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  #1  
Old 16th March 2008
saabiah04 saabiah04 is offline
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Default Aftermarket Amplifier Settings

ref: previous post on my audio project: http://www.saabcentral.com/forums/sh...d.php?t=122745

The amplifier that I am using (Alpine MRP-F250), is a 4-channel 40W RMS X4, and has built in line-level conversion as well as an integrated crossover.

The settings on said crossover:
Subsonic Filter: 15Hz (Fixed)
EQ (Equalizer): Bass EQ (Fixed Frequency): 50Hz 0 to +12dB(3/4ch.), On/Off
Crossover: 50-400Hz, HP/LP/Off (12dB/oct.)
My question is this: How do I use these adjustable dials (1 for channels 1-2, another for channels 3-4) to optimize the sound quality? Note that the signal going into channels 1+2 come from the rear deck, and channels 3+4 get their signal from the AMP1. I am just trying to figure out what these adjustments do, and how i can use them to my advantage. Any help would be greatly appreciated!
-Scotty
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  #2  
Old 16th March 2008
JMachan JMachan is offline
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Hi Scotty...

Subsonic Filter @ 15 Hz - This is what's referred to as a high-pass filter. That is, it permits signals >15Hz or so to pass attenuated. Frequencies lower than this are increasingly attenuated as it they get lower (there may be some reference to dB per octave or the like). It's labelled "subsonic" because 15Hz is below the audible spectrum of your average human being. The idea is that, since you can't hear it anyway, why send it to a speaker. Save the power, generate less heat, and avoid sending anything that would tear you speaker apart. It makes sense to engage this unless you've got some serious subwoofer stuff going on, in which case some of that subsonic stuff is still felt...great for organ music.

Bass EQ - just boosts the frequencies around 50 Hz zero to +12 db. The manual may tell you the exact function form, but it's probably fairly tight around that 50 Hz. A lot of subwoofers/speakers are less responsive as you get towards these lower frequencies, so the boost may help compensate for this. It's also a frequency that figures into a lot of the bigger tams (drums) and bass drum...but it's also pretty tough on smaller speakers.

Crossover: 50-400Hz, HP/LP/Off (12dB/oct.) - same as the 15Hz description of the filter, with the differences being:
1) you can change the frequency from 50Hz-400 Hz
2) you can choose whether you pass frequencies higher than this unattenuated (HP) or lower (LP)...or you can just shut it off entirely and apply no attenuation whatsoever.

The rear deck...if you're talking about the 6x9s, I think that's already a low-pass signal (not great to work with). If you're talking about the 4" then it's either full range (best) or high pass (not so hot)...I don't know what's being sent to those for sure.
In general, you're going to want to input a full range signal in order to have all the options on the table.

I'll look at your old post soon as there may be more info and will allow me to be more specific, but right now my wife is almost done with her ice cream and will probably want to watch some junk TV. I better go...
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Old 16th March 2008
JMachan JMachan is offline
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Okay...the baby needed feeding so my wife's doing that. Geve me a chance to review the last post...I remember it now.

Here's not only what I would do, but it's what I did in my 1999 9-3. I have a similar amp (MRV-F400)...and was also running small dash speakers...smaller even. I was using a 3" and a separate tweeter at each location with their own passive crossover. I was also running those with my HP from the alpine up at around 150-200 Hz.

So, if it were me I would:

Channels 1+2) Pull a full-range signal off the front 3.5" by running the wire all the way to the amp...then run wire back up to your dash and power your front 3.5" using the alpine amp with the HP filter set to about 150-200Hz. Start at 400Hz with some bassy music and decrease the frequency until it doesn't seem to make a difference in the sound anymore...and then give in 1/8 of a turn or so back...if you come across music that makes those guys pop, turn it back up until it doesn't.

Channels 3+4) Pull the full-range signal off hte rear 4" (like you've already done). Buy some nice BA 6.5" coaxials (same line as the dash). Intall them in the doors and power them with alpine with the crossover in the off position and the subsonic filter on.
...Alternatively...
Channels 3+4) Pull the full-range signal off the rear 4" (like you've already done). Buy some nice 6.5" 4 ohm woofers/midbass driverz. Intall them in the doors and power them with alpine with the crossover in the LP position at a point close to the HP position of 1+2...and the subsonic filter on.

Listen...then, if you want more bass, buy yourself a 2 channel amp (I know I know, sucks, but they're pretty cheap). I don't know the specifics of the amp1 output. It could be low-pass or band-pass (combined HP & LP). If it's the one powering the 6x9s, then it's probably low-pass...and that would be good. Pull the low-pass off of AMP1 and use it as input to your new 2 channel amp. Run the 6x9s off that amp...no additional filtering will probably be needed. Now, the 6x9s you have now are coaxial right? If so, you really won't be using the tweeter section, but we're really just trying to get some bass by taking advantage of that nice big trunk, anyway. If you really want to get crazy, Tang Band has some 6x9 subwoofers you could try instead. I haven' heard them, but they do make me curious. I remember my 1981 Cutlass in high school...big trunk...made my God-aweful Pioneer 4x10s sound like I had a sub in the trunk. A large chamber is not to be underestimated. ...and what the heck, leave in those 4" without any power to them as passive radiators...while we're getting crazy.

A car cabin is a funky thing. Sometimes you get lucky and love exactly what you do the first time...sometimes it takes experimemtation...or compromise. I've got the bug, so I'm constantly in search of an ever better sounding configuration...and it can be contageous. Raw drivers from places like partsexpress and madisound can help keep costs down...and you can end up with better quality pieces.

Good luck! I hope this helps.
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  #4  
Old 17th March 2008
JMachan JMachan is offline
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I should clarify regarding "what I did"...I didn't use any factory stuff. I'm sorry, it was getting late for me. What I was referring to was only the speaker sizes and locations...not which lines I pulled signal from. Sorry I wasn't clear.
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Old 17th March 2008
saabiah04 saabiah04 is offline
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In fact, you were quite clear, not to mention extremely informative. It's too bad that I will only be using the BA 6x9's for the Bass. I don't have the receipt, and got the premium (SX) set which has a set of 2 integrated tweaters on top.

I set the amp to LP, at a crossover of 200, which has really added depth to the cabin, without having the highs overpowering the stock system and producing a rear stage. So, as you suggested, I am going to play around. I plan on pulling the front dash lines and running them to the back to power the 6x9s (I know this is a waste of their bass abilities. But, they are full-range speakers with phenomenal sound quality. If this works, I'll probably bridge the remaining two channels, and add an amp.

I like your idea of amping up the front - but that might be a project for a later time.


-Scotty
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