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Finally I get into an "almost done" stage for car stereo. In the past 2 years, I've been searching and searching for setting up car stereo in proper ways, mainly on stage issues, and kept experiment on the concepts. Now I wish I can have my experience summarized and pass it on to some potential SQ lovers. If anybody see any error in my idea, please correct me. Thanks.

 
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Head Unit

The main differences in head unit are DAC and output voltage. Nothing more. The quality of DAC will dominate dynamic range, as well as signal-to-noise ratio. Look for GOOD QUALITY 16-bit or 24-bit DAC. A 24-bit 192kHz DAC does NOT imply quality. If possible, have the DAC chip number checked at Texas Instrument(TI) and check the spec of the chip before thinking of the quality. Don't be confused by Alpine's 1-bit Regulated DAC and MDAC. 1-bit Regulated DAC is actually a 16-bit chip. MDAC is Multi-Level DAC, which has a MAXIMUM (yes, maximum, depending on source) resolution of 24-bit 96kHz. 20-bit DAC used in some older head units are Sign-Magnitude Delta-Sigma are MDAC also.

Output voltage should be at least 2 volts, and 4 volts is preferred. When matching with amplifier, there is no need to have the output voltage higher than the maximum input voltage of the amp.

 
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Amplifier

Power output of an amp should be slightly above RMS power handling. Why? Just to make sure it will be: 1. loud enough; 2. provide enough headroom for possible equalization.

My experience with it was with my CDA-9815 and Alpine MRV-F540 pushing SPX-177A. HU was 4 volt max out, while the amp is 4 volt max in. Output rating was 80W@14.4V and 50W@12V, where my car's constant output is around 13.5V, so expect about 60W into the speaker. The speaker's RMS handling was 60W. I turned the gain into minimum, where there must be a point the head unit matched with the amp. Well, I played some tracks that wasn't loud enough. I eventually turned my HU into maximum(35), but it gives me no low end. I turned the bass up a little(well, didn't care of clipping at that moment, because Alpine put a light bulb on the tweeter line, so should be no problem), guess what? The entire system volume decreases as I turn up the bass. Funny huh?

Running active crossover, however, do NOT need that much power to run the speaker.

A good quality amp is not marked by power output, but marked by the damping factor. How well it will control the cone movement is more important than how much power it is giving out.

 
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Hey man, can you elaborate on this a bit more? What do you mean by controlling the cone movement? How do you know which amp controls the cone movement better??
Thanks

 
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Speaker and speaker install

A good sounding speaker doesn't mean it is expensive. As most people say, 10% equipment, 90% install. It is true until last year when I discover a fact: In Civic and most cars with huge reflections, it is better to think about how to install speaker sets, and it really is a challenge to do it.

Well, the most convenient way to install speaker in kick panel is by Q-form. However, as opposed to what Q-Logic has been saying, Q-forms are NOT plug-n-play. Tuning is still required using ordinary installation techniques, including attenuation, polarity switch, and some custom work to seal the panel. If you are like me, having Dyns 3-way system, or having some dome mid range, then you are in luck with it, because it will save you a lot of time in fabricating the rear of the panel.

Anyway, let's go with the phase issue because it makes me getting into the latest stage. I got the thread on phase matching by WhiteRabbit(?? or other one, I forgot) on elitecaraudio.com so I started to work with it. I requires time to do get the phase correctly. Once they are correct, you should not hear anything that will smear the sound stage, either to one side or another. Mid/tweet should be consistent at one place.

However, I think that the midbass on OUR DOOR are kind of "out of phase" with each other(not close to 180 but not close to 0 either) automatically when a speaker is installed there. So switching the phase on one woofer will change the sound stage dramatically. Working with tweeter and mid is hard, but take a note here. In a system, if you hear a "center" vocalist standing on one side, switch the phase of the tweeter on that side. Most crossovers today are using 6-dB low pass for mid and 12-dB high pass for tweeter. In theory, they are automatically 90 degree out of phase no matter what. The 90 degrees means that, either you will have it summed (-90 and -180)or canceled(not completely, -90 and +180). Take into account that sum (boost) is bad and cancel is better, let them cancel each other a little since it's not a complete cancellation.

Tweeter and midrange attenuation is very important after this step. In my car's speaker in Q-form, my driver's side tweeter is louder while my passenger side midrange is louder. It is very important to have them corrected either by passive/active or equalization.

