Why isn't this possible?

I couldn't find ANYTHING online about this... in any form or fashion... I'm thinking of experimenting with this in a few days.

oh yeah, the actual handle design could be different, all that matters is that the port length changes.

 

How would the slide action work? If it's at all loose, seems like you might be inviting rattles. Also, I don't know what the effect of having the port sticking out of the box would be. Any way to make it a telescoping port instead? Can't think of how to do it unfortunately, and that might affect the tuning even more.

It's a novel idea though... it would certainly be useful to be able to tune your box for different situations (competitions, SQ, etc.).

 

the port will not sound any different sticking out of the box, that does not matter.

The sliding portion will obviously be very tightly fit, and if need-be-necessary, the slider could extend the port further inwards, rather than outside the box.

The design shown above is basically just for reference, and an idea. it *should* work, but I haven't tried it yet, nor has anyone else on the internet/world, (that I could find.)

What I want to know, is why the heck hasn't anyone really messed with this? I've seen someone else on this forum have replaceable ports, but what I am suggesting is FAR beyond that.

Could you imagine something in the future that was, say, computer-controlled, and it varied the port size depending on the sound of the woofer? So you could have that 3db extra at MANY frequencies!

In all honesty, I'd prefer a passive-radiator enclosure... as they still have really 'tight' bass response, with a higher efficieny than a sealed enclosure.

Although I find it interesting that most computer subwoofers are ported, and I've heard some pretty good ones, and they usually seem to have pleasant bass output.

Thinking about it more, it seems that a bass drum works like a ported subwoofer, an acoustic guitar works that way as well... hell, any instrument that makes sound works like a ported woofer... seems like it would be a good choice for bass reproduction.

-Steve

 

What makes you think it's never been done? This is a useful tuning feature that many builders take advantage of. Once you get the in-car response you want, you simply replace the variable port with a fixed one.

 

What I am suggesting is permanent... you can change the tune of the box on the fly... no swapping out ports.

Also I was struggling to find ANYTHING on this, or even swappable-ports online... maybe you know a few links?

 

I've never come across links.

I've seen some vehicles where people would swap ports for SPL/SQ portions of competitions. They have one port tuned for the best response, and one tuned for maximum output at a specific frequency.

I see the adjustable port as being a great tuning aid, but once you get the desired result, I don't see much use in keeping it around. Once you get the best in-car response, there really won't be much more need to adjust. In cases where you may want the benefit of a higher tuning for SPL purposes, again, once you find the right length, the need for adjustability shrinks.

But... all of the conventional port tuning principles apply, so there's really no reason why you couldn't do this.

I used a somewhat similar approach when I built the enclosure for my girlfriend's camry. I designed a slot-ported box in which the ports dumped right at the top of the enclosure. I can change 1 piece of wood in the enclosure with one of a different length to adjust my tuning frequency. I wound up being happy enough with the sound on the first try that I never went back and messed with different lengths, but someday if I ever find myself bored enough to try, I may try tuning to a higher frequency to see how much SPL I can squeeze out of the box.

 

The only big prblem i see is that the port in a third gen box will most likely be so long that you won't be able to have a port that will be straight. If you tuned high like 40 htz (which IMO sounds like crap)and your box has a usable space of 1.5 cu ft and you use a port that is 4" in diameter the port will be around 10" long but the adjustment to even 30 htz in the same box is 22" long and to go to 20 htz is 54" long. Its really hard to get a ported box into a third gen that has enough port area to not have port noise and a length long enough to have a low tune if your after SQ.

 

Yet another reason to use a slot port. You can fold a slot port to make it fit into different areas. Here's an "inside" pic of the enclosure I mentioned above. It shows the folded port as well as the top piece of wood that I mentioned can be changed to alter the tuning frequency:



Keep in mind that you're looking at a picture of the INSIDE of the box before I attached the rear panel.

 

for some reason WinISD says I can have a much smaller port than you have, and still keep the port velocity well within the safety margin.

My friend has a dual-chamber 6.7cu.ft. box, sealed, and he's thinking of porting it... this is what WinISD thinks... I only put in half the box for calculation.

it shows a pretty good boost over a sealed box.

Maybe someone can point out what I've done wrong...

 

If what he wants includes that massive peak in output at 25hz, then the box looks great. If he wants a flatter, smoother response, the enclosure is going to have to be substantially smaller, and tuned to a lower frequency.

