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 Sub Woofer Science

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xaqmusic
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PostSubject: Sub Woofer Science   Tue Sep 29, 2009 7:26 pm

Vanguard92 wrote:
What I want to know is how to setup the gain on my amp if I'm using the head unit to control the sub volume. Luckily the Soundstream Amp I have has a remote gain knob I will have wired into my dash so I don't have to climb into the trunk to adjust the thing. The amp will be running 2 JL Audio 10W0-8's in a sealed enclosure. I prefer the harmonics of an 8-ohm driver more because I listen to mostly acoustic music. Jazz, Classical, Drum Corps.

I've heard that to set it perfect you have to use an oscilloscope, but I don't have one and I'm not going to get one. I'm not gonna worry about the exact instant and frequency that causes the amp to clip and go into a square wave or shutoff.

There is a lot of voodoo out there on how to set your gains. Any definitive answer?

I wasn't gonna get into harmonics, resultant tones and overtones. It's WAY complicated and I even took a course on it back in college. It's extremely complex to figure overtones, but resultant tones are fairly easy. The difference between two frequencies is the resultant tone. Which can either reinforce or detract from the original frequencies. It's hard to make people believe that the lowest notes you hear from a pipe organ are actually created by 2 tiny pipes that only dogs can hear individually. For more info on Harmonics and intonation check Chris Leuba's book, "Study in Musical Intonation". Not long, but an AWESOME read and basically the musicians bible for those interested in such things. I wish that electronics engineers who work designing new audio gear would read this book. It would open many eyes (and ears). cheers

The real science behind this subject is quite extensive and I will definitely check out that book! I think more in terms of vibrating strings and acoustic propagation so my gut reaction to sound comes from that end of the science. One thing that I did take away from my acoustics class and my conversations with Tony Bongiovi is that sound has plenty of room for interpretation in a lot of engineering circumstances. So I really try to "feel" what is happening rather than believe what my meters are showing. It's pretty common for us to put our hands physically on the cones as we are mixing or tuning to really feel what the effect of the electrical signal is on the driver we are using. I guess what I'm saying is that "engineering" perfect isn't always aesthetically perfect.

As far as setting gain for the sub goes I recommend listening to different music at many different volumes. Having the remote dash knob is ideal! I'll re-post my sub tuning comment for those who are just picking up this thread. If your impedance and phase is correct you will find the sweet spot for most situations.

I like your choice of 8" speakers. There is a direct correlation between the size of the speaker driver and the acoustic space they are meant to excite. I think you need something at least the size of a coffee shop to get the true sound of a 12" speaker! I would say if you want the bass to sound good outside the car, use 12s but if you want it to sound good inside the car use 8s. Here is a picture of some speakers we designed for one of our production rooms:

They are 4 8" drivers and a compression driver for each side. Each side is powered by a 1000watt Bryston monoblock amp. No need for a subwoofer! The urban guys who used the room probably work at about 140dB spl and their mixes sound great!

Joe


Last edited by xaqmusic on Thu Dec 10, 2009 3:55 am; edited 2 times in total
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PostSubject: Sub Woofer Tuning by ear   Tue Sep 29, 2009 7:27 pm

Re-post from the KD-S100 forum

If I may add to the crossover conversation:

Many consumer audio products do use the subwoofer to recreate frequencies well above 80Hz. Most home audio surround systems have tiny speakers that can only get down to about 250Hz so they tune the subwoofer up to take over where the small speakers leave off. Keep in mind, our ears can really only localize (place in the stereo image) frequencies 1000Hz and higher. For most situations our subwoofers are "invisible" and our ears place the sound where the higher frequencies are generated. I'm of the opinion that if you have a bi-amped system (the head unit's amps with a separate sub amp) then by all means share the load as much as possible. That is why SUB 01 sounds pretty thin with no subwoofer. I made that profile with the capabilities of the KD-S100 in mind and eeked out every ounce of power from the unit at the frequencies it is most efficient. Remember, it takes MUCH more power to reproduce low frequencies compared to highs. I tune my subs like this:

1) listen to the sub all by itself at full range (no crossover). I usually use Skinny Puppy or some other electronic music with very clean bottom for this.

2) sub enclosures (especially ported ones) are tuned to a specific frequency for which they are most efficient. 40-80Hz I consider subharmonic frequencies (808 kick drums, "quad" or rumble) 80-100Hz are "kick" frequencies (they are high enough to "knock" you in the chest with the bass drum). 100-200Hz are "bass guitar" frequencies where you hear actual notes the lower instruments play. So you should hear the "note" your sub is tuned to very clearly. As long as the sub has no built-in passive crossover, you should be able to hear muffled voices and plenty of other sounds as well.

