Yet another "large" coax build Celestion FTX1225 (ongoing, advice needed)
So my obsession with 12" coax drivers and classic monitor designs continues.
I'm slow though, I bought the drivers and material in June and I'm still assembling, and as of mid September there is quite a bit work left before testing.
Learning from previous mistakes Ive started building my speakers with removable front and rear using double baffle assembly. Meaning I can play around with driver selection and sealed vs ported designs. I decided on a 60l box cabinet inspired by Tannoy Little Red/Gold, Klipsch Heresy and JBL 4312/19 designs but with my own take on the golden ratio and available material locally. My plan is to build a few more pairs if its a success but with other drivers. This time I landed on the Celestion FTX1225 as it looks both rugged and flexible. I do not aim for the deepest bass or the clearest highs or mids but fun live and dynamic sound for reasonably large rooms. I might compliment with a sub 15 or 18" as well. I decided on a mix of MDF and oak to see if I could make it look good but still keep the price and amount of work to minimum. Stained oak should be easy to make look OK. The MDF will hardly be visible as I plan to have a full front grill.
As I usual I don't plan enough and as thing progress I start to get some questions in my head and I'm also losing my patience and start to take shortcuts. I thought I share some design specs and pics, and then list my questions in next post. I currently have no strategy for passports nor crossover, I thoughts I assemble the box first, get it connected, burn it in with some old crossovers and then perhaps try to measurements as input to crossover design. My original idea was to have it sealed but I'm getting second thoughts about that. The openings you see in the pics will be covered by the removable front and rear baffles, these cutouts are primarily to have access as the bracing makes it a bit difficult.
Some specs for the system.
Cabinet specs:
Outer dimensions: 62x40x40
Inner dimensions: 58x36x30
Aprox Volume: 60l
Front/rear: double 58x36cm 19mm MDF (outer removable, not shown in pics yet)
Sides: 58x40cm 18mm oak
Top/bottorm: 40x40cm 18mm oak
Drivers specs:
Nominal Diameter 305mm/12in
Nominal Power Rating 300W
Sensitivity 97dB
Rated Impedance 8Ω
Frequency Range 50Hz-4000Hz
Voice coil diameter 2.5in
Chassis Type Cast Aluminium
Magnet Type Ferrite
Magnet Weight 2.3kg/81oz
Cone material Kevlar loaded paper
Surround Material Cloth-sealed
Xmax 4mm
Additional HF Specifications:
Power Rating 60W
Nominal Impedance 8Ω
Sensitivity 104dB
Frequency Range 1000Hz-20,000Hz
Recommended Min. Crossover 12dB/oct 2000Hz
Voice Coil Diameter 1.75in
Diaphragm and Surround Material Polyimide
Some pics on the driver and the ongoing build attached.
To be continued.
So my obsession with 12" coax drivers and classic monitor designs continues.
I'm slow though, I bought the drivers and material in June and I'm still assembling, and as of mid September there is quite a bit work left before testing.
Learning from previous mistakes Ive started building my speakers with removable front and rear using double baffle assembly. Meaning I can play around with driver selection and sealed vs ported designs. I decided on a 60l box cabinet inspired by Tannoy Little Red/Gold, Klipsch Heresy and JBL 4312/19 designs but with my own take on the golden ratio and available material locally. My plan is to build a few more pairs if its a success but with other drivers. This time I landed on the Celestion FTX1225 as it looks both rugged and flexible. I do not aim for the deepest bass or the clearest highs or mids but fun live and dynamic sound for reasonably large rooms. I might compliment with a sub 15 or 18" as well. I decided on a mix of MDF and oak to see if I could make it look good but still keep the price and amount of work to minimum. Stained oak should be easy to make look OK. The MDF will hardly be visible as I plan to have a full front grill.
