# when do you have enough woofers/spl?

jazzcustom131
Copper - Posts: 175
Joined: October 10, 2004
Location: United States
Posted: October 22, 2007 at 4:57 AM / IP Logged
Now, I've always looked at adding sub woofers as having to deal with 2 boxes...
1) being the unit you construct to house the speakers, which is where most people put all their time
2) the vehicle's interior space... something I think is typically thought about much less, if at all.
I'm going like 5 directions with this in my head, so bear with me...
To me, SPL's definition seems to mandate that I take into account interior air space. You are trying to obtain maximum pressure levels in an area. Because these levels aren't measured from inside the enclosure, that tells me I have to take into account the airspace in which I'm sitting.
That being said, is there a way to calculate how much woofer is necessary to achieve maximum SPL in a given space. I realize we can calculate relative numbers for the box itself... but as I've stated, that's almost irrelevant, because the meter sits on my dash.
Now, I also realize that typically, you can only add so much, before you're not doing any more good. So the concept of "stuff as many woofers as you can" in your vehicle is frivolous.
But short of having 30 woofers on hand (and 70 some odd different box configurations, numerous amps, wiring, etc, etc, etc) and a meter, is there a way to calculate how many drivers are going to be necessary to get the most punch?
Example, I have an 01 Eddie Bauer Edition Explorer, with 2 JBL GTO 1202D's in a box that's pretty close to what is the recommended enclosure (I haven't had time to build a custom one... getting there). At 48Hz, it plays 145.0 dead on.
Now, what's to say that adding 2 more woofers is a good idea? It seems logical, but at the same time, I just took a couple of cubic feet of air space away from the initial run, and added more cone to the equation.
In theory, it would be an even higher SPL, but I've already stated, adding things only works to a point.
I feel that the interior space of my vehicle MUST be put into the equation, as I could put this same system in my 96 Nissan Hardbody Pickup, and I guarantee it would be louder (everything is louder in that truck), simply because the woofers have less air to compress.
Is there a set of equations laying around, that I'm just not aware of? Or can someone show me proof where calculating this does nothing for you?
With that, how much weight should be given to a speakers xmax? I realize that a larger xmax means it actually has to move faster to produce the same signal (if you have it traveling it's full excursion distance)(I assume that's done by upping voltage?)
From initial glance, a few millimeters may not seem that big of a deal in a large vehicle, but then again, what's a few millimeters off when you're building satellites and doing invasive heart surgery? I realize those are different situations, but my point is, sometimes the smallest things can make a HUGE difference.
Alright, enough for now, lets cover these bases... I appreciate everything you guys have (except for critics of JBL subs... I want equations, not your thoughts on how those things sound)
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jeffchilcott
Platinum - Posts: 2,483
Joined: April 11, 2002
Location: United States
Posted: October 22, 2007 at 6:08 AM / IP Logged
I think alot of it comes down to being streetable, or just being an all out SPL monster.
Going the ladder of the 2. For a CRX 6 10's wasnt enough, and im looking for more this year.
For MTX in 2000 40+ woofers in a Geo tracker seemed to be ok
Same goes for alam gates bronco.
I think the main issue is amount of enclosure space.   Yes the vehicle will play parts in the total output of a setup...But with you in an explorer 4 to 6 12 or even 15 inch woffers would not be a problem in my book.
The problem I see most often is someone trying to shove 4 15's in thier 93 civic, and didnt bother to read the manuals and see they required 4-5 cu ft each.   When the box is built at even half of what the total recommended airspace It can cause major issues
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chucksnee
Copper - Posts: 127
Joined: January 29, 2003
Location: United States
Posted: October 22, 2007 at 8:10 AM / IP Logged
jazzcustom131 wrote:
 Now, I've always looked at adding sub woofers as having to deal with 2 boxes... 1) being the unit you construct to house the speakers, which is where most people put all their time 2) the vehicle's interior space... something I think is typically thought about much less, if at all.
I disagree with statment #1 and agree with #2.
