'Perceive v2.0' Construction Diary

[ScottG]

Originally posted by ShinOBIWAN
So your saying that absorbtion is better than isolation in this case? Or spread the energy over a larger surface area instead of isolating through 3 discrete points.

We don't have easy access to the microsorb stuff in the UK, so something similar to Al's router mat would probably easier to get hold of.

It should be better.. At least for the midbass enclosure, but likely for the mid-tweet as well in the configuration I mentioned (enclosure/compliant material/heavyweight slab/compliant material/enclosure).

You can get microsorb from Michael Percy (compeletly reliable if not always "prompt"). HOWEVER, you might want to try taking a roller pin (and some wax paper) to a sheet of blue tack (..not nearly as good - but somewhat similar to microsorb and better than sorbathane), just to try-out the concept at a fairly low-cost. (oh, and roll it thin.. close to 1mm.)

pg. 19

http://www.percyaudio.com/Catalog.pdf

google on the blue tack turned up:

http://www.dooyoo.co.uk/household-pr...stik-blu-tack/

[ShinOBIWAN]

Scott

Would something like this be preferable:



Where the red layer is microsorb and the green is dedshete panel.

[ScottG]

Originally posted by ShinOBIWAN
Scott

Would something like this be preferable:



Where the red layer is microsorb and the green is dedshete panel.

Sorry its taken so long to respond..

(btw, nice illustration!)

Well then, this could be good or bad depending on the configuration and the drivers (generally)..

(..warning to all readers, there is a LOT of information here.. read it several times and hopefully it will become clear.. i.e. my powers of description can sometimes be described as an exercise in obfuscation.)

In your configuration (more specifically)..

For the mid-tweet "box" this would likely be a good idea in that it should provide a large degree of isolation from resonance created by the midbass "box", AND the motor and mass of each driver will likely NOT move back and forth (..what I described as "micro-rocking" in perceive 1).

For the midbass "box" it COULD be a good idea.. the problem here is that combating "micro-rocking" AND delayed cabinet energy from hitting the driver are at somewhat cross purposes. For instance, while we could be reducing delayed energy from the cabinets hitting the drivers with the proposed method in the illustration - you then have to consider how much the driver is allowed to "micro-rock" because of the compliant layer. (..*additonally you need to be concerned with how baffle energy is being isolated/stored to the baffle and hitting the drivers, as opposed to being transmitted through the rest of the enclosure - hopefully delayed and reduced in level.)

*Note that what I was orig. talking about was a method to sink midbass "box" energy by utilizing a "sink" on the top of this "box" under the mid-tweet "box" (..which would also provide a fair bit of isolation/decoupling to the mid-tweet "box").

IMO the best method, (if possible), is to have a very massive AND rigid BAFFLE that:

1B. Prevents "micro-rocking" by being VERY rigid at the interface between driver frame and baffle with ALSO enough weight to keep the baffle from moving, AND
2B. Transmits energy as quickly as possible to the cabinet.

Of course the problem here is #2 - i.e. what transmits energy away from the driver quicly usually transimts energy back to the driver quickly and at a greater level than otherwise might be the case with a material that is less "transmitive". Compound this problem with a cabinet that has modes that actually amplifys a portion of that transmitted energy in a specific band and the result could be an audible problem for that passband (..perhaps even altering freq. response).

So then, what we need is to have a CABINET that:

1C. Has little or no modes that would amplify vibrations, AND
2C. Actually dissapates (sinks) energy/vibrations transmitted from the baffle to it, so that energy that makes a "return trip" back to the baffle is both delayed and much lower in level.

So then, getting back to your loudspeaker, the "sink" I mentioned previously was to effect:

Part A (your midbass "box"):

1. Number 1B by adding weight to the speaker in general which will effect the baffle provided there isn't a compliant layer between the two (..as there IS in your illustration).
2. Number 1C by "sinking" spefic resonances that the top panel might have.
3. Number 2C (most importantly) by "sinking" overall cabinet energy, delaying the time and level of energy that will be transmitted back to the baffle.

Part B (your mid-tweet "box"):

1. Providing energy/vibration isolation between both "box's".

[ShinOBIWAN]

Thanks Scott,

I've just emailed MP Audio asking about ordering some of the microsorb.

I'm in agreement with you on the bass cabinet issue. I did mention in an earlier post that I tried decoupling it with the same method I used with mid/treble but removed the compliant foam layer since I though it blurred the sound a fraction, I think it will be the same case with the microsorb. Instead I think it would be best just to leave the dedshete in.

I plan on staying with the same plan for the mid/treble cabinet because the benefits are obvious to hear, maybe more so with the microsorb instead of the soft matting I'm using now.

[ScottG]

Originally posted by ShinOBIWAN
Thanks Scott,

I've just emailed MP Audio asking about ordering some of the microsorb.

I'm in agreement with you on the bass cabinet issue. I did mention in an earlier post that I tried decoupling it with the same method I used with mid/treble but removed the compliant foam layer since I though it blurred the sound a fraction, I think it will be the same case with the microsorb. Instead I think it would be best just to leave the dedshete in.

I plan on staying with the same plan for the mid/treble cabinet because the benefits are obvious to hear, maybe more so with the microsorb instead of the soft matting I'm using now.

