Quick & Dirty 4430-Inspired Two-Ways Part I

[Earl K]

Nobody's gonna bite on the time alignment thing, huh? I was surprised to see how shallow 2235H is once set up for comparison.

I'd suggest putting some of the known dimensions into a drawing .
- You do need to know the slope of that baffle .
- Relative locations of the component on the baffle
- Relative locations of each components' voice-coil ( approximate the mid point inside the gap )
- Need to know approx . convergence point of woofer & horn ( ie ; where you are likely to be sitting ,,,, sitting height and distance from boxes )

Just can't figure out where the "centers" are that are supposed to be aligned. If Mr. Widget measures them, we can get the answer, but I have to build up the final crossover first.

Yes :
- find the acoustic centers for a few commonly used crossover frequencies on a few of the available, "obtainable" components / such as / the 2235, the 2431 on xxxx horn-wavequide / 2426,2418 on xxxx horn waveguide . You get the idea .

[johnaec]

- Relative locations of each components' voice-coil ( approximate the mid point inside the gap )

Wouldn't you want the *radiators* lined up, not the voice-coils? Think of it hypothetically - what if the diaphragm dome was something like 2" behind the voice coil? That's where the sound waves actually eminate from, not the center of the voice coils. I admit - the sloped/curved format of the LF speaker cone make for a somewhat confusing situation...

John

[Zilch]

It's deceiving, because the sloped front baffle is recessed 4-5/8" behind the also sloping front edges.

Slope is -6.8817°

Internal volume is 4.9755 cu.ft.

Port is 4" dia. X 7.25" deep.

WinISD says I'm tuned to 25.7 Hz.

I must tell y'all, it was a pleasure taking the measurements with them playin' Shirley Horn so sweetly here....

[Earl K]

Hi John

Wouldn't you want the *radiators* lined up, not the voice-coils?

- Voice-coil alignments are a simplistic approach to the problem / I'll grant that .

- I believe it's quite a bit more complicated than just aligning all the sound producing membranes. The physical location that a person "assumes" should be point zero for the generation of a sound wave and where test equipment actually places that same "apparent" acoustic center / will just about always be two different locations in space .

- Only through the use of test equipment can a person expect to achieve reasonable alignment .

Think of it hypothetically - what if the diaphragm dome was something like 2" behind the voice coil?

Once in a while I do think about these electromechanical paradoxes / but then my head begins to hurt .

[spkrman57]

I usually refer to the voice coils as the "acoustic center". Not sure how accurate a statement that is but just my 2 cents worth!
Ron

[Ian Mackenzie]

The drivers have a phase shift in the pass band generally so this will also vary with frequency.

I prefer the square wave test.

Ian

[Zilch]

I can see now how the time alignment defines a horizontal plane in space where the distance from the "centers" (wherever they are) is the same, according also to the electrical phase relationship between the drivers.

Depending upon where I read, for 4430, that plane is tilted either 10 or 15 degrees upward from some point between the drivers.

If the drivers are aligned vertically, and perfectly in phase, that plane is perpendicular to the face of the baffle, i.e., on L200, it would be tilted 6.88° upward.

The closer the drivers are to each other, the less phase change occurs with vertical displacement from the plane of time alignment. If the "centers" are coincident, as in a perfect coaxial alignment, there is no change.

The absolute phase shift varies with wavelength, and is of most interest in the crossover region, where both drivers are playing the same frequencies. Outside of that region, it translates to group delay.

Well, that's my impression of it so far from reading here in the forum. The AES anthologies are on the way, and I'll hopefully be able to refine my own understanding.

Seems the answer is, "You gotta measure it."

Looking at the physical alignment of 2426H and 2235H in 4430's, there's a substantial element of BS involved in this, as well....

[johnaec]

I can see now how the time alignment defines a horizontal plane ... a substantial element of BS involved in this, as well....

Now MY head hurts!

John

[Zilch]

Now MY head hurts!

Come down here and listen to these puppies.


All will be well....