Peavey's spec sheet for the 18" low rider say that for a 9 cu ft box it should have two 6 " vents 12" long, it also states that the inside ends of the vent should have a minimum distance of one vent diameter from any interior wall of the enclosure. I have read in other places that there should be a minimum distance from the speaker of two times the vent diameter. I went exactly 6" from everything on the vent and the numbers don't work for a 9 cu ft box. I would need about 2500 cu inches of bracing to offset the size of the box based on those rules. I have looked at other pictures of boxes and they do not seem to adhere to any vent diameter guidlines, some next to the box wall, some next to the speaker. Other vent locations are an option but i have already cut the vent and speaker holes on 3/4" oak plywood. any suggestions? Am I interpreting the diameter rule wrong?
1) Don't treat those rules as absolutes.
2)
3) Why don't you explain how you cut your baffle? By the way, the ports don't have to be on the baffle.
2)
Do you mean that the back and 2 closest sides are at least 6" away from the internal port opening? If so, you can safely relax this so that only 6" from the back is respected.
3) Why don't you explain how you cut your baffle? By the way, the ports don't have to be on the baffle.
Possible solution
Thank you leadbelly, I sat up thinking about it last night and came up with a solution. I will install a board behind the woofer on an angle, basically sectianlizing off a corner of the box, this would give me the correct cubic inches for my box, and although you say it's just the back wall I need to keep 6" away, I will try all walls. I thought about mounting it elsewhere than the baffle, but I figured if it were on the baffle I wouldn't accidentally put something in front of a vent hole. When I get home from work today I will post a pic of my project in progress. I was wondering if you have to subtract the quilting from the total cubic inches or is it transparent to that calculation? And I am dadoing 6" PVC so in my 12" calculation, do I need to measure from the outside baffle wall hole to the inside hole of the PVC pipe edge? If so I need to subtract 3/4" from my total length. Thanks.
Thank you leadbelly, I sat up thinking about it last night and came up with a solution. I will install a board behind the woofer on an angle, basically sectianlizing off a corner of the box, this would give me the correct cubic inches for my box, and although you say it's just the back wall I need to keep 6" away, I will try all walls. I thought about mounting it elsewhere than the baffle, but I figured if it were on the baffle I wouldn't accidentally put something in front of a vent hole. When I get home from work today I will post a pic of my project in progress. I was wondering if you have to subtract the quilting from the total cubic inches or is it transparent to that calculation? And I am dadoing 6" PVC so in my 12" calculation, do I need to measure from the outside baffle wall hole to the inside hole of the PVC pipe edge? If so I need to subtract 3/4" from my total length. Thanks.
From outside the baffle, total length, for straight/flanged ports. If the curved lip is used measure from middle of the lip, for flared ports.
Port Flares
No you're fine, some say it's half the diameter from the back wall, so you playing safe here.
If your box it's a little bigger you don't need to take out the extra space, many times calculations where made for too smallish boxes to fit in special purposes/footprints. A bigger box will require maybe a smaller port length for the same tunning. It's better and easy to just recalculate the all project for reinsurance (alignment) with different enclosures (internal volume).
Port Flares
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Thank you inductor for your knowledge. Ok so now I am thinking of shaving 3" of top and bottom so it is within 1/2 diameter of sidewalls and still full diameter away from back wall. My final dimensions would then be 24"X33"X21" this would give me 9 cubic feet after vents, speaker and bracing is taken into account. I have gone to box calculators and they seem to differ from what peavey recommends for vent length @ 30 HZ. Peavey recommends 2 - 6"X12" for 9 cu ft. Calculators recommend 2 - 6"X 14.43". Do speaker characteristics change the vent requirements or are they all the same? Should I follow Peavey or calculator?
Port Length Calculator
This is the site I used, I just grabbed one randomly. The other one I tried asked for a k end correction factor, whatever that is.
This is the site I used, I just grabbed one randomly. The other one I tried asked for a k end correction factor, whatever that is.
Hi jrbluejr,
That calculator is OK....The End correction factor(s) at both ends virtually increases the port length a bit, i.e. the 'Port Air Mass in operation= the condition for resonance is larger than what the 'visual' Port Volume depicts.
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