Published on Mar 27, 2023
Well last year I had a side exit ported box, with the two subs next to each other.
This allowed me the maximum port area and length to fit in the box volume that I had at the expense of a little loading issue with the sub closest to the port exit mouth.
So after just beating the U.K. Record I decided have fun with the set and to do a center ported adaptation, removing the loading issues.
So still using old box, I just stripped it out changed bracing and put new top on.
Having the center opening limits the port area and more so the length, of which the max is 27".
So I made 3x L shaped ports, 28Hz - 25Hz - 22Hz all @ 27" long, just reducing the port area of each length to get the desired tuning frequency.
.Choke fest!!! lol.
Each port has way less port area than the previous side ported box, in which the port area on that was around 58" Square Inches and tuned to 25Hz.
My current 25Hz tuned port has only 42.5" Square Inches of area due to the length limit that I can get in the box, although I might be able to try something else.
Anyway You can see the SPL results in the pic.
Onto the ports then:
The 28Hz tuned one: - 2nd loudest on Average.
1: Highest SPL peak.
2: Highest 40Hz and 33Hz
3: Roll off is incredibly steep
4: 20Hz is rubbish lol
25Hz: Loudest on Average.
1: Still a 150dB+ peak score
2: Scores either side of the peak score are not too bad
3: Roll off still a lot, but not as bad as the 28Hz port
4: 20Hz is now over 140dB+ but I still think it`s rubbish
22Hz: Quietest one
1: Low Peak score
2: Scores either side of the peak are reasonable
3: Roll off is more or less same as 25Hz port
4: 20Hz is over 140dB but I still don`t like it.
So each port is choking the output, more so when trying to get Max SPL scores, but I have no choice as I`m limited to the port opening in the center of the box.
Listening wise, I love the 22Hz tuned port.
It contradicts the lower end scores as when listening to the usual re-bassed tunes the low sub 20Hz bass is clearly there, it appears to also play everything even the highs, and drops audibly to 16Hz after which the volume certainly drops, over double.
Surprisingly there is hardly any port noise. So that port is only coming out when I go through the lanes.
The 28Hz port although much louder does not drop low at all. Doesn`t sound as good as the 22Hz tuning. So I`m scrapping that one.
The 25Hz is the best overall for (((pd))) SPL. It has done a 142.85dB @ 20Hz. So keeping that and going to make another one with hopefully more length by changing it to a C shaped port, so should be able to tune to near 22Hz and maybe increase lower end scores whilst still hitting somewhere near 150dB.
Will also be possibly be making a 26Hz tuned and 24Hz tuned port.
And watch out BB2, Henry Thomas Fairfax Harwood (wish me luck mate, Ryan Smith said he wanted a bit of competition and said you two were up to something lol)
I might find the time to do a 6th Order Parallel Clamshell bandpass box this year.