Top Car Audio Myths...

[ca90ss]

http://www.audiovisualdevices.com.au...ne/note128.pdf

[DIYMA]

[bigabe]

Here's a myth that has been annoying me lately:

diymobileaudio = SQ

[michaelsil1]

Originally Posted by bigabe

Here's a myth that has been annoying me lately:

diymobileaudio = SQ

There are some of us that are into SQ.

[bigabe]

Originally Posted by michaelsil1

There are some of us that are into SQ.

Ok...

diymobileaudio = SQ and ONLY SQ



I can't tell you how many times I've seen people post things along the lines of, "diymobileaudio is an SQ forum"....

Bullshit.

Like SPL guys don't do things themselves???

[quality_sound]

No one ever said you can't DIY SPL, but this forum was started as an SQ forum. It wasn't until it was sold and the new owners advertised anywhere with ad space that it shifted.

[60ndown]

all car audio forum members are humble and clever.

myth bitches!

[squeak9798]

Originally Posted by ca90ss

....

20*log(2/1) = 6db

Double displacement, gain 6db

Quoting Eric Stevens won't change that.

[Andy Wehmeyer]

Originally Posted by squeak9798

20*log(2/1) = 6db

Double displacement, gain 6db

Hmmm...

[PaulD]

headroom is for transient peaks, which add very little to the average power. Clipping can double the average power at full clip (100% squre wave)

[trebor]

Originally Posted by bikinpunk

I was just about to ask about this.

So, how do we justify 'headroom'? I'm easily sending some of my speakers more than rated power and the signal is unclipped (at least, gains were set with oscope, then never went above that point). I'm not talking gobs of extra power, but there is extra power there. ... edit.... now that I think about it, I'm not able to say for sure they always see this extra power when playing music, but I'm pretty sure that the transients see it....

You want the extra power during transients for increased dynamics. Theyre brief enough the coil(s) will have time to cool in between.

Originally Posted by bikinpunk

Also, one of our valued members suggests setting amp gains with a -10dB tone because it gives extra dynamics and we can't hear that low level of distortion. <--paraphrasing, so I could be a tad off on rationale here, but it's the general idea suggested.

It can potentially decrease dynamics but does increase average power, think more average volume. Your right about being unable to notice the distortion during peaks, the idea is to get more from your amp.

[ItalynStylion]

Originally Posted by bigabe

Ok...

diymobileaudio = SQ and ONLY SQ



I can't tell you how many times I've seen people post things along the lines of, "diymobileaudio is an SQ forum"....

Bullshit.

Like SPL guys don't do things themselves???

We all like bass; no one here will deny that. Bass is a part of SQ though. You own a DD sub so I know you understand. It's not about banging your sub(s) all the time but it's nice to have the potential on tap.

I still think this is mostly a SQ forum. Not 100% but mostly.

[vecc205]

Originally Posted by killerb87

distortion does kill speakers, harmonic distortion. odd order harmonics at clipping increase power dramaticly. the first odd order harmonic will add over 33 watts to a 100 watt amp, the second odd order 20 watts and so on. just in the first 2 harmonics thats over 50 watts. thats alot of extra heat for a speaker to disipate. thats what kills drivers.

Most music in itself is not perfect sine waves but some of it may be synthesized with added distortions intended to be in the recording. Even instrumental stuff all instruments have a different sound character and thats because of the harmonics they produce and we all know a perfect sine wave doesn't produce any other harmonics except the fundamental frequency. So this would seem to rule out distortion in this sense killing your speakers but I don't think you meant this anyway but thought I would mention it. As long as the signal doesn't overdrive the mechanical limits of the speaker or its thermal limits that is what really counts.

[2DEEP2]

Originally Posted by squeak9798

20*log(2/1) = 6db

OK, (log2) * 20= 6.02, OK it's not 6 ??

[ca90ss]

Originally Posted by squeak9798

20*log(2/1) = 6db

Double displacement, gain 6db

Quoting Eric Stevens won't change that.

Now I'm

Eric's 2nd response in that thread
http://www.diymobileaudio.com/forum/...&postcount=198
Chad's response to Eric's response
http://www.diymobileaudio.com/forum/...&postcount=199

After playing around with bassbox a little it seems that adding the 2nd driver with no power increase does add ~3db and then doubling the total power adds another ~3db for ~6db total so it seems I was incorrect in my previous response.

[killerb87]

Originally Posted by vecc205

Most music in itself is not perfect sine waves but some of it may be synthesized with added distortions intended to be in the recording. Even instrumental stuff all instruments have a different sound character and thats because of the harmonics they produce and we all know a perfect sine wave doesn't produce any other harmonics except the fundamental frequency. So this would seem to rule out distortion in this sense killing your speakers but I don't think you meant this anyway but thought I would mention it. As long as the signal doesn't overdrive the mechanical limits of the speaker or its thermal limits that is what really counts.

your right i didnt mean distortion kills them but the byproduct can. a speaker can play distortion all day as long as the thermal or mechanical limits are not exceded. distortion is like a punch. i can take them all day from my niece, but not from mike tyson. well, maybe now i can. same thing with the 1000 watt sub analogy that 100 watt amp wont kill it, but a bigger amp will. if you get knocked out what caused it the fist or the force? both i guess.

[killerb87]

Originally Posted by Viperoni

Is the power level really increasing, or is it simply the same amount of power applied for a longer period of time?

