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Old 7th July 2004, 01:22 PM   #1
maxw is offline maxw  United Kingdom
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Question How do you match drivers?

Hi,
I have 2x pairs of 4 ohm mid/bass woofers. One vifa, one Jaycar response. I want to make 2x 2 way speakers, one for the car and one for the house.

What I wonder is: how do I pick a tweeter to match?
I mean in technical terms, NOT the reputation of one manufacturer or model etc.

I realise the 2 drivers frequency response has to cross at the crossover point.

Do I look for the same sensitivity?
Do they have to be the same impedance?
What happens if they are not the same impedance?
If my woofer is 4 Ohm and my tweeter is 8 Ohm, how do I work out the overall impedance?

I have searched and worked out how to make a specific crossover freq etc but the examples always seem to be with ideal drivers.

Any pointers greatly appreciated
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Old 7th July 2004, 03:09 PM   #2
markp is offline markp  United States
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The tweeter should be more effcient than the woofer by a few Db as the crossover loss is usually a couple Db and any extra is easily eliminated with a few resistors. Look for the response of the tweeter to go at least an octave lower than the desired crossover freq, more is better.
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Old 7th July 2004, 03:18 PM   #3
HiSPL is offline HiSPL  United States
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Do I look for the same sensitivity?

No, but the tweeter should be the same or higher sensitivity. You can then use an L-pad to bring it down in level to match the woof.


Do they have to be the same impedance?


No. Even your woofer is not a constant 8 ohm load. It changes with frequency. The woofer will have a big spike at the resonant freq. of the driver (highest impedence) Then it will fall to its minimum inpedence on both sides of this spike and start to steadily rise again as the frequency goes higher. A tweeter works the same way, just at higher frequencies. So know you have 2 impedence spikes in you system. If you put it in a ported cabinet you get 3 spikes. Other configurations can give you more....


What happens if they are not the same impedance?


Your crossover components will be different from an 8ohm / 8ohm system.


If my woofer is 4 Ohm and my tweeter is 8 Ohm, how do I work out the overall impedance?

The impedence rating of a loudspeaker is just a sort of an average of the lowest impedence section of the whole system. A 2-way system with an 8ohm woof and 4ohm tweet would still be rated as an 8 ohm system in most cases. Even if the woofer dips to 6.5 - 7 ohms somewhere.

Clear as mud?


I hope this helps some....
-=Tim=-
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Old 7th July 2004, 04:53 PM   #4
maxw is offline maxw  United Kingdom
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Quote:
Originally posted by HiSPL
Clear as mud?

I hope this helps some....
-=Tim=-
No, that was great and helps alot. Thanks!
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Old 7th July 2004, 05:29 PM   #5
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Quote:
Originally posted by markp
The tweeter should be more effcient than the woofer by a few Db as the crossover loss is usually a couple Db and any extra is easily eliminated with a few resistors. Look for the response of the tweeter to go at least an octave lower than the desired crossover freq, more is better.

If anything it's usually better the other way around, as the woofer has the 6dB baffle-step loss to overcome, while the tweeter does not. Also, the insertion loss of the primarily capacitive high pass filter on the tweeter tends to be less than that of the primarliy inductive low-pass filter on the woofer.

Having the components the same impedance is no biggy, but having them reasonably close in sensitivity is. One reason for the success of the MTM design is that by having two woofers wired parallel the woofer section sensitivity is closer to that of the tweeter (tweeters tend to be more sensitive to start with) and this also helps overcome the baffle-step loss. You can correct for the baffle step electronicall but it's a lot easier to deal with if the base woofer sensitivity is 6dB higher than the tweeter to begin with.

One site to find crossover values is http://www.lalena.com/audio/calculator/xover/

You can enter the impedance of each driver and it will calculate the correct component values.

Where to crossover is based primarily on the dispersion of the woofer; sound practice is not to run the woofer higher than the frequency where it is down 6dB 30 degrees off-axis compared to on-axis. Knowing that you choose a tweeter that has an Fs at about half that frequency.
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Old 9th July 2004, 12:21 PM   #6
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Quote:
Originally posted by BillFitzmaurice



If anything it's usually better the other way around, as the woofer has the 6dB baffle-step loss to overcome, while the tweeter does not. Also, the insertion loss of the primarily capacitive high pass filter on the tweeter tends to be less than that of the primarliy inductive low-pass filter on the woofer.

