Oops - it looks like I posted this in the wrong thread. I've reposted it in the cornu spiral thread. Sorry about that!
Part of the idea behind 'corners' in the spiral is that it will damp the higher frequencies better. I'm sure Mr. C experimented with true spirals before deciding on the Cornu.
As exemplified by the leak sandwich advert, where a man stood on a cone from the leak sandwich speaker, which was constructed from aluminium laminated over foam core.
Could also try gluing bits of stainless steel sheet to both sides.
There are also various heavier duty versions of foam core cardboard, such as foamex.
Foam is also pretty easy to CNC, so one could potentially cut the form and then spray it with a fiber impregnated resin and / or apply a metal skin.
Once upon a time... Surfboards are made of very soft sculpted foam covered with fiberglass and epoxy or other resin. They are quite stiff in bending mode but can be fragile in localized compression (aka dings).
Ok, getting closer to having a RatShackFoamcore playing. Found some extra time and got some extra bracing put in, a second layer for the baffle speaker wire and stuffing, then glued on the other side. Waiting for glue to dry sucks.
Aren't they still? Heck, I remember when they were about twice as long and made of wood.
Am I dating myself?
EDIT: I see you said 'are' made not 'were' made.
Ok, got my first listen to the ratshack foamcore speakers.
Now let me preface this by saying that, in order to get substantial bass out of these in the past, it takes a significant amount of volume. At lower volumes, they are pleasant but "thin" as I had expected them to be. Turn up the volume on them to get some decent bass out of them....in this instance foam core is not the answer. Way too much energy being wasted on the enclosure in my opinion. On something with moderate amounts of bass (Eva Cassidy, Live at the Blues Alley) such as string bass, it is there and sounds very good. Play something like Eagles, Hell Freezes Over "Hotel California", and the intro makes me think they just might come apart.
I know that the 1354 is not a "great" driver, but I think it might have a bit more low-energy than some of the other smaller drivers being used. Regardless, I don't think a 60" folded voigt pipe is appropriate to be built out of this stuff.
On the other hand, it DID give me a very good idea of what performance could be like if I were to build it out of plywood or MDF, so it serves a great purpose for very inexpensvie mockups! What bass was there was mighty impressive right up until it hit the point where the enclosure started going nuts. Could feel the couch vibrating and my pants legs moving ever so slightly. Just might have to build two more out of wood. Had forgotten what the "magic" sounds like...and this was just one instead of a pair.
Now let me preface this by saying that, in order to get substantial bass out of these in the past, it takes a significant amount of volume. At lower volumes, they are pleasant but "thin" as I had expected them to be. Turn up the volume on them to get some decent bass out of them....in this instance foam core is not the answer. Way too much energy being wasted on the enclosure in my opinion. On something with moderate amounts of bass (Eva Cassidy, Live at the Blues Alley) such as string bass, it is there and sounds very good. Play something like Eagles, Hell Freezes Over "Hotel California", and the intro makes me think they just might come apart.
I know that the 1354 is not a "great" driver, but I think it might have a bit more low-energy than some of the other smaller drivers being used. Regardless, I don't think a 60" folded voigt pipe is appropriate to be built out of this stuff.
On the other hand, it DID give me a very good idea of what performance could be like if I were to build it out of plywood or MDF, so it serves a great purpose for very inexpensvie mockups! What bass was there was mighty impressive right up until it hit the point where the enclosure started going nuts. Could feel the couch vibrating and my pants legs moving ever so slightly. Just might have to build two more out of wood. Had forgotten what the "magic" sounds like...and this was just one instead of a pair.
You probably did not have enough bracing. If you look at my flat BIB (nearly 60 in long) it looks like a forest of braces sticking up. Same with cornu, the channels act as tightly spaced bracing and no problem with vibration.
I can attest to the bracing in the flat BIB's. I put ten braces in the ones I built with great results!
Did you mount the speaker on the wall to help dampen the FC movement? You would have to add a front firing tweeter but some folks are adding one already. Might even help to spot a few pieces of double sided tape on the back if/when you do.
You might be right. But, I tried to follow advice and not have more than 3-4" span without any kind of bracing. I got pretty close to that, but would be difficult to go back and remeasure.
I could get noticeable difference in low frequency output by placing added mass to the top of the enclosure (25 pound plate). Maybe if I had filled the empty spaces with sand it could have helped. Regardless, there is too much energy-transfer to the enclosure to be a permanent solution to my situation.
It was a lot of fun to build and I believe that when my 3" BMR drivers come in, I will use foam core to build a cornu for them. I would suggest it for anyone to play with.
I could get noticeable difference in low frequency output by placing added mass to the top of the enclosure (25 pound plate). Maybe if I had filled the empty spaces with sand it could have helped. Regardless, there is too much energy-transfer to the enclosure to be a permanent solution to my situation.
It was a lot of fun to build and I believe that when my 3" BMR drivers come in, I will use foam core to build a cornu for them. I would suggest it for anyone to play with.
Last edited:
It might be the nature of this enclosure. Do you have vertical bracing for top walls since you say adding a weight helped. One other thing, make sure it is sealed and no pinhole leaks where joints are. A leak will kill the bass.
Good luck.
Good luck.
I don't have any "exterior" air leaks. Air is moving right along out the vent though.
I turned it over on its side and tested with and without added mass and it had the same outcome. I seriously think the enclosure is just not heavy enough. HHhhmmm.....maybe I should try carpet spikes?
Have all of your designs utilized the Vifa TC9? I ask this as there is quite a bit of difference in SPL, Vas, xmax and especially FS (57hz). When I made a single-fold pipe last time (bipole) I was hitting in the low 40's with authority. Has anyone else built a larger driver with the foam core? That was not a cornu? Would be open to seeing another similar design to see if I can compare notes as to what may or may not have gone wrong.
I turned it over on its side and tested with and without added mass and it had the same outcome. I seriously think the enclosure is just not heavy enough. HHhhmmm.....maybe I should try carpet spikes?
Have all of your designs utilized the Vifa TC9? I ask this as there is quite a bit of difference in SPL, Vas, xmax and especially FS (57hz). When I made a single-fold pipe last time (bipole) I was hitting in the low 40's with authority. Has anyone else built a larger driver with the foam core? That was not a cornu? Would be open to seeing another similar design to see if I can compare notes as to what may or may not have gone wrong.
I got eight of these for a steal a year or so ago. Six have never been unpacked -two are in my center channel. Been watching for an FC design to use with them but they are 40 oz. so it would have to be pretty sturdy. You can't go wrong with the Vifa TC9 though. They have their own magic.
Attachments
Last edited:
I am geeked about trying the Vifa in an OB project, for sure! I would bet that your drivers suffer the same problem mine do....just not meant for a foam core voigt.
I should have piped up sooner here. The 1354 would work in a spiral but not so much here. The bass is light as are the highs. I use mine as a wide range with only the last octave on either end being supplemented by other drivers. They are a great midrange, there's no denying that. Even after all these years they still seem to do some things very well.