I use foam all the way to the phase plug, and only extending a little bit past the throat, with great results. I've tried hot wire, but find it less effective than the scissor method, with reticulated foam. With regular "open cell" foam I find the hot wire more effective.
An externally hosted image should be here but it was not working when we last tested it.
Whats the difference between "reticulated foam" and "open cell" foam? I had always thought they were the same thing.
"Get results" are just based on listening tests or is there some data.
"Get results" are just based on listening tests or is there some data.
Well, I haven't gone to the extent of measuring HOMs, or doing CSDs, but I did measure a little top octave loss with the foam in place, only about 1-1.5dB
Reticulated is the web-type foam you use. Open cell is the foam type used in acoustic treatments and whatnot- it's not the "webbing" type that's minimally lossy, it's got more airflow resistance due to the presence of SOME cell walls remaining. Closed cell will not pass air easily.
Reticulated is the web-type foam you use. Open cell is the foam type used in acoustic treatments and whatnot- it's not the "webbing" type that's minimally lossy, it's got more airflow resistance due to the presence of SOME cell walls remaining. Closed cell will not pass air easily.
reticulated - they blow all the walls out, only frame is left - filter
open cell - walls may only be partially removed like for upholstery, etc
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Manufacturers call what I use "Open Cell" foam not "reticulated". There are maybe 10% cell walls remaining, max, so thats not going to make any difference.
If you're using the type of foam I understand you to be, the correct term is reticulated, as in the stuff they use in aquarium filters. It's different than 'normal' open-cell acoustic foam, which is lossier and would be like sticking a pillow inside your horn.
Case in point- the distinction may be largely in cell size, from a manufacturing perspective. The 30-40 PPI stuff is MUCH bigger cell size than the little stuff, and seems like it would be easier to blow out the cell walls with bigger cells. The normal "open cell" foam sold for acoustic treatment, packaging, etc, not only has vastly more cell walls, but also much much smaller cells.
little update :
maybe less HOM attenuation, but with some radial holes done with a hot nail (tangerine dream...) the HF are no more low passed, a lot of sibilances and titanium harshness are gone. Wow !
but the smell of hot foam...OMG!
maybe less HOM attenuation, but with some radial holes done with a hot nail (tangerine dream...) the HF are no more low passed, a lot of sibilances and titanium harshness are gone. Wow !
but the smell of hot foam...OMG!
Earl, I thought it was you who in fact first used the word "reticulated" to refer to this foam. When I started enquiring, I had some explaining to do when they wanted to know what I was looking for. They would ask "what's the application?" A little hard to answer, when they are looking for answers like air or water filtration!
This shows it pretty clearly:
I still haven't figured out what exactly is open vs closed cell foam.
This shows it pretty clearly:
I still haven't figured out what exactly is open vs closed cell foam.
I think there is various degr of how open celled it is
maybe in percentage
it starts out being closed celled
they 'burn' away' some of the cells
some types more, some less
I guess you need the most open celled you can get
I expect water will run right through it
its unable to hold much water back
unlike a normal 'spunge' that is supposed to hold the water
I reckon some suppliers may not even have a clew what it is about
maybe in percentage
it starts out being closed celled
they 'burn' away' some of the cells
some types more, some less
I guess you need the most open celled you can get
I expect water will run right through it
its unable to hold much water back
unlike a normal 'spunge' that is supposed to hold the water
I reckon some suppliers may not even have a clew what it is about
Thanks Frank, that's a good link. So it appears we are talking about reticulated foam, which is a type of open cell foam. The more familiar open cell foam that gets used in acoustic treatment and furniture, isn't reticulated. Then you have closed cell foam that you might find in packaging. It doesn't let air pass at all.
ya, you want filter applications. doesn't matter if air, h2o, oil.
gazillion ppi for mic windshields and vacuumn cleaner filters
i believe the stuff they upholster up market outdoor furniture with is probably ok, also. water goes thru it like a drain. dunno the ppi tho
gazillion ppi for mic windshields and vacuumn cleaner filters
i believe the stuff they upholster up market outdoor furniture with is probably ok, also. water goes thru it like a drain. dunno the ppi tho
Although I have spent many hours on them, I doubt my throats are 'correct', or my workmanship perfect. They are good, but I think I feel better with a little in the throats, if that counts for something. Still, I guess if I used the same ppi count in the throats, given their surface area and the fact that all sound must pass through there, they will have a relatively smaller effect than the foam further out.
