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Being the fan of exotic mid-engine ineligibility as I am, and the exotic nature of the types of drivers this future build uses, I decided to choose a name from the Italian arena. It's an old name from DeTomaso, the precursor to the Pantera, popular in the late 60's to early 70's. You see, these cars used commonplace engines from the American market, and were relatively easy to get parts for. The materials made them exotic. The Mangusta had a split wing-door arrangement covering the engine bay with very large windows, allowing an 'open view rear-end'.
Since PE is stocking the units (I think they stock the Dipolar unit, as I got a pair as a door prize at MWAF 2013. If not, another forum poster purchased a set direct from Beston for about $90 shipped, IIRC. I got the CF120-4 as a door prize at MWAF 2015.), that makes them easily accessible. Being the CF120-4 has a large motor, and the Beston RT002A-Dipolar is an open-back tweeter, the namesake fits.
I also want to point out a rendering of an updated Mangusta, called the Legacy by design student Maxime de Keiser. To me- this is absolutely stunning!
The tentative blueprint looks like it just might work.... CF120-4 will overlap the Beston's faceplate for close CTC, and I will not be flushing the difficult pincushion frame.
Since I want to retain the open-back nature of the Beston, I used the DBS from Jeff's Excel package to emulate what it will be doing, and used the manufacturer FR plot at the onset and adapted it for use. The CF120-4 looks great to 52Hz in 5 ltrs, with 2x 1.0" diameter ports, 6.1" long.
NOTE: I am not using the stock faceplate that comes with the Beston, as it has issues. There is/are resonance(s) that results from the way these are constructed since it is not glued and sealed to the steel plate. There is just no easy way to accomplish this seal myself. To top it off, there are 2 through-holes that vent from front to rear of the magnet structure into the cavities behind the stock faceplate when attached. If you don't seal these holes (even on the non-dipolar units), the faceplate *WILL* buzz loudly with any kind of woofer cabinet pressure. I recommend sealed cavities for this or the sealed Beston is you are not going dipole. Since I'm going open- the holes are less likely to leak and cause issues, but the faceplate is still not going to be used. The outer most 4 screws come out to reveal this result. Besides- that black steel plate looks awesome!!!
Stock unit with faceplate:
Same unit without faceplate:
So, on to the nuts and bolts......
The cabinet is going to be an equal sided hexagon, and volume was easy to find using the 30/60/90 geometric triangle laws as seen on the blueprint above. I hope to use the opposed lateral edges for triangular ports. That should be pretty simple. Biscuits for assembly will be a must.
Here is the initial sim. Mind you this is very preliminary, as dipolar stuff is all new to me in application. I made some assumptions, and modeled with both 6dB and 12dB additional slopes to extend the tails from 1k on the manufacturer's website. I do know that summation will be strongly affected by the room, and adjustment may be required:
I had to go third order to eliminate the dipolar peak on the rolloff of the tweeter, as well as tilt down the strongly rising response. This involved a split 10 ohm resistance by a pair of 5 ohms, as well as a shunt cap to reduce the topend. 6 parts:
The woofer wasn't really that hard to use at all. 3rd order electrical with damping resistor made easy work of the arrangement:
Sensitivity comes out to about 83dB, and an easy LR4 acoustic at 2.8k. Kinda funny how both of these units have bit of a plateau 'amidships' in rolloff, and that they align well. Reverse null tickles ~-40dB from reference for those that want to know. The next picture is that of a sim at 30* off axis overlaid with the on-axis plot:
No- it's not super flat, but it is tonally flat, and smoothing would just reduce resolution of the picture overall.
I'll be updating this as I go...
Wolf
Since PE is stocking the units (I think they stock the Dipolar unit, as I got a pair as a door prize at MWAF 2013. If not, another forum poster purchased a set direct from Beston for about $90 shipped, IIRC. I got the CF120-4 as a door prize at MWAF 2015.), that makes them easily accessible. Being the CF120-4 has a large motor, and the Beston RT002A-Dipolar is an open-back tweeter, the namesake fits.
I also want to point out a rendering of an updated Mangusta, called the Legacy by design student Maxime de Keiser. To me- this is absolutely stunning!
The tentative blueprint looks like it just might work.... CF120-4 will overlap the Beston's faceplate for close CTC, and I will not be flushing the difficult pincushion frame.
Since I want to retain the open-back nature of the Beston, I used the DBS from Jeff's Excel package to emulate what it will be doing, and used the manufacturer FR plot at the onset and adapted it for use. The CF120-4 looks great to 52Hz in 5 ltrs, with 2x 1.0" diameter ports, 6.1" long.
NOTE: I am not using the stock faceplate that comes with the Beston, as it has issues. There is/are resonance(s) that results from the way these are constructed since it is not glued and sealed to the steel plate. There is just no easy way to accomplish this seal myself. To top it off, there are 2 through-holes that vent from front to rear of the magnet structure into the cavities behind the stock faceplate when attached. If you don't seal these holes (even on the non-dipolar units), the faceplate *WILL* buzz loudly with any kind of woofer cabinet pressure. I recommend sealed cavities for this or the sealed Beston is you are not going dipole. Since I'm going open- the holes are less likely to leak and cause issues, but the faceplate is still not going to be used. The outer most 4 screws come out to reveal this result. Besides- that black steel plate looks awesome!!!
Stock unit with faceplate:
Same unit without faceplate:
So, on to the nuts and bolts......
The cabinet is going to be an equal sided hexagon, and volume was easy to find using the 30/60/90 geometric triangle laws as seen on the blueprint above. I hope to use the opposed lateral edges for triangular ports. That should be pretty simple. Biscuits for assembly will be a must.
Here is the initial sim. Mind you this is very preliminary, as dipolar stuff is all new to me in application. I made some assumptions, and modeled with both 6dB and 12dB additional slopes to extend the tails from 1k on the manufacturer's website. I do know that summation will be strongly affected by the room, and adjustment may be required:
I had to go third order to eliminate the dipolar peak on the rolloff of the tweeter, as well as tilt down the strongly rising response. This involved a split 10 ohm resistance by a pair of 5 ohms, as well as a shunt cap to reduce the topend. 6 parts:
The woofer wasn't really that hard to use at all. 3rd order electrical with damping resistor made easy work of the arrangement:
Sensitivity comes out to about 83dB, and an easy LR4 acoustic at 2.8k. Kinda funny how both of these units have bit of a plateau 'amidships' in rolloff, and that they align well. Reverse null tickles ~-40dB from reference for those that want to know. The next picture is that of a sim at 30* off axis overlaid with the on-axis plot:
No- it's not super flat, but it is tonally flat, and smoothing would just reduce resolution of the picture overall.
I'll be updating this as I go...
Wolf
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