Hi,
I am working on a project where the cabinet is a small bass reflex (~5.3 liters).
Space is tight, and I would like to give the reflex port close to 1 diameter clearance from the inside walls. The port internal diameter is 32 mm (1-1/4 inches).
I have 3 options in mind - have attached rough illustrations of each (not drawn to scale).
First 2 options use a straight port attached to a 3D printed flare attached to a 32mm inner diameter PVC pipe. The third option uses an PVC elbow joint which is attached to the 32mm pipes on both ends, and one of the pipes is attached to the flare.
Would be good to hear what the good folks of the forum think. 🙂
I am working on a project where the cabinet is a small bass reflex (~5.3 liters).
Space is tight, and I would like to give the reflex port close to 1 diameter clearance from the inside walls. The port internal diameter is 32 mm (1-1/4 inches).
I have 3 options in mind - have attached rough illustrations of each (not drawn to scale).
First 2 options use a straight port attached to a 3D printed flare attached to a 32mm inner diameter PVC pipe. The third option uses an PVC elbow joint which is attached to the 32mm pipes on both ends, and one of the pipes is attached to the flare.
Would be good to hear what the good folks of the forum think. 🙂
Attachments
I prefer the first one, I like my sound to launch from the same plane...(probably irrelevant). Any are OK, 2&3 will give a less cluttered look, so what's your aesthetic preference? For flares, I use a 45 degree router bit after I've glued the port to the baffle. FWIW, I also wrap the pipe in felt, and put a felt patch on the wall opposite the internal port end.
Jeff,
Thanks for chiming in.
I should have mentioned - I did think about a slot port - but I might be experimenting with slightly different port lengths, and with a slot port I wouldn't be able to do that. Again maybe by using spacers within the slot, I might be able to alter the tuning by lower the port CSA but keeping length same, hence lower tuning.
The driver is the Dayton TCP115-4.
Thanks for chiming in.
I should have mentioned - I did think about a slot port - but I might be experimenting with slightly different port lengths, and with a slot port I wouldn't be able to do that. Again maybe by using spacers within the slot, I might be able to alter the tuning by lower the port CSA but keeping length same, hence lower tuning.
The driver is the Dayton TCP115-4.
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PeteMcK,
Thanks for your comments.
The flare part is to make the port easily removable once the cabinet is sealed. Just take of the screws and the flare and port assembly comes out together.
You are spot on with your observation with limited vertical space at the front. If I make the cab taller, then I lose depth and cannot accommodate the port. Didn't earlier realize that a small cabinet can throw up this problem. 🙂
Thanks for your comments.
The flare part is to make the port easily removable once the cabinet is sealed. Just take of the screws and the flare and port assembly comes out together.
You are spot on with your observation with limited vertical space at the front. If I make the cab taller, then I lose depth and cannot accommodate the port. Didn't earlier realize that a small cabinet can throw up this problem. 🙂
Having the port exit on the back means any chuffing noises it makes are MUCH less audible
Most small speakers use the 2nd one with the port exit at the rear and usually in line with the tweeter. You could always increase the depth to have greater clearance to the port entry.
If you're going to significantly undersize the port for air velocity, consider putting it on the back (chuffing less audible). But if you will size it up so its large enough to be chuff-free, it can be a nice option to have it on the same baffle as the driver. Less bends/folding is ideal.
Very best,
Very best,
One has to remember that the other name for bass reflex vent is "phase invertor". Being in the same plane is likely to cause issues when vent and driver are in close proximity.
The cabinet internal depth is 18 cm.
Port length is 14 cm and cabinet wall thickness is 1.2 cm (~1/2 inch). So 12.8 cm of the port will be inside of the cabinet.
The woofer basket and magnet protrudes ~5 cm inside the cabinet.
If I bring the port position opposite to the tweeter, I have ~5 cm distance distance from the port mouth to the inside wall; but the space above the woofer magnet is only 7 cm. If I choose the center of that and place the 32 mm port accordingly, the port will be around 1.9 cm away from the inside of top, and 1.9 cm way from the back of the woofer - both look too close to me.
If I increase the depth I need to decrease the height in order to keep the volume the same; do not want to make the speaker depth and height almost the same.
If I use the flare and elbow joint option, the elbow is ~3 cm away from the woofer magnet and the entry of the port can be placed away with adequate distance from the inside walls and also further away from the back of the woofer vs the other options.
I am leaning towards the option with the elbow joint, with port exit at the back.
