This Frequently-Asked Questions (FAQ) list discusses corner-horn loudspeaker imaging, how to achieve outstanding imaging, and typically encountered issues with corner horn imaging.
Several manufacturers currently make or have made corner-horn designs: the Klipschorn and the Klipsch Jubilee, Voigt, Vitavox, ElectroVoice, JBL, and smaller companies like Pi and Decware, etc. Additionally, there are DIY corner horn designs that exist.
"Can I get Outstanding Imaging from a Corner-Horn Speaker?"
Yes. Good corner-horn imaging can be unsurpassed, in fact surpassing the imaging performance of dipole and bipole radiating loudspeakers in terms of accurate and detailed reproduction of the source music material.
"What are the Advantages of Corner Horns?"
A corner horn is designed to be used in a corner of a room or outside structure such as an outdoor stage backstop to significantly reduce the size of the loudspeaker bass bin for reproducing the lowest audible frequencies. While corner horns are not new, they are not often seen in today's audiophile circles.
Many misconceptions about corner horn acoustic performance and their proper setup exist:
"What are the Disadvantages of Corner Horns?"
"What is Different About Corner-Horn Imaging?"
Corner-horn imaging performance is a strong function of the room they're in, i.e.,
"How Do I Set Up Corner Horns to Increase Their Stereo Imaging Performance?"
One commonly heard complaint from corner horn users is that their speakers seem to have trouble achieving the same imaging performance as free-standing speakers. Loudspeakers of any type except dipole-radiators profit greatly in increased bass performance and much lower bass IMD of their speakers if they are placed in the corners of the room, toed-in to the listening position.
When many owners are polled about where they place their speakers in-room, invariably many answer "along a wall" or "a few feet from the front and side walls". Why would this occur? Paul Klipsch stated:
From the co-inventor of the Klipsch Jubilee, Roy Delgado:
What is the easiest way to control these early side and front wall reflections? Have a smooth boundary between the speakers (i.e., nothing between the speakers) and smooth front and side walls.
If this is not possible for your room and setup, the next easiest fix is to employ absorption panels. Many companies make fuzzy panels and acoustically absorbing tiles that can easily be placed along side walls and front walls of the your listening room. How much is needed? It turns out from the Haas Effect that controlling early reflections should be considered for 10-20 milliseconds of delayed reflections from side and front walls. This translates into about 11 to 22 feet (3.4-6.8 meters) of total path length at room temperature. However, the first 2-4 ms of early reflections are critical to control, translating to about 2-4 feet (0.6-1.2 m) of significantly reduced reflections. I use about 2 feet (0.6 meters) of absorption at the side-wall exit area of my corner-horn midrange horns.
Depending on your room geometry and listening position in relation to the corner horn placement (i.e., the included angle of the speakers relative to the listener--typically 90+ degrees included angle), the width of the midrange horn acoustic coverage laterally ( typically 60-100 degrees included angle), and assuming that your corner horn midrange horn controls its polar response down to its lower crossover frequency, the area that you should cover with absorption panels could be on the order of 2-10 feet along the front and side walls. I find that 2 feet of absorption along side walls works very well for Klipsch K-402 horns (i.e. Jubilee), and ~7 feet across the front wall, measured from the exit of each midrange horn's mouth.
Another approach is to place diffuser panels along the same near field areas but note that the use of diffusers in the Haas-effect areas will likely not achieve the same level of corner-horn imaging as the use of absorbers. The advantage of using diffusers is the relative liveness or deadness in smaller listening rooms.
If your listening position is more than 11 to 22 feet (3.4-6.8 meters) away, you probably have little work to do. However if you are like me and sit within 10 feet (3 meters) of your corner horns, you will find that the effect of using absorbent panels along the walls very much increases your stereo imaging performance.
"But What About the Equipment/Racks, Architectural Details, and Speaker(s) Between by Corner Horns?"
Again, the most straightforward way to deal with this is to simply remove all objects between the speakers, leaving a smooth wall. If this is not achievable, the alternatives are the same as above. I use absorption tiles on the side and top of my center loudspeaker, on the masonry, and a quilt-based cloth fabrics on other protruding objects like the mantlepiece to control early reflections.
"But What About the Television Between My Speakers?"
This one is easy--place a temporary quilt, comforter, or acoustic absorption tiles in front of the screen when you listen in music only (i.e., no video) mode.
"But What About the Floor Next to My Speakers?"
Something as simple as a thin area carpet around each corner horn or even wall-to-wall carpet will suffice. This carpet does not need to be very thick or fuzzy to be effective.
"But What About the Ceiling?"
If your ceiling is relatively high, you probably don't have a problem. If it is lower than about 9 feet, and especially if you own Klipschorns or other horn-loaded loudspeaker having collapsing polar midrange horns, you should put absorbent material around the top/bottom mouth of the midrange horn or place diffusers/absorbers on the ceiling around your speaker's midrange horn mouth (especially if you sit relatively close to your corner horns). More on this subject later.
"What If the Amount of Absorption Recommended Above Just About Covers My (Small) Listening Room?"
Then you are probably one of those unfortunate corner-horn owners that would greatly benefit by placing your speakers in the corners of a larger room: in particular, Klipschorns require a large room to perform at their best . If perhaps you are using something like Klipsch Jubilees, then you can use them in a smaller room. More on the subject of midrange horns, below.
"Is All This Really Necessary?"
If you are trying to increase your corner-horn imaging performance: the answer is "yes" if you sit within 11 feet (3.4 meters) of your speakers. If you sit further back, then you will probably have far fewer imaging issues.
"What about Amplifiers and Corner-Horn Imaging Performance?"
In order to understand the effects of different type of amplifiers on corner-horn performance, you need to understand the effects of "early reflections", discussed, above, and the treatments available to recover your stereo imaging performance in rooms with cluttered areas between the speakers and non-smooth front and side walls. Once you understand the psychoacoustic effects on imaging of corner-horn speaker midrange horns/drivers, then a productive discussion on amplifier effects can occur.
"What Are the Issues Related to Amplifiers and Corner Horns?"
Amplifiers that exhibit high output impedance have the effect of providing a "reverb effect" in-room, especially if the room is small and relatively live acoustically. What kind of amplifiers have relatively high output impedance? Tube/valve-type amplifiers.
