So, I'd like to keep the 21" cabinet's external dimensions to similar to my small 15" subs, which are around 450mm square at the front. I figure I could make the 21" sub 450x900 for the same frontal area as a pair of the 15"s.
Here's a quick comparison of a couple of designs for the 21". Both are just short of 200L, bottom port tuning of 37Hz.
Black line is ported, grey line is slot-loaded. With the larger ported chamber, the standard ported design wins right at the bottom end.
I'd quite like to go with the slot-loaded design, but building the cabinet so that the driver is removable will be difficult - the panel over the driver needs to be very strong, but also removable.
The 21" driver itself is around 10" deep, with the magnet being a significant chunk of that. I'm thinking about cutting a hole in the panel making up the port, so that the magnet vents part-way along the port - should keep things cool in there, but getting a good seal might be difficult. Definitely not impossible, though.
The 21" ported would match the 4x 15"s I have for output, so I'd probably be looking at 6dB more output, though the extra cabinet won't be small. Using this driver sealed (same as the 15"s) would net me around 3dB more output. Problem is, though, that a sealed box that just goes around the 21" driver is a touch over 100L.
Stuff to think about. Off to work now.
Chris
Here's a quick comparison of a couple of designs for the 21". Both are just short of 200L, bottom port tuning of 37Hz.
Black line is ported, grey line is slot-loaded. With the larger ported chamber, the standard ported design wins right at the bottom end.
I'd quite like to go with the slot-loaded design, but building the cabinet so that the driver is removable will be difficult - the panel over the driver needs to be very strong, but also removable.
The 21" driver itself is around 10" deep, with the magnet being a significant chunk of that. I'm thinking about cutting a hole in the panel making up the port, so that the magnet vents part-way along the port - should keep things cool in there, but getting a good seal might be difficult. Definitely not impossible, though.
The 21" ported would match the 4x 15"s I have for output, so I'd probably be looking at 6dB more output, though the extra cabinet won't be small. Using this driver sealed (same as the 15"s) would net me around 3dB more output. Problem is, though, that a sealed box that just goes around the 21" driver is a touch over 100L.
Stuff to think about. Off to work now.
Chris
Do you mean so the driver slides in sideways?
Possible, but getting all the mounting screws tight might be difficult.
I'm still playing around in SketchUp. Getting a driver this big into this form factor is proving interesting.
Chris
Possible, but getting all the mounting screws tight might be difficult.
I'm still playing around in SketchUp. Getting a driver this big into this form factor is proving interesting.
Chris
yes thats what i mean.
use hexacon bolts with t-nuts and something to keep the driver in positsion .
that way you can brace the port and cavity
use hexacon bolts with t-nuts and something to keep the driver in positsion .
that way you can brace the port and cavity
you loose 10~15 ltr netto in br ,if the woofer/baffle is recest in the front say 3 or 4 cm.
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Quick update - I've a fairly big outdoor gig in 2 weeks time, so I'm just going to knock together a sealed box big enough to go around the driver. 600x600x400mm ext dimensions.
The sealed design will play well with the 15"s I have, and is the smallest design possible for this driver, so that's what it'll have to be.
Very boring, I know. Apologies.
The full system (4x15", 1x21", all sealed) will be capable of around 120dB @1m at 20Hz outdoors, or more like 130dB from 40Hz and up. Not bad, though I'm aware that a couple of ported 18"s could match the latter figure.
Amp will be either one channel of an NU6000, or a bridged C.Audio RA3001, whichever gives me more power.
I've got a busy few weeks with gigs and work, so once those are over I'm going to look more seriously at tapped horns and ported boxes for the drivers I have.
That's all for now.
Chris
The sealed design will play well with the 15"s I have, and is the smallest design possible for this driver, so that's what it'll have to be.
Very boring, I know. Apologies.
The full system (4x15", 1x21", all sealed) will be capable of around 120dB @1m at 20Hz outdoors, or more like 130dB from 40Hz and up. Not bad, though I'm aware that a couple of ported 18"s could match the latter figure.
Amp will be either one channel of an NU6000, or a bridged C.Audio RA3001, whichever gives me more power.
I've got a busy few weeks with gigs and work, so once those are over I'm going to look more seriously at tapped horns and ported boxes for the drivers I have.
That's all for now.
Chris
So, the 21" driver has a box, and is currently in the living room.
