Screw-up by me--senior moment. In my reply just above I talk about 'dipolar' and 'dipole' but I meant to be discussing 'bipolar' and 'bipole'. Bipole is where you have a driver facing forward on the front baffle and a second driver facing to the back on the rear of the enclosure. The drivers are fed in phase signals so the sound produced is room filling with a broad polar plot without spatial dips in the response.
A dipole would result if the two drivers were fed out of phase so that a figure 8 polar plot (spatial dips to the sides in coverage around the enclosure) would be realized. This would also be the case for an open back driver on the front baffle. The spatial dips are when the signals to the drivers propagate around the sides of the enclosure and cancel each other.
A dipole would result if the two drivers were fed out of phase so that a figure 8 polar plot (spatial dips to the sides in coverage around the enclosure) would be realized. This would also be the case for an open back driver on the front baffle. The spatial dips are when the signals to the drivers propagate around the sides of the enclosure and cancel each other.
So I'm building a set of these, and I'm at the stage of sizing the bass port/tube. I have on hand 2.0" and 3.0" ID tubing material, but no 2.5" ID as specified by Dr Jim. Should I really go get some 2.5" material for the best sound, or does it make no real difference, as long as I adjust the port length for the ID, per the formula posted earlier in this thread?
I don't mind buying the right size if it makes an audible difference, but I'd like to use the 2" material I have, if it's just as good, sonically speaking.
I don't mind buying the right size if it makes an audible difference, but I'd like to use the 2" material I have, if it's just as good, sonically speaking.
Elmojo
As posted by giantstairs, for 10.3M:
https://www.diyaudio.com/forums/ful...udio-alpair-10-3-a10p-mltl-4.html#post4766726
Or 3,20" (~81mm) for 10P
Cheers
So I'm building a set of these, and I'm at the stage of sizing the bass port/tube. I have on hand 2.0" and 3.0" ID tubing material, but no 2.5" ID as specified by Dr Jim. Should I really go get some 2.5" material for the best sound, or does it make no real difference, as long as I adjust the port length for the ID, per the formula posted earlier in this thread?
I don't mind buying the right size if it makes an audible difference, but I'd like to use the 2" material I have, if it's just as good, sonically speaking.
As posted by giantstairs, for 10.3M:
https://www.diyaudio.com/forums/ful...udio-alpair-10-3-a10p-mltl-4.html#post4766726
Or 3,20" (~81mm) for 10P
Cheers
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Thanks for the links guys, but that's not what I'm asking.
Maybe I wasn't clear, let me try again...
I'm aware of how to calculate the change in port length for different diameters. Jim specifies a 2.5"dia. x 6" long port for this MLTL enclosure. I only have 2" material on hand. If I use the formula in the PDF Dave showed above, for a 2"ID port, I get a length of 4.1", with end correction included.
My question is this: will a 2" port of 4.1" length sound the same as a 2.5" port of 6" length, or is it just the best compromise available? I don't understand the underlying concept of exactly how the calculation of bass ports works, which is why I'm asking the experts. If a 2"x4.1" port is truly no different in performance, then I'll build it that way and move on. However, if using a 2" port rather than a 2.5" port would result in a degradation in sound quality or performance of the enclosure, then I'd prefer to wait until I could source some 2.5" material and do it "right".
Maybe I wasn't clear, let me try again...
I'm aware of how to calculate the change in port length for different diameters. Jim specifies a 2.5"dia. x 6" long port for this MLTL enclosure. I only have 2" material on hand. If I use the formula in the PDF Dave showed above, for a 2"ID port, I get a length of 4.1", with end correction included.
My question is this: will a 2" port of 4.1" length sound the same as a 2.5" port of 6" length, or is it just the best compromise available? I don't understand the underlying concept of exactly how the calculation of bass ports works, which is why I'm asking the experts. If a 2"x4.1" port is truly no different in performance, then I'll build it that way and move on. However, if using a 2" port rather than a 2.5" port would result in a degradation in sound quality or performance of the enclosure, then I'd prefer to wait until I could source some 2.5" material and do it "right".
I'm not sure if this will be of help to anyone, but my future self was being lazy, and didn't want to have to do that port change formula every time I needed to calculate a potential port length or size, so I made a small excel spreadsheet that allows typing in the known data, and it spits out the numbers. See, told you I was lazy.
