Just after some opinions on how high I can crossover my FR125s with a 12inch sealed sub on each side without degrading imaging etc. I was thinking around 120hz 24db/oct. The subs aren't super high quality, some JBL car subs that will be in small sealed boxes with EQ, below and slightly offset the FR125s boxes on stands.
Thanks for any advice.
Thanks for any advice.
It really depends a lot on the subs. What you propose sounds like a good starting point, but what are you doing about the filtering of the FR125?
What you might find easy to do is use the natural roll-off of the FR125 in a sealed box as one part of the crossover and match the subs up to that with an appropriate 2nd-order low-pass filter.
What you might find easy to do is use the natural roll-off of the FR125 in a sealed box as one part of the crossover and match the subs up to that with an appropriate 2nd-order low-pass filter.
What I would do.
Find the resonance frequency and Q of the FR125 in the sealed box and use that to design a complementary 2nd-order electrical filter to achieve overall 4th-order Linkwitz-Riley response. Put a complementary 4th-order electrical Linkwitz-Riley filter on the sub.
OR
Find the resonance frequency of the FR125 in the sealed box and do a textbook Linkwitz-Riley crossover at 2x the resonance frequency (thus making any effects of it engligible).
The first method might be best to avoid any nasties from the sub trying to reach up to maybe 300 Hz.
Find the resonance frequency and Q of the FR125 in the sealed box and use that to design a complementary 2nd-order electrical filter to achieve overall 4th-order Linkwitz-Riley response. Put a complementary 4th-order electrical Linkwitz-Riley filter on the sub.
OR
Find the resonance frequency of the FR125 in the sealed box and do a textbook Linkwitz-Riley crossover at 2x the resonance frequency (thus making any effects of it engligible).
The first method might be best to avoid any nasties from the sub trying to reach up to maybe 300 Hz.
Thanks for the suggestions. I'm pretty new to this, and have a lot to learn. My thought was that the 4th order on the FR125s would be better for power handling, but I'm probably looking at it too simplistically. I think I see what you are saying, that the natural roll off of the FR125s below the crossover point combined with the 4th order highpass will mean that the sub would need something like a 48dB/octave low pass to match up. Is this right?
Thanks
Adam
Thanks
Adam
No. It's that the response of the FR125 in the box will combine with the response of the filter, to end up with a response that is nothing like you thought you were getting from the textbook active filter.
I think even with my method #1 you will have plenty of volume, unless you want it really loud.
I think even with my method #1 you will have plenty of volume, unless you want it really loud.
I want it as loud as possible, without it sounding terrible. What I am aiming for is not a super "audiophile" high resolution system, I just want something that sounds musical, and good with most sources, even mp3s. I think the FR125s are part of the way there, but just need some help down low. I'll build a mike this week and measure instead of guessing. I'm still a little confused as to what sort of response you expect I would end up with using the 4th order filter, but hopefully some measurements will make it clearer. So much to learn!
If you want to know how to find the resonance frequency and Qts, I've written a white paper on my website.
If you want to know how to design the high-pass filter, the resonance frequency of the filter will be matched to (the same as) that of the speaker. Then if the speaker Qts is 0.4 for example, you make the filter Q 1.25 (determined by 0.5 / 0.4). So then the combined responses give you a total Q if 0.5 (Linkwitz Riley).
As to how to pick the components for the filter, there is a small program on my website.
If you want to know how to design the high-pass filter, the resonance frequency of the filter will be matched to (the same as) that of the speaker. Then if the speaker Qts is 0.4 for example, you make the filter Q 1.25 (determined by 0.5 / 0.4). So then the combined responses give you a total Q if 0.5 (Linkwitz Riley).
As to how to pick the components for the filter, there is a small program on my website.
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