Subwoofer FAQ (just the begining stages)

[glen]

This is a repost becasue this has been a FAQ and typically incorrectly answered for 5 years now at ATOT, and untill I get around to writing the FAQ, this is the best I can do for now.

To reproduce music accurately from about 10hz to 20khz, you are going to need about 4 15"s in an infinate baffle enclosure.

Saying 8's are tighter or quicker than 15's is like saying, "I have absolutely no understanding of high school level physics."

Sound is a perception in the brain.
This perception is caused by changes in pressure (normally air, but you can hear under water.).

The level of the pressure change is how loud the music is.

The number of time the presure changes per unit of time is the sound or tone, t(he typical unit is HZ, which is changes per second.)

For loud sounds, you need to make huge changes in air pressure.
You change air pressure by moving a volume of air.

Bigger drivers are better at this, because they do not have to move in and out as far to move the same volume of air. Because they are moving a shorter distance, they actually have less distortion.

Think about fans, what blows harder, a little fan or a large fan? Sure the little one cna keep up, but it not good engineering. I mean you could theoretically but you get distortion, balance problems, motors stress, more friction, etc....
Do Ocean linners have little propellers or large ones?

If the guy at the stereo shop tells you that you actually neeed to put 4 15" sub woofers in your attic to really get accurate sound, is he going to get a sale? Does he even know better?

regarding the MYTH about being able to hear wave lengths longer than the space you are in,"Dude you can't hear low bass in a car casue the wave can't fully develope."


This is a commonly held myth. The presure in the car increases and decreases. The wave length is a mathematical description having to do with the speed of sound. It is as absurd as saying a wave length longer than the space between your ears in inaudible. Our that if you are on a 10 foot surf board, you can't feel a tiddal wave. You do not hear the length of the sound, and you don't feel the length of the tiddal wave. You "hear" the changes in pressure, and in the other example your surf board goes WAY up in the air, and then way down, and you sure as heck will notice it, even if the wave length of the tiddal wave is a mile long. Understand?.

 

[sillymofo]

Um, you are correct, but we can't hear anything below 20 kHz any way, but rather feel, just my .02.

 

[mugs]

Originally posted by: cr4zymofo
Um, you are correct, but we can't hear anything below 20 kHz any way, but rather feel, just my .02.

I think you mean 20 hz. The human hearing range is roughly 20 hz - 20 khz. I think glen meant hz too.

 

[sillymofo]

Originally posted by: mugsywwiii

Originally posted by: cr4zymofo Um, you are correct, but we can't hear anything below 20 kHz any way, but rather feel, just my .02.

I think you mean 20 hz. The human hearing range is roughly 20 hz - 20 khz. I think glen meant hz too.

well... that too

 

[glen]

Speakers are advertized as 20 to 20khz
I would much rather have speakers do 5hz to 12,000hz
Going up is easy, 100,000 is really easy to do, but getting below 20, is hard. So, marketing has to do their best to blur physics and common sense.
it become very difficult to distinguish tonal differences below oh, even 50hz, but you can certainly hear it
so, like 1,000 hz to 1,083.333 is a 1/12th octave jump - the same as two keys side by side on a piano. They clearly sound different. 10hz to 10.833333 is the same jump, one twelvth octave, but very few people can hear the pitch differnce, but all people can hear the sound.

 

[Triumph]

12" woofer providing tighter sound than a 10"? explain how, please.

 

[Viperoni]

Originally posted by: Triumph
12" woofer providing tighter sound than a 10"? explain how, please.

Please see the other 50+ post thread, it's all explain in there. My posts touch on the mathematical side of it.

 

[Viperoni]

Here's the debunking of the "the car's cabin is too small to reproduce bass properly!" arguement:

Think about headphones. The length of a sound wavelength in feet is determined by 1128/f, where f is the frequency in hertz. As you can see, if we choose 4512hz, 1128/4512 = 1/4. 1/4 of a foot is 3 inches.
That implies that a sine wave with frequency 4512hz is 3 inches long from peak to peak, start to end, one full up and down swing, etc.

4512hz also happen to be higher than pretty much any human could possibly sing. 60hz is about the lowest (Barry White deep)

So, if you're listening to music on your headphones, BUT the headphones don't let any of the frequencies of the human voice fully reproduce because there's so little space between the headphone and your eardrum, how do you hear the music in the first place?
Because it doesn't matter if the sound wavelengths have enough space to develop or not.

Let's take this one step further. Earbuds. They go right in your ear. They're quite small too, in fact, they're smaller then MANY car tweeters. But when you put them in your ears, you get bass.
But wait a minute, you never hear bass from your car's tweeters.....
Why do you get bass from tiny earbuds, earbuds that are smaller than normal tweeters, which we KNOW cannot produce bass in a room/car?
Because you get disturbingly high amounts of "cabin gain" from having the earbud only having to play into your ear canal, and not the whole room or your car.

