Dan
Welcome to the rewarding world of DIY speaker building. I’ll try to answer each of your questions.
dan_wilkinson said:
1. Do the drivers nominal impedances need (or benifit) to be matched? [im talking specifically about a woofer and tweeter for a two-way system]
Impedances of drivers should be matched, but there are ways to compensate in the crossover for impedance mismatch.
dan_wilkinson said:
2. How do you calculate total system RMS powerhandling? ...and what kind of ratio between tweeter and woofer powerhandling is optimal?
The power handling values given for individual drivers usually are an estimate of the thermal capacity of the voice coil – magnet assembly. It says what power would cause the driver to fail, rather than suggesting a useful power range for general use. Because of their lighter construction, most, if not all, tweeters handle much less power than woofers do, especially at lower frequencies. One major purpose of crossovers is to filter out these low frequencies to protect the tweeter. Tweeters are also usually more efficient than woofers, and the crossover usually add resistors (called L pad circuits) to reduce the tweeter output to a similar level of the woofer. To get back to your question, there are a number of ways to deal with this in the crossover design rather than limit yourself to certain combinations of drivers.
dan_wilkinson said:
3. and if anyone could tell me what this little doc is trying to say about this speakers frequency response? [it claims 35-5000Hz freq response but this graph seems to contradict that]
As you have guessed, you should pay more attention to the woofer frequency response graphs than to a maximum range, such as 35-5000 Hz. To properly deal with this question I would have to write many paragraphs.
Your questions are reasonable, but they lead me to guess that you are new to DIY speaker building. If you are, I recomend that for your first try you build something designed by one of the many people who have a lot of experience at design and trouble shooting DIY speakers.
I don't know what your background is, but when I first got into this subject, I found these web sites worth reading. Some of their designs are quite popular among builders and have been tweaked and improved over the years. You will find more than a few 2-way designs.
http://www.speakerbuilder.net/web_files/default.htm
Articles at this site are well written and understandable by newcomers without oversimplification. See the article titled Finding the Optimum Crossover Frequency to properly answer your 3rd question.
http://murphyblaster.com/content.php?f=main.html
Dennis Murphy is one of the better known amateur designers. He is friendly and accessible through the Madisound discussion board:
http://www.madisound.com/cgi-bin/discuss.cgi
http://members.aol.com/_ht_a/pjay99site/speakerhome.html
http://www.lonesaguaro.com/speakers/
http://www.partsexpress.com/projectshowcase/homeaudio.html
Hope this helps.
