Impious

Crest Factor Before we can discuss amplifier headroom, we first need to discuss the music we are listening to. And the concept we need to understand is that of crest factor. Sine waves are the simplest tone. Sine waves are the "test tones" that many people use in this hobby for various reasons, although most likely familiar to everyone as the source used in the typical SPL competition. Sine waves are a periodic waveform. That is, these sine waves or test tones are quite simply a repeating waveform with equal intervals and amplitude in time. Music, in contrast, is very dynamic and transient. Music is a nonperiodic wave form. Meaning music is composed of sounds that frequently vary amplitude, vary in tone and last for varying periods of time. Most sounds and peaks in music last for very brief periods of time, many times only for a fraction of a second. Both sine waves and music have an "average level" and a "peak level". The peak level is the highest output level achieved by the tone or music. What we are concerned about is the difference between that average level and the peak level. And that difference is known as crest factor. Sine waves have a crest factor of 3db. Meaning the peak of the signal is 3db higher than the average level of the signal. Music on the other hand has a crest factor of 10db - 20db (or more) depending on the dynamics of the music and the amount of compression. On newer music, the compression is (unfortunately) typically higher reducing the dynamics and thus reducing the crest factor to the lower end of that spectrum. Higher quality recordings with less compression will be on the upper end of the crest factor spectrum with a crest factor of around 20db or more. The System Now that we understand a little bit about the music we're listening to, let's discuss how it relates to your system. So what does a crest factor of 10db or 20db mean? Well, we can use the formula 10*log(X/Y) to determine how much of a power increase is required to increase output by 10db and 20db. 10*log(10/1) = 10db 10*log(100/1) = 20db This means the amplifier must increase power by a factor of 10 to increase output by 10db and a factor of 100 to increase output by 20db. In other words, that dynamic peak of 10db will require your amplifier provide 10x the power over the average level. And to meet a 20db dynamic peak, it would require the amplifier output 100x the power over the average level. Sounds like a lot, eh? It is! So if you are using an amplifier with an unclipped power output capability of 100w, and you are listening to music with a crest factor of 20db then the average output you would be able to obtain from the amplifier and avoid clipping the dynamic peaks is 1w. The same amplifier with a crest factor of 10db, the average output would be 10w. What happens if we want to listen to our 20db crest factor music at a higher average level than just 1w of output on our 100w amplifier? Well, you certainly can.....but you will end up clipping the dynamic peaks. Going back to what we said before about the nature of music, it's very transient. Those large peaks will occur over very short durations of time and change rapidly. Due to various reasons our brain can handle some amount of clipping without negative audible effects. But it is also possible, depending on the amount of clipping, original crest factor of the music and frequency regions involved, etc, that this clipping could result in harsh or compressed sounding dynamics at higher output listening levels. This is because of the increase in distortion as a result of clipping, and due to the forced reduction of the level of the dynamic peak compared to the average level of the music. An undesirable result indeed. There are, of course, other issues involved with clipping such as potential damage to components such as speakers, but that's best left to another thread as it can be quite involved in-and-of itself. Headroom This leads us to the utility of amplifier headroom. And also the reason I'm a huge advocate of purchasing the most power your budget will allow. What is meant by the term "headroom"? It means having excess power reserves or capabilities available from the amplifier for use during those dynamic peaks to avoid clipping the amplifier and the resultant negative effects it can have on the sound of the system. The two ways of obtaining this headroom are as follows; The first is "headroom" inherent to the amplifier itself, the second is headroom allowed by purchasing an amplifier with higher power capabilities. For headroom inherent to the amplifier itself, we need to consider the way amplifiers are measured. Amplifiers power rating can be done in several ways. The first, and most commonly cited, is continuous average power (incorrectly called "RMS" power). This should be the output capabilities of the amplifier measured over extended periods of time at some distortion figure, generally 1% or less, at some supply voltage, generally 12V-14.4V. It is, however, possible to measure an amplifiers output on very short periods of time, typically fractions of a second. This is referred to as music power or dynamic power. For most typical amplifier designs, this will not change significantly enough from the continuous power output capabilities to really matter in the grand scheme of things. It is, however, possible to design an amplifier that has considerably higher dynamic power than it does continuous power output capabilities. One more extreme example of this is Rockford's 15kw amplifier with it's enormous bank of internal capacitors that can't sustain long term output support but can greatly increase power output for short term "bursts". Other companies have designed more practical applications of increasing dynamic power, but these are the exception and not the rule. Do not confuse the real measure of dynamic or music power with the fictional marketing term used by many low end companies, which in their lingo is essentially an ILS rating. That leaves use with the second consideration to increasing headroom; Buying an amplifier with higher power capabilities than we may think we need. Looking back at how power increases with regard to dynamic peaks, it's easy to see how this could be beneficial. Compare, for example, a 50w amplifier and a 200w amplifier. Let's just say, to keep things simple, that we are listening to music with a crest factor of 10db and we are listening at an average level that requires 10w of output from the amplifier. When those 10db dynamic peaks occur, they will require a 10x increase in power, to 100w. If we are using a 50w amplifier, then these peaks would require the 50w amplifier to output twice it's unclipped output capabilities.....which means we will be clipping the amplifier during those peaks, potentially leading to the ill effects previously listed. In this particular scenario, you reduced your unclipped dynamic headroom capabilities from the necessary 10db to 7db. On the other hand, if we are using the 200w amplifier and that 10db dynamic peak occurs, we are still well under the amplifier's capabilities....removing the worry about clipping and the resultant increase in distortion and compressed dynamics. Does everyone need a 200+ watt-per-channel amplifier? Certainly not. But it does explain why it makes sense to look for the amplifier with the highest power capabilities out of the viable options within your budget. All else equal (build quality, features, aesthetic value, etc) it's generally advisable to go with the higher powered amplifier. Where it can be avoided, there's no reason to make available power the limiting factor to the performance of your system. Allow yourself the necessary headroom when choosing amplification for your system. If that's a 50wpc amplifier or a 300wpc amplifier is a decision for you to make. Now, you may be thinking; But wait! My speakers are only rated at 50w, what in the heck will happen when they receive that 100w dynamic peak?! Well, the short answer here is that a speaker's power rating is typically a thermal rating based on it's ability to sustain that power level over an extended period of time. Again, due to the transient nature of music, those dynamic peaks are occurring over very short periods of time. Due to the short time frame of that dynamic peak, the speaker will quickly dissipate the heat. Speakers can handle much more power over very short periods of time than they can over longer periods of time.