As I usual I don't plan enough and as thing progress I start to get some questions in my head and I'm also losing my patience and start to take shortcuts. I thought I share some design specs and pics, and then list my questions in next post. I currently have no strategy for passports nor crossover, I thoughts I assemble the box first, get it connected, burn it in with some old crossovers and then perhaps try to measurements as input to crossover design. My original idea was to have it sealed but I'm getting second thoughts about that. The openings you see in the pics will be covered by the removable front and rear baffles, these cutouts are primarily to have access as the bracing makes it a bit difficult.
Some specs for the system.
Cabinet specs:
Outer dimensions: 62x40x40
Inner dimensions: 58x36x30
Aprox Volume: 60l
Front/rear: double 58x36cm 19mm MDF (outer removable, not shown in pics yet)
Sides: 58x40cm 18mm oak
Top/bottorm: 40x40cm 18mm oak
Drivers specs:
Nominal Diameter 305mm/12in
Nominal Power Rating 300W
Sensitivity 97dB
Rated Impedance 8Ω
Frequency Range 50Hz-4000Hz
Voice coil diameter 2.5in
Chassis Type Cast Aluminium
Magnet Type Ferrite
Magnet Weight 2.3kg/81oz
Cone material Kevlar loaded paper
Surround Material Cloth-sealed
Xmax 4mm
Additional HF Specifications:
Power Rating 60W
Nominal Impedance 8Ω
Sensitivity 104dB
Frequency Range 1000Hz-20,000Hz
Recommended Min. Crossover 12dB/oct 2000Hz
Voice Coil Diameter 1.75in
Diaphragm and Surround Material Polyimide
Some pics on the driver and the ongoing build attached.
To be continued.
Attachments
-
celestion coax monitor (1).JPG -
celestion coax monitor (10).JPG -
celestion coax monitor (9).JPG -
celestion coax monitor (8).JPG -
celestion coax monitor (7).JPG -
celestion coax monitor (6).JPG -
celestion coax monitor (5).JPG -
celestion coax monitor (4).JPG -
celestion coax monitor (3).JPG -
celestion coax monitor (2).JPG
Last edited:
So my questions / advice seeking:
1. Crossovers and simulation prior to measurements.
Celestion have a few alternative crossover designs which may fit my box but they look very different. One is 3rd order and seems to deal with resonance peaks while the other is 2nd order it probably require external eq. I have yet to find any measurements of these drivers and I have little experience with simulation anyway but looking at the datasheet I really wonder which would fit best. As most coaxes both the low end and high end have nasty peaks at 2kHz to deal with. Looking for some advice here. See attached options
Sources:
https://celestion.com/wp-content/uploads/2018/01/FTX1225_system.pdf
https://celestion.com/wp-content/uploads/2019/09/FTX1225-crossover-design.pdf
https://celestion.com/productpdf.php?id=992
2. Working with oak
A) Ive never worked with oak before but it seems extremely dry and crisp. So I decided to assemble the box using glue only, no screws to try to avoid cracks. Ive read that some people use stain on oak both inside the box and outside to prevent it from cracking. Is this a good idea? Should I screw the internal bracing after all?
B) I have a few gaping joints, I'm think about filling them with glue but are there other ideas? They are not the worst (will share pics soon), but Im afraid that over time it will be visible also after staining.
C) Finally stain: what are some good material that both look good, protects it from cracks and scratches and are there any step-by-step guide recommended by the pros here? If course I need to sand a alot before I get to this point.
3. Pass port tuning
I think Ive decided to go away from sealed but have little experience in simulating box. What would be a decent tuning for a 60l box and this driver? It it possible to have 40-50Hz without loosing punch?
1. Crossovers and simulation prior to measurements.
Celestion have a few alternative crossover designs which may fit my box but they look very different. One is 3rd order and seems to deal with resonance peaks while the other is 2nd order it probably require external eq. I have yet to find any measurements of these drivers and I have little experience with simulation anyway but looking at the datasheet I really wonder which would fit best. As most coaxes both the low end and high end have nasty peaks at 2kHz to deal with. Looking for some advice here. See attached options
Sources:
https://celestion.com/wp-content/uploads/2018/01/FTX1225_system.pdf
https://celestion.com/wp-content/uploads/2019/09/FTX1225-crossover-design.pdf
https://celestion.com/productpdf.php?id=992
2. Working with oak
A) Ive never worked with oak before but it seems extremely dry and crisp. So I decided to assemble the box using glue only, no screws to try to avoid cracks. Ive read that some people use stain on oak both inside the box and outside to prevent it from cracking. Is this a good idea? Should I screw the internal bracing after all?
