I'm hoping I can enlist the wisdom of you good folks as I contemplate building the world's largest nearfield system.😀
I'm in the process of redoing my small basement office, and I'm considering an experiment with my Fostex F120a drivers. Since space and WAF are not a factor, I'm considering building some very large enclosures to approximate an infinite baffle. Transients, clarity and accuracy are very important to me. I like airy accurate bass, but I'm not too fussed if the quantity of bass is a bit low. Also, I have a subwoofer - a HiVi D10.8 in a 120litre cabinet mounted over my head to add back in some of the dooba-dooba-dooba.
Space allows for cabs of up to about 170 litres. The Vas of the F120a is 9.8 litres, and the Qts is 0.44.
I know there is a bit of disdain for these drivers in these parts, mainly because of the cost. I've had them for a few years, though, and got them for about half what they normally cost back then, which is about a quarter of what they cost now. I also have some T90a super-tweeters I got around the same time for a similarly good price. I like the drivers on the whole. Currently, I'm using them in 14litre sealed cabs I built out of thick red oak, well-braced. I like the current sound, but there is a bit of congestion in the mids that I'm hoping I might be able to reduce if they can breathe a bit better. I'm not a big fan of BR enclosures. I seem to be a more sensitive to time issues than most people, and BR speakers always sound a bit muddy and smeared to me.
The room itself is a factor in all of this. It's a very small space, with my desk in an area that's only about five and a half feet wide. Fuzzmeasure tells me I have a big honking bulge in the 40-70hz range (without the subwoofer on), which is another reason I'm not overly worried about losing a bit of bass response.
So, am I nuts? Beyond anything, I'm hoping this will be a fun experiment, and I have to admit I kind of like the idea of two giant speaker enclosures in front of my desk like some sort of demented pipe organ, but I'd like to know there's at least a reasonable change of success before I go wasting a lot of wood. Wood doesn't grow on trees after all.
What say you all?
Oh yeah, power is coming from a single-ended tube amp.
I'm in the process of redoing my small basement office, and I'm considering an experiment with my Fostex F120a drivers. Since space and WAF are not a factor, I'm considering building some very large enclosures to approximate an infinite baffle. Transients, clarity and accuracy are very important to me. I like airy accurate bass, but I'm not too fussed if the quantity of bass is a bit low. Also, I have a subwoofer - a HiVi D10.8 in a 120litre cabinet mounted over my head to add back in some of the dooba-dooba-dooba.
Space allows for cabs of up to about 170 litres. The Vas of the F120a is 9.8 litres, and the Qts is 0.44.
I know there is a bit of disdain for these drivers in these parts, mainly because of the cost. I've had them for a few years, though, and got them for about half what they normally cost back then, which is about a quarter of what they cost now. I also have some T90a super-tweeters I got around the same time for a similarly good price. I like the drivers on the whole. Currently, I'm using them in 14litre sealed cabs I built out of thick red oak, well-braced. I like the current sound, but there is a bit of congestion in the mids that I'm hoping I might be able to reduce if they can breathe a bit better. I'm not a big fan of BR enclosures. I seem to be a more sensitive to time issues than most people, and BR speakers always sound a bit muddy and smeared to me.
The room itself is a factor in all of this. It's a very small space, with my desk in an area that's only about five and a half feet wide. Fuzzmeasure tells me I have a big honking bulge in the 40-70hz range (without the subwoofer on), which is another reason I'm not overly worried about losing a bit of bass response.
So, am I nuts? Beyond anything, I'm hoping this will be a fun experiment, and I have to admit I kind of like the idea of two giant speaker enclosures in front of my desk like some sort of demented pipe organ, but I'd like to know there's at least a reasonable change of success before I go wasting a lot of wood. Wood doesn't grow on trees after all.
What say you all?
Oh yeah, power is coming from a single-ended tube amp.
I have no idea how the F120A would sound in a big box, but I have a pair in Metronomes that I like very much. However, I didn't like them very well until I found out that they sounded awful with my solid state amps. Switching to an ST-35 from dynakitparts.com made all the difference!
