Fostex Fullrange Drivers and Enclosure Design Theory
What Makes Fostex Fullrange Speakers So Good?
1. A Fostex driver is full-range. No separate woofer, midrange, tweeter, or crossover is necessary. Without trying to blend different sizes and types of drivers together, there is a purity of sound that just can't be achieved in multi-driver systems. Also, all of the distortion and phase shifts produced in 'normal' speakers--when a crossover changes from one driver to another--are eliminated. Best of all, the music doesn't pass through any inductors (coils), resistors, or capacitors. A crossover is a necessary evil in all other speaker systems. With Fostex full-range drivers, there is no crossover to deal with.
2. In most applications, only one Fostex driver is used per cabinet. This gives perfect pointsource imaging. Common sense tells you that when someone sings, sound doesn't come from their mouth, their chest, and their knees (like it does in so-called 'normal' speakers). In addition, there are no time alignment problems (one driver being farther from the listener than another), because the sound comes from a single driver. You have never really experienced stereo imaging until you listen to a single, full-range driver. Where the artist was previously 'in the middle', now that artist 'holographically' appears as a real human being. At night, with the lights dimmed, you will find it hard to believe that there isn't a real person in your room.
3. Fostex full-range drivers have incredibly strong magnets. This gives extremely precise control of the movement of the cone. The result is a very clear, crisp, clean, and accurate musical presentation.
4. Fostex full-range drivers use very stiff and light paper cones. This allows the cone to respond to changes in the music without distortion.
5. Fostex full-range drivers are highly efficient. They will produce high sound pressure levels and excellent dynamics with amplifiers that have as little as 5 watts. The FE206E or FE207E driver produces at least 96 db for 1 watt at 1 meter. In larger cabinets, it can be even higher.
Full-Range Drivers--Some Myths
There are a lot of myths surrounding full-range drivers. Let's take a minute to address some of these:
1. Full-range drivers only work well with low powered tube amps.
Actually, it's the reverse that's true. Low powered tube amps only work well with fullrange drivers......
This is because other types of speakers require more power than these amps are capable of producing. Also, full-range drivers use no crossover. Because of this, they present a very easy impedance load to the amplifier. Low powered amps will produce full, rich sound--at normal listening levels--ONLY with highly efficient full-range speakers like these.
Quality full-range drivers work well with tube or solid state, low power or high power. The power rating of an amplifier is irrelevant, as long as it doesn't run out of power and 'clip'.
In fact, highly efficient drivers like the Fostex actually make high powered solid state amps better. How? Most of these amps run pure Class A for the first two or three watts--normal listening levels for quality full-range drivers.
Another reason that full-range drivers have been linked to tube amps is that many tube amps (especially modern ones) are very soft and warm sounding. Most modern speakers are the same. The combination can put you to sleep. The incredible detail, clarity, and realism of drivers like these will bring out the best in these amps.
2. Because of their design, Fostex full-range drivers only work well in 'bass horn' enclosures.
Some Fostex 8 inch full-range drivers (the ones with limited excursion) are designed for bass horn enclosures. However, the FE206E and FE207E are long excursion designs better suited to modern, ported, bass reflex designs.
3. No full-range driver can really go to 20,000 cycles--that's why they invented tweeters.
It's not true. Ten seconds of listening and you'll wonder why anyone builds tweeters.
4. Full-range drivers don't have great bass.
On the contrary, these drivers have strong, articulate, accurate, realistic, and tightly controlled bass. They also produce surprisingly high sound pressure levels. Recently designed 8 inch drivers like these can produce bass that rivals older style 12 and 15 inch woofers. They test down only 3dB at 40 cycles in a good bass reflex enclosure. The bass they produce is balanced and totally satisfying with well recorded material.
Of course, this is only possible with an amplifier with flat response. The myth of poor bass probably comes from many owners using low powered single ended triode amps with a rolled off bass response. However, many new single ended designs are capable of producing excellent bass. For those that don't, a quality subwoofer is the answer.