B) I have a few gaping joints, I'm think about filling them with glue but are there other ideas? They are not the worst (will share pics soon), but Im afraid that over time it will be visible also after staining.
C) Finally stain: what are some good material that both look good, protects it from cracks and scratches and are there any step-by-step guide recommended by the pros here? If course I need to sand a alot before I get to this point.
3. Pass port tuning
I think Ive decided to go away from sealed but have little experience in simulating box. What would be a decent tuning for a 60l box and this driver? It it possible to have 40-50Hz without loosing punch?
Attachments
Last edited:
I've tried for 10 minutes to reply - goofed with a PNG - have to wait as system says can't repeat as a duplicate.
Also note the Vas typo where the decimal point was shifted.
It looks good for 20v tuned to free air resonance and just hits 4mm Xmax at 20 volts input around 68Hz
Also note the Vas typo where the decimal point was shifted.
It looks good for 20v tuned to free air resonance and just hits 4mm Xmax at 20 volts input around 68Hz
Attachments
Last edited:
Thanks that doesn’t look to bad. 40hz achievable, I was a bit sceptical at 4mm being the xmax but at 68hz I assume it’s not a big problem then. I can use double ports will that somehow “help”? Is there a way to design for a smoother roll off from say 50hz and achieve higher SPL around 60 but less at 40?
you could tune lower but that will mainly make the driver work harder in the 40-50Hz region. Doubling ports for a 4 inch ID port will just about double the length so would be about 13.5 inches or so in length to tune to Fs .
I'm not sure why you want to simulate your crossover before you build in this case. It seems reasonable to do it after measuring.
Glue should be enough on its own. Where you have gaping joints with the braces you can run batten trim around the edge to sit them over.
Glue should be enough on its own. Where you have gaping joints with the braces you can run batten trim around the edge to sit them over.
Thanks both.
Regarding bass ports I thought having multiple either allowed for reducing the diameter or length or tune lower, but maybe it serves no purpose? I see many commercial speakers with multiple short ports. My aim is to have the smoothest roll off, and no boosting if possible. I don’t need the highest SPL in the lowest frequencies but it nice that they are somewhat audible without loosing too much power handling. Aiming for -10dB at Fs maybe?
Regarding the crossover alternatives yes I will definitely wait until I can measure I was just curious to understand the difference of the two, maybe electrically first and how they both deal with the 2kHz. I would assume the most complex of the two would have quite a dip in that area but I’m aiming for a less complex setup. I might also consider DSP but I want to try and see how I can do with passive.
Regarding the gaping joints the challenge is the external ones, the top plate was somewhat bent so it has a small I guess 0,5mm gap in one corser which I want to fill with something that would resemble the oak wood also after stain. I don’t think glue will do that.
Thanks for any advice.
I guess I need to learn some software soon then, intuition only get me this far.
Plan to cutout the detachable front this weekend to attach the driver finally testing a little with open back.
Regarding bass ports I thought having multiple either allowed for reducing the diameter or length or tune lower, but maybe it serves no purpose? I see many commercial speakers with multiple short ports. My aim is to have the smoothest roll off, and no boosting if possible. I don’t need the highest SPL in the lowest frequencies but it nice that they are somewhat audible without loosing too much power handling. Aiming for -10dB at Fs maybe?
Regarding the crossover alternatives yes I will definitely wait until I can measure I was just curious to understand the difference of the two, maybe electrically first and how they both deal with the 2kHz. I would assume the most complex of the two would have quite a dip in that area but I’m aiming for a less complex setup. I might also consider DSP but I want to try and see how I can do with passive.