Even having built the smallest box around the driver I could, and using a neodymium driver, its still heavy and bulky. I guess that's what happens when you use 21" drivers.
I also killed my RA3001 amp while testing. Played a sine wave for a while, sounded a bit weird. Kinda like crossover distortion, and there wasn't much bass at all. Turned it up a bit, and the driver suddenly stopped after a second or two. I hadn't killed the driver, but the amp won't power on any more (fuses check fine).
Tried an EP1500 instead, and suddenly the sub came alive. The RA3001 was, apparently, quite ill before it finally quit. Shame, really - bridged, it had the most voltage swing of any of my amplifiers.
I'm currently using the sub with one side of an NU6000DSP, with the other side driving an 8" coaxial monitor. Two filters on the bass, amounting to around 21dB of boost at 20Hz. The low-end extension is great for HT, though that amount of boost (and LF extension) isn't worthwhile for PA use. 10dB of boost at 30Hz, or 6dB at 40Hz is more like it.
Got an outdoor gig coming up, which is why I rushed this through. I need to apply some wood stain, cut the grille, and make sure everything's air tight before Saturday. Shouldn't be too difficult.
I have to say, I'm very impressed with the sound of this thing. Its running up to 120Hz and there's plenty of "snap", which is at odds to the very large cone in front of me - you might expect that "slow bass" that people keep talking about with such a big driver, but nope, it just works. First light on the NU6000DSP (-20dB) results in rattly windows. I haven't taken it any further, but be assured, this cabinet will see some power on Saturday.
Chris
Even having built the smallest box around the driver I could, and using a neodymium driver, its still heavy and bulky. I guess that's what happens when you use 21" drivers.
I also killed my RA3001 amp while testing. Played a sine wave for a while, sounded a bit weird. Kinda like crossover distortion, and there wasn't much bass at all. Turned it up a bit, and the driver suddenly stopped after a second or two. I hadn't killed the driver, but the amp won't power on any more (fuses check fine).
Tried an EP1500 instead, and suddenly the sub came alive. The RA3001 was, apparently, quite ill before it finally quit. Shame, really - bridged, it had the most voltage swing of any of my amplifiers.
I'm currently using the sub with one side of an NU6000DSP, with the other side driving an 8" coaxial monitor. Two filters on the bass, amounting to around 21dB of boost at 20Hz. The low-end extension is great for HT, though that amount of boost (and LF extension) isn't worthwhile for PA use. 10dB of boost at 30Hz, or 6dB at 40Hz is more like it.
Got an outdoor gig coming up, which is why I rushed this through. I need to apply some wood stain, cut the grille, and make sure everything's air tight before Saturday. Shouldn't be too difficult.
I have to say, I'm very impressed with the sound of this thing. Its running up to 120Hz and there's plenty of "snap", which is at odds to the very large cone in front of me - you might expect that "slow bass" that people keep talking about with such a big driver, but nope, it just works. First light on the NU6000DSP (-20dB) results in rattly windows. I haven't taken it any further, but be assured, this cabinet will see some power on Saturday.
Chris
how much liters is it netto?
because even a small high tuned br(around 38 helmholz)has more output down low+ les excursion above the hpf
keep us posted
because even a small high tuned br(around 38 helmholz)has more output down low+ les excursion above the hpf
keep us posted
Its around 100L, after bracing and driver displacement.
Problem with ports is getting enough area (and length) into the cabinet to avoid compression.
Using something sensible length = 30cm, area = 200cm^2, tuning ~39Hz...
Port velocity peaks over 40m/s, which will result in a lot of compression.
To get the velocity to around 18m/s needs a 500cm^2, 80cm long port, which is 40 litres of cabinet volume.
Ideally, I'd build a big tapped horn or quarter-wave enclosure that won't have these problems. Those cabinets are much larger, though, so I'll only build those for the 15"s.
This 21" will be used for PA for now, and probably home use when I get some THs done.
Chris
Edit - I'm glad I went for a cabinet this size (around 600x600x400 ext). The 200L designs further up would've been too big to move alone.
Problem with ports is getting enough area (and length) into the cabinet to avoid compression.
Using something sensible length = 30cm, area = 200cm^2, tuning ~39Hz...
Port velocity peaks over 40m/s, which will result in a lot of compression.
To get the velocity to around 18m/s needs a 500cm^2, 80cm long port, which is 40 litres of cabinet volume.