Same thing happens if you listen to your subwoofer in the corner of your room compared to out in the middle of your back yard... chances are it'll be louder in the corner of your room.

 

[Shockwave]

I disagree on this statement.
"To reproduce music accurately from about 10hz to 20khz, you are going to need about 4 15"s in an infinate baffle enclosure."

But would generally agree for everything else.

 

[nan0bug]

Dont they have a car audio forum somewhere that you guys can all go jerk each other off in?

 

[glen]

Originally posted by: nan0bug
Dont they have a car audio forum somewhere that you guys can all go jerk each other off in?

My original post had very little to do with "car audio."
I just wanted to try to explain some things in a clear way, not to make anyone feel insulted, but I probably did not say it in a a great way. I know my tendancy is to be blunt.

There are many myths in audio. SO far in this, I am trying to explain why you can hear a wave ina a space smaller than the wave length, and why "smaller" drivers make tighter bass is really somewhere between silly and untrue.

 

[glen]

Originally posted by: Triumph
12" woofer providing tighter sound than a 10"? explain how, please.

No one has said that statement in this thread, so I assume you did not read my first post. It is not too long, and I tried my best to use explain it.

 

[glen]

Originally posted by: Shockwave
I disagree on this statement.
"To reproduce music accurately from about 10hz to 20khz, you are going to need about 4 15"s in an infinate baffle enclosure."

But would generally agree for everything else.

Not the only way, but probably the easiest way to get 120plus db into a home theater size room.
Obviously, in a car you get cabin gain and can get there with a lot less swept air. My point really is trying to explain why when you go to the stereo shop the sales guys tell you such incorrect information. They sell you a sweet pair of Paradigms, then tell you some hogwash and sell you a little 12" sub in a small box for the courner fo your living room. That is as silly as the Ferrari dealership selling you bicycle tires for your Enzo.

 

[Shockwave]

Originally posted by: nan0bug
Dont they have a car audio forum somewhere that you guys can all go jerk each other off in?

*LOL*! Someoines jealous cause they know jack about audio i see.

 

[Triumph]

Originally posted by: glen

Originally posted by: Triumph
12" woofer providing tighter sound than a 10"? explain how, please.

No one has said that statement in this thread, so I assume you did not read my first post. It is not too long, and I tried my best to use explain it.

You said, "Saying 8's are tighter or quicker than 15's is like saying, "I have absolutely no understanding of high school level physics."

So yes, the topic was brought up in this thread.

 

[Triumph]

Ci = Ca (eq 3) or i :: a (eq 4)

Maybe my 4 years of engineering school were wasted, but that's just bad math. It should be C1i = C2a, and thus the C's do not cancel out. C2 = m, and since it doesn't divide out, m is still in there. So let's go back to their previous equation:

BLi = ma (eq 2)

Assume you have two speakers with equivalent magnetic field and voice coil lenght. BL = constant. Lets assume BL = 1 to make it easy. Now if they are two different speaker sizes, 12" and 15", the masses will be different. So we have:

12" driver: i = m1*a1
15" driver: i = m2*a2
m2 > m1

Input the same current i, then

m1*a1 = m2*a2 or
a1 = (m2/m1)*a2

If m2 > m1, then a1 > a2, hence the 12" driver has a higher acceleration than a1.

The only inhibitions I have about this is because you posted a link, which is from a seemingly reputable source, and it's possible that I'm wrong because I'm not specifically a speaker expert. But I just don't see how you can "eliminate" the mass, B, and L, simply because they are time invariant. C != C, so they don't cancel out! I'd like to see another engineer's analysis of this conundrum.

Interesting problem, nonetheless. I would love to see what is wrong with my argument, but I'll be away from AT for a few days. That'll give you guys plenty of time to write up a response.

 

[Viper GTS]

Originally posted by: Triumph

Ci = Ca (eq 3) or i :: a (eq 4)

Maybe my 4 years of engineering school were wasted, but that's just bad math. It should be C1i = C2a, and thus the C's do not cancel out. C2 = m, and since it doesn't divide out, m is still in there. So let's go back to their previous equation:

BLi = ma (eq 2)

Assume you have two speakers with equivalent magnetic field and voice coil lenght. BL = constant. Lets assume BL = 1 to make it easy. Now if they are two different speaker sizes, 12" and 15", the masses will be different. So we have:

12" driver: i = m1*a1
15" driver: i = m2*a2
m2 > m1

Input the same current i, then

m1*a1 = m2*a2 or
a1 = (m2/m1)*a2

If m2 > m1, then a1 > a2, hence the 12" driver has a higher acceleration than a1.