Next is subwoofer question. By my experiment using IASCA 01-02 track 32(low freq test track) and the spectrum analyzer, the car is boosting front speaker's low frequency for as much as 12dB(yes, 12dB). It is mostly heard in 80Hz range. I think most of the shop will tell you 80Hz to cross between sub and front stage will work. I am sure it will NOT work in our car. However, the problem seems occur in driver's side only. No idea why, but it is the fact. A 12-dB/Oct HP at any frequency around 80Hz will NOT work at all. Because of the boost, not only the low frequency seems coming from the driver's side, the image also pulls to the driver's side(if all of the above steps have been done). Leave the sub LP at 80Hz will be good, however. I've been thinking about it for a while. Here's my solutions:
1. 24-dB/oct HP at 125Hz(so 80Hz will not have effect on that) and LP at 125Hz on sub.
2. 24-dB/oct HP at 125Hz on drvier's side while keeping 80Hz 24-dB/Oct HP on passenger side, leave the sub at 80.
Either way will make the system sound much better, but crossing the mid-bass at 125Hz on both side doesn't seem making any sense. I am still in trial and error stage on this, so I will probably be able to provide an answer in the future.

 
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Equaliztion

In Civic, equalization is very important. Any frequency that is louder in one side will dramatically shift your brain into that area. For example, midbass range, around 250Hz, the vocalist will sing with the midrange at the center while you hear the "ummm" sound coming from your left leg. That is caused by a boost. Another example, listening to female supprono(high octave), when she sings "ahhh" for a while, she will eventually sings into the passenger side speaker with all the reflections. It is the boost at around 800Hz on the passenger side. Eventually, all Civics have to have heavy equalization due to the interior.

 
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Subwoofer

Thinking to get a very powerful amp and very powerful sub? Think again. If you are in SQ, you are not going to use any high power subwoofers. Subwoofer requires box to play, everybody knows that. However, not everybody knows the car interior itself is another subwoofer. The more compact the car is, the more "air tight" box it will be. If you go to Image Dynamics' website look for subwoofer spec, it will tell you that in a car it will have 14Hz F3 while open air it will have 47Hz F3. F3 is the point where frequency is reduced at 3 dB using recommended box volume. Why it happens? It's the car that is boosting the low frequencies. But I mentioned "air tight" before. What I mean is this: the car automatically boosts the very low frequency to make the sub bass sound "flat"; it will, however, boost ANY frequency that plays into it. Most subwoofer has the tendency of playing higher frequency(80-200Hz) than low frequency. Turning up the sub will make the bass sound tight, but sometimes it will just make it too tight, like every bass hit will punch your back. That's not good for SQ, but it may be fun for some people, for a while(I know it's for a while, because eventually one will get very tired of it and look for quality other than all the booms at 80Hz). So the idea in tuning sub: keep it low, keep it reasonable, and tune it to "only recognize its presense" will be the best.

 
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Speaker Q

Speaker Q is specified in almost all speaker system. Q value represents the damping control of the cone itself. In vibration theory, everything has its own resonance frequency. At resonance frequency, if no damping is used (Q->infinity) it will just keep vibrating forever, and the gain(vibration) will grow without bound in time domain at resonance frequency. A definition in Q is "magnitude of self gain(peak amplitude) right before resonance frequency given the input is at the same resonance frequency"(w=w(n)).

A general equation for Q is 1/(2*zeta), where zeta is the damping factor. Q>1 means the speaker is under-damped, which the speaker will vibrate but controlled to dimish over a time period. Q=1 means the speaker is critically damped. Any slight change on the speaker itself will push it into under-damped situation. Q<1 means the speaker is over-damped. Almost all "total Q" of speakers are over-damped. However, mechanically(Qms), speakers will not be over-damped. Only electrical Q(Qes) can be over damped, due to the inductance(high impedance).

Mechanically speaking, a high Qms speaker will have its peak amplitude(linear x) higher than other frequency in reference of 1. Saying clearly, if a speaker has magitude of 1 and Q=1 (damping factor=0.5), at resonance freqency it will have 0.5 times of the output. 0.5 times in audio means automatic 3dB down. Doubling the Q (Q=2) will make it a 1 time (same output) at resonance frequency. Doubling again will be 4 times (theroretically 3dB higher) the previous output, etc.

