I'm Building a pair of Bruce, Sachiko or similar cabinets soon. Drivers are Fostex FE207E with FT17H tweeters which I'm currently running in Singular cabinets.
I want to build a centre speaker for Home theatre use that has a similar tonal character.
The space it needs to fit into is 21 inches wide, 8 inches high and 19 1/2 inches deep. Unfortunately not quite high enough to fit another FE207E. It must vent out the front (if it vents at all).
I was thinking a FE167 with a little double vented reflex out the front on either side. Has anyone seen something that I can wrangle and rework to squeeze in there?
Tweeter optional.
I want to build a centre speaker for Home theatre use that has a similar tonal character.
The space it needs to fit into is 21 inches wide, 8 inches high and 19 1/2 inches deep. Unfortunately not quite high enough to fit another FE207E. It must vent out the front (if it vents at all).
I was thinking a FE167 with a little double vented reflex out the front on either side. Has anyone seen something that I can wrangle and rework to squeeze in there?
Tweeter optional.
Mike - it could be argued that for a custom dedicated HT center channel enclosure (rather than one identical to the L/R mains, which would certainly be impractical in this case 
), a tweeter would be superfluous.
A few months back I built a complete surround system for a customer of Dave at Planet10, that included all FE167E's for the front row. While they were very small sealed enclosures to raise the natural Fc, and simplify transition to the stereo subs, I'm sure he could juggle some existing plans in his library to suit your specific needs.
), a tweeter would be superfluous.A few months back I built a complete surround system for a customer of Dave at Planet10, that included all FE167E's for the front row. While they were very small sealed enclosures to raise the natural Fc, and simplify transition to the stereo subs, I'm sure he could juggle some existing plans in his library to suit your specific needs.
Centre speaker would be for purely vocal ranges. So it only needs to perform down to about 300Hz. That means it can be a LOT smaller. (I think)
Radio waves in bottles, pipes and air I can handle, sound waves in cabinets I don't understand. I'm at the knowledge level where I analyse what others are doing and if it makes sense to me then I copy it. For all I know I may be asking the impossible.
Dimensions stated are for the space available in the existing entertainment unit. It has been decided by the domestic design & cosmetics department that if there is to be a centre speaker it shall fit in there.
All I need is a pointer that xxx cabinet and driver should sound similar to what I want, then I'll figure out how to reshape it to fit.
Radio waves in bottles, pipes and air I can handle, sound waves in cabinets I don't understand. I'm at the knowledge level where I analyse what others are doing and if it makes sense to me then I copy it. For all I know I may be asking the impossible.
Dimensions stated are for the space available in the existing entertainment unit. It has been decided by the domestic design & cosmetics department that if there is to be a centre speaker it shall fit in there.
All I need is a pointer that xxx cabinet and driver should sound similar to what I want, then I'll figure out how to reshape it to fit.
How's this? FE167E in a sealed box. As Chris notes, it should make a fine tonal match to the 207 & gain should allow easy matching to either Bruce or Sachiko. Adding a phase plug would be useful though, they work especially well on female vocals.
Internal dimensions 6in x 15in x 8in (HxWxD). Driver centred on the front panel. Stuff cabinet equally with 0.5lbs ft^3 of hollow-fibre material or similar. Excursion at 300Hz is 0.2mm for 1w / 1m -I assume you're going to roll it off at that point? I'd probably use 12db per octave, but YMMV.
Scott
Internal dimensions 6in x 15in x 8in (HxWxD). Driver centred on the front panel. Stuff cabinet equally with 0.5lbs ft^3 of hollow-fibre material or similar. Excursion at 300Hz is 0.2mm for 1w / 1m -I assume you're going to roll it off at that point? I'd probably use 12db per octave, but YMMV.
Scott
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Scottmoose said:
Scott - Mike didn't state in this thread what electronics he'll be using ( perhaps it's mentioned elsewhere?) - but if it's any kind of full featured HT processor, wouldn't the center channel already be bandwidth filtered? An extra filter, particularly at 12dB might be excessive?
And of course, channel level matching would be built into the processor as well. There's gotta be some good use for all that silly-cone.
