# Lengthening Port



## Jay Mack (Nov 22, 2016)

Does lengthening the port in a vented sub box raise or lower the tune? What is the relationship between the port parameters and the tune and function of the sub?


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## Justin Zazzi (May 28, 2012)

Longer ports lower the tuning frequency. Smaller diameter ports also lower the tuning frequency. Smaller diameter ports however can potentially cause turbulent air flow, restrict the movement of the woofer, and cause noise. So you want the smallest diameter port for the woofer(s) you're using because a larger diameter port requires a much longer port, which can become impractical to build.

The tuning frequency of the port effects the 2nd resonance of the system: what frequency does it occur at and how loud will it be. Ideally you want it to happen just below the resonant frequency of the box so that the port creates a little shelf to extend the frequency response below that which would have been possible with a sealed box only. It's all about trade-offs though.

Try playing with this calculator (or one of many others out there):
Subwoofer Enclosure Calculators, Parallel, Series, Port Length and Volume


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## Jay Mack (Nov 22, 2016)

THat is very helpful. I had asked because the "tech" assistant at Kicker insisted that lengthening the [slot] port raised the tuning fq and shortening the length lowered it. I didn't think so.

I have a 1.75 cu.ft. vented/slot ported enclosure for a Kicker 10" CompR built to Kicker's recommended specs. The port was 10.5" x 2.5" x 20" and it just sounded floppy. I increased the slot port length by about 10" using an ingenious construct I devised myself and wow it was a game changer. It improved the whole system that was pretty good to begin (system includes two sealed 10" JL Audio 3W3s in the back seat). I'm sure it's tuned down to at least 34 Hz now.

The whole system tuned WAY down and the ported sub seems to tune the sealed subs down too, without losing the sealed sub snap and tightness. It was a big improvement. The car itself vibrates a bit.

[You don't mind if I like Kicker subs, in spite of the wanting tech help? I just find them easy to work with and unintimidating.]


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## Justin Zazzi (May 28, 2012)

Jay Mack said:


> [You don't mind if I like Kicker subs, in spite of the wanting tech help? I just find them easy to work with and unintimidating.]


Nope, not at all.

If however you were to insist on using esoteric and outrageously overpriced equipment where the salesperson insists you can smell the type of wine the singer was drinking just before making the recording, then I might mention you were scammed.


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## Jay Mack (Nov 22, 2016)

Jazzi said:


> Nope, not at all.
> 
> If however you were to insist on using esoteric and outrageously overpriced equipment where the salesperson insists you can smell the type of wine the singer was drinking just before making the recording, then I might mention you were scammed.



Jazzi, I do sense a certain, er ... , dissatisfaction with either JL or Kicker on your part. I'd be delighted to be guided to a more satisfactory line of 15", 12" and 10" products in the 300 - 600 watt RMS range.

Please feel free to enlighten me. Please, do.




{BTB, I see you are in the Bay Area. I'm a Berkeley Boy myself. I only get back there once a year or so for homecoming though.}


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## Bayboy (Dec 29, 2010)

Lengthening a port of an already existing alignment will change the response. May not be that bad since in the car you will probably have to make EQ cuts anyway, but if the goal was to have a flat response (out of car) then it will change. Normally if you want a lower tuning, then the volume of the enclosure changes as well.


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## Jay Mack (Nov 22, 2016)

Bayboy said:


> Lengthening a port of an already existing alignment will change the response. May not be that bad since in the car you will probably have to make EQ cuts anyway, but if the goal was to have a flat response (out of car) then it will change. Normally if you want a lower tuning, then the volume of the enclosure changes as well.


Well, I mean that I changed the length of the port without changing the volume of the internal non-port area. I extended the port on the outside. or do you mean that the internal non-port area must increase as well as the port length? I haven't seen that on one of the calculators, the 12 volt calculator or several of the others. Is there one you can suggest?


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## Hillbilly SQ (Jan 26, 2007)

Download winisd beta and play with box sizes and port tuning. You'll be able to see how each change you make effects the response out of car. Once in the car the response you see on the graph will change but at least you can learn how to design around your car's interior.


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## Jay Mack (Nov 22, 2016)

I've used WinISD a few times over the years. I tried it just now. It's not functional, as far as I can determine. It just says "You haven't selected a driver. Go to Database maintenance." I click on "supply your own driver" But it doesn't let you enter a new driver.

It's very difficult to figure out what they want from you.
The database itself is 20 years old.