Statment #1, depends on who you are talking too...I know more people who are worried about "HOW MANY" subs they have, no matter what size the box....
DYohn
Moderator - Posts: 10,741
Joined: April 22, 2003
Location: Arizona, United States
Posted: October 22, 2007 at 8:48 AM / IP Logged
Bottom line: yes, the entire system should be taken into account to design an optimal system, and yes, the vehicle (not just the interior, but everything about it) is part of the system.  Secondly, "more" is not always "better" (unless you are building an all-out SPL machine) and third, there are TONS of equations "laying around" to calculate the effects.  It's the science called acoustics.
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haemphyst
Platinum - Posts: 5,054
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: October 22, 2007 at 4:34 PM / IP Logged
jazzcustom131 wrote:
 Now, I've always looked at adding sub woofers as having to deal with 2 boxes... 1) being the unit you construct to house the speakers, which is where most people put all their time 2) the vehicle's interior space... something I think is typically thought about much less, if at all. I'm going like 5 directions with this in my head, so bear with me...
I only count two...
jazzcustom131 wrote:
 To me, SPL's definition seems to mandate that I take into account interior air space. You are trying to obtain maximum pressure levels in an area. Because these levels aren't measured from inside the enclosure, that tells me I have to take into account the airspace in which I'm sitting.
For MAXIMUM SPL, yes, that'd hold true. There will be different tuning frequencies for a given cab volume, all the way from windows closed (highest resonance) to windows all the way open (lowest resonance). This seems to be a bit unfair for SQ competitors in IASCA, as all subjective impressions and objective measurements are made with windows closed, but they want 105dB SPL, at the lowest frequencies acheivable by the system... Vented enclosures seem to REALLY lose their extension with the windows closed, so now you know how my TL will be affected. Dumb. But I digress.
jazzcustom131 wrote:
 That being said, is there a way to calculate how much woofer is necessary to achieve maximum SPL in a given space. I realize we can calculate relative numbers for the box itself... but as I've stated, that's almost irrelevant, because the meter sits on my dash.
If referring to burps, one high efficiency 18 inch woofer, burped with 12kW, in an enclosure tuned TO the cabin Fs, will give you LOTS of dB's, but how many times? Continuous high level output may require less power, but trading off (out for) enclosure size - you'll need more enclosure, bucause you'll be putting in more woofers. More woofers are necessary to make up for the loss of power capability... Am I making sense? (I hope so, because I'm lost in my own ramblings...)
jazzcustom131 wrote:
 Now, I also realize that typically, you can only add so much, before you're not doing any more good. So the concept of "stuff as many woofers as you can" in your vehicle is frivolous.
This is true. For each doubling of either power OR surface area, you only gain (in theory) 3dB. For a doubling of both, you gain 6dB. So what this really boils down to is this: How much surface area can you stuff into the available volume, or how much power can you drive with the given electrical capacity of the car, or what can you do to minimize the detrimental effects on both of those?
Basically options now are:
1: Do you want to trade storage for output (the single driver scenario - requiring a high current power supply)
2: Do you not care about storage, but can't (or don't want to) fit a larger power supply into the car (the multiple woofer scenario - using the stock charging system and a (releatvely) lower powered amplifier)
3: Is my desired result an all-out SPL monster (the multiple woofer, huge power scenario - to hell with storage, AND give me those 300A alternators while you're at it, please...)
jazzcustom131 wrote:
 But short of having 30 woofers on hand (and 70 some odd different box configurations, numerous amps, wiring, etc, etc, etc) and a meter, is there a way to calculate how many drivers are going to be necessary to get the most punch?
Unfortunately, no. You can come close, for anechoic response, and it is possible to get SOME cabin response curves off the internet to place over the top of your anechoic curves for THEORETICAL outputs, but generally, no.
jazzcustom131 wrote:
 Example, I have an 01 Eddie Bauer Edition Explorer, with 2 JBL GTO 1202D's in a box that's pretty close to what is the recommended enclosure (I haven't had time to build a custom one... getting there). At 48Hz, it plays 145.0 dead on. Now, what's to say that adding 2 more woofers is a good idea? It seems logical, but at the same time, I just took a couple of cubic feet of air space away from the initial run, and added more cone to the equation.
