zako wrote:

When i saw what is going on in your home,,I look with trebitation,,,Fearing this home will DEVIOR you and all will be lost…. Maron

How nice would it be if you did not have to re-cut and re-seal the "some kind of sealer" for every adjustment? If the mating surfaces had "pipe grade" interiors and exteriors, you might be able to use silicone-slicked o-rings or similar gaskets for that purpose.  Dont laugh, but some sewer pipes (and water pipes) are quite thick-walled, and some even come with a belled end and a narrow end, with gaskets pre-fitted in the belled end.  Typically, caps are also available, and you might even pre-work a cap's threads in order to gain a range of adjustment to eff with the interior volume.  Again, just use silicone grease to dope the threads. Some of the pipe systems include special flanges that can be used to mate a pipe end to a flat surface (eg, the horn).

Best regards,
Paul S

jessie.dazzle wrote:

For your rear chambers, as they will be adjustable, it would be smart to go with a max volume that is larger than the max you estimate to be necessary.

wvdave wrote:

I see this project as enhancing the value of the property…

I also see this project to enhance a value of property. If I place in the mouth of my midbass horn some kind of MF/FM driver then I will be able to present my room as so called in US “great room” with built–in speaker in the wall.

http://en.wikipedia.org/wiki/Great_room

The whole point is that my midbass horn will be built in the pace that is NOT being used currently. In fact I might cover the horn’s mouth with cloth (or drywall) and no one will know that the horns are here. So, I feel that since the horn do extend the useable space of property then I feel that they increase the value of the property.

wvdave wrote:

Back chamber volume adjustment intrigues me, but I am called towards multiple adjustment systems rather than a one time deal and hence my ideas are overcomplicated and unsuitable for your installation. The plastic pipe thing w/the rubber seals is possible as I have a piece which will accept a 4" pipe sliding into it. The other end is threaded and can be worked into a mounting flange which will then bolt to a block of wood as the baffle. I use it as a light shield w/cap on a telescope project I have. The entire telescope mount is 1 1/2" galvanized pipe and allows rotation thru 3 axes, as well as solidity.

Your idea to use multiple smaller displacements in back chamber is a way reminds me the Control Rods for nuclear reactors - I will call this concept – Nuclear Back Chamber. That would be great if a high precision is necessary but I feel that it is not.  However, thinking further about the Nuclear Back Chamber I relapsed that this concept would allow to make an absolutely universal Back Chamber tuning mechanism and what is the most remarkably to make it very very cost-efficient.

I spoke today with my machinist and it look like if I will make the displacement piece of 20”  pipe then there are very limited  chose of materials I might use.  It would be primary metal pipe but I would like to have a material that will have the similar speed of sound in itself as wood.  Also, I need to have a long thread on the displacement piece as I do not know the approximate volume of my aimed back chamber. However, if to combine all problems together and to employ a Nuclear Back Chamber idea then here is a design that would address all problems. I would call it Culminated  Nuclear.

The Culminated  Nuclear Back Chamber imply that the rough adjustments of  Back Chamber volume takes place with expendable hard-solidifying foam (it is easy to cut it off with knife after it is hard). The there is threaded plastic cylinder of smaller size (let say 8”) that displaces the last few cub inch, tuning the Fs to it final settlement. I think to find a small 8” plastic sewer pipe, cover it and fill with sand will not be a problem. I like the idea as it is very versatile. If the extrusion of pipe is not enough then more volume will be displaced by foam….

jessie.dazzle wrote:

I have not yet measured either case. As previously mentioned, at mid-project I had to put the mid-bass horns on standby (I will get back to them, but must first attend to an ongoing emergency). I can measure the free air resonance but space limitations have forced me to stand the first, nearly completed horn on its mouth while constructing the second; I am literally out of space and cannot set the first horn down to measure resonance with driver mounted, until all parts of the second horn are out of the way (the horns are made in quarters; in addition to the one assembled horn, there are currently three ten-foot-long pieces laying around, and a fourth under construction; a couple Toyotas would take less space). You've already described how to measure resonance with driver in the horn; I assume getting the free air resonance can be done via the same procedure but without the horn; if there is something different you'd like me to do, post details and I'll do the measurements this weekend.

msaudio wrote:

49Hz To 52Hz will be your peak, so the best you could hope for would be 3 hz below that flat with a perfect tuning of your length of your horn and back chamber of your box housing your woofers. If you shoot for the free air low res of your design, of your horn you will have to eqaulize at that peak to remove it. So you want at least 40Hz to 35Hz free air cone's to elimenate peaks, shooting for 42.7Hz with your calculations. It would seem you would be better off also with a 8inch input instead of 7inch witch you had mentioned, 8 is the norm in the industry for input of mid bass horns. Altec 515 B and EV 15W Are the beast's that you need they have very low res in the industry below 30 Hz. If you are interested i have 4 matched like mint altec 515b Woofer's for sale, they would be perfect for this project. If you are interested i will post picture's, they are in cardboard boxes right now, packed away. I also have a pair of stevens early woofers that have 35hz low res that would be perfect for a single driver horn, these have hugh alnico magnets larger then the altec very good qaulity. Value for the steven's $125.00 each + shipping.    Preaching Horn Religion   Msaudio

Romy the Cat wrote:

OK, the chamber is wood, very solid wood, the space felling is hard-solidifying construction foam. What material to use to make displacement plug? Let presume it will be 8”-1O”. Aluminum will be nice but I am afraid that if I do a high quality, very tight machine threads on it then it will ne hold on Aluminum. Steel of course will be the best and it is my leading chose but I am a bit worry that speed of sound across steel is too different then across the surrounding wood. The plastics are wonderful from this perspective and some of them are very hard and will maintain the threads very well. I was looking at McMaster-Carr catalog – they do have some very nice rods but the price is too high. For 10” rod of G10 for instance they want around $700, and I need two of them, too much for THE purpose.

So, I will most likely go for steel plug with application of some treatment to the surface of the steel, perhaps cork or the similar. I mish spray some red “Great Staff” over the surface of the steel plug to make it very uneven and jagged. I do not think that at LF it will make a lot of difference but as Russians use to say: you can’t spoil mashed potato with butter….