# The relationship between port area and SPL increase.



## Fricasseekid (Apr 19, 2011)

So when I design a ported box I simply try to get my port area large enough to have an acceptable group delay and port velocity. 

I recently read a couple threads frequented by some bass heads where they suggest that if your port area isn't large enough your not getting as much increase as your ported box is capable of producing. This talk usually seemed to coincide with building high Q one note wonder type boxes where port resonances are much more sensitive to different variables. 

Is this relationship between port area and SPL significant when designing SQ boxes as well? 

Would y'all care to discuss this or explain it to me?


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## Fricasseekid (Apr 19, 2011)

Nobody?


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## minbari (Mar 3, 2011)

dont think there is much correlation. obviously if you have a 15" sub with 3000 watts of power and you use a 2" port, it will only work up to a very low volume. once port velocity gets high enough to be full on port compression, the port becomes worthless. At that point, a larger port would gain you more output.

making sure that your port is of sufficient size and your port velocity is sufficiently low is all that is needed to maximise SPL. SQ is really more a function of the driver, enclsoure and tuning correctly.


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## Fricasseekid (Apr 19, 2011)

I read where some SPL guys might actually drop a sub or two on order to fit a larger port in the box. It has something to do with the friction of the air moving across the sides of the port. 

I read it here: http://www.avsforum.com/t/1305105/increase-port-area-increase-spl


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## thehatedguy (May 4, 2007)

That and the lever of the port- the column of air inside the port that does the work gets larger. I've noticed SPL increases with larger ports. But you can quickly run into diminishing returns with regards to output and port size.


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## minbari (Mar 3, 2011)

well if they port velocity is too high then adding more subs will only make the problem worse. once you are into port compression the box functions as a sealed box. SQ and nice smooth freq response is not something an SPL competitor wants.

so yes, getting the port the correct size will maintain max SPL. but if you have an 8" port and your port velocity is 50ft/s, then a 10" port will do nothing, you are already well below any port turbulence.

you also have to consider that the more port area you have the longer the port gets........fast. 

ex:

1.5 cuft box tuned to 40 hz.

4" port = 11.6"
6" port = 28"
8" port = 51.3"

you can see how out of hand it gets pretty fast.


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## Fricasseekid (Apr 19, 2011)

minbari said:


> well if they port velocity is too high then adding more subs will only make the problem worse. once you are into port compression the box functions as a sealed box. SQ and nice smooth freq response is not something an SPL competitor wants.
> 
> so yes, getting the port the correct size will maintain max SPL. but if you have an 8" port and your port velocity is 50ft/s, then a 10" port will do nothing, you are already well below any port turbulence.
> 
> ...


Yeah I understand that you can run out of volume quickly. I also notice that software like winISD won't show increased SPL for a larger port area. It only shows a given amount of increased output for a particular box size and tuning frequency. Apparently you need something like horn resp to model these variable. Which makes me think there is more to it than just avoiding high port velocities. It seems to me that there would be some significance to the ratio of port area to cone area which is also directly tied in to box volume. 

The reason I ask is; I built this ported box for my brother.
















The port is 1 1/2" x 12" and 9" long tuned to around 39 hz in a 2.7 cu ft. box. It sounds incredible and has absolutely no port noise. The group delay is barely on the charts. But a friend of his suggested that the box might've benefited more from a larger port area. 

So I got to thinking: I can't think of any reason a larger port wouldn't increase output.


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## minbari (Mar 3, 2011)

ya, WinISD is not that complex of a simulator. but if you look at the port velocity, you can design it to keep that low as possible/needed.

how much SPL does he think he will gain? if it is pretty close to ideal now, I wouldnt expect more than 1 db difference. Is he an SPL guy?


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## Fricasseekid (Apr 19, 2011)

minbari said:


> ya, WinISD is not that complex of a simulator. but if you look at the port velocity, you can design it to keep that low as possible/needed.
> 
> how much SPL does he think he will gain? if it is pretty close to ideal now, I wouldnt expect more than 1 db difference. Is he an SPL guy?


Oh yeah. He is definitely an SPL guy. 

Wouldn't more air volume in the port equate to more cone control in the box?


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## minbari (Mar 3, 2011)

best way to get good cone control for ported box is to high pass closer to the tune.

if that is tuned about 40hz, then use an SSF about 35hz. thing will pound and never unload.

if he wants a larger port it wont hurt anything, but as said above, port length may get ridiculous.


