Hi,
I'm designing an enclosure for a Peerless CSC 176 H.
Now I have 2 options for ports:
1) A round 70mm flared-port. The thing is that I've been told that you take only the real straight part of the port into acount when figuring out the lengt. This makes that the port will not fit in the front or rear baffle. So I was thinking about putting it in the bottom and placing the enclosure on some kind of "feet" so it is about 1 1/2 times port-diameter from the ground. Will this work?
2) Build a slot-port. In this case I'll have to make a 90° bend at the back of the box, or decrease the portarea so the port will fir the depth of the box. I can keep enough portarea so the end of the vent is still about 2 times the hight of the port from the backside. In this case the port will be located at the bottom of the box on the backside.
Are these some good ideas, or should I try to work out some other solution?
Thanks for the comments.
I'm designing an enclosure for a Peerless CSC 176 H.
An externally hosted image should be here but it was not working when we last tested it.
Now I have 2 options for ports:
1) A round 70mm flared-port. The thing is that I've been told that you take only the real straight part of the port into acount when figuring out the lengt. This makes that the port will not fit in the front or rear baffle. So I was thinking about putting it in the bottom and placing the enclosure on some kind of "feet" so it is about 1 1/2 times port-diameter from the ground. Will this work?
2) Build a slot-port. In this case I'll have to make a 90° bend at the back of the box, or decrease the portarea so the port will fir the depth of the box. I can keep enough portarea so the end of the vent is still about 2 times the hight of the port from the backside. In this case the port will be located at the bottom of the box on the backside.
Are these some good ideas, or should I try to work out some other solution?
Thanks for the comments.
Some modeling apps will take into consideration flared and straight ports. Try Unibox.
Yes.
Personally I would opt for a slot port and would aim to not have any bends in it.
Excel is no problem.
*edit* there seems to be a problem when I load a driver I put in the database myself.
I provided Fs, Re, Qms, Qes, Sd, Vas, Xmax, Le, Pn and Rs. But when I load the driver I got some error and no results. I think there is a problem with a devision by 0. *end edit*
Yeah, I was thinking the same. Only thing is, I don't know what the internal box-material will be, yet.
Maybe oak, maybe MDF. In case oak, it will be a 22mm oak box. In case MDF, it will be 14mm pine on the outside, 8mm MDF on the inside. The front baffle will be 30mm thick.
But if the locations is of no impotance I can deside lateron where to put it.
Anyone else any experiance with ports firing to the ground?
*edit* there seems to be a problem when I load a driver I put in the database myself.
I provided Fs, Re, Qms, Qes, Sd, Vas, Xmax, Le, Pn and Rs. But when I load the driver I got some error and no results. I think there is a problem with a devision by 0. *end edit*
Yeah, I was thinking the same. Only thing is, I don't know what the internal box-material will be, yet.
Maybe oak, maybe MDF. In case oak, it will be a 22mm oak box. In case MDF, it will be 14mm pine on the outside, 8mm MDF on the inside. The front baffle will be 30mm thick.
But if the locations is of no impotance I can deside lateron where to put it.
Anyone else any experiance with ports firing to the ground?
"...you take only the real straight part of the port into acount when figuring out the lengt. "
1) As I understand, the opposite of what you assumed it true - you do allow the flare as part of the length, and you also add a little more as the flare effectively makes the port longer! The effective length of the vent is longer than the actual vent. This occurs with all vents but I think it happens to a greater extent with flared ports. So it may be ok to make the vent shorter than you are thinking. Also keep in mind that the location of the vent may also result in an end correction factor which will further extend the effective length. If the vent is close to the floor or a wall, the effective length is increased by the radius of the port.
For a tutorial on vents, have a look at:
http://www.jlaudio.com/tutorials/ports/index.html
Sometimes it is a good idea to do some manual calcualtions - put a formula into excel and you will learn more - eg. play around with the vent design formula and you will understand how box size, number of vents and tuning affects vent size.
2) I can't see any reason to use a shelf vent with this sub. They are useful for fitting in a big and long vent into a box where a large diameter with a lot of bends would be needed. For the size you are talking about, it will be too small in one dimension and that may cause turbulence.
Make sure you allow for the space in the box that the vent takes up. If in doubt with anything, why not build a quick test box to the volume you have in mind and put the vent on the outside - see if it performs as you wanted and that you don't get turbulence etc.