IMO the single greatest mechanical improvement you could do would be:

For the Midbass "box":

1. Remove the dead sheet (and of course the compliant layer) and,
2. Form the midbass "box's" baffle (the segment that the driver attaches to as seen on the illustration) out of concrete (..with no sand).

I've found that this subjectively clears things up ( a lot actually) and seems to add another half+ octave of extension (..it doesn't of course - it just sounds like it does).

If you have any interest - just ask and I'll go into more detail on the forming of the baffle.

edit: Oh, and give MP (aka "the god of mod") quite a while from initial contact to receiving goods. Sometimes he is fast, sometimes he comes close to continental drift speed (..though never as bad as something like ordering custom transformers from tribute.nl). (..he is however completely reliable, at least I have no complaints nor have I ever heard of anyone complaining about him other than the occasional "speed" issue.)

[ShinOBIWAN]

Originally posted by ScottG


IMO the single greatest mechanical improvement you could do would be:

For the Midbass "box":

1. Remove the dead sheet (and of course the compliant layer) and,
2. Form the midbass "box's" baffle (the segment that the driver attaches to as seen on the illustration) out of concrete (..with no sand).

I've found that this subjectively clears things up ( a lot actually) and seems to add another half+ octave of extension (..it doesn't of course - it just sounds like it does).

If you have any interest - just ask and I'll go into more detail on the forming of the baffle.

edit: Oh, and give MP (aka "the god of mod") quite a while from initial contact to receiving goods. Sometimes he is fast, sometimes he comes close to continental drift speed (..though never as bad as something like ordering custom transformers from tribute.nl). (..he is however completely reliable, at least I have no complaints nor have I ever heard of anyone complaining about him other than the occasional "speed" issue.)

How would I go about forming a mold from the existing midbass baffles I already have?

[pinkmouse]

I'd suggest plasticine and lots of petroleum jelly. Or you could cast a female mold from plaster.

[ScottG]

Originally posted by ShinOBIWAN


How would I go about forming a mold from the existing midbass baffles I already have?

I haven't ever done it like that before, rather I just made the mold from mdf and used silcone lubricant for the releasing agent. I think its do-able though, and probably pretty easy.

Here is a company the produces a pour-mold product:

http://www.smooth-on.com/concrt.htm

(I've actually looked them over before, but not for their mold but rather for their plastics as a polymer additive in concrete.)

You might try searching the web and your local concrete supplier.

When looking into the product, also look at releasing agents - specifically a releasing agent that won't harm your baffle, AND a releasing agent (*if neccesary) that won't leave a slippery/greasy surface on the concrete. ((*I say "if neccesary" here because I believe that there are actual mold liquids that don't require it for the concrete pour.. could be wrong though.)

You will need to create an open box to "house" the current baffle.

You will also need to create a suspension that keeps the current baffle off of the bottom of the box and the back of the baffle flush with the top of the box. (..likely just a supportive brace/stick that is screwed into the back of the baffle, and rests on the top edges of the box.)

Depending on the product used you may need a realeasing agent for the baffle, and possibly latter for the mold.

Said differently:

1. make an open box with a depth 2 1/2 times the depth of the baffle with interior dimensions 3 inches beyond the length and width of the baffle. The box should be screwed together so that it can be taken apart more easily to release the mold from it. I wouldn't worry about minor leaks from box joints.

2. make a brace thats at least 4 inches wide and with a length as wide (or wider) than boxes outer edges.

3. screw the brace to the back of the baffle

4. spray a releasing agent on the interior of the box and on the baffle's front and edges and on the portion of the brace that is likely to come in contact with the pour-in urethene. (..or just spray the entire brace and baffle.)

5. place the box on LEVEL surface with a plastic drop cloth under the box for any minor leaks.

6. place the baffle face down in the box with the brace suspending the back of the baffle flush with the top edges of the box.

7. mix (as directed) and pour the mold up to the top of the box (..but not over).

8. wait the appropriat time and unscrew the box to release the mold from it, then pull the baffle out of the mold.

Nice thing here is you only need one mold.

[ScottG]

Oh.. Additionally..

If there is additional space (where you intended to place in deadsheet and/or a compliant layer) then you will need to add that "depth" on to the back of the baffle.

There is also the question of attaching the baffle to the "box".. you will have to describe how you are currently doing this.

[ShinOBIWAN]

Originally posted by ScottG
Oh.. Additionally..

If there is additional space (where you intended to place in deadsheet and/or a compliant layer) then you will need to add that "depth" on to the back of the baffle.

There is also the question of attaching the baffle to the "box".. you will have to describe how you are currently doing this.

Ok thanks for the tips Scott.

Its looks relative painless (on face value at least).

About the attaching of the baffle:



If you look at the photo here you'll see 6 holes in the driver recess on the baffle, in these sits a 100mm bolt thats recessed into the driver recess to allow the woofers to sit correctly and not foul the heads of the bolts.
I then simply tighten these up which clamps the baffle to the rest of the enclosure.

A few questions:

What's the quality of the finish like on the concrete, I'm primarily concerned with air cavities.

Is concrete easy to sand and shape if I do have minor or major imperfections?

I'll be painting these so how will this sit with the concrete, its obviously a somewhat porous surface but I'm primarily concerned that the paint may not take or will later come away from the surface after some time.

I really do like the look of the molding products you linked to in your post. I'm currently trying to track down something similar in the UK because the shipping for a few gallons will be prohibitively expensive. There's also talk of Hazmat on the website which could incure additional fee's too.