Questions on port area

[Kangaroux 5,000+ posts]

Alright so I'm just curious as to the benefits/disadvantages to large port area setups. My box right now is at 12 in^2 per cube and it sounds great, the response is flat, lows are nice and I'm happy. But For an 18 getting ~2k, I think it should be louder, and I assume the port is what's holding me back. My general understanding of it is, if you have more port area, your box will become peakier and thus louder. How does this effect the overall response? Do you lose output from frequencies that aren't near the tuning? How will it effect the sub unloading on low notes? What is about the limit for the amount of port area on a daily setup? (high excursion sub, 6.5 cubes, tuned to 32). The reason I'm asking these questions is because when I get a second 18, or even before that, I may make another box with more port area so I can get some more output. Speaking of 2 18's, how does increasing the port area effect efficiency, if any? I don't want to upgrade my alt because that gets expensive so I would like to get the most out of my setup off ~2k.

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[Kangaroux 5,000+ posts]

Hmm, just noticed how much of a block of text that is, sorry lol

 

[Moble Enclosurs 10+ year member]

Hmm, just noticed how much of a block of text that is, sorry lol

Thats kewl, I do it all the time, lol.

Ok, so basically I am going to keep it simple. I know I usually do not do this, but I think everybody now has an understanding of how much I can get detailed.

Basically, a larger port does not necessarily make it peaker, unless that is what the driver box combo creates, and that usually is the case when all other factors are constant, such as port length, volume, etc. BECAUSE the peak will occur at a higher frequency due to natural rolloff and low end cutoff.

So, that said, the peak is natural unless you WANT to control it, with either changing other factors to fix it, or using a different design.

Now, the benefits of this can include two of the greatest pros in audio......added efficiency and coupling.

The efficiency is because the larger the port area, the more it will accommodate the lower end response because the area of the port also has a cutoff point just like tuning.

The coupling is improved because the ratio of the port opening to the area of the room is closer to a 1:1 ratio. When this occurs, the sound becomes more intense for the frequency response it plays in.

The other great pro is the ability to avoid port noise. This should be easily understood at this point. The larger the port opening the less port noise.

But keep in mind that there can be a such thing as too large not because a port CAN be too large, but because it has to match the rest of the designs limitations for it to be able to control everything.

A good example of this is trying to create a full wave cutoff port area of about 48Hz. This would be a port area of 19600in^2. Which equals a 140x140 in port! We just have to shrink this down to a usable port area without going over our max dimensions. That is what essentially creates a portion of the cutoff in a ported design. Ever wonder why responses dip in the middle? //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif (hint hint)

So, to keep usable efficiency for even a 48Hz signal above average, the recommended minimum port size would even still be large, a 35x35 port is the smallest before you loose enough efficiency to have to compensate for power and such. But you can get away with a 16x20 with exceptional efficiency still if the compression chamber is changes to help it.

So, to answer some questions,

1. Effecting response: Changing the port dimensions all together will change everything. Phase, output, efficiency, etc.the works. You ahve to recalculate for it everytime to make sure it is what you want.

2. Losing output: Yes, this can happen just above tuning about 10-15 Hz higher than tuning, and obviously below as well. Some of this is natural though. This is where you can use cabin gain to smooth it out some.

3. unloading: Always occurs regardless of what you do if any limitations are exceeded. But in relation to port, this is effected by increasing the tuning, again, if all other factors are constant. Everything else has to accommodate the area of the port for more control at the low end. And it is possible with any driver to do.

4. Limit on port area: explained above........if you go below cross-sectional area cutoff, you will lose efficiency and output. If you go above without compensating with more volume and port length, you will get a higher response range and lose low output. So, a general limitation is not available. It depends on the design.

5. Increased efficiency: explained above.

Hope that helps and that I was simple enough to understand. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[Kangaroux 5,000+ posts]

Good stuff as usual, thanks man. So for a new box, do you think 17 in^2 or even 18 in^2 would be too much? I would probably bump up my tuning to 33 or 34 as well, box volume 6.5 - 7

 

[Moble Enclosurs 10+ year member]

Thanks, and not at all too much. If anything, make the box volume smaller, and the port larger and longer. If you calculate it correctly, it might have better control of the response. But that would depend on the specs of everything. Just an option to try out.

 

[Kangaroux 5,000+ posts]

Just curious, why make the box smaller if I want it to be more efficient?

 

[Moble Enclosurs 10+ year member]

Because the box itself does not work on increasing efficiency.....only if it is intensity driven. But volume is compression driven. Otherwise, a larger sealed box would increase efficiency also. Its the fact that the compression volume is opened up to the environment that gives it the efficiency.

Compression driven is where you get the pressure from, and intensity driven is where the sound follows the pressure. Two different factors. For example, open your mouth and blow out really hard. This is compression. No sound is present, only noise. But do this and hum at the same time. Then you get intensity. I can hum just as loud without blowing air because the two factors are based on different physics. Its the reason why some ports give hair tricks but some don't, and they both can be equally loud.

So back to the size of the compression......by making it smaller, you increase the compression and since compression in audio is driven by polarity of a sound wave from a speaker, then intensity and compression work together. And when the port give you th3e coupling and loading capabilities of both the given compression and intensity of the sound wave, increased c,impression can result in higher efficiency by allowing the port dimensions to make up for the increased tuning factor of the smaller chamber.

So, essentially, you are allowing more air to be pushed through a larger opening to balance it out the same as a larger chamber with a smaller port, but with the added efficiency of the port characteristics.

 

[knotdrummer88 10+ year member]

Thats kewl, I do it all the time, lol.
Ok, so basically I am going to keep it simple. I know I usually do not do this, but I think everybody now has an understanding of how much I can get detailed.

