[SteveRB]

Hello,

I'm currently designing a new baffle set up for my Visaton-Alpha set up. I am interested in separating the Full-Range driver from the bass drivers -- several guys on here comment on the improved performance of this set-up. However,  like the look and footprint of the single baffle.

My idea is to acoustically separate the drivers on the same heavy baffle by using a  5-ply system (3-3/4" wood plys and 2-1/8" dampening plys). The full range driver is mounted on the middle ply and sandwiched by the acoustic dampening material and then the outer wood plys are used to bolt the bass driver on. In theory there should be a major reduction of vibrations to the full range driver from the bass drivers... make sense?

I'm still working out possible materials, but at this point I'm fishing for opinions.

Will it work?
Too much effort for too little rewards?

[richidoo]

Smart idea!     

You'll also need some vertical bracing to prevent the baffle from flexing vertically. The large woofer frames will brace the horizontal as long as the baffle is not too wide. Triple thickness construction should be enough to control the small driver's horizontal vibes in the top area of the baffle, but you could experiment with a hor. batten above it if it sounds colored.

What are you using for the damping layer?

[SteveRB]

yes: bracing will certainly be added to the magnets. as well as dampening to the driver frames.

I'm unsure of what the of material to use for the damping layers. I think it should be rigid, and dense. I'm hoping that someone with professional experience will chime in and suggest some materials. I am planning to use 3/4" MDF for the wood layers. 

[scorpion]

I definitely think that you should physically separate the baffles altogether. The only difference would be a new construction differing by som 2" at most in width and that will save you a lot of interference troubles. 

That doesn't save you from building good bass baffles.

/Erling

[SteveRB]

Erling,

Would you have two separate baffles? seems like aligning them will be an issue, no?

I can't think of how to configure a separate baffle for the full ranger that is above the bass drivers without getting in the way of the bass drivers...

[JohnR]

One way is to extend the baffle with stands on the outside of the woofers. sfdoddsy did that.

[Bob in St. Louis]

One of the inner layers could be a hollow chamber filled with sand.

I've make numerous pair of speakers and the baffle vibrations are very minimal, and that's with using 15" drivers.

Highly recommended.

Bob

[scorpion]

JohnR reads my mind.   

I suppose that you will be crossing around 200 Hz so exact physical alignment would not be so critical at that frequency.
But of course some effort has to go into the construction to make it look good altogehter.

/Erling

[ebag4]

I attempted this with some success on a couple of OBs that I built.  The way I did it was to use a magnet mount for the bass driver.  The 1.5" thick main baffle was cut from the back so that the entire bass driver could fit into it with a little wiggle room leaving 1/8" of material on the face of the baffle, the hole cut into this 1/8" material was cut to the size of the cone and surround so that you did not see the 1/2" mounting rim of the driver from the front.  Ultimately I was going to spike the magnet mount to the floor through the main base of the baffle.  Here is a pick to hopefully help make sense of what I am describing:






This one should be a little easier to see:



Note that the bass driver is not attached to the main baffle, it simply slides into the hole in the back of the baffle.  Drilling 4 holes into the main baffle base and sending spikes (with depth adjustable from the top) from the magnet mount down through those holes to the floor should complete the separation of bass driver and baffle.  Of course moving the speakers after the magnet mount is spiked to the floor would be quite difficult so speaker location should be detemined first.


Good luck!

Best,
Ed

[SteveRB]

I was thinking about magnet mounting, but I though it would work better for the full range driver -- Seems like the bass driver could use the mass of the baffle.

The sand idea is interesting, but I'd worry about it settling and creating voids.

The sand idea got me thinking: what about filling the void with modelling clay. The guys in the vinyl and box speaker forum love the stuff for dampening. I'm thinking a 1/2" layer between the bass baffle and full range baffle would do the trick...?

[THWO]

How about doing it exactly the other way around as suggested in post #1?

I.e. fixing the full range on a sturdy front board (two sheets) and having the woofer separately sitting in a second, solid construction (two or three sheets) behind the front baffle? The woofer could as well be supported by an additional magnet clamp. The woofer construction could be mounted on a separate base plate which itself is physically separated from the base plate of the front baffle by having it standing on long (enough) spikes reaching to the floor through holes in the base plate of the front baffle. No physical connection of both the base plates and front and secondary baffle. Between front and woofer baffle just some thin dampening material.

Please excuse my probably humble English...   I made a quick an dirty drawing of what I mean:



Might this be an option?


Regards
Till

Edit:   Oh, I just see that this compares well to Ed´s suggestion! Sorry for that! Let´s join forces... 

[mcgsxr]

Many good ideas here about how to keep the bass driver vibrations away from the full ranger. 

When I built my combo baffle, intelligent folks warned me that my simple design would cause vibrations from the bass driver to smear the full ranger.  They were correct.  Not so bad I have done anything about it 5 years later, but it is true.

My design plan (hard to think of it as a plan if I have not done anything in so long, but the schematic exists!) is to have the full ranger on a baffle, and the bass driver in an H shaped baffle that straddles the main baffle from behind - cut a hole in the main baffle for the bass driver to fire through, and done.

[THWO]

Please think about the necessity of an vertical alignment of woofer and full range, not just the opening of the front-H and the full range (if intended). Both drivers should be sitting on or about on same vertical axis.

In a H-frame, both its "halfs" will, then, equally extend to the front and to the back of the main baffle. Just in case I understood correctly that you intend to have the front opening of the H be in line with the baffle plate, please think about the fact that the woofer will then sit far "behind" the full range. Resulting in quite some phase shifts and, if you look (listen) at the rear radiation, quite some time ahead of the rear reflection of the full range. The latter, by the way, is the reason why a time shift in front radiation can not be eliminated by DSP, as the rear time shift cannot be corrected at same time. Therefore, it has to be alined physically.


