My Nelson Pass' BOFU TL Build

[svwolfpack]

Hello all,
I just finished building Nelson Pass' TL design for the BOFU, and I just wanted to share some pictures and thoughts. The forums here greatly helped me along my way, answering pretty much all my questions, so thanks to everyone. Here are a few things additional things I learned during the build process, as well as info about my specific speakers:

-These are built out of 3/4" birch laminated plywood. It was a bit too pricey, but they look nice. WORD OF WARNING: If you use the commonly circulated plans for this design, be careful with the cutting diagram. It's fine if you're using MDF, but when you're using wood with grain, the pieces diagrammed on the 2nd sheet will wind up having the grain in the wrong direction (so you just need to rotate them 90 degrees, it's not too tricky). I noticed this only after it was too late (and still, it's not too bad because the birch doesn't have a strong grain), but it's something to keep in mind.

-I added a tweeter (a generic dome tweeter I found at an electronics store) that I crossed over at around 4000hz with a 4.7 uF capacitor. I also installed an l-pad to control them, which I find to be useful (otherwise, they can sound a bit too bright). They really make a big difference, I wouldn't run the BOFU without them.

-As for stuffing the line, I initially had them overstuffed (I couldn't find a good stuffing density for these anywhere), and basically turned them into a giant muffler, so there was no bass response. As of now, the only stuffing is quilt batting, which is attached to all the interior baffles. This seems to do the trick, although I may add a little more back in at a later date.

-I went with the removable base suggested on the forums... definitely a good idea, especially in regards to stuffing/tuning.

-I used screws and ample glue to hold it together. Since all the joints are simple square joints, screws gave good additional strength, and helped everything line up right while the glue dried. I finished them by filling in the screw holes with wood putty, sanding, and then staining them.

Other than that, I’m happy to report they sound quite nice. Room placement is very important with these to achieve decent bass, but when you find the sweet spot and turn them up, they pump out quite a lot of volume. This was my first build that wasn’t from a kit, and I’d recommend it for other first timers, with the caveat that you have the ability to make accurate, long, straight cuts. Total cost was around $200, including pretty much everything. If anyone has any questions about them, please let me know! I’d love to be able to give back to this forum as much as I’ve gained from it.

[planet10]

Originally Posted by svwolfpack

-These are built out of 3/4" birch laminated plywood. It was a bit too pricey, but they look nice. WORD OF WARNING: If you use the commonly circulated plans for this design, be careful with the cutting diagram. It's fine if you're using MDF, but when you're using wood with grain, the pieces diagrammed on the 2nd sheet will wind up having the grain in the wrong direction

Chris keeps reminding of that when i do cut-plans. I have just updated my plans to fix that.

http://homepage.mac.com/tlinespeaker...map-010910.pdf

dave

[svwolfpack]

Awesome! Those were great plans, btw, I really enjoyed the build.

[chlorofille]

Hi..so are you running your woofer fullrange?

[chrisb]

grain direction of internal panels/bracing doesn't matter, nor if you're post veneering or p-laming, or painting

but in the case of the latter finishing options, smooth sanded/filled joints & edge-grain to prevent telegraphing are critical

[badman]

I see you used some of the same tricks I did. Did you arrive at them independently? Just curious. Nice job!



Pass The Bofu Building a transmission line cabinet for the Pioneer 8-inch full range driver. Article By Jeff Poth

[svwolfpack]

Originally Posted by chlorofille

Hi..so are you running your woofer fullrange?

It's a full-range driver, the Pioneer B20FU20-51FW. It's not bad all by itself, but the tweeter really fills out the high end.

Originally Posted by badman

I see you used some of the same tricks I did. Did you arrive at them independently? Just curious. Nice job!

The idea for the base I saw in one of your posts I believe. Thanks!

[chlorofille]

Thanks. I had a look at the SPL graphs and it does indeed drop off after 4kHz.
Good crossover point you have chosen !

[Spikedart]

I am looking forward to giving them a listen some time in the near future.

[svwolfpack]

So, I've been enjoying them for a few days now, but I've run into an interesting situation... where you stand/sit in the room dictates the kind of bass response you get. (I've moved them further apart from where they are in picture I posted, they're now swapped with the crates of records, but they're not in the actual corners of the room.) When sitting on the couch which is directly opposite them, they sound fantastic... a real rich deep bass unlike that of a reflex system. However, once I move "outside" of them (i.e. to the left of the leftmost speaker or to the right of the right one), the bass tails off an is almost non-existent.

As of now, they're roughly 6" out from the wall. The right one is in a "corner", although it's a bay window, so the walls meet at a 45 degree angle. The right one is about 4 feet from the other corner of the room. Moving them further or closer to the wall behind them doesn't seem to have much practical effect, and moving them more towards the corner isn't practical in the current setup of the room. So, ultimately, my question is this: is there anything else I can do to increase the overall "bass field" (not sure of the term I'm looking for)... would some sort of baffle behind them be useful? Should they be angled where they are in a certain way? Might stuffing the line help? (initially, I had them fully stuffed, and it killed bass response... right now, the internal baffles are just covered in quilt batting, and when sitting in the "good zone", the response sounds smooth and good) Or should I just get used to them how they are?

Thanks!
-Sam