# crossover frequency question

Discussion in 'Archived Threads 2001-2004' started by Cameron_Peck, Sep 28, 2002.

1. ### Cameron_Peck Stunt Coordinator

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How can I determine what the crossover frequency is for a set of Infinity speakers that I have?

2. ### Mark_E_Smith Second Unit

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With out a speaker testing system like Clio the only way I know is to actually look at the componet values and calculate the x-over.

3. ### Cameron_Peck Stunt Coordinator

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Would I need to disassemble the crossover to do this?

4. ### Mark_E_Smith Second Unit

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Only to see the values of the componets, you would also need to know the inpedence of each driver. Why do you want to know the cross over point?

5. ### Cameron_Peck Stunt Coordinator

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I want to do a bi-amping experiment. I want to bi-amp one speaker and leave the other one alone. That way I can hear the benefits and/or the pitfalls for myself. If I like the result I am going to incorporate bi-amping into the Audax Home Theater system
I am planning to build.

6. ### Mark_E_Smith Second Unit

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Wow, you might consider geting a Clio lite or something like that, you will need to analyse the speaker system to set up the bi-amping anyway. There is a difference between book crossovers and the real world. I have a clio, I was upgrading my car stereo with a sub woofer and decided that I should bass block the speakers, the "book" method you add a 200 mF cap to the speakers. I had one of the speakers out and ran some quick tests on it then repeated the tests with the 200mF cap installed --- well it cut the bass in the 400 Hz range and boosted it in the 100 Hz range This was because of the impedence curve of the driver affected the cap and the response. Needless to say I didn't install the caps. So without any accurate measuring system its going to be real hard to design the crosovers, most likely the active x-overs will need different x-over points than the passive ones. Just my 2 cents

7. ### Stephen Dodds Second Unit

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Wouldn't the manual, sspecs or Infinity be able to tell you?

Steve

8. ### Isaac C Stunt Coordinator

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Cameron,
If you meant you wanted to try biamping with active crossovers, it can be done, but the end result might not sound as good as the stock passive crossovers. Passive filters are optimized with the speaker's complex impedance in mind. So using the calculated crossover frequency of the passive components will yield a totally different acoustic output from your speakers -- as active crossovers do not see and are not affected by the speaker's complex impedance. An active filter's transfer function reflects textbook response whereas the transfer function of a complex impedance-loaded passive filter looks "equalized."
You could still biamp using a Y-Cable to feed the two amps with a channel's signal. Biamp-ready speakers usually come with removable speaker terminal metal strips; remember to remove them prior to firing up the two amps. If your speakers come with series type passive filters, there really is no way of biamping them without completely replacing the series filter with parallel type passive filters, which need to be designed with the acoustical and electrical measurement of each driver unit in mind.
hope this helps
Isaac

9. ### Cameron_Peck Stunt Coordinator

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As simple as that sounds I hadn’t thought of it. I do not have the manuals and they are not listed on the web sight. They are about 14 years old. I did however send them an e-mail asking the question. Thanks for your help.

10. ### Cameron_Peck Stunt Coordinator

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Thanks Isaac. That had crossed my mind, but in a much more vague way. Do you know if there are any software programs out there to help design active crossovers? I know that passive crossovers are much more popular and there are many good crossover programs to help. But I can see so many positives to bi-amping.

11. ### Patrick Sun Moderator Moderator

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Not many speakers lists xover points.

The quick and dirty way to figure out xovoer points is to get a test tone CD that does at least 1/3 octave sinewaves.

Unplug one of the drivers (I'm assuming this is a 2-way speaker). You can do this by just unplugging one of the 2 leads going to the driver itself (hopefully it's connected by a spade terminal connector, otherwise, you may not want to cut the lead going to the driver terminals if it's soldered into the terminals).

Play each test tone, in the frequency region that make sense for that driver, through the driver (use a normal loudness level, don't go too loud, and use earplugs), use a SPL meter to measure the output of the driver for each frequency, plot the SPL vs. Frequecy.

Do the same with the other driver hooked up (unhook the previous driver), and plot its response as well.

Where the lines sort of intersect will give you an idea of where the xover point lies.

12. ### Isaac C Stunt Coordinator

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Texas Instruments has some utilities for designing active filters. Filter Pro lets you design Multiple Feedback Filters or Sallen-Key filters based on crossover frequency and filter order. You can specify up to a 10th-order Butterworth/Bessel/Chebychev filter and the program spits out component values -- exact or off the shelf values. The rest: power supply, printed circuit board etc. is left as an excercise to the user.
If you wanted to start from scratch, you could use the student version of PSPICE. Elliott Sound Products has some active filters that you might find interesting.
hth

13. ### Jonathan M Second Unit

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Cameron,

As long as you design the active xover with an appropriate xover point and a 4th order slope or so, you should be OK. I would do as Patrick suggested to find the xover point currently. Obviously the passive xovers should be removed completely. Another method to find the xover point is to reverse the polarity of one of the drivers and do a frequency measure. The system should then have a null centred (near enough) at the xover frequency. With active xovers, you only really need to consider a xover freq such that both drivers are near enough to flat over their respective ranges + around an octave or so either side of the xover frequency. Between 2 and 4kHz is normally where most systems lie, depending on the size of the tweeter and mid/bass units. (My 6.5"/1" vifa system I'm planning will be crossed at 2350Hz).

Cheers
Jonathan

14. ### Cameron_Peck Stunt Coordinator

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Ask and yee shall receive. Infinity e-mailed me back and told me the crossover frequency is 1200Hz. Thank you all for your help. I will post the results of my A-B test.

15. ### Jonathan M Second Unit

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Hmmm, 1200Hz sounds quite low to me. Is it a 1" dome tweeter? If so, I'd expect resonance to be around 1kHz or so, so I would personally put the active xover point higher up (2kHz minimum)

I'd definitely run with a variable xover point if I were you - especially at this experimentation stage.

Cheers
Jonathan

16. ### Cameron_Peck Stunt Coordinator

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It does sound low, but it is a two way with an 8 1/2 “ woofer.

17. ### Chris Carswell Supporting Actor

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Cameron,
What is the email address for the Infinity Tech. person who helped you?

18. ### Cameron_Peck Stunt Coordinator

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I used their web page to ask the question. The reply came from [email protected]

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