5. Full-range pointsource drivers can be overly bright.
Nonsense. Unfortunately, the vast majority of speakers available today are totally lacking in detail. They are 'dumbed down' to the lowest common denominator. That is, they are designed to soften even the worst sounding CD's. People used to these speakers initially mistake 'detail' for 'brightness'. But they quickly overcome this when they listen to a good quality recording played through these speakers. We refer to these modern speakers as 'dead, dull, dark, and distant sounding' (the four 'D's). Fostex full-range drivers are accurate and detailed, not 'bright.'
6. Full-range drivers are fragile.
Absolutely untrue. They are far more robust than systems with delicate tweeters. We have sold hundreds of pairs of Fostex FE206E drivers without a single return.
The drivers are only half the story. The enclosures you use are at least as important:
Over the many years that Fostex full-range drivers have been available, scores of different cabinets have been designed for them. Some of these are bass REFLEX enclosures and some are bass HORN enclosures. In our experience, everyone that hears these designs, side by side, prefers the sound of Fostex drivers in bass reflex cabinets.
For those of you unfamiliar with the term 'bass horn', it is a cabinet design where a small space BEHIND the driver starts very small but grows exponentially as it moves through the cabinet. The sound from the BACK of the driver follows this passageway as it winds back and forth and grows larger as it moves towards the exit. Eventually, it ends in a very large 'mouth'. This is actually called a 'folded' horn. If it were not folded, it would extend 6 feet or more into the room. . The theory behind them is similar to the way that a cheerleader uses a megaphone to lead cheers at a football game. The sound will be amplified when it finally exits the megaphone (or bass horn) at the 'mouth.' Historically, this design was created to get the most sound possible from low powered amplifiers. Unfortunately--just as the cheerleader's voice is distorted by the megaphone--so is the music.
Problems historically associated with bass horn speaker cabinets are as follows:
1. Horn-loaded designs tend to 'fatten' or 'smear' the midrange and upper bass regions of the music.
This is because the sound emanating from the BACK of the cone goes through the bass horn and reaches the listener AFTER the music from the FRONT of the cone. This time delay is especially pronounced with bass horns that exit at the front of the cabinet. All bass horns give a 'tubby' sound, one with exaggerated reverb affects. The single best feature of a full-range driver is the detail they are capable of reproducing. Much of this is either lost by cancellation or unnaturally enhanced by the sound coming from the bass horn.
2. Stereo imaging and soundstage is very poor with bass horn designs.
This is because there are three separate sound sources coming from both the left and right speakers (sound directly from the driver, from the bass horn, and from cabinet resonances caused by vibration). None of this information is time coherent. Each note on the recording arrives at three different times at the listener's ears (six, if you count both left and right speakers). This makes it very difficult to produce a precise stereo image? Historically, this was not important, because most of these designs date from the mono era. Before stereo, the concept of imaging didn't even exist.
3. Horn-loaded enclosures exhibit a ragged bass response.
Not the smooth response most people are used to--and prefer--from bass reflex enclosures. With each change in a third of an octave, bass horn enclosures may be up 8dB here, then down 6dB, then up another 7dB. They can end up making bass tones rather than clearly articulated bass notes.
4. Horn-loaded designs are very difficult--and expensive--to build, and hard to place in most rooms.
Most of them are also very large and unusual looking and have a very low WAF (wife acceptance factor!) Of course, this unusual appearance can be appealing for some people. And, of course, they can make an interesting and challenging woodworking project.
5. Horn-loaded designs do not play very low bass.
Our testing indicated that a bass reflex design will actually go significantly 'lower' in the bass region than almost all of the horn designs. All of our bass reflex enclosures are capable of flat response to 40 Hz (-3 dB) using boundary reinforcement, while almost all of the bass horn designs roll-off below 63 Hz.
6. There is no significant efficiency advantage with the bass horn designs.
The best are only around 1 or 2dB more efficient than a properly designed bass reflex enclosure.
7. It is possible to overdrive bass horns.
Drivers used in this type of enclosure can't have a lot of excursion and can't be driven too hard. If they are, the pressure builds up in the chamber behind the driver and produces distortion. If you really want thunderous bass and dynamics and bass response to 20 cycles or lower, it will be necessary to purchase a quality subwoofer.