"Why is This an Issue...What is Happening?"
The reverb effect is due to strong room reflections back to the horns/drivers themselves, which are much more efficient than direct-radiator speakers at converting electrical energy into acoustic energy - and back again (...i.e., they are acting like microphones). Klipschorns, for example, convert about 10% or more of their input electrical energy into acoustic energy (according to Paul Klipsch's own calculations and measurements), while cone-type speakers typically are only 0.1% efficient or less. Planar speakers, like electrostatic and Magneplanar-like speakers, are even less efficient.
By the way, the same reverb effect happens with headphones in that sound reflections from the ear's closed-end tube reflect back to the driver, then back into the electrical domain by headphone driver-amplifier coupling. Special thanks to Bob Carver on identifying this phenomenon.
"So Why are We Talking About the Efficiency of Corner Horns and Imaging with Some Tube Amplifiers?"
Because the horns/drivers themselves are 100x more efficient at converting acoustic reflected energy back into electric energy to your amplifier's output terminals than direct radiator loudspeakers are, some of the room's reflected acoustic energy goes right back to the amplifier's output terminals.
"So What's the Issue with Amplifiers and Horn-Loaded Loudspeakers?"
Nothing, as long as the amplifier has low output impedance, a.k.a., high damping factor, like virtually all SS amplifiers and most higher-forward-gain tube amplifiers with feedback--such as multistage push-pull designs.
But if your amplifier has relatively high output impedance, that is, amplifiers with zero feedback, SET-type tube amplifiers, and particularly output-transformerless (OTL) types, what happens is that the amplifier output stage "feels" the reflected acoustic energy as an added load and the amplifier attempts to push back against midrange and bass bin driver diaphragms, albeit this effect is delayed in time from the original signal due to the reflected energy delays in-room. The net result is a reverb effect that is sensitive to SPL coming back to your corner horns from the room.
"So What's Wrong With That?"
Well, for starters, it's artificial and you can't turn it off unless switching to a lower output impedance amplifier, or switch to a much larger listening room with high ceilings. Paul Klipsch talked about measuring speakers with a "rubber yardstick" when you start to depart from a live music reproduction standard. [See also the article "Euphonic Distortion: Naughty but Nice".] That conversation is apropos here. If accurate reproduction is the standard by which Klipsch designed and built his speakers, then amplifiers with high-output-impedance used with very efficient corner horns in corners, where the reflected acoustic waves tend to have the highest amplitude and tends to pile up, will lead to distortion - non-harmonic distortion - the worst kind.
"So Why Do So Many Corner-Horn Owners Use Tube Electronics That Have High Output Impedance?"
I believe you can answer that question yourself now. Another way to achieve the same effect is to place a reverb unit in front of your amplifier input terminals - at least you can turn it off when you get tired of it.
"So What Other Issues Are There With SET Tube-Type Amplifiers?"
Low power SET-type tube amplifiers usually have too little amplifier power headroom--even for 105 dB/W-M corner horns thus leading to fast-transient soft clipping that some tube enthusiasts apparently like. Paul Klipsch's "rubber yardstick" comments are apropos here, too: it's preferable to not have any clipping effects at all if we are to retain an accurate sound reproduction yardstick. Also, SET amplifiers exhibit a much larger amount of harmonic distortion, that is, even harmonics. It is preferable to not have these harmonics added to our stereo's output since the magnitude of harmonic distortion is an indicator of the magnitude of amplitude modulation distortion (AMD) being generated, which is non-harmonic and very detrimental to the quality of sound reproduction.
"Soft Clipping" of Tube Amplifiers that Masks Their Clipping Distortion but Introduces Harmonic Distortion
"So Why Do Class 'A' Tube-Type Amplifiers Sound So Good With Corner Horns?"
Multistage amplifiers, the type that is commonly used in SS amplifier designs (it's easy to get large amounts of amplifier gain) have more of something known as higher order harmonic distortion (which is synonymous with higher order harmonics) than do single stage or dual-stage amplifiers using little or no feedback.
Also the use of feedback to control these multiple cascaded amplifier stages tend to convert otherwise low-order harmonic distortions into higher order harmonics unless relatively large amounts of feedback are used.
But using large amounts of feedback negates the use of multistage amplifiers because it reduces the overall gain of the amplifiers in series. So typical SS push-pull, or even some class A amplifiers typically have much more higher-order harmonic distortion than do single- and dual-stage amplifiers running with no feedback.
Several manufacturers currently make or have made corner-horn designs: the Klipschorn and the Klipsch Jubilee, Voigt, Vitavox, ElectroVoice, JBL, and smaller companies like Pi and Decware, etc. Additionally, there are DIY corner horn designs that exist.
"Can I get Outstanding Imaging from a Corner-Horn Speaker?"
Yes. Good corner-horn imaging can be unsurpassed, in fact surpassing the imaging performance of dipole and bipole radiating loudspeakers in terms of accurate and detailed reproduction of the source music material.
"What are the Advantages of Corner Horns?"
A corner horn is designed to be used in a corner of a room or outside structure such as an outdoor stage backstop to significantly reduce the size of the loudspeaker bass bin for reproducing the lowest audible frequencies. While corner horns are not new, they are not often seen in today's audiophile circles.
Many misconceptions about corner horn acoustic performance and their proper setup exist:
- They provide dramatically lower bass distortion, in particular, modulation distortion, than non-corner-loaded loudspeakers. Bass modulation distortion has been found to be quite audible.
- They provide much greater low frequency dynamic range without resultant woofer compression or other forms of distortion, which limits achievable sound reproduction fidelity of other types of speakers
- They have the potential to achieve full range controlled directivity in-room if designed/produced carefully
"What are the Disadvantages of Corner Horns?"
- They require good room corners to fully achieve their low frequency response, or a large footprint in order to accommodate bass bin extensions to achieve their lowest octave of low frequency performance
- They are physically large and heavy speakers if they are to reproduce all needed low frequencies (e.g., piano, organ, string bass, etc.)
- They require amplifiers of high quality for the critical "first watt" of input power to achieve full potential
- They require careful placement of near-field objects and/or acoustic near-field treatments in room in order achieve their full imaging potential
"What is Different About Corner-Horn Imaging?"
