My first project is a 4 way speaker...

[5th element]

Not sure, but it fits in this thread. Download "Nanook Rubs It" from Frank Zappa's 1974 album, Apostrophe, and play it through those beasts and you'll hear it. Great looking speakers.

It would be Frank Zappa now wouldn't it.

[cochinada]

I wonder... now that the hole is gone, would a wood wall filled with some acoustic material be a good solution for this now naked wall behind the couch?

[BobEllis]

As I mentioned earlier, when a room such as yours forced me to have my listening position against the wall I found that an absorber behind me helped sound quality. With an open wall you have the beginnings of an absorber. If you can cover fiberglass with something acoustically transparent, you have a big absorber. Even if you must use drywall I would stuff the cavities to help damp any vibrations of the drywall. My Dad's house was built that way and sounds better than open interior walls.

[---k---]

I'm going to offer a different solution. I've seen many professionals recommend absorption on the front wall but that the wall behind the listener be diffusion in order to increase the sound field.

You can buy or build. I've seen people build something like this first google hit:


I'm sure there are white papers around on it. Maybe check Toole's book.

[BobEllis]

Ryan, I think that would be a better solution if there was more depth behind the couch. With just a few inches you're only going to get the very top end. Absorbtion on the back wall is definitely a non standard solution but it worked for me.

If you don't have it yet, look for "The Master Handbook of Acoustics" available as a free download or hard copy for a price. It discusses diffuser design and general room treatments.

[cochinada]

Yes, the couch is leaning against the wall so there is very little room or no room at all behind it. The front wall as it has my TV mounted on it will also pose an obstacle for any acoustic treatment. After all I cannot cover the screen.

I will take a look at that book "The Master Handbook of Acoustics". The problem nowadays is that with so much things to do one has very little time to do anything.

Regarding that strange 3D sculpture sort of thing I 'accidentally' found a site with some mathematical formulas for calculating the exact shape of it based on the frequency range to treat and overall dimension if I'm not mistaken. It is a relatively simple DIY job for those with some skills.

Meanwhile I've sent the plant of my room to this guy that is an acoustic engineer and he will come to my place and take some proper measurements before I decide what to do next.

[BobEllis]

That's a great approach.

[---k---]

Ryan, I think that would be a better solution if there was more depth behind the couch. With just a few inches you're only going to get the very top end. Absorbtion on the back wall is definitely a non standard solution but it worked for me.

If you don't have it yet, look for "The Master Handbook of Acoustics" available as a free download or hard copy for a price. It discusses diffuser design and general room treatments.

Good point. I was trying to be non-definitive. As I haven't built or installed diffusion myself, I was not trying to portry myself as an expert. I was just offering more options to research.

I got the Master Handbook of Acoustics fr Christmas. I've only had a chance to skim it. Looks like a lot of good / practical information. But like most books and whitepapers, I think it will take a lot of work/experimentation to translate square room theory into real word construction.

[BobEllis]

...it will take a lot of work/experimentation to translate square room theory into real word construction.

Isn't that the truth.

[Steve Manning]

I have a room that is similar to yours in that I have an opening over my left shoulder as well. Though I do not have my seat all the way against the wall. I had been working with GIK Acoustics with the intent of getting some of their products for my room. As Bob suggested, they also recommended getting a 2' X 4' X 4" absorber panel to sit on top of my dvd rack to balance things out with the opening on the other side. Have not had the option to try it out yet to see how it would work.

[---k---]

I'm curious, did you do any before and after near-field measurements?

[cochinada]

I'm curious, did you do any before and after near-field measurements?

With and without the grill, you mean? No I didn't. I don't expect any audible change but perhaps I should take some measures.

[---k---]

Yes with and without the grill. I've read there isn't an audible change. I'm always skeptical and like data. I haven't seen graphs (though I haven't really searched them out). Your project has been so thorough that I thought it might be something you did. No worries. You don't need to in order to satisfy my curiosity.