Having the components the same impedance is no biggy, but having them reasonably close in sensitivity is. One reason for the success of the MTM design is that by having two woofers wired parallel the woofer section sensitivity is closer to that of the tweeter (tweeters tend to be more sensitive to start with) and this also helps overcome the baffle-step loss. You can correct for the baffle step electronicall but it's a lot easier to deal with if the base woofer sensitivity is 6dB higher than the tweeter to begin with.

One site to find crossover values is http://www.lalena.com/audio/calculator/xover/

You can enter the impedance of each driver and it will calculate the correct component values.

Where to crossover is based primarily on the dispersion of the woofer; sound practice is not to run the woofer higher than the frequency where it is down 6dB 30 degrees off-axis compared to on-axis. Knowing that you choose a tweeter that has an Fs at about half that frequency.

nice little site, i have a tweeter with 6ohm and a mid with 4ohm.
but what do i put in the (Frequency hz box) to get my parts list?
i am very new to crossovers so im going to need alot of help.....thanks







jamie
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Old 9th July 2004, 12:46 PM   #7
maxw is offline maxw  United Kingdom
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Quote:
Originally posted by XTRMEASURES
nice little site, i have a tweeter with 6ohm and a mid with 4ohm.
but what do i put in the (Frequency hz box) to get my parts list?
i am very new to crossovers so im going to need alot of help.....thanks


jamie
Specifically what are the drivers?
You need to know some specs of the drivers, especially frequency response
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Old 9th July 2004, 01:51 PM   #8
markp is offline markp  United States
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Quote:
Originally posted by BillFitzmaurice



If anything it's usually better the other way around, as the woofer has the 6dB baffle-step loss to overcome, while the tweeter does not. Also, the insertion loss of the primarily capacitive high pass filter on the tweeter tends to be less than that of the primarliy inductive low-pass filter on the woofer.

Having the components the same impedance is no biggy, but having them reasonably close in sensitivity is. One reason for the success of the MTM design is that by having two woofers wired parallel the woofer section sensitivity is closer to that of the tweeter (tweeters tend to be more sensitive to start with) and this also helps overcome the baffle-step loss. You can correct for the baffle step electronicall but it's a lot easier to deal with if the base woofer sensitivity is 6dB higher than the tweeter to begin with.

One site to find crossover values is http://www.lalena.com/audio/calculator/xover/

You can enter the impedance of each driver and it will calculate the correct component values.

Where to crossover is based primarily on the dispersion of the woofer; sound practice is not to run the woofer higher than the frequency where it is down 6dB 30 degrees off-axis compared to on-axis. Knowing that you choose a tweeter that has an Fs at about half that frequency.
I respectfully disagree. You will be hard pressed to find a woofer with higher efficiency than a tweeter of good quality and it is always easier to lower the output of a tweeter than waste the output of a woofer needed for bsc. I tend to use higher order crossovers on tweeters and lower on woofers so the loss on the high pass is greater than that of the low pass and if decent inductors are used there is no real loss through them due to resistance. But, to each their own.
Hmm, doesn't 'an octave lower' sound like 'half that frequency'?
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Old 9th July 2004, 07:55 PM   #9
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[QUOTE]Originally posted by markp
[B] You will be hard pressed to find a woofer with higher efficiency than a tweeter of good quality

Precisely. That's one reason for an MTM setup, to use two woofers to get the LF sensitivity up closer to that of the tweeter, especially since the baffle step is going to cost you 6dB

Half frequency= an octave lower, but I wouldn't necessarily expect a newbie to know that.

Max, to find an appropriate crossover point you need to get a manufacturers off-axis SPL chart to see where it goes to -6dB at 30 degrees off axis. I'm assuming that measuring it yourself is not an option.

With a 4 ohm woofer system impedance would be considered 4 ohm, though in truth that's only an average; impedance fluctuates constantly with frequency.
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Old 9th July 2004, 08:32 PM   #10
markp is offline markp  United States
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That is why I built these:
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