BillFitzmaurice.info

Hi guys,

I have had these speakers in storage for some time now and wanted to put them in my man space for some tunes. Now then only issue is, I am unable to find the external crossover that they came with. As the mid and high are separate, I am unable to use them.

I was wondering if anyone on here would be able to help me out with advice on how I could make a simple crossover to get them working again?

I will be just putting them into a box with an old sony headunit I have and powering it with my bench power supply.

I have attached all the details I have on these speakers.

http://www.crutchfield.com/S-l9HYGFT37L ... 62-5i.html

Product Highlights:
Plus One C.M.M.D. woofer cone is 30% larger than other speakers of this size, ensuring strong bass response
high-roll rubber surround allows greater woofer movement
1" Unipivot C.M.M.D. balanced dome tweeter may be rotated up to 355° for improved imaging
2-way external crossovers (18 dB/octave, 3,500 Hz high- and low-pass)
sensitivity 90 dB
frequency response 45-21,000 Hz
recommended power range 2-75 watts RMS
peak power handling 225 watts
top-mount depth 2-1/8"

spiltmidi wrote: 2-way external crossovers (18 dB/octave, 3,500 Hz high- and low-pass)

Those are what you need. See if you can get them from Infinity. Generics will work, but not as well as purpose built.

Hi Bill,

Thanks for the quick reply. I had contacted Infinity but they no longer produce these crossovers. I was advised to search for secondhand ones from ebay or elsewhere or build my own.

I have done some searching on ebay and nothing I was able to find. The new version of the speakers have built-in crossovers now.

I knew that (18 dB/octave, 3,500 Hz high- and low-pass) would mean something to someone but not myself. The only other crossovers I have made are ones that I have purchased off Leland for my Otop12J's.

So I went for a little search for something.
http://www.apicsllc.com/apics/Misc/filter2.html

I thought to myself, if I brew my own beer and fix and tinker with my kids toys. I might as well make my own crossover. However, as I have no clue. I punched in the following from the information I know and got the following.

Would this work? Also, what is the phase shift message mean down the bottom?

Each additional 6db filter rotates the phase, just like on a circle. 90, 180, 270. Since you're doing the same filter on each driver it's no biggie. When you start mixing filters it can become a real problem.

A calculated crossover will work, but not perfectly, as it assumes the driver impedance at the crossover frequency to be exactly 4 ohms, which it will not. But without impedance charts of the drivers it's the best you can do. The phase shift doesn't matter when it's not 180 degrees.
That chart is odd, the values are off by a mile. C1 should be around 7.5uF, C2 22uF, C3 15uf. L1 should be 0.14mH, L2 0.27mH, L3 0.1mH.

It looks like that program calculated for 3.5Hz, not 3500 Hz (I can see the decimal point)

But that wouldn't make sense either - the values are not off by 1000...

Hi Gents,

Looks like it was a mistake on my behalf. Thanks for the reply's also.

It in fact was a full stop and not a comma. I have removed it and just had a direct input of 3500. Now I have something that looks correct.

All I can say is spot on both Bill's.

Looks like I have some buying to do.

If you're keen, measure the impedance of the individual drivers, then work out what that value is where you want to cross over
Impedance measuring can be done fairly easily, with a few bits and pieces. Was just reading that Room EQ Wizard has such capabilities built in

bitSmasher wrote:If you're keen, measure the impedance of the individual drivers, then work out what that value is where you want to cross over

^^^^
This would be prudent. Infinity car audio has a habit of using 2 ohm drivers in order to (artificially) increase their sensitivity spec. Designing a 4 ohm crossover for a 2 ohm speaker won't give you good results. Also, very few home audio amplifiers can handle a 2 ohm load.

CoronaOperator wrote:Also, very few home audio amplifiers can handle a 2 ohm load.

Most can't handle 4 Ohm. The vast majority of modern HT amps are rated to a minimum of 6 Ohms.