I completed my install in my '02 Ram several months ago. I set up the amp gains according to the FAQ entry. I turned the gain up not to a distortion level at 0dB, but to the loudest that I thought I would ever listen to it.

When driving, I usually have the volume set at -19dB. I'm not really into the bleeding ear effect. However, when I was attempting to entertain last weekend, I realized that it simply wasn't loud enough, even with the doors open. Sound was mostly lost beyond 10 or 20 feet. It was blaring in the truck, but still.

I realize that I could set the gain higher, but I'd like to have some evidence showing just how high and how loud I could go. I'd like to see a correlation, if any, between the RMS ratings of the amp and the RMS ratings of the speakers. I'm also interested in crossover settings. Keep in mind that this is all coming from a guy who has yet to tweak the Empeg EQ.

To break it down:

Amp 50X4 + 200X1 RMS
Fronts 2-90 RMS 45-21,000Hz 90dB Sensitivity
Rears 2-75 RMS 45-22,000Hz 90dB Sensitivity
Sub 75-350 RMS 18-200Hz 94dB Sensitivity

So that's what I've got. Having never really worked with car stereo before, I'm almost clueless where to place crossovers, filters, etc. on the amp. Here's a closeup of the dials on the amp. As of right now, I have all of the gains set to nominal. I'm not sure about the filters. I think I have those correct, for a system with a subwoofer. As for the crossover point for channels 1-4 and 5, I'm clueless about where to set those. I believe I have them set around 170 or so. I'm assuming at least that all three should be set to the same level? The subsonic filter is set at OFF, but I'll be switching that to 15Hz as the sub apparently can't reproduce notes that low anyway. The Bass EQ is basically a personal preference, I wish it had a wired remote for that.

So the amp is rated at 50W RMS for channels 1-4, whereas the speakers are rated at 2-75 and 2-90 each. Is this a problem? Does that mean that the amp isn't powerful enough to blow them, or just that the amp isn't powerful enough? As for the sub channel, the amp is 200W RMS, the sub is 75-350W RMS, same question there.

If anyone knows of an online calculator to figure this out, or any other methods to answering the dozens of questions I have, feel free to share your wisdom. I'd go to the local installer, but from what I've heard, you don't want them to know what you have in your system if they already know your address.

Greetings!

An excellent question. And one I would like to know more about also. I am a novice at car audio (yes, the empeg was my first non-factory radio - I do not like settling for "second best"...), and I would like to learn more about sizing and tuning amps and speakers as well.

Yes, I know - look for the distortion point and turn it down. Unfortunately, I would like to know more. How do you know if your amp is powerful enough? What do the speaker ratings mean? Really basic stuff that I would appreciate if someone could point me to a good tutorial.

And, one step beyond that, some advice on what to look / listen for to isolate and identify problems with your installation.

As far as I've understood it, the RMS ratings are what the speakers are supposed to be able to handle "all day long", but I doubt they'll actually take it if you played a constant sinuswave at the rated RMS power - it definately differs between brands. A lot depends on the fact that music is very dynamic and don't stay at max for long...

Try this: play a 0dB test track of a suitable frequency (you can disconnect the speakers if you want to gp easy on your hearing) and measure the AC voltage on the speaker output. If you have a graph of exact speaker impedance vs frequency, look up the impedance for that frequency. If you don't have that (and the manufacturer doesn't have it on the web), use the nominal impedance (4 Ohm, 2 Ohm...). Calculate the power P as U^2/Z where U is RMS voltage measured, and Z is the impedance.

Adjust gain until voltage read corresponds to the rated power (or power given on birthsheet of amp. You might want to check the voltage fed to the amp, as many manufacturers give different power ratings depending on supply voltage to amp) U = sqrt(PxZ). Reconnect speakers and play music. You might well find that it is lower than you expected - we're not very sensitive to minor clipping in music, so you might well have it set a bit into clipping as it is today...

