BillFitzmaurice.info

It’s really fun watching these experiments thanks for doing them and posting them!

Joe

To build my 24” lab12 loaded tuba45 it would cost as follows:
Lab12 - $230.00
3 sheets of plywood - $180.00
Other materials - $50.00
Total $460.00

To build this 18.5” dual MCM55-2421 8” tuba45:
2sheets plywood - $120
Two drivers $60
Other material - $50.00
Total - $220.00

The means that I should be able to build two of these MCM cabs for the price of one of my 24” cabs if the single peaks around 112dbspl and add 6db for the second one I should get 118dbspl which is more output than my single cab build.

I am so excited to keep using these cheap little 8” drivers in my subwoofers.

I have taken measurement with my Dayton audio UMM-6 mic and REW. Below is pictures showing the subs pointed at my wall and my laptop and mike behind.

The graph reads as follows with 1/12 smoothing:
Green trace - 18.5” dual MCM 55-2421
Orange trace - 24” Lab12
Blue trace - both cabs on separate channels

Low pass is 80hz bw12
High pass is 35hz bw24

Once I set the gain structure sufficient I ran one sweep on one cab than moved the connector over to the next cab and repeated the sweep. The whole time I was tapped into one of my sub channels only. For the blue trace I simply tapped one channel per sub. The blue trace nicely represents 6db gain roughly throughout. I have to say I am impressed with the low end extension of this smaller cab at half the cost.

I started painting my tuba45. Bought some cheap black paint and am painting all of the low wear areas. The internal area of the handles the horn throat etc. either today or tomorrow I will start the duratex application. I can’t wait.

ACUA wrote: ↑Wed Apr 13, 2022 8:26 am I started painting my tuba45. Bought some cheap black paint and am painting all of the low wear areas. The internal area of the handles the horn throat etc. either today or tomorrow I will start the duratex application. I can’t wait.

Paint everything with flat black....a couple of coats. Then Duratex. If you put Duratex on bare wood it will soak up - let the cheap stuff perform that task and use the expensive Duratex on top.

I've been out of my normal routine for the past month and am finally back to where I can put my analytical thinking cap on again.

ACUA, I'm absolutely loving these results!



My point of view; When I look at this image, I see wonderful things. Yes, there's a clear difference favoring the LAB in the 50-70Hz and 80-90Hz ranges. But, in my opinion, I don't think that matters much at all when compared to the 35-45Hz range, where they're very very close on output. Here's why... When you EQ the system, the lowest points on the response curve that are within your intended bandwidth ultimately limit the whole systems output... those frequencies are what's going to hit the limiter first. Also, you're likely to EQ the bottom end 15-20dB hotter than where it is at the crossover point (and 15-20dB hotter than the tops) which, again makes all the frequencies above 45Hz pretty much moot where max system output is concerned.

I think, when you get all 4 up, running, and all dialed in, you'll be hard pressed to tell the difference between your LAB loaded cabs and your MCM loaded cabs.

For the sake of it, I'd absolutely love to see the response of the MCM cab with a single driver (blocking off the second hole with a disk). I'd appreciate it quite a bit if you were able to do that sometime.

Just to be clear, in the initial testing you used different input voltages, but when you ran REW you used identical input voltage. Am I understanding that correctly?

If I want my cabs as durable as possible don’t I want to expend duratex on raw wood to get the strongest and deepest adhesion possible so that when it takes a nick or scratch it holds up better? I get that it costs more but for durability sake!


Seth, that is correct my post with spl values was equal power at single frequency locations read off my hand held meter. When I ran REW I maintained the same power and just swapped cabs, which with the additional 2ohm impedance of the dual series wired drivers constitutes lower measure levels. Even still the cab did graph well. I am working to finish the cab I won’t be testing with a single driver. Maybe next time.

ACUA wrote: ↑Wed Apr 13, 2022 3:02 pm If I want my cabs as durable as possible don’t I want to expend duratex on raw wood to get the strongest and deepest adhesion possible so that when it takes a nick or scratch it holds up better?

Nope. I have 4 T-39s that I built with flat black as a primer. A couple of years after that, I bought two T-39s built by an authorized builder. He only applied duratex with no primer. Those two cabs look like absolute crap compared to the older ones. Every little scrape shows bare wood. All of my other cabs don't have any bare wood showing and have been used more.

I also have my mixer case that's been in and out of the trailer 10 times more than the cabs and it gets beat around pretty good - no bare wood showing.

In know it's just anecdotal, but I truly believe the duratex adheres better to the flat black primer than to bare wood.

Flat black primer, ok any particular brand or type?

First coat applied. So far so good. Guess we will see just how durable it is

ACUA wrote: ↑Wed Apr 13, 2022 5:40 pm Flat black primer, ok any particular brand or type?

Just flat black paint. It serves as a primer.

Looking good!!

Can't wait to hear the full herd of them.

Are you planning on adding corners to the new cabs? The handle holes look a little close to the edge.. probably fine, hard to tell from this end.

Kevin, you nailed it. I was not thinking about the cabinet corners when I laid out the handles. I fully intend to install corner pieces. I should have placed the handles 1.5” closer to center!!!

I am trying to sort out how to overcome this problem.

It doesn't look like corner casters are part of your intentions. They'd make moving those cabs a breeze. Although, the cost adds up quick when you're doing a bunch of cabs. Guessing you're going to just use a hand truck in favor of keeping the cost down?

I reckon this is how I will deal with my cab handles and corner protectors.

I have a big wheel hand truck that I use which I am happy with. I had casters on one of my tubas but it only made it heavier and I find it easier to hand truck them around