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prefab ported box


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imupabove 
Copper - Posts: 369
Copper spacespace
Joined: March 14, 2009
Location: California, United States
Posted: September 01, 2009 at 3:51 AM / IP Logged  
what will it sound like if the box is too big?
wolfox 
Member - Posts: 49
Member spacespace
Joined: June 16, 2009
Location: Florida, United States
Posted: September 01, 2009 at 5:19 AM / IP Logged  
imupabove wrote:
what will it sound like if the box is too big?
Low frequency power handling may suffer, but the bass response is tighter and "dryer". You may hear the system get "louder" in a narrow frequency range as a result too. (BOOMY peaks/resonance rather than having flat, linear response.) A good read on the subject is here:
The DIY Subwoofer page - pay attention to section 1.05!
In short, a quote:
1.05 - What happens if the box is too large? Typically the low frequency extension of the system improves a little, at the expense of powerhandling. The bass will also sound tighter and "drier", which might not suit your listening tastes. In the case of vented systems, a too-large box may introduce a response peak around the resonance frequency of the system.
There is a megaton of great info on that site that applies to mobile and home theater systems.
Life is too short to build slow computers or weak audio!
imupabove 
Copper - Posts: 369
Copper spacespace
Joined: March 14, 2009
Location: California, United States
Posted: September 01, 2009 at 12:24 PM / IP Logged  
i got the dimensions:
Vent opening 33 square inches
Vent length 16 inches long
thank you.
aznboi3644 
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Gold spaceThis member consistently provides reliable informationspace
Joined: May 01, 2006
Location: United States
Posted: September 01, 2009 at 7:27 PM / IP Logged  
Type Rs have no problem with going below tuning.
I used to run a single Type R 12 in an 8 cu ft transmission line enclosure. Played 10Hz at 700 watts no problem.
For R's if the enclosure is too small it will sound like a sealed enclosure...low end starts rolling off with a hollow low end.
Me I would do atleast 2.5 cu ft tuned to 30-35Hz.
Custom Enclosure Design
imupabove 
Copper - Posts: 369
Copper spacespace
Joined: March 14, 2009
Location: California, United States
Posted: September 01, 2009 at 8:29 PM / IP Logged  
aznboi3644 wrote:
Type Rs have no problem with going below tuning.
I used to run a single Type R 12 in an 8 cu ft transmission line enclosure. Played 10Hz at 700 watts no problem.
For R's if the enclosure is too small it will sound like a sealed enclosure...low end starts rolling off with a hollow low end.
Me I would do atleast 2.5 cu ft tuned to 30-35Hz.
what do you think about the box. on the website its 2.5 cu. ft. but not sure what its tuned at. i got the port dimensions, its on the last reply.
wolfox 
Member - Posts: 49
Member spacespace
Joined: June 16, 2009
Location: Florida, United States
Posted: September 01, 2009 at 10:36 PM / IP Logged  
As close as I can model that subwoofer enclosure from listed dimensions and an educated guess from the port dimensions you listed - the computer spat out this:
Assuming an Alpine Type-R SWR-1242D running wired in parallel for 2 ohms load and 500 Watts RMS with THAT particular box at the beginning of your post...
prefab ported box - Page 2 -- posted image.
Box Properties
Name:
Type: Vented Box
Shape: Prism, square (optimum)
Vb = 2.916 cu.ft
Fb = 35.36 Hz
F3 = 33.23 Hz
Fill = none
No. of Vents = 1
    Vent shape = rectangle
    Vent ends = one flush
    Hv = 13.04 in
    Wv = 1.863 in
    Lv = 16 in
This is of course an educated guess, feeding numbers through Bass Box Pro v6. based on info you provided and trying to massage the numbers as close as possible to the dimensions you listed. (it fusses a little bit at you after a while if you go a little too far out of spec for the driver, etc. etc.) Though not a *perfect* match, it is NOT bad. It's tuned to approximately 35 Hz (give or take (L)User error on my behalf) which will make it stand out in presence. Lower end response suffers a little bit (I like extended bass myself) but then does unload steeply after 20 Hz. so be sure that your amp's low freq. filter is operational and you will have no worries.
Big ups to aznboi3644 BTW, you are right. I modeled a few changed box parameters based on my prior design for my truck. Tossing it about Vb@2.5 or so and getting it tuned lower makes it shine just that much more brilliantly. Time to pick up the tools and build. :D I got it currently in a Vb=1.7^3 ft. ported box tuned to 34 Hz. Built to your suggestion will extend the lows out just a bit more without worry of unloading - thanks for getting me thinking!
Life is too short to build slow computers or weak audio!
imupabove 
Copper - Posts: 369
Copper spacespace
Joined: March 14, 2009
Location: California, United States
Posted: September 01, 2009 at 11:45 PM / IP Logged  
OR i have another option.. .
their is this guy that has been building boxes for about 5 years. he said he has to measure my trunk first. he charging me 80 bucks but with no carpet and 110 with carpet. ive also seen his work/projects they look nice. should i go this route instead? if so where should it be tuned for really loud bass?
imupabove 
Copper - Posts: 369
Copper spacespace
Joined: March 14, 2009
Location: California, United States
Posted: September 01, 2009 at 11:48 PM / IP Logged  
wolfox wrote:
As close as I can model that subwoofer enclosure from listed dimensions and an educated guess from the port dimensions you listed
it wasnt a guess. i asked directly through the box's company.
metaljoey 
Copper - Posts: 58
Copper spacespace
Joined: July 11, 2009
Location: Indiana, United States
Posted: September 02, 2009 at 1:18 AM / IP Logged  

i have 2 12" old school(swr-1241d) 4 ohm dvc type r's for the wifes drango. the box i got for them is as fallows;

30.5"x14"x19"(out side) the port is12.25x2.5x14.5(in side) 

i came up with 34-35Hz and about 1.75ft^3 per driver.

with the port in the middle of the box does that mean its a "common air space" style box? there is not a divider just the one port in the center of the box.

and will this box do the typer r's justice?

they will be powered by a new RF power 1000db,.and they will be ran @ 1ohm.

Before you see the light, you must die!!
wolfox 
Member - Posts: 49
Member spacespace
Joined: June 16, 2009
Location: Florida, United States
Posted: September 02, 2009 at 1:49 AM / IP Logged  
More than likely the box was designed with that common airspace in mind. You can happily do that and does not mean that anything is wrong with the box build from what I have read in passing many moons ago. It just makes it difficult to diagnose if you have one woofer go bad and they are wired in a manner that allows them both to fire from one set of terminals. The working woofer will make the "dead" one jump and vibrate and it can appear that all is okay, though sound would have diminished some.
Life is too short to build slow computers or weak audio!
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