Setting crossovers in a Miata

[cwsanfor]

I realize that the usual advice is “change the settings and go by your ears”, but I’m such a novice that I’d like to get some opinions about what settings to start from.

I have a 2000 base Miata with:
1) Alpine CDE-105B head unit (http://support.alpine-usa.com/produc...E-103BT_EN.pdf),
2) Alpine PDX-F4 amp (http://support.alpine-usa.com/produc...0PDX-F6_F4.pdf), bridged to provide 200 WRMS at 4 ohm to the sub,
3) Polk db571 full range 5x7 door speakers (http://www.polkaudio.com/caraudio/sp...systems/db571/),
4) Polk dB1001 tweeters (http://www.polkaudio.com/caraudio/db/specs.php) wired in parallel with the db571’s, presenting 4 ohms, and
5) Bazooka BT6028DVC 6 inch 8 ohm Dual Passive Tube subwoofer in the trunk, (http://www.bazooka.com/products/mobi...ssive-Tube-P26) wired parallel presenting 4 ohms.

a) The HU (CDE-105B) amp is off. It has these settings:
i) bass center frequency = 80 Hz, 100 Hz, 200 Hz, 60 Hz,
ii) bass bandwidth = 1, 2, 3, 4 (narrow to wide),
iii) treble center frequency = 10.0 kHz ,12.5 kHz, 15.0 kHz, 17.5 kHz,
iv) high pass filter frequency = OFF, 60 Hz, 80 Hz, 100 Hz,
v) loudness contour = on/off,
vi) defeat = on/off.
b) The amp (PDX-F4) has a crossover, variable, 30-400Hz (-12dB / oct ), Low-Pass/High-Pass/OFF for both front and rear channels. Front channels are set to Low-Pass 80Hz.. Rear (sub) channel is currently set to High-Pass 80 Hz,
c) Front speakers have a range of 52Hz-22kHz and a sensitivity of 93db,
d) Tweeters have a range of 4kHz-23kHz,
e) Sub has sensitivity = 100 dB , and frequency response = 35Hz-250Hz.

I have two pair of Harrison Labs FMOD High Pass Crossovers (12db per octave slope, one pair 30 Hz, the other 50 Hz, one pair to be returned) that I plan to put in series with the sub for eliminating infrasonics, and a Brand-X LXSCAP17 1.7-Farad Capacitor for the amp.

Whew. So my question is: What do I do with all these settings? Should I:
I) Overlap the front and sub channels on the amp, say 100 Hz HPF for the sub and 80 Hz LPF for the fronts, per http://www.soundstage.com/maxdb/maxdb200101.htm, or set them both to 80?
II) Set the amp’s bass center frequency to 80 Hz with the widest possible amount of boost, and the treble frequency emphasis to 15 kHz or 17 kHz, per http://www.caraudio.com/forum/head-u...equencies.html?
III) Bazooka Tech Support recommends the 30 Hz bass blocker, so that seems easy, the 50 Hz one goes back to Amazon ... My first thought was since these are first level devices, the rolloff would be higher at frequencies below the nominal, say 50 Hz, so I would go with 50.

Also, lacking an oscilloscope like Richard Clark recommends at http://www.davidnavone.com/heresHow/...evelSet222.pdf, I had to resort to a procedure like that at http://www.polkaudio.com/forums/showthread.php?t=17905, “turn it up til it distorts then back it off”, except that I could not get any distortion at sound levels I could stand. I can’t find anyone around here who has or is willing to use a scope, and don’t really want to buy one for a single use.

I appreciate you reading this far, and would appreciate your comments even more.

[Installer4life]

The idea of the scope is good but not necessary with what you have. Lets start with the tube. Most ported enclosures work best 1/2 octave above and below the tuning frequency. since the frequency range of this tube starts at 35HZ we can assume that the tuning frequency is around 52 hz so that means best case is from 35hz to 70hz or so. Based on this info I would use the low pass crossover on the radio or the amp but not both at around 80 hz. Also I would set the bass center frequency at 60hz because you can't go any lower. As far as the tweeters are concerned use the passive crossovers that come with them. The 5X7's I would start at the same crossover point of 80HZ and see how they sound. I would think no higher than 100hz unless you listen to a lot of rap. If you look at the gain controls on the amp you will see the letters NOM. That is the starting point I would use with the headunit because it has a 2volt preamp output. You do not want to go any higher but you could go one line counter clockwise. The center frequency for the treble is a toss up. Most factory decks has this point at 10,000hz which isn't bad. I would start here then maybe try 12.5. I don't it will make any difference at 60MPH. Select 1 on the bass "Q" to keep it as narrow as possible so that only the Tube is affected. The reason Bazooka wants the subsonic filter is that below 35hz that tube sounds like trash. You have a nice little system but I don't think it will be enough for you at highway speeds. The Polk 5X7 will work best with a crossover point above 80hz. That 50hz note is a little to much for it. One correction you have the front channels listed as low pass and the rear (sub) listed as high pass but you have those reversed. The subchannel plays below 80hz and the 5X7's play above 80hz.

[cwsanfor]

Thanks much, installer. That makes sense. If you only do this once every 10 years it's hard to keep everything straight. I would turn this over to a pro next time.

cwsanfor

[Installer4life]

I know how that is. There is a lot of information available on the web but very little of it is useful most of the time. You have a nice simple system and you should treat it as such. Some people get carried away with a little knowledge but I try to give advice that people can use and is easy to understand..