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RSDXzec
02-24-2012, 03:19 AM
Received my pcw-12 subwoofer in the mail today. And using the subs specs on this calculator Car Audio - Ported Subwoofer Box Design Formulas & Calculator (http://www.carstereo.com/help/Articles.cfm?id=17)
It tells me I'm going to need a 7.5cuft box if I go ported.

My limits are about 10.5" high and I believe about 4cuft internal total and my boot would be full.
I'd like to use a cylindrical port tune it to 32hz, should I make the box 4 cuft? or could I go down to about 3cuft?

Cheers.

------------------------------------------------------------------------------------------
specs for reference:
RMS - 350W
Fs - 32.87 Hz
Vas - 1.839 cuft
Qms - 4.963
Qes - 0.733
Qts - 0.638
Xmax - 0.413"
SPL - 89dB
dual 4 ohm VC

SMS
02-24-2012, 07:05 AM
7.5-thats almost like running it free air. Is it hard to get good subs in Austraila?

RSDXzec
02-24-2012, 07:08 AM
7.5-thats almost like running it free air. Is it hard to get good subs in Austraila?

yeah it's a real pain.
Also from what I've read this was a pretty good sub in its time, only reason it says 7.5 on that calculator is because the sub was made for sealed, this tends to happen a lot for subs with sealed specs. Yet I have seen most of these on youtube running ported, and pretty well at that.

So I'd like to know what kind of volume I'd actually need.

Phoenix Risen
02-24-2012, 08:44 AM
generally with 12's its anywhere between 1.5 and 2.5 depending on the application and the woofer, with that sub i would shoot for around 2cubes net.

Joseph7195
02-24-2012, 08:51 AM
I would give a holla at Mobile Enclosures

http://www.caraudio.com/forums/members/moble-enclosurs.html

He could really help you out. There are certain factors a calculator couldn't take into account, like the installers needs. Give him a shout, he will help. Hope this helps!

Phoenix Risen
02-24-2012, 08:57 AM
indeed, ram_designs knows a thing or to as well, and is always happy to help.

RSDXzec
02-24-2012, 09:00 AM
I would give a holla at Mobile Enclosures

http://www.caraudio.com/forums/members/moble-enclosurs.html

He could really help you out. There are certain factors a calculator couldn't take into account, like the installers needs. Give him a shout, he will help. Hope this helps!


indeed, ram_designs knows a thing or to as well, and is always happy to help.

alright il send a message to ram_designs as I have already contacted mobile enclosures and I'm waiting for him to get back to me.

hispls
02-24-2012, 09:02 AM
That woofer really wants to be in a sealed box to sound good. You can put it in whatever ported box you want and it may get loud, but likely won't have a good response.

Volume displaced by woofer and port counts against internal volume of the box FYI

RSDXzec
02-24-2012, 09:08 AM
That woofer really wants to be in a sealed box to sound good. You can put it in whatever ported box you want and it may get loud, but likely won't have a good response.

Volume displaced by woofer and port counts against internal volume of the box FYI

are you saying that based on the specs or on previous experience with it?

and thanks I didn't take into account the port volume.

hispls
02-24-2012, 09:18 AM
are you saying that based on the specs or on previous experience with it?

and thanks I didn't take into account the port volume.

Low Fs, high Q, and somewhat low Vas. Good indication it'll play nice and flat in a large-ish sealed box. Really getting close to the kind of sub that would do well in infinite baffle. A poor choice if you planned to use ported alignment IMO. Like I said, it'll probably get loud, but without cabin accoustics working in your favor (dumb luck or a shitload of experimenting) you won't get a really flat response out of a ported alignment.

RSDXzec
02-24-2012, 09:45 AM
Low Fs, high Q, and somewhat low Vas. Good indication it'll play nice and flat in a large-ish sealed box. Really getting close to the kind of sub that would do well in infinite baffle. A poor choice if you planned to use ported alignment IMO. Like I said, it'll probably get loud, but without cabin accoustics working in your favor (dumb luck or a shitload of experimenting) you won't get a really flat response out of a ported alignment.

ah ok, well would you say it would get considerably louder if I put it in a 2 cuft sealed box as opposed to the 1 cuft sealed box that it's in now? I just upgraded from a kenwood 200wrms 12" sub and didn't notice too much difference so I was a little disappointed, I'm hoping the box can increase the output a fair bit.

hispls
02-24-2012, 09:56 AM
It will be louder in a ported box....whether or not it will sound good ???? Come back and let us know.