The only inhibitions I have about this is because you posted a link, which is from a seemingly reputable source, and it's possible that I'm wrong because I'm not specifically a speaker expert. But I just don't see how you can "eliminate" the mass, B, and L, simply because they are time invariant. C != C, so they don't cancel out! I'd like to see another engineer's analysis of this conundrum.

Interesting problem, nonetheless. I would love to see what is wrong with my argument, but I'll be away from AT for a few days. That'll give you guys plenty of time to write up a response.

One major flaw I see in your reasoning that I see:

You assumed current would be constant, which it obviously would not be. The question is not which can respond faster at a given current. Two different drivers playing the same frequency at the same pressure will use two different currents.

Viper GTS

 

[glen]

Originally posted by: Triumph

Originally posted by: glen

Originally posted by: Triumph
12" woofer providing tighter sound than a 10"? explain how, please.

No one has said that statement in this thread, so I assume you did not read my first post. It is not too long, and I tried my best to use explain it.

You said, "Saying 8's are tighter or quicker than 15's is like saying, "I have absolutely no understanding of high school level physics."

So yes, the topic was brought up in this thread.

The answer was posted in my first post. Any problem with it is just my poor teaching skills, and poor writing ability.

Let me see if I can do a better job explaining it.
What matters is the volume of air moved - surface area of the drive time how far it moves

To move an evquivalent amount of air, a smaller drive has to move farther in the same amount of time, so it does move quicker.

However, when the stereo guy at teh store is talking about "quicker" bass he is using it to describe a certain sound, like quick bass verses muddy bass.

But, 60hz at sea level is always the same. It is not quicker, tighter, better, greener, brighter, or any other adjective you want to use, no matter what the drive size is. Is it simply 60hz.


The problem is if the CD says play 60hz, the speaker will not play 60hz. It will come close, but there will be distortion. Larger drivers have an inherient engineerring advatage over smaller drivers, allowing them to come closer to 60hz, with less distortion.

 

[Apex]

Originally posted by: cr4zymofo

Originally posted by: mugsywwiii

Originally posted by: cr4zymofo Um, you are correct, but we can't hear anything below 20 kHz any way, but rather feel, just my .02.

I think you mean 20 hz. The human hearing range is roughly 20 hz - 20 khz. I think glen meant hz too.

well... that too

Actually, that's not entirely correct either. 20Hz is a generally accepted floor, because below roughly this point (it varies for different people), our hearing degrades at quite a steep curve. However, we can still hear below 20hz, it just requires a LOT of volume. Of course, it's also correct that MOST of what we think we "hear" below 20hz is impact we feel.

 

[T2T III]

Originally posted by: nan0bug
Dont they have a car audio forum somewhere that you guys can all go jerk each other off in?

Yeah, and we've all nominated you as our point person. Get in the middle, NOW!!

 

[Howard]

Just thought I'd toss some fuel into the fire.

 

[glen]

Originally posted by: Apex

Originally posted by: cr4zymofo

Originally posted by: mugsywwiii

Originally posted by: cr4zymofo Um, you are correct, but we can't hear anything below 20 kHz any way, but rather feel, just my .02.

I think you mean 20 hz. The human hearing range is roughly 20 hz - 20 khz. I think glen meant hz too.

well... that too

Actually, that's not entirely correct either. 20Hz is a generally accepted floor, because below roughly this point (it varies for different people), our hearing degrades at quite a steep curve. However, we can still hear below 20hz, it just requires a LOT of volume. Of course, it's also correct that MOST of what we think we "hear" below 20hz is impact we feel.

Here is my answer posted earlier, but I think it adresses the question.

Speakers are advertized as 20 to 20khz
I would much rather have speakers do 5hz to 12,000hz
Going up is easy, 100,000 is really easy to do, but getting below 20, is hard. So, marketing has to do their best to blur physics and common sense.
it become very difficult to distinguish tonal differences below oh, even 50hz, but you can certainly hear it
so, like 1,000 hz to 1,083.333 is a 1/12th octave jump - the same as two keys side by side on a piano. They clearly sound different. 10hz to 10.833333 is the same jump, one twelvth octave, but very few people can hear the pitch differnce, but all people can hear the sound.

 

[thomsbrain]

of course CD's are only encoded and decoded from 20 Hz up, so anything below that is a mute point (pardon the pun), unless you're playing old records which were recorded with all analog equipment (which basically means nothing since 1980 or so). but having speakers that extent below 20 is nice because it means you probably have less drop-off on the frequencies it will actually be fed.

