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JosefSchmidt
12-07-2004, 03:53 AM
I'm having trouble with a box I built - to keep from having to type it again heres an e-mail I wrote the manufacturer for advice:

dB Drive technical service -

I built an enclosure for my db Drive PL12D2 (12" 1500RMS, dual 2 ohm voice coils) subwoofer last weekend, and I adhered absolutely to the specs stated in your website. According to the tech specs, the ideal ported enclosure for the subwoofer is 2 cu ft, tuned at 35 Hz, with a 4" diameter port 13.12" long.

I built the box, 28.5 inches wide, 11.5 inches tall, and 16.5 inches deep exterior dimensions, with 3/4" MDF. The sub is mounted facing upward toward the top of the trunk, under the rear deck of my BMW 635CSi. The port is facing the rear of the vehicle, and instead of a round 4" port I used a 10.05x1.25 rectangular port, which has the identical cross sectional area of a 4" round port. The port is on the bottom of the box and is also made of 3/4" MDF. I emailed you on November 27th inquiring the displacement of the woofer so I could account for it in box design, but you never replied so I found some generic information for a 12" woofer that claimed a good displacement assumption was .13 cu ft. The total box volume is 2.29 cu ft, but once the assumed volume of the sub and the volume of the port is included, it is almost exactly 2 cu ft. I have double and triple checked my calculations.

The voice coils are wired in parallel so that the total impedance is 1 ohm, and it is connected to my Hifonics BX1000D mono 1-ohm stable amplifier.

Now heres the problem. Pardon the childish language, but it sounds like poo. It sounds fine at low volumes but when driven to any volume much beyond a normal middle-aged womans listening volume it produces a sound that sounds alot like its being overdriven. The gain on the amp is below 1/3, the subsonic filter is set at 35Hz, but the sound is still terrible. I compared it to my brothers system, which consists of a $100 Jensen 300W amplifier and a $50 Pioneer 100W RMS 10" subwoofer purchased nearly 6 years ago, in a 1 cubic foot sealed box, and mine made his sound awesome. Its somewhat upsetting to me that after all the money spent and effort put into my system I'm being outdone with $150 and a sealed box.

I thought something could be defective with the woofer, so I tried it in a different box. Another rectangular box with a slot port, it sounded wonderful. I then tried the above mentioned Pioneer 10" in the box I built, and it sounded great, infinitely better than the db Drive in the same box. So I've got two boxes and two woofers - The pioneer sounds great in both boxes but the db Drive sounds good in one and like dookie in the other.

I thought then it could be the port. The inside end of the port was somewhat close to the rear wall of the box, and due to the large mounting depth of the sub perhaps the port was too close to the subwoofer. I redid some calculations and I found that the specs on the db Drive site do not match any formulas I could find anywhere. According to the most widely accepted calculations I found, a 4" x 13.12" port would tune the box at 32Hz, not 35Hz. I don't think this should have such a drastic affect, though, so its most likely inconsequential.

So, I got a piece of MDF, some screws, and some silicone and blocked the port, got some PVC pipe and installed a 3" diameter 5" long port, which should tune the enclosure at 35Hz. I installed it facing up in the corner of the box, ensuring I had 3 inches between the end of the port and the subwoofer, and the enclosure wall. Much to my dismay, the sound is identical.

So far, I've talked to some friends and came up with the following ideas for the problem:
the sub is facing up, should be facing back
the sub doesn't have enough room in front of it (the rear deck is approximately 2-3" above the surround)
port noise resulting from A) the short 1.25" height of the rectangular port
B) the small 3" port

None of these problems would be too terribly difficult to correct, its just that I don't want to keep rebuilding my box until I get it right- I would much rather rebuild it only once and get it sounding decent.

Do you have anything to suggest? I'm getting kindof desperate here, I don't understand why the sub works in another box but not this one, I can come up with literally no logical explanation for this.

I apologize for the long e-mail, but I felt you would do best at analyzing the problem with a detailed description of the issue.

thanks

So do any of y'all have any ideas on this? I, along with everyone I've talked to, is completely stumped.

brandontw
12-07-2004, 04:57 PM
sorry... i fell asleep reading your post, and missed class... **** you!!

swimfreak26
12-07-2004, 09:54 PM
A) the short 1.25" height of the rectangular port
B) the small 3" port
This confuses me...

sumone
12-08-2004, 01:36 AM
run it free-air (not loud though) just to see if the sub by itself sounds like crap...make sure you're not sending a distorted signal to the sub...check HU & amp settings. sounding good at low volume but horrible at high volumes sounds like distortion to me.

Berry47
12-08-2004, 11:53 AM
The sub sounds great in other boxes and free air. There is only a problem in his enclosure.

BASS OUTLAW
12-08-2004, 12:09 PM
first off, subs facing upwards generally sounds bad, and it increase ratteling ...
then ur PVC port is to small, i got a 4" PVC pipe, tunned to 35hz in a 2 cuft, and i do have a port noise.


try facing the sub to the back, and port upwards...
and play a song that has a clean bass notes....

iceteebone
12-08-2004, 12:11 PM
sorry... i fell asleep reading your post, and missed class... **** you!!


me too. but i love his avatar. what the hell is that a gremlin?