Cheers, Jim
Cheers, Jim
I'm a bit confused. You say space is not a factor, then you say it is a very small room. Anyhowways, under the circumstances have you considered open baffle?
I 'm interested in the concept, mainly. Forget they're f120a's. Mentioning those drivers around here always seems to derail a conversation. What about the concept of very large sealed enclosures as a way of simulating an infinite baffle?
I can go floor to ceiling, and use the entirety of the end wall, which is about five feet wide. Too much depth is a bit of an issue, so no deeper than say 14 inches.
Gotcha, not really suitable for OB, ideally they want at least 3 feet behind them and not to be enclosed. Sounds like you could go with some kind of IB but I can't advise on that, not familiar with them except IB is generally used for low frequency reproduction. I presume when you say IB you don't mean sealed box, it can be an ambiguous term?
Assuming that Fostex's published graphs for the driver were measured on an IEC baffle - which is a sort of open baffle - except in anechoic conditions, you could expect pretty reasonable performance down to at least high 50s without reinforcement from something like a BLH or MLTL.
I've heard this driver in a small resistively vented enclosure, and they are quite captivating - certainly more so than the ferrite magnet FX120. My only real issue was, as you intimate, the cost - thanks to the use of Alnico, they will never be what most of us would consider "affordable" . From what I can recall of the two models, the cone material is rather thicker than current FE/FF series, and an enclosure / rear wall as deep as 14" shouldn't be a problem. I'd imagine Jim's Metronomes are shallower than that at driver location, and he probably would have kept to himself if there were any issues.
I've heard this driver in a small resistively vented enclosure, and they are quite captivating - certainly more so than the ferrite magnet FX120. My only real issue was, as you intimate, the cost - thanks to the use of Alnico, they will never be what most of us would consider "affordable" . From what I can recall of the two models, the cone material is rather thicker than current FE/FF series, and an enclosure / rear wall as deep as 14" shouldn't be a problem. I'd imagine Jim's Metronomes are shallower than that at driver location, and he probably would have kept to himself if there were any issues.
I agree about the cost. If I hadn't already acquired them cheap, I wouldn't even be considering them. I payed a bit over $100 Cdn each for them, which is probably an appropriate price for a nice, smooth sounding driver. I checked recently, and Solen wants $450 apiece for them, which is just silly. But, since I already have the drivers, all of that is a moot point. When you take out the price factor, I think they are a damned nice driver.
They seem to be well regarded in an open baffle arrangement, maybe not quite as much as their big brothers, the f200s, but still.. . My thought was to put them in an enormous box to get a bit of that magic and openness without getting extraneous soundwaves bouncing around a small, acoustically deficient little room. I do have some Roxul on hand I'm going to use to make some improvements in here, but it's never going to be the sort of place you'd want to set up and open baffle.
Edit: So I meant to ask, if I do decide to go big, just for the hell of it, is there an optimal size. I've heard that to get to that "infinite baffle" magic with a sealed box, you need a box volume of at least 10 times Vas, which would put me in the 100 litre range. On the other hand, a box of about 38 litres would give me a Q of 0.5, which is preferred by many. Or, I could just go for broke and make them as big a possible. WinISD obviously is no help and pretty much just throws up its hands at anything over 40 litres and says "You're on your own mate."
They seem to be well regarded in an open baffle arrangement, maybe not quite as much as their big brothers, the f200s, but still.. . My thought was to put them in an enormous box to get a bit of that magic and openness without getting extraneous soundwaves bouncing around a small, acoustically deficient little room. I do have some Roxul on hand I'm going to use to make some improvements in here, but it's never going to be the sort of place you'd want to set up and open baffle.
Edit: So I meant to ask, if I do decide to go big, just for the hell of it, is there an optimal size. I've heard that to get to that "infinite baffle" magic with a sealed box, you need a box volume of at least 10 times Vas, which would put me in the 100 litre range. On the other hand, a box of about 38 litres would give me a Q of 0.5, which is preferred by many. Or, I could just go for broke and make them as big a possible. WinISD obviously is no help and pretty much just throws up its hands at anything over 40 litres and says "You're on your own mate."