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## Hillbilly SQ (Jan 26, 2007)

You have to enter the parameters yourself. I've never thought it was hard to use. Try this link.
LinearTeam


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## edouble101 (Dec 9, 2010)

Jay Mack said:


> Well, I mean that I changed the length of the port without changing the volume of the internal non-port area. I extended the port on the outside. or do you mean that the internal non-port area must increase as well as the port length?  I haven't seen that on one of the calculators, the 12 volt calculator or several of the others. Is there one you can suggest?


If you increase the length of the port inside the enclosure you will also decrease the net internal volume. As you decrease the volume your tuning freq increases. If your calculations conclude that the amount of volume that the port requires decrease the internal volume to a point that it is too small for the speaker(s) you need a bigger enclosure.


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## grinkeeper (Jun 26, 2015)

Is there any MAC software that I can use other than the online web based tools?

I have used the RE AUDIO one for quick estimations.

The 12volt BOX DESIGNER is very nice for calculating internal volumes and ports.

BUT

I am looking for some software that uses the full T/S parameters. But it must be MAC compliant.

I used to use box design software back in the early 90s when I worked at a car audio shop. I can’t remember what it was called but it was basically the only thing available at the time. Used to run on the most advanced computer at that time which was a Windows 3.1 I believe and you still needed to know your DOS-Prompts to even make it work.

Does anyone remember what this software was back then. It used to actually do a great job. We used to design customers boxes all the time. Process was free if you bought something and $20 bucks for the box design on its own. Basically the $20 was to cover the time spent with the customer and everyone was always very happy with the service. The best part of this system was I never had to bring lunch money as the $20 fee was always pocketed and pizza was quickly ordered for the shop. Everyone won on that arrangement.


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## lurch (Jan 20, 2014)

" box plot " ?


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## Jay Mack (Nov 22, 2016)

I've gotten the Win ISD Beta to at least operate. But I still can't make much sense out of it. THe line wiggles a bit but it doesn't tell me much. It shows box sizes that are very large doing the same thing as much smaller box sizes. I don't seem to be able to change the overall Q. Is the overall Q supposed to aim for .707?

Look, this is one thing I don't get. If you look at a RF P3D2 15" sub driver, the specks say the "optimum recommended sealed enclosure" is 1.58 cu.'.

But elsewhere, like on a vendors spec. site (Crutchfield) it says : "sealed box volume: 1.5-3.0 cubic feet."

So, what happens if you go bigger than 1.58 cu.ft? What is the effect and why isn't it "optimum." What if I box it at 2.3 cu.ft? What will it do? I don't want impact, I want SQ, deep bass.


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## Bayboy (Dec 29, 2010)

Q in a vented?


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## Justin Zazzi (May 28, 2012)

Jay Mack said:


> I've gotten the Win ISD Beta to at least operate. But I still can't make much sense out of it. THe line wiggles a bit but it doesn't tell me much. It shows box sizes that are very large doing the same thing as much smaller box sizes. I don't seem to be able to change the overall Q. Is the overall Q supposed to aim for .707?
> 
> Look, this is one thing I don't get. If you look at a RF P3D2 15" sub driver, the specks say the "optimum recommended sealed enclosure" is 1.58 cu.'.
> 
> ...


Great questions!

A woofer has a Qts from the factory (in this case 0.54) and when you place it into an enclosure of any kind, the Qts will either stay the same or increase by some amount (except for aperiodic enclosures, which could lower the Q in some cases). So an infinite baffle "enclosure" is essentially an infinitely large box which has no effect on the behavior of the cone movement, and that means the Q stays the same. As you make the enclosure smaller than infinite in size, you start to effect the behavior of the cone and the Q starts to rise. The smaller the enclosure, the more the Q will increase.

The "ideal" enclosure will have a Qtc of around 0.5 since this correlates to a critically damped system and your transient response will be as good as it gets. The factory recommended enclosures are usually not this kind of alignment though because a larger box will allow the cone to have no limit to excursion and the chance of mechanical damage due to applying too much power is higher (which is not uncommon with consumers that just want more bass and don't know any better).

Also, a smaller enclosure with a higher Q will have a hump in the frequency response near resonance giving the user "free" bass, but it's not really free since the cost is a lower performance in terms of transient response and increased ringing effects (the higher the Qtc, the worse this gets).

Manufacturers like to recommend alignments somewhere around Q=0.707 (or sometimes slightly higher) since this can be a good compromise between low frequency extension, protection against over-excursion (and thus broken equipment by protecting the consumer against him or herself), and a reasonably small enclosure size too.

