right then. this is my box at the moment. i want to make a port plug that will tune the box far lower but can go in and out.

as the port is radiused this is not all that easy.

would this work?

http://www.btinternet.com/~thetroublemaker/portidea.JPG

assuming you are looking from above and the blue is the port plug.

i assume it is now in effect a ?th order bandpass?

Yeah, that should work, tho id imagine its gonna be fairly difficult to get a good seal around the plug unless youve thought up a fantastical way of doing it!:)

I wouldnt have thought that the box would then become a bandpass though, id say the bit in front of the plug wouldnt really effect the the box because of the volume of it and the size of the opening into the cabin.

Difficult to say for cetain though without dimensions etc, or has any one else got any thoughts on this?

Steve

the reason for doing it there is that there is more of a flat edge than there is in the "real" port opening!

could you maybe get problem with port pumping that close to a wall, and the sub got lots of space in front...?

how will you get the round port(if thats the blue thing..) in and out...? take out sub...?

it all depends on the other #`s on the box...
and it will not get a ?th o.bandpass unless your plug gets way inside your box making big space outside of plug...with edges and stuff...

if that came out right... :)

Personally cant see it being ?th order bandpass at all.

The main port opening is alot larger than in most bandpass boxes.

If it does affect tuning I cant honestly see it being by too much at all.

Ben

Ah yes, i see what youre getting at VD,

But i believe that the main opening wont strictly behave as a port because thats all it is, just an opening into the cabin.

It will have a cavity resonance of its own though, but due to the relatively small volume, it would think that it would be too high to really effect the frequency response in a great way.

HTH:)

Steve

You could always invert the port plug so that the port points out through the larger point negating any effect that firing against the wall of the existing port would cause.

Van Dave:

Give us a bell if you can.

I`ll Pm you my Home Number in case you haven`t got it.

byeeeee.

so am i bein thick here but why not put in another board to go from the back of the box to some point just to the left of the edge of the wall in the above pic. thus decreasing port area, no worries abut sealing it, keeping the port on the front face and lowering tuning all in the one go! right it is nearly 2 am and i am goin to bed cos i'm knackered!!!

like this! see attached file!

I think Dumdum's not so Dum. :shiny: That looks like an idea that should work. But it will depend on what the box would then be tuned to.

Loudboy

Yeah, would work but would it get it down to 30 ish that VD will want.

Time for BBP Dave.

Ben

Now.

Why is it the simplest ideas never seem to be obvious till someone else points them out.

I will have a look during the day (i have just woken up - oh the joy of shifts!)

Looks like a good plan to me!

Steve

how the hell do i get negative reputation from this thread.

WHAT THE HELL?

odd people out there, there really are!

dave i think you take out your wall, and stick in two 3cu ft boxes tuned to about 36.7877Hz....problem solved !

j/k

chat in a bit, i just got in :)

[QUOTE=zimsoundz] two 3cu ft boxes tuned to about 36.7877Hz.... QUOTE]

LOL :whatever:

cool - txt me and i will bu=zz you at home!!!

I would suggest, having put a lot of time in on that car:
Cut the radius off, ie trim the port back by 40mm or so, then you will have a flat square port to work from, and then just use some 40+ thick wood, to make a longer port in the normal way. (dont tell me its a lot of work to cut the radius back, how do you think we got the final tuning?) you could always then use a 40+mm thick packing piece between baffle and port to make the port smaller in area as well

While Dumdums idea is simple, the above will give you better results, as the box will be bigger, and the wave length will be longer both in and out of the box. The Zero length port you have got, is fine for SPL, but the subs go unloaded quicker under the tuning frequency. ie it will sound and play better with a "typical" port.

what i was IDEALLY looking for though geoff was in effect a port plug so i could remove whatever assembly i use for burps, but replace it to play music!

Well, chop the radius off, and make the long port as above. Also make a new radius bit, (half moon) that just screws onto the end of the baffle, to eactly replicate what you have already :)

This way you can experiment with box tuning as well, by adding packer pieces between the half moon and baffle.

a little while back there was a peugeot car with fibreglass build phase amps and an aliante 12 " sub. the box had a linear actuator inside which moved a plug inside the box increasing the box size and alowing a port to come into play i know an aliante sub isnt an spl sub but the principle could still be used.

On the drawing it seems to me with the plug inserted the enclosure becomes a sealed box ?

Sleeving the existing port to reduce its internal volume will lower the tuning,obviously at the risk of increasing the air velocity,as long as this doesn't induce noise then great.

you are missing summat 40's.

the kinda right hand bit of the blue port plug is representing the port area that will be used!

it will not be sealed. that is for batty riders.

oh and peter.

linear acuators? nope that is also totally gay!

Dotted lines might have helped to show that the plug was actually a port ;)

Surely reducing the port size alone would be enough to retune the box or are you looking to alter the group delay as well ?This would also have the benefit of preventing the enclosure starting to perform like a bandpass box with the narrow bandwidth that offers.

As for gay...methinks thou protesteth too much...David Van Dave :lol:

PMSL.

you want to see me in my little lord faulteroy dress dude! :)