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View Full Version : 4 cubic feet, tuned to 22 Hz, port area >= 64in^2



emilimo701
06-19-2012, 01:33 PM
The problem is that this calls for a really long port. I'm talking 80+ inches.

I have a Legacy wagon, so I have a decent amount of space to work with, but I'd like to keep the box height low enough so that I can still use the retractable cargo cover for the purpose of preventing theft.

The 15" Axis has an xmax of 30mm which calls for sufficient port area, which further increases the length of the port.

My original design had one slotted vent (16" x 4") wrapping around 3 sides plus a quarter of the front side, inside the box, which the subwoofer and port both front facing. I can post a drawing, or a picture of the box set up ready to be glued and screwed.

I think I got some of the measurements wrong so might have to scrap it.

I was thinking of designing a new one, with dual slotted ports (one of each side), and making things simpler with no 45 degree angles in the port (just 90/180 corners).

My question to the experiences box designers would be, how would you go about this is a client wanted a really low tuning frequency, where your options for space are kind of limited?

Maybe I will have to choice but to make the box height higher, and make the sub side-facing? I'd like easy and logical access to the wiring terminals.

RangerDangerV2
06-19-2012, 01:35 PM
first off why would you tune that low?? if you want to play low build a fourth order or a t line. also why would you do dual ports? just do one, more efficiency and a lot easier.

RangerDangerV2
06-19-2012, 01:40 PM
and if you are low on space you need to do a smaller port, but for really low extension go with a t line or and 8th order.

Kangaroux
06-19-2012, 01:40 PM
That low of a tuning for a ported box is a waste of time. Do a 4th order bandpass tuned to ~35hz if you want that kind of low end. My box is tuned to 40hz (it's a 4th order) and I can play down to 18hz and still have some authority, and I can play up to 55-60hz before it starts to roll off too much.

RangerDangerV2
06-19-2012, 01:45 PM
That low of a tuning for a ported box is a waste of time. Do a 4th order bandpass tuned to ~35hz if you want that kind of low end. My box is tuned to 40hz (it's a 4th order) and I can play down to 18hz and still have some authority, and I can play up to 55-60hz before it starts to roll off too much.

same for me... only I have a simple ported box... I can play from 18-50 with authority but any lower or higher and it is meh.... 27hz seems to be the peak because it absolutely murders your hold that though remix... and your never enough chopped and screwed version...

Falcons
06-19-2012, 01:46 PM
what about i cook by oj da juiceman??

RangerDangerV2
06-19-2012, 01:47 PM
what about i cook by oj da juiceman??

dont have that but I can absolutely murder midget slowed...

hispls
06-19-2012, 02:12 PM
This is why TC sounds pushed the passive radiators.

I would agree that tuning that low is pointless unless you're trying to **** off whales. I ran 15" TC-2000's tuned at 28hz and they played plenty well down to 20. This was when I was running 5.1 surround and watched a lot more movies and I never ran out of bottom end for sound effects.

I strongly suspect if these subs performed well in bandpass alignments it would have been mentioned on the old TC forums (which I can't for the life of me recall anyone ever saying was a great idea). Really you'll probably find more people who know what they're talking about with that sub on HT forums.

Any way you work it your port is going to be very long. Don't even think of doing 2 ports since they would be impractically narrow. Any way you can fold it would be about as good as the next I think, though the least number of turns/angles in it the better.

emilimo701
06-19-2012, 02:53 PM
I'm tuning at 22 Hz based on the specs of the sub, and what I want to get out of the system. I can hear the 20 Hz tone in "Put On" by young jeezy and kanye, so i'm kind of using that as my reference. Right now with the Axis in a sealed box, i'm not getting the output I want. It's about 16db down at 20Hz, and that simply is not cutting it. I want that 20Hz tone to slam with the same authority as the others. If I find out that such a lot tuning isn't necessary, I'll rebuild a new box tuned higher. But right now my goal for the enclosure is firm: 4-4.2 cubic feet tuned to 22Hz. I don't so much want high SPL in the 40-50 Hz range; rather, a flat response with a graceful rolloff. Maybe I won't end up liking it, but I want to at least give it a try, for curiosity's sake if not anything else.

I've done the simulations in WinISD, and have used another online resource that has corroborated the measurements of WinISD.


Any way you work it your port is going to be very long. Don't even think of doing 2 ports since they would be impractically narrow. Any way you can fold it would be about as good as the next I think, though the least number of turns/angles in it the better.