RSDXzec
02-25-2012, 02:08 AM
It will be louder in a ported box....whether or not it will sound good ???? Come back and let us know.

probably will go sealed... it's just finding the right point between 1.25-3cuft that I need to work out now. Manufacturer specs say 1.25 is max output and 3 is best sq, I'm trying to go for the box that will help me "feel" the bass the most. I guess 2cuft would be a good balance, but would you say leaning towards 1.25 or 3 would be best for "feeling" the bass?

The_Grimy_One
02-25-2012, 02:17 AM
probably will go sealed... it's just finding the right point between 1.25-3cuft that I need to work out now. Manufacturer specs say 1.25 is max output and 3 is best sq, I'm trying to go for the box that will help me "feel" the bass the most. I guess 2cuft would be a good balance, but would you say leaning towards 1.25 or 3 would be best for "feeling" the bass?

The bigger the sealed box, the lower the frequency... So I would probably shoot for around 2.25 or so. I think you would be much more satisfied.

RSDXzec
02-25-2012, 02:37 AM
The bigger the sealed box, the lower the frequency... So I would probably shoot for around 2.25 or so. I think you would be much more satisfied.

alright, for the record it is a hatchback so it's not a big car so feeling the bass shouldn't be hard to do. I definitely have room to go the full range between 1.25 to 3 if I need to. I probably will aim on the higher volume end of that to get the lower frequencies if I can feel them more. I'm not sure if max output means the most you can hear or the most bass you can feel, based on your statement I would assume that it's hear. I however am more interested in feeling the bass than hearing it

The_Grimy_One
02-25-2012, 02:41 AM
alright, for the record it is a hatchback so it's not a big car so feeling the bass shouldn't be hard to do. I definitely have room to go the full range between 1.25 to 3 if I need to. I probably will aim on the higher volume end of that to get the lower frequencies if I can feel them more. I'm not sure if max output means the most you can hear or the most bass you can feel, based on your statement I would assume that it's hear. I however am more interested in feeling the bass than hearing it

Max Output = Max SPL. Im not a very big fan of that kind of bass. The head hurting bass. I like the music to be more deep, and essentially "feel it" more in my chest.

RSDXzec
02-25-2012, 02:51 AM
Max Output = Max SPL. Im not a very big fan of that kind of bass. The head hurting bass. I like the music to be more deep, and essentially "feel it" more in my chest.

great, I agree with you I prefer the same type of bass. That said, why did you say 2.25 as opposed to 2.5 or 3 cubic feet? Is there some sort of advantage to less volume inside the box?

Cheers.

The_Grimy_One
02-25-2012, 03:28 AM
great, I agree with you I prefer the same type of bass. That said, why did you say 2.25 as opposed to 2.5 or 3 cubic feet? Is there some sort of advantage to less volume inside the box?

Cheers.

Well I dont think you want to sway totally to the SQ side... You are in 1 cube right now. 2.25 cubes is gonna be a HUGE difference.

RSDXzec
02-25-2012, 03:50 AM
Well I dont think you want to sway totally to the SQ side... You are in 1 cube right now. 2.25 cubes is gonna be a HUGE difference.

alright then, good to know there is a huge difference between them. I only plan on making 1 box, I wont be testing out different sizes so I'm trying to get it the right size on the first go. Whichever size helps me feel the bass the most is what I'm going for.

Cheers.

edit: just checked the qtc on competing box sizes
1cuft - 1.075
2.25cuft - 0.8601
3cuft - 0.8103

The_Grimy_One
02-25-2012, 03:53 AM
alright then, good to know there is a huge difference between them. I only plan on making 1 box, I wont be testing out different sizes so I'm trying to get it the right size on the first go. Whichever size helps me feel the bass the most is what I'm going for.

