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Old 2nd November 2011, 09:45 PM   #1
mcg123 is offline mcg123  United States
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Default Crossover for 8 ohm and 4 ohm speakers

I would like to replace the tweeters in my car. The stock woofers are pretty decent, so I decided that I could benefit greatly from some new tweeters. I would really like to use home audio tweeters rather than car ones (like these), but the problem is that the stock speakers in my car are 4 ohm. I used this crossover calculator to determine the parts to build a crossover. It accounts for the fact that I'm using an 8 ohm tweeter and 4 ohm woofer.

But my question is do I need to use an l-pad on the woofer to prevent it from being too loud? Also, if I build this crossover, what will my resulting impedance be?

I've read other posts similar to this, but I can't get a clear answer. I'm also pretty new to this kind of stuff, so I'm sorry if these are dumb questions. Thanks!
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Old 2nd November 2011, 10:44 PM   #2
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re:'do I need to use an l-pad on the woofer' - you should never use an L pad on woofers, it simply wastes power. You'll find that tweeters are by & large more sensitive than woofers, they need the L pad.
So, the next question for you is, what are the sensitivities of the woofer & tweeter you want to use?

re:'what will my resulting impedance be?' - I think you're assuming there is a simple (8 ohm or 4 ohm) answer to this question. But impedance varies with frequency, & it also depends on how you implement the crossover, in particular the tweeter attenuation. Here it won't be a problem because the tweeter impedance is higher than the woofer.

re:'I used this crossover calculator' - You are aware that you need to use the ACTUAL impedance of the driver at the crossover frequency as read from an impedance plot, rather than the 'nominal' (8 ohm or 4 ohm) impedance to get correct values?????
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 2nd November 2011, 10:54 PM   #3
mcg123 is offline mcg123  United States
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well the tweeter is 89 dB 1W/1m and the actual impedance is 5.2 ohms. unfortunately, i dont know anything about the woofer because it came with the car. i guess i could either guess or use a multimeter?

the crossover calculator gives a lot of options for different types of crossovers. what would you recommend? it seems as though 2nd order crossovers are common for two way speakers (although there are many different types of 2nd order crossovers, so i dont know which would work best). so if i do a second order crossover, what would the 'nominal' impedance be? i just want to make sure i dont blow up my stereo.
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Old 3rd November 2011, 01:03 AM   #4
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re:'the actual impedance is 5.2 ohms' - no, the actual resistance is 5.2 ohms... impedance varies with frequency, which is why you need an impedance plot to design accurate crossovers.

re:'i just want to make sure i dont blow up my stereo' - the thing you need to worry about here is the lowest impedance element which is the woofer, adding higher impedance tweeters won't cause a problem.

Re: different types on 2nd order crossover, if in doubt, use Linkwitz-Riley...

How is the existing tweeter crossed over? if just a single cap, try your new tweeter with a cap of half that value and see how they sound...
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 4th November 2011, 01:02 AM   #5
mcg123 is offline mcg123  United States
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well i havent bought any tweeters yet because i'm trying to figure whether or not this is too complicated for me to handle. anyways, yes, the current tweeter is connected with just a single cap, but the current tweeter is really small, and the woofers are actually full range drivers with a frequency response of something around 100 - 16000 hz. my thought was that i could cross over the new and larger tweeter at around 5,000 hz or so. i'm not sure what frequency would be ideal since there is such a large overlap.

the bottom line is, i'm not looking for a perfect system. i just want to make sure that my tweeter and woofer are relatively balanced in volume and that my head unit isnt harmed.
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Old 4th November 2011, 01:48 AM   #6
mcg123 is offline mcg123  United States
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i guess what i didnt really explain is that i dont really like how its set up, which is basically a full range driver with a tweeter just to add a little bit of clarity to the highs. i would rather use a two way crossover that uses the full range driver for only the lower notes and a tweeter for everything else, which would be more like actual two way speakers.

i also didnt explain that i would like to eventually replace the full range drivers with actual woofers, but its not really in my budget. so i would like to essentially like to have typical two way speakers, but using the current full range drivers as woofers.
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Old 5th November 2011, 12:16 AM   #7
AllenB is offline AllenB  Australia
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Why don't you begin by crossing the tweeters as they are recommended (often they will suggest a point for a second order crossover). Work on the level if they are too loud, and then decide whether the woofers are overlapping and need to be crossed lower...Then go round again.
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Old 5th November 2011, 12:51 AM   #8
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The tweeter resistance is 5.2 ohms ,ok ...Then use this formula.

5.2 X 1.3 = 6.76

The impedance of tweeter is 6.76 ohms

This formula too can be applied to determine the total impedance of a loudspeaker, measuring the resistance with a tester.The probability of error is minimal.

Resistance x 1.3 = Impedance

But you must know also that which determines the total impedance of a speaker is the woofer and ...... the Crossover calculations are based on individual driver impedance.





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Last edited by juliovideo; 5th November 2011 at 12:57 AM.
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Old 5th November 2011, 01:39 AM   #9
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If you start well you must have a system to measure the response frequency.

Click the image to open in full size.


Need for the first step ......

This is a free software for downloading must register at their forum .....

REW Forum at Home Theater Forum and Systems - HomeTheaterShack.com

Download

Home Theater Forum and Systems - HomeTheaterShack.com

..........you must have the microphone ECM8000 file.


Tools ............. pretty ,good and cheap

Behringer ECM8000 Measurement Microphone
Behringer - U-CONTROL UCA202

.....And finally you need a mixer, but it must have +48 V phantom.

example .... Behringer XENYX 802 Mixer





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Last edited by juliovideo; 5th November 2011 at 01:57 AM.
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Old 5th November 2011, 03:05 AM   #10
sreten is offline sreten  United Kingdom
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Hi,

FWIW just use hifi 4ohm tweeters, can't go wrong IMO with :
Vifa BC25SC55-04 1" Square Frame Tweeter 264-1024

Use a series 1st order c/o or 2nd order parallel L/R (search) @ ~
3kHz and L-pad the tweeter down to match the bass-mid unit.

rgds, sreten.
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