I've always had questions on some technical descriptions on car audio components.
Can some one please explain what does it mean in plain terms and how does it affect sonic quality?

Alpine Type R speakers has: External 12dB HP Crossover

Amplifiers have: built-in 12/24 dB per octave electronic crossovers

And how does: ___db of attenuation or boost at _____hz affect anything?

What's the correct way to set the gain on the amplifier? How does it affect power output of the amp?

Is Parametric EQ differendt from a regular EQ?

And could someone make a recommenation on a sub $250 MP3 headunit w/ a 5 band Parametric EQ?

Thank You All In Advance!

 

This one is going to take a while...

1) External 12dB HP crossover: External means the crossover is in a separate box (not attached to the speakers themselves). HP means highpass...it will allow frequencies HIGHER than the figure you set to pass.

12 dB takes a bit longer to explain, but look at it this way...every 3 dB means an additional reduction in signal strength by 50%, so 12 dB means a reduction to 6.25% of the original signal strength. A 12 dB crossover means whatever frequency you set the filter to, that specific fequency will be decreased by 93.75% (6.25% of the original signal strength), and all other lower frequencies will be even less in signal strength (sine it's a HP filter).

2) built-in 12/24 dB per octave electronic crossovers: Built-in is pretty obvious. Electronic (I'm sure you've heard the terms "active" and "passive") simply means they do the filtering on the low-level (non-amplified) signal. I explained dB in 1), but the new word here is "octave".

Previously I said "all other lower frequencies will be even less in signal strength", but I didn't say by how much. Adding the word "octave" now quantifies that amount of reduction. An octave is a doubling (or halving) of frequencies. So, we can now say that frequencies at the filter frequency are 93.75% lower than those at half of that frequency. If we say 200 Hz is our filter choice, signals at 200 Hz are 93.75% lower in energy than those at 100 Hz...those at 100 Hz are 93.75% lower in energy than those at 50 Hz, ad infinitum.

24 dB/octave merely increases the amount of signal strength reduction per the previously listed formula.

3) how does ___db of attenuation or boost at _____hz affect anything? See my previous explanation in 2). However, it shoudl be noted that passive components (such as speakers) cannot have a signal boost, only attenuation. It takes an active component (such as a sound processor) to truly boost a signal.

More in the next posting...

 

...continued...

4) What's the correct way to set the gain on the amplifier? How does it affect power output of the amp? A search should pop up some old threads on this. You can do a roudh cut by ear, but best results are obtained using an oscilloscope. Essentially, you take a look at the amp output signal when the input is at a low to moderate level. Continue increasing the amp's gain until you just hit clipping, then back off the gain just a tad...this is the ideal point that will give the most power without clipping. This has NO effect, however, on the input source clipping, so watch out for it.

5) Is Parametric EQ different from a regular EQ? Yes, but whether or not you need one will depend heavily upon your specific application. A standard EQ has set frequency bands, almost always based upon octaves (a doubling of frequency for each band...25 Hz, 50 Hz, 100, Hz, 200 Hz, etc.). A parametric EQ has the frequency centers adjustable by the user, so if you're having trouble adjusting that bass just right, you could tune several bands to be right around the area of interest, say 150 Hz.

Be careful, though...things don't always work the way you think they do. Our ears are octave based, so putting three bands within a few Hz of each other may not even have a discernible or audible difference. As a not-so-far fetched example, let's say your combination of several head unit components creates interference with each other and you get a hum at 1 kHz. A standard EQ may knock the hum down, but it may still be audible. A parametric EQ could have several bands adjusted for a center frequency of 1 kHz and attenuated, thereby giving you many times more attentuation through the use of multiple filters over what a conventional EQ could have done.

Parametrics are advantageous when the number of available bands are low. Granted, I would almost always choose a nice 10-band standard EQ over a 5-band Param, but there are always exceptions.

6) could someone make a recommenation on a sub $250 MP3 headunit w/ a 5 band Parametric EQ? I'll let someone else take this one.