As for the filters, I'd highpass the fronts to keep them from playing the lowest bass, which they usually don't handle to well in the doors. Depending on the rear speakers I'd consider doing the same. Sub channel (5) looks to be always low pass filtered, just select the crossover frequency. If your sub is in a ported box, turn on the subs sonic filter. IF your box is tuned above 35 or so Hz, set the filter to 30Hz, if tuned lower than that, set it to 15Hz.
If it's a sealed box, just leave the sub sonic filter off.

/Michael

The crossover point is the point where high/low frequencies are separated, correct? So if you set the sub crossover to 150 Hz, anything higher than that would be omitted from going to the sub.

So wouldn't you want the crossover point on the fronts to be set at 150 Hz as well? This would block anything below 150 Hz? Or would that block above 150 Hz? I guess I'm a little confused about how crossovers actually work. There must be something I'm missing, or they wouldn't have put three crossovers on the amp. I guess so you can set a different level for each pair of speakers...but do crossovers block out higher frequencies, or lower frequencies?

I just assumed for the sub channel it would block the higher frequencies, and for the fronts and rears it would block the low frequencies.

Another thing, my sub is in a ported box, so the Subsonic filter at OFF is the correct position. But if the crossover only goes down to 30 Hz, then there shouldn't be anything going to the sub lower than that. So why the need for the filter? They say that the subsonic filter removes frequencies not audible to the human ear. These frequencies are only robbing power from the amp. So I guess the new question is, how do the subsonic filter and crossover relate?

So because the RMS ratings of the amp are lower than those of each speaker, I could run the amp at full power without blowing the speakers? But I would probably fry the amp? I guess that's my question. If the gain on the amp was set to Max, what does that actually mean in terms of wattage transferred to the speakers? Would that be the max rating for the amp?

Still confused.

So wouldn't you want the crossover point on the fronts to be set at 150 Hz as well?

Not necessarily.

Speaker response isn't flat across the board. Different frequencies will play at different volumes depending on the speaker. So you might want to overlap the crossover points to give things more punch at 150-200hz (a common frequency that needs to be boosted in cars) so that both your front speakers and the subwoofer have some coverage in that range.

It's not a precise science in most cases. It's all about tuning to your ear. The idea is to get it sounding, via trial and error, as good as you can with a flat EQ. Fiddle with the crossover points until it sounds pretty good and doesn't distort. Then fine-tune with an EQ.

You can't work out what something is going to sound like from looking at the spec numbers. You can't plug a math formula into and get your crossover points. It's gotta be done by ear. For example, Doug Burnside runs his subwoofers crossed over at something like 3000hz, which most people would scoff at, but it happens to be what sounds best on that particular system.

This would block anything below 150 Hz? Or would that block above 150 Hz? I guess I'm a little confused about how crossovers actually work.

Crossovers are either high-pass or low-pass, depending on which of the two things you want to do.

A low pass crossover set to 150 hz would be for a subwoofer, i.e., it would only allow the lowest frequencies below 150hz through. A high pass crossover set to 150hz would be for the front speakers, blocking the low frequencies and allowing the highs to pass through.

Can't believe I never related the hi-lo filter to the crossover. Guess I thought it was just a switch that did something magical in the amp letting it know that they were highs.

It's all about tuning to your ear.

Yeah that's what I was afraid of. The big problem with that is the location of the amp. It's under the drivers seat, so the first time I set it up, the seat wasn't in the truck, therefore I wasn't in the best position to listen. I'm not positive, but I'm hoping that the fit isn't too tight to adjust with the seat still bolted in.

And the point about overlapping crossover points makes a lot of sense. I know I've read that, but it just never sunk in.

The big problem with that is the location of the amp. It's under the drivers seat...

You got off lucky. Mine is against the rear wall of the trunk (boot). Because I drive a very large car, I have to climb into the trunk in order to adjust the settings. The reason I drive a large car is because I am a very large person. Climbing into the trunk to adjust settings is a non-trivial experience...