BASS OUTLAW
12-08-2004, 12:18 PM
me too. but i love his avatar. what the hell is that a gremlin? a CAT !! :wacky:

iceteebone
12-08-2004, 12:24 PM
a CAT !! :wacky:


it looks like that gremlin gizmo from the gremlins movie. how easily i'm amussed by simple little **** :banghead:

JosefSchmidt
12-08-2004, 03:04 PM
actually I think its a wet cat with a persons mouth photoshopped onto it. I found it on the internet and thought it was the weirdest thing I'd ever seen.

I've done just about everything to verify the sub is fine. pberry47 has been helping me btw - so hes familiar with the situation.

We've taken it out, verified the wiring, tested it in free air, tested it in another box, tested another sub in the same box, added wood inside the box to change the volume, tuned the box to 4 different frequencies - the only time the problem arises is with the db Drive sub in this box.

kjwiehoff
12-08-2004, 03:11 PM
build a sealed box and be done with it. but maybe thats just me...

req
12-08-2004, 04:11 PM
pay mr jmac to build a box design for you. then i can almost assure you it will be right.

paikiah
12-08-2004, 11:05 PM
pay mr jmac to build a box design for you. then i can almost assure you it will be right.
i was about to say the same thing.

Spkrman
12-09-2004, 12:06 PM
I'd say it has something to do with the super skinny port - that definitely doesn't help things.

You need a different box ;) 2 4" precision ports would also do you very good: clicky and search for precision ports (http://www.kqzyfj.com/click-1608685-1457534)

Also, put it more towards the rear of the car... that 99% of the time makes a big difference right there. I'm not sure who started the box should be between your wheel wells, but whoever it was... deserves to be stuck between the wheel wells of a caddy and carted off to a very remote place....

Berry47
12-09-2004, 03:05 PM
first off, subs facing upwards generally sounds bad, and it increase ratteling ...
then ur PVC port is to small, i got a 4" PVC pipe, tunned to 35hz in a 2 cuft, and i do have a port noise.


try facing the sub to the back, and port upwards...
and play a song that has a clean bass notes....

have you ever heard of a crx style box....

also, being the one that helped him build the enclosure it is more then likely the fact that he designed the box slightly to close to the rear deck and by firing into the rear deck, is not recieving the air space it needs in order to operate. The size of the port has nothing to do with the problem. his original port had the same cross sectional area as a 4 inch round port and was made the same lengh. In order to get the proper air space, my friend will most likely design a new enclosure with the sub facing rearward and the port to the side. This is much like a setup I used to have in a prefab box when i started car audio 3 years ago.

Jmac could build a kick *** enclosure, but so can we. The design and construction was great. the enclosure would have looked great in his car, and most of his equipment was bought under my guidence. Josef now has a great system, but the aspects of his car we did not double check are leadeing to a poopy sounding sub.

holla

DFW40
12-09-2004, 04:45 PM
If the sub is facing the metal rear deck and is 3 inches away there is a good chance he might be getting some cancellation with the sound bouncing back towards the sub then running into the sound coming out of the port etc. I would seal up the port and try it as a sealed enclosure and see if he has the same problem. If so then I'd build a box with the sub facing the rear and the port facing the rear as well. BMW's trap bass in the first place and might not be getting through as well.

sumone
12-10-2004, 01:16 AM
does the sub sound the same with the box out of the car?

Berry47
12-10-2004, 01:08 PM
If the sub is facing the metal rear deck and is 3 inches away there is a good chance he might be getting some cancellation with the sound bouncing back towards the sub then running into the sound coming out of the port etc. I would seal up the port and try it as a sealed enclosure and see if he has the same problem. If so then I'd build a box with the sub facing the rear and the port facing the rear as well. BMW's trap bass in the first place and might not be getting through as well.

This is what is so strange....

It only has these charateristics in that one box. In one of my boxes it sounded great. In a sealed box it sounded great. It is most likely some wierd relation between the height above, the speaker parameters, and the ported box. I think we will be building another box this weekend.

JosefSchmidt
12-10-2004, 08:04 PM
I thought I'd update you guys on the situation - I had some people recommend polyfil, and even though I didn't really think it would solve the problem, I figured for $2 and 5 minutes it beats the hell out of building a new box.

Just as I thought, the polyfil did nothing. So as Parker said - I'll be building a new box tomorrow, after I do the brakes on my mothers car.

BTW Parker if you're not too busy tomorrow I could cut you in on some of the profits on the brake job if you wanna go up there w/ me. Nevermind answering on the forum though, cause by the time you read this I will probably already have spoken with you.

JosefSchmidt
12-13-2004, 01:51 AM
ok - I built a new box. THis time the sub is facing the rear of the car, the 4" port is facing the side, it is exactly 2 cubes including the sub and the port, it is filled with polyfil, and it sounds...

SUPERB!

Thanks for all the help guys - I guess it really was just the sub facing up and 3 inches from a metal barrier.

Now I've got a nasty rattle somewhere in the rear deck to tend to.