Hi,
I smell a burned coil if you try Rg= 89 (V) at 30 Hz,OTOH if you use a 12HP-filter inserted at ~50 Hz would make that design safe,but I agree the BMS driver is better suited for a TH than the RFC is.FYI. post#19 update:
b
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Hi,
FYI. post#19 update:
b
If you drive *any* speaker with a continuous sinewave at the box minimum impedance point at the rated power (P=V^2/Rnom) it'll fry -- not only is the current higher than normal but the coil isn't moving to pump cooling air. I fried a McCauley 6174 just this way (repetitive bass note at 25Hz reflex box tuning frequency).
At least BMS provide distortion curves measured at 1000W (89.4V) unlike any other manufacturer I'm aware of, which says a lot for their confidence in the driver performance, and the 15N850 is rated at 1200W (98V) and has 16-17mm Xmax rated by the formulae everyone else uses (adding Hg/4 or Hg/3), so it's got a lot better chance than most drivers of surviving high-power dubstep without running out of Xmax.
If you really want to move a *lot* of air at 30Hz you could consider the BMS 18N860 (Xmax=22/23mm), though you'll need a big box...
(and it's not so suited for a tapped horn)
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Ok, thanks for the info!
I've got HornResp on my other computer. I'm eager to start experimenting with that driver
I would be content with this design's (15" RCF) frequency response down to 30 if I could feed it 800W and be safe playing programmed music. Could I? I'll break 130dB @ 40hz and up, if my math is right.
That's some nice 30Hz response! But, not as efficient as the RCF as it climbs to 126dB @ 35Hz and to 131dB @ 40...and 135dB @ 80Hz. Again, the RCF box is a nice size for the performance you get - *IF* it can be driven with its rated RMS power (800W) - [program pwr is 1600W].
Hi,
FYI. post#19 update:
b
Are you referencing iand's new design post with the bms 30Hz TH?
How long does this 'continuous' sinewave have to be played for, continuously, in order to deem it dangerous? Most dubstep doesn't 'hang' on a sinewave, but sweeps to and from. Some notes will fire for a 2-count (~140bmp), but not much more than.
This RCF design reaches 121dB @ 30Hz w/800W (again, if my math is correct) which is not bad at all, given it's size and that it's tuned for 40Hz.
These will be a very important part of a very mobile setup, so I don't want to go TOO large. I'm already transporting 2 boxes that are 16 cu ft. each. If they were monsters (output wise), I wouldn't have as much of an issue accepting their size.
Justin
Ok, thanks for the info!
I've got HornResp on my other computer. I'm eager to start experimenting with that driver
I would be content with this design's (15" RCF) frequency response down to 30 if I could feed it 800W and be safe playing programmed music. Could I? I'll break 130dB @ 40hz and up, if my math is right.
That's some nice 30Hz response! But, not as efficient as the RCF as it climbs to 126dB @ 35Hz and to 131dB @ 40...and 135dB @ 80Hz. Again, the RCF box is a nice size for the performance you get - *IF* it can be driven with its rated RMS power (800W) - [program pwr is 1600W].
Are you referencing iand's new design post with the bms 30Hz TH?
How long does this 'continuous' sinewave have to be played for, continuously, in order to deem it dangerous? Most dubstep doesn't 'hang' on a sinewave, but sweeps to and from. Some notes will fire for a 2-count (~140bmp), but not much more than.
This RCF design reaches 121dB @ 30Hz w/800W (again, if my math is correct) which is not bad at all, given it's size and that it's tuned for 40Hz.
These will be a very important part of a very mobile setup, so I don't want to go TOO large. I'm already transporting 2 boxes that are 16 cu ft. each. If they were monsters (output wise), I wouldn't have as much of an issue accepting their size.
Justin
I wouldn't worry about the coil burning issue, this applies to all speakers.
The RCF design won't do 30Hz at anything near full power, the excursion rises very rapidly below 40Hz. If you really want to get down to 30Hz for dubstep you need a driver with more Xmax and a lower tuned box (longer tapped horn).
The RCF is more efficient than the BMS and has more output at higher frequencies, but less maximum output at lower frequencies. A tapped horn still has to obey Hoffman's Iron Law -- basically, pick any two from small, loud and low.
If you want the same efficiency then for an extra octave you need 8x the box size, so 2.4x the volume to reach 30Hz instead of 40Hz. Or you have to give up efficiency and maximum output.
Any tapped horn needs a sharp highpass filter (eg. 24dB/oct) just below the cutoff to prevent huge excursion with out-of-band signals, there's no small rear chamber to restrict travel like with a FLH. If you use the RCF in a 40Hz tapped horn and drive it with loud 30Hz dubstep and no HPF it'll fart like an elephant that's eaten too many beans...
Well, that's not entirely true - I guess, processed, the RCF 15 will do about 115dB @ 30Hz w/800W (as calculated using the info on page 1). But, that output, compared to the rest of the band, seems like nothing. I get your point tho.
(Just looked..) And I'm high passing as is at 35Hz (should be doin so @ 40Hz), so maybe I'll be safe after all..
Yes, I still remember that damn law lol. BUT, this design plays lower, louder and is smaller than what I've got (twice the power tho), so things are lookin good.