Regarding the gaping joints the challenge is the external ones, the top plate was somewhat bent so it has a small I guess 0,5mm gap in one corser which I want to fill with something that would resemble the oak wood also after stain. I don’t think glue will do that.
Thanks for any advice.
I guess I need to learn some software soon then, intuition only get me this far.
Plan to cutout the detachable front this weekend to attach the driver finally testing a little with open back.
About your crossover choices, sure have a look at them now if you want to learn about them. When you measure you can just put the new responses in.
For the top panel you can glue 25mm oak battens in around the inside edge of the cabinet, then put the top panel down onto them.
My passive and DSP crossovers end up doing the same thing. Whichever you can work with to get the right result.
For the top panel you can glue 25mm oak battens in around the inside edge of the cabinet, then put the top panel down onto them.
My passive and DSP crossovers end up doing the same thing. Whichever you can work with to get the right result.
Your enclosure construction is beyond help here but some tips for future timber projects are in order.
Remember, timber end grain has no glue value. You must use some sort of joinery to get
the long grain portions of the wood into the glue area.
Remember, with timber it's always best to keep the long grain running in the same direction piece to piece. Doing so allows you to control the expansion/contraction of the slabs as an assembled unit, across the width, to one direction only. When you assemble sections as you have ... top to side ... your sides will expand while the top stays relatively still. That joint (I use the term loosely) will open over time.
Remember, don't try to fight timbers' natural tendencies. It will move. Don't think that one can keep this from happening. All of the internal bracing, where it meets timber, should be mainly just screwed. The screw holes in the braces should be large enough to allow the screw to move with the panel independent of the brace itself. You can apply glue to just the center portion of the panel where it meets the bracing as this won't interfere with the panel movement.
Remember, timber expansion is greatest accross its grain in both width and thickness. Much less so in its length.
Remember, timber end grain has no glue value. You must use some sort of joinery to get
the long grain portions of the wood into the glue area.
Remember, with timber it's always best to keep the long grain running in the same direction piece to piece. Doing so allows you to control the expansion/contraction of the slabs as an assembled unit, across the width, to one direction only. When you assemble sections as you have ... top to side ... your sides will expand while the top stays relatively still. That joint (I use the term loosely) will open over time.
Remember, don't try to fight timbers' natural tendencies. It will move. Don't think that one can keep this from happening. All of the internal bracing, where it meets timber, should be mainly just screwed. The screw holes in the braces should be large enough to allow the screw to move with the panel independent of the brace itself. You can apply glue to just the center portion of the panel where it meets the bracing as this won't interfere with the panel movement.
Remember, timber expansion is greatest accross its grain in both width and thickness. Much less so in its length.
If I read your post correctly this box of mine serves best purpose in the fireplace? It will all fall apart as the oak starts to move? I was afraid of that lol. The knock test isn’t the best either.
There is always a way, if you understand the challenges. Consider traditional chair legs.
I sympathise with fabrico selecting a nice piece of oak to work with. I have a similar penchant, now especially with certain enclosure types like horn rear boxes.. though I went through a phase with all boxes once and I recognise the aspirations. When it comes to prototypes you're taking a chance that what looks good can be made to behave well as well, and maybe missing the mark.
Using MDF all round does make construction easier (if less enjoyable for the experienced). See if you like an enclosure long enough to say yes, I want to rebuild the same thing in better materials... Also, learning to use constrained layer construction and bracing reduces the differences.
I sympathise with fabrico selecting a nice piece of oak to work with. I have a similar penchant, now especially with certain enclosure types like horn rear boxes.. though I went through a phase with all boxes once and I recognise the aspirations. When it comes to prototypes you're taking a chance that what looks good can be made to behave well as well, and maybe missing the mark.
Using MDF all round does make construction easier (if less enjoyable for the experienced). See if you like an enclosure long enough to say yes, I want to rebuild the same thing in better materials... Also, learning to use constrained layer construction and bracing reduces the differences.