Another thing, my sub is in a ported box, so the Subsonic filter at OFF is the correct position. But if the crossover only goes down to 30 Hz, then there shouldn't be anything going to the sub lower than that. So why the need for the filter? They say that the subsonic filter removes frequencies not audible to the human ear. These frequencies are only robbing power from the amp. So I guess the new question is, how do the subsonic filter and crossover relate?

No, with a ported box you do want the sub sonic filter on.

The normal (low pass) filter will give the sub anything below the filter frequency (say anything below 100 Hz). But your ported box is tuned to a specific frequency (say 40 Hz). If you play content that is "much" lower than that you risk unloading the sub, because the cushion of air that prevents the coil from slamming back and forth between the ends effectively has time to leak out with those lower frequencies and the air then no longer offers any resistance to the coil/cone.

You can compare that to a leaky football - punch down on it and it offers a fair resistance because the air can't leak as fast (higher frequencies) as you punch the ball. Now instead slowly (this are the really low frequencies) squeeze the football - the air will offer very little resistance as it now has time to leak out through the hole (port).

The sub sonic filter is actually a high pass filter, but with a very low frequency.
So, with both the sub sonic filter and the low pass filter active, the sub will see signals above the frequency of the sub sonic filter (15 or 30Hz) but below the frequency of the low pass filter (say 100Hz), ie frequencies between 30 and 100 Hz.

/Michael

I have no idea why I said my sub was in a ported box. It's in a very small sealed box. So the subsonic filter is in the right spot.

I think I was typing while thinking about your previous post. So no, it's not ported. That kind of made my first line in the quote sound pretty arrogant. Sorry about that.

But still, why would you not want to filter the frequencies less than 15 Hz when my sub is only rated to 18Hz, though in a sealed (I typed ported again) box? From what I've read, that is a waste of power.

So because the RMS ratings of the amp are lower than those of each speaker, I could run the amp at full power without blowing the speakers? But I would probably fry the amp? I guess that's my question. If the gain on the amp was set to Max, what does that actually mean in terms of wattage transferred to the speakers? Would that be the max rating for the amp?

Any ideas on these power issues?

Any ideas on these power issues?

About all I want to add here is this: more power is better when it comes to amps.

As unintuitive as it might sound, the more powerful your amplifiers, the quieter you can play your music and still have it sound good. It's a function of "head room" -- amplifiers that aren't working hard can deliver better sound.

Given lots of power (my system can pump out close to 1000 watts, although I have never done so) then the only limiting factor to how much volume you can produce is how much abuse your speakers can take before they melt down.

Another counter-intuitive concept: the closer to maximum gain you run your amplifiers, they more efficiently they run, in terms of the ratio of power out to power consumed. In my case, I am willing to sacrifice a few hundred watts of my car's electrical production on the altar of sound quality.

tanstaafl.

So does that mean that you run your amps with the gain turned all the way up but you keep the volume down on the head unit?

So does that mean that you run your amps with the gain turned all the way up but you keep the volume down on the head unit?
My interpretation of what he sadi is that he's willing to accept the lower efficiency of having the gain low.

Keeping the gain at max and HU volume low is asking for noise. Any noise introduced after the HU is amplified more the higher the gain is set. This concept is the reason for line-drivers, which increase the voltage "early" in the signal chain and allows you to keep the gain on the amp lower, thus amplifying any picked up noise less.

/Michael

Sorry about that.

No worries - it happens to all of us sometime.

But still, why would you not want to filter the frequencies less than 15 Hz when my sub is only rated to 18Hz, though in a sealed (I typed ported again) box? From what I've read, that is a waste of power.

Well, if your sub can't reproduce below 18Hz, then yes do set the SSF to 15Hz, no harm in that. OTOH, unless you play stuff like Bass Mechanic tracks or test tracks there probably isn't very much content below 15Hz in "ordinary" music, so I don't think you'll waste much power in reality.