Hope this helps,
Paul
1) As I understand, the opposite of what you assumed it true - you do allow the flare as part of the length, and you also add a little more as the flare effectively makes the port longer! The effective length of the vent is longer than the actual vent. This occurs with all vents but I think it happens to a greater extent with flared ports. So it may be ok to make the vent shorter than you are thinking. Also keep in mind that the location of the vent may also result in an end correction factor which will further extend the effective length. If the vent is close to the floor or a wall, the effective length is increased by the radius of the port.
For a tutorial on vents, have a look at:
http://www.jlaudio.com/tutorials/ports/index.html
Sometimes it is a good idea to do some manual calcualtions - put a formula into excel and you will learn more - eg. play around with the vent design formula and you will understand how box size, number of vents and tuning affects vent size.
2) I can't see any reason to use a shelf vent with this sub. They are useful for fitting in a big and long vent into a box where a large diameter with a lot of bends would be needed. For the size you are talking about, it will be too small in one dimension and that may cause turbulence.
Make sure you allow for the space in the box that the vent takes up. If in doubt with anything, why not build a quick test box to the volume you have in mind and put the vent on the outside - see if it performs as you wanted and that you don't get turbulence etc.
Hope this helps,
Paul
Downfiring port......
I've got downfiring ports in a B&W sub and a sub that I have designed and built. Works very well on subs but I don't know how it would go on the CSX 176 (850122).
I'm designing some speakers at the moment using these Peerless drivers, but I'll have the port at the back.
Cheers
I've got downfiring ports in a B&W sub and a sub that I have designed and built. Works very well on subs but I don't know how it would go on the CSX 176 (850122).
I'm designing some speakers at the moment using these Peerless drivers, but I'll have the port at the back.
Cheers
@Paul Spencer:
Those JL-audio tutorials are really useful. I look them up quite frequently.
If the thing about the flares is true, then I could fit a 70mm round port. The port-mouth on the inside will be about 8.3cm fron the back of the box. Isn't that alittle close? I could give it an extra 2cm at best. But no more then that.
@ Rabbitz:
I think down-firing will work best for subs. I don't know how it works vor low/mids. But I was thinking it may keep the mids from radiating from the port-mouth. On the ohter hand I'm afraid that could make the total sound a little boomy.
Those JL-audio tutorials are really useful. I look them up quite frequently.
If the thing about the flares is true, then I could fit a 70mm round port. The port-mouth on the inside will be about 8.3cm fron the back of the box. Isn't that alittle close? I could give it an extra 2cm at best. But no more then that.
@ Rabbitz:
I think down-firing will work best for subs. I don't know how it works vor low/mids. But I was thinking it may keep the mids from radiating from the port-mouth. On the ohter hand I'm afraid that could make the total sound a little boomy.
Why not use an elbow? That should get the vent clear of the back wall. Also it is a good idea to flare both ends.
The reason for downfiring a port should not be to attenuate midrange getting through - that should be dealt with by the low pass filter. Also the enclosure should be lined with damping material, thus you shouldn't need any more than that.
The way I see it, vent location has more to do with aesthetics and placement preference - a vent to the rear means you need clearance behind the sub, a front vent means you can put it against a wall, etc.
cheers,
Paul
The reason for downfiring a port should not be to attenuate midrange getting through - that should be dealt with by the low pass filter. Also the enclosure should be lined with damping material, thus you shouldn't need any more than that.
The way I see it, vent location has more to do with aesthetics and placement preference - a vent to the rear means you need clearance behind the sub, a front vent means you can put it against a wall, etc.
cheers,
Paul
Yep, both sides will be flared.
I've used elbows with the type of port available to me, and those elbows are not realy nice. I don't know why, but they don't seem to fit like they should. I think that would create more problems then having the port at 1 or 1.5 times port-diameter from the back.
I've used elbows with the type of port available to me, and those elbows are not realy nice. I don't know why, but they don't seem to fit like they should. I think that would create more problems then having the port at 1 or 1.5 times port-diameter from the back.
If your port is 8.3cm from the back of the box, you should be OK. In the Loudspeaker Cookbook, the port end should be a minimum of 7.6cm from the wall.
Hope this helps.
Hope this helps.
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