SYSTEM INFO:
I own two ol' skool Cerwin Vega, Vega 124 12" 4ohm SVC woofers. They are each rated at 400w RMS. Following the spec sheets on Cerwin Vega's website, I constructed two tube enclosure, one for each sub. These enclosures are built to within (an I'm making a large assumption that my measuring tools are accurate) 1/100 of a cubic foot of recommended size. They are ported enclosures as this is the only design suitable for the woofer - according to Vega.
ENCLOSURE CONSTRUCTION INFO:
AS mentioned, the volume of the box meets spec., and the port length and diameter also meet spec. I even went as far as locating the port more than 4" from any wall of the enclosure and from the speaker. To visualize: picture a tube ~26" long with an external diameter of 14.25." There is a 4" diameter, round port located in the center of the rear of the tube that extends ~10" down the length of the tube. Now to accomadate Vega's rule that there should be 4" of clearance from port to all sides of enclsoure, I had to place the port in the center of the rear panel, so it is directly in line with the woofer (if you look into the port you see the magnet of the woofer).
As you can imagine, a 4" diameter port is HUGE and opens a considerable hole in the back of the enclosure.
MY QUESTION IS: since I used a tube design and could not follow the standard (mounting the port on the face of box with woofer) will the location of the port affect the effectiveness of the port and compromise the quality of the enclosure? Along the same lines, since the sound, pressure or whatever is not echoing off the back wall before exiting the port, instead spiraling down the tube and going straight out, is the tuning frequency of the box different than the 35hz Vega states the enclsorue will have?
Replies (7)
fitz1465 on 01/10/2004 00:20:29
when i design a woofer tube, i use a slot port instead of a round port. i place the slot port right below the woofer......the box looks like a cylinder with a flat bottom as to sit on the floor without rolling. it looks like an upside down U. put the slot port below the woofer. you can use the bottom of the enclosure as part of the port................slot ports are easy, just make sure the opening is the same area as the 4" diameter port so the area of the opening is equal to 4 x PI or ~12.566in^2 . you could make the opening say 1.5"high by 8.38"wide. just keep the length of the port the same to keep the tuning frequency the same and ROUND off the entrance and exits of the port to keep out the NOISE. good luck my friend.
eldevioso on 01/10/2004 04:25:32
Thank you for the input fitz...my problem is the tubes are already made, and I'm just curious if they're optimal for my speakers...however your flat bottomed tube design is intriguing. What material do you use for the rounded portion of the tube? I personally used a complete tube, with a board screwed and sealed on each end...but for this reason the entire tube is round (and yes, I do have problems with them rolling all over the place :).
fitz1465 on 01/10/2004 18:46:18
sorry for the lack of info.....you must make the two end U sections out of MDF and then the bottom that sits on the floor out of MDF also. put a small brace across the top to keep the two ends from falling over.....then wrap the U part with felt and fiberglass the enclosure with the proper techniques...they are tough at first but you can find great tips if you have never fiberglassed before on the web......especially at alpine-usa.com they have a honda they used at the CES that shows some great tips for anyone interested.....and you can go here, this guy's a little crazy but he doesn't do a bad job
http://web.njit.edu/~cas1383/proj/main/
as for as the slot port goes, you use the bottom MDF board that sits on the floor and and make a rectangular port with three smaller pieces of MDF to complete the "rectangular port" just round the edges of the entrance and exit....these are tough to make but look awesome in the end and sound good if done right.....that's the fun of it all just trying.
either way, those old giant cerwins are just made to POUND out bass LOUD...so you will probably here more of your car rattling than small inconsistencies in your box. good luck man!
eldevioso on 01/12/2004 11:42:06
Thanks again. I've viewed the Alpine fiberglass archive, it was impressive. However, as of right now, I think fiberglassing is a little over my head. One of these days though, I'll probably give it a shot. Your design sounds like it would be pretty slick looking.
As far as the Vegas pounding, that they do...they definitely hit hard and move some serious air. That was partly why I asked my question. I mean, there was so much air coming out the port of the tubes (you could feel a considerable rush of air at least 2-3 feet from the port exit) I was wondering if that was right. It seemed like to much. But, after thinking about it, if they're made to hit, and they can handle a decent amound of power, they have to move some air...therefore they're gonna need a big port.