Also consider "Hoffman's Iron Law" that is essentially: low frequency extension, small enclosure size, low power required ... pick any two. Since space in a car is always limited we want small enclosures. Also since most of us enjoy low frequency extension in our bass, we want that too. In the past when amplifier power was expensive we had to make a trade off of some kind, but today amplifier power is cheap with class-D technology being everywhere and now we can have everything we want.

So if you want "deep, SQ bass" then you want a sealed box with a Qtc=0.5 or just slightly higher. This will be hard to do with the RF woofer you have in mind since it starts with a Qts of 0.54, and a sealed enclosure will only raise it. You could run it IB style for the "most" SQ, or a fairly large sealed box and you might not notice the difference.

If you want to learn more about this, pick up a copy of Vance Dickason's Loudspeaker Cookbook. There should be plenty of used copies out there so you don't even have to pay full price for it. Also, below is a chart showing the various frequency responses of various Q alignments. Compare the green and black lines for example.









image borrowed from mh-audio.nl - TSP


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## Bayboy (Dec 29, 2010)

I wouldn't get hung up on exact Qtc, especially that low. A low Qtc can often sound too dry in the upper end. You already have considerable lift on the bottom end in a car so combining that can lead to an exaggerated bottom with upper end slop. 

OAN, a favorite shallow 12" sub on this forum is suggested in a much higher Qtc than that.... go figure. But that's the problem with modeling. Really only good for predicting bottom end response. Overall sound and ideal Qtc? You're still left in the dark. With having said all that, one thing that's very helpful that most don't know or won't measure, the particular cabin gain of the vehicle being worked with.


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## Justin Zazzi (May 28, 2012)

And sometimes (ok a lot of the time) I get caught up in trying to answer a question by teaching something I find interesting, and I don't see the big picture or explain how to apply stuff.

So yeah, like Bayboy mentions, don't worry about all that stuff *too* much. I hope I answered your question, but that doesn't mean you need to put 110% effort into getting the number to match up. Close enough is often times, close enough


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## Bayboy (Dec 29, 2010)

Yeah, as long as you're close with sealed, you'll be fine. It's the extreme ends you have to be concerned with.... where a knee response hinders bottom end or excessive tubbiness creates a lackluster kick & upper bass. But subs & personal tastes differs enough to where you shouldn't be afraid to knockout a quick box to test the waters before diving into a custom & more permanent setup. Better yet, keep a small sub/box laying around that you can throw into a vehicle to measure cabin gain, then enter the numbers into your modeling program


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## Jay Mack (Nov 22, 2016)

Bayboy said:


> Yeah, as long as you're close with sealed, you'll be fine. ...


It's a very interesting discussion. Thanks for the depth. It's mostly beyond me. When you say "as long as you're close" what are you referring to, close to what? The manufacturer's ideal box size? .707 Q? From the discussion I get that making the box smaller is generally better. "Better" meaning more accurate and less floppy. But not necessarily deeper. So if Alpine says 1.58 cu. ft., then that's about the minimum?

I used to read The Cookbook many years ago. I've forgotten most of it. It's over there on the mantle. I appreciate the graph representing "Q." That makes it more clear what it is. I'd probably not try to configure it. I certainly don't know how to measure it in a car. I mostly just want the right box size conveniently available for a Civic back seat or trunk, and whether I can use the right 15" sub without loosing something.

Add-on: I just ended up ordering a Alpine Type S (they were out of the Type R) from Crutchfield. It was Scratch and dent for $169 minus $20 rewards point, plus return a previous order for $89. So total is $50. How's that? Now I'm figuring slot ported or sealed.


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## Bayboy (Dec 29, 2010)

In sealed, box size & Q go hand in hand so yes, being close to target size whether it be custom or manufacturer suggested is good enough. Increasing size increases low end efficiency while giving up power handling and flattening upper bass to the point you start to lose some thump (dry). Going smaller gives up a bit of low end tubbiness for more upper bass (more thump), but can start to present a hump in the upper response as well. It's fairly simple. Qtc=.707 is considered ideal, but that's very general and won't apply to every sub.


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## Jay Mack (Nov 22, 2016)

Hillbilly SQ said:


> .....


HBSQ - I happened to chance upon an older thread you started regarding a 15" Alpine Type S.

