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The "designing the perfect subwoofer driver" thread...


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#41 of 734 Kyle Richardson

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Posted February 19 2002 - 12:09 PM

Dan, I would like to see the 15" before the 12" since you have already shown the existing 12" Brahma in 3 cubic feet with a couple of PR15's can be a great sub combo. Also the Brahma in a smaller sealed enclosure is nice too.
Lets go 15"!

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#42 of 734 Greg Monfort

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Posted February 19 2002 - 01:05 PM

4. So, a long throw 15" driver is a good target; that or a 12" unit. The 18" and the 10" really aren't that popular (funny, that's the way the market has pretty much always been...).
====
For strictly sub duty I don't understand the resistance to 18". The old 15" max was based more on the need to XO as high as 800Hz than manufacturing limitations.
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7. The goal is 115 dB SPL @ 20 Hz, anechoic, and somewhere around 1.5 kW powering it. That pretty much sets the defining size of the cabinet to 8 cubic feet (Hoffman's Iron Law). That's too big, isn't it? Would 110 dB SPL @ 20 Hz anechoic be a better goal? In a typical room, that should get you full reference levels...
====
Serious HT subs is IMO about the ability to feeling explosions without resorting to bass shakers, like the big EV BP subs used for "Earthquake". Also, I don't see the point in having to make a massive cab just to counteract the extreme excursion capability you cite if only one driver is used, or aneochoically flat response to DC as MS pointed out. Posted Image

So what's the feasability/cost competitiveness/interest for a pair of 18"s with ~12Hz Fs, ~6ft^3 Vas, ~0.26Qts, ~21mm min. Xmax, and at least 750W with minimal thermal compression in a stuffed 20" cube? Surely that's not too big, I've built 'bookshelf' speakers bigger than this. Posted Image

This sims a good real world alignment (very IB like) for some serious in-room output for HT or even organ music (~115dB if compression can be kept minimal) in all but the largest rooms, though a pair solves that problem. I figure if you can afford the room you can afford the extra sub. Posted Image

'Pie in the sky'?

GM
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#43 of 734 DanWiggins

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Posted February 19 2002 - 01:45 PM

Kyle,

Oh, I've got a 15" Brahma staring me in the face right now...Posted Image It's big and bad! I'll get some info posted soon on it.

Greg,

Those parameters are not too possible; for that suspension stiffness, the moving mass for a 12 Hz Fs will need to be up in the 1.75 kg (yes, 1750 grams) range... If we could raise the Vas up to the 12 cubic foot range, then the moving mass is a more-manageable 800 grams. Still heavy, but let me see what can be done.

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#44 of 734 Jeff Rosz

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Posted February 19 2002 - 02:26 PM

heyas folks,
looking at the end product as in dan's #7...
if small to mid size box is the goal/outcome, 8ft^3 fits that bill?. add some hellacious bracing(ya dont forget that)and double mdf and your up to ~9ft^3 gross. thats like a ~27" OD cube. or like ~40x20x24 (just ballparking it folks, dont dig out yer calculators). but i guess for some of ya'll Posted Image 8 cubes is small. sorry, forgot where i was for a sec.
so if its big kw amps/less efficiency then just for kicks, what can be done for a compromise in about 5-6 cubes?

1&2: dan you're stoked huh? Posted Image
3&4: sounds competitive, the market drives alot of things, ok everything
5: arrrg, but ok, gonna need it anyway for any eqing that may result

edit: sorry for using the word compromise in a no compromise subject but its unavoidable
why have one when you can have two for twice the price?

#45 of 734 Greg Monfort

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Posted February 19 2002 - 02:29 PM

Yeah, I was afraid of that, but since I'm not privy to the latest suspension materials technology.....

Since that puts it up to ~8ft^3 net, unless there's a bunch of interest there's not much point in you wasting your time. Thanks anyway. Posted Image

GM
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#46 of 734 Pete Mazz

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Posted February 19 2002 - 02:45 PM

I have no problem settling for a driver that can do 110 @ 20 sealed, considering I prefer twin driver subs anyway. Posted Image What size box are we talking about for two?

At this point, tho, how far are we from the Brahma 15?

Pete

#47 of 734 Peter Johnson

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Posted February 19 2002 - 04:09 PM

Well I'm a student, so money is an issue. I havent started building a sub, as firstly I cant afford it (in 6months I will) and new drivers are coming out all the time and none have yet been perfect for me.

The problem is I live in Australia, and shipping these 15+" drivers across the world can cost $US100's, often more than the driver itself...

Anyway, I think we need a driver that is optimal for a small, sealed design. There are enough drivers out there for massive SPL, vented configurations.

As others have said, I think efficiency can be traded for a small box with decent extension. X-max needs to be large enough to lend itself to decent EQ'ing to extend its range.

I would be happy with anything up to 4cuft. 15" is fine, but I think sealed is the key...I honestly think there are more than enough drivers suitable for large, vented enclosures out there..