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I feel like maybe I made an error mentioning the F120a in the thread title. Something about that driver seems to put people off. Maybe I'll try a new thread, purely about big honking boxes.
Thread title changed
Hi PineShack,
Having a bit more time today & reflecting on the situation, allow me to elaborate.
I said that I like the sound of the F120A, told you what cabinet I have it in, and that in my experience, it is picky about amplification. While folks here may not gush over the F120A (perhaps mostly due to its high cost), I don’t recall all that many trash talk about it. (One glaring exception I can think of to that, but he disliked Fostex drivers in general.) Don’t think that you are alone in the world in liking this driver!
You haven’t given us a lot to work with from your end:
-OK, you don’t like bass reflex much, but what is the cabinet exactly? dimensions, tuning, lining, stuffing, details about driver mounting (I tried some experiments in isolation of the driver from the baffle which resulted in Diana Krall sounding like she had cotton in her mouth!)
-what are the upstream components?
-a diagram of the room w/ dimensions would be helpful, including listening position. IME, a poor room could result in the issues you described; however, there are a dozen other things that could also cause such a problem.
-music choice & SPL
My next thought is that you might try XRK971’s Nautaloss cabinet. The infinite baffle is a way of taking the rear wave from the driver and preventing it from contaminating the frontal wave. The Nautaloss is the same idea in a smaller package.
http://www.diyaudio.com/forums/full-range/247598-nautaloss-ref-monitor.html
Make the baffle from something sufficient to support the rather substantial F120A; I might use scraps of 0.5” or 0.75 “ plywood, with the rest built from foam core or insulation board. Stuff w/ fiber according to the plan. Build just one to see how it sounds. Quick, easy, low cost. IMO, if this doesn’t work, then a big box probably wouldn’t do all that much better.
Cheers, Jim
Having a bit more time today & reflecting on the situation, allow me to elaborate.
I said that I like the sound of the F120A, told you what cabinet I have it in, and that in my experience, it is picky about amplification. While folks here may not gush over the F120A (perhaps mostly due to its high cost), I don’t recall all that many trash talk about it. (One glaring exception I can think of to that, but he disliked Fostex drivers in general.) Don’t think that you are alone in the world in liking this driver!
You haven’t given us a lot to work with from your end:
-OK, you don’t like bass reflex much, but what is the cabinet exactly? dimensions, tuning, lining, stuffing, details about driver mounting (I tried some experiments in isolation of the driver from the baffle which resulted in Diana Krall sounding like she had cotton in her mouth!)
-what are the upstream components?
-a diagram of the room w/ dimensions would be helpful, including listening position. IME, a poor room could result in the issues you described; however, there are a dozen other things that could also cause such a problem.
-music choice & SPL
My next thought is that you might try XRK971’s Nautaloss cabinet. The infinite baffle is a way of taking the rear wave from the driver and preventing it from contaminating the frontal wave. The Nautaloss is the same idea in a smaller package.
http://www.diyaudio.com/forums/full-range/247598-nautaloss-ref-monitor.html
Make the baffle from something sufficient to support the rather substantial F120A; I might use scraps of 0.5” or 0.75 “ plywood, with the rest built from foam core or insulation board. Stuff w/ fiber according to the plan. Build just one to see how it sounds. Quick, easy, low cost. IMO, if this doesn’t work, then a big box probably wouldn’t do all that much better.
Cheers, Jim
Thanks for replying again, Jim. I very much value your opinions.
My apologies for the lack of specifics. At this point, I'm still just wondering if a very large sealed cabinet is a good idea at all. It's not something you see done a lot. There are lots of big speakers, but they all seem to be more elaborate arrangements than just a big box.
Part of the issue for me is lack of tools and skills to produce elaborate designs. Straight lines and butt joints are about the limits of my carpentry skills. My current enclosures are simple sealed boxes made of nominally one-inch red oak, well braced. Their volume puts me in the range of 0.6 for Qtc. They sound quite nice, given their simplicity. I'm just wondering if I opened things up a bit and allowed the drivers to breathe a bit better it would relieve a bit of the congestion in the lower mids.
