Open baffle 4-ways under construction

[Jussi]

Hi,

I finally found a compromisse and went for a AA Beethoven inspired dynamic open baffle speaker. Heard Orions and liked them alot. I also noticed couple problems with them and I'm familiar with some aspects that could be better in original Beethoven concept as well.

So the overall setup is WWMTM main panel with Beethoven styled W-baffle dipole colums following later. Mains have drivers selected and invested. 25W/8565-01 Scan Speak is serving for lower mid (and as bass before actual woofers appear), Seas W18E is selected for upper midrange duty and Dynaudio T330D Esotar should finish the job. Esotar is fitted into a waveguide to match dipole mids front radiation pattern. Considered xover frequences 250-300Hz 1st to 2nd order and 2-2,5Khz 2nd to 4th order. Lowest cross is going to be around 80-100Hz prefering 2nd order.

Already have two poweramps and Behringer DCX-2496 for prototyping. Finally I attend to upgrade Behringer into a solid analog active filter and perhaps use passive filtering if drivers efficiencys work along. Naturally the lowest cross is going to be active anyway.

I know. It's pretty much totally crazy project. Room is relatively small but I can get these placed pretty well considering the room. 1,5m space from speakers to front wall, 1,5m from listener to rear wall, 0,60m from panels midship to sidewalls. Nice 2,5m listening triangle and uses Linkwitz recommended positioning for dipole sources. Sidewalls, ceiling and floor are concrete so dipoles nulls should be able to bite most of the problems. Front wall is mostly window and a door, rear wall is 1/3rd doorway and 2/3rds thin wall that should pass some bass frequences. Separated dipolesubs can be placed along the sidewalls outside from main panels. Turning panels straight towards listener 1st reflections should arrive around 80 degree angle from the speakers view. With dipole radiation pattern they should be pretty tamed. Acoustic treatment is also possible.

As for the mechanical structure I noticed Orions shaking problem which in my friends case wakes up some floorboard resonances and kicks butt. Literally. This is one thing I'd like to skip. Other is Beethoven and Phoenix based stuffed spine structures.

From mms view this setup has it's advantages. 25W pair, W18 pair and Esotar have only single 10" XLS mms on them. And I'll make a lot more sturdy panels than Orions are. I'm using 16mm plasmacutted steelplate as a frame for the panels. Bottomplates are 12mm steel, welded together. Frame is covered with 16mm MDF sheets to create constraint layer damping. Already got the frames and bottomplates. Working on the wood pieces. Tweeter has 50mm offset from the vertical centerline. I'll clamp the drivers between steel frame and MDF sheet, propably glue them in. This leaves drivers mounted a bit deeped in the panel so I can use speakercloth just along the panel and don't have to worry about cones banging the cloth.

Structure is heavy. Here is a picture from one of the frames. It weights 25kg. Bottomplates are about 13kg, 10kg of drivers, perhaps 10kg of wood. Recently I added a lean spine to them. This increases depth dimension at frame-bottomplate connection and propably makes whole thing stiffer. It also allows drivers magnet support and is pretty lean character so it shouldn't mess up that much rear radiation.

But does this look/sound dull, too common or how these parts look together visually? Pretty straightforward panel and then some curved at the bottomplate.

All other comments are also very welcome.

Jussi

[Jussi]

Another 3D image.

Those round pieces flying in midair? They are drivers magnets. Drawn just to give some perspective how actual drivers in place look like.


Jussi

[Jussi]

And another, a bit older but shows overall shape.

Jussi

[Jussi]

And here is the frame I promissed. Excels fitted very well.

Jussi

[Kensai]

Those are going to be some crazily overbuilt baffles. Most impressive. You cutting the steel yourself?

Kensai

[Jussi]

Originally posted by Kensai
Those are going to be some crazily overbuilt baffles.

Well. Are they heavy enough. I don't know. Pretty much guessing since I don't have proper equipment and environment to experiment things through dozens of prototypes. Pretty much normal compromisse in DIY R&D...

At least they shound't dance around that much and overall structure is kept relatively slim and elegant and still obtain very high stiffness. This is one of the problems I see in many open baffle systems. It's impossible to get ultimate damping + stiffness and maximum open structure in once without using something exotic. Oh well, is steel exotic. Very rare, even in expensive commercial systems but it isn't that tough task if you really want such solution. There are plenty of metalshops to do the thing...

But plain steelplates need some serious damping. The frame alone ring like a bell. I hope the elastic fastening and MDF sheets do the job so I don't have to name these "Hells Bells".

I guess the whole setup is blown off any reasonable proportion. But I like the idea of headroom if system needs considerable amount of planning, work, designing and of cource financial means.

