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FYI: BPD 02 series specs are up (1 Viewer)

Brian Bunge

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I'm with Jack and Kyle here. I like the idea of high Xmax, low Fs, low Vas. Again, shooting for a 3ft^3 enclosure with PR's sounds great! I'd like to try a PR-based sub. It will be a HT sub for me so I need something relatively small. I think 4-5ft^3 would be my absolute limit for enclosure size.
And let's not forget another important design aspect: downward firing!
Brian
P.S. Oh, and can we have them before summer?:)
 
A

Anthony_Gomez

a high enough excursion 15" might require more than 2 18" stryke PR's! so downfiring would be a good idea!....allows for 3 PR's...and it can still stay against the wall=)

...hey Dan....any plans on a PR other than your 15"?...what is the upper limit of mass that it can hold?
 

Jack Gilvey

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any plans on a PR other than your 15"?...what is the upper limit of mass that it can hold?
It's listed at 1500g. I would like to see more PR's on the market. More and more drivers have a Vd high enough and a Vas low enough to effectively preclude the use of ports.
Dan, add this to my list. 18" PR with lots of Mms for use in pairs in smallish boxes, but with a high Vas, Qms and Cms. No truck-tire surrounds, please. :)
 

Travis G

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I just want to make sure no one missed it. The Xmax are rated in P-P (Peak to Peak). In other words Xmax * 2 = Xmax P-P.
LOL they must think that were pretty dumb.:D
 

Jack Gilvey

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I have no problem with that, Travis, since it says "P-P" right next to the rating. I don't think anyone missed it.
 

Travis G

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Jack,

I know people that shop for Xmax, and Watts. I have friends who don't know the difference between peak and continuous. Maybe BPD didn't intend to snag a few extra ignorant shoppers dazzeled by the numbers. And I admit that maybe I was unfair in my assumtion that it was their intent to mislead. I just want to make sure everyone here makes the distinction as many of us are still beginners (myself included).
 

Michael R Price

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I'll chime in on what I think would be a really cool subwoofer driver. (Not one I could afford anytime soon, though.)

Power: Does anyone actually care if a driver can handle umpteen kilowatts? Maybe 1-1.5 kW for those who want EQ and a small box.

Efficiency: I assume that this is compromised with an extreme displacement driver. Is 89 dB (like the Tempest) too much to ask?

Driver size: 15-18". But bigger is better, right?

Fs: 18-20 Hz. Like a Tempest, can have silly extension in vented boxes and still be useful for sealed ones and IB use.

Vas: 200-300L. Wouldn't it be hard to keep Vas small if you were shooting for high excursion and low Fs? Besides, a 6-10 cubic foot box isn't *that* bad. (For me, anyway.)

Qts: 0.3-0.4. I assume a low Q (somewhere between the Maelstrom, Shiva and Tempest) would be desirable.

Dual 8-ohm voice coils. The other Adire drivers established that this is probably the most versatile way to wire a subwoofer.

Xmax: 30 mm. Dan, it seems like you can do amazing things with that new XBL motor system. Is 30mm too much to expect from a 15-18" home sub driver?

Price: $300-400. I think such a driver would be worth a lot of money.

This is pretty interesting. Maybe a 'home Brahma' is coming? Gosh, I don't know how these people do it but we're looking at some nice advances in technology.
 

Dustin B

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I don't want to have to buy a bunch of PRs, so I would still really like to see drivers that would work well in ported enclosures. Which begs the next question, what kind of price point would you expect on these 30mm Xmax drivers Dan? If you can tell us you could keep the 12" and 15" drives using XBL right around $200 then I'll get a very big grin on my face :)
I'd like to see a 12" driver with very Shiva like specs except with output capability to match a Tempest. Say for ~150L with a 4" flared port.
Then I'd like to see a Tempest like driver, but with output 1.5-2.5x current Tempests. Say for ~340L with 8" port.
Then I'd like to see a 15" driver perfect for IB use. Fs 16hz or less, Qts 0.45-0.5, 1.5-2.5x the output of a current Tempest.
 

Vince Bray

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Dan,
A stryke-killer would be nice. Based on your innovations you should be able to do this for about the same cost as the HE15:
1. Double the xmax - 45mm should do it. Can you do that?
2. Enough power handling to drive to xmax with whatever alignment - what else do you need?
3. Metal cone - it's cool.
4. A PR designed for it - 15" with enough throw that 4 of them will do the trick.
5. Works downfiring - Jack, see where I'm going?
6. Other specs - don't care, just spec it so that it all works/fits in the smallest cube that'll physically hold it all.
From a little playing it looks like this would hit around 120db from 20hz up from a box that would be about 20" cubed. To me, the HE drivers address just one thing - smaller boxes and less intrusion on your space. There are better/cheaper ways to get the spl if space is no object. This design would allow 15.4 class performance in a very small space. Scary, really. :D
A pair of Crest VS1500 bridged, with one amp on each coil would do the trick. Of course you'd spend 2/3 of budget for amps...
 

