Corner-Horn Imaging FAQ

[Chris A]

The is the third in a series of FAQs ("Frequently-Asked Questions") , the first of which was the Klipsch serial number FAQ, and the second is the Active Bi-amping/Triamping FAQ. This thread discusses corner-horn loudspeaker imaging, in particular, how to achieve outstanding imaging, and typically encountered issues with corner horn imaging.

 

Klipsch currently makes two corner-horn designs (i.e., the Klipschorn and the Klipschorn Jubilee), and has made smaller corner-horn speakers in the past (e.g., the Shorthorn series). Other manufacturers make or have made corner horn speakers (e.g., Voight, ElectroVoice, JBL, and smaller companies like Pi and Decware, etc.).

 

"Can I get Outstanding Imaging from a Corner-Horn Speaker?"

 

Yes. Good corner-horn imaging can be "unsurpassed".

 

"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). While this type of speaker is not new, it is not often seen in today's audiophile circles. Many misconceptions about corner horn potential performance and proper setup exist:

 

1) They provide dramatically lower bass distortion, in particular, modulation distortion, than non-corner-loaded loudspeakers(modulation distortion in loudspeakers ). Bass modulation distortion has been found to be quite audible (Subjective_Effects.pdf).

 

2) 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

 

3) They have the potential to achieve full range controlled directivity in-room if designed/produced carefully

 

"What are the Disadvantages of Corner Horns?"

 

1) They require good room corners to fully achieve their lf response, or a large footprint in order to accommodate "false corners"

 

2) They are physically large and heavy speakers if they are to reproduce all needed low frequencies (e.g., piano, organ, string bass, etc.)

 

3) They require amplifiers of high quality for the critical "first watt" of input power to achieve full potential

 

4) They require careful placement of objects and/or acoustic 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.,

 

1) The room's absolute and relative dimensions, its shape (including the ceiling), and the uniformity of the walls next to the Khorns (i.e., front and side walls near the speakers)

 

2) The placement of the speakers within that room on the boundary (e.g., tailpiece-to-corner fit to seal the two mouths of the bass bins, the length of the corner extensions from the bass bin on front and side walls, and whether there are any intrusions into the room by bricks and other architectural details (yes, brick fireplaces and mantles can significantly affect imaging...)

 

3) The absence of near-field furniture or equipment that reflect acoustic energy, and

 

4) The judicious use of acoustic treatments (...it usually doesn't take very much, but it usually takes some).

 

5) The quality of the "first watt" of amplifier power driving them

 

[Chris A]

"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. Example cases of this include the Khorn vs. the La Scala or Belle, Cornwall, Palladium or Klipsch Reference series, etc. When La Scala or Belle owners would profit in greatly increased bass performance and much lower bass IMD of their speakers if they were placed in the corners of the room, toed-in to the listening position. When these same owners are polled about where they place their speakers in-room, invariably the answer is either "along a wall" or "a few feet from the front and side walls". Why would this occur? PWK himself stated:

 

"The conclusion is pretty obvious. Whether you are using KLIPSCHORN loudspeakers, or speakers of some other make or type, you will get best stereo geometry and best tonality with corner placement of the flanking speakers (whether you use a center speaker or not). and the corner placement should be with the flanking speakers toed-in at 45 degrees." (Taken from Dope from Hope, Vol. 15, No.2, 01 August, 1975)

 

There is something involving room acoustics and corner horns that is critically important to achieving excellent corner-horn imaging. It turns out, 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.

 

Here is a correspondence from the co-inventor of the Klipschorn Jubilee (Roy Delgado):

 

"Imaging and creating it by having two varying acoustic signals is an interesting undertaking. I have found that a smooth, unobtrusive boundary between the two speakers works very well with well-behaved and consistent polar patterns [of speakers]. The other thing that I have noticed that works well is no boundaries--like playing the speakers outside. Both do a very good to excellent job of accomplishing the imaging goal, but the caveat is that no boundaries forgives non-consistent polar patterns while a smooth boundary is a strict enforcer of consistent polar patterns. Pretty cool how that happens."