Ideally, I'd build a big tapped horn or quarter-wave enclosure that won't have these problems. Those cabinets are much larger, though, so I'll only build those for the 15"s.
This 21" will be used for PA for now, and probably home use when I get some THs done.
Chris
Edit - I'm glad I went for a cabinet this size (around 600x600x400 ext). The 200L designs further up would've been too big to move alone.
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imo 300~400 to get it below 25m/s
but stil you need a long port
( i always end up with a much shorter port then winisd calculates)
but stil you need a long port
( i always end up with a much shorter port then winisd calculates)
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Couple of pictures. Definitely needed the extra LF at the gig.
The 21" did its job well, though it was a real pain to move around. It won't be used often, that's for sure.
Bracing:
Cabinet, iPad for scale.
At the gig, 1x15 & 1x21 one side, 3x15 at the other.
Chris
The 21" did its job well, though it was a real pain to move around. It won't be used often, that's for sure.
Bracing:
Cabinet, iPad for scale.
At the gig, 1x15 & 1x21 one side, 3x15 at the other.
Chris
Good build Chris. This and your PA thread makes interesting reading.
Question for you: have you weighed the completed item? The reason I ask is that on the face of it, a very lightweight 21" sub in a 100l box oughtn't to be too much of a job to shift. Be very interested to know how much it all weighs.
Reason I'm particularly interested is that I've built some subs recently: 85l reflex loaded with Celestion FTR15-4080HDX. I too have found these rather heavy but the drivers are less than 10kg each. The rest of the weight is in the 18mm birch ply (~21kg).
Given that less than 10kg is very good for a driver with the output capabilities of the "HDX", it got me thinking that the problem with portability and weight isn't so much these days with the drivers, as with the wood used in the box.
Same would apply with your 15kg(?) SD21's if they're a difficult lift even in 100l boxes.
If there were an alternative to 18mm birch ply with similar characteristics - even 25% lighter would be a bigger difference in weight in most practically sized boxes than Ferrite vs. Neo.
As far as I've got to date is looking into compressed recycled plastic sheet, but who knows what the audio properties are... I've seen some other builds using "foamcore", but not sure how suitable that would be for a huge 21" cab.
Question for you: have you weighed the completed item? The reason I ask is that on the face of it, a very lightweight 21" sub in a 100l box oughtn't to be too much of a job to shift. Be very interested to know how much it all weighs.
Reason I'm particularly interested is that I've built some subs recently: 85l reflex loaded with Celestion FTR15-4080HDX. I too have found these rather heavy but the drivers are less than 10kg each. The rest of the weight is in the 18mm birch ply (~21kg).
Given that less than 10kg is very good for a driver with the output capabilities of the "HDX", it got me thinking that the problem with portability and weight isn't so much these days with the drivers, as with the wood used in the box.
Same would apply with your 15kg(?) SD21's if they're a difficult lift even in 100l boxes.
If there were an alternative to 18mm birch ply with similar characteristics - even 25% lighter would be a bigger difference in weight in most practically sized boxes than Ferrite vs. Neo.
As far as I've got to date is looking into compressed recycled plastic sheet, but who knows what the audio properties are... I've seen some other builds using "foamcore", but not sure how suitable that would be for a huge 21" cab.
Hi Mark,
I haven't weighed the completed cabinet, but I'd estimate 30kg. I think it's the bulk of the cabinet that's the problem. I'm happy moving SSE Betamax around, which are 43kg, but easy enough to get your arms round. This box makes doorways and the like a challenge.
For this build, I doubled up the front baffle, so I'd guess I used somewhere around 3/4 of a sheet of 18mm ply. That's probably most of the weight there.
I'll be posting more updates on my PA thread in due course. For now, I'm messing with sims for these Beyma drivers. They can do much more than I'm letting them at the moment.
Chris
I haven't weighed the completed cabinet, but I'd estimate 30kg. I think it's the bulk of the cabinet that's the problem. I'm happy moving SSE Betamax around, which are 43kg, but easy enough to get your arms round. This box makes doorways and the like a challenge.
For this build, I doubled up the front baffle, so I'd guess I used somewhere around 3/4 of a sheet of 18mm ply. That's probably most of the weight there.
I'll be posting more updates on my PA thread in due course. For now, I'm messing with sims for these Beyma drivers. They can do much more than I'm letting them at the moment.
Chris
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