The room itself is a makeshift affair I built in the basement. I didn't have acoustics in mind at the time I'm afraid. It's L-shaped, with my desk at the end of one leg of the L. The width of the L is a little over 5 feet wide.The other end of the L is about the same. It's about 10 feet in the long dimension. The odd shape was due to the need to build around other aspects of the basement. It's a nice cozy little office, but it's not an ideal listening space. I have laid in a stock of Roxul insulation and panels and intend, with the help of Fuzzmeasure, to improve the situation during the makeover.
I had the idea, whilst having a pint or two, that I could include some Very Large Speakers in the redesign. I got reading a bit about open baffles and infinite baffles, and liked the idea of allowing the driver the ability to move as it would, without interference from the cabinet. Open baffles in this little space are obviously a non-starter, but really big cabs that might approach an infinite baffle in quality by swamping the Vas seemed like a possibility, so I decided to ask you guys.
Likely, construction will be with thick, well-braced pine, in keeping with the construction of the rest of the office (aka the Pine Shack). Nominal one-inch (which is actually about 19mm) is my preferred wood because it is relatively cheap and easy to work with. My current, tentative plan is to use those "project panels" which are available in various sizes and are actually cheaper than plywood. Using the full 80-inch height of the ceiling, I can squeeze in a couple of 200l cabs without too much trouble. I've thought to use a chunk of red oak to anchor the driver to, both for reduced transfer of vibration, and for decorative purposes.
Driving it all is a single ended tube amp, running el34s or kt88s, depending if I'm listening to Black Sabbath or Kat Edmonson.
My apologies for the lack of specifics. At this point, I'm still just wondering if a very large sealed cabinet is a good idea at all. It's not something you see done a lot. There are lots of big speakers, but they all seem to be more elaborate arrangements than just a big box.
Part of the issue for me is lack of tools and skills to produce elaborate designs. Straight lines and butt joints are about the limits of my carpentry skills. My current enclosures are simple sealed boxes made of nominally one-inch red oak, well braced. Their volume puts me in the range of 0.6 for Qtc. They sound quite nice, given their simplicity. I'm just wondering if I opened things up a bit and allowed the drivers to breathe a bit better it would relieve a bit of the congestion in the lower mids.
The room itself is a makeshift affair I built in the basement. I didn't have acoustics in mind at the time I'm afraid. It's L-shaped, with my desk at the end of one leg of the L. The width of the L is a little over 5 feet wide.The other end of the L is about the same. It's about 10 feet in the long dimension. The odd shape was due to the need to build around other aspects of the basement. It's a nice cozy little office, but it's not an ideal listening space. I have laid in a stock of Roxul insulation and panels and intend, with the help of Fuzzmeasure, to improve the situation during the makeover.
I had the idea, whilst having a pint or two, that I could include some Very Large Speakers in the redesign. I got reading a bit about open baffles and infinite baffles, and liked the idea of allowing the driver the ability to move as it would, without interference from the cabinet. Open baffles in this little space are obviously a non-starter, but really big cabs that might approach an infinite baffle in quality by swamping the Vas seemed like a possibility, so I decided to ask you guys.
Likely, construction will be with thick, well-braced pine, in keeping with the construction of the rest of the office (aka the Pine Shack). Nominal one-inch (which is actually about 19mm) is my preferred wood because it is relatively cheap and easy to work with. My current, tentative plan is to use those "project panels" which are available in various sizes and are actually cheaper than plywood. Using the full 80-inch height of the ceiling, I can squeeze in a couple of 200l cabs without too much trouble. I've thought to use a chunk of red oak to anchor the driver to, both for reduced transfer of vibration, and for decorative purposes.
Driving it all is a single ended tube amp, running el34s or kt88s, depending if I'm listening to Black Sabbath or Kat Edmonson.
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Hi PineShack,
You've got tubes! Excellent!