Corner-horn imaging performance is a strong function of the room they're in, i.e.,
- The room's absolute and relative dimensions, its shape (including the ceiling), and the uniformity and relative smoothness of the walls next to the corner horns, i.e., the front and side walls near the speakers out to a distance of at least 4 feet (120 cm)
- The placement of the speakers within the room boundary (e.g., for a Klipschorn, the tailpiece-to-corner fit to seal the two mouths of the bass bins, or the length of the corner extensions from the bass bin on the front and side walls, and avoidance any intrusions into the room by bricks and other architectural details (yes, brick fireplaces and mantles can significantly affect imaging...) or canted low ceilings.
- The absence of near-field furniture or equipment that reflect acoustic energy, and
- The judicious use of acoustic treatments (...it usually doesn't take very much, but it usually takes some).
- The quality of the "first watt" of amplifier power driving them
"How Do I Set Up Corner Horns to Increase Their Stereo Imaging Performance?"
One commonly heard complaint from corner horn users is that their speakers seem to have trouble achieving the same imaging performance as free-standing speakers. Loudspeakers of any type except dipole-radiators profit greatly in increased bass performance and much lower bass IMD of their speakers if they are placed in the corners of the room, toed-in to the listening position.
When many owners are polled about where they place their speakers in-room, invariably many answer "along a wall" or "a few feet from the front and side walls". Why would this occur? Paul Klipsch stated:
There is something involving room acoustics and corner horns that is critically important to achieving excellent corner-horn imaging. The psychoacoustic effect that comes into play in this is a special case of the Precedence Effect of listeners called the Haas Effect, and the issue is early reflections of high mid-bass and midrange frequencies (i.e., about 250-4000 Hz) off the walls of the room closest to corner-horn midrange and high mid-bass horns.
From the co-inventor of the Klipsch Jubilee, Roy Delgado:
These early reflections should be controlled (i.e., a "Zero Reflection Zone" by P. D'Antonio) in order to achieve much greater imaging performance with speakers in the corners of their rooms.
What is the easiest way to control these early side and front wall reflections? Have a smooth boundary between the speakers (i.e., nothing between the speakers) and smooth front and side walls.
If this is not possible for your room and setup, the next easiest fix is to employ absorption panels. Many companies make fuzzy panels and acoustically absorbing tiles that can easily be placed along side walls and front walls of the your listening room. How much is needed? It turns out from the Haas Effect that controlling early reflections should be considered for 10-20 milliseconds of delayed reflections from side and front walls. This translates into about 11 to 22 feet (3.4-6.8 meters) of total path length at room temperature. However, the first 2-4 ms of early reflections are critical to control, translating to about 2-4 feet (0.6-1.2 m) of significantly reduced reflections. I use about 2 feet (0.6 meters) of absorption at the side-wall exit area of my corner-horn midrange horns.
Depending on your room geometry and listening position in relation to the corner horn placement (i.e., the included angle of the speakers relative to the listener--typically 90+ degrees included angle), the width of the midrange horn acoustic coverage laterally ( typically 60-100 degrees included angle), and assuming that your corner horn midrange horn controls its polar response down to its lower crossover frequency, the area that you should cover with absorption panels could be on the order of 2-10 feet along the front and side walls. I find that 2 feet of absorption along side walls works very well for Klipsch K-402 horns (i.e. Jubilee), and ~7 feet across the front wall, measured from the exit of each midrange horn's mouth.
Another approach is to place diffuser panels along the same near field areas but note that the use of diffusers in the Haas-effect areas will likely not achieve the same level of corner-horn imaging as the use of absorbers. The advantage of using diffusers is the relative liveness or deadness in smaller listening rooms.
If your listening position is more than 11 to 22 feet (3.4-6.8 meters) away, you probably have little work to do. However if you are like me and sit within 10 feet (3 meters) of your corner horns, you will find that the effect of using absorbent panels along the walls very much increases your stereo imaging performance.
"But What About the Equipment/Racks, Architectural Details, and Speaker(s) Between by Corner Horns?"
Again, the most straightforward way to deal with this is to simply remove all objects between the speakers, leaving a smooth wall. If this is not achievable, the alternatives are the same as above. I use absorption tiles on the side and top of my center loudspeaker, on the masonry, and a quilt-based cloth fabrics on other protruding objects like the mantlepiece to control early reflections.
"But What About the Television Between My Speakers?"
This one is easy--place a temporary quilt, comforter, or acoustic absorption tiles in front of the screen when you listen in music only (i.e., no video) mode.
"But What About the Floor Next to My Speakers?"
Something as simple as a thin area carpet around each corner horn or even wall-to-wall carpet will suffice. This carpet does not need to be very thick or fuzzy to be effective.
"But What About the Ceiling?"
If your ceiling is relatively high, you probably don't have a problem. If it is lower than about 9 feet, and especially if you own Klipschorns or other horn-loaded loudspeaker having collapsing polar midrange horns, you should put absorbent material around the top/bottom mouth of the midrange horn or place diffusers/absorbers on the ceiling around your speaker's midrange horn mouth (especially if you sit relatively close to your corner horns). More on this subject later.
"What If the Amount of Absorption Recommended Above Just About Covers My (Small) Listening Room?"
Then you are probably one of those unfortunate corner-horn owners that would greatly benefit by placing your speakers in the corners of a larger room: in particular, Klipschorns require a large room to perform at their best . If perhaps you are using something like Klipsch Jubilees, then you can use them in a smaller room. More on the subject of midrange horns, below.
"Is All This Really Necessary?"
If you are trying to increase your corner-horn imaging performance: the answer is "yes" if you sit within 11 feet (3.4 meters) of your speakers. If you sit further back, then you will probably have far fewer imaging issues.
"What about Amplifiers and Corner-Horn Imaging Performance?"
In order to understand the effects of different type of amplifiers on corner-horn performance, you need to understand the effects of "early reflections", discussed, above, and the treatments available to recover your stereo imaging performance in rooms with cluttered areas between the speakers and non-smooth front and side walls. Once you understand the psychoacoustic effects on imaging of corner-horn speaker midrange horns/drivers, then a productive discussion on amplifier effects can occur.
