Lab 12 Based Offset Driver - Mass Loaded - Transmission Line (OD-ML-TL) Design by Bj

[tb46]

Hi NWCgrad,

I like bjorno's idea too, but it is not what I was suggesting. When I tried to simulate an enclarged opening in Hornresp it ended up giving too much low end boost, and increased the ripple @ 86Hz. Anyway, here are two similar ways of folding the same model; I like Rev.B better, as I'm always a little uncertain about what a short labyrinth (as in Rev.C) will do at very low frequencies. When modelling these I stayed with a constant S5 in the model. I'm looking forward to see what bjorno comes up with.

Regards,

P.S.: These are really just quick sketches.

 

[NWCgrad]

Thanks for the sketches! I really like the way this project is evolving.

I believe when this design in finalized it will be really great. These drivers are fairly inexpensive in the US, and are widely used in the horns so I assume they are very duarable.

I already have two in crappy 16" sealed boxes, actually they are propbably not sealed, they were made in Cambodia for $25 and they have developed multiple cracks I keep filling with wood filler - the boxes will not be making the return trip to the US. Based on the the modeling I may only need two, but I will build four for "head room."

 

[bjorno]

Hi,

Here is the first of MJK simulations from which i decided to try improving the port system...more to come (i.e. Olivers .pdf:s)..but it may take days...or a week until I have time to post more.

b

 

[NWCgrad]

Hi,

Here is the first of MJK simulations from which i decided to try improving the port system...more to come (i.e. Olivers .pdf:s)..but it may take days...or a week until I have time to post more.

b

Thanks bjorno! Between you and Olivier I think the LAB-12 build will be pretty nice. I am mostly interested in SQ, but the ability to play at high SPL is nice for the times when you just need it loud.

 

[NWCgrad]

I ran both this design and the Mal-X T-TQWT design in Hornresp (attached). The Mal-X will have a LPF set at 50 or 60 Hz (maybe a HPF at around 10 Hz), the LAB-12's will have a LPF at 80 or 120 Hz, 120 Hz is recommended by the designer of my main speakers for the the two flanking subs and a HPF at 20 Hz for cone excursion.

Overall, the system models +/- 3 dB from 12 Hz to over 150 Hz, of course real world performance will vary. I do have a miniDSP with 4 channels of parametric eq available if required (the Mal-X may be powered by a Crest Audio Pro-Lite 2.0 DSP [4 Ohm Bridged - 2000 W]).

 

[NWCgrad]

Hi NWCgrad,

I like bjorno's idea too, but it is not what I was suggesting. When I tried to simulate an enclarged opening in Hornresp it ended up giving too much low end boost, and increased the ripple @ 86Hz. Anyway, here are two similar ways of folding the same model; I like Rev.B better, as I'm always a little uncertain about what a short labyrinth (as in Rev.C) will do at very low frequencies. When modelling these I stayed with a constant S5 in the model. I'm looking forward to see what bjorno comes up with.

Regards,

P.S.: These are really just quick sketches.

Bjorno and Oliver,

I modified the diagrams provided by Oliver to raise the driver up from the port system. The attached diagram shows the change. The S12 and S23 distances did not change due to internal adjustments to the enclosure.

Will raising the driver cause any negative impact on sound quality or frequency extension? I would not think so as none of the modeled parameters have changed, but I want to be sure.

Thanks again for your kind assistance.

Steve

 

[NWCgrad]

I made a 1:10 scale drawing of the design, withe both the original and modified driver placement. I believe I like the original placement better visually.

Any thoughts on whether raising the driver would cause problems?

 

[BP1Fanatic]

Visually, I like the raised position. As long as the woofer is in the same position as the modeled line, then performance shouldn't change.

 

[NWCgrad]

Visually, I like the raised position. As long as the woofer is in the same position as the modeled line, then performance shouldn't change.

The internal particians were modified so the length and volume are unchanged. I keep waffling on which I prefer. No matter which way I end up going, I think they will sound very good. The four should match the Mal-X output.

 

[NWCgrad]

Hi,

Here is the first of MJK simulations from which i decided to try improving the port system...more to come (i.e. Olivers .pdf:s)..but it may take days...or a week until I have time to post more.

b

Bjorno,

Thank you for all of your valuable assistance and efforts on this design. Do you see any issues with latest design parameters? I may actually build two enclosures with the mid-mounted drivers and two with the lower mounted drivers to provide variations in response to smooth the overall system response.