Expecting higher output at resonace frequency for higher Qms? Not really. Take electrical Q into account, where it is generally very small and well over-damped by inductance, it will make current extremely hard to pass through. Impedance rises from 4-ohm all the way up to 16-ohm, which translate to 1/4 of the power from 4-ohm load. 1/4 of the power automatically gurantees a 6dB loss. So it requires very high Qms to compensate for flat frequency at resonance.

High Qms do not sound good at all. Given a Qms of 2 and Qms of 9, a Qms of 2 will have higher cutoff frequency but will sound whole lot better. Why? because the higher the Qms is, the narrower its peak will be, so distribution is not even across the affected region. Developing low Qms requires a lot of tuning and experiments, so speakers with low Qms generally are much more expensive than those with high Qms. To make speakers sound better, try to avoid powering the resonance frequency(Fs), especially on high Qms speakers.

 
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I don't have the time to read through that all right now, but I strongly suggest you edit the post and put everything in one single post, organized and in different sections with bold headings. I bet you got a lot great info here, I'll read it tonight.

 
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The thing i hate about radios is that no one rates there rca preout voltage accuratelly. which this bothers me becasue a 4volt preout can really be like 1 volt rms or less. i have an amp with 8 volt input, but my deck which says 2volts is actually less then 1 which does nothing for me.

so i bought an audio control matrix which uped my voltage to about 5 volts rms and let me keep my radio volume and amp gain down dramatically which provided me with better sound all around and less distortion and way better SQ.

 
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I guess it's true because I always put my amp gain to minimum. The output volume from DVA-7996 head unit and PXA-H701(using digital input, so no analog gain) are really 2 different stories at the same gain.

 
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you can put all the right components in your car, install them correctly, however, it takes someone with extreme knowledge and a great ear to properly tune a system for sound quality. it took my installer over an hour to tune my car and he is one of the top ten tuners in the US.

 
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I have checked that the "damping factor" of amplifier refers to "the ability of amplifier to cancel out the voltage speaker PRODUCES." Yes, produces. Speakers can generate voltage just like a microphone does, and actually a speaker can be used as a microphone. If you dare to try, connect s speaker to line level input of another channel on the amp and increase the gain slowly, push gently on the cone, you will actually hear another speaker playing. The problem now goes to how much mid/high a woofer receives and sends back to the amp then playing it out again.

 
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Some new stuffs if you read it.

No matter what kind of speaker you install in the door metal panel, even with 1/2" spacer, the speaker will still be sitting deep inside with respect to the plastic door panel. What it means is that, you are being blocked from ALL direct sound path of ANY speaker sitting on metal panel, on the side where you are sitting. A good work around is that, make a 1 1/4" 155mm spacer(same as the stock speaker, take a look if you still have that sitting somwhere), use resin or silicon to seal it with the door panel, screw it also, then put the speaker on top with that. That will make the speaker sitting inside the plastic door speaker ring, and it will be on the surface with when you put the plastic panel back, instead of sitting deep inside and the lower door pocket blocks the sound path.

However, since it must be 155mm, any speaker that is bigger than 6" will NOT work. I realized this after I trimmed off the speaker "grill" on the plastic panel.

 
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again, I can't stress to you enough how much it will clean up your thread to edit your original post and put all of your information in one post with clear descriptive headings.

 
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I think it would also be a good idea to rank the importance of each part of the car. for example, how cna anyone here expect to pay for an amp with a high slew rate and expect the gain a large bump in performance when they are running infinity reference speakers in the rear deck and nothing up front?

I think a ranking will help those here looking to get that next bit of performance from their stereo know exactly what they should do to achieve the max benefit for their investment, whether thats time or effort.

HondaSales, I agree with your point in its entirety. Should we perhaps have an older sister thread to this one to explain how to position speakers properly? this will allow for the first step, coupled with this one, equipment choice, then finally a younger sister thread to explain the principles of tuning as seen by members of this board? I think the three together would be a pretty decent resource for practical solutions to novice tuners.

 
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Well, I am not a good writer, pardon me. I am not good in any of my technical writing classes.

BTW, I switched from passive to active and the system still doesn't sound right, then I figured out it must be the installation.

 
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it would also be a good idea to qualify the word "installation" too, for those here in the dark. We shouldnt have people in here making sure they have a really good ground, separating power and RCA's, making sure the speakers have a solid mount and well separated backwave to again be running JUST coaxials in the rear deck

 
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Good point, and there shouldn't be people in here paying $200+ plus for components and zip-tying them to the doors either.