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Old 10th November 2007, 00:45   #1
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Arrow Doubts on ports

Is there any advantage in using ports with larger diameters? To get the same port frequency, larger diameter ports need to be longer than narrower ones. I see this as a disadvantage because, as the port gets longer, it starts dictating the dimensions of the enclosure.

My sub manufacturer has recommended a port with 3" diameter and a length of 10.04" to achieve a tuning frequency of 35hz.

Using the port length calculator at Subwoofer Enclosures - Fraction to Decimal, Parallel, Series, Port Length and Volume Calculators
I found that using a 2.4" diameter port, the same frequency can be attained using a shorter length - 8"

Why then would a manufacturer recommend a larger port?

Is the sole purpose of a port just for attaining a desired tuning frequency? If so why cant it be achieved using the diameter and length that best suits the user needs?

What effect does the tuning frequency have on the sound output? Which is better? A lower tuning frequency or higher? Or better still, what is the ideal tuning frequency to have for an SQL application?

I'm starting this as a new thread so that this becomes a single and unified source for all porty knowledge.
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Old 10th November 2007, 06:15   #2
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Is there any advantage in using ports with larger diameters? To get the same port frequency, larger diameter ports need to be longer than narrower ones. I see this as a disadvantage because, as the port gets longer, it starts dictating the dimensions of the enclosure.
The large diameter port would huff and chuff less than small dia port - good enough reason. Unless the enclosure is required to be shallow or small, it shouldn't be difficult. One can of course increase length by using bends.

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My sub manufacturer has recommended a port with 3" diameter and a length of 10.04" to achieve a tuning frequency of 35hz.

Using the port length calculator at Subwoofer Enclosures - Fraction to Decimal, Parallel, Series, Port Length and Volume Calculators
I found that using a 2.4" diameter port, the same frequency can be attained using a shorter length - 8"
One wouldn't save cost with a 2" difference. Also, are you sure you will get a 2.4" dia pipe? If a longer length is fouling, bend the pipe.

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Is the sole purpose of a port just for attaining a desired tuning frequency? If so why cant it be achieved using the diameter and length that best suits the user needs?
Yes. But wouldn't "suiting the user" be taking the point too far? Of course the user can choose his own length, or even use gold plated brass pipe - it's his money after all.
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What effect does the tuning frequency have on the sound output?
If by output you mean "loudness", it is independent of the frequency the sub system is tuned for.
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Which is better? A lower tuning frequency or higher? Or better still, what is the ideal tuning frequency to have for an SQL application?
There are no 'ideal' frequencies - it is matched to the driver. Of course, there is always the design objective - towards which a suitable driver is chosen, and then a box is designed.
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Old 10th November 2007, 11:15   #3
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One wouldn't save cost with a 2" difference. Also, are you sure you will get a 2.4" dia pipe? If a longer length is fouling, bend the pipe.

Yes. But wouldn't "suiting the user" be taking the point too far? Of course the user can choose his own length, or even use gold plated brass pipe - it's his money after all.
If by output you mean "loudness", it is independent of the frequency the sub system is tuned for.
There are no 'ideal' frequencies - it is matched to the driver. Of course, there is always the design objective - towards which a suitable driver is chosen, and then a box is designed.
I didnt mention cost saving as an advantage.

Its just that I prefer a straight pipe and I wanted to know why one would have to bend the pipe if the same tuning frequency can be achieved with a less dia pipe. And yes you answered that question.

The AR 65V, a flared port, has an internal dia of 2.4"

I'm still looking for answers to other questions. Here's one more. On what basis does one decide upon the tuning frequency? I know it depends on the box volume. But assuming I can build a box of any volume and a port of any length/diameter, how do I decide upon a particular tuning frequency?
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Old 10th November 2007, 15:40   #4
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The AR 65V, a flared port, has an internal dia of 2.4"
Sure, but what about the pipe behind it that you have to pick up locally?

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On what basis does one decide upon the tuning frequency? I know it depends on the box volume. But assuming I can build a box of any volume and a port of any length/diameter, how do I decide upon a particular tuning frequency?
No, the other way around. The box volume is calculated from the other parameters, including the frequency to which you want the box to be tuned to.

That tuning frequency depends on what driver you pick up (sub characteristics, incl. Fs) and how low you want to hear the notes. Sometimes you don't want to go down to the 1st octave, if the kind of music you hear doesn't have instruments that do.

Don't confuse it with the apparent 'goodness' of bass - not much is actually heard but felt (not everyone's ear 'listens' down to 20Hz) and that feeling is actually bolstered by sub and mid-bass drivers' ability to reproduce in a controlled manner the overtones (harmonics) of the lower notes. So, if you use a good sub and a bad mid-bass, the result would still be lacking. Bad drivers & systems make the harmonics linger around longer than required making the music sound "boomy" and "muddy".

The advantage of the bass-reflex (ported) enclosure is that the system mechanically boosts the output produced by the driver around the tuned frequency. But not that it can make 45Hz Fs driver sound like a 27Hz Fs driver.

So, rolling back to the start, first you select a driver (sub) based on what you need: Price, Loudness (electrical power handling AND driver sensitivity), size (depth), construction (frame, coils, ventilation etc.) and mech/elect parameters (depending on Q, some sound best in a sealed box, some in higher order like BR).

Follow LBM's process - he is doing it right now. He has been using IDQ divers in a ported box, and his system is SQL (he got 152.7dB of LOUD but accurate music). He is now revamping his bass system - and has just selected a driver.

Navin, B&T, Gunbir et al have written a lot on the forum regarding driver selection and influence of different parameters - search and read, that is the real Knowledge Base.
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Old 11th November 2007, 15:35   #5
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You dont have to "fix/attach" any pipe behind the AR 65V. It is a complete product in itself.

DerAlte, thanks for your time in posting this long reply.. But, I am not looking for options/process suggestions as to my ICE upgrade/subwoofer selection. I already have a sub. All I intend to know is about ports in this thread(Specifically answers to questions I've asked).

Anyone else who can chip in with answers to the questions.. please!
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Old 12th November 2007, 15:03   #6
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Originally Posted by jCube View Post
Is there any advantage in using ports with larger diameters? To get the same port frequency, larger diameter ports need to be longer than narrower ones. I see this as a disadvantage because, as .
.
.
.
What effect does the tuning frequency have on the sound output? Which is better? A lower tuning frequency or higher? Or better still, what is the ideal tuning frequency to have for an SQL application?

I'm starting this as a new thread so that this becomes a single and unified source for all porty knowledge.
Let's just say that some gurus (not the ones on our forum) have deduced that for a particular subwoofer driver size, certain port diameters work best. This IS generalization, empirical. For example, it is supposed that 3-4" works best for a 12" driver. These deductions are based on approximation of the volume of air that a driver of a particular size will move, and then choosing a port diameter that will be commercially available rather than say a port of 3.76" in dia which only our LBM can make.

However, in car audio, high excursion designs mean that you should choose a port size larger than what may be indicated as per this rather home-audio based chart. (I cant find a link to it)
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