Once I see you concurrence, and info on stuffing, I will be set. When I return to the States I will start a build thread on the Bjorno/Oliver Sub System.

I would like to offer again my profound thanks to both of you! What an asset to the DIY community.

 

[tb46]

Hi NWCgrad,

I hope bjorno will find the time to dig into the port design, it looks like a sophisticated piece of engineering. It will be interesting to see what he comes up with .

Regards,

 

[NWCgrad]

Hi NWCgrad,

I hope bjorno will find the time to dig into the port design, it looks like a sophisticated piece of engineering. It will be interesting to see what he comes up with .

Regards,

Bjorno seems to be on vacation from the board. Looks like this may be the final design.

Do you see any improvements that should be made?

Does raising the driver cause any issues?

Can I mix the two hieght designs (2 of each design)?

Again, I offer my profound thanks to you and bjorno for all the assistance you provided. Your help was above and beyond anything I expected or deserved!!!!

 

[tb46]

Hi NWCgrad,

Post #32: "...Do you see any improvements that should be made?

Does raising the driver cause any issues?

Can I mix the two hieght designs (2 of each design)?..."

Besides the port issue, I think this one is ready to build.

Raising the driver should not matter much in the below 100Hz range. Jus make sure that you maintain the internal length and areas.

Mixing should be fine.

Hope we'll hear from bjorno on the port details (the one in the past drawings should work though).

Regards,

 

[NWCgrad]

Thanks again for the assistance. I currently own two of the LAB-12 drivers, see attachments. I have them in two 16" x 16" x 16" "sealed" enclosure, the sealed is in quotes because the boxes were made for $25 in Phnom Penh and are not even close to airtight. I keep filling cracks with wood filler, but the boxes keep cracking.

While the wood is very interesting to look at, they do not properly cure the material. Thus, over time the boxes crack (this is why I will not be buying any wood products here to bring back to the US next summer). It is to expensive to ship plywood over here for a better build.

Best,
Steve

 

[tb46]

Hi NWCgrad,

That looks like an interesting wood grain. How about another layer on top of the existing layers to seal and strengthen it? Did you use any internal bracing?

Regards,

 

[NWCgrad]

Oliver, I don't have any woodworking tools while stationed overseas. As soon as I get back home to the states I will start building two of the enclosures from this thread.

The wood over here is very interesting, to bad they do not let it properly cure before it is used . I will bring back the boxes to chop up for some project, probably not audio related. The boxes are not braced, but they are stuffed with polyfill.

The 4 Pi main speakers (JBL 2226 and B&C DE250 drivers) are very well braced, and have an internal oak scaffolding to support the MDF during military moves. Size was adjusted to account for extra materials, they are ridiculously heavy but sound great. I have oak veneer for them but did not have time to complete before the move to Cambodia.

 

[NWCgrad]

Hi,

Here is the first of MJK simulations from which i decided to try improving the port system...more to come (i.e. Olivers .pdf:s)..but it may take days...or a week until I have time to post more.

b

Bjorno, first off I greatly appreciate all of your assistance!!!! I modifed Oliver's PDF but did not change any of the internal volumes. Have you had the time to look into improving the port system? I completely understand you are very busy and am not trying to be a pain. I will be building this design next summer regardless, because as it stands now it is far better than what I could design. You - and Oliver - are great assets to the community.

 

[NWCgrad]

oliver,

I looked at my modification today to calculate a cut sheet. I did not record the dimensions, I am going to scrap my changes and go with your revision B (the one you recommended). I assume I can lay these on their side, 4 across the front stage would minimize interference with the wall mounted projection screen (the bottom of the screen would be blocked by the taller of the two versions). Is my assumption correct?

Thanks, Steve

 

[Brian Steele]

The wood over here is very interesting, to bad they do not let it properly cure before it is used

Perhaps one layer of fiberglass and woven mat on each internal panel might be enough to seal up the box for good, and the slight reduction in volume should make very little audible difference. If you do this, make sure to lay a strip across each edge, for additional security against splitting at the edges.

 

[NWCgrad]

Perhaps one layer of fiberglass and woven mat on each internal panel might be enough to seal up the box for good, and the slight reduction in volume should make very little audible difference. If you do this, make sure to lay a strip across each edge, for additional security against splitting at the edges.

That would definately seal the cabinets, but the box size is not optimal fro the driver. Will bring the boxes back to the US and use them for something else, not sure what at theis point.