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  »  New  45Hz Bass Horn..  Can We Ever be Saved From Ourselves?...  Horn-Loaded Speakers Forum     23  314641  09-19-2006
  »  New  8" Goto Woofer for 60Hz Horn..  It's not a Goto 8in driver...  Horn-Loaded Speakers Forum     5  87176  11-03-2008
  »  New  The Macondo’s Upper Bass Channel: what is next?..  Görlich again...  Horn-Loaded Speakers Forum     30  289698  10-28-2007
  »  New  Jessie Dazzle Project..  Will this better to be auditable?...  Horn-Loaded Speakers Forum     172  1558799  08-03-2007
  »  New  Romy The Cat's new Listening Room..  Won't be the last time he makes that trip!...  Audio Discussions  Forum     478  2914108  03-28-2010
  »  New  Problems with horns: upper bass ..  Must it be about loading?...  Horn-Loaded Speakers Forum     109  1167385  03-25-2005
  »  New  Midbass Horns and Real Estate...  Just a youtube video......  Horn-Loaded Speakers Forum     247  2138054  07-26-2009
  »  New  Macondo’s lowest channel...  What truly are you tryin to accomplish?...  Horn-Loaded Speakers Forum     150  1393181  09-15-2010
  »  New  Practical Guide for Back Chambers Tuning...  Back chamber’s cost-benefit....  Horn-Loaded Speakers Forum     5  75661  10-21-2006
  »  New  Superbly interesting effect: Suspended decoupled floor ..  Superbly interesting effect: Suspended decoupled floor ...  Playback Listening  Forum     0  18029  10-08-2010
  »  New  Midbass impedance bumps -- why and what to do?..  You need to stop deceive yourself....  Horn-Loaded Speakers Forum     18  193442  10-21-2010
  »  New  Mystery of bass horn calibration: Radiating Surface Dee..  Mystery of bass horn calibration: Radiating Surface Dee...  Horn-Loaded Speakers Forum     0  17230  02-03-2011
  »  New  Impulse response, short notes and midbass horns...  A possible solution to better impulse?...  Horn-Loaded Speakers Forum     14  127845  06-13-2011
  »  New  My new “New” listening room, 2024..  That is not enough efforts in this direction....  Audio Discussions  Forum     31  17057  05-08-2024
09-14-2010 Post does not mapped to Knowledge Tree
tuga


Posts 174
Joined on 12-26-2007

Post #: 261
Post ID: 14446
Reply to: 14441
Silent blocks?
fiogf49gjkf0d
 Romy the Cat wrote:
Ok, here is another subject. I feel that I kind of screw it up as I did not foresee it in my planning.  What I need is to add some decupling devised to my horn in the location where it will be mounted to the surface of the house frame. The horn will be vibrating during its operation and I want under no circumstances to feel any micro- vibration of the house floor. So, I need some kind of compound that swill be a able to handle a lot of pressure, to keep its elastic at low and high temperature and to dump vibrations. Yes, it she be very thin as well….  Any candidates?
I once mentioned the use of silent blocks...

http://www.adina.com/cet03.shtml

http://www.openpr.com/print/31310/Silicone-instead-of-natural-rubber-first-silicone-engine-mount-proves-itself-in-series-use.html

Cheers, Ric


"Science draws the wave, poetry fills it with water" Teixeira Pascoaes
09-14-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,644
Joined on 10-12-2006

Post #: 262
Post ID: 14447
Reply to: 14445
Spreading, Dissipating and Grounding Vibration
fiogf49gjkf0d

My first thought is for a "very dense layer of foam", or maybe very good felt, between two hard, even "slipping surfaces", such as 2X4s or even "5/4" (1" net) or 3/4" net oak boards.  This might be a fairly thin sandwich that the entire length of the mouth of the horn could simply rest on, right above the beam, with felt or something also used as a slip anywhere the horn might otherwise touch on the house framing, so the horn could just sit there and vibrate, more or less by itself.  A few "cleats" fastened to the house, but not the horns (or vice-versa) could prevent the horns from "walking around".  Apart from foam, I have used strips of sheet Transite (compressed asbestos fiber) for "slipping blocks" betweeen concrete floor sections on bridges and parking structures, etc.  Much lower frequency, of course, but it certainly "works".  This scenerio could perhaps be re-created at the middle of the horn, resting the "slipping block" on something spanning the joists over another bearing point.  Steel "U-channel" is compact and strong and widely available for this purpose of distributing weight across ceiling (attic floor) joists.