"What Are the Issues Related to Amplifiers and Corner Horns?"
Amplifiers that exhibit high output impedance have the effect of providing a "reverb effect" in-room, especially if the room is small and relatively live acoustically. What kind of amplifiers have relatively high output impedance? Tube/valve-type amplifiers.
"Why is This an Issue...What is Happening?"
The reverb effect is due to strong room reflections back to the horns/drivers themselves, which are much more efficient than direct-radiator speakers at converting electrical energy into acoustic energy - and back again (...i.e., they are acting like microphones). Klipschorns, for example, convert about 10% or more of their input electrical energy into acoustic energy (according to Paul Klipsch's own calculations and measurements), while cone-type speakers typically are only 0.1% efficient or less. Planar speakers, like electrostatic and Magneplanar-like speakers, are even less efficient.
By the way, the same reverb effect happens with headphones in that sound reflections from the ear's closed-end tube reflect back to the driver, then back into the electrical domain by headphone driver-amplifier coupling. Special thanks to Bob Carver on identifying this phenomenon.
"So Why are We Talking About the Efficiency of Corner Horns and Imaging with Some Tube Amplifiers?"
Because the horns/drivers themselves are 100x more efficient at converting acoustic reflected energy back into electric energy to your amplifier's output terminals than direct radiator loudspeakers are, some of the room's reflected acoustic energy goes right back to the amplifier's output terminals.
"So What's the Issue with Amplifiers and Horn-Loaded Loudspeakers?"
Nothing, as long as the amplifier has low output impedance, a.k.a., high damping factor, like virtually all SS amplifiers and most higher-forward-gain tube amplifiers with feedback--such as multistage push-pull designs.
But if your amplifier has relatively high output impedance, that is, amplifiers with zero feedback, SET-type tube amplifiers, and particularly output-transformerless (OTL) types, what happens is that the amplifier output stage "feels" the reflected acoustic energy as an added load and the amplifier attempts to push back against midrange and bass bin driver diaphragms, albeit this effect is delayed in time from the original signal due to the reflected energy delays in-room. The net result is a reverb effect that is sensitive to SPL coming back to your corner horns from the room.
"So What's Wrong With That?"
Well, for starters, it's artificial and you can't turn it off unless switching to a lower output impedance amplifier, or switch to a much larger listening room with high ceilings. Paul Klipsch talked about measuring speakers with a "rubber yardstick" when you start to depart from a live music reproduction standard. [See also the article "Euphonic Distortion: Naughty but Nice".] That conversation is apropos here. If accurate reproduction is the standard by which Klipsch designed and built his speakers, then amplifiers with high-output-impedance used with very efficient corner horns in corners, where the reflected acoustic waves tend to have the highest amplitude and tends to pile up, will lead to distortion - non-harmonic distortion - the worst kind.
"So Why Do So Many Corner-Horn Owners Use Tube Electronics That Have High Output Impedance?"
I believe you can answer that question yourself now. Another way to achieve the same effect is to place a reverb unit in front of your amplifier input terminals - at least you can turn it off when you get tired of it.
"So What Other Issues Are There With SET Tube-Type Amplifiers?"
Low power SET-type tube amplifiers usually have too little amplifier power headroom--even for 105 dB/W-M corner horns thus leading to fast-transient soft clipping that some tube enthusiasts apparently like. Paul Klipsch's "rubber yardstick" comments are apropos here, too: it's preferable to not have any clipping effects at all if we are to retain an accurate sound reproduction yardstick. Also, SET amplifiers exhibit a much larger amount of harmonic distortion, that is, even harmonics. It is preferable to not have these harmonics added to our stereo's output since the magnitude of harmonic distortion is an indicator of the magnitude of amplitude modulation distortion (AMD) being generated, which is non-harmonic and very detrimental to the quality of sound reproduction.
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[/URL]"Soft Clipping" of Tube Amplifiers that Masks Their Clipping Distortion but Introduces Harmonic Distortion
"So Why Do Class 'A' Tube-Type Amplifiers Sound So Good With Corner Horns?"
Multistage amplifiers, the type that is commonly used in SS amplifier designs (it's easy to get large amounts of amplifier gain) have more of something known as higher order harmonic distortion (which is synonymous with higher order harmonics) than do single stage or dual-stage amplifiers using little or no feedback.
Also the use of feedback to control these multiple cascaded amplifier stages tend to convert otherwise low-order harmonic distortions into higher order harmonics unless relatively large amounts of feedback are used.
But using large amounts of feedback negates the use of multistage amplifiers because it reduces the overall gain of the amplifiers in series. So typical SS push-pull, or even some class A amplifiers typically have much more higher-order harmonic distortion than do single- and dual-stage amplifiers running with no feedback.
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"So what is bad about amplifier higher-order harmonic distortion?”
It turns out that the human ear is more sensitive to higher-order harmonics than lower-order amplifier harmonics (see Geddes, et al. on human hearing "masking" of lower order harmonics).
"Can We Get Tube-Type Sound Without Distortion?”
Yes - Field-Effect Transistor (FET) amplifiers using fewer stages and cascoded correction of nonlinear amplifier gain (and perhaps Class D amplifiers, but that is a very controversial subject for many audiophiles). Nelson Pass' First Watt FET-based amplifiers work very well to bypass the problems of both high output impedance SET and higher harmonic distortion multistage SS amplifier designs with feedback.
First Watt amplifiers sound like much like tube (valve) amplifiers but are solid state, some models having relatively low output impedance, AND they typically measure very cleanly in such areas as THD, IMD, noise, and other figures of merit. These designs largely are available in both DIY and factory-built versions.
There are also very good tube-type designs: push-pull designs with two or more stages that use some feedback to correct for tube drift and other thermal issues. But they are very expensive compared to basic SET designs, suffer from warm-up issues, short tube life, and continuously changing tube characteristics during operation.
"So What's the Bottom Line on Amplifiers and Corner-Horn Imaging Performance?"