 

THANKS MACGYVER!!! Excellent explainations!!! Just a few more points if you could elaborate on.

on number 2.
If I'm understanding correctly than the higher decible/octive the better the frequency filtering. So why would they give you a 12/18/24 selectable attenuation <-- please substitute with proper technojargon? Is there an instance where you would want to choose a lower db filter?

on number 4.
Since I don't have a oscilloscope, how can I adjust the gain level by ear? What volume level should I use? Or does that even matter? Keep in mind I'm still using the stock headunit w/ line level converters right now. My Amp is a Xtant x403.

Thanks Again.

 

When you look at a frequency response graph, you see a line that shows the component's ability to reproduce any specific frequency at 100% (this is a VERY simplified explanation, mind you). For example, look at a subwoofer's graph...you see a line that goes roughly straight across until it starts to hit the higher frequencies, like 400-500 Hz, then it begins to dip down. If you consider the straight line from 20-400 Hz the speaker's ability to reproduce a signal at 100% efficiency, notice how its efficiency drops as the frequency continues to rise. Now, the efficiency will never be 0%, no matter how high the frequency goes, but for all intents and purposes the efficiency is SO low above, say 1 kHz that you'll never hear it.

The slope of that graph's line as it moves from "efficient" frequencies to "non-efficient" frequencies can be measured/discussed in terms of dB/octave. The more vertical (or "sharp") the slope, the higher dB/octave rolloff the filter has. So, let's say we have a speaker with a fairly sharp rolloff...we might want to match the filter's rolloff characteristics with that of the speaker. Why? If the filter rolls off more slowly compared to the speaker, we're wasting energy by sending a signal frequency the speaker cannot efficiently reproduce. If we have a filter that rolls off more sharply compared to the speaker, we're not using the speaker to its full potential (or maybe we just choose not to have that speaker reproduce as wide a range of frequencies).

To adjust the amplifier by ear, you really have to have a golden ear. If you don't have one of those (and most don't after the age of 8 ), turn the gain all of the way up, then back it off about 20%...that's the easiest/simplest way to do it. If you find you need to turn up the radio really high for your level of comfort, you need a more powerful amp, or you need to tune it with an oscope to get the last few watts of power out of it.

 

Just wanted to note that if you use the 24db/octace xover for the sub, you will put it 180 degrees out of phase from the other speakers. MacGyver is right about having "golden" ears to set the gains, but as a rule of thumb, turn the amp gain all the way down............turn your deck volume up to the point of distortion, then turn it down slightly so the signal is clean.......then..........turn the amp gain up till you achieve a clean sound. If you hear distortion, turn the gain on the amp down a bit. Just remember that the "gain" adjustments are NOT volume controls.............they merely match the deck to the amp. As far as parametric eq's go, unless you have an analyzer to "see" what the curves look like, you would be better off with a graphic eq although I dont see a real reason to have one in most installs. Most eq's cause more problems than they solve................as an example, MacGyver stated that a 12db/octave xover decreases the sound energy by 97% at some adjoining frequencys..............just imagine if you use an eq to boost the bass at 100hz by 12db?..................you're asking your amp to put out 16 times what it's rated power is at that frequency! Thats how speakers are damaged and tweeters are fried. Good luck, and if you have any other questions, find a reputable installer in your area to help you through the "techie" stuff............................................. .................................................. .Bob

 

Not quite. A 12 dB/octave filter will cause a 180 degree phase shift, a 24 dB/octave filter will cause a 360 degree phase shift (or 0 degrees). So, if phase shift is an issue with the system, a 4th-order system (24 dB/octave) is preferrable (at least from that standpoint).

The problem with 4th-order systems is the price increases significantly for low frequency/high power filters. If you decide to go with a 2nd-order system (12 dB/octave), wire the speakers out of phase (+ to - and - to +) and your problem is solved.