Cheers.

I mean, wait and see what some others say. I am deff not the most knowledgeable. And I dont know the sub that well. I just know some concepts of boxes... When going sealed, I usually sway towards the bigger box. You could try to use the max volume, but I think you would lose some SPL type bass that you will end up missing.

duanebro
02-25-2012, 10:08 AM
A smaller box controls the cone better. So you can use more power. A larger box will give you more low end. I would go with a bigger box than what you have in any case.

As far as ported, you can do a ported box. But you should go with a different tuning than normal. I would say that a very low tune will help bring up your efficacy without many of the down sides that come with porting a high Q sub. If you want to go this route I'd use a PVC port because you can get a plug and try sealed also.

hispls
02-25-2012, 10:24 AM
alright, for the record it is a hatchback so it's not a big car so feeling the bass shouldn't be hard to do. I definitely have room to go the full range between 1.25 to 3 if I need to. I probably will aim on the higher volume end of that to get the lower frequencies if I can feel them more. I'm not sure if max output means the most you can hear or the most bass you can feel, based on your statement I would assume that it's hear. I however am more interested in feeling the bass than hearing it

download winisd (freeware). Model some different sealed boxes and see what the response curve does as you make the box very large or very small. I would lean towards larger as well.

RSDXzec
02-25-2012, 11:51 AM
download winisd (freeware). Model some different sealed boxes and see what the response curve does as you make the box very large or very small. I would lean towards larger as well.

oh wow thanks a lot! why didn't i hear of this program earlier, I did try looking for some but i would've had to pay for them. This software is great!

RSDXzec
02-25-2012, 12:06 PM
got some response curves, measured at RMS power at 1 meter
http://i42.tinypic.com/vsi5c4.png

I compared my previous sub to the new one in different sized boxes. I'm not sure what frequency I should really be looking to boost here. My lpf is set to 80hz so I know nothing higher than that matters, but around what frequency should i aim for the get the best "car shaking" bass.

edit:


A smaller box controls the cone better. So you can use more power. A larger box will give you more low end. I would go with a bigger box than what you have in any case.

As far as ported, you can do a ported box. But you should go with a different tuning than normal. I would say that a very low tune will help bring up your efficacy without many of the down sides that come with porting a high Q sub. If you want to go this route I'd use a PVC port because you can get a plug and try sealed also.

just checked out what a ported enclosure would be like, doesn't seem too bad to me
http://i42.tinypic.com/13z36yw.png
what do you guys think of this response curve?

only real downside it the delay is up to 30ms, whereas the sealed boxes have a delay of 6-7ms

duanebro
02-25-2012, 12:27 PM
If you go to facebook and find their page, you can get the latest version.

What that doesn't show is the excursion in the different boxes. At 250 watts you will hit xmax with the 3 cf box. I would use a 2.5 cf box. Add a 3" PVC port 17" long. This should tune the box to about 21 Hz. You can find a plumbers test plug at the same place you get the PVC. This way you can switch between ported or sealed.

Btw, model that ported box in WinISD. See if you can figure out why I said to tune so low.

RSDXzec
02-25-2012, 01:24 PM
If you go to facebook and find their page, you can get the latest version.

What that doesn't show is the excursion in the different boxes. At 250 watts you will hit xmax with the 3 cf box. I would use a 2.5 cf box. Add a 3" PVC port 17" long. This should tune the box to about 21 Hz. You can find a plumbers test plug at the same place you get the PVC. This way you can switch between ported or sealed.

Btw, model that ported box in WinISD. See if you can figure out why I said to tune so low.

ok I tried 26/23/21hz
http://i44.tinypic.com/i3b38k.png

21hz at 3" diameter is 14.7" long. I'm guessing you're saying to tune it low so it doesn't drop off at the end. But considering human hearing only goes down to 20hz would 23hz be good enough? I'm really liking the higher dbs I can get with a ported enclosure so I'm trying to get the optimum. ***** about the sub hitting xmax at 250wrms, tested that out and a 2.5cuft box with 350wrms is much better, do you think it would be able to handle up to 400wrms in a 2.5cuft box?

