How does one place the woofer and tweeter on the front baffle. Is there any calculation to it or can an arbitrary placement be made.
Also, I plan to place the port at the rear. Does it make any difference if I place it at the top or the bottom?
The tweeter should be more or less at ear height when you sit on a couch.
Personally I like a tweeter off-center. Not exactly in the middle.
The woofer is usually just placed in the centre. Usually one has little other options. In my opinion you should make your baffle..the front.. as small as possible and smoothe the right angles, so that the sound waves are not reflected by the box so that they effect is that it acts as a point source.
Yes, I've seen plots for different enclosures. If it could be placed in a ball shape that would be ideal..so to speak. I suppose the b&W NAUTILUS way and similar constructions often seen where the tweeter is on top of the speaker etc, etc.would be even better ofcourse. (These types of enclosures look like they have been designed in a wind tunnel)
Then placing it in a square where the the distance to all side are equal would be a worst case scenario. This hardly happens ofcourse because most speaker are taller than they are wide. So the secret is not having the distance to all sides being equal. I can't remember what kind of plot it was unfortunately)
I'll have a look if i can find the document and post it here.
Another thing would be do have the tweeter and woofer as close as possible. One therefore often sees a piece cut into the tweeter so that the source is as coincedent as possible. Obviously all these point are rules of thumb but no guarantee. Sometimes I suppose doing things very differently might be better.
One very reasonable way is to use the ubiquitous golden ratio. If the distance from the center of the tweeter to the opposite sides of the cabinet (assuming rectangular face) are in the golden ratio
(8:5 :: outside:inside is a good approx.), then the baffle step response for both sides gets spaced out rather well. Rod Eliot (http://www.sound.au.com) has a discussion of the baffle step response on his web page, and the Ariel/ME2 speakers (www.aloha-audio.com) use the golden-ratio rule.
Another thing to think about is time-alignment. The sound emanates from the center of the driver. For a woofer, this is considerably behind the baffle, but for a tweeter, it is much closer, or sometimes ahead. Correcting for this is more important than it sounds -- a tweeter is basically responsible for harmonics and a midrange/woofer is basically responsible for fundamentals (also harmonics for bass, but that is an orthogonal issue). When the sound hits you, you don't want the harmonics to come before the fundamental. For both physical and psychoacoustic reasons, this is a bad thing.
There are a few strategies for this. A common one for TMs is to just tilt the front baffle. Sometimes you'll see these sorts of speakers in a pyramid shape; this also helps cancel internal resonances. The angle cuts you need to make it are harder than a rectangular cabinet, though.
If you have an MTM (or an MMMTMMM, in my case) you have no other option than to sink the tweeter behind the baffle. In this case, you often have a tradeoff between woofer-tweeter distance and the sinking depth. As long as the woofer-tweeter distance is within a wavelength of the crossover frequency, it'll be adequate. I think the best strategy is to try to achieve time alignment, but not at the cost of placing the woofer/tweeter further than this.
Having built a number of systems in the past, I can verify, not from just personal experience, but from that of others, that you should keep the tweeter as close as physically possible to the woofer. Up till my last project (an IPL Transmission Line kit for a friend), following common practice, all my designs had the tweeter located in the centre of the baffle until my friend requested that I alter the IPL recommended design of central tweeter (in this case below the 8" woofer) to the sides; in other words "handed" L to R. I never thought it would make much difference... But how wrong I was! The stereo picture, soundstage on this speaker is simply amazing... And all (I am sure) due to the simple expedient of placing or offsetting the tweeters to the inside edge of the enclosure baffle... Of course if you can radius the baffle edges to lessen difraction effects is obviously also of benefit.