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## minbari (Mar 3, 2011)

cajunner said:


> looks like a single cab p/up box, with the subs firing into the seat.
> 
> that can definitely cause a lot of frictional losses as the area in front of the woofers act like a slot load and the sound pressure is forced through the aperture to where it can interact with the rest of the air space in the cabin.
> 
> not much more to be done with this kind of install, unless you'd want to produce some volume-robbing clearance tunnel from the cone.


4th order with upfiring ports would solve this too. they can be ungodly loud too.


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## Fricasseekid (Apr 19, 2011)

So considering port velocities and group delay are acceptable across the board, for a given box volume and tuning frequency a 6" and 8" port, or whatever size, should net you relatively the same SPL gains?


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## minbari (Mar 3, 2011)

Fricasseekid said:


> So considering port velocities and group delay are acceptable across the board, for a given box volume and tuning frequency a 6" and 8" port, or whatever size, should net you relatively the same SPL gains?


short answer, yes.

it may effect it a few tenths, which might be worth it for an SPL comp.


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## Oscar (Jun 20, 2010)

Fricasseekid said:


> Oh yeah. He is definitely an SPL guy.
> 
> Wouldn't more air volume in the port equate to more cone control in the box?


Don't know where you read this, but nope. It is not the same as "adding a larger mass" to the cone to minimize it's movement. A port loads the driver cone through acoustic resonance, not from the sheer/actual air mass in the port. Acoustic resonance provides an _acoustic_ mass for the cone. Two completely different sized ports (yet tuned to the same frequency) can load a cone the same exact "amount". This can be seen in the [identical] excursion graph for a particular driver/system and varying port dimensions with constant tuning frequency.

Unless you're going to alter the profile of the port, the best thing you can do is to make sure you're under the turbulence limit for your given system (in terms of vent air speed) and have radiused port ends. In other words make it large enough that turbulence becomes a non-issue for practical purposes.

Tech paper on port profiles.
http://www.mediafire.com/view/?wg733afd6pz69zn


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## Fricasseekid (Apr 19, 2011)

So for all SQ purposes I shouldn't worry about port area for anything other than air velocity. 

Thanks for the input fellas.


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## minbari (Mar 3, 2011)

Fricasseekid said:


> So for all SQ purposes I shouldn't worry about port area for anything other than air velocity.
> 
> Thanks for the input fellas.


pretty much. if you plan your ports for worst case, you will have more than enough port area.


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## Oscar (Jun 20, 2010)

Fricasseekid said:


> So for all SQ purposes I shouldn't worry about port area for anything other than air velocity.
> 
> Thanks for the input fellas.


Actually, port flare geometry can have an impact on SQ since ports can and do introduce sounds other than the fundamental tuning frequency (regardless of where the subwoofer is crossed over--it is distortion produced _at_ the port by way of the fundamental frequency). Unfortunately 3rd order harmonics dominate over the "more preferred" 2nd order which mesh "nicer" with the fundamental.

This is all dependent on the actual SPL that the system will be driven. It's all covered in the paper.


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## HiloDB1 (Feb 25, 2011)

For SPL guys when it comes to port sizes they dont use any modeling software they use experience and trial and error. Thats how they figure out every last 1/10th in their system.

For SQ I wouldnt worry about it much. As long as your port velocity is in check youll be fine.

Another thing to note is SPL on the meter vs how low you perceive it to be are totally different. What sounds ridiculously loud to you may not meter anything impressive.


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## D-Bass (Apr 27, 2012)

a port is going to tune based on inertia, not volume within the port

For the SPL guys that do use modeling software, they are the ones telling you their enclosure is tuned to 32.67Hz, or 44.56Hz, as if their software and building skills are so accurate they can tune the box, or measure system impedance curves in response to driver impedance curves at maximum power level to within 0.01Hertz, and take into account power compression as they drive 5000W into their sub that is only "linear" to 1500W, and their amp is at 15% distortion. whatever!

a good, and experienced SPL guy does not use modelling software, he doesn't need it. there are too many variables and with experience, taking notes, observation, and trial/error with those notes makes the key.

for SQ, it takes the same skills, patience, and dilligence, but also the constant changing of xover slopes, frequencies, etc...