Something to think about - thank you.
Justin
P.S. Do we know how close to it's xmech limit it gets?
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Do you mean the RCF or the BMS?
The RCF is unlikely to have a problem given the relatively low Xmax, you'll never get enough power into to it hit Xmech -- remember that at Xmax the BL is down by about 30% so you need 2x the power to move each mm compared to at rest (and the actual travel will also be less than predicted by Hornresp).
Before the 15N850 was released BMS told me that the 15N840 has Xmech of 26mm, I expect the 15N850 will be at least the same -- in fact, if the back plate is the same thickness then from the driver drawings I expect Xmech will be 29mm (coil is 3mm longer below top plate, magnet is 6mm deeper), assuming the limit is the coil hitting the back plate (could be spider hitting top plate). I'm sure BMS will tell you what Xmech is if you ask them...
Its definitely easier to find a 18" driver that will take a decent power input without running out of X-max.
Here is a design similar to Wood1y's layout using the 18" Precision Devices PD1850 The PD1850 is a robust 800W horn driver with a 5" voice coil
Precision Devices International Limited
Note
Compression ratio is 2.5 to 1
Schematic is extrapolated from the physical model - not a theoretical sim.
Hornresp shows this driver OK down to 30Hz at 730W /76.4V.
What do yer think?
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how does one calculate the cone excusion at a certain hpf?Hi,
FYI. post#19 update:
b
i use winisd alpha to aproximate this
Stayed up til 7am and could only sleep 5 hrs til my mind got swamped with the urge to keep moddeling in hornresp. Last night I found a driver that models better (for my needs) in either of your enclosures (again, unless I'm missing something or doing something wrong). Hat's off to you both for coming up with great designs. And a thank you goes out to those who have nudged me a long the way. Let me know what you think. I'm eager to land on a winning design!
I have modelled both epa's and Xoc1's enclosures with the B&C 18SW115
First up, epa's:
I have modelled both epa's and Xoc1's enclosures with the B&C 18SW115
First up, epa's:
What programs are you two using in posts 68, 72 & 73?
@ epa: how would those curved bottom pieces in post 73 be made?
@ Xoc1: yeah, that's the downside - but, I think the 2-3dB increase is worth not building 2x the amount of boxes to gain the dB not had (double the driver(s)/cab(s), add 3dB). So, instead of building 2 cabs, spend another $150 (or £ in your case) to gain that 3dB and save space.
@ epa: how would those curved bottom pieces in post 73 be made?
@ Xoc1: yeah, that's the downside - but, I think the 2-3dB increase is worth not building 2x the amount of boxes to gain the dB not had (double the driver(s)/cab(s), add 3dB). So, instead of building 2 cabs, spend another $150 (or £ in your case) to gain that 3dB and save space.
This one also intrigues me. This driver works very well in the small enclosure - better than the more costly 18SW115. Have you built/sketched this one??
I think we are looking at more of a theoretical problem then a real world problem when it comes to excursion, even if the simulations show that excusrion limmiting will occour at so and so many watts at this or that frequency, the real world experience might be different, most often to the better.
According to hornresp my THAM15 design would be pretty useless above 500W of input power, however, real world users claim they seem to handle almost twice that without any serious/notable compromise in preformance, and I'm sure this is true for most TH designs.
As for the simulations I'm sure they are correct from a purly mathematical point of wiev, hornresp is probably the best thing that has happened to us, it really is a wonderful tool and the creator of this software deserves all of our gratitude, but, there is a differance between the theory and real life usage senarios.
I just think it is important to recognize this and bare it in mind when we look at these designs, I'm sure they will preform excellent in a real life envionment where, as allways, careful and signal processing should be applied.
According to hornresp my THAM15 design would be pretty useless above 500W of input power, however, real world users claim they seem to handle almost twice that without any serious/notable compromise in preformance, and I'm sure this is true for most TH designs.
As for the simulations I'm sure they are correct from a purly mathematical point of wiev, hornresp is probably the best thing that has happened to us, it really is a wonderful tool and the creator of this software deserves all of our gratitude, but, there is a differance between the theory and real life usage senarios.
I just think it is important to recognize this and bare it in mind when we look at these designs, I'm sure they will preform excellent in a real life envionment where, as allways, careful and signal processing should be applied.
Everyone just forgets to factor in power compression, and other things that come into effect at the ends of a drivers throw.
Once you get to ~500w with a majority of drivers, it is not unheard of to be 2-4dB down already, so it is easy to see how you can throw 2-3x the power expected into an enclosure, and not have it grenade on you from over excursion. Assuming a HP is in place of course.
The best way to get around this is to not count on having the last 3-6dB of sim output. If you need 130dB at 1m, you need the speakers to sim around 133-136dB.
Once you get to ~500w with a majority of drivers, it is not unheard of to be 2-4dB down already, so it is easy to see how you can throw 2-3x the power expected into an enclosure, and not have it grenade on you from over excursion. Assuming a HP is in place of course.
The best way to get around this is to not count on having the last 3-6dB of sim output. If you need 130dB at 1m, you need the speakers to sim around 133-136dB.
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