Open Source Monkey Tower

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First of all, here's a link to the documentation of the OSMC, which will serve as the starting point for the tower idea: GitHub - mbrennwa/osmcdoc: Documentation for the Open Source Monkey Coffin

Here are a few ideas:
  • Make the box taller, and maybe a little less deep. The volume will be larger than with the Coffin, so the woofer alignment will be different.
  • Keep the baffle width and driver positions on the baffle as they are.
  • Use the same drivers.
  • Leave the x-over design as it is (maybe with small changes to the impedance compensation for the woofer, if required).
  • The taller box will have a resonance (standing wave) along the vertical axis, which will need some consideration. A stuffed Helmholtz resonator tuned to the frequency of the standing wave may be useful to "treat" the resonance.
  • Part of the additional tower volume might be used to make a separate chamber to install the x-over filters.

Comments? Ideas?
Monkey Tower

I think it's a great idea (it was my PM that started it anyway). I read through the entire MB thread, I got to the party late so just lurking and learning. I was really impressed with all the detailed hard work you guys put in on that project. Thanks for that from all of us mere mortals!

I was considering building that project, but in an exchange with Mathias I mentioned that I would prefer a tower (everybody wants something, right?)

My reasoning is.... The MB is not a bookshelf, so has to be floor standing, and as such requires a stand to get it at the right height. For a novice builder (one of the original criteria for the MB) that means building stands in addition to the speaker, which is actually more difficult than just building the box taller.

So why not just build it taller, the Monkey Tower, I like the sound of it :) That also allows you to make it less footprint as you can get the volume in height. It also allows for possibly a better port placement? That was one of the challenges in the original MB.

And if you wanted to go even further, there are obviously many other possible ideas.

MT Height

I'd say the optimum height would be between 46 in (117 cm) and 50 in (127 cm).

Bare minimum height of 37 in (94 cm), and an absolute max height of 55 in (140 cm).

I currently have a pair of very inefficient towers that are 48 in (122 cm) and they are just about perfect height. They sound good, but I'm driving them with 360 watts/channel and it's barely adequate.

I really need some more efficient speakers.


By the way, Meniscus Audio in the US is having a great sale on the Scanspeak 2904/7000 tweeters, here's the link.

Scan Speak, R2904/7000 - Meniscus Audio
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Thanks Gabo.
I never left though, just stopped commenting in the thread.

I've been looking at the numbers for a few minutes, simply tried increasing lower length of the chamber by 65.9cm. Quite a bit of resonances from 200hz up, but putting a layer of Melamine foam on the surfaces almost negate the issue, at the cost of tiny bit less output.
Resonance frequency 27.21hz, and 30hz goes just over 91db.
Suggest a round port centered about 30cm from the bottom, to get away from the floor. I used a slightly oversized 6" round 40cm long port in my calculations. Dip centered around 332hz might be an issue.


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Kaffimann, can you show on overlay of the tower curve and the OSMC curve? It would be useful to see the difference as predicted from the Hornresp software. Or, thinking of it, it would be even more interesting to get two datafiles with the tower and the OSMC curves, so I could plot these along with the measured OSMC low-frequency curve. Just to see how the Hornresp simulation compares to the observed curve.

Melamine might work to reduce the resonance, but I am not sure it's effective enough at such low frequencies. How about a Helmholz absorber tuned to the relevant frequencies? Can Hornresp calculate this? Otherwise I might try to resurrect my AJHorn tool on my virtual machine...
What was the port measurements again? It's been so long, and I have lots of different simulations.

I only adjusted the height below the 12", because that's what everyone wants, and it's easy.
Tower is not the best solution for high bass quality, since you're more likely to trigger lower frequency modes. But it's not too bad, narrow-ish bandwidth resonances since the driver is closer to the middle.
You do not need an enormous amount of dampening material to take care of these issues, because the sound will bounce around a lot on the internal surfaces.

A resonance solution might work well enough, I'd suggest using a couple stuffed pipes instead of a tuned compartment. It is possible you can even out the pressure a little bit better.
Don't know how to calculate it properly, I will have to think about it.
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I do not think that would make it significantly better.

These 12"s like to have a bit over 100 liters each, I guess you *could" use two 10"s :)hbeat: Seas A26RE4), but you don't get a huge amount of extra bass below 40 hz anyway (in terms of SPL/wattage). As far as I can understand the goal is slow type roll off to under 30hz, not max SPL, and more membrane area isn't going to contribute much unless you beef up size even further.

Personally, I would like to step up properly and do a completely different thing with the Faital 10HX230 and some 18", but that's just me I guess.
On the other hand I have some Hawthorne Audio Sterling Silver Iris 10" coax with Radian 475PB dusting down, just need to get a couple good 18" then I'm happy.
My plan results in a much wider box though, not for everyone.

I was thinking it'd be a shame to waste all the effort on the MonkeyBox, we *could* make the box deeper to increase volume (to support more displacement), but if we increase SPL/w down low then we should increase mid and tweeter SPL as well.

What's the goal here? :)
What do you guys want?

Using the Faital 15PR400 and bumping the entire design volume to 223 liters helps increase 30hz output to ca 93.36spl/w, but it ruins the front baffle.


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What I want.

What do I want?

- A high efficiency speaker, this is the primary goal.

- A reasonably amp friendly speaker. I think most small tube amps are ok with impedance down to 5 ohms.

- A relatively easy to build speaker. Basically in my mind this means nothing more than rectangular. Odd shapes, curves, and the like are the thing that's hard to build. Rectangles of any dimensions are equally easy.

- A form factor that fits..... It's a floor standing speaker. As such it needs to be as space efficient as possible, which means as small a footprint as possible with the desired volume going up instead of out, which results in a tower.

- A high quality speaker, goes without saying with the components we're talking about, this isn't going to be a low quality speaker.

- I do not have a tie to the current template or woofer/box.

I have already purchased the tweeter, the waveguide, and the midrange that was specified in the OSMC. But these components are just high quality, high efficiency components that aren't very dependent on the box. The crossover that was designed for the OSMC, with some very minor adjustments is a great starting point for using these midrange/tweeter combo in any speaker.

I don't even mind if the speaker is a split cabinet, and maybe I even prefer that. With the midrange/tweeter going in one box that sits on top of the bass cabinet. Obviously the footprint needs to be the same so they stack properly.

I have not purchased the bass driver as it's so dependent on the box that it could change.

If I have one critique of the OSMC, and I'm very careful here as you guys all did a tremendous job and did some great work. I in no way want to discredit anything you guys did, it was truly inspiring. But in that project, it seems like the box dimensions and template were designed first and was set in stone. To me this is a bit backwards, the box is the easiest thing to change and should be flexible. And reading between the lines, I think the final listening results seemed to indicate that it might be a bit light in low end.

One more thing that I think was learned in the OSMC, is that the software models are incredibly accurate. I think the only thing that was changed based on the real world testing, was the port location. And that was predicted by KaffiMann.

The take away, in my mind, is that we can design the new Monkey Tower using the software tools and be confident that it's going to work as designed. So the need for building a prototype and doing lots of time consuming measurements is probably not necessary.

After writing this, my thoughts are that I might like to build a mid/tweet box that is stand alone. Then design a bass cabinet to match up to it, but maybe that will change, it's just a thought for now. It does make a large speaker easier to transport as it's in two pieces. Would allow future builders the option of doing several things, mating it with different low end cabinets or even using them as bookshelf speakers mated with a subwoofer.

Hey, you asked for "What I Want!" :)