As I understand it... Ported boxes have two tuning frequencies. One for the driver and one for the port. Both share the effective box size as a tuning variable. So... You build a box of the correct dimensions excluding the area taken by the driver, port and braces etc. Then you feel that maybe you should have used some damping material because the sound is just isn’t right, maybe you want to use a new driver or possibly you want try a different alignment. Finally the question. Is it possible to dial in box volume by adjusting the dampening material and measuring resonating frequency of the driver in a ported box? If this is possible, then using T/S parameters you could figure the effective volume of the box as seen by the driver. To finish the new alignment, port size and length would be set utilizing the new effective volume. Am I in left field here or what? What do you think?
Replies (4)
swez on 05/14/2006 11:28:13
You have the basics down well. That's pretty much how it's done.
Polyfill will make the box seem up to 10% larger, depending on the amount used. If the box is too large, we can add braces and such to decrease internal volume to the targeted airspace required.
Some guys use Win ISD software to plot probably response curves for a given sub. You simply plug in the T/S parameters and the program will plot out response curves for various alignments.
NOTE: These predicted plots are generally accurate in free standing enclosures. However, in any given install, (HT or Mobile Audio) it will not calculate "transfer function effects". This can be as little as +6dB to over +15dB of bass reinforcement at certain bass frequencies. It all depends on the acoutical properties of environment the sub is used within.
Swez
MrBrownstone on 05/19/2006 16:10:30
little secret about boxes, if you are in the middle of it's range of sizes, you can miss by an awful lot and still get comparable sound. When you get towards the minimum and maximum sizes, that's where you run into problems. Too large, unloaded, too small, too restrictive.
Infinity's Perfect VQ does the opposite of what you mentioned--adjusting the woofer's Q factor to meet the box size. Of course, if you make the box ~ where you want to be, that would really only be fine-tuning it to match anyway.
unless you just want an exercise in miniscule improvement, there's no real need to worry about dialing in a box to the nearest 0.01cuft as you won't hear the difference anyway. Even the idea of polyfill changing the thermal properties of the box will only have a minor effect. So much depends on the thermal properties and volume of the box that if you add the polyfill, it might not make any difference at all.
Of course, if you want to see & hear what happens when you change the size of the boxes, then you could build one that the back panel slides outward.
kiowamec on 05/19/2006 20:11:46
I was just looking for a way to check the tuning of a ported box. I do not trust my ears because I have never been around quality audio. This is my first stereo install other than the usually replacement head unit and speakers.
What material is best suited to line a ported enclosure and does it deducted from the volume of the box? I have read about using closed cell foam for low Hz. I assume this would be deducted from box volume. I have also read about open cell foam and other breathable materials for higher Hz. I would not think these would have an effect on volume. I have jute carpet padding I am using for noise in the rest of the car. I would think this would make a good material to line the box with but it kind of lands in the middle of the two and I do not know if I should deduct it from my box volume or not.
Anyway... If someone has information on tuning a ported enclosure using test frequencies and a meter I would like to hear about it.
swez on 05/22/2006 10:23:42
A good enclosure calculator can be found here:
http://www.the12volt.com/caraudio/boxes.asp
Box and port calculations:
http://www.the12volt.com/caraudio/boxcalcs.asp
Swez
Replies (4)
swez on 05/14/2006 11:28:13
You have the basics down well. That's pretty much how it's done.
Polyfill will make the box seem up to 10% larger, depending on the amount used. If the box is too large, we can add braces and such to decrease internal volume to the targeted airspace required.
Some guys use Win ISD software to plot probably response curves for a given sub. You simply plug in the T/S parameters and the program will plot out response curves for various alignments.
NOTE: These predicted plots are generally accurate in free standing enclosures. However, in any given install, (HT or Mobile Audio) it will not calculate "transfer function effects". This can be as little as +6dB to over +15dB of bass reinforcement at certain bass frequencies. It all depends on the acoutical properties of environment the sub is used within.
Swez
MrBrownstone on 05/19/2006 16:10:30
little secret about boxes, if you are in the middle of it's range of sizes, you can miss by an awful lot and still get comparable sound. When you get towards the minimum and maximum sizes, that's where you run into problems. Too large, unloaded, too small, too restrictive.
Infinity's Perfect VQ does the opposite of what you mentioned--adjusting the woofer's Q factor to meet the box size. Of course, if you make the box ~ where you want to be, that would really only be fine-tuning it to match anyway.
unless you just want an exercise in miniscule improvement, there's no real need to worry about dialing in a box to the nearest 0.01cuft as you won't hear the difference anyway. Even the idea of polyfill changing the thermal properties of the box will only have a minor effect. So much depends on the thermal properties and volume of the box that if you add the polyfill, it might not make any difference at all.
Of course, if you want to see & hear what happens when you change the size of the boxes, then you could build one that the back panel slides outward.
kiowamec on 05/19/2006 20:11:46
I was just looking for a way to check the tuning of a ported box. I do not trust my ears because I have never been around quality audio. This is my first stereo install other than the usually replacement head unit and speakers.
What material is best suited to line a ported enclosure and does it deducted from the volume of the box? I have read about using closed cell foam for low Hz. I assume this would be deducted from box volume. I have also read about open cell foam and other breathable materials for higher Hz. I would not think these would have an effect on volume. I have jute carpet padding I am using for noise in the rest of the car. I would think this would make a good material to line the box with but it kind of lands in the middle of the two and I do not know if I should deduct it from my box volume or not.
Anyway... If someone has information on tuning a ported enclosure using test frequencies and a meter I would like to hear about it.
swez on 05/22/2006 10:23:42
A good enclosure calculator can be found here:
http://www.the12volt.com/caraudio/boxes.asp
Box and port calculations:
http://www.the12volt.com/caraudio/boxcalcs.asp
Swez
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