I've currently got a pair of Pensil speakers that have the Alpair 10 drivers in them but I've been taken with the idea of a spherical speaker.
How do I work out what internal area and port size and length I would need to make these drivers work?
How do I work out what internal area and port size and length I would need to make these drivers work?
If you are happy with the current boxes, measure the internal volume and port and work from there. This will keep the frequency response as it is now
Volume of a cuboid is length x width x height
Radius of a sphere = ((Volume/pi) x (3/4))^1/3
Brian
Volume of a cuboid is length x width x height
Radius of a sphere = ((Volume/pi) x (3/4))^1/3
Brian
Tyler,
The Pensils are a MLTL variant, and for that design in addition to the cabinet volume other factors matter - line length, driver position, port distance and port dimensions. It is unlikely you shall be able to maintain those for a very different enclosure like a sphere. Rather look at bass reflex cabinets for your Alpair 10 and see how much volume you need (probably 15-16 liters) and what port size you need. Basically you will have a spherical reflex cabinet vs a rectangular enclosure.
The Pensils are a MLTL variant, and for that design in addition to the cabinet volume other factors matter - line length, driver position, port distance and port dimensions. It is unlikely you shall be able to maintain those for a very different enclosure like a sphere. Rather look at bass reflex cabinets for your Alpair 10 and see how much volume you need (probably 15-16 liters) and what port size you need. Basically you will have a spherical reflex cabinet vs a rectangular enclosure.
Edit: Z beat me to it, but keeping it up FWIW.
Unfortunately the pensils are MLTL variations and the physical dimensions (length, driver position along that &c.) are functional parts of the alignment. I know, because I designed them. 😉 They're also acoustically large designs, in today's parlance at any rate, so even if those were not factors, the sphere would be quite substantial.
That being said, the underlying point is sound in terms of Helmholtz loading, so size the sphere volume according to your desired vented box volume & tuning (if you can't design it yourself, pick an existing example and simply use a sphere of equivalent volume with the same vent dimensions). Note that you may need some additional internal damping as, in theory at least, a sphere has a powerful central eigenmode due to all points being equidistant. In practice there is some disruption due to the driver and vent arrangements, but worth keeping in mind so you're not surprised. Baffle step may be a bit different, but the A10 has a bit of inherent compensation in its response, so unless there are large variations, it should be ~'near enough', or at least in the ballpark.
Unfortunately the pensils are MLTL variations and the physical dimensions (length, driver position along that &c.) are functional parts of the alignment. I know, because I designed them. 😉 They're also acoustically large designs, in today's parlance at any rate, so even if those were not factors, the sphere would be quite substantial.
That being said, the underlying point is sound in terms of Helmholtz loading, so size the sphere volume according to your desired vented box volume & tuning (if you can't design it yourself, pick an existing example and simply use a sphere of equivalent volume with the same vent dimensions). Note that you may need some additional internal damping as, in theory at least, a sphere has a powerful central eigenmode due to all points being equidistant. In practice there is some disruption due to the driver and vent arrangements, but worth keeping in mind so you're not surprised. Baffle step may be a bit different, but the A10 has a bit of inherent compensation in its response, so unless there are large variations, it should be ~'near enough', or at least in the ballpark.
If you’re going to put them in a spherical enclosure just go for a sealed alignment, otherwise you will end up with quite a big ball for a speaker which will not be easy to make. Model it with T/S parameters. You’ll lose low end a bit but have a shallower roll off.
How are you going to make the sphere?
How are you going to make the sphere?
Great stuff guys. Knowing what I do now I may well leave the pensils as they are and look at some other drivers to use.
The spheres are likely to be made from a pair of wooden bowls from Ikea, looks like all the information I might need is in this thread.
Ikea spherical speakers, first build done.
The spheres are likely to be made from a pair of wooden bowls from Ikea, looks like all the information I might need is in this thread.
Ikea spherical speakers, first build done.
+1 on the sealed idea which could work very very well in a 2.1 full range + subwoofer Since you already like the Alpair 10 I would guess one of the Alpairs would be ideal
Quick call using the mh-audio site.
For the Alpair 10’s gives
14l bass reflex with a 2”Dian by 6” long port for f3 at 51hz. 14l sphere is a diameter of 30cm (1ft) then add a little for the port and the driver and the cutoff for the speaker mounting, I would expect it to be nearer 40cm by the time you take that into account.
6.5l sealed box with Q=7.07 with f3 of 85hz. 6.5l sphere is a diameter of 23cm, again taking all of the other bits into account the you will be nearer 30cm.
These are internal dimensions. Spheres can get big pretty quickly.
These are only quick calls but gives you an idea.
For the Alpair 10’s gives
14l bass reflex with a 2”Dian by 6” long port for f3 at 51hz. 14l sphere is a diameter of 30cm (1ft) then add a little for the port and the driver and the cutoff for the speaker mounting, I would expect it to be nearer 40cm by the time you take that into account.
6.5l sealed box with Q=7.07 with f3 of 85hz. 6.5l sphere is a diameter of 23cm, again taking all of the other bits into account the you will be nearer 30cm.
These are internal dimensions. Spheres can get big pretty quickly.
These are only quick calls but gives you an idea.
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