need confirmation for ported box
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=81087
Printed Date: May 11, 2025 at 5:53 PM
Topic: need confirmation for ported box
Posted By: hsali
Subject: need confirmation for ported box
Date Posted: August 02, 2006 at 4:52 AM
Hi,
This is the first time I "properly" design a subwoofer enclosure.
I have used WinISD to calculate box and port sizes, and these are the results; I just need more experiences box builders to tell me I'm on the right track.
Subs: 2 x Mac Audio Premium 300. 200 RMS 12"
WinISD suggests 64 litres. Port will be rectangular, along an edge of the box, 34 cm long, 4 cm wide, and 26 cm deep.
What is making me uneasy is that changing the number of drivers from 1 to 2 makes no difference in port and box volume. Is this correct? I would have thought 2 subs would need a bigger volume than one sub?
If it is at all relevant, I am powering the subs from a Kicker KX700.5 amp, 425 RMS, subs are 4 ohm, but will be wired in parallel for 2 ohm.
Thanks in advance
Replies:
Posted By: stevdart
Date Posted: August 02, 2006 at 5:31 AM
Bring the sub up again in WinISD as a new project. Input '2' as number of subs at the start. Click through the dialogue boxes and let the program calculate box volume...then make your necessary changes for space consideration after that. What is making me uneasy is that changing the number of drivers from 1 to 2 makes no difference in port and box volume. Is this correct? I would have thought 2 subs would need a bigger volume than one sub? You must have been changing from one to two subs after already bringing the project up with just one woofer. The program is not going to continually alter the box size at this point, because you are now in design mode. This program is a tool, not a dictator...it allows you to design the box as you want to. If it kept changing things on you as you try to make changes yourself, you wouldn't be able to get anything accomplished! Hint: the program will normally show larger box volumes than you might have room for in a car. It will seek the flattest response. If 64 liters (2.25 cu ft) per sub is too big and bulky for the intended installation, work the program with smaller volume for the two subs to fit the space. You will see WinISD alter the port size to compensate for the difference in box volume so that it still meets the intended tuning frequency. Keep the length to width ratio of the port opening to 8:1 or less. 4 cm is a bit narrow in relationship to 34 cm. With a smaller box volume, you will see that the port size will have to grow bigger, so increase the port opening width while keeping the port opening length at a size that will fit your box.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: hsali
Date Posted: August 02, 2006 at 7:32 AM
yes, you are right. 64l is for 2 drivers. I started a new project using 1 driver and the recommended volume is 32l.
But I cannot think of a way of making the port opening 8:1, while still looking good. I wanted the box to be about 100 cm wide and 35 cm high. Any suggestions how to make the port fire forwards while still looking good?
Posted By: stevdart
Date Posted: August 02, 2006 at 4:49 PM
A ratio of 8.5:1 is fine. You just don't want 12:1 or something like that. Make sure you input the total power that will be going to those subs in the Signal tab (system input power) of your program. Then look at the graph "Rear port air velocity". You want the port noise below 110 ft/sec (do your conversions to metric as necessary). If the port noise shows higher than that at full power, you will have to enlarge the port opening, which will increase the overall port length.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
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