Regards,
Till

[matevana]

I've experimented with several inversions of baffles made of constrained layers and dampening, all with the idea of isolating the LF driver with a high moving mass from that of the FR driver(s). I now believe that the best bang for the buck can be had by building a concrete baffle, taking advantage of the modern resin/concrete products that are currently on the market for DIY concrete counter tops, etc.  You basically start by building a form, using white MDF shelving material for the baffle dimensions as well as driver cut-outs. Drivers can be mounted using through-holes that are drilled after the concrete has cured, secured with lock nuts from the back. Threaded rods can also be inserted in the still wet concrete, to allow for fastening to a wooden base, etc.

My 1.5" thick baffles measure only 14" wide by 28" tall and weigh in at about 80 lbs. They are acoustically dead and very little mechanical movement transfers from driver to driver. My LF driver is 12" with about a full inch of usable excursion. My old wood baffles would actually "creep" from the moving mass exerted from this driver.

[Ric Schultz]

I am a 95% guy.  If you do everything 95% then you are good to go.  When every bit of your stereo and room are done 95% then play with the last 5% somewhere for fun.  If you make the baffle three thicknesses thick with Green Glue in between each layer and have a three thickness green glued brace running the whole height and attaching to the baffle above the full range and to the magnet of the full range and to the baffle between the full range and the woofs and to the magnets of both woofs and then to a massive 3 thickness base then you are 95% there.  Separating the woof at that point is just over the top crazy.  Are your drivers 95% as good as it gets?  Aren't you going to want to try some other speaker in a year from now?  Don't get that crazy!  Are your amps 95% as they can be?  How about your source?  Are your speaker wires on the floor?  Do you have connectors on your speaker wires?  How about room treatment.....CD treatment....line conditioning?   Get one of the new Behringer INukers and run your woofers off it.  It has built in xover, 8 bands of eq and a ton of power.  You could eq for flat response at listening position and have flat bass to 25hz!  It costs $300.  Have fun, whatever you do.

[rdlewis]

I have been contemplating a similar idea.  But sadly due to room size, it will not be a "OB".  The baffle will use two 18mm, possibly ply/MDF, plus damping centre, and will be a two way, but the principle will be the same.

The sandwich damping material I am concidering is "Rubber Cork", as supplied by "www.siestacork@aol.com".  According to their brochure,  "the 2mm thickness provides 16dB airbourne insulation and is even more effective for impact sound".  This is, I believe, is used in various areas in the Hi Fi industry.  I have seen it as driver gaskets and turntable mats.  Worth checking out, could be suitable ?

Roy

[versus rider]

if one driver is 100mm behind another that would be 0.333 of a millisecond out of time alignment I defy anyone to hear any difference, if anyone can then you have my sympathy for having such sensitive ears and maybe you should consider a different hobby as you clearly won't ever be able to enjoy listening to music.

Please think about the necessity of an vertical alignment of woofer and full range, not just the opening of the front-H and the full range (if intended). Both drivers should be sitting on or about on same vertical axis.

In a H-frame, both its "halfs" will, then, equally extend to the front and to the back of the main baffle. Just in case I understood correctly that you intend to have the front opening of the H be in line with the baffle plate, please think about the fact that the woofer will then sit far "behind" the full range. Resulting in quite some phase shifts and, if you look (listen) at the rear radiation, quite some time ahead of the rear reflection of the full range. The latter, by the way, is the reason why a time shift in front radiation can not be eliminated by DSP, as the rear time shift cannot be corrected at same time. Therefore, it has to be alined physically.


Regards,
Till

[Ric Schultz]

If you set the full range back so the voice coil aligns with the woofs, it would help.  I have listened and it sounds better to align the mid with the woofs.....no matter what some think.....yes, I do have golden ears.....actually platinum.   You can chamfer out the front around the full range so there is no hard edge.....remember to felt all around the full range too.  I have no idea why people don't felt around all mid and high frequency drivers....it sounds way better.  Please try it.

One way to attach the brace to the magnets of the drivers is to epoxy a rectangle piece of three quarter inch birch ply to the magnet and have the rectangle be as wide as the magnet but a little taller so some of the plywood sticks above and below the magnet.....there you bolt it to the brace.  This way you can unbolt it anytime you wish and remove the driver.  Remember to leave a hole in your epoxied plywood for the vent in the magnet.  Also make the brace scooped out around the vent hole as well so it can breath.

[Mijknarf]

Questions for Ric on your magnet mount of the woofer... is this for:
A) Supporting the magnet to add additional bracing to the woofer, thus reducing driver vibrations?  (driver still mounted to baffle)

-or-

B) Supporting the driver by the magnet fully so it is not attached to the baffle at all, thus reducing the panel vibrations into the full range driver?

Thanks,
Jim

[Ric Schultz]

A is the correct answer....he he.   Woofers put out tremendous energy so not mounting it to a baffle is going to flex the whole frame when playing music.  This is especially true for the stamped framed Eminence drivers.  Maybe some super 30lb driver might work OK not mounted to the baffle.  Midranges....no problem....you can use just magnet mounting.

Here is another way to separate woofer vibration from mids/highs.....used a lot in high end and also has other benefits:  Design your speaker like Poultrygeist's speaker.  Put both Alphas in their own H-frames and stack them on top of each other.  Use braces inside the H-frames on each woofer.  Then you make a base for the full range that sits on top of the H-frames.  You can then mount the full range baffle on it so it is time aligned with the woofs...naturally with another brace for the magnet of the full range.  You can then use some constained layer materials to isolate the full range base from the woofs below.  Another advantage of having H-frames is that they will play lower without eq and probably sound better.  So you get easy time alignment, better bass and some isolation of the bass from your fullrange.