If you have to make your enclosure smaller, you may or may not reduce the total output (relative to two woofers) enough to actually double your output (gain 3dB) by doubling your cone area.
jazzcustom131 wrote:
 In theory, it would be an even higher SPL, but I've already stated, adding things only works to a point.
True, again... Eventually you run out of either cone area or power capacity. Well before this point is called "the point of diminishing returns", meaning that for twice the money, you WON'T get twice the performance/output/sound quality, etc. As per my response above, you'll have to build them in the virtual world... WAY cheaper than the physical world, as you know. Here's a possibility for you as well. Build the present enclosures in software, get it's curve, and subtract the virtual curve from your actual curve in your actual truck. This will give you a transfer curve that you can then apply to every response curve you ever build, and you'll be able to get closer to a real-world response forever. Plus, you'll be able to build all of your systems in the computer first!
jazzcustom131 wrote:
 I feel that the interior space of my vehicle MUST be put into the equation, as I could put this same system in my 96 Nissan Hardbody Pickup, and I guarantee it would be louder (everything is louder in that truck), simply because the woofers have less air to compress.
Maybe or maybe not... One frequency, or across the band? See... Herein squats the toad. You can't say that "t'll be louder" just because of the volume of one cabin vs. another. Concert venues might only use a few hundred watts per woofer, (yes, DOZENS and DOZENS of woofers) and one of the loudest rock concerts on record was 126dB, 100 feet from the stage. ( reference: http://en.wikipedia.org/wiki/Loudest_band_in_the_world ) Now, while a concert venue IS larger than your truck, it probably wasn't too much louder at the stage than your truck presently is, and they used (potentialy) far less power (per woofer) than you have right now.
jazzcustom131 wrote:
 Is there a set of equations laying around, that I'm just not aware of? Or can someone show me proof where calculating this does nothing for you?
As DYohn says:
DYohn wrote:
 and third, there are TONS of equations "laying around" to calculate the effects. It's the science called acoustics.
jazzcustom131 wrote:
 With that, how much weight should be given to a speakers xmax? I realize that a larger xmax means it actually has to move faster to produce the same signal (if you have it traveling it's full excursion distance)(I assume that's done by upping voltage?)
None. Longer throw woofers are typically ABYSMALLY efficient, when what you are after (in the case of an SPL car) is high relatve efficiency to start with. XMax is desirable if you want extension, but Kirschoff's Law won't allow both, easily. You get output or extension. You can't have both without a compromise of one or the other. I'm trying to locate the thread we had regarding this very thing... We did it about 12 to 18 months ago, I think. (About an hour of searching later, and no love... I'll keep looking, though...)
jazzcustom131 wrote:
 From initial glance, a few millimeters may not seem that big of a deal in a large vehicle, but then again, what's a few millimeters off when you're building satellites and doing invasive heart surgery? I realize those are different situations, but my point is, sometimes the smallest things can make a HUGE difference.
A few millimeters in refernce to what? The Xmax? The enclosure volume? Ya lost me here...
jazzcustom131 wrote:
 Alright, enough for now, lets cover these bases... I appreciate everything you guys have (except for critics of JBL subs... I want equations, not your thoughts on how those things sound)
There's my input... Do with it what you will!
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice.﻿ You should write it down."
haemphyst
Platinum - Posts: 5,054
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: October 22, 2007 at 5:17 PM / IP Logged
Here's that link! I knew I'd find it!
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice.﻿ You should write it down."
haemphyst
Platinum - Posts: 5,054
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: October 22, 2007 at 5:38 PM / IP Logged
haemphyst wrote:
 XMax is desirable if you want extension, but Kirschoff's Law won't allow both, easily. You get output or extension.