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## Fricasseekid (Apr 19, 2011)

D-Bass said:


> a port is going to tune based on inertia, not volume within the port
> 
> For the SPL guys that do use modeling software, they are the ones telling you their enclosure is tuned to 32.67Hz, or 44.56Hz, as if their software and building skills are so accurate they can tune the box, or measure system impedance curves in response to driver impedance curves at maximum power level to within 0.01Hertz, and take into account power compression as they drive 5000W into their sub that is only "linear" to 1500W, and their amp is at 15% distortion. whatever!
> 
> ...


That's all fine and dandy but your response didnt really answer the question. I never asked about modeling software.


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## HiloDB1 (Feb 25, 2011)

Fricasseekid said:


> That's all fine and dandy but your response didnt really answer the question. I never asked about modeling software.


When it comes to real life scenarios there are to many variable to just say a bigger port will net more SPL. I have built enclosures where decreasing my port size (to an extent) increased my output on a meter, and times where changing port size hurt my numbers.

And again numbers on a meter are different from what you hear. Loud on the mic doesn't meant loud when your listening to it and vice versa.

So what are you more concerned about? SPL on a meter or how loud it sounds to you?


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## Fricasseekid (Apr 19, 2011)

HiloDB1 said:


> When it comes to real life scenarios there are to many variable to just say a bigger port will net more SPL. I have built enclosures where decreasing my port size (to an extent) increased my output on a meter, and times where changing port size hurt my numbers.
> 
> And again numbers on a meter are different from what you hear. Loud on the mic doesn't meant loud when your listening to it and vice versa.
> 
> So what are you more concerned about? SPL on a meter or how loud it sounds to you?


I just want to get the most out of my box designs without sacrificing SQ. Isn't that what any audiophile wants?


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## minbari (Mar 3, 2011)

Fricasseekid said:


> I just want to get the most out of my box designs without sacrificing SQ. Isn't that what any audiophile wants?


ya, but wringing the last 2% of max SPL out of a box isnt going to matter. how often are you going to push an "SQ" system that hard?


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## Fricasseekid (Apr 19, 2011)

minbari said:


> ya, but wringing the last 2% of max SPL out of a box isnt going to matter. how often are you going to push an "SQ" system that hard?


I don't make those kinds of compromises. I want my systems loud and SQ. That extra 2% is worth it of it is a simple design change. But if that 2% requires so much work that you get into diminishing returns....

But what are the real world gains? I value you opinion more than many Minbari but if you come up with a stat like 2% can you back that up with some science?


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## HiloDB1 (Feb 25, 2011)

I keep bringing this up because it makes a difference but are we talking on a meter trying to get every 1/10th or perceived output?

Why because if you care about every 1/10th on a meter you're not going for SQ and if you're going for perceived output then 1/10th or even a few 10ths on the meter are not going to matter.


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## minbari (Mar 3, 2011)

no, it was just an example. but even 2% would be optimicstic. we are talking about 2% of maximum. so if your subs are capable of 130db and you gain another 2% that is nearly 3db. you know how it works 

but does another 3db over an already large number really matter in the big picture? it is up to you to determine those diminishing returns. for me, designing a system that is carefully thought out is important, but eeking out every last watt is not terribly important.


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## minbari (Mar 3, 2011)

HiloDB1 said:


> I keep bringing this up because it makes a difference but are we talking on a meter trying to get every 1/10th or perceived output?
> 
> Why because if you care about every 1/10th on a meter you're not going for SQ and if you're going for perceived output then 1/10th or even a few 10ths on the meter are not going to matter.


exactly my point


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## Fricasseekid (Apr 19, 2011)

I don't disagree with you guys. I'd just like to see a little science these 1/10 and 2% figures. In other words I'd like know why increasing port size only gives you a negligible increase in volume.


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## HiloDB1 (Feb 25, 2011)

Again are you even going to meter this? And do you care more about how it sounds than how it meters? You still havent answered that.


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## Fricasseekid (Apr 19, 2011)

HiloDB1 said:


> Again are you even going to meter this? And do you care more about how it sounds than how it meters? You still havent answered that.


No, I never mentioned a meter.


