Does anybody here have access to the AES E-Library or maybe someone has these on a hard drive already......?
I am trying to find the following ----->
J. Backman, “The Nonlinear Behaviour of Reflex Ports,” presented at 98th AES Convention, Paris
https://www.aes.org/e-lib/browse.cfm?elib=7767
J. Vanderkooy, “Loudspeaker Ports,” presented at 103rd AES Convention, New York 1997
https://www.aes.org/e-lib/browse.cfm?elib=7256
J. Vanderkooy, “Nonlinearities in Loudspeaker Ports,” presented at 104th AES Convention, Amsterdam 1998
https://www.aes.org/e-lib/browse.cfm?elib=8432
Attached is a 1999 patent from Roozen et al. which is no doubt a follow on from all their work on flared ports in the mid-nineties
I am trying to find the following ----->
J. Backman, “The Nonlinear Behaviour of Reflex Ports,” presented at 98th AES Convention, Paris
https://www.aes.org/e-lib/browse.cfm?elib=7767
J. Vanderkooy, “Loudspeaker Ports,” presented at 103rd AES Convention, New York 1997
https://www.aes.org/e-lib/browse.cfm?elib=7256
J. Vanderkooy, “Nonlinearities in Loudspeaker Ports,” presented at 104th AES Convention, Amsterdam 1998
https://www.aes.org/e-lib/browse.cfm?elib=8432
Attached is a 1999 patent from Roozen et al. which is no doubt a follow on from all their work on flared ports in the mid-nineties
"So what were the results?
The non-flared slot port was the first to start making port noise, which comes as no surprise with its sharp edges and corners.
The non-flared round port took a little more power but not much. The flared ports both took quite a bit more power before they started making noise. Turns out you can put about 2.5 times as much power into a flared port vs a non-flared port before you get any port noise.
So 2.5 fold increase of power will increase your port velocity by about 37%, so port that would start making noise at 17 m/sec can now flow a little over 23 m/sec. Knowing this I should be able to reduce port size by 37% if I use well flared ports.
Now we are getting somewhere!
While I definitely learned some interesting info from this test, it also left me with more questions. While I can measure how much power increase it takes to make a flared port chuff I don't have a way of knowing how many actual watts it took or what my actual port velocities were and I really wish I did. I know that when it comes to fluid dynamics things don't scale linearly with size, just because a 2" port chuffs at 17 m/sec doesn't mean a 4" or 6" port will. This is why I think Small's formula, while certainly a good starting point, gives us a little too simple of an answer. Really just how much velocity can I push through a 75 sq. in. 4.5" wide flared port before I get a noticeable amount of port noise? I suspect its a lot more than 23 m/sec. I guess finding a way to figure that out will be my next goal."
https://www.stevemeadedesigns.com/board/topic/178548-flared-vs-non-flared-ports-an-experiment/
The non-flared slot port was the first to start making port noise, which comes as no surprise with its sharp edges and corners.
The non-flared round port took a little more power but not much. The flared ports both took quite a bit more power before they started making noise. Turns out you can put about 2.5 times as much power into a flared port vs a non-flared port before you get any port noise.
So 2.5 fold increase of power will increase your port velocity by about 37%, so port that would start making noise at 17 m/sec can now flow a little over 23 m/sec. Knowing this I should be able to reduce port size by 37% if I use well flared ports.
Now we are getting somewhere!
While I definitely learned some interesting info from this test, it also left me with more questions. While I can measure how much power increase it takes to make a flared port chuff I don't have a way of knowing how many actual watts it took or what my actual port velocities were and I really wish I did. I know that when it comes to fluid dynamics things don't scale linearly with size, just because a 2" port chuffs at 17 m/sec doesn't mean a 4" or 6" port will. This is why I think Small's formula, while certainly a good starting point, gives us a little too simple of an answer. Really just how much velocity can I push through a 75 sq. in. 4.5" wide flared port before I get a noticeable amount of port noise? I suspect its a lot more than 23 m/sec. I guess finding a way to figure that out will be my next goal."
https://www.stevemeadedesigns.com/board/topic/178548-flared-vs-non-flared-ports-an-experiment/
You can if you use enough of them for given design.
I actually had 4 x 4" diameter ports for an isobaric BP4 enclosure with four 15's.
I wish I had pics of the enclosure. If was the 1st item that sold in a garage sale in 2002. It was for a 1983 Mercury Grand Marquis LS that I donated to the Volunteers of America after the head gasket blew the same year.