The sling idea is a good one (if you could figure out where to hang the slings!).  Rather than rubber, consider industrial "web" slings, which can be rated for use on truly gigantic loads that are moved with cranes, etc.  Slings like this are widely available, once you start looking.  Again, this also creates "point loads".

No doubt someone else will mention the "motor mounts", which are indeed compact and plenty strong, but which may have a disadvantage in your case, especially at this point in time: they create very severe "point loads" that would be hard to counter with wood framing alone.  Perhaps you could mount them on metal plates or "U-channel" to distribute the load across a sufficient number of framing members.

Depending on how (and how well) the "dissipation" points work to bleed energy, one might still face the need to "drain to ground" any unwanted energy not "converted to heat".

Best regards,
Paul S

09-14-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 263
Post ID: 14448
Reply to: 14441
Decoupling: It takes balls
fiogf49gjkf0d
Go buy a load of tennis or racket balls and use them to float the horns. You can vary the number until you get just the right squish. 

As it is just the edge of the mouth that rests on the attic floor, this will require a some prep work... 

Here's how I'd do it:

Add permanent legs similar to what's shown in the most recent photo.

For each leg, cut a 1ft square board from thick (2 x 3/4 inch) plywood and add a shallow boarder around its perimeter, making a sort of very shallow box. Place "boxes" open-side-down under legs and over a bunch of balls, so that the boarder keeps the balls from rolling.

Voilà, a floating horn.

I once used racket balls under massive concrete slabs with excellent results as confirmed by playing music loud while placing front teeth in contact with suspended element.

Over the course of a month, the balls did take a set before finally stabilizing... I had this setup in use for about a year and only took it apart due to a pending move... I still have the balls, and they still have air.


jd*


How to short-circuit evolution: Enshrine mediocrity.
09-14-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 264
Post ID: 14449
Reply to: 14448
I need absolutely no noticeable vibration on the listening floor.
fiogf49gjkf0d

Again, none of the pneumatic methods would work as any pneumatic leak air with time and it will be no access to it after the horns are installed and the walls are finished.  Not mention that we have no high to play wit. We will be doing the following:

1) Places e the horns into the wholes in the wall
2) Before binding the bottom of the mouths to the attic joists (7 joists per mouth) we will shim the space between the joists and the bottom horn with shims. The shimming will assure that each of the joist (joists will have cut corners to accommodate the horn) care own portions of the horn load
3) The shims will be composite: a later of parallel wood (to keep the total shim angle under 12 degree), a layer of cork and a shim.
I think it all that we can do at this point from front side of the horn. Let hope that significant mass of the horn and the frame will do the trick and make the bone-transmitting vibration not detectable.

I kind of forgot about it as I did not have for years and years anything that vibrated. The bass towers that I had in my old room were absolutely free from any vibration and they were sitting on concrete slob. The last nigh I have a reminding that I might think about it in my new room.

I was visiting yesterday a local guy that made me to think about the structure vibration. He has an interesting arrangement – a pair of mono-strapped EV 30” woofers sitting in basement and fairing up into disabled air ducts in listening room floor. Since the ducts are relatively small and since he has a compression chamber before the ducts then it formed 4th order bandpass configuration. Regardless how good or pad the installation sound the vibration from 2 monster woofers was very much detectable across all floor. The give me almost panicky mode and made me to think how to make sure that my horn will not detectable on the listening room floor. Unfortunately it was a bit too late for me.

BTW, the idea that my local guy employed is still lucrative and I have some thoughts about it. I will share them when I finish my midbass channels and will deal with my next, the lowest octave, sub 40Hz channels. For now let pray that it will be no vibration on the listening floor.

The Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
09-14-2010 Post does not mapped to Knowledge Tree
scooter
Posts 161
Joined on 07-17-2008

Post #: 265
Post ID: 14451
Reply to: 14449
Straps and shocks
fiogf49gjkf0d
The straps seem like a good first step given limited space, weight and access to several beams. Unfortunately they can eliminate some vibration but will transmit through other points in the house frame. Hanging horns by straps will do little to restrict upwards movement and some resulting bouncing. Of course you could strap from three dimensions around the horns but that gets a bit difficult and likely directly transmits more house frame vibrations (there will be certain points of strapping that may not vibrate at certain frequencies but I don't know it that matters from a practical perspective given complexity of horns and music).

 I would think about incorporating some bicycle shock absorbers typically used in the frame of mountain bikes (not the forks at the front wheel). These shock absorbers may incorporate a spring and oil based dampening system and provide varying levels of adjustment. Some you can adjust remotely. You could mount (four) shocks on the sides of each horn as feet bolted to a floor beam. Alternatively, you could run straps to suspend the front and back of each horn using four shocks to connect the strap ends to the shocks and each shock to a beam (in compression mode); lack of rigidity of the straps could cause some odd vibration issues here but the shocks may dampen that.

I think these shocks start at about $150 (wheelworks in belmont is huge shop with knowledge) but you might be able to contact a local distributor (allied cycle in waltham I think) for a volume discount if you can convince them to sell to you. Lousy $250 bikes come with unadjustable shock absorbers so cost has to be below $10 to manufacture lousy shocks.

Here is a picture of a more expensive
http://www.gearbuyer.com/products/fox_racing_shox_van_rc_coil_rear_shock.html
09-14-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 266
Post ID: 14452
Reply to: 14439
This is as idiotic as it I could be.
fiogf49gjkf0d
 Romy the Cat wrote:

Midbass_progress_95.JPG

Practically all surfaces of horns are sanded and relatively good looking, I was priming today the rest of the horns. I was priming it as was thinking how much I got worse. Formerly I was listening some music at this part of day but nowadays I am partially covered with pain was manufacturing tools that would let me to stick myself into the horn. My apologies that I did not make a video of it - trust me you do not what to see it. The problem is that the horns are assembled I can’t reach the section 2 and 3. A roll or a brash on boom helps to a point but there are some locations where boom is useless, it is not to mention that the horn has a few degree curves after the section 5. I kind of a large fellow and I can stick myself into the horn up to the point. Then I begin to slide back. As you can see the horn curves down a lot, the back chamber is all the way up. The biggest curve down in the sections 6 and 7 and this is where my heaviest part is – stomach lies what I am stretched in the horn. So, since I have no support to push myself forward to the section 2 I truly was not able to prime it. I try a few ad-hog methods to stick myself into the horn but they did not work. After some consideration and some fight with my own embracing I found ridiculously effective way to prime the sections 2 and 3 – I dived into the horn. I undressed, spayed the sections 7 to 4 with water, run into the horn with extended arm and let myself to slide in. As a result I have 2-3 seconds in the horn where my hand, in fact fingers, can paint something. I t is in way funny and stupid but it is what it is….


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
09-15-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,644
Joined on 10-12-2006

Post #: 267
Post ID: 14453
Reply to: 14452
Weenie
fiogf49gjkf0d
What you need is a "weenie roller"; the German type with the fuzzy end works especially well, it gets into the corners; rollers are 6" or 4" long.  Put the frame on an extension and you can feel your way along.  Use mirrors if you must to see what you are doing, and/or what you have done.

...not to interfere with your Naked Lunch...

Best regards,
Paul
09-15-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 268
Post ID: 14454
Reply to: 14453
The horn painting job
fiogf49gjkf0d
It is hard to see from the picture but the inner walls of the horns are not parallel. In fact there are no two parallel surfaces in the horn – that was the requirement. Some when any kind of roll lays on the section 2 or 3 surface then it is expected that the handle of the roll to be in horizontal 90 degree angle against the painted surface. Unfortunately in this horn it is not possible and even if I stick a roll to where it needs to be then the roll attached to broom will not lay parallel to surface. What is needed is some kind of special rolling frame where roll has freedom against own frame, some kind of ball join. If someone know this type of frame then let me know ASAP as I need it for final paint. The final paining will be two coats – first is textured layer (paint with sand) and second is flat paint over the textured layer. The textured surface will be there but it will be a bit smoothed out by the second layer….

The Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
09-15-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 269
Post ID: 14455
Reply to: 14454
Romy the cork
fiogf49gjkf0d
Articulated roller handles (frames) do exist, but they are made to be adjusted and locked before use:
http://www.thebossmaker.com/benefits.htm

Instead I would consider using a thick, angled brush, not a paint brush, clamped to a long pole, used not in a sweeming motion, but in a dabbing up and down motion, which would help maintin the texture.
http://remodelista.com/img/sub/dustpan_brush.jpg

If not for the texture you want to apply, you could try one of these articulated sanding devices, fitted with a fluffy paint applicator pad (available at Home Depot etc).
http://www.diamondwall.com/images/DW_051cs.jpg

Here are some images of applicator pads:
http://www.google.fr/images?hl=en&safe=off&q=paint+pads&wrapid=tlif12845518212842&um=1&ie=UTF-8&source=univ&ei=lLSQTKCpJJWT4gbWn4mLDg&sa=X&oi=image_result_group&ct=title&resnum=6&ved=0CDkQsAQwBQ

I'm surprised nobody has suggested bringing Koshka in on the mission!

jd*


How to short-circuit evolution: Enshrine mediocrity.
09-15-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 270
Post ID: 14456
Reply to: 14455
Stairway to throat heaven.
fiogf49gjkf0d
Painting the horn in my way the old joke come me. Question: how a woman can detect that she is fat? Answer: when she laying in a beach in her swimming suite the people from Greenpeace are trying to push her back to the water.  That was pretty much how I felt about myself when I was trying to rich the last sections….

Ironically this morning I woke up at 5AM, after watching the US Open final up to 2.30 and what any “sane” person would do after they wake up? Right, painting the horn before leaving to work at 6AM. When I just woke up it suddenly hit me how I can stick myself into the horn. What I did was passing throw the horn’s throat a rope with nuts and use it as something  sort of horizontal ladder I was able to “clime” or to punch myself deep into the belly of the horn where I was able to use a regular grove-brash.

A note to followers.  The 7” throat is small but it is still semi-manageable. If you go for let say 5” then you first sections would be even smaller and longer. So, think deep and foreseeingly how to sand/prime/paint those narrow openings before it will become ugly. 
 
BTW, there is a change that the quality of my paint would be less relevant as I might stretch a semi-transparent screen over the horn mouth, it will not be non- transparent screen but rather something like women stockings – translucent but a bit defusing. This way I will be able to get some light from the horn but prevent dust go inside… In fact I think about an insertable light frame with pantyhose fabric (nylon and microdeniers blend) that will be placed in the mouth of the horn. Well, I hope to see the times when the dust filter will be my the only problem….

The Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
09-15-2010 Post does not mapped to Knowledge Tree
RF at Ona
Posts 12
Joined on 05-29-2007

Post #: 271
Post ID: 14458
Reply to: 14449
Weight bearing decoupling inches back from mouth end of horn
fiogf49gjkf0d

You can improve the vibration decoupling by lessening the weight on the horn mouth edge.

There is no need for the edge of the horn mouth to bear a great deal of the weight of the heavy end of the horn, although that seems your current plan. The mouth edge can be virtually weight free and, if you insist, connected to the framing to stabilize the mouth for acoustical reasons. But it is far better for vibration decoupling to have the weight carried to the joists several inches back from the horn mouth with significant anti-vibration padding at the weight bearing points.

Personally, I think it debatable whether the mouth edge should be free or attached as there are desirable aspects to both approaches. If attached, it need not be attached with great pressure.

The fewer points of contact, the less area of contact and the less weight of contact yield the less mechanical (vibration) coupling.

Putting the weight-bearing region behind the mouth edge would allow sufficient space for a variety of decoupling approaches and materials at the critical points and not be compromised by the limited space available for the mouth edge.

I am sure you have found or can easily find a variety of anti-vibration products on the net.

