So, this is just a bunch of overlays showing what happens when you move the measurement mic around over the cone. You might've thought the centre of the cone would yield an accurate result, and you'd be wrong.
Here's a few data points. It'll be location followed by the notch frequency. The cabinet was horizontal.
Edge of dustcap furthest from port, 35Hz
Dustcap nearest port, 33.5Hz
Edge of cone nearest the port, 23Hz and 26Hz (this one is obvious on the graph)
Edge of cone furthest from the port, 35Hz
Edge of cone nearest the floor, 33Hz
Edge of cone nearest ceiling, 33Hz
Looks like there's some kind of cancellation happening between the port and driver, even though the mic was 1/2" away from a 15" cone. That's not something I've come across before.
I'm happy to say I've decided this will conclude the testing for the time-being. The cabinet has gone to the recycling centre, and broke a table when it landed in the container (not even a mark on the cabinet, though).
Next round will be plywood, but I have some life-stuff to sort out for now, so it might be a couple of months before they happen. They will happen, though - one of these cheerfully annihilates the sealed boxes until you want to go really really low. I might've tried the sealed boxes for HT a couple of times. Flat-to-12Hz in-room is pretty cool.
Here's a quick shot I took while outdoor testing.
Cheers, all.
Chris
Here's a few data points. It'll be location followed by the notch frequency. The cabinet was horizontal.
Edge of dustcap furthest from port, 35Hz
Dustcap nearest port, 33.5Hz
Edge of cone nearest the port, 23Hz and 26Hz (this one is obvious on the graph)
Edge of cone furthest from the port, 35Hz
Edge of cone nearest the floor, 33Hz
Edge of cone nearest ceiling, 33Hz
Looks like there's some kind of cancellation happening between the port and driver, even though the mic was 1/2" away from a 15" cone. That's not something I've come across before.
I'm happy to say I've decided this will conclude the testing for the time-being. The cabinet has gone to the recycling centre, and broke a table when it landed in the container (not even a mark on the cabinet, though).
Next round will be plywood, but I have some life-stuff to sort out for now, so it might be a couple of months before they happen. They will happen, though - one of these cheerfully annihilates the sealed boxes until you want to go really really low. I might've tried the sealed boxes for HT a couple of times. Flat-to-12Hz in-room is pretty cool.
Here's a quick shot I took while outdoor testing.
Cheers, all.
Chris
Very interesting results there. Throws the whole approach of determining Fb by measuring driver response into question.
Luckily I always go instead by a 3-second impedance response measurement via WT3
.
How about building a 12hz version and compare it to a 12hz sealed enclosure!
Hi all, bumping this again.
So I picked up a set of four Faital Pro 15HP1060 drivers for cheap. Ran the sims, and everything looked identical to the Beymas (0.1dB difference in SPL at the same voltage). It was after I got them home and sat them side-by-side that I realised there's a difference in mounting depth, and quite a substantial one.
I've been playing with the sims, and it looks suspiciously like I could omit the panel directly behind the driver. Here's the two compared:
First lot of Hornresp inputs are as-built, second lot is what I think would happen if you skip the panel behind the driver, effectively giving a ported box with a long tapering port.
I had to guess a little at the internal dimensions of what would be the rear chamber, but I think its pretty close. The TL response curve has a sharp narrow peak around 110Hz.
If I can omit the panel inside, it'd be very easy to drop the new Faital drivers in, so I hope I'm not missing something.
What do you guys think?
TIA
Chris
So I picked up a set of four Faital Pro 15HP1060 drivers for cheap. Ran the sims, and everything looked identical to the Beymas (0.1dB difference in SPL at the same voltage). It was after I got them home and sat them side-by-side that I realised there's a difference in mounting depth, and quite a substantial one.
I've been playing with the sims, and it looks suspiciously like I could omit the panel directly behind the driver. Here's the two compared:
An externally hosted image should be here but it was not working when we last tested it.
First lot of Hornresp inputs are as-built, second lot is what I think would happen if you skip the panel behind the driver, effectively giving a ported box with a long tapering port.
I had to guess a little at the internal dimensions of what would be the rear chamber, but I think its pretty close. The TL response curve has a sharp narrow peak around 110Hz.
If I can omit the panel inside, it'd be very easy to drop the new Faital drivers in, so I hope I'm not missing something.
What do you guys think?
TIA
Chris
Chris, to go back to your earlier tribulations with the rubbing VC, it's always worth doing the final bolt tightening when you mount a driver whilst playing some 15/20Hz sine, (you can't hear the tone, you can hear problems...), through it. The bigger baskets of 15"+ drivers actually distort quite easily if stressed, and this is frequently the cause of rubbing issues.