That's HOFFMAN'S Law... Not Kirscoff's Law.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice.﻿ You should write it down."
jazzcustom131
Copper - Posts: 175
Joined: October 10, 2004
Location: United States
Posted: October 22, 2007 at 7:08 PM / IP Logged
There seems to be a general consensus of "It depends, is this a daily, or an SPL monster?" For the sake of this thread, lets go with the SPL monster stand point.
jeff... Got any pictures of THAT!? Had to look crazy!
chuck I sorta roll the two together... people worry about packing 10 woofers in the car, and then trying to figure out how to build the box... either way, more time is spent on that enclosure I feel, than designing the system to the vehicle.
DYohn, short of going to college and majoring in Acoustical Engineering, where should I start researching to find these? The last time I tried "just walking into a library" I ended up spending more time on robotics than acoustics. Got any titles that make a good starting point?
Haemphystlol, yeah, I only listed 2 for the moment... it was late, and I was concerned about rambling as it were...
For the sake of this... windows up, single freq burps.
Storage... who needs it. I demand hearing loss! Lets make it a beast, through whatever means necessary.
This Anechoic Response... how do I obtain this?
You said...
"If you have to make your enclosure smaller, you may or may not reduce the total output (relative to two woofers) enough to actually double your output (gain 3dB) by doubling your cone area."
...at which point I'm lost. Are you saying if I build a smaller box for the same 2 speakers, or add 2 more, and give each woofer less space than what the 2 had originally (proportionally... if each of the 2 originally had 1 ft^3 each, they now get .75 ft^3 each)-Not how it's set up, but just trying to figure this out.
After re-reading what you quoted from me, I'm thinking you may have misunderstood me. I wasn't saying that it would take away enclosure space from the subs, but that it would take away cabin volume, because it is now part of the enclosure
Concerning the Rock bands... I am aware (I do concert Lighting for those that don't know), but (and I may be lost in the sauce) but Pro Audio uses Compression Drivers, which are more efficient therefore don't need excessive power, because less is lost as heat, etc. Car Audio uses Dynamic Drivers, which aren't as efficient, therefore we tend to need ridiculous amounts of power to achieve the same thing.
I hope I got that drivers thing right... otherwise I feel dumb.
The few millimeters statement was regarding excursion limits.
From reading that, it seems to me what you're saying is find a high efficiency driver, with minimal xmax? If that's true, you're gonna have to do some major explaining to me, because that seems to violate physics. Let me explain...
For every action there is an equal and opposite reaction... When I'm playing my music at low levels, most of my drivers move a very small amount, but when I crank it up, they're nearly coming out of the basket. In order for sound to be created, something must vibrate, correct? It would seem the bigger the vibration, the more...profound? the sound wave should be.
That is based strictly on observations of stated at the beginning of that last paragraph. That alone makes me raise an eyebrow to your statement. Please enlighten me, cause I know you know something I don't.
WOO!!! Alright, that was alot... keep it comin guys.
Greed is for amateurs.
Disorder,chaos,anarchy now THAT is fun!!
jeffchilcott
Platinum - Posts: 2,483
Joined: April 11, 2002
Location: United States
Posted: October 23, 2007 at 3:09 AM / IP Logged
There are pictures floating aroun don this fourm....and some new ones should be coming up soon enough or the new setup, once it is completed
2009 0-1000 Trunk WR 154.0DB 2009 1001+ Trunk WR
2007 USACI World Champion
2007 World Record
2006 USACI Finals 2nd Place
Steven Kephart
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Joined: November 06, 2003
Location: Oregon, United States
Posted: October 23, 2007 at 10:39 AM / IP Logged

jazzcustom131 wrote:
 DYohn, short of going to college and majoring in Acoustical Engineering, where should I start researching to find these? The last time I tried "just walking into a library" I ended up spending more time on robotics than acoustics. Got any titles that make a good starting point?

Check out Fundamentals of Acoustics linked below.  I should warn you though that it is VERY math heavy.

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