Here is one quick example:  Atlanta Vibration Pads. They actually list loudspeaker vibration isolation as one of the uses for their products, for what it's worth. They make both a rubber with cork center sandwich pad and a rubber with a composite foam center pad. I’d consider a combination of the two layered together. You would need to watch the psi loading on these kinds of products.

http://atlantavibrationpads.com



Rubber-foam vibration pad.jpg


Thought for today:
There may not be time to do it right but there may still be time to do it well.

Hope this helps,
Robert

09-15-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 272
Post ID: 14459
Reply to: 14458
A horn like a snow plow all the way down.
fiogf49gjkf0d
 RF at Ona wrote:
Personally, I think it debatable whether the mouth edge should be free or attached as there are desirable aspects to both approaches. If attached, it need not be attached with great pressure.
 Robert, can you elaborate why if attached, it need not be attached with great pressure?  I was under opposite impression. In fact, we consider binding the front for to all joists and to all beams across the entire horn. The leading edge of the mouth is 2x4 and 1.5” of plywood – it is a lot of thickens to bind through. In our view the leading edge of the mouth is what all horn mass will be “grounded” Take a look in the picture - the horn tail all the way up and the horn is like a large snow plow  that is lowered down and lies on the payment – in my case the payment are the locations where the roof joists and the frame’s beams come together.


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
09-15-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 273
Post ID: 14460
Reply to: 13597
How "smartly" to displace air from the back chamber.
fiogf49gjkf0d
Ok, the attic is all prepared and ready is host the horns. I installed the final 14/50 drivers and put in the first layer of foam. I do not like the result. With the large death of the foam that need it will take for me weeks to pile a layer by layer as it will not dry properly otherwise.  I need to find another way to displace air from the back chamber. I will take the foam out....

Midbass_progress_96.JPG

Midbass_progress_97.JPG

Midbass_progress_98.JPG






"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
09-16-2010 Post does not mapped to Knowledge Tree
RF at Ona
Posts 12
Joined on 05-29-2007

Post #: 274
Post ID: 14461
Reply to: 14459
Coupling vs Decoupling at Mouth End
fiogf49gjkf0d
 Romy the Cat wrote:
 RF at Ona wrote:
Personally, I think it debatable whether the mouth edge should be free or attached as there are desirable aspects to both approaches. If attached, it need not be attached with great pressure.

 Robert, can you elaborate why if attached, it need not be attached with great pressure?  I was under opposite impression. In fact, we consider binding the front for to all joists and to all beams across the entire horn. The leading edge of the mouth is 2x4 and 1.5” of plywood – it is a lot of thickens to bind through. In our view the leading edge of the mouth is what all horn mass will be “grounded” Take a look in the picture - the horn tail all the way up and the horn is like a large snow plow  that is lowered down and lies on the payment – in my case the payment are the locations where the roof joists and the frame’s beams come together.





I was referring to the fact that if you used my idea of supporting the horn a short distance from the edge (with extra anti-vibration padding) you would be free to stabilize the horn mouth edge if and to the degree necessary in such a way as to reduce the vibration transmission at that point.

Further thoughts:

To a large extent supporting the weight of the horn and mechanically decoupling it to prevent the transmission of mechanical vibration are mutually opposed. In decoupling you try to isolate the horn and leave it to vibrate on its own - with those internal vibrations more or less suppressed and damped by the construction materials and design of the horn itself. In tightly affixing the horn to the structure supporting it you are trying to control the vibration by using the external structural stiffness, mass, vibration transmission and damping. Sometimes you can use both elements in a frequency selective way.

I was under the impression that you wanted to tightly couple the horn mouth to the attic framing into order to control the vibration of the horn mouth – these vibrations are a genuine issue as to the basic acoustical operation of the horn. But you also realized that tightly coupling the mouth without sufficient anti-vibration padding could easily allow it to transmit its vibration to the house structure.

It is these conflicting approaches which require some balancing.

Had you wanted 1 or 2 inches of anti-vibration padding around the horn mouth, your original design to support the horn at the very end would have been fine, although you might have had a smaller mouth area as a consequence.

