I was actually thinking if it would be possible to make a "mode suppressor" inside the box.
Might not work, but it would be interesting to know for sure.
A bit similar to the solution Yamaha came up with, just pipes with stuffing to "consume" the resonances at fixed locations.
They did it in a sealed box though, might be hard to get it working in a vented box.
Might not work, but it would be interesting to know for sure.
A bit similar to the solution Yamaha came up with, just pipes with stuffing to "consume" the resonances at fixed locations.
They did it in a sealed box though, might be hard to get it working in a vented box.
Asked MJK about the TL worksheets, not available anymore.
I tried to simulate the box in Hornresp as MLTL:
Clearly a resonance is seen with the current box and woofer position, but could be cancelled if woofer was roughly half way of the "pipe".
Obviously not gonna happen unless the box was made ~20cm taller
One could add length to "the pipe" with some internal structure but this adds length to the pipe (obviously) and brings all resonances down in frequency, which means the next resonance comes down and is not that much higher than the first was originally. Not much help here it seems Maybe this + some filling would damp the resonances enough if the slot port at bottom was mandatory.
Anyhow, best thing is to put the port somewhere the resonance is not so audible. As it's already done. And carry on
I tried to simulate the box in Hornresp as MLTL:
Clearly a resonance is seen with the current box and woofer position, but could be cancelled if woofer was roughly half way of the "pipe".
Obviously not gonna happen unless the box was made ~20cm taller
One could add length to "the pipe" with some internal structure but this adds length to the pipe (obviously) and brings all resonances down in frequency, which means the next resonance comes down and is not that much higher than the first was originally. Not much help here it seems
Maybe this + some filling would damp the resonances enough if the slot port at bottom was mandatory.Anyhow, best thing is to put the port somewhere the resonance is not so audible. As it's already done. And carry on
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Yes, agreed.
Right now I have only 1 concern.
The rear port might limit placement for some of the potential builders, especially since this is a Monkey Coffin type speaker, it should be possible to place it in a constricted location such as a bookshelf or equivalent, without sacrificing performance. Another factor is a slight potential for induced room mode interaction, a third would be the lessened sense of "impact".
All this from rear port, one might argue the importance of the various factors, but they should be considered IMO.
Right now I have only 1 concern.
The rear port might limit placement for some of the potential builders, especially since this is a Monkey Coffin type speaker, it should be possible to place it in a constricted location such as a bookshelf or equivalent, without sacrificing performance. Another factor is a slight potential for induced room mode interaction, a third would be the lessened sense of "impact".
All this from rear port, one might argue the importance of the various factors, but they should be considered IMO.
Bookshelf placement would Indeed be a problem with a rear port. A front port would be required, but it would have to be different from the original slot port, which caused colorations if the lower midrange. A much smaller front port would be required to make it fit next to the mid and tweeter. This would not be ideal for the reasons I pointed out earlier (diffraction, port locking up at loud music). However, the Monkey Coffin is a bit too large for an average bookshelf, so bookshelf placement will not be very popular anyway.
I dont see how port placement could make a difference in terms of room modes. Room modes have wavelengths of several metres, which is much more than the difference between front or rear port positions (about 0.4 m).
I do not hear less "impact' with the rear port. I therefore think this point is not relevant with the Monkey Coffin design.
The solution with the rear port sounds and works good as it is. I guess if noone comes up with a concrete design alternative for the port I will just leave the rear port as it is and continue with building the filters once I am back from holidays.
I dont see how port placement could make a difference in terms of room modes. Room modes have wavelengths of several metres, which is much more than the difference between front or rear port positions (about 0.4 m).
I do not hear less "impact' with the rear port. I therefore think this point is not relevant with the Monkey Coffin design.
The solution with the rear port sounds and works good as it is. I guess if noone comes up with a concrete design alternative for the port I will just leave the rear port as it is and continue with building the filters once I am back from holidays.
Impact is not something you can hear with your ears unless you know exactly what you're listening for. It is much easier to feel, especially if you wear some slightly loose clothing.
But that's ok. I know it is a lost battle now. Just think it's a shame, so much attention to detail everywhere, but no love for getting the BR system done right.
Juhazi has a good point though, one could replace the bottom slot port with a tube port that curls up into the middle of the enclosure. Down there it would not be in the way, and the tube could be angled anywhere, away from the modes.
This is not a battle, and its not about winning or loosing. I was simply asking if there are any additional suggestions about where to put the port, while keeping in mind the design restrictions of the Monkey Coffin design.
Also remember it's not so much a question about "where the port samples the enclosure volume". The measurements in post 742 clearly show that the resonance at the entry of the long bottom port exists only if the port is open. The resonance does not exist when the port is closed. It is therefore not an internal resonance within the main enclosure that happens to be "sampled" by the port. It is rather the port itself that is involved in creating the resonance.
Also remember it's not so much a question about "where the port samples the enclosure volume". The measurements in post 742 clearly show that the resonance at the entry of the long bottom port exists only if the port is open. The resonance does not exist when the port is closed. It is therefore not an internal resonance within the main enclosure that happens to be "sampled" by the port. It is rather the port itself that is involved in creating the resonance.
Also, tmuikku's post #763 supports my view that it is the port placement in relation to box dimensions and driver placement, that are the cause of the undesired resonances.
It is completely fine that the slot port cannot be used, there is no sense in choosing a slot port, if the only place you can have it results in sub-par performance.