Jack Gilvey

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I don't want to have to buy a bunch of PRs, so I would still really like to see drivers that would work well in ported enclosures.
I know what you mean, Dustin. Really tough, though, given the type of Vd we're talking about, especially in the case of a 12" model. If we keep box sizes as they are, but double the Vd, we're still stuck with the porting limitations of the old Vb. If we assume a 12" with 2.5L or greater Vd, I really think there'd be a huge performance gulf between a 4" port (or anything realizable) and a couple 15" PR's. I can hear this even with my modest PR sub. Expensive, though...no doubt. :frowning: Just my take.
Yeah, I see where you're going Vince...I like it. ;) I agree that a 15" would have the most potential as far as decent box size and useability with standard crossover points/slopes.
Of course, it'll have to have a classy "Jack Gilvey Special" logo on the dustcap, understated and elegant. There will be signed units available in limited quantities depending on demand. No telling how an item with this kind of cache' can catch on even among the non-DIY crowd if just for the status of ownership.
 

Michael R Price

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I wonder if someone could make a really big PR. Maybe 21". That would simplify things quite a bit. And look really cool too. :)
If you'd need a port 6 feet long, or 4-5 15" PRs, etc... sealed box is starting to look like a pretty good idea. Maybe if someone could make an 8" flared port it would help. But that's also getting into the range of absurdity. Who knows.
 

Jack Gilvey

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That big a PR sounds like fun, but you'd need a big box just to fit it, and you wouldn't want it so big that you couldn't use two of them due to unweildy Mms (really wouldn't want to use the big PR's singly, that Mms can do a whole lotta shakin').
If you think of a PR as a port whose surface area is equal to the Sd of the PR, you'll see how difficult it becomes to try and equal the potential output of a PR with a port. It's estimated in the Lambda PR FAQ that a pair of 15" 1400g PR's in a small cab would be the equivalent of an 18" port 46 feet long. Other more subjective qualities notwithstanding, they do have that advantage.
 

Dustin B

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Jack,

Do you think an 8" port wouldn't cut it with a Vd of slightly over 5L?

I guess a 4" port could cause some problems with a Vd of 2.5L, but Hank Frankenberg reported very positive results from his Tempest that used a single 4" flared port.

Do you have some links to some articles that discuss port compression and port noise?
 

Jack Gilvey

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Do you think an 8" port wouldn't cut it with a Vd of slightly over 5L?
An 8" port would perform very well, the question is how long is it going to be? In a 200L cabinet, an 8" port tuned to 18Hz is 52" long, with organ resonance starting at 122Hz, about half an octave from an 80Hz crossover.
Used with something like a Blueprint 1803 (6L) in an EBS (14ft^3, 18Hz), an 8" port would hit 20m/s @ 20Hz with about 720 watts input, well below the max excursion of the driver. Very loud, yes.
There are two problems, as I see it, that can arise from inadequate porting: noise and compression. Noise is an obvious thing, and greatly reduced in level by the Aeroports. Compression is not necessarily something someone would "notice" as a problem, unless they heard "uncompressed". From what I understand, though, port compression can begin well before noise becomes a problem.
I don't have much in the way of links, although this page from Deon Bearden's "Beast" project goes into it a bit, and that PR FAQ I linked above talks about PR advantages in that area.
I'd really recommend Vance Dickason's "The Loudspeaker Design Cookbook". He goes into some detail about port compression, and finds that 4" ports can begin showing compression artifacts with about 40 watts input. In the latest edition (I only leafed through it in the bookstore), he finds that the flares do help noticeably.
The big advantage to PR's is with smaller boxes/high-Vd woofers where it would be impossible to adequately port, like the proposed Dharman variant above. In big boxes where you can use nice,big ports, they'll work great and are certainly cheaper.
 

Michael R Price

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Jack, what kind of limitations to PRs have as far as compression at high levels, or bottoming out? And what's the general rule for PR size vs. driver size? (I've seen a lot of examples where the sub uses 2 PRs 1 size larger than the active driver.)

Also... what kind of differences are there between PRs that account for the sometimes large price differences?

Well sorry for all the questions, but I never really read about PRs much, I'll try to learn about it some. Seems like we may be moving towards them (and away from ports) with these new super drivers we're talking about.
 