3) Usually the speaker and enclosure will generate harmonics or other "notes" above the note it is tuned to. I listen for those by trying to notice muddiness in bass lines, boominess in the voice or a general honky sound. I then begin to turn the crossover frequency down until I get to a "sweet spot" where most of the voice is gone and the bass line and kick drum clean up nicely. The "Slope" control is how sharp (in dB per octave) your crossover affects the signal from the crossover frequency on down. This in turn affects the harmonics (higher slope number = more pronounced upper harmonics) so that control can be used to as well to shape the sound of your sub.

4) After this process, the sub should sound big, ballsy and tight and very musical all on its own. I find my 12" sub in the studio sounds great at about 150Hz when used in conjunction with my NS-10M studio monitors. We have our Bryston crossover (or the sub's internal one) set to a 6dB/oct curve to keep the subwoofer's tone natural and to blend it into the low end of the NS-10. I designed VAR SUB 01 with the sound of NS-10's in mind to kind of re-create that particular studio sound in the car. The high mids are fairly well pronounced and the bass is rolled off at about 100Hz. The DPS processing is quite aggressive in this profile which should allow for very nice performance on low cost drivers. I find the best drivers are your standard paper cones with a decent magnet.

5) Once the subwoofer sounds good, turn it all the way down and turn on the speakers in the cab. Set the KD-S100 with no bass or trebel boost. Play the same songs and find the approximate listening volume you normally use. It will sound bright and weird now so slowly turn the sub back up until you reach that magical "sweet spot" where the music "comes back together" and the sub is a natural extension of the cabin speakers. If at all possible to do safely, try this whole process while someone else is driving for you on the highway. Road noise is a HUGE factor in car audio that most people never take into account while tweaking their systems in the driveway. Your ears will automatically take the road noise into account as you tune your vehicle so when you are happy at 50mph, you will be happy in the parking lot! Also keep in mind that the subwoofer output is the only output on the KD-S100 that has no DPS processing.

I'm trying to speak in musical term instead of engineering terms because in the end, that's all that really matters. It does take some time and patience to get the hang of this stuff and hey, it's also totally subjective! If anyone has any other techniques, I'd be happy to hear them. cyclops
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PostSubject: REALLY long response on Bass production and harmonics   Wed Sep 30, 2009 6:04 am

Don't want to disappoint you Xaq, but I'm actually using 10" drivers. I would have preferred to use 3 8's but budget won out and I ended up with 2 10's. I am using 8 ohm drivers though for better transients and the amp will like the 4ohm load when bridged.

As to the book. It is very easy to figure out the resultant tone. Here's the math. Subtract the frequency of the lower of two frequencies from the upper frequency and that number is the frequency of the resultant tone. You can hear the resultant tone painfully when you hear two little girls screaming really high and loud or two people whistling really loud but in differing pitched that are fairly close, that buzzing you feel in your ear and that lower grating pitch is the resultant tone. You know exactly what I'm talking about if you've ever heard it.

For instance.... you have a tone at 200 Hz and another at 150Hz. 200-150=50. The resultant tone is 50Hz. If the upper two tones are played loud enough you will hear audibly a 50Hz tone even though there is not one being played. This very simple math can lead to some very surprising effects.

200Hz tone and 100Hz tone. If the two are played perfectly in tune, the 100Hz tone even though it's the same volume should register on a spl meter to be louder because of the resultant tone which is ALSO 100Hz.

200Hz tone and 75Hz tone. You actually get a resultant tone that is ABOVE the lower of the two tones being played. 125Hz!

Again. These tones have to be fairly loud to generate a resultant tone loud enough for the human ear to detect, but that tone is there regardless if we can hear it or whales or dogs.

This effect was found out sometime during the late 1600's to early 1700's if I remember correctly. It was discovered that it was much easier to make 2 little tiny pipes and blow the snot out of them to produce bass notes for a pipe organ, instead of building a HUGE pipe. and WAY cheaper. 2 little tiny whistles that are only 20Hz apart in difference are played so freaking loud that the floor rumbles from the resultant tone at 20Hz, however the two little tiny whistles are pitched out of the audible range of human hearing, so you never actually HEAR them. COOL!

There is also a famous solo piece written for French Horn where the musician is playing one pitch and humming through the horn at the same time and you can hear the resultant tone quite audibly, thus creating a chord, even though there's only one musician on one instrument which is only capable of producing one tone at a time.

You can see why accurate clean sound is so important, and why good sound engineering is so so important. It can have drastic consequences or it can be magic! It can reinforce the quality of the sound or clash and destroy it.

