Questions

[nikki1]

1- Concerning the placement of the horn in relation to the woofer. It occurs to me that high freq waves travel faster than low freq. In a radical example if one were 1/2 mile away theoretically you'd hear the horn before the woof and the sound would be "out of synch". In a home envioronment the distance between speakers and ears is so short that this becomes almost unnoticeable I assume. But for those who pursue perfection, like me, I assume there's an ideal compromise to have the waves hitting one's ear at the same time. Course there's still the diff between very high and very low in the music which will occur no matter how they're mounted. Does that make sense and is it worth pursuing? Is that why the HF drivers are sometimes connected in reverse to compensate? Perhaps the solution is to simply experiment with the placement of the horn until it sounds just sweet. Maybe I'm full of it here. Not being a true audiophile I'm treading in unfamiliar territory and some of you have forgotten more than I'll ever know. What about an electronic device which could be put in line with the HF driver to vary the time delay? One could then just adjust it for best sound. If such an animal exists.

2- Damping the interior of the woof enclosure. What's the purpose of doing this? The theory. It's nice to know something has to be put in there but why? There is all sorts of stuff one could use including, I imagine, stuffing the space with toilet paper or kleenex but there has to be one material which has been shown to do the best job. So what is it? I'm not going to spend all this time and money building these things only to put anything less than the best in there.

3- Grille cloth. Assuming it's 100% acoustically transparent then I would imagine the choice boils down to appearance alone. True?

Thanks in advance for cluing in an old man who's tired of chasing after windmills.

[gearfreak]

It occurs to me that high freq waves travel faster than low freq.

I don't think that's the case, unless there's some minute/esoteric physics angle that is being considered.

Frequency is higher for higher pitches of course, but the speed of sound is the speed of sound afaik.

The speed does vary with the medium it is passing through though. Light diffraction through a prism, or the apparent 'bending' of a skimmer pole stuck in a pool being common examples of this at work in wave theory.

*addition: another example would be the speed of light. It is or is considered and used as a 'constant'. Longer wavelengths (e.g. red) don't travel slower than smaller (e.g. blue).

Is that why the HF drivers are sometimes connected in reverse to compensate?

More often, it is either:
-the apparent reversal (as in the case of compression drivers) when the +/- or '1' and '2' in altec cases doesn't match the operators expectation...
-reversal because the crossover (e.g. 2nd order butterworth - or any 2nd order filter?) puts the signal 180? out of phase.

[GM]

Frequency is higher for higher pitches of course, but the speed of sound is the speed of sound afaik.

The speed does vary with the medium it is passing through though.

Yup, temperature, humidity changes it, especially over distance, causing an increasing HF roll off with increasing distance which needs to be accounted for in large outdoor venues.

GM

[gearfreak]

2- Damping the interior of the woof enclosure. What's the purpose of doing this?

To change the medium which the sound travels though, thus changing the speed of the sound waves.

This changes the apparent size of the box, as seen by the wave.

This is exploited for the purpose of making the box seem larger (oft beneficial) and to change (reduce) the presence of standing waves, and/or reflections back through the woofer cone.

You may wish to search for posts by GM on Eigenmodes.

[whitebroncoii]

Your #1 question;
Driver Alignment Comments:
Many years ago a friend of mine published a paper about alignment of a multi-horn cluster. His conclusions were that the closer to alignment, the more destructive the common frequencies can become, until perfect alignment. The farther out of alignment (up to a point), less damage. I assisted him with a few experiments and one of them was using an A7 variant called A700-8A.

We used a digital speaker processor to align (you asked about electronically aligning the HF and LF, digital speaker processors have been doing this for years), then misalign the A700. Misalignment was not clearly audible until almost 10ms out of alignment. Did I mention my friend has really good ears? Anyway, in an A-B test of aligned vs significantly misaligned I can detect a slight "smearing" around crossover. This would be difficult to hear without the A-B.

I think the bigger issue is the possible damage to frequency response. I always suggest connecting, even physically moving the HF and selecting the polarity for best response through crossover.

Up/Down - Left/Right Comments:
Your ear can, and will, identify the location of the HF (tweeter) or LF (woofer) source. A professional system installed in an arena can separate the HF and LF by quite a distance and the listener will not notice because they are 30 - 60 - 100 feet away. The closer you are to the speaker, the easier for you to hear a position difference. This is the primary reason for coaxial speakers. I suggest placing the HF and Mid or LF as close together as possible for near-field listening. Although sub frequencies are not as easily located by the listener, I always suggest the sub be in the front of the room and centrally located.

[nikki1]

Thank you all for the answers. I am now a wee bit more informed about this business.

[GM]

3- Grille cloth. Assuming it's 100% acoustically transparent then I would imagine the choice boils down to appearance alone. True?

True, but since there's no such thing, not true. Most manufacturers and advanced DIYers use it to fine tune a speaker, usually to 'hide' excessive sibilance and/or too 'sharp' a tweeter. IOW, to allow as cheap as practical components.

Many years ago, I auditioned a pair of $80 k, so called SOTA, speakers and all I saw was maybe $60 total/pair (in quantity) worth of 'plain Jane' drivers, though the cabs probably cost $5-6 k custom ordered since they were beyond the scope of most DIYers, but it was the passive XOs where all the real $$, engineering was. Sheesh! They had enough components to make a main frame computer, it took so many to make those drivers sound HIFI.

GM