Best Sub Driver for small enclosures (1 Viewer)

[Martice]

How much power would I need to push a BP 1203 in a 14x14x17 cabinet? I know the smaller the box the more power needed so any general information would be welcome.
Thanks
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What if it gets no better than this!?!

 

[Jack Gilvey]

quote: How much power would I need to push a BP 1203 in a 14x14x17 cabinet? I know the smaller the box the more power needed so any general information would be welcome.[/quote]
Well, I think that a Linkwitz transform, or at least some form of eq, is the only way to make a sealed 1203 viable (even a best-case f3, Q = .7, would be around 70Hz unassisted). Given that, I'd want to have about 800-1000 watts on tap depending on the chosen Fc/Qtc. It might be obvious by now that this is not a cheap way to go. Although, if you look at my QSC thread, you can score 830 watts for $300 right now...
Honestly, I think the PE 12"DVC/plate amp combo is a very good sub, and an excellent first project. The 1203 would be more involved. See how that goes, and if it leaves you wanting for more.
[Edited last by Jack Gilvey on November 08, 2001 at 06:17 AM]

 

[Martice]

Thanks Jack. Will do.

 

[Jon Hancock]

The BP1203 would work OK in a box like your description of the Velodyne- it would be about 2000 cu in, or 33 liters, and would have a Q of about 0.4 to 0.41, depending on the effective damping.
With this low a Q, you don't need the complexity of a Linkwitz transform equalizer like the Marchand Bassis; a parametric or simple shelving EQ (12 dB at 20 Hz) will probably do. That can even be implemented passivly, if there's some crossover gain available to make up the insertion loss.
With 250 watts, the maximum output at 20 Hz is 96 dB. OK for a smaller room, possibly. With 1 kW, 102 dB at 20 Hz.
But what a heavy little box it would/will be!
That's why I'll try this in a re-inforced 44 L Woodstyle box. A bridged Aragon 8008 ST should be able to hit close to 1200 watts into this load, though a BB or Palladium would be more comfortable driving it.
Regards,
Jon

 

[Jack Gilvey]

With this low a Q, you don't need the complexity of a Linkwitz transform equalizer like the Marchand Bassis; a parametric or simple shelving EQ (12 dB at 20 Hz) will probably do.

This is an interesting point, and one which I've wondered about. Half the function of a true Linkwitz transform circuit seems to be "correcting" the hump in response seen in high values of Qtc. If this is not present, if our Vb can be kept large enough so that Q

 

[Jon Hancock]

Actually, Jack, in my opinion the cutoff point for Linkwitz transform versus shelving equalizer is a Q of 0.5, which is critically damped. Now, in practice, I'd be willing to let that go to a bessel alignment, 0.577. It's also true, that for someone who does reflex systems, a Q of 0.707 shouldn't be any big deal- but that would be the absolute upper end, and in actuality, it requires a more complex EQ curve than you can realize with a simple 6 dB/octave shelving EQ. That's why I like to stick to the range of 0.5 to 0.577.
Now, with a lot of these humongous motor driver speakers, the *real* problem winds up being the large voice coil inductance- typically in the range of 4 to 10 mH. This is a REAL problem, because it limits the power transfer as frequency goes up. Look at the impedance curve of an HE-15 or the BP drivers. They start rising quickly above 70 Hz.
http://server2045.virtualave.net/ttriff/Bp1203z.bmp
This impedance rise due to VC inductance is so pronounced that it limits power transfer. The impedance minima due to VC inductance is in the 50-70 Hz region, *not* the 100 to 250 Hz region of most standard woofers. This is what causes the apparent "hump" in the 50-70 Hz responese of these drivers.
What to do? One way is to use a parametric equalizer like the BFD to "knock down the hump" to the same overall level as the 100-125 Hz area. Then, apply EQ for the lower range. This is a little expensive, but works very well.
Another path is to use a lower crossover, about 70 Hz (which is what I prefer for these drivers even when I do use the EQ technique), then just use shelving EQ for the low bass correction. The only problem, is you have at least one extra pole in the roll off rate of the subwoofer in the upper end; this make getting a good blend between mains and sub a bit trickier. For example, if you're using a 3rd order sub crossover on the LP, you'll wind up with a 4th order LP, roughly. But you may never notice the ripple in the transistion region *unless* you've taken a lot of care in your room layout and listening position, and have optimized the setup using something like RPG Acoustics Room optimizer to determine sub and mains and listener location for flattest response. (RPG Room Optimizer is the *best* bar non $99 tweak you can do for your system).
Best regards,
Jon

 

[Brian Bunge]

Jon,
So are you saying that if your Qtc is between .5 to .577 then you can get away with using a simple EQ to boost low frequency response but if it's higher than this a LT circuit is a must (in your opinion, of course!)?
Just trying to simplify it in my own mind!
Brian

 

[Jack Gilvey]

Thanks much for the explanation, Jon. Fortunately, these modern low-Vas/low-Qts woofers make a Qtc ~.5 pretty easy.