But if a solution can be to put a tube port with a bend inside the box, in the location of the completely useless implementation of a slot port, why is that not a viable solution?
It is a real alternative to having the port on the rear, and it would allow the box to be placed in a large number of different locations in the room, if the port is on the front you can even hang the speaker on a wall and it would be fine.
Put it on a counter back against a wall next to the aquarium or what else people might have.
If all my other arguments do not reach you, what about:
A rear port forces you to put the speaker on a stand, further away from the rear wall, takes more room, reduces the potential amount of people willing to build the design. Might as well make a tower speaker.
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I am struggeling to understand how to implement a front port with a bend in place of the original slot port at the bottom. The port will have to bend upwards around the woofer, so it will have to be very long. But maybe I am in the wrong boat... Can someone make a drawing, using the Monkey Coffin drawing in post 346 as a template?
Take a look at this:
http://www.fravolini.com/Kits/Vent-PC/VENT-PC%20Parte%202%20-%20AR%2099%20-%20novembre%201990.pdf
http://www.fravolini.com/Kits/Vent-PC/VENT-PC%20Parte%202%20-%20AR%2099%20-%20novembre%201990.pdf
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My Italian is crap, but this looks like a description of "ports" with exponentially increasing cross section. Does that somehow help us to decide WHERE to put the port?
Changing the front baffle dimensions would change the diffraction pattern. This would imply building a new prototype, repeating the far field SPL measurements (on axis, off axis), and then redo the xover design. Sounds like a huge effort just to try another option for the BR port.
Also, the port next to the mid or tweeter is not great for diffraction reasons (see earlier posts).
Two round ports below the woofer might work, but I don't see how they could bend around the woofer without getting very/too long. That's why I asked if someone could make a drawing.
Also, the port next to the mid or tweeter is not great for diffraction reasons (see earlier posts).
Two round ports below the woofer might work, but I don't see how they could bend around the woofer without getting very/too long. That's why I asked if someone could make a drawing.
Extending the baffle's lower edge does nothing to diffraction, practically. And neither does a small increase in volume to tuning.
Port diameter and length go hand-in-hand. If we use 2 tubes, each must be twice as long as a single tube. Makes it easier to bend them up.
I vote for 2 bent tubes below the woofer and a bit taller cabinet. Still, there will be some resonances in the cab and in port tubes... ¤75mm drain pipe
Port diameter and length go hand-in-hand. If we use 2 tubes, each must be twice as long as a single tube. Makes it easier to bend them up.
I vote for 2 bent tubes below the woofer and a bit taller cabinet. Still, there will be some resonances in the cab and in port tubes... ¤75mm drain pipe
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Hold your horses, If I calculated correctly the slot port is currently equal to two 100mm drain pipes, 30cm long. 75mm pipes would be too short and chuffing
IF hornresp MLTL model reflects to reality you could add panel between mid and tweeter and make the box ~12cm longer to get the woofer in the middle of the "pipe" and then there shouldn't be any 250hz resonance at the slot port. And you'd get some room for 100mm drain pipes and turn them up from the bottom. Just speculating here
IF hornresp MLTL model reflects to reality you could add panel between mid and tweeter and make the box ~12cm longer to get the woofer in the middle of the "pipe" and then there shouldn't be any 250hz resonance at the slot port. And you'd get some room for 100mm drain pipes and turn them up from the bottom. Just speculating here
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If anyone is interested I made some screenshots of the Hornresp model. Its made with Hornresp MLTL wizard from the monkey box drawing in post 346.
Check out the first attachment. Current woofer position where the woofer is ~212mm from the enclosure bottom there is the strong resonance at 250Hz visible in port output view (bottom right on the attachment) as well as in the combined output view (top right).
If one adjusts L12 so that the woofer is middle of the "pipe" the 250Hz resonance cancels out and is not showing at the port output anymore. 500Hz resonance is more pronounced here, but maybe easier to filter out by crossover and polyfill. See the other attachment.
Only thing changed between the attachments is the woofer location (L12, L23), huge difference.
If one simulates the same box from different perspective so that the port will stick from the box side or back panel (middle), the resonances are way higher up since box dimensions are shorter and the first resonance is cancelled since the woofer is in the middle of those dimensions. Didn't make any screenshots of these, one minute job to try yourself
I wish there was an option in hornresp to change the port location somehow
Anyway, a lesson here is don't put port at the end of an long enclosure and put woofer in the middle of the baffle to cancel out the lowest standing waves in the enclosure.
Check out the first attachment. Current woofer position where the woofer is ~212mm from the enclosure bottom there is the strong resonance at 250Hz visible in port output view (bottom right on the attachment) as well as in the combined output view (top right).
If one adjusts L12 so that the woofer is middle of the "pipe" the 250Hz resonance cancels out and is not showing at the port output anymore. 500Hz resonance is more pronounced here, but maybe easier to filter out by crossover and polyfill. See the other attachment.
Only thing changed between the attachments is the woofer location (L12, L23), huge difference.
If one simulates the same box from different perspective so that the port will stick from the box side or back panel (middle), the resonances are way higher up since box dimensions are shorter and the first resonance is cancelled since the woofer is in the middle of those dimensions. Didn't make any screenshots of these, one minute job to try yourself
I wish there was an option in hornresp to change the port location somehow
Anyway, a lesson here is don't put port at the end of an long enclosure and put woofer in the middle of the baffle to cancel out the lowest standing waves in the enclosure.
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