The ProSoundWeb LAB Subwoofer Project (1 Viewer)

James W. Johnson · May 15, 2002

The guys at ProSoundWeb are working on an interesting subwoofer called the LAB Subwoofer.
The design is free and anyone can build it.
They have a dedicated forum for this subwoofer,
http://www.prosoundweb.com/community/forum.php?board=3
Its a dual 12" driver horn loaded subwoofer, 22.5" wide x 45" deep x 45" tall.
I am looking for a very high output subwoofer to be used for mostly demos and partys, I want my living room to have
the same sort of hard hitting bass that is usually only
heard in cars with massive stereo systems or some really nice clubs.
Here Mark Seaton talks about how this sub could work well for HT use...
I am considering building one or two of these for my room for an extremely high output music only subwoofer(s).
I do not want to give it any assistance so I would just cut it off at 30Hz.
I though I would start a thread about this subwoofer in case any of you guys are looking for extremely high output.
I am not sure what one or two of these subwoofers would put out from 30Hz on up but I have read each sub would take about 2000watts and with the efficiency around 107dbs we are talking major output.
I am guessing a pair in my room would put out ~21 more dbs than my dual Tempests from 30Hz on up..thats about 133dbs in my room...this should give me the chest thumping bass I am looking for.
The main negative to this project is that the boxes seem fairly complicated.
Positives are that a pair of these stacked and firing into a corner would take up very little space and this is a fairly inexpensive subwoofer.
I think this is the project I have been waiting for but I am still not quite ready to commit because the boxes look like a pain, I would appreciate a more detailed 'how to' on building these enclosures.

Chris Tsutsui · May 15, 2002

This might be an idea for an SUV competition box. Maybe put in 2 JL audio W7s that have an xmax of 28mm.

Mark Seaton · May 16, 2002

This might be an idea for an SUV competition box. Maybe put in 2 JL audio W7s that have an xmax of 28mm.

While different drivers can work in the horn, there will be variances, and it is rather unlikely you will get much better output than the optimized driver Eminence has designed per Tom Danley's requests. Above 30Hz, the horn is largely power limited, not excursion limited. Where very high excursion/linearity benefits is in distortion levels and allows for EQ of the bottom end. If 2 boxes or less were used OUTDOORS, or in an open space, slight benefits could be had from a different driver. That said, a bass horn with a 2:1 compression ratio places much greater forces on the cone. There are some minor aspects which are different from what would never be a problem in a "home" woofer, where such cone assebly and construction differences will make for a more reliable driver in this case.
As for car use, some have tried that before with our BassTech 7 and while they did get great output, it was more from the Vd of dual 15" drivers than from the horn loading. Once you get into the "pressure mode" operation of a space, many of the reasons for using a horn, and the assumptions it is designed with fall appart. Basically once you get below the LF corner of the transfer function of the car, you are changing the radiation resistance at the mouth, and you can quickly find that you are not getting any real horn loading at all, just cabin gain.
Now, what is really interesting is that the same effect occurs in a home, but at much lower frequencies. Tom had done a quick model of some corner loading options and came up with a 29Hz -3dB point, yet he wasn't happy with the model. An enclosed space is somewhat different from how horns are typically modeled, so there are some other effects going on. What is certain, is that the corner loading can both lengthen the horn, and increase the mouth size greatly. This both lowers the low frequency corner and smooths the response in general.
Where things get quite interesting is where you have a limited height to the space, where both the top and bottom of the horn are near a boundary, in this case, the floor and ceiling. This limits the expansion to one dimension and allows for a proper match of the expansion rate of the horn's mouth. What this means is that the 90deg expansion of the corner formed by the wall the mouth is facing, and the side of the actual box form the effective mouth of the horn. Our expectation which co-incides with other measurements we've done, is that in a moderate sized room, you could get down to the low frequency gain corner of the room (19-26Hz in mid size rooms) and achieve VERY deep response without much boost to the bottom end. This would be about ideal in that it would provide horn loaded bass with near zero phase angle down to the LF gain corner of the room. Tom and I are very curious to find a proper room we can measure this in to verify what Tom "suspects." Of course I've learned by now that when Tom says "I suspect" ... it's only a question of how well it works, not if... so hold onto your hat!

Click to expand...

Mark Seaton · May 16, 2002

I am not sure what one or two of these subwoofers would put out from 30Hz on up but I have read each sub would take about 2000watts and with the efficiency around 107dbs we are talking major output.
I am guessing a pair in my room would put out ~21 more dbs than my dual Tempests from 30Hz on up..thats about 133dbs in my room...this should give me the chest thumping bass I am looking for.