Allows me to place the XO on the inside floor and install the speaker terminals below the port .
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If you consider 3d printing you could go for an optimized port geometry:
https://www.diyaudio.com/community/...rbers-and-port-geometries.388264/post-7943524
(Soon to be updated to version 0.2)
re:'Being in the same plane is likely to cause issues when vent and driver are in close proximity' - in theory, perhaps, but I have never had any issues doing it this way
re:'chuffing noises' - do you really listen to music at volumes that cause this?
re:'chuffing noises' - do you really listen to music at volumes that cause this?
PeteMcK,
For this small speaker and it's application, the SPL is not likely to be high; so for me, no.🙂
But in certain cases there are smallish (for a sub woofer) drivers e.g. Tang Band W6-1139 that have high excursion, and when using narrow ports people have complained of audible chuffing noises. The TB W6-1139 is able to go fairly low in a compact box, but fitting the port inside can become a challenge; a port with bigger diameter means a longer port for the same tuning...
For this small speaker and it's application, the SPL is not likely to be high; so for me, no.🙂
But in certain cases there are smallish (for a sub woofer) drivers e.g. Tang Band W6-1139 that have high excursion, and when using narrow ports people have complained of audible chuffing noises. The TB W6-1139 is able to go fairly low in a compact box, but fitting the port inside can become a challenge; a port with bigger diameter means a longer port for the same tuning...
Only somewhat below tuning frequency the port output is getting near 180° of driver phase (or "inverted"). At these frequencies radiation is omnidirectional and speaker dimensions are far smaller than wavelengths, so vent and driver are "in close proximity" anyway.
As with any vented enclosure, the vent is in phase.
The out of phase proportion is what creates any standard cutoff rate.
The whole thing that makes the transfer function alignment what It is, the udder basic science of a port.
Nothing will ever change that, being close to the speaker more ideal.
The port is already close to the lower boundary and rear boundary.
No big deal, its length will actually be shorter to reach desired Fb.
Standard port with no boundary has end correction of .7 or .732 to be exact.
This port is leaning more towards .8 to .830 end correction.
That is why the " rule of thumb" is to not be too close to a boundary.
But if it is, not the end of the world. It just changes the end correction, or actually makes the length = shorter
People seem to be concerned with the " rear wall distance" when in a small enclosure it is already close to the lower boundary too.
So who cares. Change the end correction it will be shorter anyways.
The port can actually rest on the lower portion of the cabinet if you wanted it too.
Being round it likely wont take it to the full 1.23 end correction. but could take it up to .9
Same thing just make it shorter.
The out of phase proportion is what creates any standard cutoff rate.
The whole thing that makes the transfer function alignment what It is, the udder basic science of a port.
Nothing will ever change that, being close to the speaker more ideal.
The port is already close to the lower boundary and rear boundary.
No big deal, its length will actually be shorter to reach desired Fb.
Standard port with no boundary has end correction of .7 or .732 to be exact.
This port is leaning more towards .8 to .830 end correction.
That is why the " rule of thumb" is to not be too close to a boundary.
But if it is, not the end of the world. It just changes the end correction, or actually makes the length = shorter
People seem to be concerned with the " rear wall distance" when in a small enclosure it is already close to the lower boundary too.
So who cares. Change the end correction it will be shorter anyways.
The port can actually rest on the lower portion of the cabinet if you wanted it too.
Being round it likely wont take it to the full 1.23 end correction. but could take it up to .9
Same thing just make it shorter.
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I've built a lot of small speakers and that port length looks too long. For 5.3 litres with 32 x 140mm gives Fb around 53Hz which is below driver Fs. Fb maybe would be better 55-60Hz but don't know the driver but would give a shorter port 100 - 130mm so would have ample clearance.
A good reference would be Jeff Bagby's Soprano which was 4.7 litres 35 x 104 port for Fb around 62Hz. Have a read of Jeff's article and his take on a small hump of 2-3dB before roll off to make the speaker sound more balanced. In addition read the whole article on the choices and BTW, the Soprano is a great but under rated speaker as drowned out by his more expensive creations.
A good reference would be Jeff Bagby's Soprano which was 4.7 litres 35 x 104 port for Fb around 62Hz. Have a read of Jeff's article and his take on a small hump of 2-3dB before roll off to make the speaker sound more balanced. In addition read the whole article on the choices and BTW, the Soprano is a great but under rated speaker as drowned out by his more expensive creations.