Seos 12 8" Faitalpro MTM 12" Subwoofer towers

Everyone thank you for the feedback in another thread about my first pro woofer project, I wanted to post my latest configuration and my initial progress.

I've done dozens of builds with audiophile raw drivers like Vifa, Morel, Dynaudio, Peerless and Dayton drivers, but having recently gotten back into speaker building wanted to try some of the great new pro driver options out there.

These speakers are solely intended for 2 channel audio.

I wanted to build something very loud, dynamic, transient and clean with flat response, home audio drivers sound good at reasonable volume levels but aren't very efficient and don't always have the fastest transient response or "attack".

Plus it will be a new experience and I'm sure to learn some stuff. =)

The Drivers

Initially I was thinking a build with the Seos 12, a decent horn driver, a 12" mid and 18" pro subwoofer. After spending weeks researching/modeling different drivers and options, I finally settled on the following:

Seos 12 horn with B&C DE250 compression driver

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Dual Fatal 8FE200 8" in MTM configuration, final impedance 4ohms, price is right and they were well rates and had good response too, also the smaller drivers should reduce issues with lobing.

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Magnum 12" Subwoofer from DIYSG, I nauseated over this choice the longest, I wanted 18" initially because well, they're freaking cool and I was really eying the B&C 18TBW100 but ultimately decided I really didn't need that much bass (I know, some of you are ROFLing right now), plus I can always build some bass modules later on if I want.

I was hesitant on the Mag 12 as I really wanted to use something with an accordion surround, I was down between the Kappalite 3012LF as it modeled really well and very close to the Mag 12, but advice from Erich put me over the edge.

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Crossover/Amps

These will be active run off my miniDSP 4x10, compression drivers will run off an Adcom GFA-545II, mids off an Adcom GFA-555, subs off a GFA-5800.

Crossover points will be initially 1500hz and 120HZ but everyone will be REW'd and EQ'd

The Enclosure

I decided on a largish tower, OD are 50" tall, 15.5" wide and 15" deep.

Mids will see about 1.75ft in a sealed enclosure, they will go flat to 90hz, Subs will get about 3ft each with port tuning around 30hz with two 4" ports each.

Construction is heavily braced 3/4" maple plywood, bracing is 1/2" thick pine plywood.

I cut 1/2" dado grooves for the internal bracing, the bottom is only screwed in so I can remove it, that allows bracing panels to slide in from the front and bottom and stack in precisely how I need. I'll post more as it develops so you can see what I'm doing.

Bracing will be vented to maximize air space and rigidity.

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I'm thinking of a 1.25" roundover on the front edges and possibly a 3/4" bevel on all other edges, I love the look of the exposed plywood layers.

Fun to note I have no CAD drawings, I literally do this all out of my head as a thought exercise and challenge, it takes an almost meditative focus (no distractions like someone talking to you) to keep track of everything and get it all right in one shot.

BTW I build all my speakers with this cheap and portable table saw, incredible piece of equipment if you're looking for a simple, accurate and cheap setup

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More to come, I welcome any comments or feedback, thanks!
 

lousymusician

Member
Paid Member
2005-11-24 4:10 am
NorCal
The SEOS 12 may be overkill for a 1500 Hz xover to 8" drivers. It's intended to be a polar pattern match for 12" drivers. The SEOS 10 or EOS 8 might be a better match both for directivity at the xover point and to allow closer spacing for reduced vertical lobing. The DIYSG speaker kits pair 8" mid-woofers with the EOS 8 (or the 8's side by side with the SEOS 15, but with the cabinet started that ship has probably sailed).

Bill
 
Seos 12 8" Faitalpro MTM 12" Subwoofer towers

The SEOS 12 may be overkill for a 1500 Hz xover to 8" drivers. It's intended to be a polar pattern match for 12" drivers. The SEOS 10 or EOS 8 might be a better match both for directivity at the xover point and to allow closer spacing for reduced vertical lobing. The DIYSG speaker kits pair 8" mid-woofers with the EOS 8 (or the 8's side by side with the SEOS 15, but with the cabinet started that ship has probably sailed).

Bill



Bill thanks for the comments, initially I was going to pair the Seos 12 with a 12" but ultimately went this route, I did consider picking up a smaller Seos unit but after some research have been able to determine that center spacing to the 8" won't be an issue in the 1500-2kHzrange.

Basically center to center distance will be about 7" from each 8" to the Seos 12 which makes a 1/4 wavelength of 500hz or 1/2 of 1000Hz.

Should be ok, right?

The Seos 10 only improves things 1/4", Seos 8 really doesn't mount to a CD horn like the DE250.

I really have no concerns about off axis response as this is for 2-channel audio with a very discrete listening position.

Thanks!
 
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Center to center spacing of your 8" drivers alone (i.e. without even a horn inbetween) would already be 8". So your calculation is a little off ! ;)



Regards



Charles



True, but any further input @phase_accurate?

1/2 wavelength for the 8" in MTM is about 500hz, for a 12" mid and Seos 12 it's about 650hz.

Seems most MTM designs ever made and any large diameter mid paired with a horn would have an inherent lobing problem. So what am I missing? Thanks!
 
You are missing nothing !
I just wanted to say that you are not on the save side by the marging you think you are - but you still are. For the center-to-center distance you have to take the centers of the midrange drivers. I.e midrange diameter + waveguide height. So your 1/2 wavelength and 1/4 wavelength frequencies will be about an octave higher than you thought.
OTOH I am currently building a large MTM that will definitely violate the 1/4 wavelength rule.