Apparently I didn't make my first post clear enough. Let's try it again; YOU DO NOT NEED A LINE DRIVER. Your uncle is wrong, plain and simple, that the sound difference is related to his 4v outputs (UNLESS YOU DID NOT PROPERLY RESET THE GAIN. IN WHICH CASE, CORRECTLY RESET YOUR GAIN). With a properly set gain, there will be NO DIFFERENCE AT ALL in the power output of the amplifier. Get this line driver thing out of your head. You don't need one. It won't help. Waste of money. Go back to my previous post. It explains everything. Things you don't think make a big difference do, in fact, make a huge difference.

Having a speaker connected isn't going to change the voltage an amplifier can supply before clipping occurs. The impedance rise will affect how much power the speaker sees, but not how much voltage the amplifier can cleanly supply.

There could be many factors at play here, none of which are related to the headunit's output voltage. For starters, as was mentioned, the gain control is included on amplifiers for the express purpose of allowing the amplifier to reach full power output with a wide range of input voltages. You first need to properly set the gain control. With a properly set gain control, there will be no difference in output from the amplifier between your uncle's headunit and your headunit. This is exactly what the gain control is there for. You do not need a line driver. Second, you could be experiencing a difference in vehicle acoustics. The exact same system in two different vehicles will sound and behave completely differently. While I don't know the details of the entire system (i.e. this would have been helpful information to have included in your original post) or what the two vehicles are a discussing here, trying something such as different placement and/or positioning of the subwoofer in your vehicle may change the sound of the system for better or worse. But without fairly advanced attempts at creating "equal" results, there will be some unavoidable differences in sound simply due to the two different vehicles. A third issue could be due to the strength of the respective electrical systems of the two vehicles and the amplifier. If the amplifier is not tightly regulated, and your electrical system is much weaker than the electrical system in your uncle's vehicle, then the amplifier will not be performing as strongly. A fourth issue could also be due to difference in various system settings between the two installations (EQ, crossover settings, "loudness" settings, etc) as well as differences of the other speakers and their respective performance involved in the two systems, integration of the speakers and subwoofers in the system, etc. And that's the short list based on limited information. Long story short; Hard to blame a single factor when there is a multitude at play that need to be fully considered. And to eliminate it from your list, the headunit's preout voltage is not one of the factors with a properly set gain.

