The "designing the perfect subwoofer driver" thread... (1 Viewer)

[Jeff Rosz]

holy cow dan,

shoulda reloaded before i posted, your last post answered a few things. but now i have a question about Qes. .45 seems to be a steady value in your posts...can i change it and what are the hidden bad effects of such a thing? thanks again.

 

[Dan M~]

Dan Wiggins,

I posted before, if I am considering two drivers for a bipole design, lets talk Isobaric. I know efficincy is lost (do to lack of cone area), but if you were designing a driver for isobaric use ONLY, what could you do? You are using two (presumed) smaller/less expensive motors, you have better control of the excursions and can't you use an enclosure 1/4 the size of a bipolar?? Go vented for low end extension. With 2 Ohm VC's to regain efficiency what is possible?? It just seems that mabe a design possibility is being ignored. Has anyone tried to optimize a driver design for Isobaric ONLY installations? It seems that the cabinet size is the real concern for most people (as well as over all costs)... Isobarics use smaller cabinets.

Maybe I'm out in left field on this but I would like to know if it's possible.

Thanks for your time,

Dan M~

 

[Dustin B]

Dan M,
I always thought an isobaric design allowed you to but the enclosure size in half, not quarter it. Also when you cut the pox size like that it becomes impossible to fit adequate porting in it (so sealed or PR is the only way). Can't find the picture. But picture a little box with one of those fexible vents that you use for drier exhausts curled up like a snake above the box.
Dan W,
1140cm^2 Sd, is that a typo, is this still a 15" driver? That's an 8L Vd

What kind of power would you recommend for the 5ft^3 box and what would it's Q be? What if you wanted to do a TubeZilla type design with it (drivers on opposite ends of a sonotube and wired in phase). Forget maxing them out, just how much power to reach reference level in a 2000-2500 ft^3 room? By reference I mean with all speakers set to small, so to handle both LFE and all the sub 60-80hz sound from the other channels, capable of 121dB in room.

 

[Chris Popovich]

Another vote for a small (~4 cubes) sealed box.

Chris

 

[Brian Bunge]

Dustin,

I think Dan is correct. IIRC, an isobaric configuration allows the two drivers to work in an enclosure 1/2 the size of a single driver. In other words, 1/4 the airspace normally required for two drivers.

Brian

 

[Anthony_Gomez]

1140cm^2 Sd,

that has to be a typo.

That is practically the SD of the Maelstrom (1180cm^2)

 

[Dustin B]

Brian, ah I see. Since an isobaric acts like a single driver, I always just talk of them like single drivers, my bad.

 

[Hank Frankenberg]

Vote: Sealed, but I suggest up to 5 ft^3. Dan, tell us more about your dipole idea.

 

[Greg Monfort]

>I've wondered where this "point of diminishing" returns was as far as power input.
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It depends on the motor design. Some begin compressing with as little as 1/10 of rated power. If it's not published I use half power as the point of diminishing returns.
I forget who it was on this forum sometime back 'upgraded' to a mega power amp so he could use up all of his sub's PE rating, only to find out when he cranked it up it measured slightly less peak SPL than with the smaller amp. There was nothing wrong with the amp, just all that extra power was raising the sub's Q, flattening the response over a wider BW, and dissipating the rest as heat instead of acoustic energy.
Of course if thermal efficiency is the goal, JBL has some drivers that have no audible compression at 800W with high efficiency, but if you have to ask the price you can't afford them.
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> So, the higher we can push Pe, the less compression would be a factor?
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I wish! Normally all it means is the VC can withstand more heat before burning up and/or the magnet/basket assembly is a better heatsink. The only reason the average driver today doesn't have the 30-60W ratings of yore is due to advancing materials/manufacturing technology. Neither the copper to wind the VC nor the amount required hasn't changed, so the only other option to lower compression is to improve cooling. Unless there's some new tricks I don't know about, of course.
Or you can do like Babbs does with its new Lorelei fullrange design and use the heat to create the desired alignment and keep it stable by preheating the VC. If you can't get rid of it, then put it to work.
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>Greg, I need you to teach me about dipole subs now, Dan knows why.
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What's to know? See Linkwitz's site. Basically it like making HP, there's no replacement for displacement as long as it's over a narrow enough BW to keep Doppler distortion low.
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>Now THAT should work well for a dipole! A pair in a room should get you over 120 dB SPL @ 25 Hz. So reference levels from a dipole sub - that's not bad...
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Hmm, yeah, you might get this much with good boundary coupling and some room gain at 750W/driver. For sure it would make a bodacious IB driver.
In 10ft/14Hz vented, it looks way too underdamped for me, with 5ft^3 sealed being borderline, though with a good EQ and stuffing could make them winners.
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>What exactly are the benefits of a dipole sub?
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No box sound and properly set up excites room modes far less.
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> And what exactly a dipole sub?
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A driver(s) mounted on an open baffle.
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>Would it be set up the same as regular dipole speakers?
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You can, but there's more efficient layouts for subs. Review Linkwitz's site: http://www.linkwitzlab.com/index.htm
GM