If you wish to add additional decoupling at this late stage of construction then you can obtain it in a fairly simple way by moving the support points for the mouth end back several inches or perhaps or a foot or more to where the horn geometry gives you enough space to put an inch or two of anti-vibration padding with some appropriately shaped wood supports.

The very end of the horn mouth could be free standing as it might have been had you extended the horn a few inches past the wall into the listening room or it could be lightly loaded. You can attach it to the frame in a number of different ways including the shims you have mentioned. If the fit is tight you would only need a thin layer of padding. If there is a gap, you could use a series of screws or bolts with the horn end slightly off the framing, or you could stuff padding tightly between it and the frame – the trick being to prevent horn edge vibration without a high-pressure constraint lacking anti-vibration material.

However, I do not know what level of stabilization the extreme mouth end needs if any.

But as you know bass frequencies are extremely penetrating in ordinary house materials. And I would also like to point out that your horn is made of the same material as the house framing  - wood. Identical materials maximize the vibration transmission potential to and through the framing. One technique for controlling vibration transmission is to use dissimilar materials another is to use materials that dissipate the vibration as frictional heat. So I have suggested anti-vibration pads which sandwich dissimilar materials and even layering two pads with dissimilar cores.

If you were supporting the horns with concrete or steel posts sunk in the ground or foundation the concept of mechanical grounding would make more sense. With wood attached to wood the tighter the attachment the greater the vibration transmission as well as the stiffness control.

The other day I was stopped at a red light when another car pulled up. The airborne bass from this true boom box on wheels had my car trembling like a vibrating lounge chair and my rear view mirrors flapping to the point that they were unusable. I could only laugh and I thought of your experience with the 2 EV 30” woofers. I suspect the vibration you felt with those woofers was principally the effect of airborne vibration shaking the floor and not the mechanical vibration of the speaker mounting. Airborne bass can be very powerful so bear in mind that mechanical vibration control and sound isolation are two different but sometimes related things.

In the end, I don’t think the mechanical vibration of your horns will be a significant problem. Although decoupling is a worthwhile precaution I think it also reasonable to stay with your original installation plan. If your horn vibration is significant than the potential for the exterior of the horns to radiate sound into the attic, vibrate the wallboard and largely pass through into the listening room would be a problem decoupling wouldn’t influence.

Ever the optimist,
Robert

09-16-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 275
Post ID: 14462
Reply to: 14461
If everything goes as I planed....
fiogf49gjkf0d
Robert, I understand what you say. Unfortunately this boat had sailed. I did not think about it from beginning and if I did then I would put into the design some decoupling provisions. At this point there is no time and there is not design margins what I would be able to squeeze any reasonable decoupling mechanism. I might devise something but it would dearly the hoisting the horns up. I would like not to delay as I would like to get over with it already. This one I have screw up. Bad for me, a lesson for someone who go after me.
 
You wrote: “I don’t think the mechanical vibration of your horns will be a significant problem.” I receive a number of emails when people expressed similar sentiments. It is possible that you are right and considering the mass of everything (horns, frames etc…) the bone-transmitted vibration will not be a problem at all. At this point it is hard to guess. My only hope that the SUSPENDED floor in my listening room will be the one that might decouple me from the house frame. Will see how it goes.
 
In the end – your example of airborne bass from that boom box on wheels is not accurate. I wrote much time about the subject of acoustic pressure vs. tonal pressure. Bass section with large amount of distortions (many of them have 60%-90% of distortions do produce airborne vibrations, something that I call “chest pressure”.  The bass that I am looking for has absolutely no resemblance with chest pressure bass.  If everything goes as I am planing then even at extra 6dB-9dB of additional tonal pressure I will not have elevated airborne chest pressure. 
  
The Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
09-16-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 276
Post ID: 14463
Reply to: 13597
Getting hectic.
fiogf49gjkf0d
As the time closing to Saturdays, the day we will be hosting the horns I am getting increasingly hectic.  I am still not absolutely convinced that l placing the horn into attic would be a problem-free operation, in fact I see many trouble. My carpenter does not care and his attitude to deal with problems as they rise. He actually does have a proven record of successful dealing with problems as they arrive but it is not my way to administering the projects.