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## minbari (Mar 3, 2011)

Fricasseekid said:


> I don't disagree with you guys. I'd just like to see a little science these 1/10 and 2% figures. In other words I'd like know why increasing port size only gives you a negligible increase in volume.


I am not a scientist, lol. but you are not changing the tuning, only the volume of air being used to tune it.

if the tune is already optimal, then bigger wont help. (or it will help so little that it wont matter) I wouldn't be hung up on the numbers.


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## HiloDB1 (Feb 25, 2011)

Fricasseekid said:


> No, I never mentioned a meter.


Then it wont matter. Only way to really know is to build, test, build, test. If you dont care or wont be metering then build it and see how it sounds.


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## HiloDB1 (Feb 25, 2011)

If he is not getting any port noise as is I doubt he will "hear" a difference by going up a few sq inches of port.


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## Rrrrolla (Nov 13, 2008)

minbari said:


> no, it was just an example. but even 2% would be optimicstic. we are talking about 2% of maximum. so if your subs are capable of 130db and you gain another 2% that is nearly 3db. you know how it works
> 
> but does another 3db over an already large number really matter in the big picture? it is up to you to determine those diminishing returns. for me, designing a system that is carefully thought out is important, but eeking out every last watt is not terribly important.


3dB is 100% more, or 50% less and is perceivable but does not SOUND twice as loud. 10dB's aparently sounds twice as loud, and that would mean a 10X gain in output or 1000% increase in output to "sound" twice as loud. If you really only gain 2% than there is no way in hell you are going to know the difference.


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## minbari (Mar 3, 2011)

Rrrrolla said:


> 3dB is 100% more, or 50% less and is perceivable but does not SOUND twice as loud. 10dB's aparently sounds twice as loud, and that would mean a 10X gain in output or 1000% increase in output to "sound" twice as loud. If you really only gain 2% than there is no way in hell you are going to know the difference.


I am not talking about power. 2% 130 is 2.6. I fully understand the logrithmic behavior of how db and power are calculated.

I agree with the last part though. the tiny gain he will see will not be audible in most cases.


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## cubdenno (Nov 10, 2007)

Aren't the numbers that are being thrown around arbitrary? As in they were used as an example?


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## Fricasseekid (Apr 19, 2011)

This thread got complicated quick. Lots of opinions being thrown around with very little technical discussion. 

Cajunner summed up the point very well with his last post. Either there is a perceivable difference that makes a bigger port worth while or there isn't. And considering I use WinISD that won't model such variables the point is kinda moot until I've had time to do some trial and error. 

I'd really like to build 3 or 4 ported boxes with all things being equal except port area and do a test. And no I won't be measuring this because my main concern is perceived output.


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## Rrrrolla (Nov 13, 2008)

It'd be worth the effort for 2.6dB's I think. I'd do it. I thuoght you were saying it would only net 2% linearly, not logarithmically. I'd rebuild for almost 3dB's for sure.


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## Fricasseekid (Apr 19, 2011)

cubdenno said:


> Aren't the numbers that are being thrown around arbitrary? As in they were used as an example?


Examples are useless if they don't exemplify the truth. 

They could be considered a hypothesis. As in that is just their best guess as to what gains might be netted. But still without testing it's just that, a guess.


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## Fricasseekid (Apr 19, 2011)

Rrrrolla said:


> It'd be worth the effort for 2.6dB's I think. I'd do it. I thuoght you were saying it would only net 2% linearly, not logarithmically. I'd rebuild for almost 3dB's for sure.


The main sacrifice to consider is loss in box volume and that can be modeled easily. It's not like it takes any more work to build a 12" port instead of a 10".


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## minbari (Mar 3, 2011)

cubdenno said:


> Aren't the numbers that are being thrown around arbitrary? As in they were used as an example?


mine were complettely arbitrary, made up even. Was just trying to make a point.


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## minbari (Mar 3, 2011)

Rrrrolla said:


> It'd be worth the effort for 2.6dB's I think. I'd do it. I thuoght you were saying it would only net 2% linearly, not logarithmically. I'd rebuild for almost 3dB's for sure.


I wouldnt. in my original example I picked 130db as the maximum output. that is WELL above any level I will listen to, EVER! so rebuilding to get more output above what i would ever listen to in the first place would be expensive and useless.

this was my original point. if you are lacking output, go ahead and try to get more. a more efficient port _might_ gain you something. but if you are already putting out more than you use, why bother?