Right, I have seen recommendations that a rectangular port should not have a ratio higher than 1:8 and have even seen 1:5 as the max. The design I have right now is one rectangular port: 16" x 4". The annoying thing is that it wraps almost all the way around the box, unless I want to incorporate 180 degree turns into the port design.

The benefit to using dual slotted ports (besides the aesthetics) would be that I would be able to locate the wire terminals conveniently in the back of the box without have to route them through the port space. Also, this would mean that the subwoofer would be able to be front-facing and centered.

I was thinking of decreasing the height of the box and going with a 15.5" x 2.25" port on each side. Eh?

emilimo701
06-19-2012, 02:54 PM
This is more of an experiment and learning experience than a box I see myself using long term.

RangerDangerV2
06-19-2012, 02:55 PM
you dont have to tune that low to play that low. Im tuned to about 37 and I can play down to 18 with authority.

---------- Post added at 02:55 PM ---------- Previous post was at 02:55 PM ----------


This is more of an experiment and learning experience than a box I see myself using long term.

if you are experimenting go with aeros or a removable port to get the desired response

chillin
06-19-2012, 02:58 PM
Why dont you use an aero port or sono tube and use elbows inside the box or have some of it outside the box?


Edit: Ranger beat me

emilimo701
06-19-2012, 03:50 PM
Why dont you use an aero port or sono tube and use elbows inside the box or have some of it outside the box?

Edit: Ranger beat me

I had considered that.

What is a good source of said sono tubes?

Kangaroux
06-19-2012, 03:55 PM
I'm tuning at 22 Hz based on the specs of the sub, and what I want to get out of the system. I can hear the 20 Hz tone in "Put On" by young jeezy and kanye, so i'm kind of using that as my reference

Is that the slowed version or the original? The original is at 28hz. It's hard to actually hear 20hz clearly, it takes a lot of cone area to pick up a note that low.

emilimo701
06-19-2012, 03:59 PM
Is that the slowed version or the original? The original is at 28hz. It's hard to actually hear 20hz clearly, it takes a lot of cone area to pick up a note that low.

Ah! You might be right actually. My bad. I'll have to go check again in audacity, I think it's listed on some website as well. But yeah 28 Hz sounds right...

chillin
06-19-2012, 04:07 PM
Home Depot

emilimo701
06-19-2012, 04:08 PM
2653360626533607

RangerDangerV2
06-19-2012, 04:09 PM
tuning that low with that much port can cause damge to subwoofers.... you dont need to tune that low to play that low.

Kangaroux
06-19-2012, 04:09 PM
2653360626533607

Do you know the cabin gain?

RangerDangerV2
06-19-2012, 04:11 PM
Do you know the cabin gain?

theres a way to simulate it in winisd...

emilimo701
06-19-2012, 04:15 PM
Tuned at 22 Hz it should be around flat with <1db rolloff at 28 Hz.

Tuned at 32 Hz I will gain about +4db centered at 38 Hz, albeit with a little bit of a peak, which may not be that bad and maybe desirable in some cases.

Maybe I will use an expandable aeroport to see what I like the best. I can't really find any 8"+ diameter aeroports on the web. I Might have to use 2 or 3 aeroports on smaller diameter?

What's the minimum port diameter I should use? According to this calculator (http://www.carstereo.com/help/Articles.cfm?id=31) it's about 64in^2, of course I probably won't be utilizing the full 30mm of excursion. I don't want to beat up on it.

Kangaroux
06-19-2012, 04:16 PM
theres a way to simulate it in winisd...

I know, I was the one that showed you guys that lol. But to simulate it you still need to know what it is.

emilimo701
06-19-2012, 04:17 PM
tuning that low with that much port can cause damge to subwoofers.... you dont need to tune that low to play that low.

damage how so?

I do intend to set subsonic filter properly. I remember in WinISD Pro there was a feature to determine maximum excursion plot vs frequency for a given subsonic filter. Unfortunately the Pro version doesn't like my new computer.

emilimo701
06-19-2012, 04:19 PM
Do you know the cabin gain?

Not yet. I do intend on measuring it. I have a thread going at the other car audio forum (I'm not sure if it's against forum rules to talk or give links to the others?). Basically the thread is about spectrum analysis which I have to start soon, as long as my Firebox analog-digital converter will run on Windows 7.