 

[Jon Hancock]

Exactamundo!
That's exactly what I'm saying! Not to poo poo the usefulness of the LT, but it's most necessary with higher Q drivers in small boxes, with a Q resulting in passband hump/ripple before the roll off. Say, if you start with a driver with an Fs of 24 Hz, and a Qts of 0.5, then put it in a small box and the Q jumps to 0.84, then you can deal with that with the LT. But, as Jack points out, with the low Qts/low VAX drivers available, the LT isn't necessary because it's easy to wind up with a low Qtc.
That's kind of how my X1 Klones work- very low Qts drivers, small box, shelving EQ- but they're a reflex alignment, tuned to 27 Hz, that is over damped because of driver Q- they roll off at 3 dB/octave from 120 Hz down to 25 Hz. (driver Qts is about 0.15).
Regards,
Jon

 

[Randy G]

Martice,
Hmmm...an HGS-12 on the cheap? :^)
A noble aspiration, but hen all is said and done, I don't think it'll be all that easy to do. I don't know what the Xmax is on the Velo, but I do know that the magnet itself weighs about 20 pounds, and the input wattage is listed as 1250 watts(not sure how accurate THAT is). And don't forget, the exterior dimensions are 14 x 14 x 14.5 = 2442 cu.". Not sure if my math is right, but I think that's around 46 liters EXTERIOR, right? Is it even possible to fit that 1203 driver, plate amp, eq, etc. into a box that small? Or do you not mind having some exterior electronics? I'd love to be able to put together some kinda HGS-12 clone for a fraction of the price as well, but I think it's beyond my capabilities at this point. Now maybe if I put it into an ACI Titan sized sealed box....
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[Jack Gilvey]

Not to poo poo the usefulness of the LT, but it's most necessary with higher Q drivers in small boxes, with a Q resulting in passband hump/ripple before the roll off...with the low Qts/low VAX drivers available, the LT isn't necessary because it's easy to wind up with a low Qtc.

Ok, got it. It would still be necessary, though, to have a true shelving eq to maintain the rolloff characteristics we desire, would it not? Can this type of eq profile be duplicated by parametrics such as the BFD or 551? That would certainly be preferable, since one of them would be needed anyway.

 

[Brian Bunge]

Jack,
That is exactly my question as well. If I can get by without the LT that's great since, like you said, a parametric EQ would probably be needed anyway.
Awaiting a reply from the subwoofer gods...
Brian

 

[Martice]

Ok to recap this thing. If I wanted to put the BluePrint 1203 in a 14x14x17 cabinet, I wouldn't necessarily need an anything more than a BFD or any other capable parametric EQ to get excellent performance?
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What if it gets no better than this!?!

 

[ThomasW]

Jon's not a big fan of using parametric EQ. Most of the time he puts any necessary EQ in the form of shelving networks into his custom electronic XO designs for each woofer.
Since this is not something everyone has the ability to do, use a stock parametric. With the better designed parametrics it's possible to create something very close to shelving EQ and deal with room problems at the same time.
Once the operation/programming of the DSP1100P is understood it's easier to operate than the 551. This is because the 'taper' of the 551 pots is such that a RTA or other similar measurement device is needed to ensure the accuracy of the settings. Since the DSP1100P is has a digital readout it's really easy to know when the settings are exact.
Martice
quote: Ok to recap this thing. If I wanted to put the BluePrint 1203 in a 14x14x17 cabinet, I wouldn't necessarily need an anything more than a BFD or any other capable parametric EQ to get excellent performance?[/quote]
This question has already been answered, look at Jon's post of November 08, 2001 12:21 PM on page #2 of this thread
[Edited last by ThomasW on November 09, 2001 at 09:16 PM]

 

[Jack Gilvey]

Since this is not something everyone has the ability to do, use a stock parametric. With the better designed parametrics it's possible to create something very close to shelving EQ and deal with room problems at the same time.
Once the operation/programming of the DSP1100P is understood it's easier to operate than the 551. This is because the 'taper' of the 551 pots is such that a RTA or other similar measurement device is needed to ensure the accuracy of the settings. Since the DSP1100P is has a digital readout it's really easy to know when the settings are exact.