Cool
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PostSubject: continuation..... Bass boost!   Wed Sep 30, 2009 6:07 am

This leads to a very important electronics design flaw in many bass boost and bass reproduction these days. (for non musicians) Each doubling or halving a tone's frequency is called an octave.

440Hz is A used by orchestra's worldwide to tune their instruments. 220Hz is also A but an octave lower, and 880Hz is also A but an octave higher. Get it?

As I referenced in a previous post, I had some retards in an electronics shop try to sell me a bass reproducer or whatever you want to call it that took the lowest tone it saw and reproduced a tone 1.5 octaves lower. Sounds cool right? These guys thought it was the shit and worth the $300 price tag. Well the problem with that is that at 1 octave it would sound fine because it's just reproducing the same exact tone only one octave (or half the frequency) lower. adding that next 1/2 octave is where the problem lies harmonically and musically. It creates what is called a tritone. It is a VERY WEIRD sound.

It doesn't fit into almost ANY music unless specifically WRITTEN into the music and it is used most of the time to cause and uncomfortable feeling to the listener because it is not a natural type of combination and fits neither a Major or Minor chord structure. The first two notes of "Maria" from West Side Story is a tritone. Just the first 2 notes, "Ma- Ri-" not the "a". It sounds awkward to leave it hanging out by itself. Uncomfortably awkward.

When purposely adding a tritone an octave and a 1/2 BELOW the bottom note when listening to 99% of the music out there, it will sound like an elephant farting in the seat next to you. It may shake your ass but it will sound quite literally like crap!


lol!
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PostSubject: Re: Sub Woofer Science   Wed Sep 30, 2009 6:15 am

Sorry Xaq, I wasn't trying to hijack your thread. Just up really late. Embarassed
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PostSubject: Re: Sub Woofer Science   Thu Oct 01, 2009 12:38 am

Vanguard92 wrote:
Sorry Xaq, I wasn't trying to hijack your thread. Just up really late. Embarassed

No worries about hijacking the thread! That's what this is all about.
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PostSubject: Re: Sub Woofer Science   Thu Oct 01, 2009 12:52 am

Vanguard92 wrote:
This leads to a very important electronics design flaw in many bass boost and bass reproduction these days. (for non musicians) Each doubling or halving a tone's frequency is called an octave.

440Hz is A used by orchestra's worldwide to tune their instruments. 220Hz is also A but an octave lower, and 880Hz is also A but an octave higher. Get it?

As I referenced in a previous post, I had some retards in an electronics shop try to sell me a bass reproducer or whatever you want to call it that took the lowest tone it saw and reproduced a tone 1.5 octaves lower. Sounds cool right? These guys thought it was the shit and worth the $300 price tag. Well the problem with that is that at 1 octave it would sound fine because it's just reproducing the same exact tone only one octave (or half the frequency) lower. adding that next 1/2 octave is where the problem lies harmonically and musically. It creates what is called a tritone. It is a VERY WEIRD sound.

It doesn't fit into almost ANY music unless specifically WRITTEN into the music and it is used most of the time to cause and uncomfortable feeling to the listener because it is not a natural type of combination and fits neither a Major or Minor chord structure. The first two notes of "Maria" from West Side Story is a tritone. Just the first 2 notes, "Ma- Ri-" not the "a". It sounds awkward to leave it hanging out by itself. Uncomfortably awkward.

When purposely adding a tritone an octave and a 1/2 BELOW the bottom note when listening to 99% of the music out there, it will sound like an elephant farting in the seat next to you. It may shake your ass but it will sound quite literally like crap!


lol!

I've heard of those devices. It sounds like a rectifier circuit. I can imagine it would sound AWFUL! I've tried such plugins on bass guitars and other instruments every once in a while for strange effects but I usually end up with the elephant farts! Or at least the harmonies get turned upside down like you mentioned before re. tritones.

Tony's philosophy is don't make a device do what it isn't meant to do. So if a system can't reproduce the sub harmoinc frequencies we all want to hear, pass them UP into the device's operating range using properly designed equalizers with the proper Q. Along with the more esoteric processes involved with the Digital Power Station it is possible to make a speaker sound like it is reproducing much more than it is supposed to be capable of according to it's specifications. I'll have to ask the bosses if I can delve any deeper into those discussions involving our proprietary stuff. It's really neat to share with folks who get it!

Keep up the awsome posts!
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PostSubject: Re: Sub Woofer Science   Wed Oct 07, 2009 2:50 am

Hey Xaq. Did you get my PM? Question
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