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The ProSoundWeb LAB Subwoofer Project (1 Viewer)

Jack Gilvey

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Mar 13, 1999
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Thanks Mark! You guys have quite a braintrust there at ServoDrive, when I read either of your posts my vision gets a little hazy and I have to take breaks.

One thing I hadn't realized (although I suppose I should have) is that a horn has the same 2nd-order rolloff as a sealed below cutoff...should have good implications in a smaller room.
 

AlexKunec

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Couple more questions:

That 103-104db efficiency, should I also expect about 5-7db due to room gain in a 3000cuft room, or does that efficiency take that into account already?

I understand how doubling the amount of drivers doubles the efficiency. But if two of these LAB horns is about 35% (107db) efficient, then four would be 70%(110db)? What if you had 8 of these? 140% efficient???? I think not. What happens then??
 

Mark Seaton

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Hi Alex,

Unfortunately the doubling of efficiency per doubling of drive units is really an approximation that holds reasonably well to about 30-35% (I had to ask Tom Danley to verify this one). With 2x the number of boxes you can certainly produce twice the acoustic power, but the efficiency does not go up. That said, it IS possible to achieve more than 112dB reference sensitivity by confining the radiation angle. Remember that the 112dB sensitivity number is referenced to full, 4pi radiation. Also realize that you quickly get to a point where the source is large relative to the frequencies being produced, so there is directivity to consider, even for a subwoofer when you use enough!
 

Mark Seaton

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Since this thread keeps getting hits and I keep getting asked for a link to it, I figure I should bump it up.

Now, has Chad K. started on his project yet?
 

Mark Seaton

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I know of a few people who have recently completed a few more of these, but haven't heard too much about how it worked out in an enclosed room. Maybe we can see some feedback in the near future.
 

Fred Seger

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Anybody here get one of these done.. Really curious as to how people like them.
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
Also curious as to be impressions to vented shiva and tempest they have/or have heard.
 

Mark Seaton

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Actually, I know Dan Wiggins is building a pair for his church... AND is corner loading them as I had described. His are loaded with DPL-12s which should be quite close to the LAB12 with differences as I had mentioned above. I'm sure Dan will do some measurements, and might give them an evaluation before they go in the church.

There will be other means to get flat response lower, but there will be little which can match what these can do above the mid 20s, and I suspect in a confined room with minor EQ great output will be achievable easily to 20Hz.
 

Dan Hine

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My biggest concern/question is how do you mount the drivers and should one get damaged how do you gain access to it in order to replace it. The CAD drawings really don't help and even the actual construction pictures I've come across don't show a completed unit (only the first half). The rest of it seems pretty straight forward.
If anyone hasn't seem some of the construction pics I've only found these.
 

Fred Seger

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Dan,

From what I recall, there are removable access panels in the sides which some are making out of wood, lexan, or aluminum.
 

Fred Seger

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A question for you Mark. Is this how I understand you describing the best implementation for a single unit in a home.
(please let me know if you can't see the picture)
It's just a quick sketch, so the internal structure of the horn isn't compelete, but enough to get an idea of orientation.
room.jpg
 

Mark Seaton

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Hi Fred,

Indeed, that is one possible configuration... The above rendering would probably yeild as much as possible from a single horn. There are two other options as well. You could stack two LAB horns and place their mouth at the 29" dimension where the above drawing couples to the height of the room. The other option is to place a 45 degree "cap" over a single horn. This would be done by moving the mouth of the horn in the above drawing to 29" from the wall, and then creating a "top" for it which spans from the most forward top edge of the horn to a point 45"-74" from the corner on the adjacent wall.
 

Fred Seger

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I know two horn is the ideal solution, but I'm afraid one would be the most I could make.(right now)
I think this is the other single configuration you were describing.
labroom.jpg

Would you want put a corner panel(as shown in purple) to help the horn, or just leave the corner square.? With a EQ, do you think I would be able to obtain a reasonable 20 hz output in a 13' x 12' room( that has open doors to rooms about the same size).
This just looks like such a fun project that I really want to do it, but definatly don't want to be disapointed because of unrealistic expectations:)
Also, what difference would it make what size how far you have the extention go out on the adjacent wall form 45" to 72"
Thanks for your time.
 

Mark Seaton

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Hi Fred or anyone still following...

I realize I hadn't responded to the second question. If you were looking for 20Hz with EQ, you COULD do it, especially since you do still have a pair of 12" sealed drivers. What I would do to make the job easier though would either go with the first extension to the full height of the room and even include another piece to close in the area above the box to the cieling. With the second drawing you have, I would want to further extend the confined height by making the "top" continue out to almost the furthest end of the subwoofer from the corner and continue to a similar distance on the opposing wall. Realize the first drawing will have a longer horn, a larger effective mouth, and will couple into the height of the room, producing smoother and deeper results. How much better is tough to say.

Regards,
 

Mark Seaton

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Bump...

I know a few more people have been completing these, and a friend of John Janowitz's built a pair. Just wondering if anyone has come further.

Chad, you still lurking?
 

Fred Seger

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I just got my started last weekend. Coming along pretty good. I'm just building one first, probably will build a second a couple months down the road. If I can get down to PE before they close tommorrow and get the LAB12's I'll have it running by sunday... can't wait. I post the impressions here with some informal measurements in room with and without flare extendions.
 

Mark Seaton

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Tom Danley and I are both quite interested in the impressions in an encosed space. It should be very interesting to hear how things work out for Dan in his church. (they have no idea what they will be getting :cool: )
I have also seen posts recently on the HE forum at Audio Asylum that a few others should be getting some boxes together rather soon.
Regards,
 

DanWiggins

Second Unit
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Aug 15, 1999
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Oh, I know what I'm getting...;) I may be contacting you for some more, too! But man, can you build these guys any heavier? It's not easy hefting these things around, especially when you're 35 feet in the air!
And those bass horns... Well, what can I say. They are REALLY BIG! Will be fired up for the first big performance this weekend - should make our bassist grin...:D
Dan Wiggins
Adire Audio
 

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