I have a crazy thought, why not try it since you have all the components?
Hypothetical situations are meant to be tested.
Good luck,
Dirk
Hypothetical situations are meant to be tested.
Good luck,
Dirk
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fEarful Cabinet Question...
- Thread starter yodedude2
- Start date
thank you. yes. good advice. i will. i'm trying to think about how to cut the port shelf top in half after it's been installed and glued into place. i do have a jigsaw...i lack only skills, knowledge, other tools, and disposable funds.
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Passinwind
I know nothing.
- Dec 3, 2003
- 23,049
- 45,913
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- Designer/Toaster Tech @ Passinwind Electronics
Personally, I wouldn't try to cut all the way back to the side walls. If you left an inch or two on each side you could add foam spacers under the leftover wood pretty easily and more than likely still have a big enough port cross section for the driver you're using. That'll complicate tuning a little, but less so if you use my method of intentionallly cutting the shelf short, than adding trial pieces to extend and fine tune. Duct tape works OK for that phase IME.
You asked for help understanding the shelf dimensioning aspects. It's not as simple as tuning a beer bottle's pitch, where a bigger volume = a lower pitch. It's more like tuning springs against each other for a desired null point in one spring, where the other one does all the moving. I found a decent layman's explanation of this on a home theater oriented site yesterday, but didn't get a chance to fully vet the article yet. I try to be picky about what I cite, let me see what I can scare up.
thanks, that helps. and yes, cutting near the side walls is the real challenge. i like your suggestion better! also, the 'spring' tuning helps me understand. a more technical explanation would be lost on me at this point, i fear. thanks again for the advice and for revisiting the thread!
Not really the enclosure is a certain volume and the port is a only so wide, deep and high.
It's a 3012HO it's looking for the same old 1.8 to 2.6 cubic feet of volume that almost any 12" live sound driver is looking for.
Likewise it's just a plain old ported, reflex cabinet. You calculate the volume and calculate the port and your all done
I don't know the tuning of the original fearful cabinet. Assume it should be around 55hz
Fs or resonant frequency of the HO is 52hz. Meaning like any reflex alighnments it's going to tune 7 to 12 hz above or below that.
In your case and most cases a 3rd or 4th order alighnment is going to tune at Fs or slightly above it.
So you can tune to 50 to 60hz and be fine.
Tune to 55hz like a zillion other 12" reflex cabinets
Calculate the volume and calculate your port with a port calculator.
Seems the port was shortened, just add a little length to what's there.
It's just a basic shelf port. Definitely not rocket science or accurate with tuning lengths. Shelf port shares 3 walls. End factor corrections will be wrong with almost any calculator.
In plain English the length will need to be slightly shorter than what's calculated.
Most calculate to long.
If you shortened the shelf port. Add length to it. It's a shelf port. Should be a single piece of wood and your done.
People wanna freak out over a box.
A 3012HO can work in anywhere from 1.6 to 3 cubic feet.
2 cubic feet is pretty normal trade-off for a live sound 12". Not to small and bloomy or not to large for power handling.
Probably over 20 or more drivers that would drop right in to a fearful 12" box and be fine. Assuming it's designed to anything close to what makes sense to pretty much standard pro audio 12' drivers.
It's a 3012HO it's looking for the same old 1.8 to 2.6 cubic feet of volume that almost any 12" live sound driver is looking for.
Likewise it's just a plain old ported, reflex cabinet. You calculate the volume and calculate the port and your all done
I don't know the tuning of the original fearful cabinet. Assume it should be around 55hz
Fs or resonant frequency of the HO is 52hz. Meaning like any reflex alighnments it's going to tune 7 to 12 hz above or below that.
In your case and most cases a 3rd or 4th order alighnment is going to tune at Fs or slightly above it.
So you can tune to 50 to 60hz and be fine.
Tune to 55hz like a zillion other 12" reflex cabinets
Calculate the volume and calculate your port with a port calculator.
Seems the port was shortened, just add a little length to what's there.
It's just a basic shelf port. Definitely not rocket science or accurate with tuning lengths. Shelf port shares 3 walls. End factor corrections will be wrong with almost any calculator.
In plain English the length will need to be slightly shorter than what's calculated.
Most calculate to long.
If you shortened the shelf port. Add length to it. It's a shelf port. Should be a single piece of wood and your done.
People wanna freak out over a box.
A 3012HO can work in anywhere from 1.6 to 3 cubic feet.
2 cubic feet is pretty normal trade-off for a live sound 12". Not to small and bloomy or not to large for power handling.
Probably over 20 or more drivers that would drop right in to a fearful 12" box and be fine. Assuming it's designed to anything close to what makes sense to pretty much standard pro audio 12' drivers.
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Reflex is very simple. With positive pressure coming out the front or leaving the cone, the opposite negative pressure in the box.
Box is certain volume. When it fills up with pressure. Cone movement gets restricted. And the ports fill up with same negative pressure.
On the next half cycle the cone has negative pressure going out the box or leaving the cone. Positive pressure now on the inside.
