There are a great many instructional articles on loudspeaker design and speaker building from do it yourself manuals for audio hobbyists to the nuts and bolts of dome tweeter and woofer design for professional engineers. Speaker crossovers, capacitors, inductors, wiring and cabinet construction all figure in clean sheet speaker projects but the comments below look beyond the nuts and bolts of speaker building.
Loudspeaker design strategy has to do with how the speaker is going to be used. What kind of room will they be placed in and where in the room will they be installed? Who and how many people will be listening to them? Where will these people be sitting?
Different loudspeaker designs have different dispersion patterns and these work for specific rooms and listening positions. A D’Apolito speaker configuration is meant for the seated listener and won’t do for people who like to stand up and move around a great deal. Ditto short Ribbons.
Dome based systems will bounce a great deal of sound off the ceiling while linesources and panel speakers won’t. Is that an issue in your installation?
Taking the long view, recognize that room correction and digital crossovers are practical and affordable now. Some receives and pre-amp processors even have both capabilities built in. You may want to keep passive crossovers external or allow for their easy removal from the cabinet.
Digital signal manipulation will not cure everything but it can help immensely in specific areas of phase and amplitude. Design your loudspeakers and the room setup to allow these devices to fully apply their strengths. Keep your designs simple and go with drivers with broad and smooth frequency response. See that the radiation pattern is similar for all drivers. And don’t try to squeeze the last bit of output from the bottom end by porting the speakers. Ported speakers have resonances that will always be heard no matter how skillful their implementation or how sophisticated the digital correction.
Digital correction cannot compensate for poor drivers, disparate radiation patterns and hopeless placement.
If your room has a particular acoustic “character”, make sure your chosen design doesn’t exacerbate it. Are you willing to acoustically treat the room for a more even response?
Lastly, design in lots of dynamic headroom. As higher resolution recordings are now the norm (SACD, DVD audio, True Digital etc. and high res downloads) dynamic range has increased dramatically. Also, good, cost effective amplifiers are becoming more common. Design your speakers and your system to take advantage of these factors.
Obviously Newform feels that tall, wide dispersion Ribbons and LineSource midbasses offer the best design approach for most home music systems but tall loudspeakers aren't practical or affordable for every application.
Whatever your audio project, it is best to stand back and apply some strategic planning before buying components and cutting wood. Design your speakers for your room, your audience and to take advantage of cheap and acoustically transparent digital signal processing.
Good speaker building!