Basically, a larger port does not necessarily make it peaker, unless that is what the driver box combo creates, and that usually is the case when all other factors are constant, such as port length, volume, etc. BECAUSE the peak will occur at a higher frequency due to natural rolloff and low end cutoff.

So, that said, the peak is natural unless you WANT to control it, with either changing other factors to fix it, or using a different design.

Now, the benefits of this can include two of the greatest pros in audio......added efficiency and coupling.

The efficiency is because the larger the port area, the more it will accommodate the lower end response because the area of the port also has a cutoff point just like tuning.

The coupling is improved because the ratio of the port opening to the area of the room is closer to a 1:1 ratio. When this occurs, the sound becomes more intense for the frequency response it plays in.

The other great pro is the ability to avoid port noise. This should be easily understood at this point. The larger the port opening the less port noise.

But keep in mind that there can be a such thing as too large not because a port CAN be too large, but because it has to match the rest of the designs limitations for it to be able to control everything.

A good example of this is trying to create a full wave cutoff port area of about 48Hz. This would be a port area of 19600in^2. Which equals a 140x140 in port! We just have to shrink this down to a usable port area without going over our max dimensions. That is what essentially creates a portion of the cutoff in a ported design. Ever wonder why responses dip in the middle? //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif (hint hint)

So, to keep usable efficiency for even a 48Hz signal above average, the recommended minimum port size would even still be large, a 35x35 port is the smallest before you loose enough efficiency to have to compensate for power and such. But you can get away with a 16x20 with exceptional efficiency still if the compression chamber is changes to help it.

So, to answer some questions,

1. Effecting response: Changing the port dimensions all together will change everything. Phase, output, efficiency, etc.the works. You ahve to recalculate for it everytime to make sure it is what you want.

2. Losing output: Yes, this can happen just above tuning about 10-15 Hz higher than tuning, and obviously below as well. Some of this is natural though. This is where you can use cabin gain to smooth it out some.

3. unloading: Always occurs regardless of what you do if any limitations are exceeded. But in relation to port, this is effected by increasing the tuning, again, if all other factors are constant. Everything else has to accommodate the area of the port for more control at the low end. And it is possible with any driver to do.

4. Limit on port area: explained above........if you go below cross-sectional area cutoff, you will lose efficiency and output. If you go above without compensating with more volume and port length, you will get a higher response range and lose low output. So, a general limitation is not available. It depends on the design.

5. Increased efficiency: explained above.

Hope that helps and that I was simple enough to understand. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

wow. teach me.

 

[Moble Enclosurs 10+ year member]

wow. teach me.

wish I had the time to. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif it gets very detailed when you get into the actual formulae. The good thing is, once you figure them out, you can rewrite them in excel to make it work with graphs so you do not have to automatically recall them at anytime lol. There are literally more than what we want to comprehend. Each acoustic behavior changes everything else about the design. So, each variable....acoustical impedance, electrical impedance, phase, gd, td, distance, losses, etc etc etc etc all have their own formula. But the great part about it is, once you actually get down to the science of it all.......it can get as simplified as the ohms law chart based on 2 or more variable changes affecting another.

Unfortunately, you cannot go into a formula and solve it without knowing how to solve other formulae for each variable in the first one. For instance the original Sabin formula based on time and absorbance and try to calculate for acoustical losses without a factor of absorption or how to figure it out. The next formula will have the previous ones solution and so on and so on. Much like ohms law. Once you figure for the main factors of acoustics, you can bounce them off each other. Pretty neat.

 

[knotdrummer88 10+ year member]

wish I had the time to. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif it gets very detailed when you get into the actual formulae. The good thing is, once you figure them out, you can rewrite them in excel to make it work with graphs so you do not have to automatically recall them at anytime lol. There are literally more than what we want to comprehend. Each acoustic behavior changes everything else about the design. So, each variable....acoustical impedance, electrical impedance, phase, gd, td, distance, losses, etc etc etc etc all have their own formula. But the great part about it is, once you actually get down to the science of it all.......it can get as simplified as the ohms law chart based on 2 or more variable changes affecting another. Unfortunately, you cannot go into a formula and solve it without knowing how to solve other formulae for each variable in the first one. For instance the original Sabin formula based on time and absorbance and try to calculate for acoustical losses without a factor of absorption or how to figure it out. The next formula will have the previous ones solution and so on and so on. Much like ohms law. Once you figure for the main factors of acoustics, you can bounce them off each other. Pretty neat.

man, I hate math, however if i was taking classes in this, I would be all about that ****. I really do wanna learn the science behind this. is there anywhere where i can find a lot of the equations for this stuff?

 

[Moble Enclosurs 10+ year member]

man, I hate math, however if i was taking classes in this, I would be all about that ****. I really do wanna learn the science behind this. is there anywhere where i can find a lot of the equations for this stuff?

Not that I personally know of. Most of what I know is from the military and college. Sorry.

 

[pro-rabbit 5,000+ posts]

Not that I personally know of. Most of what I know is from the military and college. Sorry.

From what I can tell online I never really seen much for the equations. I like Moble got mine from school and trial/error to fix what they don't teach you in classes. No matter how "perfect" you are taught real world and book typically wind up being a bit different lol(not always though). I'm a big fan of researching and then trial/error method to better understand what is going on with what you learned. It will allow you understand the math and why things happen at a much deeper level.

I do wish this is something that one of the installer schools would touch on more. This would save thousands from getting horrible installs every year.

 

[Moble Enclosurs 10+ year member]

Very true Rabbit. Trial and error is just as important as third/second party education. A lot of what I learned about bandpasses was from building and testing and calculating the changes for every factor. Can take years to do.

 

[knotdrummer88 10+ year member]

yeah, the real world is pretty much jut exactly how ill learn haha