An empty cavity is a closed box resonator, so considering you can hear the effects of small voids in plywood, just imagine what a big cavity can do.
The alcove is a high band-pass filter with its own resonant modes, so about the worst place to position a BLH. Visualize if you can the horn as being the driver into the throat of a fast expanding, long two stage (stepped expansion) plane wave tube (PWT) with its actual driver an increasingly out of phase ultra wide, ~flat BW active (passive) radiator. Not a pretty 'sight', ergo 'sound'.
Regardless, BLHs need to be fine tuned in the actual corners used and if this happened to be one of them it would need to be damped to the point of 'killing' most of the horn's usable output since all the alcove's first eigenmodes are in its mid-bass gain BW.
GM
The alcove is a high band-pass filter with its own resonant modes, so about the worst place to position a BLH. Visualize if you can the horn as being the driver into the throat of a fast expanding, long two stage (stepped expansion) plane wave tube (PWT) with its actual driver an increasingly out of phase ultra wide, ~flat BW active (passive) radiator. Not a pretty 'sight', ergo 'sound'.
Regardless, BLHs need to be fine tuned in the actual corners used and if this happened to be one of them it would need to be damped to the point of 'killing' most of the horn's usable output since all the alcove's first eigenmodes are in its mid-bass gain BW.
GM
1/ 11mm 5 ply plywood will need further bracing to stiffen it up (the BB we use id 8 layer 12mm (or usually 15mm now))
2/ the FE126 (especially untreated) is very susceptable to reflection back thru the cone from an unchamphered driver cutout. It can remain cylindrical until the basket cutouts.
3/ the purpose of the suprabaffle is to minimize/cure the baffle step dip that happens between about 150-500 Hz in the supra-baffless FH.
4/ the cavity could be contributing, it is about the right size to affect those frequencies.
dave
2/ the FE126 (especially untreated) is very susceptable to reflection back thru the cone from an unchamphered driver cutout. It can remain cylindrical until the basket cutouts.
3/ the purpose of the suprabaffle is to minimize/cure the baffle step dip that happens between about 150-500 Hz in the supra-baffless FH.
4/ the cavity could be contributing, it is about the right size to affect those frequencies.
dave
Ok, so the wasted space chamber needs sand or kitty litter fill. Not a problem. If we get too heavy they can go in separate suitcases.
And I need to move the horns into a different room. No problem.
The problem is that there is no chance my sister is going to tune these "in room" so I have to do the best I can to provide a generic tuning that hopefully will work in a variety of situations.
Scott, I realize those were not frugal horn measurements, but IIRC Dave said the level 0 frugal horn was mostly consistant with the horn shop expansion. The FH is of course a bit wider, but other than that, how different are they? Do you have a FR graph for the level 0?
And I need to move the horns into a different room. No problem.
The problem is that there is no chance my sister is going to tune these "in room" so I have to do the best I can to provide a generic tuning that hopefully will work in a variety of situations.
Scott, I realize those were not frugal horn measurements, but IIRC Dave said the level 0 frugal horn was mostly consistant with the horn shop expansion. The FH is of course a bit wider, but other than that, how different are they? Do you have a FR graph for the level 0?
Scottmoose said:
But maybe not so different.
The FH is supposed to be quite equvalent to its "cousin" measured by Stereophile.
Attached is one of my measurements together with that of Stereophoile for the HSH. There are some distinct similarities.
The problems of the peaks in the 200-300Hz area producing the boxy/hollow sound of voices has also been discussed in other threads such as this one: New Frugel Horns: Tuning Problems. I still do not know if anybody have been able to cure it, other than by a lucky matching to the room.
SveinB
Attachments
Still off-topic, and belated
Originally posted by TerryO:
Super glue would also be considerably less time consuming; don't know how well it would soak into baltic birch before hardening, but MDF, why not.
Fiona and I got the outer hull cleaned of epoxy; and got the gunwales (outwales), keel, outer stems, and skeg in place. Skeg and stems need some shaping, which won't happen 'til Fi gets some time off from school (she's doing grad work in another city). Thanks for asking.
just a guy - sorry, I'll get off your thread now. Hope the tuning works out well. I was glad I had Moray's help with mine.
Regards.
Aengus
Originally posted by TerryO:
Super glue would also be considerably less time consuming; don't know how well it would soak into baltic birch before hardening, but MDF, why not.
Fiona and I got the outer hull cleaned of epoxy; and got the gunwales (outwales), keel, outer stems, and skeg in place. Skeg and stems need some shaping, which won't happen 'til Fi gets some time off from school (she's doing grad work in another city). Thanks for asking.
just a guy - sorry, I'll get off your thread now. Hope the tuning works out well. I was glad I had Moray's help with mine.
Regards.
