Thanks, that makes sense, not so much "based on" the K402 but intended to surpass it.
Looks nice and very much in the Don Keele tradition so no surprise that it resembles the JBL 2360, as I wondered.
Best wishes
David
Like NC5535 I think the throat adaptor is a concern.
Throat adaptors are not a problem inherently but if the woofer is a 15" and the crossover is 650 Hz then I don't see how you can keep the tap within 1/4 of the compression driver and simultaneously keep the woofer tap within 1/4 of the woofer cone.
The nominal 15" woofer cone is ~170 mm radius, a central tap uses up your entire 125 mm 1/4 WL allowance.
Then from the centre of the tap to the start of the adaptor is ~ 170 mm, already over the limit and still another 45 mm of adaptor to the face of the compression driver.
Any additional acoustic path inside the compression driver only makes the problem worse and the JBL 2446 is not shallow.
Even no adaptor is borderline, I suspect this won't work well.
Maybe worth an experiment on a cheap horn but I wouldn't cut holes in an expensive horn like yours without a detailed simulation first.
Best wishes
David
By the way, the horn is fibreglass?
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Thank you David, Droco, and NC535 for continuing to hash these details out.
I was surprised to see the plans to use a 15" and a 650Hz crossover, wondering about the points David just raised.
I took Tom D's comment to me that I could probably use a 12" with a 500Hz crossover, to mean that I could probably use up to a 12".
So I've been thinking if I wanted to cross at 650Hz, I would have to use something smaller than a 12"....??????
Oh Droco, yes the RCF 405 12" surely rolls off too high to be used sealed to 100Hz.
I'm happy with vented to get the extension, but am looking forward to seeing whatever you ultimately settle on for sealed, as I might want to go that way too.
I was surprised to see the plans to use a 15" and a 650Hz crossover, wondering about the points David just raised.
I took Tom D's comment to me that I could probably use a 12" with a 500Hz crossover, to mean that I could probably use up to a 12".
So I've been thinking if I wanted to cross at 650Hz, I would have to use something smaller than a 12"....??????
Oh Droco, yes the RCF 405 12" surely rolls off too high to be used sealed to 100Hz.
I'm happy with vented to get the extension, but am looking forward to seeing whatever you ultimately settle on for sealed, as I might want to go that way too.
Maybe it would be a good idea to first make and test a similar-to model from foam core (like the horns that xrk971 has made, they seem like they might not take too much time to put one together).
Listen to Bill. Prototypes, even partial prototypes, save time and $ in the long run.
As to that target 650 Hz XO with a large woofer -my 15" companion woofer only just or didn't quite make it there and it didn't have the handicap of a round to rectangular adapter.
I think the real problem with this design is its goal of serving two masters or rather two applications. Were it to be used solely in home with subs for 100 Hz down, you could happily use 8" woofers and not have to deal with any of these issues. Wanting to be able to hit SPL levels absurdly high for the home is motivating those large woofers with their attendant difficulties.
Can both be done without some compromise in one application or the other? Unlikely. Best compromise might be sealed 8" in the home converted to vented 8" on the road with box tuning of 80-100 Hz. The B&C 8NDL51 handles 400W and has 7mm Xmax
4 of them vented tuned to 80Hz will get you to >135 db sound power HR sim on a conical horn. Sealed performance is only 8 db or so lower, so plenty of headroom for equalization at reasonable in home levels. You would likely also need a volume reduction mechanism for that sealed mode.
As to that target 650 Hz XO with a large woofer -my 15" companion woofer only just or didn't quite make it there and it didn't have the handicap of a round to rectangular adapter.
I think the real problem with this design is its goal of serving two masters or rather two applications. Were it to be used solely in home with subs for 100 Hz down, you could happily use 8" woofers and not have to deal with any of these issues. Wanting to be able to hit SPL levels absurdly high for the home is motivating those large woofers with their attendant difficulties.
Can both be done without some compromise in one application or the other? Unlikely. Best compromise might be sealed 8" in the home converted to vented 8" on the road with box tuning of 80-100 Hz. The B&C 8NDL51 handles 400W and has 7mm Xmax
4 of them vented tuned to 80Hz will get you to >135 db sound power HR sim on a conical horn. Sealed performance is only 8 db or so lower, so plenty of headroom for equalization at reasonable in home levels. You would likely also need a volume reduction mechanism for that sealed mode.
Maybe some extra info is warranted about the design, as most you actually raise some very good points.
1. I'm using the JBL 2446, which is a fine driver and very powerfull. On the other hand I'm not sure it's gonna be the driver I'm gonna end up with. If I do keep it as the permanent driver it's gonna be Be upgraded. It has a -6db point of 550hz.
One of the main reason why I designed for a 650hz crossover is when looking at one of the drivers I really want to end up with, the Radian PB951. It has a natural -6db point of 650hz. I mean 'natural' because I plan to push them to their max at certain points.
The coaxials do remarkably better, and can easily use a 500hz (maybe even 400hz -6db) crossover.