 

These early reflections should be controlled (i.e., a "Zero Reflection Zone" that one acoustic panel manufacturer uses) in order to achieve much greater imaging performance with speakers in corners of rooms (especially corner horns). What is the easiest way to control these 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 "fuzz" panels and tiles that can easily be placed along side walls and front walls of the your listening room. How much? It turns out (from the Haas Effect) that controlling the early reflections should be done for about 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.

 

One way to determine how much absorption you need about the midrange horn mouth area on the front and side walls is to draw a plan view of your room (i.e., looking down on the floor plan), and draw circles from your listening position in increments of 12, 14, 16, 18, and 20 feet (4.9, 5.5, 6.1 meters). Then draw circles of 2, 4, 6, 8, etc. feet (0.6, 1.2, 1.8, etc. meters) from your midrange horn mouth locations in-room. Where the circles intersect along the walls with total path length of less than 11-22 feet (3.4-6.8 meters), mark those areas with a highlighter, then go open a bottle of wine with your spouse. Wait until the wine takes effect, then start the negotiations on how much absorbent tiles/panels are acceptable (...hopefully, the answer isn't "zero"...). I use about 2 feet (0.6 meters) of absorption at the side-wall exit area of my corner-horn midrange horns: YMMV.

 

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 (~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 areas, but note that the use of diffusers in the "Hass effect areas" will likely not achieve the same level of corner-horn imaging as the use of absorbers. More on the reasons why later.

 

If your listening position is more than 11 to 22 feet (3.4-6.8 meters) away, you probably have little work to do. 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 is spectacular in increasing your stereo imaging performance.

 

* More on the subject of horn polar control and imaging performance later.

 

"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 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 Belle, on the masonry on each side of my fireplace, and a quilt-based cloth fabric on the mantlepiece to control these 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 stereo 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".

 

"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 have Khorns, you should think about either putting absorbent material around the top/bottom mouth of the K-400 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 the reason for this 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: this is a large portion of the argument, "...Khorns require a large room...". If you are using Klipschorn Jubilees, then you can use them in a smaller room than Khorns. More on the reason why this is--later.

 

"Is All This Really Necessary?"

 

If you are trying to increase your corner-horn imaging performance: the answer is "yes" if you sit within 15 feet (4.5 meters) or so of your speakers. If you sit further back, then you probably don't have many imaging issues.

 

Next up: discussion about amplifiers and corner horns...

[Chris A]

"What about Amplifiers and Corner-Horn Imaging Performance?"

 

I've saved this juicy subject up to this point for a good reason: 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 more rational discussion on amplifier effects can be achieved.

 

"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 or 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). The Khorn, for example, converts about 10% or more of its input electrical energy into acoustic energy (according to PWK'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. BTW: the same reverb effect happens with headphones. [special thanks to Bob Carver on explaining 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 radiators are. This means that the room's reflected energy goes right back to the amplifier's output terminals.

 

"So What's the Issue with Amplifiers and Horn-Loaded Speakers?"

 

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 multi-stage 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 tries to "hold the driver diaphragm in place" against the reflected acoustic-electric energy. 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. PWK talked about measuring speakers with a "rubber yardstick" when you start to depart from a live music reproduction standard. That conversation is apropos here.

 

If accurate reproduction is the standard by which PWK 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.

 

EDIT: 7 November 2016:

 

There is more going on with higher output impedance amplifiers than just the reverb effect. If using a transconductance amplifier (also known as a "current source" amplifier) having effectively infinite output impedance, then back-EMF from the woofers and other drivers (from physical woofer/air mass and electrical reactance effects) is not fed back into the amplifier's output feedback loop, then the sound has more fidelity to the input signal.  More on this subject in the following book:

 

 

But note that the output impedance of the amplifier cannot be close to the input impedance of the loudspeaker (a rule of thumb is 8x to 10x ohms away from the maximum loudspeaker input impedance), or passive crossover filter frequency shifts will occur, along with the typical shifts in response of the loudspeaker vs. frequency.

 

"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.

 

EDIT 7 November 2016: 

 

Note that the above edit moderates the comments in this section, simply because there are both positive and negative effects of higher output impedance amplifiers--especially output impedance in range of 0.5-16 ohms.  With transconductance amplifiers, loudspeaker-induced back EMF noise is blocked by the amplifier, and this is very beneficial for fidelity.  SET-type amplifiers have higher output impedance--but not high enough output impedance--introduce issues with loudspeakers having passive crossovers. 

