BillFitzmaurice.info

Nice to know it's a technical deliberation and not just stuck for time / opportunity.

Bill Fitzmaurice wrote: ↑Wed Dec 04, 2019 8:05 am Poplar is a good choice, balsa is not, assuming you're not adding a carbon fiber skin to it. Poplar is considered a junk wood, because it often has green streaks through it that make it unsuited for a natural finish. But it's strong and light, and when there are 7 plies or more in 1/2" thickness it's also very stiff.

Thanks Bill. Would be great to save a buck and a bit of weight too. Looks like it's going to be Poplar

Re: the balsa ply, the thought did cross my mind to skin it with fiberglass. I had also wondered about fiberglass skinning foam insulation sheets and +/- doubling up the internal bracing in Swiss Cheese'd 1/4 ply. I had to slap some sense into myself; concentrate dummy, focus... Let's get these done by the book and not make things more difficult.

Fiberglass is too heavy. It's not stiff enough in very thin sheets, so balsa plus fiberglass that's thick enough to be stiff wouldn't be lighter than BB. Carbon fiber is stiff enough in thin sheets, but cost prohibitive.

Charles Jenkinson wrote: ↑Wed Dec 04, 2019 8:07 am Nice to know it's a technical deliberation and not just stuck for time / opportunity.

If I'm going to be honest, it's both. A good old fashion case of analysis paralysis... Stuck for time/opportunity due to technical deliberation.

What about something along these lines?

https://rover.ebay.com/rover/0/0/0?mpre ... 2802125201

Aluminum needs to be at least 1/4 inch thick or it will flex too much. That puts the price out of reach.
https://www.ebay.com/itm/5052-Aluminum- ... 0005.m1851

Oh, I meant as a skin over a softer, lighter plywood.

Fellas......these subs are easy to move if you put casters on 'em. The difference between 75 pounds and 90 pounds is not going to make a difference in how you move them.

Bruce Weldy wrote: ↑Thu Dec 05, 2019 10:12 pm Fellas......these subs are easy to move if you put casters on 'em. The difference between 75 pounds and 90 pounds is not going to make a difference in how you move them.

That's true. Wouldn't matter too much if it's never more than just wheeling them around. However, the difference could be very noticeable if I ever need to schlep them up/down flights of stairs or hoist the fourth layer of a stack up/down.

Ultimately, I just want to keep things as lean as reasonably possible. Just seems like a smart thing to do.

I'm a bit at odds.
Seth, you want to save weight in the cab by using something like poplar ply.
Your driver choice alone is costing you over 4lbs (compared to a 3012lf) per cab. Toss in the increased output with the 3012lf too.
Regarding the increased sensitivity with the chamber reducers, well, I'm not sure what current plans say, but really, in older plans, they were only required for lower Fs drivers, like the lab 12, and I'm not sure increased sensitivity is an issue with 8 cabs.
The lab 12 weighs 14lbs more than the 3012lf, and 11lbs more than the 12LFA.

If you want lighter, but better wearing, build with BB outside, poplar inside, use 3012lf's, build wider, and you can call it done with 4 cabs instead...

Grant Bunter wrote: ↑Fri Dec 06, 2019 2:04 am I'm a bit at odds.
Seth, you want to save weight in the cab by using something like poplar ply.
Your driver choice alone is costing you over 4lbs (compared to a 3012lf) per cab. Toss in the increased output with the 3012lf too.
Regarding the increased sensitivity with the chamber reducers, well, I'm not sure what current plans say, but really, in older plans, they were only required for lower Fs drivers, like the lab 12, and I'm not sure increased sensitivity is an issue with 8 cabs.
The lab 12 weighs 14lbs more than the 3012lf, and 11lbs more than the 12LFA.

If you want lighter, but better wearing, build with BB outside, poplar inside, use 3012lf's, build wider, and you can call it done with 4 cabs instead...

Grant, apparently our minds work very similarly. That sounds just like the mess I've got going on upstairs most of the time.

In response to the couple points you bring up;
You're completely right about the 3012LF. Although, paying $100+ extra per cab to save 4 pounds isn't what I'd consider reasonable. That's just me personally and based on my needs and resources.

Re: Chamber Reducers, yes, that's pretty much what it says. My personal opinion... again, I'll take the bump in efficiency over 40Hz, whether I'm running 2,4, 8, or 16 of them. Especially since they'll be getting so little power limited at 30-35 volts... 113 to 153 "watts". Any increase in sensitivity, IMO, becomes a larger advantage with increased system size. By the numbers anyway.

According to Bill there's no gain... well, more accurately, there are losses incurred by going any wider than I already plan to.

And... you may revisit my number crunching thread. Bill made it pretty clear that due to the difference in mouth area, 8 Delta loaded cabs would out perform 4 3012LF loaded cabs.
viewtopic.php?f=1&t=25509&p=281245&hili ... rs#p281233

I do have several amplifiers capable of putting out 55-60 volts, so going with premium drivers is an option I'm somewhat prepared for. However, I'd really just like to do a low powered (per channel) system with more channels. I now have 4 of the 8 channel amps and have enough to power 16 Titans, 8 DR's, and 8 Wedgehorns... each with their own amplifier channel. That would be pretty wild. But really, the plan is to start small with 4, 4, & 4.

Ultimately Grant, there are many many ways to skin this cat. I appreciate your feedback and sharing your thoughts. Doing it a little different is enjoyable for me. Don't be at odds, enjoy the ride with me.

Grant Bunter wrote: ↑Fri Dec 06, 2019 2:04 am Regarding the increased sensitivity with the chamber reducers, well, I'm not sure what current plans say, but really, in older plans, they were only required for lower Fs drivers, like the lab 12.

The chamber reducer doesn't increase sensitivity. They're required to prevent a loss of sensitivity with low Fs drivers, or in the case of the T48 a wide chamber. The three dollar term that describes their function is reactance annulling. Using one where it's not called for in the plans won't make the cab work better, it will make it worse.

Grant Bunter wrote: ↑Fri Dec 06, 2019 2:04 am Regarding the increased sensitivity with the chamber reducers, well, I'm not sure what current plans say...

According to the T48 plans,
Chamber reducers may be used in a "wide" cab. A "wide" cab for a 12" driver is up to 24", but not less than 16½"
If the driver Fs is less than 32Hz, chamber reducers must be used.
If the driver Fs is more than 32Hz, reducers are optional.
When reducers are used with high Fs drivers the cab will have a bit better sensitivity above 40Hz, a bit less below 40Hz.

Hmmm.
The purpose of building T48's is to have a HP of 35Hz with 4 or more cabs?
So why would you want to cruel response below 40Hz by decreasing sensitivity in that region?

You may as well just build T39's. You'd save in ply and pack space.

There was a time when going without the chamber reducer and accepting the loss of sensitivity above 40Hz to get lower extension with the T48 made some sense. That time was before I designed the T60.