Yes, you could use 25.8 ports of 1cm radius (20mm diameter) to equal the area of one four inch (101.6mm diameter) port.
Or 103 of the small ports to equal the area of four 4" diameter ports 😉
The previously linked AES papers and measurements regarding port shapes have shown that for a given Fb using radiused ports have less measured loss and less turbulence noise than straight cylindrical ports of equal or greater enclosed volume.
That said, doesn't look appear any papers have a simple formula to reliably predict the "best" port shape to use for reduction of noise, loss, and enclosed volume for a given Fb.
Art
That port has flared ends, which will reduce turbulence noise, but won't reduce port losses or the cabinet volume for a given Fb, as they occupy slightly more volume than a pipe.Oh, you are referring to THIS
Ports with the radius over the entire have both less measured loss and less turbulence noise than straight cylindrical ports of equal or greater enclosed volume. That type of port would be "Port D" or the one below "P3":
Wow, nice! Is there ready made ports like this in the market? Wondering if they have some acoustical (or other) drawbacks compared to conventional round ports.
I have not searched for commercially available ports with the radius over the entire length, but a port of this type would have to be specific for cabinet volume, desired Fb, and excursion.
The drawback would be the start up cost tooling up for manufacturing so many different products for a limited market that is already full of alternative products like the one depicted in post #67 that can use a standard pipe section between the ends.
2 of these ports together would be excellent for a BP4 enclosure where higher tuning is required.
https://www.parts-express.com/Preci...MIkNObqJCkgwMV3SmtBh1s-QZ6EAQYAiABEgLwvPD_BwE
https://www.parts-express.com/Preci...MIkNObqJCkgwMV3SmtBh1s-QZ6EAQYAiABEgLwvPD_BwE
This camp has been very busy and has much to report, but for now, I wanna run this brain fart past you guys
Just think about something for a second, the flat floor of the L-Vent KS21 L'acoustics single driver subwoofer enclosure.
Exactly like so.....
Now imagine that flat floor is a square(-ish) 3-d printer bed turned upside down inside the enclosure.
i.e. it has adjustable (and lockable) threaded bolts on each corner of the flat floor and these will do three things.
Raise the whole flat floor ... Raise the back side..... Or raise the front...... As desired to give a level of adjustability to the port.
This will obviously give the port some level of corrective tuning, yes.....?
And allows one to very cheaply play will these L-vent parameters.
After all their double enclosures are just a mix of two large flares and two flat walls.
I have been reading a lot of the literature posted in this thread regarding flare gradients and it would seem the L-Acoustics vent is just too steep and could bee improved on surely....?
Much more gradually flared designs are even better.
Read the attachments.
Also..... That flat floor is a really sh!t place for a handle..... Why do they do this.......?
Any way......Brain fart over..... Adjustable L-Vents for the common man.......?
Just think about something for a second, the flat floor of the L-Vent KS21 L'acoustics single driver subwoofer enclosure.
Exactly like so.....
Now imagine that flat floor is a square(-ish) 3-d printer bed turned upside down inside the enclosure.
i.e. it has adjustable (and lockable) threaded bolts on each corner of the flat floor and these will do three things.
Raise the whole flat floor ... Raise the back side..... Or raise the front...... As desired to give a level of adjustability to the port.
This will obviously give the port some level of corrective tuning, yes.....?
And allows one to very cheaply play will these L-vent parameters.
After all their double enclosures are just a mix of two large flares and two flat walls.
I have been reading a lot of the literature posted in this thread regarding flare gradients and it would seem the L-Acoustics vent is just too steep and could bee improved on surely....?
Much more gradually flared designs are even better.
Read the attachments.
Also..... That flat floor is a really sh!t place for a handle..... Why do they do this.......?
Any way......Brain fart over..... Adjustable L-Vents for the common man.......?
Last edited:
It would make the tuning adjustable, but would be difficult to make air-tight, and would reduce cabinet or port volume. The optimum port arc profile would be dependent on the Fb and box volume.
A single arc requires a steeper gradient to achieve the same design goal as a dual flare.
Any port design is a compromise, L-Acoustic's laminar flow vent fits their philosophy and used plenty of testing to confirm it met the goals they set.
That "flat floor" is usually a side, the 35 mm pole-socket is on top.