Aengus
I got the horns into a more suitable room with real corners and ran them with a tube amp for a midnight session. The screaming midbass honkiness is greatly reduced, but the low bass is reduced as well, no big deal. There is still too much midbass coloration, but tuning should take care of a great deal of that. It's much easier to eq pleasantly now.
OTOH, I read about a dozen B horn variant reviews, formal and informal, and except for one, every single review noted the same ~ 200 - 300 hz coloration, affecting mainly female voices and instruments in that range. Every single review was positive though, so I'm confident I can work this out satisfactorily.
In my usual turtle-pace fashion, it will be at least a week before I get them tuned. I was able to borrow the tools necessary for the finish, so they will end up looking good before they sound good.
I'm also going to change the internal wiring. Currently using a single twisted pair of plenum rated cat5 (24 gauge?). This may not be the best choice considering my bloated (mid)bass and lack of high end "air".
BTW, with plenum rated cat5, is it the outer jacket or the actual wire coating or both that has the teflon?
OTOH, I read about a dozen B horn variant reviews, formal and informal, and except for one, every single review noted the same ~ 200 - 300 hz coloration, affecting mainly female voices and instruments in that range. Every single review was positive though, so I'm confident I can work this out satisfactorily.
In my usual turtle-pace fashion, it will be at least a week before I get them tuned. I was able to borrow the tools necessary for the finish, so they will end up looking good before they sound good.
I'm also going to change the internal wiring. Currently using a single twisted pair of plenum rated cat5 (24 gauge?). This may not be the best choice considering my bloated (mid)bass and lack of high end "air".
BTW, with plenum rated cat5, is it the outer jacket or the actual wire coating or both that has the teflon?
just a guy said:
The 2 pairs of FH that I've assembled and actually listened to both had the large void cavity opened up after assembly with a flush trim router, so resonances weren't an issue. OTOH, veneering and finishing the inside of that area was quite a bey-ach
If you're concerned about that, you could always drill a small hole from the inside of the CC, fill the void with kitty litter, then cover the hole with a small plate or tapered plug. Since it sounds like you're still playing with adjusting the volume of the chamber, a small chunk of ply or MDF shouldn't mess things up much at all.
It also wouldn't hurt to fill the void cavity behind the final mouth deflector panel with either sand or kitty litter.
As for wire, my experience would suggest that what you're using is not the cause of coloration issues or lack of detail and air - in fact the opposite
I left the bottom cavity open on the bottom. Not ideal if it sits flat on the floor, but I am going to make a 1 inch spike (or similar) to prop the front up, so that chamber is open. The internal wasted space chamber will be filled with kitty litter in exactly the fashion you described later today or tomorrow.
Thanks for the tip on the wire - I'll leave it for now. The wire can be changed at anytime, so I'll do the rest of the tweaking first and if necessary try different wire as a last step. I have a feeling that lining the cc with carpet underlay or similar will do great things. Also, in the reviews of the B horns, apparently some people add stuffing to the throat and/or near the mouth. Lots of stuff to try.
Thanks for the tip on the wire - I'll leave it for now. The wire can be changed at anytime, so I'll do the rest of the tweaking first and if necessary try different wire as a last step. I have a feeling that lining the cc with carpet underlay or similar will do great things. Also, in the reviews of the B horns, apparently some people add stuffing to the throat and/or near the mouth. Lots of stuff to try.
If I understand you correctly, the side panels are not cut out at the angle of the lower deflector, but extend to the floor? If that's the case, then I think you could still expect some resonances in that cavity. As owners of Frugelhorns and other rear mouthed BLH's have noted, filling the lower cavity not only adds stability to the cabinet, but deadens resonances in the largest unbraced panel area, thereby improving the definition and articulation of the bottom end.just a guy said:
It's a bit of a pain, but play with the damping in small stages - I'd start with a thin layer of cotton felt on one side wall only, and corrugated acoustic foam on the rear wall of the chamber. Add a bit of dacron fill to the throat later, and leave any stuffing of the horn mouth to last.
My babies gained some weight. I filled both the voids with kitty litter. Immediately after I finished and sealed the holes, I remembered reading about how kitty litter can be toxic to wood, so I checked the box, and sure enough, this stuff is full to the brim with all kinds of chemicals, to the point of a "don't touch if pregnant" warning. I don't see much point in removing it now, the bad stuff pressed tight in there and has already had full contact with the wood. Oh well, hopefully I have a few years of service before it rots from the inside out.
Is this toxic kitty litter fact or myth anyway?
Is this toxic kitty litter fact or myth anyway?
Well, about all I can say is that I started using it in the '60s and no one's ever complained about rotting wood/whatever. Unsterilized sand is a different story though. If you want high density with no potential problems other than the initial fine dust generated, then use Portland cement and keep a vacuum running while filling.
GM
GM
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.