I'd love to edit the sheet to give credit to the original creator(s) of the PDF I chopped up to make this, but it didn't have any ownership info on it. If whomever is responsible for that PDF will let me know, I'll be happy to attribute your work. This is assuming you're ok with me using your graphic at all. If not, I'll take it off. I just thought it was handy to have a visual for reference.
I'm including both a current version (XLSX) and legacy version (XLS) of the file, for those who may have older versions of excel, or need to open it in a non-Microsoft program.
The forum will not allow me to upload Excel files directly, so they will have ".zip" extensions. Just rename the file to match the corresponding name (ie port calc_xls.zip, rename to port calc.xls)
Moderater Edit: attachments removed at poster’s request, updated version sin post #254
I'd love to edit the sheet to give credit to the original creator(s) of the PDF I chopped up to make this, but it didn't have any ownership info on it. If whomever is responsible for that PDF will let me know, I'll be happy to attribute your work. This is assuming you're ok with me using your graphic at all. If not, I'll take it off. I just thought it was handy to have a visual for reference.
I'm including both a current version (XLSX) and legacy version (XLS) of the file, for those who may have older versions of excel, or need to open it in a non-Microsoft program.
The forum will not allow me to upload Excel files directly, so they will have ".zip" extensions. Just rename the file to match the corresponding name (ie port calc_xls.zip, rename to port calc.xls)
Moderater Edit: attachments removed at poster’s request, updated version sin post #254
I believe the concern with using smaller diameter tube is not that the sound will change (it won't if length is adjusted accordingly, as the tuning will then be the same), but rather that the port velocity may increase to the point where chuffing can be heard.
You could ordinarily compensate by using 2 ports of twice the length. I'm guessing for an MLTL design where port location is specified, the 2 ports should be placed side by side (ie same distance from the driver).
You could ordinarily compensate by using 2 ports of twice the length. I'm guessing for an MLTL design where port location is specified, the 2 ports should be placed side by side (ie same distance from the driver).
Thanks Dave, I'll edit the file to credit you. How would you like the notation listed?
So, my build is coming along pretty well, but I have a question.
I'm not sure I've put in enough polyfill. I stuffed in what I could reasonably get in through the driver hole, but now I notice that I have more left over than I should.
What's the effect of too little stuffing?
Cool, thanks Dave. I'll edit and repost.
As for my other question...
What's the effect of not putting the specified amount of polyfill in my enclosure?
I see references to tuning by adding and removing stuffing, but I don't know what sort of changes I'm listening for. It would be a challenge to get the amount of fill Dr Jim spec'd in the OP into this space, due to the bracing, but I'll give it a shot if it's likely to make a big difference.
As for my other question...
What's the effect of not putting the specified amount of polyfill in my enclosure?
I see references to tuning by adding and removing stuffing, but I don't know what sort of changes I'm listening for. It would be a challenge to get the amount of fill Dr Jim spec'd in the OP into this space, due to the bracing, but I'll give it a shot if it's likely to make a big difference.
Here's the revised version of the port length calculator spreadsheet, including the attribution line for Dave's beautiful graphic.
I'm including both a current version (XLSX) and legacy version (XLS) of the file, for those who may have older versions of excel, or need to open it in a non-Microsoft program.
Due to file type restrictions, just remove the ".zip" extension to get the real file name.
Dave: can you delete the attachment (or entire post) in #246, so that only this one with the credit line appears?
I'm including both a current version (XLSX) and legacy version (XLS) of the file, for those who may have older versions of excel, or need to open it in a non-Microsoft program.
Due to file type restrictions, just remove the ".zip" extension to get the real file name.
Dave: can you delete the attachment (or entire post) in #246, so that only this one with the credit line appears?
The damping is to try to remove the unwanted quarter-wave harmonics. Too little and you will have more bass, but more ripple higher up. Too much will kill the bass, just right gives appropriate bass and sufficient ripple removal.
How much you need will depend as well on room, room placement, taste, and the amplifier you use.
dave
Elmojo,
I suggest that you do not 'try to cram in some more'. I recommend that you place the damping in the internal space from 2-3" below the driver to the top of enclosure. I tease the polyfill (pull it apart to eliminate clumps) and then insert it into the box. Do not cram it in the volume! If too much damping is used you will over damp the radiated sound and the results will not sound as natural as it should.