The two ground runners on the bottom and two matching tracks on the top make stacking easy, lifting ergonomics dictate the four side handles placement.
The two smooth profile handle restrictions are part of the vent/box Fb determination, without them the Fb would go up a bit in frequency, as it would if the port ended at the speaker baffle, rather than arcing over the cone, covering two of the speaker's mounting holes..
Art
Interesting..... Thank you Art, as always.
Hmm, maybe my idea really is just over-engineering.
I did have another thought where only the "flat floor" could bee raised..... in increments of 3mm using layered hardboard.
This sounds like a much simpler and more straight forward. approach.
I have toyed with a bunch of almost identical designs over the winter and think I am sold on the "PLAN KS28 SINGLE 18" SUB" on MrFlexys SMPS youtube channel I posted upthread in post #10.
Here it is again for convenience
But I would like to make a change..... Make the box 50mm wider so instead of 550mm wide the enclosure is 600mm
This is it's narrowest dimension.
One guy in the comments states that the 80mm wide at the port length centre is wrong, and should bee 70 and not 80.
So I thought of making this dimension at least 80mm wide (and wider if necessary) and then coming down in 3mm layers of hardboard while I measured the actual tuning.
Mr Flexys claims that these go down to 25Hz in this specification .
This design looks easy and simple..... I am planning on using 3 layers of 6mm plywood curved, glued and screwed together to make the curved vent.
Many enclosures can bee made in a short space of time if needed too.
Regarding fixings and all that, four relatively large ugly castors will bee screwed to the back end, also the longest side.
It will bee just tip 'em cone up and roll 'em on out.
Easy peezy lemon squeezy
Two handles for not too much lifting (no more than 2 stacked high at any one time is plenty)
But they will not bee in the port, but either side of the woofer intruding into the box behind the cone.
I think that particular box can fill many criteria for me.
Would I bee right in saying this exact vent design cannot bee modelled on any of the usual free software packages......?
Hmm, maybe my idea really is just over-engineering.
I did have another thought where only the "flat floor" could bee raised..... in increments of 3mm using layered hardboard.
This sounds like a much simpler and more straight forward. approach.
I have toyed with a bunch of almost identical designs over the winter and think I am sold on the "PLAN KS28 SINGLE 18" SUB" on MrFlexys SMPS youtube channel I posted upthread in post #10.
Here it is again for convenience
But I would like to make a change..... Make the box 50mm wider so instead of 550mm wide the enclosure is 600mm
This is it's narrowest dimension.
One guy in the comments states that the 80mm wide at the port length centre is wrong, and should bee 70 and not 80.
So I thought of making this dimension at least 80mm wide (and wider if necessary) and then coming down in 3mm layers of hardboard while I measured the actual tuning.
Mr Flexys claims that these go down to 25Hz in this specification .
This design looks easy and simple..... I am planning on using 3 layers of 6mm plywood curved, glued and screwed together to make the curved vent.
Many enclosures can bee made in a short space of time if needed too.
Regarding fixings and all that, four relatively large ugly castors will bee screwed to the back end, also the longest side.
It will bee just tip 'em cone up and roll 'em on out.
Easy peezy lemon squeezy
Two handles for not too much lifting (no more than 2 stacked high at any one time is plenty)
But they will not bee in the port, but either side of the woofer intruding into the box behind the cone.
I think that particular box can fill many criteria for me.
Would I bee right in saying this exact vent design cannot bee modelled on any of the usual free software packages......?
Last edited:
Excuse my double post if this offends your posting etiquite.
Just for comparison and a little context, the original dual 18" KS28 design that this is based on has a narrowest port measurement of 140mm and that is feeding for two.
Just for comparison and a little context, the original dual 18" KS28 design that this is based on has a narrowest port measurement of 140mm and that is feeding for two.
I wanted to post those types of flared ports, but my original post stated using spare wood from the actual build.
You may be able to model something close in AKABAK, of which there are free versions.
As far as I know, L'Acoustics does not make a single version of the KS28.
70mm port minimum width would make the Fb lower than 80mm, neither is "wrong".
The KS28 Fb appears to be 31Hz.
https://www.production-partner.de/test/l-acoustics-ks28-im-test/
The Production Partner tests are very close to L'Acoustics published specification of 25Hz -10 from 110Hz.
Whether the Fb would remain the same with a dual radius port split in half (and the two cabinets and ports stacked, rather than adjacent) is an interesting question- the "end correction" would not be identical, so my guess is the Fb would change.
