passive crossover - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 21 Old 07-15-13, 02:55 AM Thread Starter
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passive crossover

Does anyone know where I can find a good range of crossovers. Diy build is ok. For small hifi speakers. About 75 watts. Thanks in advance.
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post #2 of 21 Old 07-15-13, 03:59 AM
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Re: passive crossover

Crossovers need to be designed for the individual drivers used. Do you have a list of drivers you are considering?

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post #3 of 21 Old 07-15-13, 07:41 AM Thread Starter
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Re: passive crossover

im using a Peerless 830860 HDS 134 PPB MidWoofer Speaker
and a Peerless Vifa XT25SC90-04 Tweeter
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post #4 of 21 Old 07-15-13, 09:16 AM
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Re: passive crossover

The MidWoofer you have chosen is an 8 Ω unit whereas the Tweeter is 4 Ω. Typically these need to be the same impedance.
I would recommend either finding a suitable 8 Ω Tweeter, or a 4 Ω MidWoofer.

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post #5 of 21 Old 07-15-13, 12:34 PM Thread Starter
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Re: passive crossover

the problem is that these 2 drivers have been chosen as part of the box design. Im sure a crossover design could compensate for these ohm numbers to give a more satisfactory ohm reading in total.
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post #6 of 21 Old 07-15-13, 03:51 PM
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Re: passive crossover

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snapvalonia wrote: View Post
the problem is that these 2 drivers have been chosen as part of the box design. Im sure a crossover design could compensate for these ohm numbers to give a more satisfactory ohm reading in total.
I personally would consider adding a second MidWoofer in parallel with the first to achieve a 4 ohm nominal impedance.

However, here is a simple first order crossover using the stated resistance of the two drivers of 5.7 and 3.2 ohms and a crossover frequency of 2 kHz. (From http://www.diyaudioandvideo.com/Calculator/XOver/ )

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You will need to add a level matching circuit to balance the output from each driver and this is best done by measuring the finished system.

Note: There are more complex crossover design calculators but it depends on what you are trying to achieve.

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post #7 of 21 Old 07-16-13, 01:33 PM Thread Starter
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I cant add a second woofer as these are small bookshelf boxes that are designed with a separate sub box. It should be fine with a slightly strange ohm rating. Thanks for advice.
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post #8 of 21 Old 07-16-13, 01:39 PM Thread Starter
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Im looking for a crossover that is clean as possible yet simple. The speakers are very good quality
So sound is everything
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post #9 of 21 Old 07-25-13, 01:58 AM
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Re: passive crossover

Put a 4 ohm resistor in series with the tweeter. That will give you your 8 ohms.
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post #10 of 21 Old 07-26-13, 09:57 PM
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Re: passive crossover

You're not asking the right questions, or supplying the right info. As robbo has said, each speaker combination needs to have a crossover designed for it.

First off the drivers you are choosing and specifically the woofer don't really work all that well together ( or at least not in the modelling I've done ). The woofer has a very low Vas which means it should be good for a small enclosure but in reality anything under about 15 liters is going to sound horrible.
I ran the specs through a number of scenarios with uni-box and 15 liters appears to be optimum, in a vented enclosure. This yields good numbers in general all though at max SPL it is possible theoretically to exceed xmax. You wanted 75 watts but the limit will be whatever the woofer provides, in this case 50 watts appears to be the limit.

I ran a number of models for the crossover as well. Best result without huge expense comes when the drivers are crossed at 3000 kHz, as seen in the first image. The graph shows how the crossover matches and the 3rd image shows why it is almost never a good idea to just put a resistor in series with speaker in an unequal setup. The graph shows a really nasty rise in the tweeter which would sound horrible. To demonstrate this I simply zeroed RP2 and changed the value of RP1 to 4 ohms. Even when impedance equalisation is added back to the crossover the hump remains from the 4 ohm resistor.


Both the tweeter and woofer need to have impedances equalized and there needs to be a 5 dB L-pad on the tweeter with the polarity reversed as well. This design assumes a vented 15 liter enclosure.


If I were using these drivers this is how I would have them running. You can then look at the drivers graphs and see if there are any really large dips in the frequency response graphs and perhaps add a contour/notch/zobel circuit if needed. As it stands the crossover below may well yield a pleasant result and no further tweaking may be necessary. I generally try to arrive at that scenario as start point, then adjust after a couple of hundred hours of run in time. This allows new drivers to settle in. Measuring at this point is always a handy thing but I generally tune to my ear and leave it at that. The purist wouldnt recommend this but unless you have a dedicated listening room accurate measurements can be very difficult to achieve.
Attached Thumbnails
passive crossover-schematic.jpg  

passive crossover-graph1.jpg  

passive crossover-no-eq.jpg  


Last edited by Kiwilistener; 07-26-13 at 10:14 PM.
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