First Steps, Classic Monkey Coffin

e6zion

Hey All,

I'm working on a monkey coffin with the following drivers: Transducer Lab Ceramic tweeters, Satori MR16PNW midrange, and DIYSG Magnum 12 woofers.  The goal is 90-91db efficiency with an F3 between 40 and 45.  I will be doing roundovers on the edges and a separate housing for the mid and tweeter sections.  Cabinets will be mirrored.  I even considered doing different designs on each one--sort of a Soviet versus US space propaganda.

(1) Before I start drawing up blueprints, I would like feedback on the very rough mock up below.  The design idea is a tribute to the stereo era, as well as to the golden age of space exploration.  Admittedly, there are preferable [acoustic] ways to design a cabinet today, but I'm trying to do the best within the confines of this general aesthetic.

(2) How recommended is a waveguide on that tweeter on such a wide baffle?  It should naturally cross around 2k to the Satori, but I'm wondering about diffraction on such a large baffle, or anything else tweeter-wise I should be considering.

(3) Any other thoughts or foreseen design challenges before I get into it are most welcome!

Thank you!

jr@mac

I respect the targeted aesthetic, but offsets on HF drivers play hell with imaging and ports adjacent to the HF drivers are a diffraction breeding ground.

That being said, beautiful! Make it so. 

Wolf

I'm hoping the woofer is good enough for those mid/high drivers, but you made some solid choices.

No need for a waveguide on the TL in that xover area or to a 5.5" woofer.

rjj45

ani_101 said:

The offset is bad or the extreme offset is bad?
I never understood imaging vs baffle width? Would s tapering tower have better imaging?

Dual ports at the bottom would avoid the diffraction be issue, but still look retro.

Ani - It's my understanding that horizontally offset drivers may produce a better on axis FR, but off axis to the left and right will differ a great deal, and it's best to have both off axis FR consistent. 

PWRRYD

As silly as those Spica TC-50 might look, the felt applied like that is probably extremely effective.  Also note the driver time alignment and non-parallel baffle/rear panel.  I've never heard them but I can imagine they could be quite good with a good crossover design.

ani_101

You can cross the satori even lower as low as 100hz and let the woofer just handle the low bass. That mid is no slouch. It just won't do 30hz like the MW woofer...  So if you don't like the low mids from the woofer, cross lower, but it puts more stain on the mid. Try moving the xo up or down.

dcibel

If you want to offset the mid and tweeter, I'd keep the mid and tweeter vertically aligned. Moving both the mid and tweeter will retain the polar pattern between the drivers, which will be a lot better than offsetting just the tweeter, or offsetting both but neither one aligned vertically.

Personally I'd use a waveguide before adding felt to the baffle. The Tlabs tweeter has a nice flat faceplate, so should be fairly easy to mount on a waveguide. Visualizing the difference that baffle width and driver location has on the diffraction is fairly easy with the free diffraction simulator software available.

ani_101

Not able to make out, is the baffle recessed or chamfered?

e6zion

ani_101 said:

Not able to make out, is the baffle recessed or chamfered?

Sorry, this is due to a poor illustration.  The blue baffle and walnut edges would be flush, leading into a roundover.  The baffle is not recessed due to potential diffraction issues.  I don't think the box will be thick enough to have a useful chamfer.  

ugly_woofer

+1

Kornbread

Since we've been discussing wool/felt, I was wondering if it might be beneficial here, but I don't see how it could be done without destroying 'the look'.   

PWRRYD

I love the look but agree with JR.  I would move those two woofer ports to the rear panel and reduced the TM horizontal offset.  Those look to be very high quality drivers.

ugly_woofer

yes excellent drivers

ani_101

The offset is bad or the extreme offset is bad?
I never understood imaging vs baffle width? Would s tapering tower have better imaging?

Dual ports at the bottom would avoid the diffraction be issue, but still look retro.

jr@mac

1. Build speaker with offset HF drivers. Any offset.

2. Take polars in both directions.

3. Compare. 

Baffle width is not really correlated with imaging, at least not to my knowledge. 

ani_101

That is interesting, as one of the other issue is having symmetrical distance on the baffle. So we are fighting imaging vs diffraction? No offset better imaging, offset lower diffraction or at least spread it around?

e6zion

Thank you all for your input!  Yes, definitely nice drivers, and this project will consume a lot of time, so trying to make some good decisions.

1) Regarding felt, are we talking like Ryan Audio (which also happens to have an offset) or Spica TC-50 [see below]?  I'll need to look for the thread--I'm definitely not opposed to the idea.  In this case, does the felt diminish the need for cabinet roundovers since you are dampening the high frequencies, or is it still recommended? 

2) Noted on the port placement, so either below the woofer on the front, or move them to the rear panel. Makes sense, and thank you!

3) Troels has done a mixture of classic 3 ways.  Most have horizontal offset mids and tweets.  Are these naturally inferior to a centered design (e.g. Harbeth 40.2)?