 

If you're using active crossovers and direct-coupling the amplifier outputs to the drivers, and are re-EQing the loudspeaker output to compensate for impedance-driven frequency response changes in your loudspeakers' outputs, then SETs can be effectively integrated without producing frequency response and crossover filter center frequency shifts.

 

"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. PWK'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 because it's easy to get large amounts of amplifier gain doing this, 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 from drifting and from uneven overall response, tend to convert otherwise low-order harmonic distortions into higher order harmonics unless relatively large amounts of feedback is used. But using large amounts of feedback negates the use of multi-stage 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.

 

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. These work very well to bypass the problems of both high output impedance SET and higher-harmonic-distortion multistage SS amplifier designs with feedback. The new JFET and MOSFET single-stage amplifiers made by Nelson Pass, in his First Watt series, that sound like tube amplifiers but are solid state AND they have relatively low output impedance AND they measure very cleanly with respect to measurable distortion, such as THD, IMD, noise, and other figures of merit. More on that subject later in this thread (ref. Nelson Pass's audibility of amplifier distortion article). 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, very short tube lives, 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.

 

Next up: discussion on the Khorn K-400 and Klipschorn Jubilee K-402 midrange horns...

[LarryC]

"So Why Do Class "A" Tube-Type Amplifiers Sound So Good With Corner Horns?"

Well, there another effect taking place - one that apparently has yet to be measured well. The acoustic effect is a "softening" on the hard-edged sound that tends to accompany multi-stage BJT solid state amplifier output.

I have read a number of times that Class A sounds purer and better because of the absence of "crossover notch distortion." This was certainly true of my SS Class A Mark Levinson ML-2 monoblocs and my current Joule Electra Class A tube monoblocs (see avatar). http://en.wikipedia.org/wiki/Crossover_distortion

[Chris A]

"So What's the Issue With the Khorn's K-400 Midrange Horn and In-Room Imaging?"

 

PWK, during his time of development of the original Klipschorn, had several constraints relating to the original midrange/tweeter horn performance (i.e., the Khorn was originally a 2-way speaker). Eventually, the recording companies in the 1950s expanded their advertised upper-frequency limit above 12 KHz to include the very limit of human hearing: ~20 KHz (measured with young adults). The constraint that he worked to was the lack of high-quality, low cost electronics to correct for the naturally drooping FR of the midrange horn in its upper FR pass band.

 

One approach was to provide passive crossover "balancing networks" that not only crossed the drivers electronically, but it also corrects for FR issues. 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, PWK pulled a horn out of the trash that had been rejected by the then-Jensen chief engineer. That horn became the K-400 horn that is used in the Khorn 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 Smith horns.]

 

The naturally falling FR of a horn (designed to output nearly constant polars) with increasing frequency was an issue then since digital active crossovers were decades away from existence and cost effectiveness. The trick of the K-400 horn is that is covers a relatively constant horizontal polar azimuth (horizontal polars) 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. This is the "collapsing polars" characteristic that is sometimes discussed on this forum.

 

"So What's The Issue With the K-400 Horn and K-Horn Imaging In-Room?"

 

This "collapsing polar" characteristic means that the K-400 horn actually begins to lose polar control of its output frequencies in the vertical axis below about 1.7 KHz - down to its design crossover frequency of 400 Hz with the Khorn 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 Khorn. 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 K-400 horn (like the Peavey QT horn) or to place diffusers or even absorption tiles on the ceiling. This would be especially true for basement-located Khorns with low ceilings.

 

Peavey QT Horn

 

"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 main tradeoffs of the K-402 horn can be summed up in multiple ways:

 

1. 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)
2. 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.
3. 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.
4. 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 and low cost digital crossovers with their embedded EQ capabilities. The advantages of active bi-amping are described in the Active Bi-amping/Tri-Amping FAQ.

 

1. It is larger than most other midrange horns, and,
2. Since it is controlling its polars in a controlled directivity fashion all the way up the passband, the driver must be EQed at ramping +6 db/octave rate 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:"TANSTAAFL".
    

