How on earth do you choose which drivers to use when you have little to no technical information on the units you have available?
This is a tough one because everybody has their own taste and may require their speakers to do different things. Some may be looking for volume, others may want accuracy or maybe you'd rather an easy listening setup you can enjoy for hours. There are also other factors to consider, like budget, time frame and the physical size. Also there is a question of wood-working/electronics skills and available tools.
So lets assume you are somebody who has a fair collection of drivers and you want to build a musical system with good bass at low volumes and you don't want to spend your life savings on it. Lets say you have basic wood working skills and you have a ruff idea about speaker cross overs.
I'm of the opinion that a very good two way speaker can be achieved, and quite easily too, if you have a good source of drivers to experiment with and you don't crave a perfect flat response.
My ideal two way would be something like an 8" bass/mid in a tl and an open back tweeter sitting on top. I'd simply use a first order crossover but this will make choosing your drivers quite difficult. You want the tweeter to go fairly low aswell so you can take advantage of the "open back sound".
I think most of us would agree that a three way is going to achieve the best results so I will focus on this design method. However I'm going to suggest a rather unorthodox method for choosing drivers.
First driver to pick is the mid-range. you need to play it naked, no crossover, no cabinet. Try to keep in mind that its the mid-range were listening for, if you like the sound as it is you have a good starting point. If you don't like the sound then don't waste time on it, smash it up with a hammer and find another driver.
If you play a kef B110 naked it sounds fairly naff, well, it is a bass driver after all. However if you play an old Philips AlNiCo or an EMI ect, you should find it quite satisfying. Please don't use dome mid-ranges here unless you really like them for some reason. You want to try and go paper cone, with paper surround and AlNiCo if you like.
Now you need a tweeter. I do a similar thing as the mid but I use a single capacitor in series with the tweeter to protect it. I would start with a 4.7uf for 8ohm tweeter and keep the volume low. Try and pick several tweeter options from this test so you can choose the "perfect one" latter on. A Kef T27 sounds like crap here but a pair of decent paper cone open backs should sound glorious. Open back tweeters can be hard to find but a decent AlNiCo dome like the one below will work very well in most cases.
PLEASE NOTE: If you have a 16ohm tweeter the 4.7uf cap wont filter as well so I would use a 2uf. Likewise, if you have a 4ohm tweeter the 4.7uf could filter too much and you wont get the natural sound of the tweeter.
Now you need a bass driver. Go no smaller than an 8" and personally I would use a kef b200 if your other drivers are of similar sensitivity. When choosing a bass driver you want a very low resonance. If you hold the speaker to your ear and tap the edge of the cone you will hear a nice bass thud. The lower the tone the better. I always look for something around 20-30hz but the cabinet you place it in later will change this value. A small sealed box will increase the resonant frequency. So if your building a small bookshelf speaker, a driver with 60hz resonance will be fine. I personally would only ever use a transmission line for the bass because I can't resist that deep rumble organ bass.
Now you have at least three drivers, you can have a quick listen to them all together using an existing 3-way crossover network from an old speaker system. If you hear peaks in the spectrum, try reversing the polarity of the drivers until it sounds right. This is only ruff but you should be getting an idea of how well matched your selected drivers are in terms of sensitivity.
From this you should now have three drivers your happy with. Now you need to build your enclosure and I'm leaving that part up to you. But lets say you are using a transmission line for the bass and the mid and tweeter will sit on top open back.
Fit your drivers in place and start the lengthy process of making your crossover, by ear if you're feeling brave. Building a speaker in this way means you are constantly playing with values and you really get a feel for what the individual components are doing. I have been playing with crossovers for months in some cases. You can of course use a cross-over calculator which are plentiful online. These don't allow for the sound you will actually hear in your listening room but are certainly a very good starting point.
Im sure many will disagree with this method of building speakers but Its more fun and you can tailor the sound to your preference. Would you rather sit on the computer looking at numbers or sit on the floor surrounded with vintage drivers?
Let the MUSIC flow!
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