In retrospect, how does that sub look to you? I sent for one but it's a new brand to me and I can't quite get comfortable with it. I was originally looking for the Type R though I probably don't need quite that much.


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## Hillbilly SQ (Jan 26, 2007)

Jay Mack said:


> HBSQ - I happened to chance upon an older thread you started regarding a 15" Alpine Type S.
> 
> In retrospect, how does that sub look to you? I sent for one but it's a new brand to me and I can't quite get comfortable with it. I was originally looking for the Type R though I probably don't need quite that much.


Hands down my favorite sq woofer to date THAT I'VE PERSONALLY RUN. Clean and disappeared into the frontstage. I had it in 1.5 sealed iirc and it just plain worked. Was a little awkward in my quadcab Ram so didn't run it long. That truck was a royal pain to get anything over 10" in without making it obvious there was a subwoofer in there...AND get the sub firing the right direction for the sake of cabin gain. Never could get a center console box to work to my liking in there, but that's old news now. I would own a type-S 15 again in a second, but would probably do a pair of 12's instead for my install to keep the box from being too tall. It's only a Grand Cherokee afterall and the plan is to hide the sub box in plain sight.

Alpine makes great subs. No need to worry about them at all. The Type-R is the go-to woofer but for straight-up sq that some would consider "too clean" at times the S is a great choice, but that's a good thing unless you listen to muddy bass lines all the time


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## Jay Mack (Nov 22, 2016)

I'm enthused. 

I have not yet determined whether to stick with a sealed or go vented. I have not found a calculator that demonstrates slot port size as a function of cabinet volume. All I see is port length as a function of width, height and desired tuning frequency.
Does the tuning frequency vary along with box size or is the effect of the port entirely separate from the box size? Going back to my original question, can I use the recommended box size from the manufacturer and lower the tune simply by adding length to the port? Is there anyway to maximize the "tightness" of a vented enclosure?

Is there such a calculator?


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## Hillbilly SQ (Jan 26, 2007)

Winisd will tell you what you need to know. I just modeled the Type-S 15d4 for you (not sure which one you got but should model about the same for d2 and d4). For a .71 qtc you want to go with 2.4 cubes sealed. For ported 3 cubes tuned to 28hz looks really good. For sq you'll have to pull some of the "happy zone" between 30 and 50hz out with eq like with most any ported enclosure but the efficiency you gain is usually well worth it. Easier to cut what you don't need than it is to try to add it in when it's lacking. With a square/rectangle/slot/whatever port with 90* angles I wouldn't go with anything less than 20 square inches to prevent chuffing. With two 4" round ports the length would be way too long for that option to be beneficial, and a single 4" round port would be on the ragged edge of being too small and might cause chuffing.


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## Victor_inox (Apr 27, 2012)

simple question 25 posts, exactly why after calculating box in Bass Box Pro I design the port that I can tune precisely in the car it will be installed.


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## Jay Mack (Nov 22, 2016)

Hillbilly SQ said:


> Winisd will tell you what you need to know. I just modeled the Type-S 15d4 for you (not sure which one you got but should model about the same for d2 and d4). For a .71 qtc you want to go with 2.4 cubes sealed. For ported 3 cubes tuned to 28hz looks really good. For sq you'll have to pull some of the "happy zone" between 30 and 50hz out with eq like with most any ported enclosure but the efficiency you gain is usually well worth it. Easier to cut what you don't need than it is to try to add it in when it's lacking. With a square/rectangle/slot/whatever port with 90* angles I wouldn't go with anything less than 20 square inches to prevent chuffing. With two 4" round ports the length would be way too long for that option to be beneficial, and a single 4" round port would be on the ragged edge of being too small and might cause chuffing.


WOW. You really looked into it. Thank you.

2.4 cubes sealed is quite a bit larger than the Alpine recommended. Alpine is at about 1 cube. Why does it come out like that? I can do 2.4 cubes?

Regarding ported, when you say to cut 30-50 with an eq, I don't have an equalizer. Just the factory head unit with high level input. So, I don't think that will work.

Regarding the slot port, 20 sq. inches in area, and then how long? 22" long? 
How long can one go?


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## Hillbilly SQ (Jan 26, 2007)

I'd go with sealed then if you have no real eq. "Recommended" is a happy mix of keeping box size down and keeping power handling up. A higher q like .8 or .9 can also give you a more "punchy" sound. There's nothing wrong with a higher q in a vehicle. 1.5 gives you a q of .83 and that's about what I ran mine in and it sounded great.


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