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Quote:
Originally Posted by Earl K
Whoa, whoa, whoa....I see a 5 dB dip at 4 kHz...exactly what my ears were telling me and pretty close to where I had added a band pass filter adjustment at.... Okay, I'm leaving work early....stopping at a commercial hvac distributor I got some buddies at and start work on this extended lip work tonight. ...very interesting and thanks Earl!
Thanks, the graph opens when you click on it.
From the looks of that, I'd say that the foam lips are worse! :eek:
Will have to see if I can dig up my measurements. Not as fancy as ARTA, but they did show more/better effect.
- Yes, I'd like to see your measurements .Quote:
Originally Posted by Panomaniac
- FWIW, to my eyes, the blue foam lips used by Urei on their duplexes looks to be made from open cell foam ( as viewed in pics ) .
- The 3800 hz notch seen in my measurements has a wavelength distance of around 3.568 " / which is pretty darn close to twice the physical diameter of the foam tubing that I used ( which was 1.75" ).Quote:
Originally Posted by Steve
- The foam I used was definately closed cell type and would be reflective at these higher frequencies . I think it's half-circle sticking into the horn bell caused a bunch of diffraction anomolies .
>< cheers :)
ps ; I guess my point of getting into this thread is that one should always measure changes to make sure they are desirable ( though I never liked 4K very much anyway ;) .)
Found my graph:
http://www.michaelmardis.com/images/towell-test.gif
What this is is an 811 horn high passed at about 800Hz. The red line is taken as the zero point (The FR isn't that flat.) It is with a towel on both the top and bottom of the horn mouth. The green line shows the difference (only) with one towel on the top of the horn mouth. The hard to see yellow line shows the difference (only) with no towels.
It's easy to see the difference. And one towel makes 1/2 as much difference as two. The kink at 800Hz to 1KHz is gone as well as some other junk. The difference in sound was more subtle than the graph might indicate, but it was nice. Like something went away, leaving a more direct sound. At first it sounded like something was missing.
Thanks Panomaniac for digging that up !
>< cheers :)
The devil's in the details ain't it Earl...;)Quote:
Originally Posted by Earl K
The cut edge lends a psuedo "open cell" edge where it's needed, and the following outer closed cell "roll" provides the transition.
When I mentioned you could get really creative with the stuff (and I wasn't talking about the hard, cheap stuff from HD), I figured someone might actually do just that (get creative that is).
And yes, measurement is the best way to quickly see the results of various implementaions.
Another version (the sheet I mentioned before), Armaflex RD, offers an open cell alternative with more predictable (documented) properties. As you can see on p4 of the linked product sheet, small differences in thickness drastically alter the attenuation BW:
http://www.armaflex.com/www/armacell...neralUKROI.pdf
Admittedly, it's a long way from rolled up towels, but you gotta start somewhere...:)
Thanks Brad for the foam tubing idea .
- So far I've blown all of ten bucks & had a lot of fun .
- Audio accessories bought via Home Depot are much cheaper . ;)
>< cheers :)
You're welcome. I sure understand the low budget approach, and would be right there if I hadn't had plenty of scrap from work. Over the years, I've thrown away enough Armaflex to treat hundreds of horns, and have found lots of extra-label uses for it too. :)
Added;
Many of you have Armaflex insulation on the suction line of your outdoor AC unit. Leave it there. If you're gonna kype some, get it from your nosy neighbor's AC. :D
I checked this stuff out...this is not the same as the armasound product.Quote:
Originally Posted by bfish
But it's better for the support rods...even better covered with black satin.
Anyway, The sound deadening version is so far impossible to find and would be
more suitable for this I would think than the hvac stuff.
I do want to get some panels of the armasound and cut neat chambers for the rear
as opposed to the felt batting that's tied back there now.
I draped a pile of my old wife beater t shirts on the top bells. I like it!
I've got this weekend to play and then I'll take more measurements to
compare to the measurements with the cheapo foam but I can hear it already.
These big bags of polyfill I have laying around are perfect for this if I could
shape and cover properly...ultimately it would be nice to overlay black satin over this too.
Any thoughts on how this stuff will work? The fiberglass is rigid so it would be tough to bend but I think it could be segmented to fit a curve. I?m thinking here of stripping the paper from the fiberglass and using it raw or perhaps fogged with some flat black paint.
Fiberglass insulation, copper tubing insulation, fiberglass pipe insulation