Amplifiers with very low distortion, the least number of amplifier gain stages possible, low noise figures, high slew rates, and low output impedance--like suitably designed tube amplifiers and well designed single-stage MOSFET and JFET amplifiers--will provide the most uncolored AND pleasant listening corner horn imaging performance, retaining the acoustic detail so dearly sought after by many audiophiles, and providing the original dynamic range of the actual performance due to the absence of driver compression that comes with direct radiator speakers of any type.
"So What's the Issue With Collapsing-Polar Midrange Horns and In-Room Imaging?”
At time of development of the original Klipschorn, Paul Klipsch had several constraints relating to the original midrange/tweeter horn design. The Klipschorn was originally a 2-way speaker, but after the recording companies in the 1950s expanded their advertised upper-frequency limit from 12 KHz to include the very limit of human hearing: ~20 KHz (measured with young adults), Klipsch had to add a tweeter to the design since then-current compression drivers were not capable of extending their FR to that limit. The constraint that Klipsch worked to was the lack of high-quality low-cost electronics to correct for the naturally drooping FR of midrange horns in their upper FR pass band. One approach was to provide passive crossover "balancing networks" that not only crossed the drivers electronically, but it also corrected for high end FR droop. To this day, Klipsch calls their crossover networks--"balancing networks" because they are performing EQ (via increases and decreases in impedance rather than by using L-Pads) in addition to low-pass, high-pass duties that are required for multi-way speaker designs.
On a visit to Jensen in the 1950s, Paul Klipsch pulled a horn out of the trash that had been rejected by the then-chief engineer of Jensen. That horn became the K-400 horn that is used in the Klipschorn and La Scala, and essentially the design to be used in all other horns of the Klipsch Heritage series. [Other manufacturers have followed suit with midrange horns that have a small vertical dimension of the horn's mouth relative to its width, such as the JBL Smith horns. The dimensions of a horn's mouth determines the frequency at which the horn loses pattern control in that dimension - the larger the horns mouth, the lower the horn can control its polars.]
The naturally falling FR of a midrange horn designed to output nearly constant polars with increasing frequency (the definition of a constant directivity horn) was an issue then since digital active crossovers were decades away from existence and cost effectiveness. The trick of the collapsing-polars midrange horn is that is covers a relatively constant horizontal polar azimuth (horizontal polars) without much EQing fairly well up to its typical crossover frequency of 4.5 KHz. It achieves this feat by allowing its vertical polars to "collapse" to smaller and smaller angles as the horn's frequency increases, due to the small vertical dimension of the horn's mouth relative to its horizontal dimension. This is the "collapsing polars" characteristic of wide but squat-height midrange horns that are sometimes discussed on this forum.
"So Again, What's The Issue With the Collapsing-Polar Midrange Horn and Corner Horn Imaging In-Room?"
This "collapsing polar" characteristic means that the midrange horn actually begins to lose polar control of its output frequencies in the vertical axis below ~2 KHz - down to its design crossover frequency (typically ~400 Hz with the bass bin). This energy winds up on your ceiling and floor as 400-1700 Hz band-passed "extra early reflections". If your room has good carpet and high ceilings, the effect of this extra spilled-bandpassed energy on imaging is to impart a timbre shift in the sound of the corner horn loudspeaker. At worst, with low ceilings or hard uncovered flooring, it becomes a tonally imbalanced speaker.
The remedy to this "spilled energy" issue is to have high ceiling and carpeted floors. If you don't have high ceilings (i.e., at least 9 feet or 2.7 meters), then it is recommended to either put acoustic absorption material around the top and bottom of the mouth of the collapsing-polars midrange horn (like the Peavey QT horn) or to place diffusers or even absorption tiles on the ceiling. This would be especially true for a basement-located corner horn with low ceilings.
Peavey QT Horn with its integral foam absorption inserts around it's mouth to control polar energy below the frequencies below the horn's loss of pattern control
"So What's The Deal With the K-402 (Jubilee) High Frequency Horn and Imaging?"
The K-402 high frequency horn, as seen in picture of the Klipschorn Jubilee, has some very special advantages:
The K-402 horn is able to support more than 4 1/2 octaves of bandpass that the newer 2" titanium and beryllium diaphragm drivers can reproduce well with very little narrowing of its hf polars from ~450 Hz up to ~17 KHz.
This need to EQ its output is a very small price to pay with today's high quality/low cost digital crossovers with their embedded EQ capabilities.
It is larger than most other midrange horns, and, since it is controlling its polars in a controlled directivity fashion all the way up the passband, the driver must be EQed ramping up at +6 db/octave due to the natural falloff of SPL due to the compensating effect of the horn to maintain relatively constant polar response all the way up to the limit of the driver's output.
Using the K402 horn and the updated Jubilee bass bin design, Paul Klipsch's original Klipschorn design goal of a two-way corner horn speaker has come full circle once again with the availability of Klipsch Jubilee, but with much improved imaging and soundstage performance over its predecessor design.
The avoidance of a tweeter/midrange crossover with the avoidance of midrange-tweeter driver time misalignment results in a very high performing speaker, a two-way design.
Reverse Side of the Klipsch K-402 Horn with K-69-A Compression Driver Assembly
The Jubilee's K-402 horn also allows the loudspeakers to be more easily acoustically integrated into rooms due to its outstanding polar control of mid-high frequencies. The Jubilee can be placed into a much smaller room than a Klipschorn and still retain very good imaging performance due to the K-402's outstanding polar control characteristic, without the need for excessive room acoustic treatments.
A small room with low ceilings - just the sort of room that K-402 horns will excel in
It turns out that the human ear is more sensitive to higher-order harmonics than lower-order amplifier harmonics (see Geddes, et al. on human hearing "masking" of lower order harmonics).
"Can We Get Tube-Type Sound Without Distortion?”
Yes - Field-Effect Transistor (FET) amplifiers using fewer stages and cascoded correction of nonlinear amplifier gain (and perhaps Class D amplifiers, but that is a very controversial subject for many audiophiles). Nelson Pass' First Watt FET-based amplifiers work very well to bypass the problems of both high output impedance SET and higher harmonic distortion multistage SS amplifier designs with feedback.
First Watt amplifiers sound like much like tube (valve) amplifiers but are solid state, some models having relatively low output impedance, AND they typically measure very cleanly in such areas as THD, IMD, noise, and other figures of merit. These designs largely are available in both DIY and factory-built versions.