I would guess you are a possible 10dB conservative in your estimates. BTW, dB, just like in. ft. or mi. is proper notation for singular or plural, although I continually see some of the "experts" type out "a few dBs." (sounds like fingernails on a blackboard to me) No offense intended to you James, just those who have confused so many.
To give you an idea of the power a properly sized bass horn can provide, with 4 of our BassTech 7s in the middle of the floor of our workshop, which is >20'tall, we can easily shake the ceiling and walls of our office using a single amp capable of a little more than 2kW total. What makes this so impressive is that between our office and our workshop are TWO, full height, cinder block walls, and someone else's (poor souls) office! For bass to be transmitted through cinder blocks, something has to move the air on the other side, and as Tom likes to say "those aren't supposed to move." We used to do a funny demo where a single BT-7 could blow out a birthday cake at 1M, or 4 could do it at 10' outdoors.
My hope/guess is that a pair of these boxes stacked and properly loaded into the corner with a 7.5-8' ceiling would reach well into the 140dB range equivalent at 1M, and should peak to that range at a 10-12' listening position.
James, sounds like it's time to start looking at some horns for the top end again.

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Chad Kuypers · May 21, 2002

Hello all,
I just wanted to mention that I will be building one of these beasts as soon as I get back home. (Out of town at the moment) I am very excited about this design as I have been experimenting with and building so many subwoofers lately. This looks to be a blast. I will probably end up building a few of them because I know a couple of friends who will probably want one, once they hear mine.

I have been upgrading and pushing the limits of my car audio subwoofer system for the past year+. The kind of bass that can be achieved in car is scary. I don't necessarily listen to it all day at over 150 dB, it just has huge amounts of dynamic power that gives it an effortless sound. I started to neglect my home subwoofer because of this.

Mark's explanation of horn loaded bass "sound" is certainly what I am looking for at this point. I am looking for maximum "slam" from low bass. I want it to be effortless and gigantic.
This looks to be a lot of fun and a perfect solution to what I am looking for. I love to build and try new speaker and subwoofer designs. I build at least a couple of new speakers each month for me or for a friend. I am addicted to building anything, ESPECIALLY speakers.

I am just excited about the thought of sitting down at my home theater and having a couple of these staring at me. I will certainly post my opinions on this design as soon as I have finished building. I can't wait..
Chad

Shawn Solar · May 21, 2002

This is a very interesting design that doesn't get much talk time on these boards. 22"x45"x45" is quite large and is probably why. But even with a high excursion sub in an optimised ported enclosure it would take 3-4(or more) to equal the output. And at least twice the amp power. I think this would be a good project for anyone with a large room and a strong stomach

Mark Seaton · May 21, 2002

I am just excited about the thought of sitting down at my home theater and having a couple of these staring at me. I will certainly post my opinions on this design as soon as I have finished building. I can't wait..
Chad

One correction. If possible, you actually want them staring away from, or across from you. Ideally with the mouth firing into the corner, with one stacked on top of the other against the wall. It doesn't matter which wall the subs are against, but the side wall and corner will add a lot to the bottom end and smooth the response. If using only a single box, I have one possible idea to make a large "top" to extend the flare for only one horn which would basically make for a large shelf/table top in your corner. Lots of interesting possiblities...
Regards,

Click to expand...

Charlie G · May 21, 2002

Mark,

I'm building a pair of speakers using Bruce's 100hz bass horns and some round horns w/ compression drivers. I've been looking at a couple things to fill in the bass...

I can't really bring the speakers out into the room much, which means I doubt I can put the LAB in the corner, it would have to be in the center of the front wall.

To me that means I'd have to put the horn facing down or up... With a reflector of some kind?

Also, I've been looking at the plans... do you think it could be built so it could break apart somewhat (like in half?) for moving?

Charlie

Mark Seaton · May 22, 2002

Charlie,

Indeed, you can use any wall/corner as a reflector of sorts. On the front wall, I would probably build a stand for it and have it fire down toward the floor. Ideally you would want to slide this up against the side wall, but modal distribution in the room might make the midpoint of the front wall more desireable. This will indeed help with the loading, but the biggest advantage does come when you can properly continue the expansion of the horn. Using the floor and ceiling, you are able to limit the expansion to only the horizontal, and thereby get a significant expansion of the horn. This is where my suggestion above for a top piece when using a single horn comes from. This allows you to confine the expansion in the vertical dimension. If someone got creative, you can extend the expansion in any dimension.

Hmmm... thinking about that some more I have another idea for firing the mouth up at the ceiling or any boundary with a side extensions not much deeper than the horn. We're keeping Tom pretty busy lately, but I'll try and bounce some more ideas off him.

As for segmenting or breaking down the horn, that's just a matter of how creative you are with assembly and the cabinet construction. I would think it could very easily be accomplished by making the side walls of the horn and the bottom, and maybe even the back separate. It would take a little more wood and might make the external dimensions a few inches larger to allow for T-Nuts and machine screws to hold it together, and the overlaping portions to allow it, but certainly possible. I don't make any claims of being much of a woodworker, but I'm sure Chad might have some good ideas. My suggestion would be to create the core of the wrapped horn as its own unit with sides and all back to the section which starts down the back of the box where I would have the sides, back and bottom bolt on.

Mark Seaton · May 30, 2002

Hey Chad,

I thought I would bump this back up and check in to see if you had started working on any plans for this beast?