Regards

Charles

P.S.: I like speakers like this !
 
You are missing nothing !

I just wanted to say that you are not on the save side by the marging you think you are - but you still are. For the center-to-center distance you have to take the centers of the midrange drivers. I.e midrange diameter + waveguide height. So your 1/2 wavelength and 1/4 wavelength frequencies will be about an octave higher than you thought.

OTOH I am currently building a large MTM that will definitely violate the 1/4 wavelength rule.



Regards



Charles



P.S.: I like speakers like this !



Gotcha, yea in the end anyway I calculated it seemed problematic even in what would considered proven and popular designs.

Tough to weigh what can actually be heard with a lot of the theory that floats around, or what the "level of significance" is as they'd question statistically.

I've got a lot of experience building speakers but a lot of these more advanced dynamics are new to me like lobing, diffraction, comb filtering, etc. for me actually building speakers and seeing what can be measured and heard is an incredible leaning experience.

Thanks for the comments and interest!
 
Some progress on the baffling.

This enclosure will be extremely well braced but will loose minimal space and gain minimal weight.

Final sealed volume for the mid enclosure will be about 1.6 cubic feet, should result in an F3 of about 100hz.

Subwoofer will be at 3.0 feet and will be tuned to 35hz.

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https://vimeo.com/163781223

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https://vimeo.com/163781263

All the panels pictured are glued up and drying currently, tomorrow I'll finish up the bracing for the subwoofer portion.

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The voids accomplish several things:

1 - they reduce the amount of volume the bracing takes up while still allowing great structural rigidity. I didn't want to take up any extra air volume than necessary.

2 - they allow proper airflow to the right speakers and places in the enclosure.

But those points seem quite rudimentary, was there something else you'd like to assert or you're really asking? (Honest question, happy for any additional input).

Hadn't considers magnet braces as the mounting of the drivers will be extremely secure, would also require me to have removable panels.

Enlighten me to CLD, not familiar with the acronym.

Thanks @mindsource!


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I thought so many holes were superfluous.

CLD is constrained layer damping. It's adding a viscoelastic material followed by a non actuating constrained layer to certain parts of your enclosure(base layer). The unwanted resonance/vibration in your base layer causes bending which is constrained by the viscoelastic layer between the base layer and constrained layer, this causes shear deformation in the VE layer which dissipates the energy as heat.

No matter how stiff you make an enclosure it is going to have a resonant frequency, the stiffer you make it the higher the resonant frequency, and the more sensitive the ear is to it. The only way to bring down the amplitude of the resonance is to dissipate that energy and an effective way to do that is through CLD.

-Shawn
 
The reason I thought the holes were superfluous was because I personally would see a window brace with a cross in the middle as being effective and less work. So long as you are getting an accurate measurement of the volume of each brace so you're able to get an accurate total internal enclosure volume then I guess it's no biggie. Using a hole saw might actually be easier than jigging square windows.

I would really suggest doing more research on CLD, and incorporating magnet braces. The thing about CLD is that although in industrial engineering they have it down to a science, I don't think many or any of us audio diy'ers do.

A really simple method that I think would work without you having to do a total redesign would be to surface mount your woofers, and then use another front baffle that is the depth of the front of the woofer frame, so it lines up flush, and then build another enclosure around yours using that front baffle. Then smear a very thin layer (<. 5mm) of green glue on your entire enclosure and attach the new enclosure around it. Don't connect the two enclosures with screws or nails, it's basically a floating enclosure.

It's really not ideal because the outer enclosure (constraining layer) should also be very rigid. The speaker I'm building use the main enclosure(base layer) inside the second enclosure (constrained layer) but the second enclosure continues above and below the original enclosure, and it's at those above and below points that it is internally braced.

My method isn't scientifically proven. But I have a hunch it is going to work. I don't even know if green glue is the right viscoelastic material to be using. Whatever.

-Shawn
 
I used a combination of both holes and Windows, keep in mind like Windows I stacked on top of each other when I cut them to greatly reduce the effort by up to 4 times less. The hikes are trivial to cut, this is a fun project for me and not really about efficiency per se, I have about 8 hours total into all the bracing for this enclosure.

I have precisely calculated the internal volume while trying to keep the external size as small as possible (they're still go to be over 50" tall, also trying to keep weight down which the holes and Windows help with.

Familiar with the concept of CLD and would love to try it on a future project, enclosures I've built like this, I can put my ear directly on the wood with the speaker at reference volume and hear minimal sound through the enclosure wall, on less braces walls it's very apparent that the enclosure is acting like a speaker.

I like your idea and it seems very doable, choosing the right dampening medium is critical obviously, seems some layers of mass loaded rubber or asphalt would be very effective as well to sandwich. Also check out the 3M auto window adhesive, very tough when dry but maintains good pliability.

I saw a speaker mounted on springs in a frame once too =)


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Hello Mindsource, how to fight with room mode is probably the endless subject, but I certainly couldn't get any good result with this Geddes idea.

When we bought Lipinski 707 (The world class MTM mastering monitor) + L150 subs, we struggled to locate subs in our studio. We already had a pair of Velodyne, so we experimentally happened to place those 4 subs all over the studio, but our conclusion was the subs should be located as close as possible to the main speakers. It is the least artificial sounding location for the bass. We human can locate the sub for some reasons. This is an experience in the very well acoustically controlled room, so the result might be different in the regular home theater, but I still believe it's better to place the subs as close as possible to the main, then reduce the room mode as much as possible with the conventional way, such as Owens Corning, EQ, resonator, etc.
 
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