 

[Shockwave]

Originally posted by: thomsbrain
of course CD's are only encoded and decoded from 20 Hz up, so anything below that is a mute point (pardon the pun), unless you're playing old records which were recorded with all analog equipment (which basically means nothing since 1980 or so). but having speakers that extent below 20 is nice because it means you probably have less drop-off on the frequencies it will actually be fed.

 

[glen]

Originally posted by: thomsbrain
of course CD's are only encoded and decoded from 20 Hz up, so anything below that is a mute point (pardon the pun), unless you're playing old records which were recorded with all analog equipment (which basically means nothing since 1980 or so). but having speakers that extent below 20 is nice because it means you probably have less drop-off on the frequencies it will actually be fed.

no.

This guy simply analysed the data and listed its frequency and how loud it is recorded.
Top 30 Bass Cd's
frequncy bits from max recordable level track number time

So, for the first in the list, it is ranked #1, the frequency is 5hz, it is recorded at 13.7 db from the max recordable level on a cd it is track number 1 and occurs between 3:30 and 8:10 name of CD etc...


1 5hz -13.7 1 3:30-8:10 Battle Music of Beethoven and Liszt Beethoven Telarc CD-80079
2 5hz -16.1 4 5:14-5:15 Big Notes Flim & The BB's DMP CD-454
3 7hz -14.5 1 12:30-15:10 1812 Overture Tchaikovsky Telarc CD-80041
4 7hz -22.1 35 ALL Sonic Booms 2 Mobile Fidelity Bainbridge BCD 6285
5 8hz -20.1 10 4:15-4:16 Toxic Bass Toxic Bass I.B.P. IBP-0008-2
6 9hz -14.8 8 0:20-0:40 Sonic Booms 3 Mobile Fidelity Bainbridge
7 10hz -11.8 20 3:10-3:20 Great Fantasy/Adventure Album Erich Kunzel Telarc CD-80342
8 10hz -15.5 21 ALL Great Fantasy/Adventure Album Erich Kunzel Telarc CD-80342
9 10hz -19.5 1 0:20-0:30 Food For Woofers Volume #3 B&W KOTF I.R.S. FFW 003 CD
10 10hz -20.5 5 2:20-2:40 Fantastic Journey Erich Kunzel Telarc CD-80231
11 12hz -14.9 12 3:10-3:20 Illegal Bass Bass Outlaws Newtown NTN 2210
12 13hz -17.3 1 ALL Time Warp Erich Kunzel Telarc CD-80106
13 16hz -11.7 16 3:00-3:40 Romantic Organ Music Volume 2 Peter Hurford London 421 296-2
14 16hz -11.9 18 0:12-END It Came From Outer Bass 2 Techmaster P.E.B. Newtown NTN 2211
15 16hz -12.5 2 3:20-END Quad Maximus Bass Mekanik Pandisc PDD-8848
16 16hz -14.5 3 ALL Bass Box Seventh Order Hip Rock DIDX 018599
17 16hz -16.7 10 0:38-5:06 Tyranny For You Front 242 Epic/Sony EK 46998
18 16hz -21.8 1 0:48-0:50 Joshua Judges Ruth Lyle Lovett Curb / MCA MCAD-10475
19 17hz -8.6 1 0:10-0:20 Chiller Erich Kunzel Telarc CD-80189
20 18hz -7.1 1 3:50-3:55 Illegal Bass Bass Outlaws Newtown NTN 2210
21 18hz -14.5 3 1:30-1:43 Bass Ecstacy Bass Erotica Neurodisk NRD-31005
22 19hz -6.7 7 0:00-0:10 Drivin Bass Bass Connection Neurodisk CD-31004
23 19hz -9.6 6 1:10-END More Bass Boom Bottom Power Supply Hip Rock DIDX 022094
24 19hz -9.9 2 ALL Cyberbass Virtual Reality Bass Syndicate D M Records
25 20hz -4.5 5 1:10-1:20 Bass Society Bass Society Majammy E-SA-1010
26 20hz -7.9 1 ALL It Came From Outer Bass 2 Techmaster P.E.B. Newtown NTN 2211
27 20hz -8.1 12 0:00-0:10 Bass Is Loaded Bass Hit Neurodisk CD-31002
28 20hz -10.5 9 ALL Bass Overload Bass Alliance D M Records DMR-41269
29 22hz -4.3 11 ALL Drivin Bass Bass Conection Neurodisk CD-31004
30 22hz -7.4 12 0:40-END Bass Overload Bass Alliance D M Records DMR-41269


Frequency: lowest significant frequency with potential to be percieved.
DBfs: decibels below maximum digital record level.
Time: point(s) during track to find lowest frequency (ALL=various points in track).
CD's were played on a SONY CDP-610es (confirmed flat to below 2hz) and Measured on a Tektronix 2630 FFT analyser.