Cal, You move fast and take action! I like that. You could be done with gluing channels tonight and by morning the top cover will have had time to set. Make sure you use lots of weights to clamp the top down for glue to set. I probably had about 70 lbs of weights on mine. Can't wait to see spirals glued in. Thanks for taking photos and sharing.
That plywood looks really nice for underlayment that no one sees! What does the quarter inch sureply cost? It looks like it is Birch plywood?
Uh...thanks for the encouragement but tonight is set aside for cutting the foam core strips, layout and pre cutting, scoring and shaping of the channel pieces so it will just be 'puzzle' assembly next day. I'll keep going as long as I don't get the 'speaker widow' look from SWMBO. I know better than to cross that line. I've taken over the dining room table but she backed down when I said I could do it out in the shop instead. Funny aren't they?
Hey, diy is all about sharing, I'm just returning the favour.
I have to try this plywood, a 4 x 4 sheet is exactly enough for two of my 20 inch speakers. Speakerwidow ha ha - good one.
Speaker widow was in a good mood so I got a start. I found it easier to begin on the inside and spiral out, making sure I waited at each corner to catch up with the next piece so as to give my working room but I made sure I used a full piece at the mouth to cut down on visible seams.
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I started my foamcore project today. Ill have to wait for my internet to be connected before i can upload pics. I just estimated horn length so i hoping it sounds acceptable. Using 4x3inch instwad of the 4inch drivers. They sound fresher than the bigger ones. Which i think will be better suited for what ill be using them for.
Driver at the mouth like the B&W Nautilus where the horn is acting as an infinite tube? I guess we will see when you post pics. 75 cm has a characteristic freq of only 114 Hz, is that low enough bass for you?
I forgot to mention that I also double up on the glue by liberally applying white, or in your case, yellow glue on top of the hot melt just in case there are any cracks that need to be sealed, plus it ensures that if hot melt ever gives you have a backup bond. I assume you are waiting for cap to bond right now. You are right about getting the approval of the OWMBO prior to starting new campaigns....
This particular speaker has a very high WAF though.
75 cm (29.5 in) is actually adequate for a mass loaded transmission line like the TABAQ (circa 32 in) which uses a restriction on terminus to 'mass load' the TL to bring the resonant tuning frequency down to about 55 Hz. You really should take a look at the TABAQ TL thread. The design has been built by many folks over the years (I think the thread has like 130,000 views) and was designed for small 3 to 4 in drivers to get deep bass. Your requirement of 4 drivers does make it more difficult to fit all that in.
The design can be found here:
http://coolcat.dk/bjoern/TABAQ_TL_for_TB.pdf
http://www.coolcat.dk/bjoern/TABAQ BOX Cabinet build.pdf
Goodness no. WYSIWYG, I will try and do the other spiral today. We'll see about doing the caps. Yes, I used some hot glue where there are gaps but I'm not too worried, there is a similar SPL on either side of the channels inside the the horn isn't there?
It's not about SPL (as there is very little pressure build-up in horns in general since they are so open) but I worry about small air leaks which can cause the low frequencies to have a hard time in establishing a standing wave. If you have played a flute or any other woodwind instrument you know that a tiny leak on the finger seal above the low note you are trying to play causes the note to collapse. I am just being careful and using plain hot melt is fine as long as there are no obvious leaks.