4th order bandpass, wheel well design :) (design inside)

TWOJZ

Disabled Account
2007-09-02 12:57 am
going to attempt to make something like this.

its not drawn to scale, but it was rather difficult explaining to people what I wanted to make without having a pic.

so, there it is!

going to have a semi circle perspex window in the top, 4th order bandpass, using the spare tyre well, and the area available above it.

vented through the rear deck

basically no trunk space used!

anyone see any massive problems with the general design? lol, ofcouse, nothing is to scale, so volumes arent correct, that will all be worked out once I start building, or atleast after I measure the car :D

[IMGDEAD]http://img222.imageshack.us/img222/9062/wheelwelltoprg7.jpg[/IMGDEAD]
 
Looks like one I built, but mine wasn't in the wheel well. I actually built it against the rear seat but still in the trunk. It vented into the cabin and was VERY loud. I just didn't build the sealed side large enough and the response dropped off quickly under 40hz. The woofer I used was an early ImageDynamics IDQ 12. It was cool because there was absolutely no loss into the trunk and it didn't move the trunk lid at all. I say go for it, you'll definately need to do a lot of tuning but surely it will be fun. What size sub do you plan on using, an 8 maybe?:)
 
Your port is way too narrow and long for proper front chamber tuning, it would only work as a rear port or as part of a conventional reflex enclosure. In practice you need a big front chamber (like 20 liter for a 12 inch driver) and a very short front port (a few cm long) with large surface (1/3 driver SD or better).

Consider a 6th order bandpass with a low Q rear chamber tuned low (36Hz), a high Q front chamber tuned high (95Hz) and a tilted downwards (6 to 12dB/oct) frequency response (that integrates very well with cabin gain and front speakers). While the proposed rear vent provides little improvement in output, it reduces cone excursion (and the resulting distortion) and improves power handling. As a result, efficient drivers (low Qts like 0.3) with moderate Xmax (+/-5mm) and clean midbass output are suitable for this arrangement.

Leading the ports to the cabin produces the best results, particularly for the front port, but since it must be short, it becomes a difficult chamber layout task.

Alternatively you can consider a tapped horn (take a look at the loudspeakers forum).
 

TWOJZ

Disabled Account
2007-09-02 12:57 am
^^

the proposed design has a 60 litre sealed chamber, 15litre ported chamber, tuned to 50Hz, with a 6inch diameter port, which needs to be 53 inches long.

the design was never drawn to scale, however, the area of the port is, but not the length.

sorry about the big graphs...

you really should all buy bigger monitors :p


[IMGDEAD]http://img217.imageshack.us/img217/9854/responseqp3.jpg[/IMGDEAD]

[IMGDEAD]http://img98.imageshack.us/img98/7734/powersg6.jpg[/IMGDEAD]

[IMGDEAD]http://img215.imageshack.us/img215/107/excursionvk0.jpg[/IMGDEAD]

[IMGDEAD]http://img217.imageshack.us/img217/1848/portvelocityuv5.jpg[/IMGDEAD]
 
TWOJZ said:
going to attempt to make something like this.

its not drawn to scale, but it was rather difficult explaining to people what I wanted to make without having a pic.

so, there it is!

going to have a semi circle perspex window in the top, 4th order bandpass, using the spare tyre well, and the area available above it.

vented through the rear deck

basically no trunk space used!

anyone see any massive problems with the general design? lol, ofcouse, nothing is to scale, so volumes arent correct, that will all be worked out once I start building, or atleast after I measure the car :D

[IMGDEAD]http://img222.imageshack.us/img222/9062/wheelwelltoprg7.jpg[/IMGDEAD]

Yes, I built one of these - almost identical to this, about fifteen years ago. It was louder than your average twin 8", but I think it was mainly attributed to the lack of energy spent rattling the trunk lid. Since it was so long ago...I don't remember what it sounded like. After all, it was one of dozens of "custom installs" our shop did at the time - every year. Can't keep them all straight...
 