Also I definitely plan on getting a plug, considering 2.5cuft is near what I was going to go sealed anyway so it's a win-win situation for me right now. Either way ported/sealed I get what I want.

duanebro
02-25-2012, 02:14 PM
ok I tried 26/23/21hz
http://i44.tinypic.com/i3b38k.png

21hz at 3" diameter is 14.7" long. I'm guessing you're saying to tune it low so it doesn't drop off at the end. But considering human hearing only goes down to 20hz would 23hz be good enough? I'm really liking the higher dbs I can get with a ported enclosure so I'm trying to get the optimum. ***** about the sub hitting xmax at 250wrms, tested that out and a 2.5cuft box with 350wrms is much better, do you think it would be able to handle up to 400wrms in a 2.5cuft box?

Also I definitely plan on getting a plug, considering 2.5cuft is near what I was going to go sealed anyway so it's a win-win situation for me right now. Either way ported/sealed I get what I want.

I went from memory on the port length, but you must calculate the volume displaced by the port. I think I modeled it at 2.25cf for the ported. Take a look at the group delay at the different tunings. The delay is higher around tuning. Phase shift does the same thing. One more detail, at tuning, the port air speed is really high. A bigger port is needed. But if you tune below where you will be using the sub then these issues are also moved down to where they don't matter.

RSDXzec
02-25-2012, 08:57 PM
I went from memory on the port length, but you must calculate the volume displaced by the port. I think I modeled it at 2.25cf for the ported. Take a look at the group delay at the different tunings. The delay is higher around tuning. Phase shift does the same thing. One more detail, at tuning, the port air speed is really high. A bigger port is needed. But if you tune below where you will be using the sub then these issues are also moved down to where they don't matter.

Ok that's good, looking at the delay if I tune to 20hz the highest delay at 20hz is 21ms and at 22hz its 27ms. Is it ok to tune subs this low? I don't want to cause any damage to it. Also what kind of delay is ok for maximum at 20hz? I'm trying to get good spl too and the lower I tune it the less spl I get.

Considering the length of the port, in order to hold it in place would it be a good idea to have it near the wall of the box and drill a couple of holes into the pipe and the box, then use a nut and bolt to secure it in place as well as adding the glue on the outside edge of the port (on the 3/4" length contact around the pipe touching the wall of the box)? I think if done well this would be a good method to secure the port and reduce "port noise" but I'm not sure if it would introduce any leaks.

edit: here are the graphs of spl and group delay showing sealed vs 21/22/23 hz
I'm really liking 22hz, it seems to have the "flattest" response (if I'm using the terminology correctly) and the group delay isn't too high i guess.

spl
http://i39.tinypic.com/rcvfnq.png

group delay
http://i40.tinypic.com/s42qsj.png

I also downloaded the latest version of winisd and I'm unable to get an xmax graph based on the information I have available to me.

duanebro
02-26-2012, 01:00 AM
Ok I will try to clear up a few things, and post some graphs of this also. Please do remember that your car plays a big part of the response Ė and WinISD does not model that.
I used 10.7Ē for Dd. This might not be correct, I guessed based off of other drivers Iíve modeled.
Let me post a few graphs:
http://i1091.photobucket.com/albums/i386/duanebrow/Car%20Audio%20Designs/pcw12specs.jpg
http://i1091.photobucket.com/albums/i386/duanebrow/Car%20Audio%20Designs/pcwspl.jpg
Black line is 1cf sealed (400 watts)
Purple is 2.5cf sealed (300 watts)
Red is 2.4cf ported @ 23hz (400 watts)
I reduced the power on the bigger sealed box because of excursion:
http://i1091.photobucket.com/albums/i386/duanebrow/Car%20Audio%20Designs/pcwexcursion.jpg
I didnít include Group delay or phase shift because all the models are about the same above 30hz. I donít expect this sub to be used below 30 hz very often, and if you do, Iíd guess port noise will be the biggest concern. Speaking of port noise, donít drill any holes in the port. Just make a brace at the end to hold it. Just like the side of the box where it ends. Use SCH-40 pipe, it will be very stiff. If you have a router rounding over the ends of the port will be a good idea. With the 23hz tuning your 3Ē port will only be 12.75Ē long and should take up less than .1cf.