Great Scott! Sorry, I cant resist really, really bad jokes.
Thanks.
Yes the HT receiver can be set to "small" speaker mode for centre channel. The manual doesn't say what the freq is or the slope of the filter. When the center is in SMALL and others are LARGE bass from the center channel is sent to front left and right. Yes it has channel level adjustment too, in actual proper dBs too!
I'll see how it goes, SMALL might equal "ridiculously tiny Bose high excursion headphone driver in a cute little box."
So a sealed box with a plugged FE167 it is then. Exactly what I was looking for Scott.
On reading the book for the silly cone box of sand I found that if fronts are large and no sub is selected the "point one" LFE channel from surround mode is fed through the fronts.
I was wary of the Sachiko's (spelling?) lumpy calculated response.
I might be better off with these than the Bruce if their low end is better.
Thanks.
Yes the HT receiver can be set to "small" speaker mode for centre channel. The manual doesn't say what the freq is or the slope of the filter. When the center is in SMALL and others are LARGE bass from the center channel is sent to front left and right. Yes it has channel level adjustment too, in actual proper dBs too!
I'll see how it goes, SMALL might equal "ridiculously tiny Bose high excursion headphone driver in a cute little box."
So a sealed box with a plugged FE167 it is then. Exactly what I was looking for Scott.
On reading the book for the silly cone box of sand I found that if fronts are large and no sub is selected the "point one" LFE channel from surround mode is fed through the fronts.
I was wary of the Sachiko's (spelling?) lumpy calculated response.
I might be better off with these than the Bruce if their low end is better.
The differences between the two cabinets is that Sachiko is a hybrid BLH of the type usually seen (OK, so it's a double-horn with stepped expansion which aren't exactly common, but you get the idea!), while Bruce is in reality a bass reflex design with huge, expanding vents (or BVR: Big Vent Reflex).
In general terms, Bruce will go lower, more smoothly (I recommend the FE207E for this box), as you'd expect from a BR cabinet. Sonically, it will also give the large scale to the presentation horns are known for, albeit over a somewhat narrower passband / frequency range.
Sachiko OTOH has a slightly higher Fc, and more ripple to its disadvantage. Flip-side is that it has more gain over a wider passband, and has tighter control over driver excursion, so it will go louder before breaching linear excursion (FE206E would be my choice for this cabinet).
If you're interested in the technical side of things, the ripple you see in Sachiko's response is typical of a trunkated BLH where the mouth is reduced in size over the ~ideal for horn loading down to the chosen cut-off frequency (in this case 40Hz). The ripple is caused by the standing wave (supersonic shock-wave) created by the acoustic-impedence mismatch at the mouth being reflected back along the horn-path and modulating the driver response. In practice, Sachiko is better in this respect than a lot, and the multiple bends & stepped expansion should help reduce this compared to what is seen in the simulation, but horns are usually a love / hate thing.
In general terms, Bruce will go lower, more smoothly (I recommend the FE207E for this box), as you'd expect from a BR cabinet. Sonically, it will also give the large scale to the presentation horns are known for, albeit over a somewhat narrower passband / frequency range.
Sachiko OTOH has a slightly higher Fc, and more ripple to its disadvantage. Flip-side is that it has more gain over a wider passband, and has tighter control over driver excursion, so it will go louder before breaching linear excursion (FE206E would be my choice for this cabinet).
If you're interested in the technical side of things, the ripple you see in Sachiko's response is typical of a trunkated BLH where the mouth is reduced in size over the ~ideal for horn loading down to the chosen cut-off frequency (in this case 40Hz). The ripple is caused by the standing wave (supersonic shock-wave) created by the acoustic-impedence mismatch at the mouth being reflected back along the horn-path and modulating the driver response. In practice, Sachiko is better in this respect than a lot, and the multiple bends & stepped expansion should help reduce this compared to what is seen in the simulation, but horns are usually a love / hate thing.
Am I right in thinking that exceeding the Xmax on the 207 would not cause any damage? when I was cutting mine up I gently pushed on it, it has at least 10mm of mechanical travel. So overdriving (without being ridiculous) can only overheat it or cause it to sound terrible as the VC leaps out of the field.
