Horn Question

[Mustang Marvin]

This question has probably been asked before, but I must have missed the answer.
When installing a horn on top of an enclosure, do you position the voice coils in alignment or as the Altec documentation states, align the cone and the horn opening?
Thanks.

[bfish]

For precision;

(Re)wire the HF driver backwards. (Leave the XO in place, everything but the HF wired normally).
Play a test tone the same frequency as the crossover point.
Measure (software/mic, RatShack dB meter, or ears if that's all ya got) a ~meter away (not critical exactly how far). Height halfway between the drivers vertically;
Have a helper slide the HF horn forwards and back, while you monitor the sound level for the lowest reading.
Leave the horn where the lowest reading was observed and rewire the HF back to normal.

(Why not just look for the highest output without the rewire? Because cancellation is more powerful than addition, and therefore more obvious).

Added
Then have your helper fetch a beverage while you cue some tunes.

[rontec]

Very helpful, thanks bfish. I'll try this with my 828 cabs with top mounted 808's
and 421's. And the beverage idea is good too!

[Mustang Marvin]

Actually the beverage comes first!
Maybe thats my problem...:laffingassoff:

[bfish]

Very helpful, thanks bfish. I'll try this with my 828 cabs with top mounted 808's
and 421's. And the beverage idea is good too!

You're welome. I should add that the higher the XO frequency, the smaller the sweet spot becomes.

[Mustang Marvin]

Using an "L" pad the balance in volume can be achieved. I was more concerned with the timing. I have heard different opinions regarding the positioning of the horn for timing reasons.

1, Align voice coil with diaphram.
2, Align horn flare opening with cone.

The Altec documentation I have suggests #2.
I have also heard #1 from a reliable sorce.
Opinions???

[whitebroncoii]

Mustang Marvin and Altec Best: Please re-read bfish's response. He describes an excellent method for aligning a two-way loudspeaker. The acoustic center (source of the sound) on a woofer is not the voice-coil or the edge of the frame, and the acoustic center of a HF horn/driver is not the voice-coil or the edge of the horn. bfish's method is described in old Altec literature for theater system set-up . . .

Another way to align a two-way loudspeaker is to measure the time difference using an analyzer. A passive system is then physically aligned (fore/aft position of the source). You can adjust the alignment in a by-amp system using digital delay. Delay the closer acoustic center to the distant acoustic center. These methods require special equipment (expensive), highlighting why bfish has described an excellent method for most of us to use.

An AES white paper that I assisted on offers this;
The closer the acoustic center is to aligned, the more phase damage, until they are perfectly aligned and in-phase. The converse is that the farther out of alignment the less damage occurs. Aligning the mouth of the horn with the front edge of the woofer can sound better than lining up the voice-coils!