mtm crossover

[barspin89]

I'm designing a crossover for a center channel mtm speaker. I'm using an 8ohm tweeter and two 4ohm woofers wired in series to create an 8ohm load. When doing my calculations for the low frequency section of the crossover, do I use the 4ohm rating of a single woofer or do I use the 8ohm rating for the two woofers together. I'm not new to speaker building but I am new to crossover design. Any help would be appreciated.

[sdclc126]

The 8 ohm load is what the crossover will "see" - so it should be calculated as such.

[barspin89]

I have a couple more questions and I apologize if they sound stupid but I'm still trying to understand the basics. Again, my design is a center channel mtm speaker that runs at 8ohms. I'm using two 4ohm woofers and an 8ohm tweeter. I know that running the woofers in series will create an 8ohm load but will the tweeter also effect the overall impedance? Also, does an mtm design require a special type of crossover, or can a basic 2-way crossover be used just routing both woofers through a single low-pass filter? Once again, any help is appreciated.

Andy

[BobEllis]

Yes, you can us a single crossover to filter your series connected woofers.

However, the textbook "8 ohm" crossover is unlikey to work well. Take a look at the impedance curve of the woofers you are planning to use - they are very likely not at their nominal impedance at more than a couple frequencies.

You'll get much better results using the tools at http://www.pvconsultants.com/audio/frdgroup.htm Use SPL Trace with the impedace curve (just double the values on the graph and add 6 dB to the 2.83V output) and design a crossover with PCD.

You'll get even better results if you build the speaker and measure the response/impedance in the box and design your crossover from that data.

Edit: Sounds like in your research you've come across a couple of 2.5 ways that look like MTM's. While that may work better in a horizontal configuration, given your woofers it's pretty hard unless you want to delve into series crossovers. Stick with a 2 way for this project.