Fostex HP reflectors

[no xo]

Last nite I covered the magnet with foam tape,1/4'' thick X 1 & 1/4" wide, basically weather stripping, and covered the bottom of the cc with 1" deflex. I kept the polyfil in and moved it up so most of it is directly behind the driver. I only had 45 min. to listen, and I`m very happy with the results. That sort of droning resonance is pretty much gone and now, I really like these speakers. If my opinion changes with extended listening I`ll post what I hear...at this point huge improvement.

[Taperwood]

That's great news. I'll try some of your ideas when I get the time and see what happens.

Doug

[noxonewbie]

Doug,

I'm NOXO's friend with the camera, finally got in the forum to upload the pics of the finished horns. I was having some difficulty resizing them so as to post them. Anyway here is a couple of shots.

[noxonewbie]

Ok, I'm still working on this to get decent pics up. here's some more views
Mike

[noxonewbie]

Well looks like I can post the same pic twice easy enough let me try another.
Mike

[Taperwood]

Cool! Nice work on the cabinets. They are bigger than I imagined, looking at the plans. Are they in cherry?

Doug

[noxonewbie]

Hi,
No they are done in Walnut with a clear finish, and yes they are BIG. We estimate they weigh around 150# each.
Mike

[Pendergast]

I think they are magnificient! Congratulations on what looks like a really nice job!

We picked the wood for mine: Russian wild cherry tree. I cannot wait to start!

We hired a wood worker to cut the pieces right and the whole thing will come down to about $220 canadian (wood and cuts). We did not have much of a choice as the stores did not seem to offer much help, and we are not equiped to cut this accurately. But we should be able to glue it right!

[ScottG]

Here is an interesting experient that should not cost anything other than time:

1. remove all stuffing - except minimal amounts on the driver frame/magnet used to reduce reflections from bleeding through the cone. Try to make sure such material provides as little acoustic resistance as possible.

2. stuff the horn mouth with a pillow.

Note that it will attenuate the response from the lower midrange down (considerably), BUT typically something extraordinary occurs with respect to the mids and upper mids (..that is not related to simply attenuating the midbass).

[blumenco]

yeah in alot of builds stuffing the mouth kills bass. acoustic impedance is one of the prime determiners of the effect of qts on bass from a horn. you change the design by changing acoustic impedance and would need to shorten or lengthen the horn as a result.

one thing to try is to change the dimentions of the compression chamber itself. you can't make it much bigger, but you can make it smaller. that would raise the resonance frequency of the compression chamber to a point that looks like what would normally be a dip at 500 hz... the japanese seem to like bags of sand.... THIS ALSO provide mechanical damping instead of acoustic damping. mechanical keeps the rest of the horn from resonating. acoustic would kill the sound.

will this work? no idea, but I certainly see alot of CC with some sand bags, both on japanese websites and in the reccommended enclosures. I think that sometimes, especially with the special edition stuff from fostex, the sortof assume that we know what to do with them, and how to get them to our personal tastes so they give us sparing instructions. interpretation and creative implimentation brings about the very audio society we have here, no doubt.

in BLH I find that polyfill, deflex, synthetics, is geerally undesirable. instead stick with natural materials. river rock, sand, wool felt.

the wool felt I like is that used to seal doors with. found in most hardware stores.

for the magnets I glue on wool felt to just the front side of the magnet. this takes away that immediate reflection.

some can be used in the compression chamber. gradually increasing (very gradually) with alot of listening in between tweaking.

I find generally that in alot of builds with these high efficiency BLHs that people use wayyy too much damping. at least in my opinion. we do not want to use an anvil to smash an ant, as in the rest of the world of overbuilt, overengeneered, and ultimately bad sounding audio.

in 99db efficient enclosures, we get that much more sensitivity to change. a handful of stuffing gets amplified into a truckload... same as the bass is so magically acoustically reinforced. are our souls sensitive enough to weigh the small changes we must make in this realm?

also, the p-16 sound reflectors can have a profound effect on the overall sound of a horn. I think that in alot of fostex reccommended enclosures, they benifit immensely from the use of such. course, that means that you have to pay 10 bucks a hit, and fostex makes a little more money, but the p-16s are awesome because they do not kill the sound at all, the clean it. yay! implimentation matters though... ideal placement can be different from room to room.

well, hope any of that helps. these backloaded horns are strange but ultimately very very rewarding beasts. I by no means claim to have all the answers here. just suggestions from having tried everything else and simply come back to natural materials myslelf. honestly, I have heard verry few back horn setups I considered to be even remotely refined and acceptable to listen to. I am not even sure why I try sometimes. t.v. run run, ipod, loud music, next big thing, we loose our finer sensitivities. back loaded horns take a long time to tune to a room. I am working on a year now on the sound of the 166es-r horns I have. still tweaking minorly. getting more refinement daily. have patience, grasshopper.


Clark Blumenstein