4) Lastly, in the interest of making the most out of the drivers, I suppose the design could also go a different direction, with a slight trapezoid shape.  Oswald Mills Audio makes some esoteric looking things for the audiophile community.  Their monitor is a hardwood frame with dovetails and a slate baffle.  I'm not using slate, and I am concerned that hardwood would run the risk of cracking, just referencing the shape.

Sorry to flood the thread with photos, just showing examples of what I'm talking about.  

Ryan Audio R630

 

Spica TC-50

Harbeth 40.2

OMA Monitor

ugly_woofer

Definitely  move the ports, but if you  want the drivers offset, do it.  Hell if you want to square off the edges, do it.  It's  a retro build, so have fun.  If you have to beat the frequency  response into submission  with a bunch of xo parts so be it.  Now if you want to squeeze every last ounce of performance from your drivers, then go with a more modern cabinet with big groundcovers and such.  I personally  like the monkey coffin idea and have one planned myself.

e6zion

The Spica TC-50's do in fact sound really good, probably one of the most modern sounding of the vintage speakers I have owned.

e6zion

Wolf said:

I'm hoping the woofer is good enough for those mid/high drivers, but you made some solid choices.

No need for a waveguide on the TL in that xover area or to a 5.5" woofer.

It is one of the elements I am most worried about to be honest, but it is slim pickings finding a 91 db'ish woofer after baffle step.  There's a bms 12n630, but it is $300+ each.  I'm hoping the paper eminence lends a vintage sound to the low end in the worst case.

e6zion

In the end, I may keep it square, with centered drivers, and experiment with felt to address diffraction.  It will require some nice speaker grilles, but that may be for the best because I have a 6 year old.  I'll face the loss of the graphics, but that's ok--I still like the look of a big rectangle.  So much help on this forum!  Thank you, all!  

e6zion

ani_101 said:

You can cross the satori even lower as low as 100hz and let the woofer just handle the low bass. That mid is no slouch. It just won't do 30hz like the MW woofer...  So if you don't like the low mids from the woofer, cross lower, but it puts more stain on the mid. Try moving the xo up or down.

I'm going to play around, but I'm hoping I can cross the woofer as high as 400, but I'll see how it plays out.  I'm power constrained by the mid first, so I'm thinking that the more I can remove the heaving lifting the better.

6thplanet

You could stick felt rockets around the tweeter.

e6zion

UPDATE:
All, thank you so much for the input!  I took much of it and came up with this.  A departure from the earlier design, but I still like it,  and the non-parallel sides have their merits.  My son said I needed to make something with dragonflies (his favorite insect), so here we are. Though not reflected in the picture, the baffle will be flush with the walnut, and the top will slope towards the rear panel--to avoid the temptation for people to place something on top of them. Please feel free to pick it apart or make suggestions.  I really appreciate it!

Note: this is no longer a true monkey coffin--so it's now a misleading thread title.  Sorry!

Nerd bug trivia: The dragonfly has an estimated 95% success rate in capturing prey, making it the deadliest hunter on earth.  They are also the fastest insects.

ugly_woofer

Very nice, still retro looking.  Non parallel side are always a good thing acoustically.

kenrhodes

That looks amazing! I think you nailed a mid-modern hifi look. Fits with the time period and has very little drawbacks for the physics of a speaker.

Ed_Perkins

If you're going to slope the top baffle you might consider measuring the acoustic offset between the mid and tweeter early on.  With the right slope you could get the offset close to zero, like Jeff did with the Kairos.  That in turn would let you use LR2 slopes without resorting to complicated delay networks.  Of course it still depends on amount of offset and you driver's responses.  Just food for thought.

ani_101

Ed_Perkins said:

If you're going to slope the top baffle you might consider measuring the acoustic offset between the mid and tweeter early on.  With the right slope you could get the offset close to zero, like Jeff did with the Kairos.  That in turn would let you use LR2 slopes without resorting to complicated delay networks.  Of course it still depends on amount of offset and you driver's responses.  Just food for thought.

Not sure if it's a slanted baffle (the baffle would be 90deg to the floor top to bottom) - i thought the cabinet top will not be parallel to the floor, but sloped down a like a roof, so you can't put a potted plant on it! 

e6zion

ani_101 said:

Ed_Perkins said:

If you're going to slope the top baffle you might consider measuring the acoustic offset between the mid and tweeter early on.  With the right slope you could get the offset close to zero, like Jeff did with the Kairos.  That in turn would let you use LR2 slopes without resorting to complicated delay networks.  Of course it still depends on amount of offset and you driver's responses.  Just food for thought.

Not sure if it's a slanted baffle (the baffle would be 90deg to the floor top to bottom) - i thought the cabinet top will not be parallel to the floor, but sloped down a like a roof, so you can't put a potted plant on it! 

Ani is correct, but maybe I could do a gentle slant for potential LR2 mid-high.  Not sure if it really fits aesthetic wise.  What are y'alls thoughts?

That said, whether or not people appreciate it, the slope says "this is not a plant or drink stand."

PWRRYD

That's how I read his plan too Ani.  Sloped top, not a sloped baffle.

rjj45

Man oh man, that OMA Monitor looks great, and with 100 dB sensitivity. Funny, tough, I think the ESS Heil is specified as 95 dB sensitivity.