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Replacing a HT subwoofer with a car sub. - Page 4

post #46 of 89
Parts Express sends some speaker caulk along with woofer orders btw.
post #47 of 89
Thread Starter 
Here are the final deminsions of the box: 17.25 x 17.25 x 17.5 (so maybe I dont have very good wood working skills ) with 3/4 inch MDF. The amp is not in the same chamber as the driver. Also, I have around 2 -3 inchs of insulation around on 5 of the 6 walls.

Here is the port The longest I could get it was 11 inches, which is what it is at now.

I used the speaker caulk that came from parts express around the sub and I believe I have a good seal because I cant feel any air coming out of it. The box is completely sealed.

Actually now that I look at it, I didnt use caulking around the port. I will add caulk tonight and test it tomorrow (everyone is asleep right now, so I dont think they would appreciate the floor shaking)
post #48 of 89
If you really need to, PVC piping makes excellent ports, it's sturdy, cheap and generally easy to cut.
post #49 of 89
But not easy to cut in a nice presentable fashion

Good luck with that sub. I think you're in good hands with gerG.
Btw, are those the internal dimensions or external?
post #50 of 89
Another question: what do you have the crossover set at? A low setting and a high level setting would make it come in rather abruptly.

Good job sealing the port, and being considerate of others. Since cabinet pressures peak at resonance, leaks around the port will make all sorts of noise.

Try your frequency test again tomorrow (set the x-over above 100 hz to get it out of the picture). As you decrease the signal frequency the cone motion will increase, but at some point it will drop off to a minimum, then go waaay up at frequencies below that. That point of minimum motion will be the cabinet tuning frequency, and it will give us a hint as to how long the port needs to be, and where to set the filter for best performance. That point of lowest motion will also have the highest air velocities in the port, so noise problems should peak there.

These are predictions for the latest info. I will recheck my numbers tomorrow just to be sure (don't trust myself this late). These should be output, excursion, and port velocity. You can see where the excursion limit is exceeded where the color changes from red to, uh, darker red. Sorry about that.

post #51 of 89
Thread Starter 
Quote:
Originally Posted by ooheadsoo
Good luck with that sub. I think you're in good hands with gerG.
Btw, are those the internal dimensions or external?
Those are external dimension. I feel safe in gerG's hands

Thats some pretty cool software you got there gerG.....
post #52 of 89
Thread Starter 
After sealing the port, the port noise is noticable around 34 and the cone starts to go nuts around 27.
post #53 of 89
Ah, much better. At least the numbers make sense now.

Thanks for the vote of confidence guys. I figure that I have made most of the screw-ups that can be discovered when building these things, so I try to steer people out of the various traps.

The software is pretty capable for the money. I would love to have LEAP, but it is a lot more bucks. BassBox Pro has a lot more features than I use. A less expensive alternative is WinSpeakers (or MacSpeakers) available through Trueaudio.com. I used it for years, with very reliable results. I am sure that there are more out there, but those are the ones that I have experience with.

I will fiddle with the tuning point and the rumble filter values to tweak out the performance (more to be found).

Oh, one more caution, make sure that the "Loudness" control on your receiver is switched OFF. It may also go by the name of bass boost or DBB. Whatever it is called it is a terrible thing for subwoofers. While you are checking make sure the tone control for bass is set flat.


gerG
post #54 of 89
I added the filter (assumed Q = 1.0 and fc = 19 hz). I tried changing the filter settings, but didn't really like the results. I had better luck tuning the cabinet down to the filter to take advantage of the low cut and extend the LF response. 3 traces are 38 hz (current), 30 hz, and 25 hz.



I would offer the following suggestions:

Switch to a 4" inner diameter port. I think that your remaining port noise is due to leakage through the telescoping port, so I would use a solid ABS plastic port.

Set up with a long straight port connected to the baffle, with a long 90 connected to the rearward end. You can cut various lengths for the vertical piece to change the tuning as you like.

Go fro the 25 hz tuning. This will require a total port length of 25.5 inches. 30 hz requires 15.5 inches. This is for a 4" id port. To use a different id you have to hold the ratio of tube length to port area constant.

Keep the subsonic filter where it is for now.


gerG
post #55 of 89
Thread Starter 
Quote:
Originally Posted by gerG
Set up with a long straight port connected to the baffle, with a long 90 connected to the rearward end.

Hm...Im not sure if I understand what you mean. Can you clarify please? Basically just a tube with a 90 degree turn on the end?


I will be ordering the tube as soon as I hear back from parts express.
post #56 of 89

The picture isn't of a person btw.

I think he means like this, you're supposed to do it if the box is too short.

post #57 of 89
Yeah, basically. To get the length you will probably need 3 pieces: the straight that connects to the baffle, the 90, and an extension piece. Most hardware stores have a cutoff saw, and they will do nice square cuts at pretty accurate lengths.


gerG
post #58 of 89
Thread Starter 
Well I just got a response from parts express:

"The outer flare is wider than the inner flare on this port. The outer flare is 7-1/4."

7 and 1/4!! That wont be able to fit in my cabinate Should I just order this tube and connect pvc pipe to it?

Or do you think I might be able to use the inner flare to mount it?
post #59 of 89
Lets consider the port that you have first. PE lists the diameter as 4 5/16 (ID, I assume). ABS pipe has an ID of 4", and an OD of 4.5" (a guess at the moment). The rear sleeve of your port has to fit over the the front section. I am guessing around a 1/16" wall, so 4 7/16"? If you are lucky, the ABS pipe will fit inside the sleeve and you can use your existing port. If not, the PE port may be an option, although it would be good to have all of the dimensions. I would avoid the flared port just now.

What is the ID of the hole through the baffle?


gerG
post #60 of 89
Thread Starter 
Good idea gerG, I didnt think of that.

Is ABS pipe the same thing as PVC? If not, where can I find ABS pipe?

The diameter of the hole that goes through the wood is roughly 4-3/4 give or take a 1/16th of inch due to my wonderful cutting skills.

Ill take the port into Lowe's tomorrow and see if any of the PVC (or ABS?) pipe will fit nicely into it.
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