More crossover help

[bs1777]

hey guys. i have decided to build my own crossovers and know to parts i need. I just wanted to know what to do. I have a 4 ohm woofer and a 4 ohm tweeter. I went to a online calculator and got all the parts to do it(not yet ordered). The thing is that my amp is 8 ohms and i got 2, 4 ohm speakers that i have ran in series. I just wanted to know what will happen to my impedance once i hook up the parts to cross it over. The crossover design is a 2nd order linkwitz-riley.

[bs1777]

2nd Order Linkwitz-Riley

4000 Hertz

4 Ohm Tweeter / 4 Ohm Woofer
Parts List
Capacitors
C1 = 4.98 uF
C2 = 4.98 uF
Inductors
L1 = 0.32 mH
L2 = 0.32 mH

[Pano]

Some question are in order:

• You say that your amp "is 8 ohms." That seems unlikely unless you have very high impedance tube amp or a current source amp. It's probably rated into an 8 ohm load. What do you actually have?
• Which 2 speakers are run in series? The woofers? You have 2 per side?

[bs1777]

Ok. The amp says ''use 8 ohms''. It have 2 channels that are non-bridgable. I have built some cabinets with 1 tweeter which is 4 ohms and 1 woofer that is also 4 ohms. I plan to wire those in series and go into the amp. But i want to cross it over. its just that i dont know how to run the crossovers in series. (refer to pic).

[bs1777]

To sum it all up i just wanted to know if i can run all those parts in series and how to do it.

-Thanks

[Pano]

You want to wire the tweeter and woofer in series? That will not work well at all.
Or do you mean you want to wire the left in series with the right?

[BobEllis]

There are series crossovers, but that still doesn't get you a safe load for an 8 ohm load only amp. A better solution would be to would be to add another woofer and wire them in series. Your 8 ohm amp can handle a 4 ohm tweeter properly crossed because it won't be delivering a lot of power to the tweeter, especially if crossed fairly high.

How did you calculate your crossover components? Do the driver sensitivities match? Are you planning to measure the driver responses in your cabinet and design the crossover from there?

Textbook crossovers generally don't work well because they assume a constant driver impedance and flat response a couple octaves outside the passband. Take a look at the spec sheet and you'll see that this probably isn't true. Better to plug the published frequency responses and impedance curves into a simulator. There are free/free demos available, such as ARTA, Basta and Speaker Workshop. You'll get mush better simulations and results if you measure the drivers responses in your boxes, though.

[bs1777]

I have tested that if i run the tweeter in series with the woofer in ONE cabinet it that it works with my amp. I have done all the testing and it will work. My amp can handle it.

-Thanks

[bs1777]

One more thing. I tested it with an old JBL 3 way crossover and sound superb. The frequency's were 800hz and 4500hz. So what should i tune my new crossover to?

-Thanks

-P.S. Im new to this.

[BobEllis]

Tested how? Without a crossover?

At low volume 4 ohm impedance won't be an issue. Often an amp rated 8 ohms minimum has minimal heat sinking. This becomes an issue at high powers when the output stage is dissipating more heat. If you use a series crossover, the effect is to short out the tweeter for low frequencies and short the woofer for highs. You still end up with a roughly 4 ohm nominal impedance and may run into issues as you crank it up.

It would help to know what drivers you are using and links to any known data sheets. Box dimensions and layout? Any goals for the system other than not blow up your amp?

GOOD crossovers are designed for a particular set of drivers on a particular baffle placed in a particular position in the room. You may have been happy with the random crossover that you used but a properly designed crossover will work much better if you prefer flat frequency and power response.