[Group 1]

My group is making a set of speakers using 55-1870 drivers and an MMTMM design.  What kind of crossover should we use?

[S Clark]

What can you tell us about your tweeter? Without that info it will be impossible to make recommendations. 

Did you find the frequency response graph for your woofer? I measured and posted it last week in another thread in this circle.

[HAL]

The woofer response graph is about 1/2 way down this thread page:

http://www.audiocircle.com/index.php?topic=79580.0

[Group 1]

The number on the back of our tweeter is 842001. I looked at one of your posts, Mr. Clark, and noticed that you already had some info on it. The dc resistance (Re) is 4.8 ohms? Now do I just go to lalena.com and plug that number in to get a theoretical crossover?

-Daivis

[S Clark]

The crossover calculator at http://www.diyaudioandvideo.com/Calculator/XOver/ will give you the values for a crossover if you have the Re (dc resistance) for both woofer and tweeter.  You need to read up on different crossovers to  have an idea about how they work.  Google first and second order crossovers.  Then you can ask specific questions that the members can help you with. 
A place to start would be ... http://www.parts-express.com/resources/build-a-speaker.cfm

[Group 1]

Okayy thanks!!

[Danny Richie]

Also keep in mind that those crossover calculators create a textbook (theoretical) crossover based on electrical parameters and NOT the actual acoustic output. So consider it a good starting point and not a solution. Put it together and take a some measurements to see where it is.

Another thing to note is that the textbook values based on electric parameters do not take into account the baffle size (reflections or baffle step loss). Typically with a small baffle there is an output loss in the lower region that needs compensated for, and that will require a larger inductor value than what the textbook calculations will give you.

[S Clark]

Thanks Danny.  I've told them that the theoretical crossover is only a starting point, but one that is required for the project.  We start with actual crossover design with the Clio measuring system next week. 

The hint about the larger value for the first inductor on the woofer is a good one that I hadn't covered.  Although we have talked about Baffle step loss, we hadn't discussed dealing with it yet. 

[Group 1]

Okay, I went to that website (diyaudioandvideo.com/Calculator/Xover) you gave me, Mr. Clark, and plugged in all the information. Do I randomly pick a crossover type from the ones given to me on that website? For example, 1st Order Butterworth, 2nd Order Bessel, ect. Or do I need to research each type and determine which crossover type would be best for my specific speaker?

[S Clark]

Group 1,
So many times the choice is determined by the drivers that you are using.  The primary breakup of that woofer isn't until around 10KHz which would let you cross rather high- but I still don't advise that.  However, read Duke's advice to Group 6 in this thread. 
http://www.audiocircle.com/index.php?topic=79580.msg758565;topicseen#new

As far as which crossover design, ask a specific question- perhaps ask for the differences on butterworth vs. Linkwitz-Reily (two commonly used designs).

[Danny Richie]

Another hint: When you see those peaks in the top of a woofers range then it is going to take more than a first order crossover to control it.

[Group 1]

Would the 2nd order Linkwitz-Riley model be a good place to start for my set of speakers (MMTMM)? At least for now..?

[S Clark]

How are you planning on combining your woofers?  All four in parallel ( ), all four in series, or some combination?  Are planning on keeping this a simple two way system, a 2.5, or a three way?  These are decisions that must be made before any theoretical crossover work. 
Remember that you need to keep the impedence of the system from dipping much below 4 ohms in order to protect whatever amplifier is hooked up to it. 

After that, I'd probably look at your second order crossover options.