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


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#1 of 734 OFFLINE   Jack Gilvey

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Posted February 18 2002 - 09:43 AM

I've started this thread to continue the discussion begun inthis thread,since it needed one of its own.
Basically, Dan Wiggins (Adire Audio) posed this question:
Quote:
I'm interested in what you would see as a good set of T/S parameters and design goals... Let's have some fun! How about a custom driver for a specific application - the Ultimate Home Theater Subwoofer. Choose an alignment (some mondo-wicked vented thing), and let's see what we can - as a group - dream up. All the T/S parameters are up for consideration. Power handling? Assume 5 kW RMS is the upper limit. Sd/Xmax? How much do you want (can do up to 18" diameter drivers).

I'll copy his last post from that thread, and we can continue the discussion/dreaming here. It'd be good to read through that other thread, though.

Quote:
Hi all,

A few thoughts...

1. I think a different thread dedicated to driver design/dreaming would be in order.

2. Hoffman's Iron Law still rules: small and deep means low efficiency. So if you want a small sub, then you WILL NEED a big amp. We're talking at least $400+ for the amp alone. Keep that in mind in the discussion.

3. PRs are great, if you can afford them (cost and space). A fully-tricked-out XBL2 motor'd Tempest would require a pair of VERY high excursion 18" PRs. This will run in the $150+ range for each PR. So you're looking at $300 plus the driver (figure $250+ for a monster excursion 15" driver), and $400+ for the amp. Or an entry cost around $1,000, not including the cabinet.

But from a size issue, you need to be able to physically mount the PRs and the driver. Which means your box is at least 20" high and 20" deep, and at least 18" wide. That's not too small to start with.

4. If EQ is the goal, why even use PRs/vents? What if you had a 15" driver with a clean 35mm of one-way Xmax? In an EQ'd sealed box, you could do some serious damage with it, at a lower cost - no PRs or vents needed, just a big amp (which we might be resigned to).

5. Motor strength? It has to be strong enough to move the cone in the size of box you want, and no more. You can have too much motor strength for effective use as a subwoofer. Means you MUST equalize to get the response back, but in that case why drop all the bucks into a super strong motor only to equalize it away?

Anyway, just some thoughts. But it seems like the summary goal would be:

- 3 cubic foot box
- high power handling
- capable of 5+L of linear displacement (twin Tempest range)
- suitable for sealed or vented boxes

Thanks,

Dan Wiggins
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#2 of 734 OFFLINE   Jack Gilvey

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Posted February 18 2002 - 10:14 AM

Quote:
I think a different thread dedicated to driver design/dreaming would be in order.

Ok. Posted Image

Quote:
. Hoffman's Iron Law still rules: small and deep means low efficiency. So if you want a small sub, then you WILL NEED a big amp. We're talking at least $400+ for the amp alone. Keep that in mind in the discussion.

Understood. Kilowatts are getting fairly cheap, so I think efficiency is the thing I'd give up first if required.

Quote:
PRs are great, if you can afford them (cost and space). A fully-tricked-out XBL2 motor'd Tempest would require a pair of VERY high excursion 18" PRs. This will run in the $150+ range for each PR. So you're looking at $300 plus the driver (figure $250+ for a monster excursion 15" driver), and $400+ for the amp. Or an entry cost around $1,000, not including the cabinet.

Steep, indeed. What type of box requirement do you see for this uber-Tempest, though, as adequate porting would be considerable.


Quote:
But from a size issue, you need to be able to physically mount the PRs and the driver. Which means your box is at least 20" high and 20" deep, and at least 18" wide. That's not too small to start with.

No, but that's not bad for the type of performance it could give, at least to me.

Quote:
If EQ is the goal, why even use PRs/vents? What if you had a 15" driver with a clean 35mm of one-way Xmax? In an EQ'd sealed box, you could do some serious damage with it, at a lower cost - no PRs or vents needed, just a big amp (which we might be resigned to).

Good point, very high Excursion and Pe make even extreme Linkwits transform designs feasible.