I really don't have any experience with huge cabinets, but I think you could do some experiments on the cheap to get an idea of how the drivers would work. Heck, I have a pair of Mark Audio Alpair 10.3 in 0.25 cubic foot cardboard boxes (sealed, ha ha ha!) breaking-in, and you might be surprised at how good they sound in such crappy boxes. I intend to put them in BIB cabs when the weather is more favorable for working out doors.
XRK started building with foam core board because he didn't have the tools to work with wood. Inspired by XRK, I began using foam core for prototyping. Much faster, easier & cheaper than trying to build proper prototypes from real wood. Take a look at his threads & think about it. For your purposes, if you don't want to try the Nautaloss, how about hunting down a discarded refrigerator carton. Is that big enough to qualify as infinite baffle?
Cheers, Jim
You've got tubes! Excellent!
I really don't have any experience with huge cabinets, but I think you could do some experiments on the cheap to get an idea of how the drivers would work. Heck, I have a pair of Mark Audio Alpair 10.3 in 0.25 cubic foot cardboard boxes (sealed, ha ha ha!) breaking-in, and you might be surprised at how good they sound in such crappy boxes. I intend to put them in BIB cabs when the weather is more favorable for working out doors.
XRK started building with foam core board because he didn't have the tools to work with wood. Inspired by XRK, I began using foam core for prototyping. Much faster, easier & cheaper than trying to build proper prototypes from real wood. Take a look at his threads & think about it. For your purposes, if you don't want to try the Nautaloss, how about hunting down a discarded refrigerator carton. Is that big enough to qualify as infinite baffle?
Cheers, Jim
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What you are really asking about is what used to be called 'infinite baffle'. The general rule of thumb was 10x Vas for a high Q driver(.5-.8), down to 4x for low Q(.2-.,3). Since you have some measurement capability, I'd suggest putting them in the wall open, and testing them open and with various sized boxes behind. The smallest box(or none) with no objectionable changes and you're good to go. Measurement makes it easier as it takes so much different music to find every problem, but the old-fashioned way works too. Should be fun.
Heh, yeah there doesn't seem to be many people who have experience with this sort of thing. Size is obviously the biggest reason. Also, this hobby has historically been geared towards doing clever things to make a small box sound like a large box. Most people don't have a lot of space, and therefore have to make do with cleverness and skill. I have neither cleverness nor skill, but I do have room for a couple of bloody big boxes.
The old-school aspect of this kind of appeals me as well. The F120a is a very old design done right. It makes up for modernity and cleverness with high quality construction and top-notch materials. Similarly, my amp is 70-year-old technology. It's simple, but I've snazzed it up with the best capacitors and tubes I can afford, and now it sounds pretty darned good.
So, I think I'll have a go at this. Ideally, I've read, one wants to get at least five times Vas. Ten times is better. I'm not sure where the point of diminishing returns is, but by the time I get to 150 litres or so, I doubt there's much more to be gained.
I'm going to screw the front panels in place at first, so I can always subdivide what's inside if things don't work out. Who knows, maybe I'll end up with 14 litre cabs with the rest converted to shelving. 🙂
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Thanks Boswald. I had seen those numbers elsewhere, but it's really good to have them confirmed. The F120a is in the middle ground with a Qts of .44
This is turning into a fairly ambitious project. I'm going to add Roxul sound insulation in the walls (which are thin and made of pine paneling) and make some acoustic panels to put in key areas. This office is terrible acoustically, and fixing that is the real project. This scheme to add in some crazy big speakers kind of grew out of the whole acoustic renovation idea.
Jim, you mentioned the BIB, and I have been wondering about that too, as they are only slightly more complex than my giant box idea. Discussions of them are tend to be very contradictory, however. On one hand, a lot of effort and hand-wringing goes into the tuning of them and getting them just right, but on the other hand there is a lot of talk about how forgiving they are, and many people have apparently swapped quite dissimilar drivers into them with pleasing results. Is it possible that the BIB is really just acting as an infinite baffle to a large extent?
If you are really into 'old school' leave the back off the box, this was quite common too. Nowadays they call it U frame 😀
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