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## Fricasseekid (Apr 19, 2011)

minbari said:


> mine were complettely arbitrary, made up even. Was just trying to make a point.


It was a point well made. The hypothesis right now (based on the point you made) is that there very well could be a perceivable difference that makes consideration worth while in the planning stages but its not gonna be a night and day difference. And maybe not enough to make it worth rebuilding an already well planned set up. But if your power is maxed out and you really want those extra 2-3 dbs (assuming that is the gain) without sacrificing SQ, this could be a viable option.


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## minbari (Mar 3, 2011)

Fricasseekid said:


> It was a point well made. The hypothesis right now (based on the point you made) is that there very well could be a perceivable difference that make consideration it worth while in the planning stages but its not gonna be a night and day difference.


assuming you are already pretty close to optimal, yes. very little difference.

like Canjunner mentioned, if you have port noise or you have too little port area and are limiting output based on that. Then a rebuild will help.


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## cubdenno (Nov 10, 2007)

Fricasseekid said:


> The main sacrifice to consider is loss in box volume and that can be modeled easily. It's not like it takes any more work to build a 12" port instead of a 10".


I suggest using external ports . Makes everything easier. Make the port wall have just a say square opening that you can bolt securely a second piece that has the varying port sizes (ID 4",5",6" etc). then you can more easily see the length increase of the port in relation to the tuning. The model will tell you what the predicted port velocity will be. 

Getting even a rudimentary (meaning cheap) SPL meter will be very helpful. you can select a volume set point and just swap the ports and do a quick measure to see if you get any increase in output.

Also remember when trialing that you have to make sure there are no leaks when designing an adapter for the ports. Any leak really screws up a ported enclosure.


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## Fricasseekid (Apr 19, 2011)

cubdenno said:


> I suggest using external ports . Makes everything easier. Make the port wall have just a say square opening that you can bolt securely a second piece that has the varying port sizes (ID 4",5",6" etc). then you can more easily see the length increase of the port in relation to the tuning. The model will tell you what the predicted port velocity will be.
> 
> Getting even a rudimentary (meaning cheap) SPL meter will be very helpful. you can select a volume set point and just swap the ports and do a quick measure to see if you get any increase in output.
> 
> Also remember when trialing that you have to make sure there are no leaks when designing an adapter for the ports. Any leak really screws up a ported enclosure.


Think I could use my Dayton mic and true RTA software to collect some useful data?


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## minbari (Mar 3, 2011)

yup, you dont have to max them out. infact, you might get a more useful reading if you tested at a more nominal level. (maybe both? then you can see if port velocity is playing a part)

obviously, you have to play the same tone at the same volume level for the test to be valid.


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## Fricasseekid (Apr 19, 2011)

minbari said:


> yup, you dont have to max them out. infact, you might get a more useful reading if you tested at a more nominal level. (maybe both? then you can see if port velocity is playing a part)
> 
> obviously, you have to play the same tone at the same volume level for the test to be valid.


Oh yes, definitely all this! 

What about port direction? 

I would definitely set it up so that boundary loading won't be affecting the outcome. But do you think the port would be fine coming out the top or sides or should it come out the front so it's facing the same direction as the sub and thus facing the mic?


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## minbari (Mar 3, 2011)

as long as you are not blocking the port internally or externally, it wont make much difference. play a 40-50hz tone and position shouldnt be much of a factor.

you might want to make the port open to the cabin so you can see if port noise occurs durring the test.


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## Fricasseekid (Apr 19, 2011)

minbari said:


> yup, you dont have to max them out. infact, you might get a more useful reading if you tested at a more nominal level. (maybe both? then you can see if port velocity is playing a part)
> 
> obviously, you have to play the same tone at the same volume level for the test to be valid.


Well I will try and design the test so that all possible port sizes have inaudible port noise. Remember the point of this thread is to determine if there is any point in increasing port area beyond the size needed to operate silently. You don't think that tuning frequency as it relates to the test speakers fs would be a significant factor? I don't just want to pick an arbitrary tuning frequency. 

I'm thinking one of these would suffice nicely:
http://www.mcmelectronics.com/product/MCM-AUDIO-SELECT-55-2421-/55-2421


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## minbari (Mar 3, 2011)

I would still design the enclosure based on best size/tuning. the tuning will still be the same, just different port area.