Quote:
Motor strength? It has to be strong enough to move the cone in the size of box you want, and no more. You can have too much motor strength for effective use as a subwoofer. Means you MUST equalize to get the response back, but in that case why drop all the bucks into a super strong motor only to equalize it away?

So, sometimes Qes and Qts can be too low? Seems that way from the drivers I've looked at.

Quote:
Anyway, just some thoughts. But it seems like the summary goal would be:

- 3 cubic foot box
- high power handling
- capable of 5+L of linear displacement (twin Tempest range)
- suitable for sealed or vented boxes

I think the 3ft^3 goal would be what I'd want for a 12", a home-variant of a Brahma. Maybe ~2.5-3L of Vd for use with two high-performance 15" PR's tuned to 18Hz. And I'd like flat response down there, not -6dB @ 20Hz.
As far as a 15", Vd in the neighborhood of dual-Tempests sounds incredible, but I'd want it to be similar to Tempest as far as alignments are concerned. I'd like smaller box requirements, but that would almost necessitate PR's.
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#3 of 734 OFFLINE   Dustin B

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Posted February 18 2002 - 10:22 AM

I don't want to have to drop more on PR than I did on the driver. So I would still like the driver to be friendly to 300L+ enclosures that make 8" or larger diameter ports feasible.

Although I think my parents would like the idea of a much smaller enclosure that uses a pair of 15" PR and a 12" driver that could perform very similar to what an Adire Allignment Tempest currently does.
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#4 of 734 OFFLINE   Jeffrey Noel

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Posted February 18 2002 - 10:41 AM

Quote:
What if you had a 15" driver with a clean 35mm of one-way Xmax?


Posted Image Posted Image

Dan, I'm going to start saving up my money right now. A driver with 35mm one-way Xmax designed for a sealed enclosure would be awesome. It would definitely save us some money not having to buy PRs.

I'm all for it! Posted Image Posted Image

Could we name it the "Holy Shit" sub or the "Jaw Dropper"? Posted Image
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#5 of 734 OFFLINE   Vince Bray

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Posted February 18 2002 - 11:16 AM

Dan,

I'm just curious, don't think I'll be shopping a sub for awhile since the HE15 is kickin' and the next purchase will hopefully be a dlp projector Posted Image

But since you asked, what is the maximum xmax we could have in a 15"? Can you do 45mm? Jack and I are of the mind that 15" is an ideal size - enough for displacement (given higher xmax) and you don't pay for two motors, etc that dual 12" drivers dictate. 15" is cost and box-size effective. 18" dictate too-large a box, IMO.

1. 120db from 20hz up - means 45mm linear xmax one way
2. Bottomless like HE15 - add an extra plate so the coil physically cannot get mashed.
3. Metal cone - looks cool.
4. Dual 2ohm coils - get the last drop of current from that amp!

I guess kind of like this but with just a little more xmax, and for $4-$500. That definitely hasn't been done...

#6 of 734 OFFLINE   DanWiggins

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Posted February 18 2002 - 11:32 AM

Jack Gilvey posted:
Quote:

Understood. Kilowatts are getting fairly cheap, so I think efficiency is the thing I'd give up first if required.

Got it. We'll figure around 1.5 kW (like a Mackie 1400i, or a QSC PLX1602) as a good "level" of power, that most people can get from a single circuit in their home.

Quote:

Steep, indeed. What type of box requirement do you see for this uber-Tempest, though, as adequate porting would be considerable.

Well, for the Uber-Tempest, probably a box in the 6-8 cubic foot range. Tuning to 19 Hz can be accomplished with an 8" diameter vent, 40" long. Big, but a vent nevertheless...

Quote:

So, sometimes Qes and Qts can be too low? Seems that way from the drivers I've looked at.

you bet! Remember, F3 is inversely proportional to Qes - lower Qes, raise F3.

You've probably heard of EBP before? Small's recommendation using Fs and Qes to determine driver applications? You divide Fs by Qes to get EBP, and Small gave some recommendations.