Mark Seaton

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Hi Dan and all,

This should indeed be an interesting exchange of design issues. I might suggest that Jack or someone start a new thread where you can get more community input and learning, as this is still under the BPD 02 thread title.

Since small box size is of interest, people need to do some thinking as far as their feelings on EQ and efficiency. If you do want a relatively flat response in a small box, I'm expecting the best means to the solution would be a pair of long throw 12" drivers with a pair of 18" PRs on the sides. This makes for a potentialy tallish and modestly deep box of agreeable proportions. A friend of mine, Dave Paton recently finished a pair of subwoofers using some of the Shivas I still had around. With 2 12s on the front face vertically, and a 15" PR on either side of the box, it makes for a very nice scale (about 26" high).

The other issue that I expect we should be getting to next are the limitations of designing a driver for a small box with very low frequency extension. There are reasons you don't see many 18" drivers with flat response in a small box. If you have free reign on the parameters of the driver, and you have an alignment you want, there are some interesting relationships to consider. Now obviously we need Vd of some form (driver or PR), and doubling the Sd allows for halving the Xmax required for the same displacement, but at what expense? Something Tom Danley continually reminds me of when I have some hair-brained idea is that for a given alignment, doubling the radiator size requires you to quadrouple the mass, and double the motor strength. (or is it the other way around? - brain fart) Regardless, with high mass drivers, you have to watch out for VC rocking, which is counter productive to gaining more motor strength. This is a large reason that the majority of small box drivers are 12", and 15" drivers require large boxes for flat, deep bass response. This also proves the point that low mass of a driver is NOT in and of itself desireable over a heavier system.

If you are not adverse to shelf EQ and other forms of electronic correction, or we can work out an alignment to apporximate a room's transfer curve over a limited bandwidth. Tom Danley recently designed a free DIY bass horn for the Live Audio Board, where it was found that to keep the box at all reasonable in size, and to use drivers which could be built, a pair of 12" drivers were determined to be the best solution.

Something I would suggest for Dan Wiggins and David Hyre to look into would be how what would be a practical, maximum motor strength for some chosen Xmax. This will give some good direction as to what cone sizes are practical. Also, while we normally consider low Vas more suitable for small boxes, a high compliance woofer can work in a small box if you have enough motor strength to keep the Qts and fs low. This basically is going to be dictated by motor strength. What does get interesting with high Vas drivers is that once you are at less than 1/8th the Vas, minor changes in box volume have minimal effect.

Should prove to be an interesting discussion.
 

Jack Gilvey

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Check out theLambda PR FAQ, excellent info.
Well sorry for all the questions, but I never really read about PRs much, I'll try to learn about it some. Seems like we may be moving towards them (and away from ports) with these new super drivers we're talking about.
I only started to research them recently myself, but they do seem an ideal solution to the problem of ports in a less-than-huge box.
 

Jack Gilvey

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Mark's here, cool. I think a new thread is in order, but there's already so much in this one that I think I'd rather wait till Dan gets back to address some of this stuff.

One thing I haven't mentioned is motor strength, whether it be Qes or Bl, because I don't fully understand how it effects performance. In a reflex alignment, I figure linear Xmax will be the major determinant of performance above Fb as the driver's doing all the air-moving, but what determines performance as we near Fb, when driver motion starts to become heavily damped? If we have two drivers in *identical* alignments, same porting, power applied, but one has greater motor strength (I don't know if that's possible but bear with me)...what would the difference in performance be? Let's assume we're not port or PR limited, and that we're close enough to Fb that Xmax isn't a factor.

Is this even the right question? Oy.
 

Hank Frankenberg

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Well, I'll chime in. Dan, what about two versions each of the Shiva and Tempest? One version optimized for sealed, the other for vented? The ultimate for each, so that those convinced that sealed is the only way to go for music, can have the very best of that application. Likewise for ported afficianados. What about Mark's motor strength comments? I would like to see design around smaller cabinet sizes - what about that as a design goal? Your reputation is "bang-for-the-buck" subwoof drivers. I suggest you don't stray. There are 2-3 impressive performance sub driver companies with very high prices. Why not take on the challenge of remaining best value and work your magic to offer drivers that are just about as good in performance, but cost significantly less? For instance, how far can you go without having to incorporate the more expensive cast basket frames? I know nothing about PR designs, but haven't I read that that they are not as transient-fast as sealed and regular ported?

Dustin, I used a 4" double flare port based on Dan's recommendation a year ago when he was doing lots of posts explaining his design philosophies and there was a port size debate going on. Dan maintained that a dual-flare port performs like it has the i.d. of its flare o.d. His example was that a dual-flair 4" port performs like a 6" diameter straight port tube. That's why I used it and so far don't hear any problems with it.
 

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