#48 of 734 Hank Frankenberg

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Posted February 20 2002 - 01:02 AM

Dan, #5 grabbed my attention. You know I favor a best in the world Hertz for the buck, which is your forte, but I don't want to have a low-cost driver that requires an expensive "mega-watt" pro power amp. What I'm asking here, is: what compromise could be reached that would get that best driver that does NOT require 1,500 watts? OR, am I dreaming?

I tend to agree with Peter in that there seems to be far fewer sub drivers optimized for outstanding sealed Home applications.

#49 of 734 Brian Bunge

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Posted February 20 2002 - 01:29 AM

Hank,

I believe ThomasW stated that he is "only" using 500W to each of his Blueprint 1503's in the sealed enclosure known as Tube-Zilla! So maybe we should shoot for a driver that can give great performance with 500-700W (use Dan's HS500 plate amp for 720W into a 4-ohm load) but be able to handle 1500W easily if you have it on hand. I'm still looking for a used K2!

Brian
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#50 of 734 Magnus Lindqvist

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Posted February 20 2002 - 01:32 AM

A very interesting thread I must say.
I have been thinking, a driver for a small sealed application looks very tempting, plus the low inductance with the XBL2 technology, but there is still need for some kind of EQ, LT or BFD to get good low end extension and in that case a BPD 1503 could be the perfect driver(if the hump is tamed).I know XBL2 has other advantages but I think the price of a BPD 1503 will be hard to beat(we nonamericans have the shipping cost and tax to think about as well).
In Sweden a QSC RMX 1450 costs 640$, and that is even a special price!!
Keep the ideas coming Dan!
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#51 of 734 Jack Gilvey

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Posted February 20 2002 - 01:39 AM

Quote:
Yes, I'm serious about rolling a driver for this design. There seems to be more interest in small/mid sized boxes, and equally split for sealed and vented. So let me see what I can do.

Alrighty, I've got Unibox all warmed up.

Quote:
We should start looking at a budget - would something in the $250-$300 range work?

I think that's reasonable for the type of state-of-the-art performance we're discussing, and considering what else is on the market. We've already Shiva and Tempest at the lower brackets.

Quote:
You can't have efficiency, small box, and deep bass extension; violates Hoffman's Iron Law (Greg Monfort's post expounds on this). So if we go with smaller boxes and deep bass extension, then low efficiency it will be. Prepare for the assault of the kilowatt amps!

To be specific, and I recall you've mentioned them before, how would the QSC RMX1450 fare in this role? It's 1400w into 4ohms bridged, and is widely available now for $399.

Quote:
The goal is 115 dB SPL @ 20 Hz, anechoic, and somewhere around 1.5 kW powering it. That pretty much sets the defining size of the cabinet to 8 cubic feet (Hoffman's Iron Law). That's too big, isn't it? Would 110 dB SPL @ 20 Hz anechoic be a better goal? In a typical room, that should get you full reference levels...

You're talking sealed with these numbers? It's apparent that there'd be a tough market for a 15" driver whose parameters dictated a small (even medium) reflex alignment, since the investment in the requisite passive radiators seems a bit much. Having said that, though, the Stryke Power15 has it niche, and if you could outdo that by the margin that seems possible in the same 22" cube...
Short of that, I wouldn't want to use the 15" in less than 10 ft^3 reflex due to porting issues.

For sealed, I'd like to see an optional "black box" Linkwitz-transform circuit (the actual construction of which proves daunting to me and, I assume, other non-"solder-savants") sold with the driver that could be used between pre- and power amps and which would flatten response to a known frequency/Qtc when used with a Vb defined by you. A variable one like Marchand's Bassis would be expensive, but a dedicated circuit, or maybe a choice of 2 or 3 Fc/Qtc's, I would think should be fairly cheap given what I know of the electronics involved. Anybody like this idea?

Quote:
in that case a BPD 1503 could be the perfect driver(if the hump is tamed

Now that would be a interesting motor comparison with XBL2, wouldn't it, Dan?
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#52 of 734 Brian Bunge

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Posted February 20 2002 - 01:59 AM

Jack,

I definitely like the additional LT circuit idea! But you probably knew that already! I say shoot for an alignment that would give you as low a QTC and Fc as possible (in other words as flat as possible) as one of the options since my open floor plan and vaulted ceiling probably will not yield much room gain. Just keep power requirements within the range of a K2. I guess we'd need to know exactly what the power limits would be for the driver as well. Rated at 1500W is fine, but tell me what type of transient spikes it can take. Anyone want to test the limits of this thing and report back?Posted Image

Also, the LT circuit could be offered either assembled or in kit form. I know my buddy Hank will be glad to build mine for me since he told me he can "solder all day long!"

Brian
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#53 of 734 Jack Gilvey

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Posted February 20 2002 - 02:25 AM

Quote:
Also, the LT circuit could be offered either assembled or in kit form.

The kit form is probably a better idea, cheaper and allows more flexibility in the long run. A circuit board with clearly detailed locations for insertion of the appropriate components would be great.
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#54 of 734 Jeff Rosz

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Posted February 20 2002 - 02:34 AM

can anyone point me to a LT circuit on the web. if its anything like what im thinking the parts would cost less than $5 plus a small project box and jacks and such, and...just about any old wall wart from that old telephone that doesnt work anymore to power it. this could be a very small "black box", im thinking the circuit board would be no more than 2^2".
why have one when you can have two for twice the price?