HOWEVER, in my experience here's what I recommend from EBP:

EBP < 40: sealed box
40 < EBP < 80: sealed or vented box
80 < EBP < 120: vented box
120 < EBP: not a subwoofer

Essentially, if your EBP is too high, you simply cannot get adequate response down in the 20s - you have a tough time breaking past the 32 Hz range. And I don't consider that a subwoofer. You need to be in the 25 Hz range or lower to be a sub, IMHO.

Quote:

I think the 3ft^3 goal would be what I'd want for a 12", a home-variant of a Brahma. Maybe ~2.5-3L of Vd for use with two high-performance 15" PR's tuned to 18Hz. And I'd like flat response down there, not -6dB @ 20Hz.

Oh, we got that one covered already, then...Posted Image Try a Brahma 12 in 3 cubic feet, tuned to 20 Hz with a pair of PR-15s (each loaded with 1100 grams of mass). You have an anechoic F3 of 18 Hz. Add in a crossover, and that drops down to the 17 Hz range.

And it will take a clean 1200-1300W straight out, without reaching Xmax (above 17 Hz). And you'll have SPL levels in the 110+ dB SPL range above 18 Hz. Spooky levels of output!

Quote:

As far as a 15", Vd in the neighborhood of dual-Tempests sounds incredible, but I'd want it to be similar to Tempest as far as alignments are concerned. I'd like smaller box requirements, but that would almost necessitate PR's.

OK, so something in the 8 cubic foot range, 15" driver with 30+mm of Xmax. And definitely suited for vented/PR applications - not so much interest in sealed boxes?

Dustin B posted:
Quote:

I don't want to have to drop more on PR than I did on the driver. So I would still like the driver to be friendly to 300L+ enclosures that make 8" or larger diameter ports feasible.

Although I think my parents would like the idea of a much smaller enclosure that uses a pair of 15" PR and a 12" driver that could perform very similar to what an Adire Allignment Tempest currently does.

OK, so you and Jack are both looking at good performance in the 200-300L range, with the 15" driver. Vented options are definitely feasible then.

Jeffrey Noel posted:
Quote:

Dan, I'm going to start saving up my money right now. A driver with 35mm one-way Xmax designed for a sealed enclosure would be awesome. It would definitely save us some money not having to buy PRs.

I'm all for it!

OK - so that's a vote for a sealed box driver. So we'll shoot for a Qts around 0.38-0.42 or so, which should work well in both vented and sealed boxes.

Dan Wiggins
Adire Audio

#7 of 734 OFFLINE   DanWiggins

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Posted February 18 2002 - 11:36 AM

Vince Bray posted:
Quote:

Dan,

I'm just curious, don't think I'll be shopping a sub for awhile since the HE15 is kickin' and the next purchase will hopefully be a dlp projector

But since you asked, what is the maximum xmax we could have in a 15"? Can you do 45mm? Jack and I are of the mind that 15" is an ideal size - enough for displacement (given higher xmax) and you don't pay for two motors, etc that dual 12" drivers dictate. 15" is cost and box-size effective. 18" dictate too-large a box, IMO.

1. 120db from 20hz up - means 45mm linear xmax one way
2. Bottomless like HE15 - add an extra plate so the coil physically cannot get mashed.
3. Metal cone - looks cool.
4. Dual 2ohm coils - get the last drop of current from that amp!

I guess kind of like this but with just a little more xmax, and for $4-$500. That definitely hasn't been done...

Vince,

We can get you that GZ Plutonium Xmech right now (that's what they really have; the 4HP motor from TC Sounds isn't capable of 45mm one way linear, although the suspension is). In most car audio subs, they list mechanical throw, not linear. I don't know of a single driver anywhere in the world with more linear throw (DUMAX measured) than Brahma, at 27.32mm one way. Many claim more, but when it comes time to measured results...

Now, for 45mm of linear throw? OK... We can do that! Let me kick some ideas around, and see what we can come up with. But it is entirely possible. Our XBL2 motor technology can do some amazing things.

As far as the metal cone, do you absolutely need it? It doesn't really help all that much, and costs a LOT more money... How about a nice basic black cone...Posted Image But definitely the DVC 2 Ohm design, as much linear Xmax as possible, and in an 18" frame. Let me roll some ideas around, and see what I can come up with!