[cochinada]

Yes with and without the grill. I've read there isn't an audible change. I'm always skeptical and like data. I haven't seen graphs (though I haven't really searched them out). Your project has been so thorough that I thought it might be something you did. No worries. You don't need to in order to satisfy my curiosity.

No worries. I will take the data (as soon as I overcome this inertia), because I'm curious too.

[augerpro]

Regarding that strange 3D sculpture sort of thing I 'accidentally' found a site with some mathematical formulas for calculating the exact shape of it based on the frequency range to treat and overall dimension if I'm not mistaken. It is a relatively simple DIY job for those with some skills.

What was the site?

[cochinada]

What was the site?

This one, it has also a link to a BBC study:

http://web.archive.org/web/20070429235805/http://www.mhsoft.nl/DiffusorCalculator.html

...and this other one is interesting as well:

http://www.pmerecords.com/Diffusor.cfm

[cochinada]

Well... I have bad news. As if it was not bad enough already to have to live with all the gaps and faults it seems that my carpenter didn't seal or stabilize the BB so well as now I have those nasty cracks as well
I just noticed this about a month ago or so and have no idea if they are still increasing. Curiously enough, I only have cracks on the bottom boxes and even more strange (or not) on roughly the same places. I will post a couple of pictures latter on for you to see.

[Steve Manning]

Well... I have bad news. As if it was not bad enough already to have to live with all the gaps and faults it seems that my carpenter didn't seal or stabilize the BB so well as now I have those nasty cracks as well
I just noticed this about a month ago or so and have no idea if they are still increasing. Curiously enough, I only have cracks on the bottom boxes and even more strange (or not) on roughly the same places. I will post a couple of pictures latter on for you to see.

That so sucks ...... had the same thing happen with mine. It's a painful way to learn about wood movement. Is it fixable?

[---k---]

That sucks. I'm starting to wonder if it is even possible to seal/stabilize a translam project of this size to avoid these problems or are they inevitable.

[Steve Manning]

That sucks. I'm starting to wonder if it is even possible to seal/stabilize a translam project of this size to avoid these problems or are they inevitable.

Hey Ryan ..... after I had mine crack I did a lot of research online into the issue. First, I was rather surprised by how much the BB actually moves over time, I thought it was a lot more stable. That being said, sealing it helps but will not stop it it completely. I think the biggest part is learning to work with it and not constrain the layers from moving. What I found in most cases where these projects crack and what I did myself, is we glue the baffles, backs, sides, what ever, in place across the lamination's. This "try's" to prevent the wood from moving ....... not.

If you look at say what Magico did when they used BB with the aluminum baffels and backs for their cabinets ..... they had o-rings in the baffels and backs and the two were bolted together as a unit. That way they floated independent to the wood portion of the cabinet. That way the BB could breath as needed without cracking.

This is of course all conjecture on my part, but I don't think I'm too far off.

Steve

[Steve Manning]

This is how I fixed mine ...... you can hardly see where it happened. With the edges taped up just fill the seem with 5 minute epoxy. When it dried I used the smaller of the scrapers shown and smoothed the epoxy. You might have to do several coats of the epoxy until it levels. Pull the tape and buff the surface.

[cochinada]

Thanks a lot Steve. :T I wish I had you expert craftsmanship skills but I will definitely give it a try. I'm just thinking if wouldn't be better to wait some more time until it hopefully stabilizes before attempting to fix it or should I tackle it right away? What do you think?

[Steve Manning]

Thanks a lot Steve. :T I wish I had you expert craftsmanship skills but I will definitely give it a try. I'm just thinking if wouldn't be better to wait some more time until it hopefully stabilizes before attempting to fix it or should I tackle it right away? What do you think?

Just go at it slowly and take it a bit at a time and you should be fine. Keeping the painters tape in place while you scrap not only protects the surrounding area, but it will also give you a good indicator if your getting too aggressive in what your taking off. Chances are the built up stress has released itself. Since I fixed my cabinet I have not had an issue with it again. Also it only happened to one cabinet and not the other.