My thinking is that the throat is the most tube like of the structure, and thus would be most prone to standing waves/HOMs/ETC, so this is where I'm focused on.
I have, however, been playing with enhanced termination of the horn mouth. Attached is a diagram showing the current state of foam (the most foamy version) and also the halfway version with just a foam collar.
In these instances it's open cell rather than reticulated. The attenuation isn't problematic since loss is outside the desired coverage window, in fact it's very much desired to extend the directivity (but not the loading) of the horn lower in frequency and absorb energy as it transitions from the coverage pattern to free-air.
Jury's still out, I haven't validated with measurement or even a serious listening test, just went ahead and fabricated the collar and a couple crescents to try the sideways cat's eye. Listening the past few days has been very impressive. I do seem to be getting much of the benefit of a more directional vertical without the horn unloading within or near the passband (common issue with normal asymmetrical horns)
I have, however, been playing with enhanced termination of the horn mouth. Attached is a diagram showing the current state of foam (the most foamy version) and also the halfway version with just a foam collar.
In these instances it's open cell rather than reticulated. The attenuation isn't problematic since loss is outside the desired coverage window, in fact it's very much desired to extend the directivity (but not the loading) of the horn lower in frequency and absorb energy as it transitions from the coverage pattern to free-air.
Jury's still out, I haven't validated with measurement or even a serious listening test, just went ahead and fabricated the collar and a couple crescents to try the sideways cat's eye. Listening the past few days has been very impressive. I do seem to be getting much of the benefit of a more directional vertical without the horn unloading within or near the passband (common issue with normal asymmetrical horns)
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I'm so sure thats true. If a tube is driven by a perfectly flat wavefront then there are no HOM. But in any waveguidse there will be more and more HOM generated as the wave propagates. So the answer is "it depends".
I don't follow. What do you mean by "unloading" and why do "asymmetrical horns" do this?
Thanks Frank
I got my first plugs from these guys (way too expensive) and looking at the site, I am using open cell and not reticulated. When I look at what I have, the number of non-open cells walls is very small. The reticulated is far too open to do much of anything. It would take a lot of it.
I think you pegged most audio issues in two words here 😀
By unloading I mean pattern control cutoff. The lower you maintain pattern control, the less output required of the CD for a given on-axis SPL.
Asymmetrical (I'm thinking rectangular here) horns tend towards having a shorter pathlength in their narrower range, and thus lose pattern control higher in frequency in the veritcal than in the horizontal. Some of the cool horns in JZGAGA's group buy get around this by having an extended lip in the narrower range.
Interesting! I think the larger cell size may move towards reticulated just by matter of manufacture method. Any chance of a close-up pic or two of the foam? (with a coin for scale please)
The difference with the small reticulated plug is pretty dramatic. The measured FR difference is mostly limited to the top octave (which is suppressed in my system anyway)
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Not what I would think of with the term "unloading".
Extending the lip in the narrower direction has been used in the past, its downside is that it can't be placed in a baffle (not easily) and I am very adamant that baffles are beneficial. I do not like the idea of a free standing horn.
Extending the lip in the narrower direction has been used in the past, its downside is that it can't be placed in a baffle (not easily) and I am very adamant that baffles are beneficial. I do not like the idea of a free standing horn.
Mind elaborating on the loading?
As far as the baffle benefit, it seems to me that for your speakers, the baffle acts very much like a large mouth roundover a la LeCleach etc, providing a gentler, and somewhat varied transition from 90 degree conical, to hemispherical, to free air. The foam is just another method of making sure that the transition from the pattern controlled bandwidth to free space is gradual and gentle.