If you guys can convince me I'm not taking the right turn to maximise the SPL by doing it like this, please let me know 😉 I do however want to keep the speaker sealed (although, I'm maybe open to selective/modifiable venting, as long as the vent can be placed outside the horn) and a 2-way.
Could I maybe use a mild boost on the compression drivers, as they will be primarly limited in their highest frequencies. THat way I figure they would still have some potential left in the lower ranges. Maybe a boost of 1,5-3db? Could move up the crossover of the JBL 2447 and of the Radian PB951 pretty close to 500hz.
1. I'm using the JBL 2446, which is a fine driver and very powerfull. On the other hand I'm not sure it's gonna be the driver I'm gonna end up with. If I do keep it as the permanent driver it's gonna be Be upgraded. It has a -6db point of 550hz.
One of the main reason why I designed for a 650hz crossover is when looking at one of the drivers I really want to end up with, the Radian PB951. It has a natural -6db point of 650hz. I mean 'natural' because I plan to push them to their max at certain points.
The coaxials do remarkably better, and can easily use a 500hz (maybe even 400hz -6db) crossover.
If you guys can convince me I'm not taking the right turn to maximise the SPL by doing it like this, please let me know 😉 I do however want to keep the speaker sealed (although, I'm maybe open to selective/modifiable venting, as long as the vent can be placed outside the horn) and a 2-way.
Could I maybe use a mild boost on the compression drivers, as they will be primarly limited in their highest frequencies. THat way I figure they would still have some potential left in the lower ranges. Maybe a boost of 1,5-3db? Could move up the crossover of the JBL 2447 and of the Radian PB951 pretty close to 500hz.
Attachments
Maybe a way to model how much I can boost the compression drivers in their lower range, without limiting their ouput? I know how to do this for woofer, but not for CD.. Any tips?
Also, you guys claim the port shape doesnt really matter, but I cant believe a 3x4" port (for a 15"er) doesnt have any disadvantages.. isnt it way to wide? The length of the port will also be defining for the design, and it can make or break the symmetry of the dual ports over the single woofer.
It does matter but it's not very critical unless you have an extreme shape, a slot across the mouth for instance.
I recommend the way Bill did it in the SmallSyns - acoustically very nice, reasonably simple, even looks nice.
Best wishes
David
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I started with a JBL 2447, similar to the 2446 but improved, and also think a 650 Hz looks feasible for that driver.
But there is some complication, if you want to keep the crossover low then you need an exponential(ish) horn to load it well.
This leads to the usual trade offs - polar patterns, diffraction slot anomalies and increased depth, with consequent time offset and space restrictions.
(I went to the newer neodymium JBL 2453 driver just because it was much smaller so I had more depth to trade.)
The coaxials look better if you are determined to have a 15", this is what Chris uses for his K402 15" MEH.
If you don't use a coaxial then the JBL 2169 is purpose built as an MEH driver to match with a CD, used in their top of the line tour system.
Best wishes
David
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Sorry, it was Art Welter's SynTripP that I had in mind.
SynTripP: 2-way 2-part Virtual Single Point Source Horn
First picture at the bottom shows the taps.
Not that the Smallsyns aren't nice.😉
Best wishes
David
Natural experiment is good model 🙂 . Measure and\or listen and select appropriate xo and boost.
Question: we already established that modeling relative distance between woofer(center) and port(center) is not possible, but that we can try to follow some base rules. Still some uncertainty about what reference points to use (using center from both? Farthest point? Center to farthest point?).
In any case, a 500hz cover looks reasonable for a 15" woofer, 650hz for a 12" woofer.
Some thing I'm not clear on is whether I can measure this. Because isnt the effect of using too large woofers that there will be cancelation in those higher frequencies? So building, and then measuring would show how well the exact configuration works right?
In any case, a 500hz cover looks reasonable for a 15" woofer, 650hz for a 12" woofer.
Some thing I'm not clear on is whether I can measure this. Because isnt the effect of using too large woofers that there will be cancelation in those higher frequencies? So building, and then measuring would show how well the exact configuration works right?
I decided to buy a pair of Beyma 12P80Fe drivers, which are massive beast that model extremely well down to 120-150hz (2pi). In home, cornerloaded (0,5pi) they can easily reach 125-130dB at 80hz when using just the one woofer! Using multiples will only ameliorate this. For PA use I can use them down to 150hz 123dB (2pi) for each woofer, so around 135dB when using
4. At 120-150hz I will be able to couple it to a kickbin/subwoofer positioned directly below as it will still be within 1/4th WL. Probably something like a Skram (the new subwoofer by Ricci from databass).
Starting construction up again this weekend. A lot off stuff got between it, but hoping I can get going now. Will start with just the one woofer (with only 1 elongated port), and the calculated 650hz positioning. Will measure once done, and decide how much more woofers I want right now, depending on construction complexity and measurements.
This single port position will be made so I can easily add another one on this same side. The port will run through the center of the 12" more or less.
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