Sub needs a massive ported box?

[globalminds_ent 10+ year member]

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 10+ year member]

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:

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:

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 10+ year member]

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 10+ year member]

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 10+ year member]

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 10+ year member]

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 5,000+ posts]

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 10+ year member]

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 10+ year member]

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 10+ year member]

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

Group delay

Excursion

And port velocity, just incase anyone notices it's abnormally high or low let me know.

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 10+ year member]

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 10+ year member]

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.)