Bass HORN Enclosures
Is there any situation where we could recommend a bass horn enclosure? Well, actually, there is one....
Classical music is unique in that the concert hall is an integral part of the enjoyment of the sound. It is virtually impossible to make a recording which can accurately capture a classical music performance. This is because when you sit in a concert hall, you hear many different sources of sound--the music coming directly from the orchestra--the reflections off side walls, the ceiling, the back of the hall--resonances coming from the floor under the orchestra and the hall itself. And stereo imaging is not an important element in orchestral works.
In this case, the colorations of a bass horn can mimic what goes on at a classical concert. It's not accurate, of course, but if it can simulate the actual event, then isn't that what's important? So, some of the liabilities of the bass horn design CAN become assets if many factors are carefully considered (like room placement, etc.)
There is a way to produce the same results with bass reflex enclosures and we have done so. By mounting a second driver on the top of the speaker--pointing up--it is possible to produce the same wide, spacious, ambient sound. Coincidentally, we call it the Fostex 2.5 'Ambience'! It produces a wonderful ambient presentation--much as the bass horns do--but without many of the problems mentioned previously. Many people prefer it to bass horn designs for classical music.
The Fostex 2.5 'Ambience' has better imaging, lower distortion, and all the accurate, realistic bass that can only be achieved with a bass reflex design. Of course, it doesn't image quite as well as the 'normal' bass reflex enclosure when both drivers are operating. But this tradeoff may be worth it for the increased ambience and sense of space that it offers. We believe that it is the best answer for classical music.
In addition, we recommend that this speaker be built with a switch for the top driver (so it can be turned off). With this switch, it is possible to have your cake and eat it too! You can operate the front driver for most 'normal' types of music. You can turn on the top driver when you listen to classical music. Using two drivers also gives a wonderful ambient sound for parties and for background music. The increased bass also makes the two driver setup preferable for more dynamic recordings.
Bass REFLEX Enclosures
Probably 99.9% of all speakers ever made are bass REFLEX. Why? Because this design produces the most realistic bass and most accurate midrange and treble. So, we strongly recommend the bass reflex enclosure.
Our first bass reflex design for Fostex 8 inch full-range drivers was called the '1.3'. The external dimensions are 32x10x11 inches (with the grill mounted). This enclosure uses the internal volume originally recommended by the Fostex factory. We have altered the porting somewhat to improve bass performance.
Further development resulted in a larger enclosure we call the Fostex '2.5.' Overall dimensions are approximately 36 1/2 x 14 1/2 x 12. There are two main variations. The original 'Series I' has a wide front baffle. The 'MkII' has a thin front baffle. The 'Series I' gives a bit softer, smoother, and warmer presentation and is preferable in 'live' rooms. The 'Mk II' is slightly more detailed and efficient and is preferable in 'soft' rooms. The greater internal volume (twice as many cubic feet when compared with the '1.3') has resulted in stronger bass response and a slightly more balanced overall presentation. Along with our original Twin Port MkII, we also offer a 'Big Port' variation which offers more mid bass at the expense of some lower bass.
Both the '1.3' and the '2.5' can test relatively flat (minus 3 or 4 dB) to 40 cycles and give at least 96 dB from one watt (at one meter) with the FE206E or FE207E driver. We say 'can' because changing the porting will shift the bass emphasis. We find that some people prefer more output in the 63 to 100 hz range and we developed the '2.5 MkII Big Port' to emphasize this range.
In response to demand for a smaller 'monitor' speaker, we completed a design of only 19 by 10 1/2 by 12 inches. We had our reservations about putting the Fostex driver in such a small enclosure but we were knocked out by the results. The bass rivals any other minimonitor in output and far surpasses them in clarity, detail, accuracy, and realism. And, of course, all of the astonishing midrange and treble is unchanged by the smaller cabinet. This speaker should become a reference for all recording studios serious about making great recordings. And it should also become a standard for small speakers in the home environment. It can also be used successfully as a surround speaker or center channel.
