ported enclosure volume

Alright, I have a question...I hope it's understandable.  Say I have one subwoofer and the recommended vented enclosure volume is 2.0 cu. ft.  If I want to add another subwoofer and build a new enclosure, using a single chamber with a slot port in the middle, does the volume of the enclosure double to 4 cu. ft., or does it stay the same at 2 cu. ft.?  I'll disregard the port and sub displacement, just looking for a general answer!  Thanks! 

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2003 Dodge Neon R/T
Alpine CDA9813, RF T2000.1bd, RF T162S, RFT142C, RF T600.4, RF T215D4
140.7 @ 28Hz

In general, if the recommended volume for one speaker is 2 cuft then for two you'd use 4 cuft, but this will not always give you the same sort of performance so your best bet is always to use modeling software like WinISD or Unibox or BassBox and see what will happen  The port geometry, on the other hand, is not so simple as simply doubling the recommended size.  You need to calculate a new port for the same tuning frequency in your new larger enclosure, and realize that two woofers will move more air than one so the port opening might need to be larger.

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Thank you very much!  Assuming that the port opening itself might need to be larger, the length shouldn't change, correct?  I've been playing with bassbox lite and find it a little more user friendly than WinISD.  What do you think?

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2003 Dodge Neon R/T
Alpine CDA9813, RF T2000.1bd, RF T162S, RFT142C, RF T600.4, RF T215D4
140.7 @ 28Hz

Post opening size needs to be large enough to minimize noise of air rushing through it.  I am not familiar enough with BassBox to know if it calculates port velocity, but you need to size the opening to keep port air velocity below about 17 m/sec.  Once you have the opening sized appropriately, you can calculate the necessary length to tune the enclosure volume to the target frequency.

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I remember reading about 2 years ago an article in Car Sound and Performance about calculating the resonant frequency of any car, and that for pure SPL, the idea is to have the tuning frequency match the resonant frequency of the vehicle.  I've since lost the magazine, and am unable to find the article online.  There were a few equations used, and if I remember correctly, the tuning frequency of the box used to achieve max SPL would change depending on where, in the vehicle the box was located.  Does this make sense?

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2003 Dodge Neon R/T
Alpine CDA9813, RF T2000.1bd, RF T162S, RFT142C, RF T600.4, RF T215D4
140.7 @ 28Hz

Yes it does.  And if you are going for pure SPL, port air velocity is a non-issue.  I do not have the equations you mention right off hand, but most passenger car-sized vehicles have cabin resonant frequencies in the 60Hz range.

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you say port air velocity is a non-issue, but doesn't port noise damage a speaker?  Also, generally speaking, when the cabin's RF is matched by the enclosure, max spl is achieved?  How does changing the woofer affect this?  I understand that a physically larger woofer will move more air, increasing SPL, but does a different woofer of the same size and power input change the output?  Is there a way to "max out" in terms of SPL and vehicle, assuming the vehicle is a daily driver with none other than basic electrical system modifications?

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2003 Dodge Neon R/T
Alpine CDA9813, RF T2000.1bd, RF T162S, RFT142C, RF T600.4, RF T215D4
140.7 @ 28Hz

audiomaninc wrote:

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you say port air velocity is a non-issue, but doesn't port noise damage a speaker?  Also, generally speaking, when the cabin's RF is matched by the enclosure, max spl is achieved?  How does changing the woofer affect this?  I understand that a physically larger woofer will move more air, increasing SPL, but does a different woofer of the same size and power input change the output?  Is there a way to "max out" in terms of SPL and vehicle, assuming the vehicle is a daily driver with none other than basic electrical system modifications?

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Wow, lots of questions.  OK, here's my 2 cents.

Port noise does not damage anything.  It's just if you are building a system you plan to listen to (ie: not just for SPL comp) then you want to make sure any port noise is minimized so you don't have to listen to it.

In general if you are trying to build an SPL competition vehicle, you want to maximize SPL from all available sources, so matching a subwoofer system resonance frequency to the vehicle's resonance frequency can get you a few extra dbs.

Yes, all woofers will perform differently, even two different woofers of the same size and power input.  It is not just about cone size and power, it is also about displacement (Xmax) and about the enclosure.  Indeed, the enclosure is by far the biggest contributor to big SPL numbers, much more so than simply large power numbers.

Finally, I am not certain what you mean by "max out" a system, but sure you can design a system for max output given the parameters of the woofer and the available system and electrical power.  But for a "daily driver," unless you are building a boom car it is not about SPL, it is about sound quality.  Build a system that sounds good and you will be far happier a lot longer than you will be with one that just gets loud.

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Thanks for all the input!  It's been a pleasure talking with you.  What I mean by "max out", is simply put, is it possible to achieve the maximum spl potential of a car, or can it always be louder?  I suppose it would be possible to achieve the limit of any given system, but as soon as you introduce new equipment, everything changes!  I think I just answered my question!

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2003 Dodge Neon R/T
Alpine CDA9813, RF T2000.1bd, RF T162S, RFT142C, RF T600.4, RF T215D4
140.7 @ 28Hz

it can always be louder...but it just takes more time, more money, some more time, and even more money lol

So in conclusion, there is no way to determine the max spl limits of any one vehicle!  Brilliant!  Wait...if you blow the windshield out of a car that certainly seems like a limit...drats!  But now that's just silly

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2003 Dodge Neon R/T
Alpine CDA9813, RF T2000.1bd, RF T162S, RFT142C, RF T600.4, RF T215D4
140.7 @ 28Hz

That would be correct.  And no, blowing the windshield out does not mean a limit has been reached. 

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DYohn] wrote:

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That would be correct.  And no, blowing the windshield out does not mean a limit has been reached. 

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It just means the "limit of that particular piece of glass" has been reached! Time for more power!! BWAHAHAHAHA

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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."