At very low frequencies, where all drivers are within 1/4 wavelength of each other, an array acts as a point source. At medium frequencies, each pair of drivers is within 1/4 wavelength, but the ends are further. The array becomes directional at this point. And at high frequencies, each driver is further than 1/4 wavelength, and complex comb filtering results in dense interference. Through each transistion, the frequency response and directivity will be affected and the system will act differently in each of these frequency ranges. A single driver just has collapsing DI and that's it.

Honestly, I think you, Jim and Earl are probably all on the same page here, but semantics and maybe lack of specifics cloud the discussion.

If an array is used above the frequency where driver spacing is greater than 1/4 wavelength, dense interference results. Jim Griffin would agree that sucks. So specificity is required in any discussion like this.

One thing is for sure, and that is a single driver measurement is not sufficient to develop a crossover for an array. Array geometry information is required.

Using Dr. Griffin's white paper, I've been careful to watch the side of the speakers, their closeness, and the appropriate crossover frequency. Its not all that hard, even for a fella who has taken any math since 1965. Additionally, I'm of the belief that the critical mid range area of 300-3000 should remain as un bombed out by cross-overs as possible. This also figures into my "calculations".

My array crossed over to a sub woofer electronically at 24 db slope at about 80 hz.

What I appreciate with Dr. Griffin, is that he takes the time from his busy university schedule to explain things to non-technical people so we can build better speakers.
I enjoy this discussion, but I often wish that people would not autmatically assume that everyone here is an audio engineer.

thanks,

eric j.

My mother in law claims that she has a right to say what the things she means. The reality is that she just says mean things.

Nobody has a right to be a troll and then claim that its just their way (I know you said that and Earl did not.) I'm getting tired of people who take their belief that its their rightful place: on email lists, on message boards, on the highways, etc. Last night at Borders book shop there was some lady who stepped in the front of a line of fifteen people who had patiently waited. Nobody even pointed the end of the line to her. They just "took it" from her.

No one has a right to be tactless to others, and excuse it by calling it "their style". On message boards, this is how flame wars start, and its how moderators can limit conversation to a select few of the elite, and exclude conversation from everyone else.

And don't tell me I don't know. I spend too much time moderating and encouraging a message board with more than a 1000 participants, in another field altogether. I've had to tell or remove posts from people who are quite famous and clearly giants in the field because they made tactless comments, that caused people to leave the message board because of them.

eric j

I mentioned three frequency ranges where arrays act differently. One is very low frequencies, where all drivers in the array are within 1/4 wavelength of each other. The next is where adjacent drivers are within 1/4 wavelength, but the array length is greater than 1/4 wavelength. And then the next is when each driver is further than 1/4 wavelength from each other.

There are also room interactions. The floor acts as a reflector, so your lowest driver acts like there is one below it, twice the distance to the floor. The whole array is mirrored that way. The array's directionality at high frequencies tends to mitigate this, but as frequency goes down, it becomes more apparent. And if the array is positioned too close to a side wall, that will reflect it too, acting like a horizontal array.

I'm not the moderator of the Array forum, but I do have the same concerns as you. I share your sentiments, 100%. That's really why I jumped in here. I was just hoping to help out a bit.

Thanks again,

eric j.

While I have a great amount of respect for Earl I think there's still quite a bit that's not fully understood about the performance of line arrays in a typical home listening environment. Most of the original theory was based on large venues and until Jim Griffin did his paper there was very little information for home audio applications. I've found what things work best after building several arrays and my advice would be to measure,listen,measure,listen...

Rick