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#8 of 734 OFFLINE   Pete Mazz

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Posted February 18 2002 - 11:47 AM

Why bother with PR or vented if we can get low Fs and high SPL from a small sealed box? A lot of us are already running pretty good size amps, and many already have a BFD to tame the anomalies/room interaction.

So, my vote would be a 15" driver (two for me, please) that can have a .5 -.6 Q in a ~3 cu/ft sealed enclosure, and will deliver 115 dB from 20 Hz.

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#9 of 734 OFFLINE   Mike_A

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Posted February 18 2002 - 12:53 PM

i've got to throw in a vote for something that works well in a ~120L or so sonotube, so ported instead of PR's and goes as flat as possible without EQ down to 20Hz or below. Basically, a super shiva, with more Xmax and able to work in slightly smaller enclosures. honestly, i think for the DIYer, there's a lot more market for such a driver. give it an alloy or poly cone (something besides paper) and a santoprene (or some other rubber variant) type surround and this thing would really dominate...

just a thought from a slightly less extreme perspective Posted Image

#10 of 734 OFFLINE   Mark Seaton

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Posted February 18 2002 - 01:28 PM

Hi Dan and all,

Dan's breakdown of the costs involved in PR'd options make the best arguement for going the sealed route. For around the cost of the PRs, you might as well buy another driver. In real-world useage, the benefits of power reduction per driver, excursion, and consideration of real spectral content point heavily toward multiple sealed drivers. Most who have read my posts know I'm a big proponent of what Martin Logan has trademarked "Balanced Force Configuration" where drivers are configured to cancel the net rocking forces on an enclosure. A dual 15" with this sort of excursion would make for one seriously potent subwoofer. A single driver would be quite good on it's own in many rooms. The big question with a sealed subwoofer is what people's thoughts on EQ or other electronic correction is. I would suggest a natural F3 in the mid to upper 20s if possible. I'm guessing 3 cu.ft. per cabinet or maybe a pair in 5 cu.ft. would fall in the reasonable range for many homes. Basically what you will have here is a Krell MRS killer.

For those wondering about the benfits of having 30+ mm of excursion on a decent sized radiator, I can confirm it to be quite pleasing to the ear. Posted Image
Note that most of my comments about motor strength come into play if you want to get away from using EQ and modest box sizes. It is indeed all about the final ratios within a driver. IF you have room to still play with other parameters, high motor strength can indeed offer some interesting options (ok, it's starting to show I've been around Tom Danley too much Posted Image ). Noting the EBP product, the ratio also demonstrates that if you can lower Fs AND Qes, you can maintain the EBP, but this also has some very interesting things with required box volume. This is by no means the only way to get deep bass from a sealed box, but realize that a driver placed in an enclosure even equal to its Vas will raise the Fs of the system by a factor of ~1.4. This quickly shows that an Fs of 20Hz or below is required.

Another nice benefit of sealed designs for DIYers is that if we have a single driver system which can work well without any EQ, those with more power and interest in EQ can squeeze more drivers in to less than full multiples of the space and not really take any hits in actual efficiency, only un-equalized frequency response.

Dan,

One factor I am curious if you have looked into much: In relating the output limited Xmax, or power input to Xmax as shown in most programs, are these numbers RMS excursion values, or real p-p values? I'm under the impression that the real measured p-p values within linear limits represent about 1.4x the predicted value. Of course this is certainly useable for our electrical Xmax values where BL does indeed "curve" rather than brickwall. Of course such real values of Xmax do correlate well with your simulated sine wave tracking for the XBL^2 motor. My interest is more in terms of the suspension's travel. Your thoughts/experience?

Mark Seaton
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#11 of 734 OFFLINE   Brian Bunge

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Posted February 18 2002 - 02:00 PM

Dan,

I'm with Pete on this one! I have a decent sized room that's completely open to the rest of the house. Because of the "open floor plan" I only have 1 place to put the sub. It would be up against my back wall next to my sofa and about 2-3' from the left side wall. It will also most definitely have to function as an end table in a sealed enclosure (whether or not this is an ideal application for is moot as this is my only choice). For this reason, I'd really want something that can be downfiring. Maybe that goes without saying for your designs, but I had to throw that requirement in.