Art
You would have to build the enclosure, take measurements, and then see if you can model in HR with just 4 segments for the port.
Atc and Vtc would be the enclosure volume.
S1 to S3 would be the 1st half of the port.
S3 to S5 would be the 2nd half of the port.
L12, L23, L34, & L45 should be equal lengths. Divide the port length into 4 quarters.
Hopefully, your model will match your measurement.
Atc and Vtc would be the enclosure volume.
S1 to S3 would be the 1st half of the port.
S3 to S5 would be the 2nd half of the port.
L12, L23, L34, & L45 should be equal lengths. Divide the port length into 4 quarters.
Hopefully, your model will match your measurement.
When really, it should bee the other way round (eye roll)
Thanks guys, your input has been so helpful
Update -
To bee honest I haven't been able to get my head around HR yet, nor even had the time to look at AKABAK.
I found WinISD easy to use so I have more or less stuck with that for now.
Quite a few plans were drawn out, which were basically a L'Acoustics KS28 cut in half, and scaled up for 25mm MDF and widened 50mm to 600mm
This is the shortest dimension of the box but this width fits my top much better.
The same was done with 3 MrFlexy designs (all posted in this thread) and a L'Acoustics KS21.
Just so I could get a "feel" for these particular subs.
The materials for the scaled up MrFlexy "PLAN KS28 SINGLE 18" SUB" (post #74) have been ordered and picked up so there has been some progress.
And using the outside dimensions of that, we have a final (external) volume of 325 litres
I have also decided to follow through with my simulation upthread (post #3) (292 litre BR sub with 2 6" Precision ports) so this means the 2 driver enclosures
will bee different designs and not a pair.... No doubt I will follow through with another "PLAN KS28 SINGLE 18" SUB" but for now, I would like to build
these two and test the differences.
One thing that I am unsure of is the internal baffle in the rear of the throat in the single 18 KS28 (the Wobbly Board)
No dimensions for this piece are given.... Would anyone like to take a guess......?
Maybe a few different baffles should bee tested.
Anywho.... I have been busy.... Build coming soon
Thanks guys, your input has been so helpful
Update -
To bee honest I haven't been able to get my head around HR yet, nor even had the time to look at AKABAK.
I found WinISD easy to use so I have more or less stuck with that for now.
Quite a few plans were drawn out, which were basically a L'Acoustics KS28 cut in half, and scaled up for 25mm MDF and widened 50mm to 600mm
This is the shortest dimension of the box but this width fits my top much better.
The same was done with 3 MrFlexy designs (all posted in this thread) and a L'Acoustics KS21.
Just so I could get a "feel" for these particular subs.
The materials for the scaled up MrFlexy "PLAN KS28 SINGLE 18" SUB" (post #74) have been ordered and picked up so there has been some progress.
And using the outside dimensions of that, we have a final (external) volume of 325 litres
I have also decided to follow through with my simulation upthread (post #3) (292 litre BR sub with 2 6" Precision ports) so this means the 2 driver enclosures
will bee different designs and not a pair.... No doubt I will follow through with another "PLAN KS28 SINGLE 18" SUB" but for now, I would like to build
these two and test the differences.
One thing that I am unsure of is the internal baffle in the rear of the throat in the single 18 KS28 (the Wobbly Board)
No dimensions for this piece are given.... Would anyone like to take a guess......?
Maybe a few different baffles should bee tested.
Anywho.... I have been busy.... Build coming soon
For anyone who is interested, here is a rough sketch for comparison of 2 MrFlexy designs, the first is his "[PLAN] 18" 25Hz Flexy KS28 subwoofer"
And the second "KS28 subwoofer PLAN but it PLAYS LOUDER because I modified it!"
Mr Flexy claims a 25Hz Fb in the first one but someone in the comments seems to think it is actually 31Hz.
And his second modified design is tuned to 40Hz.
I was interested in the changes he had made in the box and the throat to change the box tuning frequency.
Okay, that's enough of that for now.
And the second "KS28 subwoofer PLAN but it PLAYS LOUDER because I modified it!"
Mr Flexy claims a 25Hz Fb in the first one but someone in the comments seems to think it is actually 31Hz.
And his second modified design is tuned to 40Hz.
I was interested in the changes he had made in the box and the throat to change the box tuning frequency.
Okay, that's enough of that for now.