Hey.
I'm thinking about making seriously compact and light, yet exceptionally powerfull tops for my universal home/smaller gigs setup.
What sims great is two mighty 8"s (like B&C 8NDL64 or 8MBX51) in quite tight V-slot configuration, and Strong 1,4" driver in 60x80 horn. The question comes when I think about crossover frequency. Due to the configuration, it will not be possible to cross it higher than 800-850Hz. The box will be 600-800w. Will some good driver as RCF ND840 be able to handle that? Possible suggestions appreciated. Thanks.
I'm thinking about making seriously compact and light, yet exceptionally powerfull tops for my universal home/smaller gigs setup.
What sims great is two mighty 8"s (like B&C 8NDL64 or 8MBX51) in quite tight V-slot configuration, and Strong 1,4" driver in 60x80 horn. The question comes when I think about crossover frequency. Due to the configuration, it will not be possible to cross it higher than 800-850Hz. The box will be 600-800w. Will some good driver as RCF ND840 be able to handle that? Possible suggestions appreciated. Thanks.
Yes. Got that suggestion too. They use it with HF950 horn. I would propably use slightly smaller - 28cm wide as maximum (front baffle width), so it indeed is a tight fit and challenge. I'll also look at suggested drivers too. Thanks you. (P.S.: I know about BMS coax drivers, but due to the horn size and project price, it will propably be a no go...)
I did a similar project, with mixed results, maybe it can help in your design process to determine what to do or avoid
2x8" PPSL midtops made from junk - Speakerplans.com Forums - Page 1
DIY 2x8" ppsl midtop | Facebook
2x8" PPSL midtops made from junk - Speakerplans.com Forums - Page 1
DIY 2x8" ppsl midtop | Facebook
Bob, thank you! I recently rushed across your thread, but at the time, my thoughts were not as similar as they're now with your setup, so I didn't pay too much attention. It seems that things play into my cards positively, as I was very conservative about the Hornresp simulation output at high frequencies. If I get the same shift as you got (slightly up), I would be safe to cross it at 900Hz. Now I propably need to pick my balls and spend $1000 for some lovely drivers, ton of time for unsure development and later on another $350 to get those boxes made professionally. Daaamn, that's gonna hurt, and even more if it fails... I'll bring some sims and thoughts soon.
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hey crashpc, I'm very happy if my data is of any use to you. 
looking forward to that!!
How are your woodworking skills & time ? maybe build a prototype?
I have to admit it took me a few months to build mine, but I'm a master procrastinator anyway.
looking forward to that!!
How are your woodworking skills & time ? maybe build a prototype?
I have to admit it took me a few months to build mine, but I'm a master procrastinator anyway.
I'm finishing my preliminary requirements, speaker setup and way of working to end up with least wallet damage if it all fails.
I will develop it on my own, so woodworking skills are good for non-production results. But if it works, I'll have to get it made....
It can definitely take few months, even more when it's serious and for quite some money. I think my simming and discussions before start will not take more than a week, then I propably start if it will still look good after some argumentation.
Here is first preliminary sketch:
PicFront - dual8_sat.png
Size: 11x11x20 inches including "legs".
The box will be absolutely stuffed.
Sims to come once I get to my PC...
If any problem comes to mind from the image, let me know....
I will develop it on my own, so woodworking skills are good for non-production results. But if it works, I'll have to get it made....
It can definitely take few months, even more when it's serious and for quite some money. I think my simming and discussions before start will not take more than a week, then I propably start if it will still look good after some argumentation.
Here is first preliminary sketch:
PicFront - dual8_sat.png
Size: 11x11x20 inches including "legs".
The box will be absolutely stuffed.
Sims to come once I get to my PC...
If any problem comes to mind from the image, let me know....
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So here is newer info:
Simulation:
PicFront - Sim01.png
Physical setup:
PicFront - Setup01.png
To actually achieve this, there will be something like phaseplug needed.
I.E. almost zero starting s1 area and not much of the volume in speaker cones used.
If I don´t do that, the response goes significantly left, leaving suggested driver (RCF ND840) 4db "shorter" on SPL, using 10db attenuation and 800Hz crossover frequency.
With this one, and another expectation of 50Hz shift to the right, it should fit if done well.
Now the expected response (hope for another 50Hz shift to the right):
PicFront - Response01.png
Next issue is impedance. Two 8Ohm speakers and quite loaded driver make me think that with some additional components in the physical crossover, it could go under 2Ohms worst case. Not good.
For that reason I´m thinking about 8NDL64 instead, which would give me 0,3-0,4Ohm more, BUT, it is propably excursion limited in this setup. Here is Max SPL comparison:
PicFront - SPLMAX01.png
With more wattage, 8NDL64 can go higher, but struggles to keep up under 220Hz.
8MBX51 on the other hand (if we cut the mid honk) should do generaly well, but loads the amp more, while it takes less max power...
Simulation:
PicFront - Sim01.png
Physical setup:
PicFront - Setup01.png
To actually achieve this, there will be something like phaseplug needed.
I.E. almost zero starting s1 area and not much of the volume in speaker cones used.
If I don´t do that, the response goes significantly left, leaving suggested driver (RCF ND840) 4db "shorter" on SPL, using 10db attenuation and 800Hz crossover frequency.
With this one, and another expectation of 50Hz shift to the right, it should fit if done well.
Now the expected response (hope for another 50Hz shift to the right):
PicFront - Response01.png
Next issue is impedance. Two 8Ohm speakers and quite loaded driver make me think that with some additional components in the physical crossover, it could go under 2Ohms worst case. Not good.
For that reason I´m thinking about 8NDL64 instead, which would give me 0,3-0,4Ohm more, BUT, it is propably excursion limited in this setup. Here is Max SPL comparison:
PicFront - SPLMAX01.png
With more wattage, 8NDL64 can go higher, but struggles to keep up under 220Hz.