Another aspect that I am falling now is the displacement of air from back chamber. According my plan the back chamber has to be all done now with approximate tuning but I am not near there. In fact I do not have a clear vision HOW I will minimize the volume of the back chamber now. This itself will not hold the elevating of the horns but when the horns will be installed then it will be much more difficult to deal with back chambers.  I am kind of getting so frustrated that I am planning to take tomorrow a day off to be with my horns the lay day they are on ground. It is funny but I feel that deploying my midbass horns to attic is like sending a space probe to one of the Jupiter’s moons …

Rgs, Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
09-16-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 277
Post ID: 14464
Reply to: 14463
Quick stuff job
fiogf49gjkf0d
Based on your claim that spray can foam takes time (days) to stabilize, it seems limiting the quantity used would be the right approach.

To do that you need to fill the majority of space with something solid.

The following might work for you:

Get some 1.5" thick foam insulation panels; usually blue or yellowish foam (available at Home Depot etc.). This foam is roughly equal in density to what you would get from spray can foam, and has similar physical properties and the two materials will easily bond.

Line the insides of the rear chambers with tape and protect drivers with a sac as in the photos you previously posted.

Spray a thin film of silicone on the taped inner surfaces of the chamber, but not on the sac. If you can't find silicone spray lubricant, use a petroleum-based spray lubricant such as WD40 (wipe off any excess). Better yet, use bees or carnauba wax in paste form, heated and applied with a cheap paint brush (heat it in a microwave oven).

Using a sharp knife (serrated works best) cut the foam boards into small, random chunks (like foam packing "peanuts"); max size 1 cubic inch (the smaller the better).

With chambers face down, spray in about an inch of spray can foam and immediately add cut pieces of the solid foam of a quantity that does not completely burry the spray foam. Push the pieces into the spray can foam before it sets. Add more "dry" foam pieces if necessary, submerging them below the spray foam as well. Spray in another inch of spary can foam and continue the process until the chamber is full.

Once set, the foam will have fairly uniform consistency and you can easily cut out what you don't need.

I have not tried this, but in theory it should work.

The silicone or petroleum lubricant or wax will allow you to more easily remove the foam in the event you need to access the driver.

What I don't like about it is the fact that the sac will be trapped, and any venting to the rear side of the membrane is not straight forward... You will need to carefully drill holes through the foam and sac so the driver can breath. The reason for not applying lubricant (mold release) to the sac is simply that you want the foam to stick to the sac doesn't rattle around between the foam and the basket. Obviously, you'll want to cut a hole in the sac to match the throat opening once the driver is mounted. It it were me, I'd consider not using a sac and protecting the rear of the driver with tape.
 
jd*


How to short-circuit evolution: Enshrine mediocrity.
09-16-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 278
Post ID: 14465
Reply to: 14464
Quick stuff; option II (better)
fiogf49gjkf0d
Use an acoustically transparent fabric to cover the rear of the driver (as used on old Klangfilms etc.).

Fill rear chamber volume with chopped up pieces of foam (see above post) or whatever you want as long as its in small pieces. You could even use cork; maybe even wine corks, available from places that sell wine making kits.

Vary the quantity of solids to adjust the volume of air.

I like this solution much better.

jd*




How to short-circuit evolution: Enshrine mediocrity.
09-16-2010 Post does not mapped to Knowledge Tree
scooter
Posts 161
Joined on 07-17-2008

Post #: 279
Post ID: 14466
Reply to: 14465
I would avoid silicones and petro based chemicals near foam (and drivers) where possible
fiogf49gjkf0d
Agreed JD. Also I have seen silicone and other petro-based products in contact (or proximity via vapors) to cause certain foams to break down over a period of several years. They might have a similar negative impact on driver components and bonding agents.
09-16-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 10,131
Joined on 05-27-2004

Post #: 280
Post ID: 14467
Reply to: 14464
Jessie, this is funny.
fiogf49gjkf0d
What funny is that what you proposed was exactly what my carpenter suggested me to do as soon he saw my frustration with foam. In particularly funny that he used pretty much the same words. I got the 2” foam and 300 feet 6ga stranded cupper wire from welding machine. This is my big project before the horn goes up…


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
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