There are several assumptions involved when setting the gain with a DMM and the voltage formula. These assumptions may or may not be accurate. As a result, your gain setting with the DMM may or may not be accurate. There is no guaranty clipping will not occur with the DMM method because, as stated, the DMM doesn't measure the shape of the wave....only the voltage. The DMM method helps get the gain setting within the general ballpark so people aren't going crazy with the gain control. But in reality it's not an exact or accurate method.

Just an FYI; To find a half octave you can just multiply the frequency by .75 32 * .75 = 24

You would be correct that 22.5hz is half an octave below 30hz. Half an octave is one of many general recommendations. One thing you could do would be to load your sub and enclosure into an enclosure simulator and run an excursion plot. Look at the graph and see when the plotted excursion exceeds the capabilities of your subwoofer.

Wording could use a little refinement, but I think you have the jist of things. Correct, it doesn't matter which filter is set to the higher frequency and which to the lower frequency. As you approach 2nd crossover frequency, the rate of attenuation (or slope) will increase (or steepen). And I just want to clarify that you understand the slope of the crossovers themselves doesn't change. It is the effect of the multiple crossovers summing that increases the final rate of attenuation of the signal. Also want to point out that the word highlighted in red above should be "rate of attenuation", or "slope". Octave describes the interval between frequencies. The term "decibels per octave" is used to describe the crossovers rate of attention, or slope, (in decibels) per the interval between frequencies (octave).

They can be used for that, and that is the reason most manufacturers include them in an amplifier. However they are simply a highpass crossover with a different "label", so if you choose to use them in another manor that is perfectly acceptable also Correct. When you run a driver in a ported enclosure below tuning you run the risk of damaging the driver due to unloading. The SSF can and should be used to help protect the driver.

Correct. You can do a basic active setup with the crossovers in some amplifiers, such as the Sundown amps. IIRC this is the reason Jacob chose the frequency ranges he did for the crossovers in his amplifiers. It will not be the epitome of flexibility, but it will technically work.

Completely false. Don't know who told you that, but it's completely untrue. Thanks for confirming it. I didn't do a direct quote becuase it's on a different forum. . So in a nutshell for basic situations, the xover slope is summed together. In a basic nutshell, correct. This is the essence of a Linkwitz-Riley crossover

Hrmph. I guess maybe I presumed you knew something you didn't when I was writing out my previous responses. Suppose maybe I should have began by asking if you understood the crossovers, slopes, etc Maybe this post I made a few years ago will help some also? http://www.caraudio....548&postcount=2 Let us know where you're still a little confused, we'll try to help

fixed for reality I dont understand where you are coming from with this. We changed everything around and then tested the power handling. I dont know if you knew this or not. If you did could you please enlighten us on how to fix the speaker installation so they will be able to handle more power. I believe his point was that once the doors are properly deadened and sealed the speakers may not need as much power to reach an acceptable volume level.

You mean, for example, if we set them to 500hz how would 1000hz be affected? Go back to the BCAE1 link I posted earlier in the thread and look at the graph. I think it would help if we stopped calling the subsonic filter a subsonic filter, honestly. It helps for identification of which filter we are talking about, but I think it might be causing you to think of the subsonic filter as something it's not. Subsonic filter is just a fancy (an in many ways, wrong) term that we use to describe a highpass crossover that can be set to very low frequencies. It is no different than the highpass crossover on the amplifier, or in your headunit. They are the exact same thing, we just use different terms to identify them. We'll call the headunit's highpass crossover Filter 1 and the "subsonic" crossover Filter 2. If we stick with our highly idealized situation and continue to assume they are both the same slope; Setting Filter 1 to 500hz and Filter 2 to 750hz is exactly the same as setting Filter 1 to 750hz and Filter 2 to 500hz. The results would be identical. A better question is; Why would the result be different? They are both doing the exact same thing to the signal. It doesn't matter which comes first if they are both doing the same thing.

Completely false. Don't know who told you that, but it's completely untrue.