TWOJZ

Disabled Account
2007-09-02 12:57 am
ok, the other issue I have, is that I want to put a round port through the rear deck, but I want to have a rectangle port coming out of the box...

is there any real issues with having a round port coming out the side of a rectangle port, assuming they are both the same crossectional area?

edit: for those of you who have no imagination...

[IMGDEAD]http://img89.imageshack.us/img89/5255/wheelwelltopdonebg2.jpg[/IMGDEAD]
 
In a bandpass box you are likely to get better performance with a driver designed with more common sense (I mean no donut surround, no bulky cosmetic motor not to be seen by anybody, no ultra heavy cone and voice coil, etc...)


With this approach you are likely to get 2 cavities tuned to 2 different frequencies, and as a result, very very low Q. Bends in a port also hurt efficiency badly because the moving air mass has to change direction and some energy is lost in the process.
 

TWOJZ

Disabled Account
2007-09-02 12:57 am
Eva said:
In a bandpass box you are likely to get better performance with a driver designed with more common sense (I mean no donut surround, no bulky cosmetic motor not to be seen by anybody, no ultra heavy cone and voice coil, etc...)


umm... donut surround?

what exactly are you trying to say? lol

that it wont get loud?
 
TWOJZ said:



not really... although mounting it at an angle may reduce the height needed for mounting the basket, the basket will then stick up higher... if that makes sense? :)

http://www.mtx.com/caraudio/products/flash/subsT9500_slideshow.cfm

Yeah, mounting it at an angle would help a couple of things including height, which you'll need to try and save if you want it as low as possible in the well.


TWOJZ said:
ok, the other issue I have, is that I want to put a round port through the rear deck, but I want to have a rectangle port coming out of the box...

is there any real issues with having a round port coming out the side of a rectangle port, assuming they are both the same crossectional area?

edit: for those of you who have no imagination...

[IMGDEAD]http://img89.imageshack.us/img89/5255/wheelwelltopdonebg2.jpg[/IMGDEAD]

Eva was partially correct in that if you use a design exactly like the picture (we know its not to scale) the transition from the square port to the round tube will cause issues.... BUT if you are creative and can negate turbulence by a creatively designed port with smooth transistions, you can increase the lowpass rolloff and keep the efficiency.


Eva said:
In a bandpass box you are likely to get better performance with a driver designed with more common sense (I mean no donut surround, no bulky cosmetic motor not to be seen by anybody, no ultra heavy cone and voice coil, etc...)


With this approach you are likely to get 2 cavities tuned to 2 different frequencies, and as a result, very very low Q. Bends in a port also hurt efficiency badly because the moving air mass has to change direction and some energy is lost in the process.

Whatever.. Mtx makes great speakers and amplifiers. They are some of the most technologically advanced woofers out there. Sure they make some low line models that are marketed for penny pinchers, but the 9500 series is a very well designed woofer.


TWOJZ said:



umm... donut surround?

what exactly are you trying to say? lol

that it wont get loud?

He's probably trying to hate on the large surround because some cheap companies have woofers with huge surrounds. What he's failing to mention is that the cheapo companies try to emulate designs of better companies to sell their flea market stuff. Mtx just happens to make nice woofers with good xmax. The large surround just happens to help achieve this.


Eva said:
Sorry, it's just more wise to quit.

Negative much??


pinkmouse said:


Why not? It's good advice.

TWOJZ is doing what many people have given up on.. some because some think they've learned everything there is to know.. and others because they've lost the energy and motivation to try. He's experimenting and trying to be creative. Why not be positive and give some helpful positive suggestions. Some people here brag about using cheapo woofers to get awesome results. Why mock an excellent woofer that has the capability of making excellent spl and sq if used in a properly designed system. Who knows? He might hit the sweet spot his car and speaker like with that box and impress a lot of people. I wish I still had the spare time and motivation to play around with my system like that.






(I love Mtx. I'll be first in line when they come out with their shallow subs. I just hope its soon!!! :bawling: )
 
The first example that came handy...
 

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