Hey pinkmouse,
That's a good point!
It seemed better after a good break-in period, but I didn't have time to check at the last gig they played to make sure it was working properly. I've got a bit of time now, so will go and check them all. Might also start breaking in the Faital units, since they were BNIB.
Looks like you're just around the corner from me. If you like, shoot me a PM and maybe we can see about meeting up.
Chris
Hi Chris,
Happy New Year!
Looking at Post #106 I'm getting similar results. This is pretty much as expected, there still may be a difference in sound, so you'll have to be the judge of that.
Regards,
Happy New Year!
Looking at Post #106 I'm getting similar results. This is pretty much as expected, there still may be a difference in sound, so you'll have to be the judge of that.
Regards,
Attachments
Happy New Year, Oliver!
The sims are close enough for me to go ahead and build another from MDF, without that panel. I expect the one that went to the tip has been reduced to small chunks of wood by now, though I like to think it put up a fight.
I've noticed you've got a question mark by the 9.5mm Xmax on the driver description. I find the drivers are perfectly fine running around 19mm p/p, but get to more like 30mm p/p before distortion is obvious (when running free air). So, I'm happy to let them exceed rated Xmax a little in the sims, because I know it'll just about start sounding distressed when the amps clip at about 90v RMS.
It feels like I'm getting the most out of the drivers this way, though its easy enough to put a limiter in and stop at 80v and reduce power compression.
Just had a look at the PDF. You're a star.
Would I be right in thinking the 1 degree internal angle is still there?
Cheers
Chris
The sims are close enough for me to go ahead and build another from MDF, without that panel. I expect the one that went to the tip has been reduced to small chunks of wood by now, though I like to think it put up a fight.
I've noticed you've got a question mark by the 9.5mm Xmax on the driver description. I find the drivers are perfectly fine running around 19mm p/p, but get to more like 30mm p/p before distortion is obvious (when running free air). So, I'm happy to let them exceed rated Xmax a little in the sims, because I know it'll just about start sounding distressed when the amps clip at about 90v RMS.
It feels like I'm getting the most out of the drivers this way, though its easy enough to put a limiter in and stop at 80v and reduce power compression.
Just had a look at the PDF. You're a star.
Would I be right in thinking the 1 degree internal angle is still there?
Cheers
Chris
Bumping this, a few months later. Got some MDF cut for a prototype of the ported box. I'm getting more comfortable with my new power tools, but this box will be more practice.
For those following along, I've got 4x Beyma 15P1200Nd and 4x Faital Pro 15HP1060. They're very very similar in the sims, to a point where I expect tolerances between individual drivers will be of greater difference.
I'm going to have a lot of fun when all eight are built, that's for sure. 2x2 stacks with the tops on top, or all 8 as a centre-cluster, or a pair of end-fire arrays...
Lots of possibilities!
Festival season is coming, and I want to make sure I have at least four finished for then. I'll also get some load straps.
Chris
For those following along, I've got 4x Beyma 15P1200Nd and 4x Faital Pro 15HP1060. They're very very similar in the sims, to a point where I expect tolerances between individual drivers will be of greater difference.
I'm going to have a lot of fun when all eight are built, that's for sure. 2x2 stacks with the tops on top, or all 8 as a centre-cluster, or a pair of end-fire arrays...
Lots of possibilities!
Festival season is coming, and I want to make sure I have at least four finished for then. I'll also get some load straps.
Chris
We still need to do that beer!
Very true!
Tell you what, what're you doing on the 3rd of June? Three Valleys Beer Festival is happening near me. Should have a big pile of subs to play with, and there's some great beer on tap.
Chris
Just a quick note to say I've got one of the Faital drivers in the prototype cab. Fb comes in at 40Hz.
Nearfield measurements suggest a 5dB drop from 100Hz down to 40Hz, and a bit of a peak around 160Hz. The phase response stays pretty smooth around the 160Hz peak, so I think it could be EQ'd out and then I'll have some flexibility on where to cross to the tops. It'll be somewhere in the 100-150Hz range.
The shop where I got the wood cut managed to get all the internal panels to be 396mm width instead of 400mm. With the 393mm external diameter of the Faital drivers, I found my router + circle jig wasn't quite accurate enough to make something perfect, so I skipped the second baffle layer on this prototype. Next time, I'll either buy elsewhere or ask them to cut too big and then get the panels the right size myself.
Changes for the final build:
- add 12mm of depth to the top, bottom and sides, and set the internal baffle back by the same amount. Add an extra layer to the baffle so that a grille can be attached with no chance of the cones hitting it. The grille will be full-face, since I don't want to have to open the cabs up periodically to empty them of whatever they've eaten. Maybe a foam screen somewhere in the port would be a good move to prevent dust buildup inside.