So fucking tired of hearing about Tiger Woods. Need to start a show that investigates the pasts of all of these news reporters and Hollywood watcher-types and continually broadcast all of their indiscretions, nationally rub their mistakes in their faces for a while.

Two of the same type of filters (highpass and highpass, for example) won't "cancel out". They will be cumulative, they will combine. How they combine will be affected by a multitude of factors, including but not limited to the slope of the filters and the crossover frequencies. In your example, the signal would be affected by the subsonic filter until the signal begins approaching 300hz, at which point the net slope will be a combination of both the subsonic filter and the headunit's highpass filter. It will increase the attenuation of the signal, or in other words, it will cause the slope to steepen and increase the -Xdb/oct rolloff rate of the signal.

Crossovers unfortunately can be an extremely complicated subject. The above wouldn't even qualify as a snowflake on the tip of the crossover iceberg. But for the basics, if you haven't read it yet, you can start here; http://bcae1.com/xovrslop.htm

I guess I'm a little confused on what it is you are actually asking. Jacob's description is spot on. But I'll give it a shot and we'll go from there. A subsonic filter is nothing more than a highpass filter (crossover). Filters (crossovers) are cumulative; If you are using more than one filter, then the slope of each filter used will combine. For example, lets say you have the highpass filter on your headunit set to 500hz, and it's slope is 24db/oct. You then also use your amp's 24db/oct subsonic filter and likewise set it to 500hz. We will assume both are butterworth filters, which means the crossover frequency is the point at which the signal has decreased by a level of -3db. Now, in this particular scenario since we are using two crossovers of the same slope and alignment, both set to 500hz, the net result is that the signal will be down -6db at 500hz and the net slope will be -48db/oct. This is because, as noted earlier, the two crossovers combine. They both affect the signal. Or we could cascade the filters. We could set the crossover on the headunit to 500hz and set the subsonic filter at 250hz. In this scenario, the signal would only be down -3db at 500hz and the slope at that point will continue at the original 24db/oct rolloff. Now, normally at 250hz (one octave lower than 500hz) the signal would be down -24db due to the 24db/oct slope of the headunit's crossover. However, as we approach 250hz the signal will begin to decrease in level quicker than 24db/oct because the 2nd, cascaded, filter (in this case, the subsonic filter) will also begin affecting the signal. The signal at 250hz will instead be down -27db (original 24db/oct slope + -3db from subsonic filter) and from there continue to decrease at 48db/oct due to the combined effects of both the headunit's 24db/oct filter and the 24db/oct subsonic filter. So the frequencies below 250hz will be attentuated much more quickly than above 250hz. This can be done with any two filters (crossovers). You could use the lowpass crossover on your headunit and the lowpass crossover on your amplifier to obtain the same affect on the top end of your midrange, for example. Or the highpass in your headunit and highpass on your amplifier to steepen the highpass filter on your tweeters. Etc. This is a simple, idealized example for explanation purposes. In reality there may be some other factors to take into consideration such as the Q of the filters and such.....but it should provide you an idea of what Jacob was talking about. Clear as mud ?? Help, not help?

Have you done anything M5 or myself have previously suggested in this thread? If not, then there's no point in continuing to try to assist you. If yes, please report back with what you have done and the results.

The specs appear to be 75w x 4 or 180w x 2 @ 4ohm.

It's going to be hard for us to tell you which set of features are important to you. Preamp output voltage isn't important, so scratch that off your list. If you primarily use your Ipod, keep the Alpine. If you use both Ipod and CD, keep the Kenwood.

If your main goal is vibration damping in various areas in your vehicle, I think I would still stick with the Dynamat Extreme. It gives you the most square foot coverage for the money out of the listed options and is a high quality damper, so you're not really sacrificing anything.

I wouldn't believe the specs on that website. Looking @ US Amps website, they rate the amplifier at 75w x 4 @ 4ohm and 90w x 4 @ 2ohm (2ohm rating is the same on the audiosavings website), which would correlate to only 180w x 2 @ 4ohm bridged.....not 500w. US Amps website states 500w x 1 @ 1ohm bridged, but I would presume they were meaning the sub channel is 500w @ 1ohm and not that the main channels were 500w RMS when bridged. The Memphis 16-MC5.1400 has more power capabilities, assuming I'm correct, if that's what you're looking for.

The other option is ofcourse to sell the gift cards and use the cash to buy whatever you want from where ever you want.