I have a Legacy wagon, which is a fairly common vehicle, maybe it has already been done by other people.

emilimo701
06-19-2012, 04:30 PM
Two of these (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=268-354) would do, but the company (http://www.psp-inc.com/products_6.html) doesn't seem to make angled extensions for them, so they'd have to protrude out of the box significantly at 6 feet, but it might help for prototyping

Kangaroux
06-19-2012, 04:48 PM
Not yet. I do intend on measuring it. I have a thread going at the other car audio forum (I'm not sure if it's against forum rules to talk or give links to the others?). Basically the thread is about spectrum analysis which I have to start soon, as long as my Firebox analog-digital converter will run on Windows 7.

I have a Legacy wagon, which is a fairly common vehicle, maybe it has already been done by other people.

Easiest way to figure out a rough idea of cabin gain is to measure from corner to corner of your vehicle and figure out the quarter wave of that.

emilimo701
06-19-2012, 06:02 PM
Easiest way to figure out a rough idea of cabin gain is to measure from corner to corner of your vehicle and figure out the quarter wave of that.

OK.

So what would the formula be from there?

emilimo701
06-19-2012, 06:16 PM
Original design. Calculated some of the dimensions wrong.

26533610

hispls
06-19-2012, 10:11 PM
I'm tuning at 22 Hz based on the specs of the sub, and what I want to get out of the system. I can hear the 20 Hz tone in "Put On" by young jeezy and kanye, so i'm kind of using that as my reference. Right now with the Axis in a sealed box, i'm not getting the output I want. It's about 16db down at 20Hz, and that simply is not cutting it. I want that 20Hz tone to slam with the same authority as the others. If I find out that such a lot tuning isn't necessary, I'll rebuild a new box tuned higher. But right now my goal for the enclosure is firm: 4-4.2 cubic feet tuned to 22Hz. I don't so much want high SPL in the 40-50 Hz range; rather, a flat response with a graceful rolloff. Maybe I won't end up liking it, but I want to at least give it a try, for curiosity's sake if not anything else.

I've done the simulations in WinISD, and have used another online resource that has corroborated the measurements of WinISD.



Right, I have seen recommendations that a rectangular port should not have a ratio higher than 1:8 and have even seen 1:5 as the max. The design I have right now is one rectangular port: 16" x 4". The annoying thing is that it wraps almost all the way around the box, unless I want to incorporate 180 degree turns into the port design.

The benefit to using dual slotted ports (besides the aesthetics) would be that I would be able to locate the wire terminals conveniently in the back of the box without have to route them through the port space. Also, this would mean that the subwoofer would be able to be front-facing and centered.

I was thinking of decreasing the height of the box and going with a 15.5" x 2.25" port on each side. Eh?

You're just plain not going to get a really fierce 20hz tone without a huge box or more cone area. I promise tuned @ 27 you'll be able to play it fine (Mine didn't totally unload until around 18hz).

I haven't had great results with multiple ports though and both would still be very long and now half as narrow


2653360626533607

I knew this woofer wanted to tune that low to model linear. Really I think you'd like the way the peaky looking one sounds though. With vehicle accoustics it should actually give you a good boost in output over a decent bandwidth.


tuning that low with that much port can cause damge to subwoofers...

Wrong. Tuned that low he won't hurt that sub with less than 1500W. Also the point of tuning that low is because that models linear.


Tuned at 22 Hz it should be around flat with <1db rolloff at 28 Hz.

Tuned at 32 Hz I will gain about +4db centered at 38 Hz, albeit with a little bit of a peak, which may not be that bad and maybe desirable in some cases.

Maybe I will use an expandable aeroport to see what I like the best. I can't really find any 8"+ diameter aeroports on the web. I Might have to use 2 or 3 aeroports on smaller diameter?

What's the minimum port diameter I should use? According to this calculator (http://www.carstereo.com/help/Articles.cfm?id=31) it's about 64in^2, of course I probably won't be utilizing the full 30mm of excursion. I don't want to beat up on it.

Of course physics is really against you trying to play that low regardless of where you tune a conventional woofer just isn't efficient at reproducing ultra low frequency.


damage how so?

I do intend to set subsonic filter properly. I remember in WinISD Pro there was a feature to determine maximum excursion plot vs frequency for a given subsonic filter. Unfortunately the Pro version doesn't like my new computer.

Even tuned in the high 20's you would have a hard time hurting that woofer with less than 1500W of power. I never ran subsonic filter when tuned that low.


OK.

So what would the formula be from there?

length from furthest point in trunk to furthest point on the dash corner to corner in feet. Divide that into 1150 fps, then divide that by 2. Gives your peak freq anyway.