I modeled one of those the other day. not great low end response, from what I could see. -3db around 65hz, plus they dont work well in enclosures larger than 0.5 cuft. This will make the test hard, since a 35hz tune with larger than 3" port gets stupid long.


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## Fricasseekid (Apr 19, 2011)

minbari said:


> I would still design the enclosure based on best size/tuning. the tuning will still be the same, just different port area.
> 
> I modeled one of those the other day. not great low end response, from what I could see. -3db around 65hz, plus they dont work well in enclosures larger than 0.5 cuft. This will make the test hard, since a 35hz tune with larger than 3" port gets stupid long.


Got any suggestions on a cheap sub then? One of the Dayton's maybe?


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## minbari (Mar 3, 2011)

how cheap? a sub that requires a kind of big enclosure will make the test easier, since it will not require pole vault length port tubes.


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## Fricasseekid (Apr 19, 2011)

minbari said:


> how cheap? a sub that requires a kind of big enclosure will make the test easier, since it will not require pole vault length port tubes.


An 8" in about 1 cuft is what I had in mind. I'd like to keep it under $50 since I've recently been dropping some coin for my Honda. If I broke off another $100 plus and told my wife it was just to test some things, I think she'd be none to happy about it. 

Maybe one of the peerless models? 

So you think the Fs spec of 25 hz on that MCM 8 is bs? I've read good things about that little sub. Wanna say I even modeled em before.


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## minbari (Mar 3, 2011)

dont think it is bs, but look at QES, QTS, very stiffly damped. pretty high LE too. IBP is 116

I have no real experience with, its just models poorly


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## cubdenno (Nov 10, 2007)

Like minbari suggested, the bigger the enclosure the easier it is to do this based on port length. 

When I did this, i can say where the port faced did make an impact on measurements. Now we had a TermLab to use so that helped. Move sub play sweep, document, move sub play sweep, move sub, play sweep, document..... Untill you get a good baseline of what you are measuring for.

The kick will be is during testing, you find that as long as you are good on port area to minimize any chuffing/port turbulence/port compression and you go bigger you get zero gain.  Seems like a waste of time at that point.

we also used different tunings to find a sweet spot of response in car that modeling just does not show. Used PVC pipe for the port with a "high tune and just attached extensions to go lower. There is that point where the bump in output flattens and even rolls off where it more closely looks like a sealed enclosure with more extention. THAT is what i found to really help blend with the midbass. Tune lower to get a little bump in extention and efficiency while still keeping the lower excusion/distortion of the ported enclosure... it was win win for our applications.

good luck!!


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## minbari (Mar 3, 2011)

ok, believe it or not.

Pyramid WX85X 8" White Poly Woofer 290-272

models pretty nice in 1.5 cuft tuned to 35hz. wont take alot of power though.


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## Fricasseekid (Apr 19, 2011)

cubdenno said:


> The kick will be is during testing, you find that as long as you are good on port area to minimize any chuffing/port turbulence/port compression and you go bigger you get zero gain.  Seems like a waste of time at that point.


 Well hell! This is exactly what I'm testing, it's the topic of this thread! 

If you have done this and recorded no net gain then there is no point in me doing it. The only reason I was considering doing the test is because nobody chimed in with any concrete experience/science stating what would or wouldn't happen. Ugh...


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## cubdenno (Nov 10, 2007)

Fricasseekid said:


> Well hell! This is exactly what I'm testing, it's the topic of this thread!
> 
> If you have done this and recorded no net gain then there is no point in me doing it. The only reason I was considering doing the test is because nobody chimed in with any concrete experience/science stating what would or wouldn't happen. Ugh...


NOT SO FAST!!!

In the application I was doing this at.... With the subs we tried. and in some cases the gain was not worth the increase in size. 1-2 db is not worth it it means my box size increases .25-1 cubic foot or more due to port displacement.

Throw in a deep displacement sub and more power and guess what, your port velocity changes! 

What power are you using. What subs (I may have missed)? HiLo and Minbari already said that without measuring this was probably not necessary. UNLESS you are trying for those possible decimal places of increase for a SPL contest.

Hell these things were learning experiences for me and my son. Plus i like to build boxes and play with my tablesaw. You may find that a bigger port will yield you an audible increase in output.