There are also very good tube-type designs: push-pull designs with two or more stages that use some feedback to correct for tube drift and other thermal issues. But they are very expensive compared to basic SET designs, suffer from warm-up issues, short tube life, and continuously changing tube characteristics during operation.
"So What's the Bottom Line on Amplifiers and Corner-Horn Imaging Performance?"
Amplifiers with very low distortion, the least number of amplifier gain stages possible, low noise figures, high slew rates, and low output impedance--like suitably designed tube amplifiers and well designed single-stage MOSFET and JFET amplifiers--will provide the most uncolored AND pleasant listening corner horn imaging performance, retaining the acoustic detail so dearly sought after by many audiophiles, and providing the original dynamic range of the actual performance due to the absence of driver compression that comes with direct radiator speakers of any type.
"So What's the Issue With Collapsing-Polar Midrange Horns and In-Room Imaging?”
At time of development of the original Klipschorn, Paul Klipsch had several constraints relating to the original midrange/tweeter horn design. The Klipschorn was originally a 2-way speaker, but after the recording companies in the 1950s expanded their advertised upper-frequency limit from 12 KHz to include the very limit of human hearing: ~20 KHz (measured with young adults), Klipsch had to add a tweeter to the design since then-current compression drivers were not capable of extending their FR to that limit. The constraint that Klipsch worked to was the lack of high-quality low-cost electronics to correct for the naturally drooping FR of midrange horns in their upper FR pass band. One approach was to provide passive crossover "balancing networks" that not only crossed the drivers electronically, but it also corrected for high end FR droop. To this day, Klipsch calls their crossover networks--"balancing networks" because they are performing EQ (via increases and decreases in impedance rather than by using L-Pads) in addition to low-pass, high-pass duties that are required for multi-way speaker designs.
On a visit to Jensen in the 1950s, Paul Klipsch pulled a horn out of the trash that had been rejected by the then-chief engineer of Jensen. That horn became the K-400 horn that is used in the Klipschorn and La Scala, and essentially the design to be used in all other horns of the Klipsch Heritage series. [Other manufacturers have followed suit with midrange horns that have a small vertical dimension of the horn's mouth relative to its width, such as the JBL Smith horns. The dimensions of a horn's mouth determines the frequency at which the horn loses pattern control in that dimension - the larger the horns mouth, the lower the horn can control its polars.]
The naturally falling FR of a midrange horn designed to output nearly constant polars with increasing frequency (the definition of a constant directivity horn) was an issue then since digital active crossovers were decades away from existence and cost effectiveness. The trick of the collapsing-polars midrange horn is that is covers a relatively constant horizontal polar azimuth (horizontal polars) without much EQing fairly well up to its typical crossover frequency of 4.5 KHz. It achieves this feat by allowing its vertical polars to "collapse" to smaller and smaller angles as the horn's frequency increases, due to the small vertical dimension of the horn's mouth relative to its horizontal dimension. This is the "collapsing polars" characteristic of wide but squat-height midrange horns that are sometimes discussed on this forum.
"So Again, What's The Issue With the Collapsing-Polar Midrange Horn and Corner Horn Imaging In-Room?"
This "collapsing polar" characteristic means that the midrange horn actually begins to lose polar control of its output frequencies in the vertical axis below ~2 KHz - down to its design crossover frequency (typically ~400 Hz with the bass bin). This energy winds up on your ceiling and floor as 400-1700 Hz band-passed "extra early reflections". If your room has good carpet and high ceilings, the effect of this extra spilled-bandpassed energy on imaging is to impart a timbre shift in the sound of the corner horn loudspeaker. At worst, with low ceilings or hard uncovered flooring, it becomes a tonally imbalanced speaker.
The remedy to this "spilled energy" issue is to have high ceiling and carpeted floors. If you don't have high ceilings (i.e., at least 9 feet or 2.7 meters), then it is recommended to either put acoustic absorption material around the top and bottom of the mouth of the collapsing-polars midrange horn (like the Peavey QT horn) or to place diffusers or even absorption tiles on the ceiling. This would be especially true for a basement-located corner horn with low ceilings.
Peavey QT Horn with its integral foam absorption inserts around it's mouth to control polar energy below the frequencies below the horn's loss of pattern control
"So What's The Deal With the K-402 (Jubilee) High Frequency Horn and Imaging?"
The K-402 high frequency horn, as seen in picture of the Klipschorn Jubilee, has some very special advantages:
- It can control its polars in both the vertical and horizontal directions down to below 300 Hz (i.e., below the crossover point to the bass bin)
- It is a controlled directivity horn without a diffraction slot (more on this subject later), which results in an extremely natural sound without the typical "frying eggs" sound of the older Constant Directivity (CD) horns pioneered by ElectroVoice and JBL.
- It doesn't have the characteristic "horn sound" of other horn profiles, due mostly to its conical horn profile (also called a "straight-sided horn"). This is also extremely important to the resulting output sound.
The K-402 horn is able to support more than 4 1/2 octaves of bandpass that the newer 2" titanium and beryllium diaphragm drivers can reproduce well with very little narrowing of its hf polars from ~450 Hz up to ~17 KHz.
This need to EQ its output is a very small price to pay with today's high quality/low cost digital crossovers with their embedded EQ capabilities.
It is larger than most other midrange horns, and, since it is controlling its polars in a controlled directivity fashion all the way up the passband, the driver must be EQed ramping up at +6 db/octave due to the natural falloff of SPL due to the compensating effect of the horn to maintain relatively constant polar response all the way up to the limit of the driver's output.
Using the K402 horn and the updated Jubilee bass bin design, Paul Klipsch's original Klipschorn design goal of a two-way corner horn speaker has come full circle once again with the availability of Klipsch Jubilee, but with much improved imaging and soundstage performance over its predecessor design.
The avoidance of a tweeter/midrange crossover with the avoidance of midrange-tweeter driver time misalignment results in a very high performing speaker, a two-way design.
An externally hosted image should be here but it was not working when we last tested it.