#55 of 734 Jeff Rosz

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Posted February 20 2002 - 02:50 AM

Quote:
A circuit board with clearly detailed locations for insertion of the appropriate components would be great.

i agree it would be nice. you're talking about a silkscreen overlay? but it really wouldnt be required. could be done with just a sharp magic marker. would that suffice? whats the rolloff of a sealed box again? 2nd order:12dB/oct? there is time for this anyway because you of course need the driver and box before you could set its frequency. but wouldnt hurt to get up to speed on it.

edit:duh, nevermind 12dB/oct [bonks himself in the head] gotta stop playing EQ , rots yer brain.
why have one when you can have two for twice the price?

#56 of 734 Brian Bunge

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Posted February 20 2002 - 02:52 AM

Jeff,

Here you go!

http://sound.westhos...m/project71.htm

The PCB is 1.5" x 3".

Brian
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#57 of 734 Dustin B

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Posted February 20 2002 - 02:53 AM

I would have preferred the 150-200 range, but realize that isn't possible with the kind of driver we are talking about. However I think Magnus's point needs to have serious consideration. Unless this thing has significantly better perfromance than BP1503, the price is gonna have to be very close to the $240 cost of a BP1503.

When I said 120dB at 20hz (or did I say 115, ah I want 120, last sub I'll need :P)). I was thinking more along the lines of two drivers in Thomas's TubeZilla configuration. I was also hopeful that something like a QSC RMX1450 and BFD would be all that pair of drivers would need to achieve the 120dB at 20hz and a flat in room frequency response.

What would that translate to for a single driver?

Those who only want one driver and want more output from it can build a larger ported enclosure, while those that want a smaller sealed enclosure will have to be happy with the 110-115dB range from a single driver.

Either that or you do the one for very large ported allignments and one for smaller sealed allignments. I'm fine with anything from 3-16ft^3 for a single or dual driver configuration.
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#58 of 734 Jack Gilvey

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Posted February 20 2002 - 03:02 AM

Here are all the LT links I've got:

http://www.trueaudio.com/st_lkxfm.htm

http://sound.westhos...m/project71.htm

http://sound.westhos...z-transform.htm

This spreadsheet tells you the components you need based on the existing Qtc/Fc and the desired Qtc/Fc:

http://www.pvconsult....downloadlt.htm

Quote:
i agree it would be nice. you're talking about a silkscreen overlay? but it really wouldnt be required. could be done with just a sharp magic marker. would that suffice?

I have no idea. Posted Image

Quote:
whats the rolloff of a sealed box again? 2nd order:12dB/oct? there is time for this anyway because you of course need the driver and box before you could set its frequency.

The LT does more than counter the sealed rolloff, which can be more severe in small boxes with the ripple in the FR accompanying high Qtc values. And, as I mentioned, if we have a known Vb for a known driver, then the exact components can be supplied. Although a kit form could allow for any configuration using the spreadsheet to determine values.

I think what we're shooting for is a driver which works well with a typical rooms' transfer function in a reasonably-sized box, a fairly low F3 in a Qtc of 0.7 . If LT-type eq is still required, it's best to have to apply as little as possible so as to avoid power compression and other VC-heating penalties.
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#59 of 734 DanWiggins

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Posted February 20 2002 - 07:09 AM

OK, so we're aiming more at the sealed box thing... For all who have commented on it, yes Hoffman's Iron Law is a pain! But it's the law, and you have no choice but to live with it. No small, efficient, deep-playing boxes.

Anyway, if an LT/sealed box woofer is the way to go, then how about this set of parameters:

Fs: 16 Hz
Qms: 5
Qes: 0.45
Vas: 150L
Xmax: 35mm one way
Sd: 750 cm^2 (15" driver)

Drop that in a 3 cubic foot box, and you have an anechoic F3 of 26 Hz, without EQ. A little bit of EQ via an LT (4.2 dB) in that box gets you an F3 of 20 Hz.

So, how does that sound as an option? Driven with a 1400W amp (QSC or Mackie model), the unit should be capable of ~105 dB SPL @ 20 Hz anechoic. In-room, this should get you right around 115 dB SPL @ 20 Hz, and a pair would put you over 121 dB SPL @ 20 Hz.

As far as the comparison of the Brahma incarnation of the XBL2 motor (which is just one way to optimize the motor) with the Blueprint 1503, you can find it at:

http://www.adireaudi...BP1503Paper.pdf

I've also done a similar comparison with the MASS 2012S4 driver (a TC Sounds underhung unit that is seen in other commercial offerings with a few small tweaks). That can be found at:

http://www.adireaudi...vsMASSPaper.pdf

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#60 of 734 Brian Bunge

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Posted February 20 2002 - 07:24 AM

Dan,

I plugged the parameters into Unibox. Response looks good. I have just two questions. When can we have this and how much?!

Brian
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