Tuning a sub really low will not hurt the sub unless excursion is to high above tuning, It should be fine even with 400 watts in this case. It is rare to see subs tuned this low in car audio, but with your sub I think it is the best way to get the most SPL while retaining SQ.

its_bacon12
02-26-2012, 01:38 AM
That high of a Qts is suited more for IB, which is why you're getting huge box requirements

Try something with a Qts under .3 and Fs above 30 for a decently sized ported box.

globalminds_ent
02-26-2012, 01:53 AM
why do u want it ported..? I've seen plenty of subs made for sealed sound as good as ported. And extra deep on the lows at that

RSDXzec
02-26-2012, 02:22 AM
Ok I will try to clear up a few things, and post some graphs of this also. Please do remember that your car plays a big part of the response – and WinISD does not model that.
I used 10.7” for Dd. This might not be correct, I guessed based off of other drivers I’ve modeled.
Let me post a few graphs:
http://i1091.photobucket.com/albums/i386/duanebrow/Car%20Audio%20Designs/pcw12specs.jpg
http://i1091.photobucket.com/albums/i386/duanebrow/Car%20Audio%20Designs/pcwspl.jpg
Black line is 1cf sealed (400 watts)
Purple is 2.5cf sealed (300 watts)
Red is 2.4cf ported @ 23hz (400 watts)
I reduced the power on the bigger sealed box because of excursion:
http://i1091.photobucket.com/albums/i386/duanebrow/Car%20Audio%20Designs/pcwexcursion.jpg
I didn’t include Group delay or phase shift because all the models are about the same above 30hz. I don’t expect this sub to be used below 30 hz very often, and if you do, I’d guess port noise will be the biggest concern. Speaking of port noise, don’t drill any holes in the port. Just make a brace at the end to hold it. Just like the side of the box where it ends. Use SCH-40 pipe, it will be very stiff. If you have a router rounding over the ends of the port will be a good idea. With the 23hz tuning your 3” port will only be 12.75” long and should take up less than .1cf.

Tuning a sub really low will not hurt the sub unless excursion is to high above tuning, It should be fine even with 400 watts in this case. It is rare to see subs tuned this low in car audio, but with your sub I think it is the best way to get the most SPL while retaining SQ.

wow thanks a lot for going through the trouble of simulating this sub. Although I do have to ask what is the Dd and is there a way I could measure this? Because it seems even slight changes in the Dd change the excursion a fair bit so I want to make sure it's right. I tried google but it only directs me towards a brand called dd audio or something...

edit: more reading suggests it's the effective diameter of the sub, using a tape measure I measured 11" from the outsides of the surround and 9.5" from the insides. Attempting to make the tape measure touch the cone I got 10.2" measuring inside the surround. (from the points just before the surround starts to stick outwards from the sub.
so pi*5.1^2 = 81.71in^2 = Sd
when typing that in to winisd it gives me a Dd of 10.2
is this correct? I really hope it's 10.7, because at 10.2 it can't handle as much power.

I do know the car plays a big part in the sound I hear but does it make a difference to if the sub may be damaged? if I make a box that won't damage it I doubt that the car could cause the sub to act in a way as to damage it. For the record I am driving a hatchback, and from what I've heard they reproduce the audio very well.
If it matters the sub will be facing upwards in the car and the port will most likely face the rear of the vehicle. I have 10.5"x32"x24"(HxWxL) external dimensions to work with so next I'll be sorting out what shape to make the box once I'm set on the size which right now looks to be 2.5cuft internally.

I will probably use sandpaper/file to round off the edges of the port.

