# Ported Box DB Gain?



## RichB (Jun 3, 2013)

I read from a decently reputable source that you can gain 3-*9* db using a ported box over sealed. ((EDIT: Assuming they're built to spec.)) I know the 3 db gain to be absolutely true, but how would a box add 9db?? Am I missing something or is this even true? 

If so, someone please explain this. That's quite a bit of db gain from just the box alone and I'm gonna take a guess thay you'd have to sacrifice quite a lot of SQ on a pretty highly tuned box with a rather large Vb for the specific sub.


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## nervewrecker (Oct 5, 2009)

http://www.diymobileaudio.com/forum...generate-more-spl-without-spending-penny.html


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## minbari (Mar 3, 2011)

its not a myth. if SPL is all you are after, then 6-9db gain is not unheard of


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## cubdenno (Nov 10, 2007)

As in anything, the gain is tied to specifics.Apples to apples the gain is smaller. If you can make the ported enclosure correctly, yes you can see those gains. Especially when you factor in cabin gain.
just saying up to a 9db gain is silly. I have seen 15db in <40 hertz gains.

Do you have unibox or WinISD?

Easier to explain with a modeling program.

If a typical small (.5cubes) sealed box for a 10" starts rolling off ~60 hertz, at 30 hertz let's say it's 12 db down. And the same sub in a 1 cube ported enclosure is let's say flat to 30 hertz and then starts rolling off with equal sensitivity at 60 hertz. 3 db higher at 50 hertz 6 db at 40 and 12 at 30 (arbitrary numbers). But gains that are there and higher than the 3 db that is given as ported gain.


Edit: Crap. Forgot to post this and then went to lunch. Thanks for the graph Min!!


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## Hanatsu (Nov 9, 2010)

The increased efficiency with a vented box is 3dB. The output can be lots more but it also requires more power... and a driver designed to withstand the heat generated in the VC.


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## minbari (Mar 3, 2011)

Hanatsu said:


> The increased efficiency with a vented box is 3dB. The output can be lots more but it also requires more power... and a driver designed to withstand the heat generated in the VC.


3db across the entire passband? care to explain?

(if the output is "lots more" then wouldnt that be more than 3db gain?)


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## Hanatsu (Nov 9, 2010)

minbari said:


> 3db across the entire passband? care to explain?
> 
> (if the output is "lots more" then wouldnt that be more than 3db gain?)


Not exactly. A vented box with the same enclosure size will be 3dB more efficient, however efficiency and output are not the same thing. Model two drivers in WinISD, one sealed, one vented. EQ them to the same response. Try a -3dB PEQ centered somewhere (into the rolloff/stopband), they will produce the same SPL. 

However, the output can be lots more. IF (big IF) the VC can take the abuse you can feed the driver sometimes thousands of watts before it runs out of Xmax at Fb (port resonance frequency/tuning frequency). It requires lots lots and lots of power, but you can have immense gain from the port that far exceeds 3dB (but that ain't about efficiency).


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## minbari (Mar 3, 2011)

Hanatsu said:


> Not exactly. A vented box with the same enclosure size will be 3dB more efficient, however efficiency and output are not the same thing. Model two drivers in WinISD, one sealed, one vented. EQ them to the same response. Try a -3dB PEQ centered somewhere (into the rolloff/stopband), they will produce the same SPL.


problem is no-one uses the same size enclosure for ported and sealed. so I dont buy this for a second.


> However, the output can be lots more. IF (big IF) the VC can take the abuse you can feed the driver sometimes thousands of watts before it runs out of Xmax at Fb (port resonance frequency/tuning frequency). It requires lots lots and lots of power, but you can have immense gain from the port that far exceeds 3dB (but that ain't about efficiency).


this is true, but you are only going to get that gain at exactly the fb. above and below the fb you are going to destroy the woofer with the kind of power you are talking about.


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## Hanatsu (Nov 9, 2010)

minbari said:


> problem is no-one uses the same size enclosure for ported and sealed. so I dont buy this for a second.
> 
> this is true, but you are only going to get that gain at exactly the fb. above and below the fb you are going to destroy the woofer with the kind of power you are talking about.


Same size can surely be used, why not? A low Qtc designed sealed enclosure will have a larger enclosure and a vented design with good transient behavior (smooth rolloff, for example a QB3 alignment) might very well have the same enclosure size (model a Exodus Anarchy 6,5" for example). Efficiency is also tied to the impedance response, wherever the impedance peaks, the amplifier output goes down. If you modify the enclosure size, the impedance peak will move around, too small enclosure and the peak will move outside the area we're gonna use the woofer and the design will be inefficient anyway. The vented design got two impedance peaks however, one below Fb and one at enclosure resonance. The one below Fb is of no use to us whatsoever.

To be able to compare something we have to put it in relation to each other, in this case it's the enclosure size and losses that occur. If no parameter remain the same we can't compare them to each other, simple as that.

- - - - - - - - - - - - - 

Most likely destroy it anyway from unloading... Tuning frequency ain't a constant value. It varies with output and temperature for example.


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## minbari (Mar 3, 2011)

Hanatsu said:


> Same size can surely be used, why not? A low Qtc designed sealed enclosure will have a larger enclosure and a vented design with good transient behavior (smooth rolloff, for example a QB3 alignment) might very well have the same enclosure size (model a Exodus Anarchy 6,5" for example). Efficiency is also tied to the impedance response, wherever the impedance peaks, the amplifier output goes down. If you modify the enclosure size, the impedance peak will move around, too small enclosure and the peak will move outside the area we're gonna use the woofer and the design will be inefficient anyway. The vented design got two impedance peaks however, one below Fb and one at enclosure resonance. The one below Fb is of no use to us whatsoever.
> 
> To be able to compare something we have to put it in relation to each other, in this case it's the enclosure size and losses that occur. If no parameter remain the same we can't compare them to each other, simple as that.


all true, but you will get more return from a larger ported box than a larger sealed box.


> - - - - - - - - - - - - -
> 
> Most likely destroy it anyway from unloading... Tuning frequency ain't a constant value. It varies with output and temperature for example.


pretty much what I was saying. unless you are going to play a single hz tone and find the exact freq it is tuned for, this is pointless. a little higher or lower than FB and the woofer explodes. certainly cant play music like this.


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## Hanatsu (Nov 9, 2010)

minbari said:


> all true, but you will get more return from a larger ported box than a larger sealed box.
> 
> pretty much what I was saying. unless you are going to play a single hz tone and find the exact freq it is tuned for, this is pointless. a little higher or lower than FB and the woofer explodes. certainly cant play music like this.


Yep pretty much so


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## Golden Ear (Oct 14, 2012)

I had an arc 10 in a spec sealed box and then switched over to a larger slot ported box and gained 6db. With some eq I don't think you'll lose sq but everyone's taste is different.


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## Hanatsu (Nov 9, 2010)

Golden Ear said:


> I had an arc 10 in a spec sealed box and then switched over to a larger slot ported box and gained 6db. With some eq I don't think you'll lose sq but everyone's taste is different.


My opinion is that a ported enclosure sounds better than a sealed (generally). This is under the condition that it's properly tuned/built and use a driver designed for vented boxes. You will most likely need a good parametric EQ too. Low tuned vented subs tend to peak like 10-15dB around the cars resonance point.

Less excursion = less distortion.

Sent from my Samsung Galaxy 3 via Tapatalk.


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## RichB (Jun 3, 2013)

Cool, thanks for all the replies!


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