Thanks, Thomas. Excellent, useful information. And only $.02, such a deal!

I guess that the 551 should sound better due to its analog signal path, but would that matter in such a limited bandwidth application as a subwoofer eq?
Also, would it be feasible to configure one or more bands of the FBD to function as an infrasonic filter for vented use?

 

[Jon Hancock]

ThomasW and I worked with both the analog EQ unit and the BFD. The analog unit had problems with non-linear behavior of the pot rotation versus EQ setting; it was very tedius to get setup with a desired characteristic.
Once you master the slightly idiosyncratic interface of the BFD, it's quite easy to use, and quite easy to use *precisely*, which is key. The BFD's circuitry did *not* seem to compromise bass definition at all, digitizing the signal- I might even have to say, because it was so easy to get the results we wanted, it sounded better than the analog EQ. We were only using it in the range of 100 Hz and lower.
Now, because of how you can use cut and boost with variable bandwidth and positioning, we used this type of EQ with the AS-15 project. Here's the resulting EQ curve to tame that beast:
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This doesn't show the roll off in the infrasonic fully, because the scale doesn't go that low. If you were concerned about this behavior because of known source anomolies (record warp, for example, or stygnian bass on a DVD), then a notch/dip could be added tuned roughly to the lower impedance peak of the reflex system.
So, within the parameters we describe, you could do very well on any compact sub system just with a BFD for EQ. I just happen to have a Bassis sitting underneath mmy bed, so I have more options. *However*, with the 50-70 Hz hump of TC-Sounds sourced woofers, that *may* not be enough.
Link Removed
Best regards,
Jon

 

[ThomasW]

Jack
The 551 can be configured to provide boost as low as 8Hz. This requires overlapping 2 EQ bands, each set at a 10Hz setting. Nousaine's doing this. I played with this config on the big IB. And yes it has an effect when running test tones. But in the real world there's virtually nothing down there to boost, and setting the 551 provide that boost introduced a characteristic 'pumping' into the system.
I'm reasonably sure the DSP1100P can also boost slightly lower than 20Hz, by using the same dual overlapping filter method. Obviously it wouldn't go as low as the 551. One should be able to 'model' it's effects using the Behringer software

 

[Jack Gilvey]

Thanks, gents.

 

[Ville Javanainen]

I would like to say hello to everyone! I've been reading this forum about 9 months and tried to register once before, but they did not accept my real name.. which is Ville-Joonas Javanainen, but it'll work with just Ville Javanainen
Now some questions
How about the SQ of 1203 sealed box? My last sub was Velodyne CT-150 and I would like to build a sub which is better than it was.. I have tools for woodwork and I have build couple "subs" before and currently I'm building DIY speakers..
Can I buy somewhere ready Linkwitz Transform crossovers? it should have: phase adjuestment, lowpass at least 12db/oct and from 30/35hz-?, subsonic if possible at 15hz, remote?...
How much power will 1203 need to work properly?
Damn that Blueprint doesn't have an European retailer yet.. It's so expensive to order 1203 directly from USA...
BTW, if someone has icq could someone talk with me?
my icq #115910909
And sorry for my bad English, I'm from Finland

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Colorado Avalanche, since 1995!
#6 Clown : you don't have to answer to anything or anyone.

 

[ThomasW]

Hi Ville
No one I'm aware of makes an active XO with built-in LT, and phase adjustment, let alone one with remote control
The only assembled LT unit I know of is the Marchand BASSIS, it lacks phase adjustment and is expensive US$399. The kit version is US$249 http://www.marchandelec.com/wm8.htm
Phil Marchand could probably create a custom BASSIS (sorry no remote) that has the phase control added in, but it would be very expensive
If you're capable of building from scratch, then you can get basic LT pcb's from Rod Elliot in Australia US$12ea http://sound.westhost.com/project71.htm http://sound.westhost.com/purchase.htm
I'd recommend having around 500 watts to use with the 1203
[Edited last by ThomasW on November 10, 2001 at 11:49 PM]