[TEK]

Can it be that the translam and front panel expand/compresses at different rates, and due to this you get stress in the joints between the front baffel and the box?
As the translam has quite a different structure than the front panel I would suspect that they expand at different rates, then you get stress and finally cracks.

If that is the cause the cracks is likely to be caused by either the front baffel expanding more than the translam, or that the translam is compressing.
The first thing I'm wondering about then is if this is something that is caused by the wood setteling into a new stable state, or if it is caused by changes in how try the air is.
As these are quite new I would expect it to be quite a good change that this is due to the wood/glue in the translam drying out and the transam compressing due to this. If that is the cause it should stabilize when the wood is dried out.
If this is caused by air humidity the translam will expand again when the air gets more moist. Maybe that extra length added by the gule will not be a problem even if the translam expands a bit - but it might be worth thinking about.

If my hypothesies is correct then I think the only way to awoid this would be to disconnect the baffel from the side/back of the speaker to allow for wood moements.
I saw one that had similar problems, but even worse. He had used metal roods that he had stacked the translam on and fastened those into the metal. As the metal and the wood extract/compress at different raites. That again caused the translam to break up the same way as you experience.

[Hdale85]

I imagine if you used something like LBL that's more stable than the birch ply most people use it wouldn't be a problem. Granted that's a lot more money than cabinet grade 13 ply.

[Steve Manning]

I imagine if you used something like LBL that's more stable than the birch ply most people use it wouldn't be a problem. Granted that's a lot more money than cabinet grade 13 ply.

It's one of the main reasons we went with lbl when we made the Minerva's.

[Browncoat]

As the translam has quite a different structure than the front panel I would suspect that they expand at different rates, then you get stress and finally cracks.

I agree. I think the lamination is moving more than the other panels, because wood mostly moves perpendicular to the grain. Measuring perpendicular to the grain on those laminations is well over a foot, I'd guess? Even if it only moved 0.010" per inch, that's still about a quarter inch of movement every two feet.

In any case, I'm still in awe of this project. Like somebody else pointed out, blazing a trail isn't easy!

[cochinada]

Interesting theories indeed and they make all the sense. I'm just wandering, why didn't the top boxes show any sign of cracking if the construction is exactly the same? The only thing it comes to my mind is that the ones at the bottom support all the weight but even so I don't know how crucial this might be...

Yes lbl was an option I considered at some point, namely a sandwich of BB and MDF but I was only thinking about damping/absorption advantages as I didn't know this technique is more stable in terms of would expansion. If I new better at the time I would have probably gone for it at least on all exterior panels but I don't know if this would have prevented or minimize my problem. Bamboo I had to let it go because here it costs about 4x the price of BB. 8O

I certainly hope this was caused by the wood/glue drying out and not by exterior moisture. It's not that I live in Singapore as Mike does although I do have a river nearby. :roll:

[cochinada]

I agree. I think the lamination is moving more than the other panels, because wood mostly moves perpendicular to the grain. Measuring perpendicular to the grain on those laminations is well over a foot, I'd guess? Even if it only moved 0.010" per inch, that's still about a quarter inch of movement every two feet.

Way over. More like two feet...

In any case, I'm still in awe of this project. Like somebody else pointed out, blazing a trail isn't easy!

Thanks. A friend of mine never misses the chance to say I was crazy and this was a very ambitious project.

[dsrviola]

This makes me wonder about my translams. Unfortunately my curiosity would require me to remove the veneer to see the BBirch underneath. THAT'S not gonna happen! Fortunately (on the other hand) the enclosure is for a tweeter and upper mid driver and not a woofer.

[cochinada]

This makes me wonder about my translams. Unfortunately my curiosity would require me to remove the veneer to see the BBirch underneath. THAT'S not gonna happen! Fortunately (on the other hand) the enclosure is for a tweeter and upper mid driver and not a woofer.

Do you have pictures or a thread of your own? I'm curious to see this. In my case on one hand I was 'lucky' that I went for a varnish finishing so I can see all these problems. If I don't fix this soon my cabinets will eventually become vented instead of sealed.