As far as port noise, and rounding edges, you might find this amusing. These tubes were the first enclosures I've built, and as such I read a lot about design and what not. I read several places about rounding the edges of the ports to reduce noise. So here I am, with my PVC pipe thats maybe 1/16 of an inch thick and I'm "rounding the edges" by filing it down at an angle. The funny thing is the thickness of the PVC pipe is so small, especially considering it has a 4" diameter that I feel, it was probably useless in my design :) oh well, like you said, the fun is in trying...thanks again.
erikcooper on 01/12/2004 12:49:24
So what exactly is meant by "round the edges"?
cplkittle on 01/12/2004 18:34:27
As far as placement of the ports, it dosen't matter with car audio. I think the furthest allowable distance is around 48" from the speaker, so in any car audio application, that would not apply.
Rounding the edges or sanding the sharp corners down is extremely important, it reduces port whistle or noise.
I have seen alot of slotted port boxes, and personally like the design, however all of the do it yourself information on the internet tell you that if you go with anything other than a round port, to make the port as close to square as possible. I am not a genius in soundwave behavior, but I can see where you could severely alter a soundwave by pushing it through a narrow passage. On the other hand, some of the websites that recommend 'close to square' ports, also have tested slotted designs that they recommend over computer generated designs. JL tests each sub in different enclosures, and will work with you on a design for one of their subs. Most of the time with a slotted port.
Port air velocity should be below 20-25Mph to further reduce port noise, but if there is no problem with it, I wouldn't change anything. The only way to reduce port air velocity is to increase the diameter of the port, or add a second port. In both cases, to be tuned to the same frequency will require a much longer port length. You have to find a balance here between possible port length and air velocity.
eldevioso on 01/13/2004 14:19:40
Thanks a lot guys. These posts are exactly what I was looking for.
cplkittle: I don't mind the amount of air coming out, or the rate at which it is. I was merely concerned with the functionality of so much air moving and the port placement. It appears that the placement is not an issue, and that the only determining factor is tuning frequency and port noise. Well Im not sure, but since I built the tube and port to Cerwin Vega's specifications it should be tuned at their stated frequency. So that should be okay for me, since I'm no expert or master tuner. As for port noise, I don't notice any at all, even standing behind my car, close to the tubes, with the trunk open. It would have to be an AWFUL lot of air moving to make that 4" diameter port whistle any...
Oh well, I guess my question is answered. I was just wondering if I had used a different enclosure design and/or port placement built to the same specs if the speaker would perform better. from what I gather, however, it should be about the same.
Thanks a lot guys.
I own two ol' skool Cerwin Vega, Vega 124 12" 4ohm SVC woofers. They are each rated at 400w RMS. Following the spec sheets on Cerwin Vega's website, I constructed two tube enclosure, one for each sub. These enclosures are built to within (an I'm making a large assumption that my measuring tools are accurate) 1/100 of a cubic foot of recommended size. They are ported enclosures as this is the only design suitable for the woofer - according to Vega.
ENCLOSURE CONSTRUCTION INFO:
AS mentioned, the volume of the box meets spec., and the port length and diameter also meet spec. I even went as far as locating the port more than 4" from any wall of the enclosure and from the speaker. To visualize: picture a tube ~26" long with an external diameter of 14.25." There is a 4" diameter, round port located in the center of the rear of the tube that extends ~10" down the length of the tube. Now to accomadate Vega's rule that there should be 4" of clearance from port to all sides of enclsoure, I had to place the port in the center of the rear panel, so it is directly in line with the woofer (if you look into the port you see the magnet of the woofer).
As you can imagine, a 4" diameter port is HUGE and opens a considerable hole in the back of the enclosure.
MY QUESTION IS: since I used a tube design and could not follow the standard (mounting the port on the face of box with woofer) will the location of the port affect the effectiveness of the port and compromise the quality of the enclosure? Along the same lines, since the sound, pressure or whatever is not echoing off the back wall before exiting the port, instead spiraling down the tube and going straight out, is the tuning frequency of the box different than the 35hz Vega states the enclsorue will have?
Replies (7)
fitz1465 on 01/10/2004 00:20:29
when i design a woofer tube, i use a slot port instead of a round port. i place the slot port right below the woofer......the box looks like a cylinder with a flat bottom as to sit on the floor without rolling. it looks like an upside down U. put the slot port below the woofer. you can use the bottom of the enclosure as part of the port................slot ports are easy, just make sure the opening is the same area as the 4" diameter port so the area of the opening is equal to 4 x PI or ~12.566in^2 . you could make the opening say 1.5"high by 8.38"wide. just keep the length of the port the same to keep the tuning frequency the same and ROUND off the entrance and exits of the port to keep out the NOISE. good luck my friend.