Now after all that wanna know what I have done? I bought passive radiators to use when trying out a tuning. Then just factor the results and tuning in on the design. look at CSS. They have them on sale at least once a year. You load the weight in the front as well.


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## Patrick Bateman (Sep 11, 2006)

Fricasseekid said:


> So when I design a ported box I simply try to get my port area large enough to have an acceptable group delay and port velocity.
> 
> I recently read a couple threads frequented by some bass heads where they suggest that if your port area isn't large enough your not getting as much increase as your ported box is capable of producing. This talk usually seemed to coincide with building high Q one note wonder type boxes where port resonances are much more sensitive to different variables.
> 
> ...


Yeah, big ports make a huge difference.

The problem with big ports, is they take up a lot of space.

That's the bad news.

The good news is that turbulence is mostly a problem at the inlet and the exit.

So you can get a LOT of the benefits of A Very Large Port by simply using a crazy ass radius on the inlet and the exit.










Here's a cutaway of one of Danley's "Invisible Bandpass" boxes. (I did this drawing based on his CAD file, off of his website.)

As far as I can see, this box is just a manifestation of this; there's a crazy amount of flare on the inlet AND the outlet of the port.

If you look over at Harman or oven on my thread at diyaudio, I linked to a JBL paper where they basically figured out what type of ports will give you the most 'bang for your buck.'

It's not just about using a big port, because a big port takes up a lot of space. It's subtler than that, the best bang for the buck uses a specific port shape, and that shape seems to be a bowtie. (Actually an *asymmetrical* bowtie, to be exact.)

Have fun!


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## Patrick Bateman (Sep 11, 2006)

HiloDB1 said:


> Then it wont matter. Only way to really know is to build, test, build, test. If you dont care or wont be metering then build it and see how it sounds.


In a world of Akabak and Hornresp, you can get pretty darn close with a few minutes on the computer 

True, there's going to be a bit of variation in the real world, particularly if the walls of the sub flex or leak.

But hornresp can show you the effect of using a big ass port, and it is NOT subtle. We're talking an extra 3-6dB at the tuning frequency. And if your sub is only covering one or two octaves, that can be the equivalent of going from one sub to two... with the same amount of power.


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## Patrick Bateman (Sep 11, 2006)

Fricasseekid said:


> An 8" in about 1 cuft is what I had in mind. I'd like to keep it under $50 since I've recently been dropping some coin for my Honda. If I broke off another $100 plus and told my wife it was just to test some things, I think she'd be none to happy about it.
> 
> Maybe one of the peerless models?
> 
> So you think the Fs spec of 25 hz on that MCM 8 is bs? I've read good things about that little sub. Wanna say I even modeled em before.


Here's what that sub measures:

Actual measurements:

Fs=30.95 hz
Qms=12.2863
Qes=0.2365
Qts=0.2320
Vas=23.88 l
SPL=86.59 1w/1m
Re=3.4
Le=2.42
BL=13.15

I've probably used that sub more than anything else out there. At $30 it's untouchable; for $100 the Alpine Type-R 8" is better tho.


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## nervewrecker (Oct 5, 2009)

minbari said:


> you also have to consider that the more port area you have the longer the port gets........fast.
> 
> ex:
> 
> ...


Not really. (sorry to go so far back in the thread). 

I see port length to cross sectional area almost steadily increasing. 

A 6" port is just over double the cross sectional area to that of the 4" and it reflects in the length (just over double). 
Same with the 8" that is actually 4 times the cross sectional area of the 4" and the length is a tad bit longer maybe as there is less friction with the side walls. 

4" * 4" * 0.785 = 12.56" ^2

(6" * 6" * 0.785) / (4" * 4" * 0.785) = 9/4 or 2.25. 
The 6" port area is 2.25 times that of the 4"
6" port length is just over double that of the 4"

(8" * 8" * 0.785) / (4" * 4" * 0.785) = 4
The 8" port area is 4 times that of the 4" 
8" port length is just over 4 times that of the 4" (as said before, maybe due to decreased friction with the side walls)

Just thought i'd mention it.


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## minbari (Mar 3, 2011)

nervewrecker said:


> Not really. (sorry to go so far back in the thread).
> 
> I see port length to cross sectional area almost steadily increasing.
> 
> ...


wasnt my point. the 6" port is nearly 3ft long and that is in a box that is 1.5 cuft. go smaller and the problem gets worse. 