[cochinada]

This is how I fixed mine ...... you can hardly see where it happened. With the edges taped up just fill the seem with 5 minute epoxy. When it dried I used the smaller of the scrapers shown and smoothed the epoxy. You might have to do several coats of the epoxy until it levels. Pull the tape and buff the surface.
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Hi Steve, I can find only transparent epoxy here. How did you tint yours?

[Steve Manning]

Hi Steve, I can find only transparent epoxy here. How did you tint yours?

I just went with the clear stuff and it was close enough. If you want to tint it you could try something like this stuff which I've used on wood filler before. http://www.woodcraft.com/product/147...tones-set.aspx It can mix with just about anything.

[TEK]

I suspect that you can "tint" it by mixing in some sawdust as well if you need to.
But you will probably get a good result by just using clear epoxy as well.

[BobEllis]

Adding birch sawdust tends towards a dark brown putty. Nice for sticking things together that don't fit perfectly and are going to be painted but not so much for a clear finish. I used that method to make my Ardent bases and install braces in a quick subwoofer. Better to use trans-tint dyes if color is needed.

[knowledgebass]

Clear epoxy will pick up tint from the adjacent plys. Use a cabinet scraper to flatten it after to save on dust mess (or wet sand). Here's my post from a couple years ago. It's a long one but the relevant stuff is near the bottom of the post.

http://www.htguide.com/forum/showthread.php?p=598976

[BobEllis]

Back home, so here's a shot of clear epoxy with birch sawdust mixed in to thicken. Not what you want on a top coat.

[cochinada]

Thank you guys for all your help and valuable tips! I will use the epoxy as it is, that is, transparent.
BTW do you think it might drip if I apply it to the speaker as it is, that is in a vertical position?

[BobEllis]

It will run. You might try a hair dryer to warm it up and speed up the gel time once you've applied it. Practice on scrap first to see if it works for you.

[Steve Manning]

Yep, I hate to say it, but laying the speaker on it's side would be your best best, though understandably not easy with what they weigh.

[knowledgebass]

Careful warming the epoxy. It will make the epoxy significantly less viscous. This is good to get the glue down into the crack, bad because it can run through. Warming will also help remove gas bubbles.
I used a toothpick to apply a thin line over the crack and a heat gun to help it flow deep into the crack, making tape to help dam it where I wanted it to stay. If you apply more epoxy during the gel period, usually 24-48 hours for a long set epoxy, it will bond chemically, no need to sand to help the bond.

[5th element]

Warming will also speed up the curing process so if you're going to go that route you definitely need to use a long set type.

[Steve Manning]

If it were me I would remove the driver that give me the best access to the crack, tape the crack on the inside of the cabinet with painters tape to act as dam. Lay the cabinet on it's side, tape the offending area and fill the crack with epoxy. Let it cure and top off the crack if required with another round of epoxy. Scrape smooth and away you go. No heat gun, no runs ....... a bit of a PIA, yes, just my $.02.

[5th element]

Oh I thought the cabinet was going to be laid on its side to do this...but what Steve says. Also depending on how well the epoxy flows you could also inject it into the crack using a syringe and fine needle.

[cochinada]

Well since I'm a bit lazy for certain things I'm still gaining momentum for performing this operation. The shear though of having to lay down these beasts takes any enthusiasm out of me so this idea of the syringe is most interesting.

Anyway I've ordered this new set of spike base pads to replace the ones that came with the Viablue that are too small in my opinion.
These are much larger at 49x12mm comparing with 11x3mm so I expect to be much easier to move the speakers around which right now it's an impossible task. As soon as they arrive I'll tackle this for sure. It's decided.

Also today I went to customs to pick up my replacement tweeters because I was tired of waiting. Interesting is the SPL vs Freq the manufacturer sent me. For those that are curious and want to compare, here are the curves of both pairs.
They are fairly similar although this new pair looks a little less flat between 5kHz and 8KHz.

old:

Image not available

new:

Image not available