM dome tweeter has an Fs trap, 3rd order high pass -3db @ 3.5K, and some mild Eq in the lower to mid-treble. The system is a critically damped QB3 alignment in a 23l encl. 91db/w sensitive, a flat 8 ohm load, and runs from about 35 to 13k. The drivers were made by the Fostex (Japan) back then known as Foster. Both are long-gap short-coil designs.

The stands are dished-top columns and the slope of the circular baffle can be adjusted easily.

My idea is to place a mike - where I'd be sitting halfway between my ears - and set the tweeter OOP with the mid-bass driver and feed discrete tones from 3k to 4k in and plot the results, OR use a warble tone centred @ 3.5k. Whichever baffle slope gives the deepest interference null OUGHT to be the right slope, I reckon. ?

Checked by restoring correct polarity to the tweeter, re-measuring, and by listening.

More Q'ns, is there such a thing as a clinometer to measure the slope? I can manage by using a finely adjusted vertical, and a spirit level, and a carpenter's angle jig I bought once and never used.

I've always just adjusted the slope and the toe-in, by ear. Further, absolute polarity is very easy to hear, even by non 'philes, on real-stereo recordings, or ones with a stereo-array basis.

Over the years I've wondered whether going to these lengths might be possible, and I can recall reading something along the lines I have mentioned, several times.

Another reason is that I might try stacking them with a 2nd pair I bought a while back, perhaps with a small ribbon tweeter set back in the middle of the two enclosures, and at my listening ear height. The additional height under the lower sphere would be used to add Vb and better bass extension. You might be able to visualise that I'll need to settle on the correct baffle slope before I start drilling or cutting holes into the bottom surface of the lower sphere. I'd also be using the inverse slope for the upper sphere.

How to hold it all together? An adjustable vertical stand, a friction lock ball joint, and a section of structural foam in between both spheres. Mass / gravity and friction should do the rest.

IF the procedure for 'collimating' tweeter and woofer is valid, I can do the same with the dome and ribbon, using just one sphere.

So, is it a valid procedure?

TIA


Timboinoz

[planet10]

Originally Posted by TimboinOz

Fostex (Japan) back then known as Foster.

Foster is still Foster. Fostex is a subsiduary aimed at a specific market niche.

dave

[jerome69]

Originally Posted by TimboinOz

So, is it a valid procedure?

I don't understand well but to see something your measurement must be anechoic, because multiple reflections include interferences in the signal and you will not see anything. You must do a gated measurement without any furniture on the signal path, including your rocking chair.

A photo of your loudspeaker can tell us more about this design. Drivers and a schema of the crossover ?
If you can do a physical alignment of the two drivers, it will be better and can simplify the crossover.
The polarities depends on the crossover which generate the acoustic slopes.