eldevioso on 01/10/2004 04:25:32
Thank you for the input fitz...my problem is the tubes are already made, and I'm just curious if they're optimal for my speakers...however your flat bottomed tube design is intriguing. What material do you use for the rounded portion of the tube? I personally used a complete tube, with a board screwed and sealed on each end...but for this reason the entire tube is round (and yes, I do have problems with them rolling all over the place :).
fitz1465 on 01/10/2004 18:46:18
sorry for the lack of info.....you must make the two end U sections out of MDF and then the bottom that sits on the floor out of MDF also. put a small brace across the top to keep the two ends from falling over.....then wrap the U part with felt and fiberglass the enclosure with the proper techniques...they are tough at first but you can find great tips if you have never fiberglassed before on the web......especially at alpine-usa.com they have a honda they used at the CES that shows some great tips for anyone interested.....and you can go here, this guy's a little crazy but he doesn't do a bad job
http://web.njit.edu/~cas1383/proj/main/
as for as the slot port goes, you use the bottom MDF board that sits on the floor and and make a rectangular port with three smaller pieces of MDF to complete the "rectangular port" just round the edges of the entrance and exit....these are tough to make but look awesome in the end and sound good if done right.....that's the fun of it all just trying.
either way, those old giant cerwins are just made to POUND out bass LOUD...so you will probably here more of your car rattling than small inconsistencies in your box. good luck man!
eldevioso on 01/12/2004 11:42:06
Thanks again. I've viewed the Alpine fiberglass archive, it was impressive. However, as of right now, I think fiberglassing is a little over my head. One of these days though, I'll probably give it a shot. Your design sounds like it would be pretty slick looking.
As far as the Vegas pounding, that they do...they definitely hit hard and move some serious air. That was partly why I asked my question. I mean, there was so much air coming out the port of the tubes (you could feel a considerable rush of air at least 2-3 feet from the port exit) I was wondering if that was right. It seemed like to much. But, after thinking about it, if they're made to hit, and they can handle a decent amound of power, they have to move some air...therefore they're gonna need a big port.
As far as port noise, and rounding edges, you might find this amusing. These tubes were the first enclosures I've built, and as such I read a lot about design and what not. I read several places about rounding the edges of the ports to reduce noise. So here I am, with my PVC pipe thats maybe 1/16 of an inch thick and I'm "rounding the edges" by filing it down at an angle. The funny thing is the thickness of the PVC pipe is so small, especially considering it has a 4" diameter that I feel, it was probably useless in my design :) oh well, like you said, the fun is in trying...thanks again.
erikcooper on 01/12/2004 12:49:24
So what exactly is meant by "round the edges"?
cplkittle on 01/12/2004 18:34:27
As far as placement of the ports, it dosen't matter with car audio. I think the furthest allowable distance is around 48" from the speaker, so in any car audio application, that would not apply.
Rounding the edges or sanding the sharp corners down is extremely important, it reduces port whistle or noise.
I have seen alot of slotted port boxes, and personally like the design, however all of the do it yourself information on the internet tell you that if you go with anything other than a round port, to make the port as close to square as possible. I am not a genius in soundwave behavior, but I can see where you could severely alter a soundwave by pushing it through a narrow passage. On the other hand, some of the websites that recommend 'close to square' ports, also have tested slotted designs that they recommend over computer generated designs. JL tests each sub in different enclosures, and will work with you on a design for one of their subs. Most of the time with a slotted port.
Port air velocity should be below 20-25Mph to further reduce port noise, but if there is no problem with it, I wouldn't change anything. The only way to reduce port air velocity is to increase the diameter of the port, or add a second port. In both cases, to be tuned to the same frequency will require a much longer port length. You have to find a balance here between possible port length and air velocity.
eldevioso on 01/13/2004 14:19:40
Thanks a lot guys. These posts are exactly what I was looking for.
cplkittle: I don't mind the amount of air coming out, or the rate at which it is. I was merely concerned with the functionality of so much air moving and the port placement. It appears that the placement is not an issue, and that the only determining factor is tuning frequency and port noise. Well Im not sure, but since I built the tube and port to Cerwin Vega's specifications it should be tuned at their stated frequency. So that should be okay for me, since I'm no expert or master tuner. As for port noise, I don't notice any at all, even standing behind my car, close to the tubes, with the trunk open. It would have to be an AWFUL lot of air moving to make that 4" diameter port whistle any...
Oh well, I guess my question is answered. I was just wondering if I had used a different enclosure design and/or port placement built to the same specs if the speaker would perform better. from what I gather, however, it should be about the same.
Thanks a lot guys.
Copyright ClubKnowledge 2009 * All Rights Reserved