IE: a signal that is 15vac peak to peak gets clipped to look more like 15vdc peak to peak is still 15v peak to peak... but there's more current being applied for a longer period of time.

i do believe its the duration of the peaks.

[squeak9798]

Originally Posted by ca90ss

After playing around with bassbox a little it seems that adding the 2nd driver with no power increase does add ~3db and then doubling the total power adds another ~3db for ~6db total

Exactly

The theoretical difference in output between two displacements (Vd1 & Vd2) is expressed by the equation 20*log(Vd1/Vd2).....which as 2DEEP2 correctly pointed out is 6.02db ( ) when the displacement is increased by a factor of 2 (i.e. doubled).

[FoxPro5]

Ensoheavy blockalot in a single layer all over your car on top of 19 layers of foil-tar stickem will make your SPSQLPSQL vehicle quieter than mausoleum.

[Boyd1184]

Everyone has always told me that 12s put out a lower sound than 10s.

[ClintMJ23]

Originally Posted by 06BLMUSTANGGT

Capacitors actually help!

They do help, within an amplifier...

[ClintMJ23]

Originally Posted by Boyd1184

Everyone has always told me that 12s put out a lower sound than 10s.

I think you mean, more low freq output. Assuming we are concering the same line of subs, just different sizes, each in optimal enclosures!

[tspence73]

Originally Posted by trebor

You want the extra power during transients for increased dynamics. Theyre brief enough the coil(s) will have time to cool in between.

I think this is a safe assumption.

It can potentially decrease dynamics but does increase average power, think more average volume. Your right about being unable to notice the distortion during peaks, the idea is to get more from your amp.

I think the reason the "-10db" number was thrown out there is because most modern music is heavily compressed but almost always is at least an average of -10db below the 0db peak during mastering. This means that when any frequency hits 0db, it is usually a split second peak.

I tried this method recently while setting my older brother's system and must now disagree with the -10db advice.

Here is what I found:

My older brother's amp is a Hifonics 5-channel amp rated at 55x4 + 200x1 @ 4-ohms. I did not do this test with a load connected as my previous tests have proven to me that if the math is done properly, the amp DOES NOT NEED A LOAD to be set accurately.

I first used the -10db test tone disc @ 75% of the HU volume (46 out of 62 on the dial) @ 300Hz and maxed out the speaker outputs' gain and could only reach 7.1 volts (or 13 watts for a 4-ohm speaker).

Then I put in the 0db test tones and found that same setting (max gain) reached an astounding 30-volts! Outrageous. That would not only be distortion, but very audible as music playback showed.

After further testing I settled on using the 0db test tone disc and chucking the -10db disc, then applying a 19-volt (14.8-volts = rated RMS watts of amp) setting on the speakers and a 34 volt setting for the sub channel (28-volts = RMS rating on that channel). Even with these FAR more conservative settings, I could STILL detect distortion/clipping at a volume setting of 42 creeping in on the music playback.

My recommendation based on my personal listening tests is that if you are setting the amp for midrange/hi speakers, and only if your amp is running it's RMS right at your speaker's RMS, then it seems good to use 25% more voltage than the RMS of the amp is rated for and your volume will be higher and the distortion will be negligible until you reach the volume point at which you set the amp on the dial. For subs that number is more like 50% more voltage since it's far more difficult to hear distortion/clipping on bass.

So, I can say, pretty safely that the -10db test tone recommendation is WRONG. Don't use it. I know it makes sense when you think about how studios master their music, but in practice, I could definitely hear clipping on music playback WAY before coming even close to the 75% headunit setting.

[FoxPro5]

Originally Posted by tspence73

I could definitely hear clipping on music playback WAY before coming even close to the 75% headunit setting.

I bet you dollars to donuts I could play 5 random songs and you couldn't tell me which ones were clean at -10 dB RMS and which ones had all the tips of the mountains cut off (heavly clipped at 0dB). I'd let you use all audiophile equipment and the best headphones in the world, if you wanted.

[tspence73]

Originally Posted by FoxPro5

I bet you dollars to donuts I could play 5 random songs and you couldn't tell me which ones were clean at -10 dB RMS and which ones had all the tips of the mountains cut off (heavly clipped at 0dB). I'd let you use all audiophile equipment and the best headphones in the world, if you wanted.

I'm not going to submit to that test. I will however submit to any blind test under the conditions where I set the amp using the -10db test tone. It was not only clear to hear, there is no way you could make it back to that 46 volume setting without fearing the speakers would be ruined. It wasn't even a fine line I'm talking about here. It was enormous. I invite you to set your amp voltage with a -10db tone and compare that output voltage to a 0db tone. Then try playing back music with the -10db set amp. If you don't hear the distortion by the time the volume control reaches even 50%, you're a liar. Just my 2 cents on this. It's pretty obvious and it's not an exaggeration. It's so obvious that I would take any average Joe with bad jackhammer hearing and he could tell you when it sounds like shredded beef at 50% volume. It's literally that obvious.

[bikinpunk]

Andy needs to chime in on this...

But, FWIW, I believe the reason for using the -10dB tone vs. 0dB tone is due to the constant (can't think of the word here) of the test tone. Music isn't nearly as constant, therefore the suggestion to set it with a tone more along the lines of what we would expect out of music is suggested.

My $.02