I might compliment with a sub 15 or 18" as well
Do. Coaxes sound much better this way because the cone is the WG for the tweet and you want it to move as little as possible. I started doing this with Tannoys back when they were still affordable and even with the 15s it improves them considerably.
My surrounds are coaxes, a Faital 8HX200 and an AE TD15X, though after the rebuild may be JBL2226s so I can use the AEs in another project. Another later will be with Faital 6HX150s but the rest I'll detail after some more testing. They will be 3 way though.
Do. Coaxes sound much better this way because the cone is the WG for the tweet and you want it to move as little as possible. I started doing this with Tannoys back when they were still affordable and even with the 15s it improves them considerably.
My surrounds are coaxes, a Faital 8HX200 and an AE TD15X, though after the rebuild may be JBL2226s so I can use the AEs in another project. Another later will be with Faital 6HX150s but the rest I'll detail after some more testing. They will be 3 way though.
Not yet but I’m close to connecting. Had to do quite a bit of sanding to make the baffle hole fit properly to the driver as I dont use routers, further had to sand the edges of the removable baffle to make it loose enough to fit into the frame. Manual work takes time. Right now the removable front is drying from some paint. I also had to find a local dealer to support in M6x60mm bolts as 50mm wouldn’t cut it on this think caste frame. I’ll soon screw it together and connect but still with open rear and no damping so its not going to be realistic testing, just to begin with burn in as I continue sanding and cutout of terminals for the rear. I haven’t even started sanding of the oak joints but that’s of no rush. I think it looks good already after just a simple round of clear ikea furniture oil.
Attachments
Its alive!
Using the Eminence BXB2:2K5CX crossover doesn't sound too bad.
With no rear though the bass suffers but the treble is surprisingly clear.
Cant wait to break it it properly, put in damping and close the rear.
Not too unhappy with the looks either (don't mind the walls in my crappy home-office...).
Using the Eminence BXB2:2K5CX crossover doesn't sound too bad.
With no rear though the bass suffers but the treble is surprisingly clear.
Cant wait to break it it properly, put in damping and close the rear.
Not too unhappy with the looks either (don't mind the walls in my crappy home-office...).
Attachments
Looks nice!
There is a Klang + Ton 6/2014 (a German magazine) built coaxial speaker, Celeste K+T.
It is built around Celestion TF1225CX, which is today obsolete. FTX1225 is the successor.
You can see the construction in Celeste K+T
Also it is possible to buy the original article from https://klangundton-magazin.de/index.php
FR is visible here: 2A3 Maniac: Hochwirkungsgrad: KLANG+TON "Celeste"
There is a Klang + Ton 6/2014 (a German magazine) built coaxial speaker, Celeste K+T.
It is built around Celestion TF1225CX, which is today obsolete. FTX1225 is the successor.
You can see the construction in Celeste K+T
Also it is possible to buy the original article from https://klangundton-magazin.de/index.php
FR is visible here: 2A3 Maniac: Hochwirkungsgrad: KLANG+TON "Celeste"
I’m aware and I think this design supersedes it: BUILD THIS! 12-inch Coaxial Floor Monitor - Celestion
Thanks for that. I could use that as a floor monitor and as a top for my bass guitar cab for larger venues.
If I am to say anything about the sound of these drivers its all positive. They are much more clear than the EB12CX/ASD1001 combo using the same filter. I cant say anything about the bass as my box are still open on the rear side but I'm surprised by the mid-range and high clarity. It definitely need a different crossover than the one I use though its very bright and I think perhaps Ill go for active/DSP for once. Ill keep you updated as I learn more. Eventually try to do some measurements as well after break-in. But I'm positively surprised, the driver seems very eager to play music and both near field and as main works equally dynamic and I cannot hear much artifacts yet, just how I like my PA coax - in your face. Perhaps this is the time to say that I'm listening to electronic music primarily. I'm starting to look at 18" subs to support it now. Ill be back in the club in no time.
Last edited: