how about the amplitude of the pipe resonances? does the larger or smaller port have the loudest resonances,or are they equal
Lower frequencies carry more acoustic energy, i.e. they ring the bell louder. That's why higher frequencies are easier to damp.
Here's a pic to help visualize. The frist arrow (left to right) is for a port that is 68" long, second 34", third 17", Notice the amplitude of the third pipe harmonic of the 68" is stronger than the primary of the 17".
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in my diagram the port still offered a increase in overall output, when compared to a sealed box it looked alot better.
my demand is to amplify low frequencys, just less over a longer range
many agree the port is too big... not all agree, weather or not, it will add output to the overall responce of the speaker
the port is now going to be resized and at the rear of the enclosure 40/50/60cm from the corners of the room
life experiance has shown many a time. i hear 10inch drivers in boxes and they have too boomy a bass. i had a feeling this alinement, if correcly placed in a room would add a cleaner extended low end
i guess the real question i am now being faced with, is does this port tunig atually add to the overall responce (as per my graph) or does it not, as keriwena and tomom are saying
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i have ran a simulation for 28hz tuning, it adds 1db across the range, but as Keriwena pointed out, the higher tuning causes the driver to fall off rapidly below 50hz, to be replaced by the time delayed port output. so i cannot see any advantage to this apart from possible reduction in cone motion.
i am going with 24hz version, because it feels right.
ok this is just a proposision as the final cabinet following a few design constraits i have learned so far
one cabinet including feet cannot be higher than 80cm due to having the mids and tweeters at ear level...
two, cabinet port idealy should have 90 or 180 degree turns.... (i didnt think this mattered at these frequencys, going by Tomons statements)
three port internal diamater length cannot be smaller that 10x10x55
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please correct me if i am wrong, as i have have never made a vented cabinet, and am not entirely sure about this port location myself....
but what i do know, port is too low to affect mid and high pitches
bass waves are very indirect, vent exit is nearish to the woofer
negative atributes. it may look stupid, dust might get in the box, may not function as well as half way up the rear of the enclosure. if i keep the enclosure 80cm high though. the port will simply exit at the top without the visible chimley. or a even more far fected option is to have the port right out of the box so its near the ceiling...😱 but thats just a little joke..
here is option 2. close to the floor, out of sight no dust. negative atributes.. maybe too close 90degree turn at port end....
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i am going with 24hz version, because it feels right.
ok this is just a proposision as the final cabinet following a few design constraits i have learned so far
one cabinet including feet cannot be higher than 80cm due to having the mids and tweeters at ear level...
two, cabinet port idealy should have 90 or 180 degree turns.... (i didnt think this mattered at these frequencys, going by Tomons statements)
three port internal diamater length cannot be smaller that 10x10x55
An externally hosted image should be here but it was not working when we last tested it.
image hosting
please correct me if i am wrong, as i have have never made a vented cabinet, and am not entirely sure about this port location myself....
but what i do know, port is too low to affect mid and high pitches
bass waves are very indirect, vent exit is nearish to the woofer
negative atributes. it may look stupid, dust might get in the box, may not function as well as half way up the rear of the enclosure. if i keep the enclosure 80cm high though. the port will simply exit at the top without the visible chimley. or a even more far fected option is to have the port right out of the box so its near the ceiling...😱 but thats just a little joke..
here is option 2. close to the floor, out of sight no dust. negative atributes.. maybe too close 90degree turn at port end....
An externally hosted image should be here but it was not working when we last tested it.
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here is the 3rd and in my opinion "best" configuration, obviously box depth will be adjusted to match box volume.. the port exits in the best location, and there is a "nice" place for the crossover...
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An externally hosted image should be here but it was not working when we last tested it.
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If you can do it, 2nd option with modification that output is actualy going under the cabinet, facing the floor, may be the best. Ports on front baffle may transmit unwanted midrange frequences reflected within cabinet. Those on the back can not be placed too close to the wall. Ports facing floor will give predictable and repeatable performance ( according to text book and manufactureres who did that way). I haven't try it, but am thinking off for my next project.
Just another idea; speaker2 is optimum design for your driver. At 30Hz just under -6dB, at 50Hz just above -3dB. Tunning 29Hz ( I'm not insisting on that, just presenting simulation), port 47.4cm long, area 100cm^2.
Speaker22 is around -7dB at 30Hz, and -3dB at 50Hz. Tunning 24.7Hz, port 68.8cm long, area 100 cm^2.
What you get here is reduction in box size - 64.5 Liters.
Speaker22 is around -7dB at 30Hz, and -3dB at 50Hz. Tunning 24.7Hz, port 68.8cm long, area 100 cm^2.
What you get here is reduction in box size - 64.5 Liters.
I looked at this thread late last night, was surprised at how far it had gone, and was tempted to reply to several points, but went to bed, instead. Again, things are rolling along, and most of my intended comments have been covered.
Regarding the suggestion to point the port at the floor, the problem is reflections from the floor load the port and complicate the design. Nothing that can't be overcome, but it does require attention.
To questions about the audibility of the port output, while increasing the bass through merged speaker/driver output has become a bullet point in the benefits of ported systems, one shouldn't overlook the fact that a ported cabinet also affects the response of the driver. Even if the port output is negligible, greater bass extension of the driver itself may be beneficial, especially when optimising for small rooms with 'gain', or assuming 'bass lift' EQ. Aperiodic cabinets are perhaps an example of this.
Regarding the suggestion to point the port at the floor, the problem is reflections from the floor load the port and complicate the design. Nothing that can't be overcome, but it does require attention.