There sure is a lot to horn design. Interesting about the standing waves, surely this is a problem with any horn at low frequencies with a mouth that isn't enormous.
Completely off the wall half-baked loony idea coming up, be warned.
When I forgot the top and bottom on the Bruce cut plan the other day a weird idea came to me. I'm sure it's been done before somewhere so it's only a new idea for me, consider it a step up from corner loading.
Using the floor, or more precisely using 2 walls, the floor and the OUTSIDE of a cabinet for an extension of bass horn mouth, Picture a cabinet something like a great big square pinball machine with a sloping bottom stuck in the corner on tall legs. the lowest part of the cabinet is in the corner. In the cabinet is a compression chamber and the first part of the horn, it vents out the bottom back corner.
The walls, floor and bottom of the cabinet form the next part of the horn.
It would look like some weird messed up ugly corner table, Wife Acceptance Factor of about minus 2000 so I'll never build one. Concrete floors only I expect.
There sure is a lot to horn design. Interesting about the standing waves, surely this is a problem with any horn at low frequencies with a mouth that isn't enormous.
Completely off the wall half-baked loony idea coming up, be warned.
When I forgot the top and bottom on the Bruce cut plan the other day a weird idea came to me. I'm sure it's been done before somewhere so it's only a new idea for me, consider it a step up from corner loading.
Using the floor, or more precisely using 2 walls, the floor and the OUTSIDE of a cabinet for an extension of bass horn mouth, Picture a cabinet something like a great big square pinball machine with a sloping bottom stuck in the corner on tall legs. the lowest part of the cabinet is in the corner. In the cabinet is a compression chamber and the first part of the horn, it vents out the bottom back corner.
The walls, floor and bottom of the cabinet form the next part of the horn.
It would look like some weird messed up ugly corner table, Wife Acceptance Factor of about minus 2000 so I'll never build one. Concrete floors only I expect.
OzMikeH said:
Right. Xmax is only the linear excursion of the driver. When it's breached, distortion starts to rise. Depending on the driver this can be more or less benign. The Fostex units are generally quite forgiving. Mechanical excursion is typically far greater, and should in a well designed driver limit travel before damage occurs to the voice coil (99.9% of drivers are fine in this respect).
OzMikeH said:
Indeed, although this does make the assumption that it's radiating into full-space (which they never are, unless suspended somewhere up in the stratosphere, which is a trifle impractical for home-audio). Sticking with the basics, the mouth circumference wants to be at least the wavelength of the lowest frequency to be reproduced, so to get full horn-loading down to the lowest fundamental of an acoustic instrument (ignoring pipe-organs), which is 40Hz, give or take, then you're looking at a mouth with a minimum circumference of 339in. If you build that as a square, you could drive a small car through it, as it would be 84.75in x 84.75in (HxW). Necessary path-length varies according to the chosen profile, but, again ideally, wants to be at least 1/2 wavelength of the lowest frequency to be reproduced.
OzMikeH said:
Not loony at all. Using the reflection boundary conditions of a room (we all have at least a floor) means you can reduce the mouth size of the horn. Have a look here for a basic introduction: http://yu-ra.tripod.com/horn.htm#Basics
In 1/2 radiation-space (a floor), we can reduce by 1/2.
In 1/4 radiation space (a floor & a wall at right-angles to each other) we can reduce by half again, to 1/4 the size necessary in full radiation-space.
In 1/8 radiation space (a floor or ceiling, and two walls at right-angles to each other, i.e. a corner) we can reduce it by half once again to 1/8 the size necessary in full radiation space.
The last-mentioned is a corner horn, and probably the easiest to get the full required mouth size out of in domestic terms, assuming, of course you have a couple of corners available (path-length can still be tricky though). The first two still often result in very large cabinets, so are usually reduced somewhat in mouth CSA and length, and we attempt to balance the QW action with the horn action via different means -selecting the best flare (or varying the profile as Ron does), careful thought over the folding scheme etc. The over-under double-horns allow an interesting blend of actions over a broad frequency range as the lower mouth comes in lower than the upper due to the different proximities of reflection boundary conditions.
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