I think 115dB at 20Hz in a 3ft^3 enclosure would be every male's wet dream. Sealed would be manageable and you could still go ported or PR'ed. If necessary, I'd be willing to EQ as I am fully prepared to buy a K2 and have a BFD 1124 laying around. I've been planning on the K2 anyway.

Mike_A,

As far as poly cones, I think they are strictly out of the question for this application. IIRC, poly cones aren't nearly as stiff as a good pulp filled paper cone. I could care less about flashy looks. I've seen enough of that from the car audio market. Far too much form over function (Reminds me of "White Men Can't Jump" where Woody Harrelson accuses Wesley Snipes of caring more about looking good than winning!). One look at my 1803 and you can tell it's all business. I want something even more extreme than this!

So I'm for the ultimate sealed sub driver that can still be used in 4th and 5th order alignments.

Brian
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#12 of 734 OFFLINE   Jack Gilvey

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Posted February 18 2002 - 02:01 PM

Great stuff all around, especially the points about the sealed variations. As I mentioned above, drivers like those being discussed have almost unlimited possibilities in a Linkwitz transform. Especially if they're so mounted as to cancel their inevitable huge motions,such as the ML or Krell, or what ThomasW has done in with dual Blueprint 1503's in his "Tube-Zilla" with one on each end.

I guess it might be easiest to have a "perfect" sealed driver or a "perfect" reflex driver if we have one for each purpose...maybe that would be the best way to go, two different optimised drivers.


Quote:
i've got to throw in a vote for something that works well in a ~120L or so sonotube, so ported instead of PR's and goes as flat as possible without EQ down to 20Hz or below. Basically, a super shiva, with more Xmax and able to work in slightly smaller enclosures. honestly, i think for the DIYer, there's a lot more market for such a driver.

The problem becomes, Mike, that you're still stuck with the same porting that you'd use with a regular Shiva (even less, if we have a smaller enclosure), but you're trying to get twice the output from it. At least as I see it.
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#13 of 734 OFFLINE   Brian Bunge

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Posted February 18 2002 - 02:09 PM

Jack,

While I'm over the whole sonotube look, Thomas' Tube-Zilla might be something I'd be willing to do! If not for me, my crazy Bass-A-Holic friend is gearing up to build his first house. While it will be a "starter" home (1800 square feet or so), his family is in the construction business and are diehard overbuilders. So he's not going to be happy with anything less than the ultimate. When I told him about my 1803 he said he wanted two! So I think dual 15's with 30+mm of Xmax in what could be considered a "space-saving enclosure) is right up his alley. I can pretty much talk him into anything audio-wise!

Brian
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#14 of 734 OFFLINE   Mark Seaton

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Posted February 18 2002 - 02:22 PM

Quote:
i've got to throw in a vote for something that works well in a ~120L or so sonotube, so ported instead of PR's and goes as flat as possible without EQ down to 20Hz or below.
As much as I have seen some purport the flat anechoic response to be desireable to as low a frequency possible, there isn't much out there to support it. In the ideal you want to USE the transfer function of your room to your advantage. This is the same concept of how a quality car subwoofer is designed. As such, you can get a fairly good prediction with a variety of programs, even using those which can account for car, "cabin-gain." You just need to determine the approximate corner frequency. Of course some will find that significant gain in the room won't occur until the mid teens, but without checking into it, you could be wasting valueable box volume which isn't really needed. A PR'd box tuned very low can easily be made to match up with the gain of the room over a given range, and a sealed box does it nicely on its own. If you have a sealed box in a room too bit to ideally complement the transfer function, a simple shelf filter often will get you in the right ballpark for larger rooms. Our designer, Tom Danley, recently measured FLAT in room response down to 5Hz (using TEF) with a sealed subwoofer in a room a bit over 3000 cu.ft. The outdoor response is about -10dB around 12Hz.