Six of one, half dozen of the other. Either method accomplishes practically the same goal, so it's more a matter of personal preference. Your method will probably get a larger dynamic range out of the amplifier, but it also requires listening to an audio signal at the near extremes of the amp's capabilities to tune it. This is going to be interesting, to say the least, if it's a powerful amp and you crank up the volume just to listen for some distortion...personally, I'd rather waste a few Watts and preserve my hearing.

Parametrics should probably be used in the car domain, if ever, only when doing some sort of audio quality contest...even then, its usefulness is questionable. However, while an EQ can cause more problems than they solve for the inexperienced user, the experienced user should find the EQ an invaluable tuning tool. It's a tool used not only to help mask deficiencies in other components and/or the source signal, but to allow tailoring that sound to the user's taste. To otherwise dismiss all EQs out of hand is pushing it.

You are doing no such thing! What you are doing is increasing the SIGNAL STRENGTH at that frequency (for the moment I'm disregarding the increase in signal strength of surrounding frequencies)...the EQ does not control what the amplifier does, it only modifies the input signal. You may have to turn down the stereo's volume control to avoid overdriving the amplifier, but that's no different than if the stereo was playing a louder musical passage. You wouldn't listen to a very quiet violin passage at max volume, and then expect the amplifier to compensate automatically when a cymbal crash is played, would you? Certainly not, so if you modify the input signal's strength at certain frequencies, you have to adjust the overall signal strength to avoid overdriving the next component down the line.

Well, overdriving the amplifier into heavy distortion is certainly not a good thing for the speakers, but that situation can be avoided through my comments above.

Agreed...but it's difficult to know who is giving you quality information to begin with. Even the most intelligent sounding explanation can be completely wrong if you don't know the right questions to ask. If you ever get confused, ask on here and you'll eventually get the correct info...

 

Good installers are really hard to find. *sigh* that's why after I had my system installed (CDT-CL61, Xtant 403, Wlaurent Enclosure w/ E8A) I felt the need to understand more so I can tune the system to my liking. But whether it's due to better system and/or signal quality of the stock HU, my mp3 based audio cd's just don't seem to sound as good. That's why I'm looking for a new HU and plan to do the install myself with the help of the Lucid DCI.

Based on the above information you gentlemen provided, I now have a few more questions.

1. How does 4V pre-out affect amplifier efficiency/sound quality?

2. What's the easiest way to test for speakers that's out of phase? Is it audioable? Or do you have to use test equipment?

3. With the ever changing audio characteristics of our car - top up, top down, top down window up, top down window down etc... won't a EQ, parametric or otherwise be helpful in tunning sounds to these different environments?

4. Will either of you be moving so SoCal anytime soon?

Thanks

 

1) The higher the pre-out voltage, the better off you are (assuming your amplifier can handle the voltage levels). Look at it this way, would you rather travel down a gravel road on a tricycle or a huge 4-wheeler? The 4-wheeler is going to give a smoother ride because its shocks/suspension offers more room to move compared to the size of the rocks on the road. This is the same with pre-outs...you want as much voltage as possible (the shocks) when you compare it to the size of the noise on the line (the rocks). Once you hit the amplifier, we're talking 10's of volts, so a few millivolts of noise on the line won't make much difference (kind of like riding in BigFoot ). It has no effect on the amplifier's efficiency other than to say the amplifier is now amplifying more of the true signal instead of a higher level of noise versus signal.

2) There's no need to test for it. Your speaker will be labeled with +/- as well as the amplifier...merely swap the leads. I'll be honest, though...in the grand scheme of things, you'll be hard-pressed to notice the difference.

3) I definitely recommend an EQ for almost every application that involves more than a Radio Shack brand component, for exactly the reasons you mention. However, unless your EQ has several settings and you plan on swapping between them with every change in the environment, you'll have to compromise on the sound quality for most of the environments. Even with the varied environments, you can still enhance your sound significantly with an EQ.

4) I'd love to at some point...it all depends on if I decide to open up a West coast branch

 

Hmmmmmmmmm......................come on MacGyver..................that makes a HUGE difference!