Personally I can defend myself with this Linkwitz wisdom: "Extreme as these designs may seem, the goal here is to keep non-linear distortion low at high volume levels or, conversely, have very low distortion at normal levels.
I think it is important to be able to play back at live like levels. If the system has low distortion it will not sound loud, just natural. The level needs to be realistically high, so that the ear produces the same distortion and timbre as it would at a live event. Then you can experience maximum involvement and enjoyment. "

This fits very well into my own perspectives and preferences. Not that I play at very high levels often but systems with almost ridiculous headroom play music with all its dynamics less stressed and more effortless. I played some of my normal test CD:s with one perhaps overkilled system and noticed how fearsome some of the dynamic parts really are. People commonly complain about compressed recordings and sure, it is a big problem. But in the same time many "normal" home systems have pretty significant compression problems with those "not that compressed" recordings. And is there another way to solve this than total overkill?

You cutting the steel yourself?

Nope. I have a friend in a metalworkshop and he made the frames and bottomplates. I have place where I can weld them together and do the finishing if whole thing works acoustically...

New ideas and suggestions are also welcome if something comes in mind... Just frames and plates are ready, woodplates aren't.

Jussi

[Kensai]

Didn't mean anything derogative about your build. Just expressing awe and admiration for the magnitude.

Anyway, if they ring badly as is, then you may not want to weld them to the base plates. Use something that will isolate them accoustically, like wood or rubber, perhaps.

As for sheathing the steel, first off I don't like the idea of so permanently mounting the drivers between the MDF and steel. I would personally just sheath them and then mount normally. Also, I would probably use a nice solid plywood of some sort and then MDF on the back, simply for the aesthetics, though there have been some statements made as to the acoustics of ply over mdf in OB in a current thread. You'd probably also want to edge the frames in MDF (make the front ply plate bigger than the steel plate so you can put a tight edge of MDF behind the lip) so you don't get any ring off the baffle edge. On the back, you might even go with multiple layers of MDF, though not uniform. Thicker toward the edges would probably make a much better performing shape while progressively dampening the underlying steel toward the edge. Make sure to clear out the driver openings on the back side to maximize air flow.

Just the thoughts I had in mind. With your design, the crossover is going to be a huge factor in how good they sound, which is not my department (I usually hang out in the fullrange driver page over yonder). This will be fun to watch

Kensai

[ScottG]

to dampen the steel the best..

lead:microsorb:steel:microsorb:lead

2 things should be clear here:

1. the outer material should be heavier than the steel, NOT lighter (like mdf).. and the coupling material should be EXTREMELY lossy.

2. dampen both sides of the material.

I'd prob. only use this at the outer edges of the steel baffle/support. The best course of action is a quick sink for the energy from frame to baffle that is dampened as far away from the frame/baffle coupling as possible.

[LineSource]

I like to completely physically isolate the woofer array from the mid-tweeter with both a separate stand and a separate baffle. Having two separate structures also allows separate toe-in/out options. My room sounds best with a very tiny toe-in on the mid-tweet and a modest toe-out of the woofers toward the wall.

[Jussi]

Originally posted by Kensai
Didn't mean anything derogative about your build. Just expressing awe and admiration for the magnitude.

I didn't take that as insult. Quite opposite.

Anyway, if they ring badly as is, then you may not want to weld them to the base plates. Use something that will isolate them accoustically, like wood or rubber, perhaps.

Yep but that makes whole things overall stiffness much lower. One of the main reasons why I choose steelframe is that joint between baffle and bottoplate. There is no way to make that look so elegant and at the same time so stiff and sturdy by using MDF or such.

Thicker toward the edges would probably make a much better performing shape while progressively dampening the underlying steel toward the edge. Make sure to clear out the driver openings on the back side to maximize air flow.

I didn't got your first point here but the woodparts of the baffle form a 50x25mm elliptic curve along both sides so they should be as diffraction free as possible. I know there is still going to be problems above 1Khz before tweeter come into play since there is at least one dipole null at 1-2Khz range.

Midrange drivers have 45 degree cuts on their opening and without cutting the overall thickness it's pretty much as open as possible. Allthought that's not enough. We measured single 7" Peerless HDS in free air, no baffle at all, and it just doesn't work as a dipole much above 1Khz. Spider and magnet structure just mess it up.

Just the thoughts I had in mind. With your design, the crossover is going to be a huge factor in how good they sound, which is not my department (I usually hang out in the fullrange driver page over yonder). This will be fun to watch

Thanks. Crossover and finally electronics. I have Behringer DCX for the prototyping so I can easily try different setups but finally it sure needs a well done passive network (with active lowest cross to actual woofers) or full active HQ analog filter.

Originally posted by LineSource
I like to completely physically isolate the woofer array from the mid-tweeter with both a separate stand and a separate baffle. Having two separate structures also allows separate toe-in/out options. My room sounds best with a very tiny toe-in on the mid-tweet and a modest toe-out of the woofers toward the wall.

I agree. Positioning can be different, separated woofers can have sidewall boost without compromising main baffle response and most of the shaking also happens in physically separated box and doesn't disturb most of the frequency range.

Jussi