Mark Seaton · Aug 1, 2002

Hi guys,
I thought I would bump this to the top as the Eminence drivers are now available from the listed distributors. Reports so far are following my own suspicions, which is that this will be about 2/3rds of a BassTech 7 or near equivalent output with more power and somewhat more distortion. I did have some BassTech 7s set up at the office the other night and dialed in for some high power, stereo listening. I think I'm convinced we do need to make a horn loaded sub for (admittedly large) home use in the future.

The really scarry part was the confirmation that a pair of ContraBasses don't quite allow the various Unity loudspeakers quite enough headroom... Yikes! Concert, or live level dynamics? NOOOOOO Problem.

LAB Subwoofer Info

AlexKunec · Aug 1, 2002

How much do these drivers cost?

Mark Seaton · Aug 2, 2002

How much do these drivers cost?

Doh... my bad, I meant to include that, but it is also in some of the posts at the LAB. In the US, some have mentioned pricing to be $149 per driver. An absolute steal for the quality/robustness of the driver and considering it is a smaller run item, with lots of development behind it. Put in perspective of the output possible from the sub, it is cheap. If you wanted to go even cheaper, the Adire DPL-12 could also work, but if you want to beat on it at all, go for the intended drivers, as I have no idea as to the longevity of the DPL-12 in this application.

Regards,

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Mike.D.K · Aug 3, 2002

Mark how would the lab subwoofer work with a blueprint 1803? Could a 18inch driver be used?

Mark Seaton · Aug 3, 2002

Short answer... NO. If you look back in the posts at the subwoofer forum, you will see lots of discussion by myself and others as to why this is not very feasable. Possible? yes, but not with current drivers or in the same size enclosure. More important is the question of WHY bother with an 18 when a pair of 12s offers so many advantages over the single 18?

Mike.D.K · Aug 3, 2002

I already have the 1803's. They are in sonotubes they have lots of output. How would the lab subwoofer compare to the ported sonotubes. 10 cubic ft tuned at 18hz. Would one lab with the Eminence drivers best these? I have Klipsch Lascalas so I do like the horn loaded bass. Thanks

Mark Seaton · Aug 5, 2002

Hi Mike,

The dual ported 1803 subwoofer is worlds appart from this sub. The ported 1803 you have will provide more very low end output. The main question will be if you can load it into a corner to effectively extend the flare. If you can, I would expect the LAB sub to still provide much more output to 25Hz, and depending on the size of your room, maybe lower. Above 25Hz, it won't even be close. Even a single LAB sub(properly boundary loaded) will have a solid 8-10dB of headroom over the 1803s, and lower distortion for the same output levels. It will also have a phase response which more closely matches your LaScallas, but you would ideally want the capability to delay the LaScallas to account for the path length of the bass horn.

If someone is into the sound and feel of a live kick drum, and effortless bottom end, a bass horn does have a different sound than a direct radiating subwoofer. The other night I was playing with some BassTech 7s at the office and was hugely impressed with the power from them, even for stereo listening use(ie not just at a large concert). Mind you I normally listen to ContraBasses. No, they didn't have the extra extension of a Contra, but if you use 2 of these subs, you should have the headroom to EQ in flat response to ~20Hz, or you could use a separate sub to cover below 25-30Hz. If you are one who has never found a sub that gives you the output you wanted available, this is an option you should seriously consider.

AlexKunec · Aug 5, 2002

How efficient would just a single lab horn sub be? About 105db?

What kind of room gain should I expect from a 3300cuft room?

Are the LAB12 drivers 4ohm?

Would 250w be enough to power this thing?

Jack Gilvey · Aug 6, 2002

This box looks well beyond my capabilities. However...

Can you summarize the advantages of using the DPL12 in this horn instead of the LAB, Mark? Assume just one corner-loaded in a 1400 ft^3 room. What extension might I expect?

Mark Seaton · Aug 7, 2002

Hi guys,
Efficiency is a rather tough one to pin down in this case, as the boundaries not only confine the spacical radiation as in corner loading, but they also extend/mirror the flare. I found the post Tom made about extending the flare, and he mentioned 35% efficiency from two loaded as I describe above. That equates to ~107dB/1m/1W(not 2.8V)!!! That makes the 250W plenty adequate.

You can check out Tom's post here: Try this !!!!!!!!
The issue with loading only one in the corner is that you would then want to confine the vertical expansion with a top cover. The other option would be to move the box another 24" from the opposing wall and continue the expansion vertically, basically connecting the top of the box to a point 90" high, 24" in front of the mouth. This then would expand around the corner and make for a very long path length and large mouth. A good combo for high efficiency. I couldn't see one box with even only a doubling of the mouth area not producing at least a 100dB sensitivity, probably closer to 102-103dB, but the boundaries would likely make this even greater. What is interesting is that the pair stacked in the corner make for a 13.3-15' path length which means the length will not limit the low end until about 20Hz! In this case, I would expect that the DPL-12 might offer lower extension with the greater Mms and Bl when the flare is sufficiently extended.
There are some complicating issues with modeling an accurate radiation resistance to the horn at low frequencies because of the room dimensions. As I mentioned above though, below some frequency you will also see gain from the room which could extend the response to a VERY low frequency and could be put to great use with some modest EQ. Tom and I are both very curious to give this a try.
Regards,

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