The negative pressure that was in the port from the beginning. Gets pushed out from the positive pressure now coming in.
Hence why port pressure is in phase. With what's coming out. Negative pressure was stored in the port. Negative pressure is leaving the cone. And the opposite positive pressure coming in pushes it out.
No springs or anything fancy. Box is certain volume. Port is certain volume and it's just pushing out pressure that stayed there from the previous cycle.
Box is certain volume. When it fills up with pressure. Cone movement gets restricted. And the ports fill up with same negative pressure.
On the next half cycle the cone has negative pressure going out the box or leaving the cone. Positive pressure now on the inside.
The negative pressure that was in the port from the beginning. Gets pushed out from the positive pressure now coming in.
Hence why port pressure is in phase. With what's coming out. Negative pressure was stored in the port. Negative pressure is leaving the cone. And the opposite positive pressure coming in pushes it out.
No springs or anything fancy. Box is certain volume. Port is certain volume and it's just pushing out pressure that stayed there from the previous cycle.
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the 12sub is tuned to ~ 46 Hz. Just making sure we're all on the same page.
edit: i was using a pair of them as p.a. subs. they were great for that! but i am out of the p.a. business for some time now, and i won't be going back. they only were used for about 10 gigs as it was. one of them got used more often hooked up to the band leader's p.a. for smaller club gigs. it saw very light duty there.
Then again I understand the spring description or often called a brake as well.
At Fb or port tuning , cone movement is restricted or moves less when the port starts to take over. Cone movement is restricted from reaching equal pressure from the stored pressure already in the box and ports. And the opposite pressure being applied to push out what's there.
This is easily calculated by pretty normal reflex equations. And is all pressure related depending on volume of the box and size and volume of the ports.
Hence usually the box volume is preset. But to change Fb or tuning usually the ports are sized accordingly.
The restricted cone movement can be used as a advantage to improve power handling.
Hence why a 15" or 18" might have same frequency response in 3 cubic feet.
But say the 18" has a Fs of 25hz compared to the Fs of a 15" at 45hz
The 18" allows a lower tuning at 25hz where cone restricting of the " Spring" or Reflex " Brake" reduces cone movement at the frequency response of most sound systems. So not only does the frequency response of the system end around 20hz but the ported or reflex enclosure also restricts cone travel at the end of the system response.
With the 15" tuned high around 45hz. Once you go below port frequency. The system unloads and you have extreme cone movement. The port is not active. It's literally a big hole or leakage. So you have very large violent cone movement.
Hence if you have a ported system set low to the end of the frequency response around 20 to 25hz it's impossible to get violent unloading of the woofer. There is simply no signal or frequency response to make it do that.
That's usually where the " spring" or
" brake" terminology comes in. Tuning can help restrict cone movement
At Fb or port tuning , cone movement is restricted or moves less when the port starts to take over. Cone movement is restricted from reaching equal pressure from the stored pressure already in the box and ports. And the opposite pressure being applied to push out what's there.
This is easily calculated by pretty normal reflex equations. And is all pressure related depending on volume of the box and size and volume of the ports.
Hence usually the box volume is preset. But to change Fb or tuning usually the ports are sized accordingly.
The restricted cone movement can be used as a advantage to improve power handling.
Hence why a 15" or 18" might have same frequency response in 3 cubic feet.
But say the 18" has a Fs of 25hz compared to the Fs of a 15" at 45hz
The 18" allows a lower tuning at 25hz where cone restricting of the " Spring" or Reflex " Brake" reduces cone movement at the frequency response of most sound systems. So not only does the frequency response of the system end around 20hz but the ported or reflex enclosure also restricts cone travel at the end of the system response.
With the 15" tuned high around 45hz. Once you go below port frequency. The system unloads and you have extreme cone movement. The port is not active. It's literally a big hole or leakage. So you have very large violent cone movement.
Hence if you have a ported system set low to the end of the frequency response around 20 to 25hz it's impossible to get violent unloading of the woofer. There is simply no signal or frequency response to make it do that.
That's usually where the " spring" or
" brake" terminology comes in. Tuning can help restrict cone movement
Okay, port tuning can be summarized much more simply. The main two variables are cross-sectional area and length. Forget about port volume.
To lower tuning frequency, do either or both: (1)lengthen the port, (2) decrease the cross-sectional area.
To raise the port tuning: (1) decrease the port length, (2) increase the cross-sectional area.
The concept here is the same as a trombone or a slide whistle: a long skinny tube will have a lower tuning frequency than a short fat one.
The only time port volume comes into play, that I'm aware of anyway, is when you calculate the box volume for the driver. Do not include the volume of the port when you do that.
To lower tuning frequency, do either or both: (1)lengthen the port, (2) decrease the cross-sectional area.
To raise the port tuning: (1) decrease the port length, (2) increase the cross-sectional area.
The concept here is the same as a trombone or a slide whistle: a long skinny tube will have a lower tuning frequency than a short fat one.
