3way speaker impedance

[JLsandiego]

hey forum. I'm currently designing the crossovers for my first set of 3way speakers. One question that's been bothering me has to do with the impedance. The receiver I'm running them on is stable down to a standard 8 ohms. However, the tweeter, midrange, and woofer are all 8 ohms. From what I know this would equal an impedance of around 2 ohms. So how does everybody building 2 and 3 way speakers deal with this? The most obvious solution is to do some wiring in series but all the crossover schematics i've seen are in parrellel? Do i simply have to add resistors in order to keep it down? Or will it never actually get down to 2 ohms and I never have to worry about it? I have a feeling that there is a very simple answer to this question and i'll feel dumb for asking it but oh well. Thanks for your help in advance.

[PeteMcK]

the crossover separates the signal into different bands, so the impedance seen by the amplifier is similar for each band.

So IF your woofer, mid & tweeter are all 8 ohms, a properly designed xover will provide an 8 ohm load to the amp.

However, 8 ohms is used as a nominal figure by manufacturers, for your xover to work properly you will have to measure the actual impedance of the drivers at the proposed crossover frequencies
(or at the very least, get the figures from the manufacturers published graphs)

[Dave Bullet]

Are you building someone elses design?
If not, are you using any modeling software for your new design?
If you are designing your own did you measure the drivers yourself in the enclosure you plan to use? (or are you using other people's measurements?)

If you are building someone elses design - you should be able to get the overal system impedance plot from them to determine how nominal the load is.

I'm guessing you are designing your own. Do not even attempt to do this - especially for a 3 way if you cannot model or measure your design.

As far as impedance goes - you can use manufacturer impedance plots (google SPLTrace) and load these into a speaker modeling program to work out what the load would be to your amplifier.

Without doing the above - you could very well design (by accident) a low impedance load and destroy your amplifier (let alone produce a speaker that could sound horrible).

Being able to model and measure is a must for new designs.

Cheers,
David.

[omni]

I am currently in the tweaking phase of my three way system.........I designed and built the boxes and crossovers using a variety of tools and by using this forum...........The first thing to know is what drivers you are using and find out what kind of resourses you have .............there are some good crossover designing tools on the internet.......And it takes some time, patience, and a lot of research.................All starting with your drivers if you already have them, and what kind of enclosure you are using or are going to use.........Working with the manufacturers specs is what I did, because I don't have a lot of measurement tools..............My crossover came very close in performance to the simulations I did using manufacturer specs and a few tools available online..........Now I am in the process of tweaking, and anticipate excellent results........You can do all this, but it will require a great committment on your part............There are also cookbook formula calculators on line as well, however they may not give you the finest results possible..........It's all up to you, as to your level of committment, and I for one would be willing to share with you my experience.......not that I am a guru, because I am not, and there are probably more qualified people out there and in this forum, however, I have been given a lot of support by a few people on this forum, and wish to freely give the experience back, that which was so freely given me.............For a little bit of history of my project, check out the thread :3 way xover help greatly appreciated.....It was started by Grant, who has, over the time become a friend of mine.........................Respectfully......Omn i

[PeteMcK]

an excellent site with a good intro to xover design:

http://sound.westhost.com/lr-passive.htm