That is an interesting size Brian. Something that tall might be easy to move around with if you put a couple corner casters on the bottom and a couple handles on top and make it it's own cart.
I am going to proceed if there are no glaring issues with my post above.
I will be making this out of 1/2" ply so I want to ensure I have adequate bracing. I will use the spreadsheet's suggested bracing locations using 1/2" ply with hole sawed reliefs to start. I was also thinking about adding 4 additional bracings as shown in black below. These 4 will be at 1/3rds and 2/3rds of the box. Then affix a metal grill at the mouth at multiple points per panel.
I will be making this out of 1/2" ply so I want to ensure I have adequate bracing. I will use the spreadsheet's suggested bracing locations using 1/2" ply with hole sawed reliefs to start. I was also thinking about adding 4 additional bracings as shown in black below. These 4 will be at 1/3rds and 2/3rds of the box. Then affix a metal grill at the mouth at multiple points per panel.
An externally hosted image should be here but it was not working when we last tested it.
I was messing with the filter wizard in hornresp looking at finding a suitable HPF for the parameters in post 23 and I have two questions.
1. Is it a correct assumption that I want to set a HPF that will move the lowest diaphragm displacement curve below the xmax value for the driver?
and
2. Is that 11mm displacement value around 55Hz a concern with an xmax of 9.6 and xlim 17?
1. Is it a correct assumption that I want to set a HPF that will move the lowest diaphragm displacement curve below the xmax value for the driver?
and
2. Is that 11mm displacement value around 55Hz a concern with an xmax of 9.6 and xlim 17?
An externally hosted image should be here but it was not working when we last tested it.
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Thanks for the advice.
I may need to rethink things here. I set up a 12db high pass at 48Hz to decrease the displacement around 55hz but it is dropping the power below 50hz to where I don't think I will gain much, if anything, over a vented box.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Got to disagree here. As we've seen from the sims, the relatively shallow slope means you've got to start attenuating early to cut the out-of-band excursion.
24dB/octave works just fine. Sure, there's a bit more group delay, but I don't think it'll be an issue. It's low in frequency and not particularly important in this application. A 12dB slope is deliberately under-utilising this design imo.
Chris
So back to my question in post 25 above. Is that in band diaphragm displacement at 55hz beyond the 9.6mm xmax of the 3015 a concern? I am looking at a couple other designs on the forum that use the 3015lf and they have the same bump in displacement at that point.
When you try to exceed Xmax, some compression will occur, since the driver isn't in its linear range any more. So, say the sim says 12mm one-way travel, but for that power input at that frequency, you might only get 10.5mm of travel. You'd need to calculate the new SPL there, but it's clear to see that it's going to be quieter. So, at high levels you'll lose a bit of output at 60Hz.
FWIW, I prefer to test drivers in free air to see how much excursion can be had before the suspension etc starts going non-linear. Some manufacturers have a different definition of Xmax to others, so it's worth knowing what your drivers will actually do.
For example, the JBL GTO1214 drivers I have claim 14.5mm Xmax, but they've gone very nonlinear by then, probably to prevent car audio people from damaging them. I also have some Beyma 15P1200Nd drivers, which claim 9.5mm Xmax, but will manage about 14mm before distortion becomes noticeable.
Chris
FWIW, I prefer to test drivers in free air to see how much excursion can be had before the suspension etc starts going non-linear. Some manufacturers have a different definition of Xmax to others, so it's worth knowing what your drivers will actually do.
For example, the JBL GTO1214 drivers I have claim 14.5mm Xmax, but they've gone very nonlinear by then, probably to prevent car audio people from damaging them. I also have some Beyma 15P1200Nd drivers, which claim 9.5mm Xmax, but will manage about 14mm before distortion becomes noticeable.
Chris
Agreed about the JBL (and by extension Infinity) car audio drivers. The brakes definitely look like they're being applied as Xmax approaches. On the good side, that may mean that you can use them in a vented or TH alignment without a HP filter and not worry about the driver getting damaged if it receives a high level signal below the lowest resonance frequency of the alignment...
Thanks for the explanation. I looked around the site for a couple other 3015LF designs and the hornresp parameters I found for them have a similar bump around 60hz.
I applied a little EQ at 58Hz to flatten the response and it looks to my eyes like it has solved the displacement problem at 58Hz. I am using a Driverack PA2 for my DSP so I would guess this problem will go away once that bump around 58Hz is eq'd flat. Is this a good assumption?
An externally hosted image should be here but it was not working when we last tested it.
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Yep, looks good to me.
That said, if a loud note at 58Hz comes along, you'll still pass Xmax - it just takes another 2dB from the mixer to do it.
I wouldn't worry too much about exceeding Xmax by a couple of mm. The worst case scenario is that, on peaks, there's not quite as much 60Hz as there should be. I'm not even sure it'll be audible.
I'd be much more concerned about what happens below 40Hz - that's where any damage is going to happen. The 24dB/octave filter will ensure you don't have much to worry about.
Chris
That said, if a loud note at 58Hz comes along, you'll still pass Xmax - it just takes another 2dB from the mixer to do it.
I wouldn't worry too much about exceeding Xmax by a couple of mm. The worst case scenario is that, on peaks, there's not quite as much 60Hz as there should be. I'm not even sure it'll be audible.
I'd be much more concerned about what happens below 40Hz - that's where any damage is going to happen. The 24dB/octave filter will ensure you don't have much to worry about.
Chris
Thanks for the info. I have an inuke 6000 DSP that will be powering these so I will use the limiter and HPF on that for protection.
Now, as far as setting my HPF, do I just choose something that will keep the lower displacement curve well below xmax? For example, this 24db slope at 34 Hz?
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An iNuke DSP amp is almost the perfect amp for THs.
1. Set a 48dB HP BW filter about 1/2 oct or so below lowest resonance frequency. No more over-excursion issues for signals below that frequency, and your passband remains virtually untouched
2. Use the parametric EQ to flatten the passband, extend it down to the lowest resonance frequency and remove the out of band response peaks.
3. Use the dynamic EQ option to control excursion within the passband at peak levels.
See The Subwoofer DIY Page v1.1 - Projects : "Proof of Concept #3" for how the amp's DSP can transform the output of a TH.
(BTW, I think you can still push for a wider bandwidth TH for this particular driver).
The NU6k will put out around 85v rms into that driver. Set your limiters well - the 3015LF won't take that sort of power for long.
Chris
Chris
Agreed. I am working out something around 275L right now in hornresp but have been short on time.
As far as DSP is concerned. I was planning on using my Driverack PA2 to handle the crossover and eq duties and use the inuke just for limiting and the subs HPF. I currently use the graphic auto eq wizard to flatten response on my current BR system before a show and it works like a champ. I am hoping it will work as well with a set of THs.
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