/Michael

So because the RMS ratings of the amp are lower than those of each speaker, I could run the amp at full power without blowing the speakers? But I would probably fry the amp? I guess that's my question. If the gain on the amp was set to Max, what does that actually mean in terms of wattage transferred to the speakers? Would that be the max rating for the amp?


Any ideas on these power issues?

At full rated power the amp shouldn't hurt the speakers. And your amp should be just fine at that level.

If you set the gain to max, it will take a fairly small signal from the empeg to give the rated power. If you increase the volume setting on the empeg above that, the amp will start to clip Iie your gain setting and input voltage multiplied will be higher than the internal rail voltages - ie max output voltage on the speaker terminals - and the tops of the sinus signals will be clamped to that rail voltage and the tops of the sinus curve thus flattened. Increase the volume even further and the output signal will more and more look like a square wave signal.
And here lies a danger: the power of a square wave signal with a given amplitude (rail voltage) is twice that of the sinushaped signal with the same amplitude. So a 50W per channel amp can, when driven to full clipping, actually put out 100W.

See this page for more info on gain settings and clipping

/Michael

My interpretation of what he sadi is that he's willing to accept the lower efficiency of having the gain low.


Correct.

tanstaafl.

This has gotten a little old but I haven't visited in a while. In case you have questions stil...

We used to use an old osciloscope and some test tone CD’s. I suppose the test tones could be ripped to MP3 for the empeg… This was in the old days when you had a head deck, EQ, line driver, noise gate, and finally an amp. Seems these days it’s all built in…

Anyways, we’d set every gain on every piece all of the way down, and take the RC leads just before the amplifier and plug them into the o-scope with an adapter. Cue up the test tone CD to 1kHz and hit repeat (also 60Hz, and maybe some others depending on where the sub crossover was – early in the chain or built into the amp). Then start at the CD player and turn the volume up as far as it would go without clipping. Once it clipped we’d back off a notch and then go to the next item in the chain and do the same thing. Turn the gain on it up until we saw clipping and then back it off a notch. And so on.

Lastly we’d plug the amps back in, with the gains all the way down, and only turn up what was needed to make it sound balanced to your ears. Normally the front speakers got turned up a little in relation to the rears, and then the sub went up a little to finish it off. We ended up with the amps set low, all pieces within the chain set high, and the volume control on the CD player took it from there.

Usually it was loud enough in the end. If you wanted it louder, we’d set it by turning the CD player volume until it hit that clipping point / or all the way up (some would go 100% without clipping), then just “have at” the amp gains until it either made your ears hurt or you could hear the speakers distorting, whichever came first.

Of course you need to have an old o-scope from a science lab available… luckily we did when in school, which was the last time I did this. Since then it’s been deck –to-amp connections for me, and through reading or surfing I’ve seen that the head decks I’ve bought would go 100% without clipping anyways.

On the crossovers, what’s always worked for me was to set the fronts and rears at high pass at roughly 100Hz, and the sub low pass at the same spot, and do all of the gain settings. After that, we’d yank the RCA’s on say everything except the front speakers. Turn the volume up to about as high as you’d really ever listen to it, and then turn the crossover point down until you got distortion from the bass. Up it a little bit, and then do the same for just the rear speakers. Finally get everything plugged back in, and set the sub by ear. Almost always it got set for a low pass point just a little bit under where the fronts were set, and usually it was something like 75 / 80 Hz.

Of course there are other methods, but this always worked for me, my friends, and is very much what a lot of the IASCA people did at the time as well. However I can remember someone on this board, I don’t recall the name, but I think he had a Taurus SHO? He had completely different settings than anyone else I’ve ever heard of, but it seems to have worked great for him. In the end, it’s about what sounds best to yourself I guess. But hopefully that gives some ideas where to start.

tanstaafl (Doug Burnside) with the SHO Wagon.