Best results for uniformity of the damping fill would be to use the bonded Dacron sold by Meniscus Audio. See this link:
Bonded Dacron - Meniscus Audio
for details. Cut sheets to fit and place them inside the enclosure to fill the volume.
Jim
I suggest that you do not 'try to cram in some more'. I recommend that you place the damping in the internal space from 2-3" below the driver to the top of enclosure. I tease the polyfill (pull it apart to eliminate clumps) and then insert it into the box. Do not cram it in the volume! If too much damping is used you will over damp the radiated sound and the results will not sound as natural as it should.
Best results for uniformity of the damping fill would be to use the bonded Dacron sold by Meniscus Audio. See this link:
Bonded Dacron - Meniscus Audio
for details. Cut sheets to fit and place them inside the enclosure to fill the volume.
Jim
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Thanks for the excellent tips Jim.
However, I'm confused about something you can perhaps clarify for me.
In post #1, you state a fill density of 0.75lb/ft3. This enclosure is just a hair over 1ft3, so I calculate a required fill of roughly 12.5oz per enclosure, in the top half of the box.
In order to get that much stuffing in the box, I have to pack it in fairly tight. I don't have the option of using that bonded dacron you linked (materials already ordered, cabinets sealed), and perhaps it's heavier than the polyfil material I'm using. What else could I be missing?
I was able to get the specified amount of material in both boxes and get them buttoned up, and they sound fine as far as I can tell. My ears aren't trained enough to tell the difference, to be honest.
I'm a little disappointed that these speakers aren't louder overall, but that could be because I'm currently driving them off of a small board amp in my shop. They sounded about the same before I put any stuffing in them, so I don't think that has anything to do with the volume. I'm hoping that once I get them inside and connected to a proper amp, they will sound better. At least I hope so. I have a lot of time and money tied up in these, and they are to be a gift for a friend. :/
However, I'm confused about something you can perhaps clarify for me.
In post #1, you state a fill density of 0.75lb/ft3. This enclosure is just a hair over 1ft3, so I calculate a required fill of roughly 12.5oz per enclosure, in the top half of the box.
In order to get that much stuffing in the box, I have to pack it in fairly tight. I don't have the option of using that bonded dacron you linked (materials already ordered, cabinets sealed), and perhaps it's heavier than the polyfil material I'm using. What else could I be missing?
I was able to get the specified amount of material in both boxes and get them buttoned up, and they sound fine as far as I can tell. My ears aren't trained enough to tell the difference, to be honest.
I'm a little disappointed that these speakers aren't louder overall, but that could be because I'm currently driving them off of a small board amp in my shop. They sounded about the same before I put any stuffing in them, so I don't think that has anything to do with the volume. I'm hoping that once I get them inside and connected to a proper amp, they will sound better. At least I hope so. I have a lot of time and money tied up in these, and they are to be a gift for a friend. :/
By weight you should calculate the stuffing weight by only the portion of the cabinet that contains stuffing. The stuffed volume you actual use is only about 1/3rd to at most 1/2 of the total cabinet volume. No stuffing should fill the volume from 2-3 inches below the driver and downward. The beauty of the bonded Dacron is that it is 0.75 lbs per cubic foot so all you do is cut and stack it to fit the volume around and above the driver.
I suspect that you have enough stuffing without adding any additional amount at this point. I insert all of the stuffing via the speaker cutout so a closed cabinet isn't a problem.
Stuffing will not add volume to the sound that you hear but it will damp out and flatten the peaks and dips that you would experience without it.
I suspect that you have enough stuffing without adding any additional amount at this point. I insert all of the stuffing via the speaker cutout so a closed cabinet isn't a problem.
Stuffing will not add volume to the sound that you hear but it will damp out and flatten the peaks and dips that you would experience without it.
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Aha! That explains a lot, thanks.
That's different than the instructions in Post #1, hence my confusion.
I've got them both fully stuffed (too much as it seems) and buttoned up, so I'm not sure if it's worth pulling the drivers out to remove stuffing or not. What do you think Jim? Is the effect of too much stuffing likely to be noticeable enough to warrant removing some of it? From what you said above, it seems like I have about twice as much in there as there should be.