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#15 of 734 OFFLINE   Jack Gilvey

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Posted February 18 2002 - 02:36 PM

How about this: design for flat anechoic response down as low as possible, then attenuate LF via EQ as needed depending on the amount of actual room gain experienced. I'd imagine this would make for an enormous amount of headroom. Maybe somewhat profligate from an enginneering standpoint.
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#16 of 734 OFFLINE   Vince Bray

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Posted February 18 2002 - 02:52 PM

Quote:
As far as the metal cone, do you absolutely need it? It doesn't really help all that much, and costs a LOT more money... How about a nice basic black cone...
That's fine too Posted Image The 15.2 does have a very nice look and the metal cone gets good WAF numbers, at least at my place. The 45mm is the kicker. If you can fit an 18" in a 4ft^3 box, fine, but a 15" is what I was thinking... at least I think it might suffice for most reasonably sane guys. Jack, you're SOL!

Quote:
I think 115dB at 20Hz in a 3ft^3 enclosure would be every male's wet dream.

It's called the 15.2 Just add 1.5kw

I am very interested in the sealed discussion. If you could yield 115db (20hz up-any type of eq, but no more than 1.5kw) from one driver sealed with only 1.5kw in (in a small box), that would be something! What would it take to get that kind of efficiency? Edge wound coils? The old Altec VOT had edge-wound coils and they were scary efficient, like 96db or something, can you do that? Does the small box dictate the efficiency at this point?
Quote:
Especially if they're so mounted as to cancel their inevitable huge motions

Maybe we should be looking for 12" drivers with huge throw, that work sealed in 1.5ft^3, and put 'em back to back to cancel the motion. It would be like portable nuclear detonation Posted Image
Quote:
As much as I have seen some purport the flat anechoic response to be desireable to as low a frequency possible, there isn't much out there to support it

I suffer from 'open plan-itis' and in my room it seems the room gain is diminished to the point of being useless. The 15.2 models flat to very near 20hz, and in-room I am getting more or less that response, not a huge excess of LF that would result from lots of room gain.

#17 of 734 OFFLINE   JimPeitersen

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Posted February 18 2002 - 03:17 PM

Wonderful discussion! Just so that I am clear on this; Dan, are you seriously considering this "imaginary" driver for possible production? I am just guessing, but I think you would have quite a market for it. Let's all hope.
JP

#18 of 734 OFFLINE   Mike_A

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Posted February 18 2002 - 03:35 PM

ahhh darn port flow problems - what's the most xmax that reasonable porting could handle? (say three 3" ports tuned to ~20hz - SVS CS+ style)

i still vote for flat anechoic response down to at least 20hz for the simple reason that it's not always possible to plan for the room. what if you move? do you really want to rebuild your sub? (ok i should realize the answer to this question maybe yes since it's the DIY forum Posted Image ). I like Jack's EQ solution better personally.

Maybe there's already a driver out there that meets my needs?

One of these days when i can get a 1kW amp, the small, sealed, EQ'ed design sounds perfect to me Posted Image

#19 of 734 OFFLINE   Dustin B

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Posted February 18 2002 - 04:22 PM

These dual driver sealed designs similar to Thomas's Tubezilla, what kinda of amp power do you figure they will need. Are we talking a kiloW to each driver, or would something like a QSC RMX1450 or Mackie M1400 be enough for both?

If these dual driver sealed allignments with a 0.5-0.6 Q can post 115dB plus at 20hz with some moderate room gain I think I could be convinced to give up on my love of the vent.
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#20 of 734 OFFLINE   Randy G

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Posted February 18 2002 - 05:09 PM

The Velodyne HGS-12 Series II that I presently have my eye on has exterior dimensions of 1.65^3ft. Sure would be nice to have a bit better performance in the same sized sealed box. For me, 115@20hz seems to be waay too much to ask for in such a small enclosure, and to be honest, I don't NEED that much horsepower. My priority is small size and GOOD performance....not over the top. In addition to the miniscule size of the HGS-12, it's also nice to have all the electronics built into the box.
Oh yeah...I don't mind saving a little money over the Velo as well.

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