I want to fill a 4dB hole between 400Hz and 150Hz on a pair of mids, and then roll them off second order below 150Hz. I have been using a passive shelf along with a passive first order high pass to do this so far. If I go active and combine the job into a single high Q high pass filter that has a 4dB peak, will it sound OK?
Is your mid cabinet about 12 to 14 inches wide? The dip might be a baffle step, in which case a shelf is the right thing to correct it. We'd be able to figure out what was happening if you showed response curves.
In other news, a high Q highpass won't solve your problems: a 4 dB peak woud be much narrower than the hole you're trying to fill. Without calculating, I'd guess it'd be about a half octave wide at best,while your hole is three times that.
In other news, a high Q highpass won't solve your problems: a 4 dB peak woud be much narrower than the hole you're trying to fill. Without calculating, I'd guess it'd be about a half octave wide at best,while your hole is three times that.
It's really not that high-Q for 4dB. Looking at a 2nd order high-pass, Q around 1.5, F3 around 140Hz will give +4dB about 230Hz and is effective from about 150Hz-500Hz. Trouble is, it's not symmetrical. Roll off is steeper on the low end, and more gradual above the peak.
I wonder how low the mids need to go...
Not bad, though. And after all, this is car audio. Lots of unpredictables, close is often good enough.
I wonder how low the mids need to go...
Not bad, though. And after all, this is car audio. Lots of unpredictables, close is often good enough.
OK, these are midwoofers in the front doors. I tested them by sitting in the drivers seat with an RS meter and a sine wave generator. The dip at 400Hz was sudden but I didn't expect measuring a car to be easy. It looks to me just like a baffle step.
The linkwitz transform sounds ideal except for one thing. The passive crossover is working well for me except that the drivers bottom out at higher volumes (they are not perfectly sealed in the doors and are compliant drivers). I just need a few more dB to be happy. While I am crossing them over, I really need the 2nd order for power handling.
I tried simming it with passive components but it isn't easy to get a good peak at 400Hz and a significant drop by 80Hz using only passives.
The linkwitz transform sounds ideal except for one thing. The passive crossover is working well for me except that the drivers bottom out at higher volumes (they are not perfectly sealed in the doors and are compliant drivers). I just need a few more dB to be happy. While I am crossing them over, I really need the 2nd order for power handling.
I tried simming it with passive components but it isn't easy to get a good peak at 400Hz and a significant drop by 80Hz using only passives.
About the possible wavelength null, do you think it could be the way I've mounted them? These are six inch drivers and I've drilled and tapped holes in the rear of the magnet then epoxied and bolted them to a bracket that mounts on to a reinforced section of the door. They do not touch the trim and the fronts of the drivers are free. There is a small gap in front of them that could allow front to rear cancellation.
The original drivers were mounted this way. If anything, they sound more solidly mounted than if they were on the trims.
One thing though, the original speakers had open cell foam stuck around the outside of the roll surround, reaching forward to the trim. Maybe I should try this.
I haven't been able to re-measure yet but if this is the case, will I just have to live with EQing for my location at the expense of complexity and other seats sounding out of balance?
This problem also goes for my sub/woofer. I wish it didn't sound so much louder in the back.
EDIT: Maybe I should stuff my doors, they could be causing not only cancellation but peaks in the upper midrange?
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OK, that's great. 
I've been working on smoothing the upper midrange and the sound seems to be coming together. The problem in the lower midrange is less of a concern and I've been able to get back to listening. I adjusted my crossover to ease the lower mids back up a little. Just a few more tweaks, I think...
I've been working on smoothing the upper midrange and the sound seems to be coming together. The problem in the lower midrange is less of a concern and I've been able to get back to listening. I adjusted my crossover to ease the lower mids back up a little. Just a few more tweaks, I think...
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