- Tophat socket on one side, rubber feet on the other. I like the look of these cabs on their side, and they'll form a good solid base for the tops when only a pair of subs would be needed.
- Holes in the top for the rubber feet to mate to for stable stacking.
One cabinet comes in around 2/3rds of a 4x8' sheet, so it looks like it'll be 5 or 6 sheets of 18mm ply for eight cabs, plus a sheet of 12mm extra for the baffles. I'll likely build them in sets of two or four, since I don't really have space to assemble all eight at once with room to work around them.
One thing that does concern me is that the impedance dips to 4.8ohm around 40Hz. It's fine over the rest of the range, but a pair of cabinets in parallel could be abusive for the intended amplifier (NU6000). I guess setting the HPF so power is being reduced at 40Hz would save them, though. -6dB would halve the current demand there, which means a 24dB/octave Butterworth filter with a -3dB point somewhere in the 45Hz range. Once I've got a set of four done, I'll see if it's going to be a problem. If it is an issue, then it's time to look at the amplifier situation. Another pair of NU6ks would solve it, and would probably be the best bang/buck, since I've already got two awaiting sub duties.
This is easily the biggest project I've ever taken on, and I'm excited to press forward.
First, though, I'm going to go and pull one of the Beyma drivers and run some more sweeps.
Cheers, all
Chris
Nearfield measurements suggest a 5dB drop from 100Hz down to 40Hz, and a bit of a peak around 160Hz. The phase response stays pretty smooth around the 160Hz peak, so I think it could be EQ'd out and then I'll have some flexibility on where to cross to the tops. It'll be somewhere in the 100-150Hz range.
The shop where I got the wood cut managed to get all the internal panels to be 396mm width instead of 400mm. With the 393mm external diameter of the Faital drivers, I found my router + circle jig wasn't quite accurate enough to make something perfect, so I skipped the second baffle layer on this prototype. Next time, I'll either buy elsewhere or ask them to cut too big and then get the panels the right size myself.
Changes for the final build:
- add 12mm of depth to the top, bottom and sides, and set the internal baffle back by the same amount. Add an extra layer to the baffle so that a grille can be attached with no chance of the cones hitting it. The grille will be full-face, since I don't want to have to open the cabs up periodically to empty them of whatever they've eaten. Maybe a foam screen somewhere in the port would be a good move to prevent dust buildup inside.
- Tophat socket on one side, rubber feet on the other. I like the look of these cabs on their side, and they'll form a good solid base for the tops when only a pair of subs would be needed.
- Holes in the top for the rubber feet to mate to for stable stacking.
One cabinet comes in around 2/3rds of a 4x8' sheet, so it looks like it'll be 5 or 6 sheets of 18mm ply for eight cabs, plus a sheet of 12mm extra for the baffles. I'll likely build them in sets of two or four, since I don't really have space to assemble all eight at once with room to work around them.
One thing that does concern me is that the impedance dips to 4.8ohm around 40Hz. It's fine over the rest of the range, but a pair of cabinets in parallel could be abusive for the intended amplifier (NU6000). I guess setting the HPF so power is being reduced at 40Hz would save them, though. -6dB would halve the current demand there, which means a 24dB/octave Butterworth filter with a -3dB point somewhere in the 45Hz range. Once I've got a set of four done, I'll see if it's going to be a problem. If it is an issue, then it's time to look at the amplifier situation. Another pair of NU6ks would solve it, and would probably be the best bang/buck, since I've already got two awaiting sub duties.
This is easily the biggest project I've ever taken on, and I'm excited to press forward.
First, though, I'm going to go and pull one of the Beyma drivers and run some more sweeps.
Cheers, all
Chris
Chris,
I'm running a pair of PPSL Dayton PA385S-8 drivers for a 2.92 ohm impedance minimum with two channels of a NU4-6000 bridged mono into that load. I have a large boost going on at fB, 38 Hz IIRC.
Have not done a lot of shows so far, but the amps runs cool with it, did my first gig in Florida at the DeLandapalooza festival, 10 metal bands over 10 hours.
Art
Hi Art,
Thanks for the datapoint, I was hoping you'd chime in. Sounds like I'll be fine then.
Didn't get around to the Beyma drivers today, so I'll get that done tomorrow. Today was mostly fettling a GL78 turntable, which works nicely now. It's good to spin the novelty-sized circles again.
Chris
Thanks for the datapoint, I was hoping you'd chime in. Sounds like I'll be fine then.
Didn't get around to the Beyma drivers today, so I'll get that done tomorrow. Today was mostly fettling a GL78 turntable, which works nicely now. It's good to spin the novelty-sized circles again.
Chris
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