 

[Michael R Price]

Holy cow, Dan, are you sure those parameters are right?
Sd seems high.
Unibox says... 85.8 dB sensitive and Qts = 0.44. A sealed box would have to be pretty big to get a useful non-EQed system, but it looks like it's capable of 110 dB at 20Hz anechoic. And the fact that the Fs is 14.5 Hz makes it reach extremely low. (A good IB driver.)
In a large vented/PR box it looks good too. 10ft^3 tuned to 12-14Hz looks like a good option. Either way that's almost 115 dB anechoic. Wow.
So when does the preorder start?

 

[Jack Gilvey]

That is practically the SD of the Maelstrom (1180cm^2)that has to be a typo.

I just figured it was an 18" driver with a bigger surround.
Fwiw, I think that isobaric is a waste of a driver in almost all cases

 

[Pete Mazz]

I thought 15" was the general consensus. 18" will be too big for me. It will likely cause some tube builders some headaches as well.

Pete

 

[Jeff Rosz]

for the 15"....

can i get the Vas of this thing up to tempest range, say 300L? is 150L set in stone?

 

[Tyson]

Why not just make a Tempest, but with much higher output, so we can avoid having to go "dual" tempests?

 

[George W]

Let me add my vote for a 3^3ft sealed sub. I want maximum output but I'm a fan of the better transient response delivered by sealed subs since I would use this for music as well. I would be willing to sacrafice some size for efficiency but probably wouldn't want it going over 4^3 or so. This has been a fascinating thread so far and I can't wait to see the result. Thanks for taking up several hours of study time!
George

 

[Charlie G]

JOOC, anybody know offhand what the transient response of the Linkwitz transform looks like?

Everyone says, "Lets go sealed to keep good transient response." and then says "Let's EQ the hell out of it to get lots of bass." I'm not quite certain that this EQ is free in terms of phase/transient/etc.. response, is it?

I don't know for sure, so maybe this is baseless. Thanks!

 

[Jack Gilvey]

JOOC, anybody know offhand what the transient response of the Linkwitz transform looks like?

Everyone says, "Lets go sealed to keep good transient response." and then says "Let's EQ the hell out of it to get lots of bass." I'm not quite certain that this EQ is free in terms of phase/transient/etc.. response, is it?

Charlie, read the LT links I provided earlier. The LT allows you to have just about any transient response/Qtc/F3 you desire. The EQ is certainly not free, though,as it can require prodigious amounts of power. The more power delivered to the voice coils, the more chance for heat induced non-linearities like power compression and the rise of Qts/Qtc above spec.

 

[Dan M~]

Dustin,

Brian is correct. Compared to a standard two driver design, a two driver isobaric would use 1/4 the box volume.

My thoughts are that if I need to buy two drivers anyway, could Dan W. design a driver optimized for isobaic use that would be cheaper to build then a standard driver?? I don't have a clue ... maybe it would be more expensive.

The primary limiting factor in sub woofer design seems to be box size (as I see it). Typicaly an isobaric system is 1/2 the size of a standard design. The cost goes up because you need two drivers for every one in a standard design.. BUT... has anyone every tried to build a driver optimized for isobaric use only? There are many advantages (I.e. More Musical)of isobaric subs, has anyone tried to exploit the design by producing a driver "tuned" for this use? What would Dan W. do to a driver design to optimize it for isobaric use? Would it actualy reduce the cost of the driver (though you would need two)?

Any insight from the masters?

-Dan M~

 

[Jack Gilvey]

There are many advantages (I.e. More Musical)of isobaric subs

Huh?

 

[Jeff Rosz]

hey folks,
well i guess i will just show ya'll what i got...please keep in mind the total number of drivers i have designed in my life is ah, lets see ah erm, [counting toes]...1-2-3-4-0, ya zero. lol.
so for the 15"er...
2.5ft^3 with some bracing and double walls gets you