Although I must say I am surprised to see the 2.5cf box underpowered to be going over the excursion limit as it is what was recommended.


why do u want it ported..? I've seen plenty of subs made for sealed sound as good as ported. And extra deep on the lows at that

I'm really liking the response curves for ported, it's getting a decent amount of extra db across the frequency range, and even more in the lower notes.

globalminds_ent
02-26-2012, 02:36 AM
its just me but I like for a sub to play atleast 160 and down the kick drum is around 150hz if u cut off at 80 seems like u would be missing that punch that some subs make so well

RSDXzec
02-26-2012, 02:43 AM
its just me but I like for a sub to play atleast 160 and down the kick drum is around 150hz if u cut off at 80 seems like u would be missing that punch that some subs make so well

if you check the graph duanebro posted you can see ported hits that range as well as a 1cuft box does, getting a better sealed box would only lower the response in that region. My lpf is set to 80hz as that seems to be what most set their lpf to from a quick google search. Also my old amp just had an lpf switch which just went to 80hz with no option to change the frequency so I'd say 80hz is a fairly decent spot to leave it at.

globalminds_ent
02-26-2012, 02:58 AM
just because an amp has a low pass doesn't mean u have to use it. If your using a class d its not going to have a range but of 300hz and down anyways. I like to get more outta my subs then 80 and down. As a producer I know that some of my bass hits a lot higher than 80.
this is just my pinion 150 and down will be perfect u will still get that punch. I love that chest throbbing punch.

RSDXzec
02-26-2012, 03:05 AM
just because an amp has a low pass doesn't mean u have to use it. If your using a class d its not going to have a range but of 300hz and down anyways. I like to get more outta my subs then 80 and down. As a producer I know that some of my bass hits a lot higher than 80.
this is just my pinion 150 and down will be perfect u will still get that punch. I love that chest throbbing punch.

alright then I guess I'll have to test it out a bit more then, my amp doesn't play any higher than 250hz.

RAM_Designs
02-26-2012, 04:12 AM
its just me but I like for a sub to play atleast 160 and down the kick drum is around 150hz if u cut off at 80 seems like u would be missing that punch that some subs make so well

160hz is way too high for your sub to be playing at a loud level...talk about being able to localize the bass. Also, most kick drums are in the 50-60hz area. If you need the sub to play higher than 80hz, then your midbass must seriously be lacking...or you run PA style mids that have no midbass. I have my sub crossed at 63hz and wish my amp had a LP crossover so I could do my usual 36db crossover at 63hz to kill nearly all midbass from getting to my sub. If I change my crossover point up to where you're saying, that midbass coming from the sub is just annoyingly loud and irritating. Maybe it's just me...

RSDXzec
02-26-2012, 04:37 AM
160hz is way too high for your sub to be playing at a loud level...talk about being able to localize the bass. Also, most kick drums are in the 50-60hz area. If you need the sub to play higher than 80hz, then your midbass must seriously be lacking...or you run PA style mids that have no midbass. I have my sub crossed at 63hz and wish my amp had a LP crossover so I could do my usual 36db crossover at 63hz to kill nearly all midbass from getting to my sub. If I change my crossover point up to where you're saying, that midbass coming from the sub is just annoyingly loud and irritating. Maybe it's just me...

thanks for clearing that up. I did briefly test setting the lpf higher but in the 50-100hz range sounded best to me so I went with 80hz. I didn't do much testing to confirm that though so I was getting a little confused.

globalminds_ent
02-26-2012, 01:35 PM
dude I mix music for a living kick drum is 150 Hz look the **** up please before u come at me like I don't no what I'm talkin about please

RSDXzec
02-27-2012, 05:01 AM
ok well hopefully I get some more info on working out the Sd or Dd from duanebro since it seems an important part of calculating excursion. But up to now I've decided on a design that I think suits my needs fairly well. Having a 2.4cf box and a port tuned to 24hz seems to be the sweet spot for me.

My maths:
port is 4" diameter, 21.5" long gives me a displacement of 0.156cf. Sub displacement is 0.9cf so all together I need about o.25cf head room. Which means I'll need a box with 2.65cf. My limits are 30.5" wide and 9" high internal dimensions.
2.65*1728 = 30.5x9xL
L = 16.68
Internal dimensions should be 30.5x9x16.7, using 3/4" wood external dimensions should be 32"x10.5"x18.2"

Setting the Sd to 82.5, a guess based on other soundstream subs, gives me a Dd of 10.25"
Using that number I took some response curves that I'm pretty happy with.
in the following graphs, the red line is the 1cf box I currently have, the blue one is what I get if I cover the port giving me about 2.5cf, and the green line is the ported box at 24hz.