8MBX51 on the other hand (if we cut the mid honk) should do generaly well, but loads the amp more, while it takes less max power...
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No, it won't.
The absolute lowest impedance a cabinet can show is the DC resistance of the driver(s). A pair of 8ohm drivers in parallel (usually a 6ohm DCR) might drop to 3ohm in places, but never below 2ohm.
Chris
Nope. If you want to bypass some signal heavily, you might use componets in such way, that it will go lower impedance than native Re resistance of paralleled speakers. Got mine current speakers that way, and measured While 8Ohm, lowest impedance is about 3Ohm at crossover frequency. But as my amp can go little under 2Ohm, it´s not an issue. BUT, I guess I might consider different crossover setup when this would about to happen in this project.
Anyway I got things more sorted thanks to your argument. That way there is only this decision between 8MBX51 with more cone excursion and 8NDL64 with more power input capacity and MaxSPL between 400-900Hz. Maybe, the decision will be made solely on the availability or non-availability of these drivers.
Anyway I got things more sorted thanks to your argument. That way there is only this decision between 8MBX51 with more cone excursion and 8NDL64 with more power input capacity and MaxSPL between 400-900Hz. Maybe, the decision will be made solely on the availability or non-availability of these drivers.
Fair point, if you're doing a passive crossover the impedance can go as low as you like.
For something like this, I'd consider active crossovers, though. You can do steeper slopes (saving the compression driver from LF), and EQ each band seperately. With the component costs of a good passive crossover, you might be able to pick up a Behringer iNuke.
Chris
For something like this, I'd consider active crossovers, though. You can do steeper slopes (saving the compression driver from LF), and EQ each band seperately. With the component costs of a good passive crossover, you might be able to pick up a Behringer iNuke.
Chris
Finaly bought two pieces of B&C 8NDL64 for development.
PicFront - dev01.jpg
Stiff as hell. Hope they'll do around 100-200Hz after some eq. Will definitely have to tune these high.
PicFront - dev01.jpg
Stiff as hell. Hope they'll do around 100-200Hz after some eq. Will definitely have to tune these high.
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Hey guys. Finished my development. The expected crossover point ended up like 200+Hz lower than expected. The box would need very deep re-arrangement and rebuilding. It would change the shape of the box, and it would make it even more difficult to build. Not that it´s not possible, but it´s too much for me. No time for that. Photos and measurement coming soon.
Here is How I ended up:
Imgur: The magic of the Internet
The frequency response drops down too soon before I´d need - and where good drivers could be crossed over. Small "phaseplug" won´t do a thing. It would need complete box rebuilding, which would inevitably end up with larger box. At least I learned few things on my way.
Imgur: The magic of the Internet
The frequency response drops down too soon before I´d need - and where good drivers could be crossed over. Small "phaseplug" won´t do a thing. It would need complete box rebuilding, which would inevitably end up with larger box. At least I learned few things on my way.
Hi CrashPC
I'm surprised to see such an early falloff on your 8" V-slot drivers. I just completed a V-slot design for a 15" woofer and it did just as well - with EQ it should be usable from 40 to 600 Hz. My HR simulations of an 8" driver showed potential response out almost to 2 Khz.
Are you exposing the entire cone of the speaker into the "V"? Key for me was rear mounting the driver behind the V's wall and then covering most of the front half of the cone and a little bit at the rear, for a compression ration of about 2.3:1. I also closed off the rear of the V, blunting it, to raise the frequency of the reflection null and added flares on the sides so it was Ved both front to back and side to side. If you haven't already, you should try things like this before throwing in the towel.
I'm surprised to see such an early falloff on your 8" V-slot drivers. I just completed a V-slot design for a 15" woofer and it did just as well - with EQ it should be usable from 40 to 600 Hz. My HR simulations of an 8" driver showed potential response out almost to 2 Khz.
Are you exposing the entire cone of the speaker into the "V"? Key for me was rear mounting the driver behind the V's wall and then covering most of the front half of the cone and a little bit at the rear, for a compression ration of about 2.3:1. I also closed off the rear of the V, blunting it, to raise the frequency of the reflection null and added flares on the sides so it was Ved both front to back and side to side. If you haven't already, you should try things like this before throwing in the towel.
Hey. The simulation was expected to be 200Hz higher, which would be doable with high-end driver and processing. Didn´t happen though.
Yes, the whole cone is exposed. I also tried to turn one speaker, so there was magnet in the chamber. Helped a little bit, but only quarter way to supposed outcome. Due to space limitations, it´s not possible to mount my speakers behind the wall. It would hit something else that way. So that is also no-go, unless I rebuild the enclosure, and make it larger, which is also no-go for my purposes. I believe that with some covering and better shaping, it is doable. The problem with the towel is, that anything I do, will change the box enaugh for me not being interested in it, for my purpose. It should be super compact. So it´s not only challenge for the topology, but also for size. After more sims, trying and measuring, it would need to be too big. I can cram powerfull 10" in the box instead, and it will do too. Just not that exciting.
Yes, the whole cone is exposed. I also tried to turn one speaker, so there was magnet in the chamber. Helped a little bit, but only quarter way to supposed outcome. Due to space limitations, it´s not possible to mount my speakers behind the wall. It would hit something else that way. So that is also no-go, unless I rebuild the enclosure, and make it larger, which is also no-go for my purposes. I believe that with some covering and better shaping, it is doable. The problem with the towel is, that anything I do, will change the box enaugh for me not being interested in it, for my purpose. It should be super compact. So it´s not only challenge for the topology, but also for size. After more sims, trying and measuring, it would need to be too big. I can cram powerfull 10" in the box instead, and it will do too. Just not that exciting.
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