[/URL]Reverse Side of the Klipsch K-402 Horn with K-69-A Compression Driver Assembly
The Jubilee's K-402 horn also allows the loudspeakers to be more easily acoustically integrated into rooms due to its outstanding polar control of mid-high frequencies. The Jubilee can be placed into a much smaller room than a Klipschorn and still retain very good imaging performance due to the K-402's outstanding polar control characteristic, without the need for excessive room acoustic treatments.
A small room with low ceilings - just the sort of room that K-402 horns will excel in
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Dr. Floyd Toole, former chief engineer of Harmon International, wrote an excellent book, Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms (Focal Press, 2008) that discusses the preference that listeners in blind test have for speakers that have relatively constant polars (like certain horn-loaded speakers and some direct-radiator speakers) over those speakers that do not exhibit constant polars (e.g., dipolar speakers).
Geddes points out that the most important characteristic of horns (he typically calls them waveguides) is controlled directionality, not acoustic efficiency. But he independently acknowledges that controlled directivity of loudspeakers is most preferred among loudspeaker characteristics, including freedom from distortion (i.e., of certain types). He also discusses the concept of higher-order modes (HOMs) of waveguides (horns) that augments typical horn equation approaches.
"What is Controlled Directivity?"
For the moment, think of a theoretical pulsating sphere in free space away from all acoustic reflections and room boundaries: its output is not sensitive to the horizontal azimuth or elevation that you hear it--if you are looking straight at it. At the other end of this extreme, if you think about a "sound bar" transducer, its output is more like that of a laser or a collimated beam of acoustic energy.
In between these two extremes is the concept of "controlled directivity" - the speaker limits its acoustic output to an angular sector of space, just like a directional antenna does for radio frequencies.
The assumption is that the speaker's output is almost constant within that covered angular sector. We don't want its acoustic SPL output to droop toward the edges of the covered angular sector for all frequencies that it covers (i.e., flat, neutral-color sound coverage in its passband horizontally and vertically), and we want its SPL output to be almost zero just outside of that sector.
"Again...Why is Controlled Directivity Important?"
Because it keeps the direct room output frequency spectra at different azimuths within the coverage sectors from being different (i.e., different "color" of sound) at different output angles. This is the key to controlled directivity horn speakers being preferred among listeners. The exact reasons why this is are covered in Toole's book, which is highly recommended for those who want to know more.
"Can You Just Tell Me, In a Nutshell, Why Controlled Directivity is Important?"
For the key to understanding this effect, think back on the discussion of the Precedence effect: early reflections (from ~1 to ~30 ms delay relative to the initial direct sound) are perceived differently by listeners than those reflections that are less than ~1 ms delay and those that are greater than ~30 ms delay.
If you are putting a lot of reflected energy on the walls, ceiling and floor around your speakers, what this does is smear out the sound image into a larger area (which can be a good thing from a casual listener's perspective) AND introduces phase delays in the direct-to-reflected energy (which is always bad in terms of small-room imaging performance) if you are in the "Haas zone" of delayed reflections.
We want to present a sound image that is in-phase horizontally and vertically from ~10 ms up to ~30 ms (depending on frequency content and loudness), without introducing "diffraction" of that image to the listener. But this is true only for delays of greater than ~10 ms and less than ~30 ms. Strange...but true.
"Why do Some Speaker Manufacturers Design Their Speakers to Reflect Off the Walls, Ceiling, and Floor (such as Bose)?"
If you are not interested in presenting a focused stereo image to the listener, the effects of spreading the energy around the front of the room (like Bose does...) is actually perceived pleasantly by casual listeners because it increases the "apparent source width" (ASW) of the speakers (see Floyd Toole's book for more on this).
The typical "anti-Bose story" goes something like: "Why do Bose speakers sound like they do? Because they sound uniformly bad everywhere you listen, but they sound the same way at all listening azimuths".
"Why Do Planar Speakers Have a Focused Sound Image (Albeit in a Small Azimuth of Listener Position)?"
Because they reflect very little SPL off the side walls, floor and ceiling due to their dipole characteristics, but most of the non-direct energy comes from the front wall reflections, AND planar speakers should be placed out into the room more than the 10-40 ms delay (total path length to the listener) from the front wall.
However, planar speakers, such as MartinLogans, still exhibit non-constant polars in azimuth and elevation--which is not preferred in blind testing by many listeners, especially when playing mono or "hard-cut" stereo material (see Toole's book, once again). Also, planar speakers can't be toed-in effectively to increase their imaging performance unless the room is quite large with no near-field azimuth reflectors present, i.e., greater than 10-20 feet (3-6 meters) in all directions around the speakers.
"What Can I Do About Ceiling Bounce of collapsing-polar midrange Horns (e.g., K-400 Series Horns and Smith horns)?"
A quick fix is to place an absorbent tile such as this to the top of the speaker cabinet, cut to fit appropriately but allowed to extend forward of the front shear line of the speaker's cabinet a couple of inches. This will have the effect of absorbing some widely dispersed polar acoustic energy exiting the horn (400--1700 Hz) that would otherwise wind up undesirably on your ceiling. While this technique is certainly limited in effectiveness, it may partially mitigate having to place absorption tiles on your ceiling in low-ceiling environments.
It will have a secondary effect of precluding random placement of drinks on top of your speakers (i.e., the pad will discourage placement of drink glasses and cups there due to its sponginess and corresponding uncertainty in supporting drinks by those random individuals). It will also act as an acoustic coating over any plate glass that you might have placed on top of your cabinets --which reflects more acoustic energy towards your ceiling.
Note that there will be a slight timbre shift when you do this, and slightly improved imaging.
Geddes points out that the most important characteristic of horns (he typically calls them waveguides) is controlled directionality, not acoustic efficiency. But he independently acknowledges that controlled directivity of loudspeakers is most preferred among loudspeaker characteristics, including freedom from distortion (i.e., of certain types). He also discusses the concept of higher-order modes (HOMs) of waveguides (horns) that augments typical horn equation approaches.
"What is Controlled Directivity?"
For the moment, think of a theoretical pulsating sphere in free space away from all acoustic reflections and room boundaries: its output is not sensitive to the horizontal azimuth or elevation that you hear it--if you are looking straight at it. At the other end of this extreme, if you think about a "sound bar" transducer, its output is more like that of a laser or a collimated beam of acoustic energy.