Original design. Calculated some of the dimensions wrong.

26533610

Looks decent. What's wrong with that one?

Kangaroux
06-19-2012, 10:50 PM
length from furthest point in trunk to furthest point on the dash corner to corner in feet. Divide that into 1150 fps, then divide that by 2. Gives your peak freq anyway.

Don't you divide it by 4? I thought cabin peak was quarter wave not half wave

hispls
06-20-2012, 02:44 AM
Don't you divide it by 4? I thought cabin peak was quarter wave not half wave


Probably get a peak at 1/4 as well, but that would put you up at or over 100hz in most cars. You may be thinking "quarter wave" box (transmission line varient)

Kangaroux
06-20-2012, 09:34 AM
Probably get a peak at 1/4 as well, but that would put you up at or over 100hz in most cars. You may be thinking "quarter wave" box (transmission line varient)

"We can use these response graphs to enable us to control the design so we get the response curve we are shooting for. So in the 30 to 35 Hz range we usually find that this is the common range of quarter wave resonance in vehicles."

Pulled from Moble Enclosurs blog: Why is 30-35Hz used most commonly? (http://commontuning.blogspot.com/)

emilimo701
06-20-2012, 11:14 AM
Looks decent. What's wrong with that one?

I might just do that. All that would need to be done would be to cut a couple more pieces that need to be longer, and one needs to be shorter. I have extra board left anyway.

IIRC, it would have been ~4.1 cubic feet after displacement, tuned at just under 23 Hz. The way it's taped up now, I think the port would be an extra 3/4" wider all the way through, which would bring the tuning frequency up slightly. Per your advice, that wouldn't be a bad thing at all. Maybe I should even ditch the last 180-degree port turn?

emilimo701
06-20-2012, 11:25 AM
"We can use these response graphs to enable us to control the design so we get the response curve we are shooting for. So in the 30 to 35 Hz range we usually find that this is the common range of quarter wave resonance in vehicles."

Pulled from Moble Enclosurs blog: Why is 30-35Hz used most commonly? (http://commontuning.blogspot.com/)

Regarding the cabin gain curve, I intend on measuring that once I find my mic/Firebox, hopefully this weekend. When I do, I'll post the graphs.

It will be a frequency sweep tone (maybe I'll try pink noise too), with a plain old FFT done on the raw recorded file in MATLAB. Then possibly convolved with a Hanning window.

however I forgot to mention something very important:
This setup is being designed for open air. It will be used more sparingly than my other woofers (Polk SR 12", and Orion XTRPRO 10" for when I need more cargo space for stuff), most specifically it will be the subwoofer that I use for tailgating, with my hatch up, and all that goodness.

hispls
06-20-2012, 02:15 PM
"We can use these response graphs to enable us to control the design so we get the response curve we are shooting for. So in the 30 to 35 Hz range we usually find that this is the common range of quarter wave resonance in vehicles.
Pulled from Moble Enclosurs blog: Why is 30-35Hz used most commonly? (http://commontuning.blogspot.com/)
My bad, yeah, quarter would be @ 25-30. Still there's a bigger peak @ half wave. You may get a bit of a bump at 1/4 wave if you're tuned in the mid/low 20's


I might just do that. All that would need to be done would be to cut a couple more pieces that need to be longer, and one needs to be shorter. I have extra board left anyway.

IIRC, it would have been ~4.1 cubic feet after displacement, tuned at just under 23 Hz. The way it's taped up now, I think the port would be an extra 3/4" wider all the way through, which would bring the tuning frequency up slightly. Per your advice, that wouldn't be a bad thing at all. Maybe I should even ditch the last 180-degree port turn?

If you just do a 45 or roundover on that last corner the wall will act as an extension of the port anyway and I'd definitely rather not see the opening to the port too close to the woofer.

Moble Enclosurs
06-22-2012, 12:32 AM
Very true. 1/2 wave resonance is more efficient in car audio and is very important to understand as far as tuning goes. As mentioned before, you do not have to tune low to play low. Most of that is how the phase correlates to the response curve more than the gain. In fact, most of the response we encounter in such a small "room" is due to gain, so its importance is needed. Usually, there will be that very common heard of -6dB difference from 1/2 wave resonance to quarter and full wave efficiency....not exact, but this is a great point to mention for those interested in SPL mainly. (hint hint)

Calikid
06-22-2012, 01:00 AM
that;s probably too low