SPL
http://i43.tinypic.com/1zx8tb9.png

Group delay
http://i42.tinypic.com/v4qd10.png

Excursion
http://i44.tinypic.com/zmnyqg.png

And port velocity, just incase anyone notices it's abnormally high or low let me know.
http://i41.tinypic.com/2130ilc.png

Let me know if you have any ideas or feedback based on these response curves.

Thanks for any help/advice you can give me.

Cheers.

duanebro
02-27-2012, 03:34 PM
I missed a few updates on this thread... but it looks like you have a good start on your design. I think that you will not have an issue with the port air speed. For home use recommended is below 17. Or 25 if your not that picky. In a car with the sub in the back below 25 meters per second - at the frequencies you are using it - should be fine.

Your measured SD is the correct way, You do go over xmax with the new design. I wouldn't worry about the ported version, it is close. But you could be able to push the sealed version to do bad things. Basically you won't be able to turn it up as loud as the ported version. Try it out, the sub should let you know when it has had enough.

you might want to double check your port displacement. A 4" PVC pipe has an osd of ~4.5".

I would add .75" on to the end of the box to allow for some bracing to be added.

RSDXzec
02-28-2012, 01:21 AM
I missed a few updates on this thread... but it looks like you have a good start on your design. I think that you will not have an issue with the port air speed. For home use recommended is below 17. Or 25 if your not that picky. In a car with the sub in the back below 25 meters per second - at the frequencies you are using it - should be fine.

Your measured SD is the correct way, You do go over xmax with the new design. I wouldn't worry about the ported version, it is close. But you could be able to push the sealed version to do bad things. Basically you won't be able to turn it up as loud as the ported version. Try it out, the sub should let you know when it has had enough.

you might want to double check your port displacement. A 4" PVC pipe has an osd of ~4.5".

I would add .75" on to the end of the box to allow for some bracing to be added.

Just got back from my local hardware store, found the most suitable pipe to be 3.45" internal diameter, 3.55" external diameter. Is this pipe too thin(0.05" around the edges)? or should I be alright? I didn't see any thicker pipes there... well the next one up was 5.9" lol
(odd measurements are because everything is in mm here, so 3.55" is a 90mm pipe)
With that pipe its air velocity hits 25m/s at 31.5hz as opposed to the 4" pipe getting there at 27hz.

realistically what frequency should I expect to be played? on as low as rap music would generally get. Because I'm considering tuning to 25hz, group delay is a little more, and so is port speed (25m/s @ 32.5hz) but the excursion is a little less and as long as the music never goes below 23hz my excursion should be fine. It also gives me about maybe 0.2db across the frequencies although I know this probably won't be noticed.

The reason excursion is on its limits as opposed to your design is due to the Dd being 10.2 instead of 10.7, I'm pretty sure 1mm over xmax should still be fine, as I understand 10% over doesn't cause any problems.

I do still need to work out what bracing I will have, although I don't think too much will be necessary for a ported design.

edit:
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Alternate idea: using a wood vent.
Because the wood I can get is 1200mmx600mm if I buy two of those I can use the wood effectively.

the new design would involve getting two of these, box dimensions would be 600x600x266.7
so 23.6"x23.6"x10.5"
The port tuned at 25hz to maintain the spl and reduce the port length has a 1.2" diameter across the 9" internal height of the box.
This means the port will be 17.9" and I will have 22.1" internal width, which means there is 4.2" without obstruction, would you say this is enough? (this idea gives me 2.25cf internal volume)
If I make the port 1.3" diameter then I will need the port to be 19.5", giving me 2.6" before the wall hits, really need an idea of how much room I need so I can make the diameter as big as I can reducing air speed.

This is an idea that I just had, it makes things a lot easier for me since I don't have the tools to cut good circles for the pipe port. Sorry for the long mixed up post but I'm 95% to completing my design and almost at the point of going out and buying the parts to get started. This design also lowers port speed compared to the round port design.

(also I don't think I will have any bracing on this ported design, unless you think I need it.)