In between these two extremes is the concept of "controlled directivity" - the speaker limits its acoustic output to an angular sector of space, just like a directional antenna does for radio frequencies.
The assumption is that the speaker's output is almost constant within that covered angular sector. We don't want its acoustic SPL output to droop toward the edges of the covered angular sector for all frequencies that it covers (i.e., flat, neutral-color sound coverage in its passband horizontally and vertically), and we want its SPL output to be almost zero just outside of that sector.
"Again...Why is Controlled Directivity Important?"
Because it keeps the direct room output frequency spectra at different azimuths within the coverage sectors from being different (i.e., different "color" of sound) at different output angles. This is the key to controlled directivity horn speakers being preferred among listeners. The exact reasons why this is are covered in Toole's book, which is highly recommended for those who want to know more.
"Can You Just Tell Me, In a Nutshell, Why Controlled Directivity is Important?"
For the key to understanding this effect, think back on the discussion of the Precedence effect: early reflections (from ~1 to ~30 ms delay relative to the initial direct sound) are perceived differently by listeners than those reflections that are less than ~1 ms delay and those that are greater than ~30 ms delay.
If you are putting a lot of reflected energy on the walls, ceiling and floor around your speakers, what this does is smear out the sound image into a larger area (which can be a good thing from a casual listener's perspective) AND introduces phase delays in the direct-to-reflected energy (which is always bad in terms of small-room imaging performance) if you are in the "Haas zone" of delayed reflections.
We want to present a sound image that is in-phase horizontally and vertically from ~10 ms up to ~30 ms (depending on frequency content and loudness), without introducing "diffraction" of that image to the listener. But this is true only for delays of greater than ~10 ms and less than ~30 ms. Strange...but true.
"Why do Some Speaker Manufacturers Design Their Speakers to Reflect Off the Walls, Ceiling, and Floor (such as Bose)?"
If you are not interested in presenting a focused stereo image to the listener, the effects of spreading the energy around the front of the room (like Bose does...) is actually perceived pleasantly by casual listeners because it increases the "apparent source width" (ASW) of the speakers (see Floyd Toole's book for more on this).
The typical "anti-Bose story" goes something like: "Why do Bose speakers sound like they do? Because they sound uniformly bad everywhere you listen, but they sound the same way at all listening azimuths".
"Why Do Planar Speakers Have a Focused Sound Image (Albeit in a Small Azimuth of Listener Position)?"
Because they reflect very little SPL off the side walls, floor and ceiling due to their dipole characteristics, but most of the non-direct energy comes from the front wall reflections, AND planar speakers should be placed out into the room more than the 10-40 ms delay (total path length to the listener) from the front wall.
However, planar speakers, such as MartinLogans, still exhibit non-constant polars in azimuth and elevation--which is not preferred in blind testing by many listeners, especially when playing mono or "hard-cut" stereo material (see Toole's book, once again). Also, planar speakers can't be toed-in effectively to increase their imaging performance unless the room is quite large with no near-field azimuth reflectors present, i.e., greater than 10-20 feet (3-6 meters) in all directions around the speakers.
"What Can I Do About Ceiling Bounce of collapsing-polar midrange Horns (e.g., K-400 Series Horns and Smith horns)?"
A quick fix is to place an absorbent tile such as this to the top of the speaker cabinet, cut to fit appropriately but allowed to extend forward of the front shear line of the speaker's cabinet a couple of inches. This will have the effect of absorbing some widely dispersed polar acoustic energy exiting the horn (400--1700 Hz) that would otherwise wind up undesirably on your ceiling. While this technique is certainly limited in effectiveness, it may partially mitigate having to place absorption tiles on your ceiling in low-ceiling environments.
It will have a secondary effect of precluding random placement of drinks on top of your speakers (i.e., the pad will discourage placement of drink glasses and cups there due to its sponginess and corresponding uncertainty in supporting drinks by those random individuals). It will also act as an acoustic coating over any plate glass that you might have placed on top of your cabinets --which reflects more acoustic energy towards your ceiling.
Note that there will be a slight timbre shift when you do this, and slightly improved imaging.
Attachments
Last edited by a moderator:
I’m still having a hard time wrapping my head around the original post having been posted in 2014 with only my reply until today. I guess there isn’t a lot of corner horns out there. Chris’ post has explained why my La Scalas sound and image better than the Khorns I picked up last year. I have some work to do to rectify this disparity in performance.
There is a longer thread by Chris (ChrisA) on the Klipsch forums that has many replies, and further discussion and info, originally posted at around the same time…
https://community.klipsch.com/index.php?/topic/131163-corner-horn-imaging-faq/
I have good concrete block corners, but there is a La Scala between the two Khorns. The La Scala is a surround speaker in part of a five La Scala surround sound set up. It always seemed like a waste using a pair of LS as surround speakers, and this post has motivated me to get them into another room where they can be better enjoyed. I’m guessing a small set of speakers, that are wall or ceiling mounted, will create fewer problems with reflections. There is a screen door between the two Khorns with a heavy curtain covering it. The room is 16 by 25, with a 7 foot ceiling. The surround setup is on the long wall, and the Khorns are on the short wall.
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I can delete it all...if that's what you're implying, Dave. It's not a problem for me. [Of course, if someone quoted my entire post in their reply, I can't do anything about that. Perhaps you can edit the member's entry that quoted my post, above, so that the subject can buried permanently.
My original post here isn't really a forum post but rather a "FAQ" wiki entry (...yes, just like a Wikipedia topic...) from 8 1/2 years ago, when this forum had a separate section for user-contributed wiki entries. It was later "lost" during a forum software upgrade, but has apparently been recently reposted by I suppose you or the Forum Admin, Jason. It believe that it was Jason that remarked that he had better things to do besides restoring/repairing old wiki entries. I concur.
At this point in time, I have nothing to gain by seeing this ancient thread reopened, and I certainly don't require any complements like that I quoted, just above.
Kindest regards,
Chris
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Thank you OP for the information. Very helpful. I want to build a corner speaker system but I am experiencing "paralysis by analysis" due to my ignorance and inexperience. I have all the parts necessary for making a good system but having trouble deciding on the best way to implement them. Information such as you provided is much appreciated.