The only time port volume comes into play, that I'm aware of anyway, is when you calculate the box volume for the driver. Do not include the volume of the port when you do that.
it is not possible to increase the port cross-sectional area without destroying the cab, so shortening the port length it is!
Rightio then.
You have a jigsaw.
A really sharp little chisel would be helpful, hammer to drive it.
How about a power drill?
You are looking to remove a strip from the back edge of the port. It doesn't have to be all in one tidy cut but it would be best if you can insert the jigsaw near the middle and cut straight across to each side, as far as it goes. It might not like coming up to the divider, but chisel or drill will.
Then you bodgy out to the back leaving you a T on the port divider. Whack off the sides of the T and please yourself if you take out the remains of the divider and what's still hanging off the sides of the cab with your chisel.
It doesn't have to be perfect. I don't think port tuning is an exact science. BUT, if you wanna be perfect, your best bet is to get or borrow an oscillating tool. You can get a decent one for less than $100, and they are super handy.
If you need to tweak it down the road, than you can take off more of the shelf, or, if you overshoot, plug part of the port as you were considering before.
If you need to tweak it down the road, than you can take off more of the shelf, or, if you overshoot, plug part of the port as you were considering before.
i do have a power drill and a hole saw around here somewhere...this stuff is rather good plywood so this will be tough, but i am sure i can pull it off somehow. since it is all inside, cosmetics are not a concern. i would like to make it reversible...gonna stick with mr. wind's plan for now.
Mr Wind 's plan is what I had in mind. If you make a neat job of cutting across then putting back a sliver should be easy.
Maybe build one of these... oh wait.
No longer available - MOVING SALE Feeler fEarful 12sub x2, nEarful headcase
No longer available - MOVING SALE Feeler fEarful 12sub x2, nEarful headcase
wanna buy a cab? heh heh heh but if anyone is interested, i do have the 3012lf drivers and their crossovers up for sale still.
heck, if anyone wants to buy the assembled sub, i will make a deal. do it now before i hack into it and make a full-range cab. it costs about $125. to ship...which killed more than one previous sale.
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easy is relative of course. it will be a challenge for me, but i think i can pull this off. i plan to start with 4" of port shelf behind the front baffle and go from there.
Seems the fearful sub is tuned to 45hz
3012HO has Fs of 52 hz
For the most part the standard tuning can work. Or if you shortened the shelf tuning will raise.
45hz would be fine for me. I tend to tune as low as possible. Usually at Fs of the driver.
7 hz below Fs is feasible
Most would tune higher. But 45hz is fine not only for the driver. But for the application for bass guitar.
I should probably read the thread better but was getting confused. Some mentioned reducing port area to yeild a lower tuning, some mentioned shortened shelf to raise tuning. All in all 45hz is fine.
The response graph could have a slight
" shelf" if modeled and most would freak out and say Raise the tune....Oh my God
In reality it's not bad. The real concern would be if the tune was way way to high or the box was to small.
In this case box volume and tuning would be fine. Being 5 to 7 hz above or below Fs
And having decent box volume. Means a happy 3012HO
A really bad box can have impact. In reality the driver makes the sound and is what it is. The 3012HO is a very good driver with higher sensitivity and better mid/ high clarity than the LF
Id assume you'll be happy with the box and tuning anywhere from stock 45hz to 55hz. And I'd rather tune lower anyways
You can confirm box tuning or Fb with the " rice" test. I actually just use salt it's better.
At Fb there is very minimal cone movement. You can use a phone app tone generator to slower sweep from 65ish hz on down. With enough signal to get the salt to bounce on the cone as you start to reach Fb the salt will bounce less then hardly at all at Fb.
You'll still get a 5 to 7hz gap to where the salt stops bouncing then starts again.
I slightly rest my finger on the cone edge and feel it when the salt starts to have very little movement. Doing 1hz steps on your test tone. The 5 to 7hz gap you see from minimal bouncing can be narrowed down to 1hz by actually feeling with the tip of your finger where the minimal movement actually is.
And Fb can be confirmed to realatively high accuracy by watching the salt and feeling cone movement
At Fb there is very minimal cone movement. You can use a phone app tone generator to slower sweep from 65ish hz on down. With enough signal to get the salt to bounce on the cone as you start to reach Fb the salt will bounce less then hardly at all at Fb.
You'll still get a 5 to 7hz gap to where the salt stops bouncing then starts again.
I slightly rest my finger on the cone edge and feel it when the salt starts to have very little movement. Doing 1hz steps on your test tone. The 5 to 7hz gap you see from minimal bouncing can be narrowed down to 1hz by actually feeling with the tip of your finger where the minimal movement actually is.
And Fb can be confirmed to realatively high accuracy by watching the salt and feeling cone movement
thank you for the input. perhaps i should try it 'as is' first before modding? the response graph showed a ~6db dip form 80-400Hz or so, but there was a better low-end extension before rolling away.
obtw i tune to d standard.
obtw i tune to d standard.