To questions about the audibility of the port output, while increasing the bass through merged speaker/driver output has become a bullet point in the benefits of ported systems, one shouldn't overlook the fact that a ported cabinet also affects the response of the driver. Even if the port output is negligible, greater bass extension of the driver itself may be beneficial, especially when optimising for small rooms with 'gain', or assuming 'bass lift' EQ. Aperiodic cabinets are perhaps an example of this.
according to a simulation increasing the port length and making th box smaller (speaker22) atually shows a fall of 2db at 30hz, when compared to the current alinament
in regards to the higher tuning, kriwena, did show me how the driver rolls off below 50hz to b replaced by th port,
where as at 24hz- the driver extention is extended, to be suplemented by the port, lower down...
im curious though. in the option where the cone coveres more of the responce.. it will have to move more. so the maxspl will be limited slightly...
i dont want to be trying to get too much from too little. im just wondering what the comparitive max spl of each alinement would be
(not that im convinced i want to change to a higher tuning....)
what would really be helpfull was if Ron-E could post me another 28hz pdf, just so i can get a more accurate comparative of all these factors..
i plan to disregard the port@floor opinion, for 2 reasons- one: i dont want to raise the box from the floor. and two: i dont like the idea of it. three: i cannot be bothered for your reason given above
i really dont think that at these frequencys the shape of the port is a concern. thats why i am happy with the square port with 90degree entrance and exit.
i dont feel too well tonight do i am having a break. i am happy with the current design, and would like to thank you guys
i think in my small-mediem sized room -6db at 30hz is fine. and from studying all these graphs. factoring correct placement and room gain....
also i have observed that the cone is still doing less work than in a sealed varient. so i dont think spl will really be a issue.
and "if" it all goes pear shaped... which i doubt it will... i can always shove a block in the port. i think for music i will be more than happy, as the driver looks like it will sound the 100-500hz range nicely (as well as the 30-100hz range, i hope🙄)
and for movies... if the infrasonic content becomes a concern i can always make a pair of removable plugs for the ports, that will "magically" turn the box in to a sealed one when needed.......
as long as this design wont pose any concerns concerning arguementation to my midrange (H1262-08 - Seas MCA15RCY midrange - Europe Audio) then i am happy 🙂🙂 with it, and its various trade offs...
here is something i have just thought of. so i will through it in the mixIf i where to replace the 55x10x10 port
with three smaller ports, then they need only be 4cm in diamiter and 19.20cm longthis would move the organ frequency higher still and make them even less of an issue, and they would fit in the box without requiring any angles. i dont see many speakers with 2 or 3 ports though, so is there a disadvantage to this?
The total area of the three small ports should be the same as the area of the single port, if you want to maintain the same tuning.
In the UK, drain pipe comes in 1", 1.25" 1.5" 2" 2.5" and 4".
It's a cheap way to make ports. It is also very easy to experiment with port length.
In the UK, drain pipe comes in 1", 1.25" 1.5" 2" 2.5" and 4".
It's a cheap way to make ports. It is also very easy to experiment with port length.
thanks for the sizes. saves me popping over to b&q. i understand that the 3 ports have to be a comparitive area to maintain the same tuning. i just wondered if it would work as well as 1 big port, i understand pysics wise the ports share the same volume, i just wondered if the air mass being devided may cause some issue with the wave front (i dont know what im talking about) thats why i was asking!
That is certainly why I am here.
I cannot count how many topics I have learned from this Forum. Fingers and toes does not come near it.
I cannot count how many topics I have learned from this Forum. Fingers and toes does not come near it.
Hi,
The 3 ports are shorter because they have less area than the long port.
Same area, ~ same length for a given box tuning, 3 ports would be fine.
rgds, sreten.
in that case, something like this will do... FloPlast 3m x 40mm PP Wastepipe Black, 5055149900174
it says 40mm, asuming the inside is 34=3mm thick (by eye, need to to go measure...) i can have 4 ports, nicely spaced in a square, around a central point half way up the back of the cabinet
this will give each port a length of 20cm, easy to fit in the cabinet.... with a mach of 0.09@1w (according to winISD)
better than the 10x10x55 square port's, mach 0.14, with its 90 degree turn at both ends....
that is so looong as multiple ports dont through any negative factors into the mix, which i have been told they wont so... im happy!🙂
going on what i have learned to far, the higher highmonics of a 3.6cm x 20cm pipe will be lower in amplitude, and be moved even higher
then i can simply modify the box size, once again leaving 8-10liters spare to be calculated later (allocated for bracing, driver moter, volume of ports oh and volume of padding
(will have to learn how to caculate the volume of a cilindrical object... 🙁 )
but overall its shaping up nicely🙂
it says 40mm, asuming the inside is 34=3mm thick (by eye, need to to go measure...) i can have 4 ports, nicely spaced in a square, around a central point half way up the back of the cabinet
this will give each port a length of 20cm, easy to fit in the cabinet.... with a mach of 0.09@1w (according to winISD)
better than the 10x10x55 square port's, mach 0.14, with its 90 degree turn at both ends....
that is so looong as multiple ports dont through any negative factors into the mix, which i have been told they wont so... im happy!🙂
going on what i have learned to far, the higher highmonics of a 3.6cm x 20cm pipe will be lower in amplitude, and be moved even higher
then i can simply modify the box size, once again leaving 8-10liters spare to be calculated later (allocated for bracing, driver moter, volume of ports oh and volume of padding
(will have to learn how to caculate the volume of a cilindrical object... 🙁 )
but overall its shaping up nicely🙂
wait am i getting confused here..if one port has 10x10 by 55 how can four ports be a lower mach and be 3.6x20 each??? is something wrong with the program? cos you could fit 4 40mm pipes into a 8cm square with space to spare, so if there is a obvious reduction in the overall size of the vent hole, and the length is shorter to match... how can the program say the mach of the 3.6mm by 20cm pipes is less??
does length effect mach 😱 this makes no logical sence, going to have to think about this
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