I am not suggesting that the relationship is not linear. I am suggesting that larger ports are hard to get into a car.


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## HiloDB1 (Feb 25, 2011)

Patrick Bateman said:


> In a world of Akabak and Hornresp, you can get pretty darn close with a few minutes on the computer
> 
> True, there's going to be a bit of variation in the real world, particularly if the walls of the sub flex or leak.
> 
> But hornresp can show you the effect of using a big ass port, and it is NOT subtle. We're talking an extra 3-6dB at the tuning frequency. And if your sub is only covering one or two octaves, that can be the equivalent of going from one sub to two... with the same amount of power.


Have you ever designed, built and measured in car and verified that they come out close? I have and they do not match. I have used HornResp, BBP, and WinSD to design and then tested with a TL and WT. Tuning and output differ greatly between real world and models. Maybe if I was in the middle of a field and tested it would be close, but Im not listening in a field Im in my car.


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## nervewrecker (Oct 5, 2009)

minbari said:


> wasnt my point. the 6" port is nearly 3ft long and that is in a box that is 1.5 cuft. go smaller and the problem gets worse.
> 
> I am not suggesting that the relationship is not linear. I am suggesting that larger ports are hard to get into a car.


Oh, now understand what you saying. 

I keep forgetting I dont have to cater for port displacement, went through that headache trying to fit my enclosure and decided on an external port so I can get the length I wanted.


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## Patrick Bateman (Sep 11, 2006)

I posted a thread specifically to examine the behavior of kidney shaped ports.

It's an interesting subject, because I'd generally shied away from vented boxes. I'd found that vented boxes tend to sound 'slow' and 'sluggish.'

But I wonder is this 'slowness' is simply because the response gets 'peaky' as you crank up the volume?

For instance, if you took a sealed box, and you applied a big boost at 80hz, it would ALSO sound slow and sluggish.

And that's basically what happens when your ports start to compress. The vented box frequency response starts to go to ****, because there's turbulence. And if you look at the ports we use, you can see how this happens so quickly. For instance, the vented box I used in the 90s had a 3" port and a 10" woofer. So the port area is just a *ninth* of the cone area. That's a tiny tiny fraction of what the cone can move, and you can see how it's going to get very very resistive as the power goes up.


Just some food for thought. It may very well be one of the major reasons that ported boxes just tend to sound SO BAD


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## minbari (Mar 3, 2011)

and why its the first question I ask people on here when they want to biuld them, lol. what size port are they thinking. because most people use WAY too small of a port.

I have always liked ported boxes, but you do have to biuld em right and they are alot more picky. you cant just get em "good enough" and expect em to sound good like sealed.

interesting read on the kidney ports, BTW.


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## ATOMICTECH62 (Jan 24, 2009)

The larger the port area,the larger the group delay.


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## minbari (Mar 3, 2011)

ATOMICTECH62 said:


> The larger the port area,the larger the group delay.


maybe winISD is not modling it correctly, but if I put in 1" or 50" port, the group delay is the same for any given enclosure, tuned to the same freq.

only thing that seems to effect it is box size and tuning freq.


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## ATOMICTECH62 (Jan 24, 2009)

With BB6 if I go from like a 4" to an 8" same FB it goes up.


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## Fricasseekid (Apr 19, 2011)

ATOMICTECH62 said:


> With BB6 if I go from like a 4" to an 8" same FB it goes up.


Did you adjust your box volume to keep all things equal?

I'd suspect that group delay is more related to a ratio of port size to box volume than just port area alone.


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## ATOMICTECH62 (Jan 24, 2009)

I just tried a design that had (3) 4" ports and when I changed it to (4) 4" ports the net volume and Fb of 31.41 was the same but the program increased the gross volume and port length.
The Group delay went from 19ms to 22ms and I gained about 1db from 40-20hz.


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## chad (Jun 30, 2005)

Found this while digging for something else....

http://www.synaudcon.com/site/wp-content/uploads/2010/01/nl073_impedancemeasurement.pdf


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## ATOMICTECH62 (Jan 24, 2009)

I came across a paper the other day that was similar.Basically the larger the port area=longer port=more cubic inches of air=more mass the speaker has to move=greater group delay.


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