I modeled that driver using the t/s specs shown in your picture. The "ideal" enclosure for that woofer is .841 cubic feet tuned to 16hz. With this alignment, it yields a -3dB point of 14hz

The problem with this setup is that you run into a situation like I did where the port length is retardedly long. To run a 4" diameter port in this arrangement, you'd need to make it 12.75 FEET long!!! You're forced to make the box MUCH bigger and accept a terrible spike at the tuning frequency, or build a sealed box.

The reason your port is smaller than mine (in length I'm assuming, not diameter) is that you're dealing with a larger enclosure volume. The larger the enclosure volume is, the shorter the port needs to be to achieve the same tuning frequency.

Anyway, this is a sub that's begging to be put into a sealed enclosure. In a .5 cubic foot sealed enclosure, you'll get an F3 of 28hz, which is pretty impressive.

I'm beginning to wonder which specs in the t/s list that Kicker is lieing about. There's no way you can achieve bass that deep in an enclosure that small with a sensitivity as high as kicker specified for this woofer. It violates Hoffman's Iron Law. My guess is that Kicker has grossly overstated the driver's sensitivity... which really isn't that bad considering the low cost of massive amplifier power.

 

While I have and do use box programs to aid in designing boxes, it should only be used as a starting point. From my experiance a 3.5" port on a speaker that moves that much air will probably have port noise at higher volumes on anything above tuning. It is possible I'm wrong and the only way you will know for sure is to build the box and try it.

A good example as to why box building programs aren't always the best thing to use is I have bass box pro and what im coming up with for an optimal flat response box is 63 cu ft @ 15 htz. Like jim said things don't add up right on that sub and there is no real industry standard for taking most of these measurments.

 

while we are on the subject..... what are some good box building programs out there..

i have winISD which is pretty cool, but i have one gripe. I wanted to use it for my senior project but i cannot print the graph that i came up with...

 

printSCREEN

pwned.

 

I'm a fan of WinISD because it's so quick and easy, and is as accurate as any other modeling program. While these programs do give pretty accurate results, they allow you to go to extremes that you can't really go to in the real world. I've fooled with designs that give you the impression that you're actually going to get deep bass out of tiny drivers, but in reality, their limited excursion makes it impossible.

A more complex (and less user friendly) program is an excel file built by Jeff Bagby that also shows cone excursion, and allows you to impliment active filter slopes into the final design, which is great for home sub systems that typically have amps with a built-in bass boost.

For car audio applications, I like WinISD. Car subs these days all have a foot of excursion and can handle 3 million watts, so as long as you don't get retarded with your design, you can usually come up with something decent.


9177, your 63 cubic foot enclosure will have a big spike at the tuning frequency (a characteristic of all oversized ported enclosures), but because the tuning frequency is so low, it's probably "off the radar" so to speak. Plug in .841 ft^3 tuned at 16hz and I'll bet you get a good flat response. If BassBox shows a flat response with no bump at tuning, I'd be suspect... that's a very common characteristic of oversized ported enclosures, which is why the SPL guys are so fond of them.

 

I want one of THOSE subs! a whole foot! sheesh!

My PPIs only have 9" of xmax, and 2 million power handling...

oh well, you get what you pay for.

/inch?

 

Try correcting the VAS to 9.1 cu ft. If you used what was up above it is in liter and is wrong. But I still doubt we will come up with the same numbers. On bassbox pro it has a feature that will look for what it thinks is the best sounding box design and that was all I used for this.

 

WinISD looks for the "optimal" design too, but those could pratically be anything. WinISD seems to do a good job figuring it out for drivers with reasonable specs, but gets wierd when stuff gets out of whack, especially then the qts is high.

But either way, both of these programs should provide accuate plots when the USER specifies the box volume and port tuning. That's where these programs are most useful.

Oh man... yeah, I changed the Vas and now my results are MUCH more in line with what I'd expect from a Kicker sub.
This thing needs an entire minivan to provide a reasonable response.

20 cubic feet tuned to 12 hz looks pretty good.

Stupid kicker.

 

ah... so I guess I can't use that .0001 cuft box that it recommended???

 

You could alway duct tape the back of the basket then no box is needed

 

use a baloon... and i tried printscreen.....

 

did you try pasting the picture (after you did printscreen) in a graphics program (like irfanview)?

printscreen takes a pic of everthing Ive ever tried.. except some videos it wont take a picture of perfectly if you don't get it just right.

 

meh.. i dono whats up with my comp but b4 when i tried printscreen it did nothing.. even b4 that i tried file > print > graph and the print thing came up but nothing printed..... last night i tried the print graph again and boom.. i have a grpah on my desktop now

 

hit "Print Scrn" > open up MS paint > ctrl+v > click yes > edit pic > print

problem solved.

send donations via paypal

 

lol if only i hadnt figured it out b4 you told me