Further research has recently resulted in the development of an even smaller speaker.....the Micromonitor. It is only 16t x 10w x 8d. It was mainly developed as a surround speaker small enough to be hung on the wall. We also found it to be a simply stunning computer speaker. For those of you who like to listen to music at your computer, this speaker will simply astonish you! The 'footprint' is ony 10 by 8 inches.....small enough for almost everyone to use with their computer. Finally, we tried the Micromonitor with a quality subwoofer. With careful matching, we were able to achieve a sound rivaling our largest 2.5 enclosure! But you will have to spend quite a bit on a quality sub to achieve this so--if you have the space--you are still better off with one of our larger systems. Finally, the Micromonitor can also serve as a quality center channel speaker.
While the 'Minimonitor', '1.3' and '2.5' are satisfying full-range systems in their own right, for those who value extreme dynamics in their listening, any of these systems can easily be supplemented with a quality subwoofer. We have done extensive testing of this combination and can tell you, quite honestly, that this will provide all the bass and dynamics you could ever possibly want. We enthusiastically endorse HSU Subwoofers (800-554-0150). These are as good as any on the market and cost much less. They have an excellent powered subwoofer for as low as $500. You can buy factory direct with a return policy if you are not satisfied. Of course, there are other good brands on the market but be careful. You want a TRUE subwoofer, not just a bass module.
Once you've decided on bass reflex, it is important to note that the material used to make the cabinet is an important factor. Plywoods will generally give a softer sound, particle board--intermediate, MDF will give the most detail. For a soft listening room, you may prefer MDF. Medium rooms--particle board. And for live rooms we recommend high quality Baltic Birch plywood. As the quality of your source material goes up, so too can the density of the material you use to make your cabinets.
You can also experiment with different damping materials and how much of it you use. The main role of the material is to absorb the back wave from the speaker cone (any speaker cone sends sound to the rear as well as to the front). If this back wave is allowed to reflect off the back of the cabinet and then go forward and strike the cone, it will introduce distortion. Standard procedure is to apply damping material to all sides inside the cabinet except the front baffle. But you can get different--and sometimes better--results by varying how much you use.
Dual Driver Bass Reflex Enclosures
Some people have some special needs that their speakers need to address. For them, we have developed two different dual driver bass reflex enclosures. Why use two drivers when we've been praising the virtue of using only one? There are some situations where the compromise of using more than one driver in each cabinet is worthwhile. These two situations are as follows:
One. You have an extremely large room or like to play music at extreme volumes. For you, we have developed the '2.5 Dynamic.'
Two. You like to listen to classical music or want to fill every corner of your listening room with ambient sound. For you, we have developed the '2.5 Ambience.'
Of course, there are some tradeoffs. A dual driver system will not image quite as well as a system using only single drivers. However, the reduction in imaging is less than you might imagine. And because these are Fostex full-range drivers, even the dual driver systems image better than any other speaker. For some people, it may be a worthwhile tradeoff in exchange for what these dual driver systems can do.
Fostex 2.5 'Dynamic'
We took a standard '2.5' enclosure and added a second driver below the first one on the front baffle. Both drivers are wired in parallel for an effective impedance of 4 ohms. This combination gives more bass and effortless dynamics. It is a good choice for very large rooms or for people who prefer their music LOUD!
Fostex 2.5 'Ambience'
For this design, we again took a standard '2.5' enclosure and mounted a second driver on the top, pointing up at the ceiling. Both drivers are wired in parallel for an effective impedance of 4 ohms. This design gives an incredibly spacious sound. Bass is increased substantially. While it probably doesn't produce any more bass than the 'Dynamic', it gives the impression of more bass because a lot of midrange and treble output from the top driver is 'lost' in the room before it reaches the listener. But the increased bass is not. So, the overall tonal balance is softer with more bass. But it will not produce the extreme dyamics and sound pressure levels of the forward facing 'Dynamic.'
One interesting advantage of the Ambience is
that you can put a switch on the top driver. For the best imaging and soundstage,
you can turn the top driver off and enjoy all the advantages of the original
'2.5.' For more ambience (especially good for classical music), you can
turn the top driver on.
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