Using the K402 horn and the updated Jubilee bass bin design, PWK's original Klipschorn design goal of a two-way speaker has come full circle once again in the Klipschorn Jubilee with dramatically improved imaging and soundstage performance over its predecessor design.

 

The avoidance of a tweeter/midrange crossover with the resulting midrange-tweeter driver time misalignment due to midrange and tweeter horn-mouth mounting instead of the correctly time aligned driver mounting at the center of acoustic pressure, and polar lobing issues due to vertical separation of midrange and tweeter drivers inherent in 3-way designs, results in a high-performing speaker of the consumer version of the Klipsch Jubilee, which is a two-way design.

 

The K-402 horn also allows the Jubilee to be more easily acoustically integrated into rooms due to its outstanding polar control of mid-high frequencies. The Jubilee can be placed in a smaller room than a Khorn 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.

[Chris A]

"What are the limitations of corner-horn placement in a corner?"

 

Corner horns typically need to be placed within 18 inches of each corner wall in order to pick up "boundary gain" to a major degree. The gap between the corner and the speaker will only have a negative effect on the bass performance if the bass bin is of the Khorn design, with the last fold of the horn being the corner of the room. It the Khorn's case, a tight fit into the corner is required in order to avoid a 250 Hz FR "suck out".

 

Additionally, the Khorn design (without false corner) must be placed symmetrically into the corner (i.e. at a 45 degree angle) in order to avoid the condition of the two horn mouths being different geometries. The Jubilee design (and Khorn in a false corner) allows you to position the speaker more asymmetrically in the corner in order to provide the freedom to aim the midrange/tweeter horns directly at the listening position. The advantage of aiming all horns on-axis at the listening position will show up as flatter FR at the listening position and better imaging due to the symmetry of the off-axis response about the listener's position.

 

"What About Placing my Corner Horn Speaker Along A Wall (Away From A Corner)?"

 

My experience is that you will take about a 1/2 to one octave hit on lf performance, which is a great deal of performance loss.

 

Non-corner placement of Klipschorn Jubilees

 

"What About Not Toeing-In My Speakers?"

 

This condition is actually the most serious in-room placement issue in my experience in order to achieve imaging. Imaging performance depends heavily on toe-in of your speakers, whether they are corner horns or floor-standing speakers. If you find yourself pointing your speakers in a line (i.e., zero toe-in), then you are probably dealing with severe room acoustics issues, to include objects/furniture between your speakers, a low ceiling, strong early reflections, unusual ceiling geometry like ceiling vaulting, unusual length-width-height room dimension ratios, and extremely poor power amplifier quality that masks speaker imaging.

 

The suggestion is to deal with these issues first in order to allow for speaker toe-in to achieve imaging performance.

 

"What About Twisting the Midrange/Tweeter Horn(s) to Point in a Different Direction Than the Bass Bin?"

 

Perhaps surprisingly, this technique does not work very well in my experience, although it may be related to chosen crossover frequency from the bass bin to the upper horns. My experience indicates that this doesn't work even if you are crossing at 400 Hz. The effects are a fragmentation of the acoustic image. It is tempting to do this with Khorns - a better approach is to construct shortened false corners to place your Khorns into tightly, then place the false corners within 18 inches of the corner of the room, aiming your speakers at the listening position.

 

A K-402 horn assembly twisted with respect to its bass bin

[Chris A]

Quote

I have read a number of times that Class A sounds purer and better because of the absence of "crossover notch distortion."

Larry,

I've heard this theory a number of times, however, I don't remember seeing a technical report with data showing measured psychoacoustic effects versus degree of nonlinearlity of the waveform (i.e., zero-crossing distortion).

EDIT: Note that the ear is not sensitive to phase distortion in steady-state signals, so the crossover distortion that you mention can't be the only factor in listening differences between Class "A" amplifiers and push-pull type amplifiers that exhibit crossover distortion, unless the % crossover distortion--which typically occur at micro-Watt output levels when driving horn-loaded speakers at normal consumer levels--is at least a few tenths of a percent. There is something else going on with Class "A" amplifiers relative to listening performance that helps them to sound better. (20 Dec. 2011)

EDIT: The Nelson Pass Article on audio distortion and feedback (referenced later in this thread) I believe explains a great deal more than "zero-crossing distortion" on why class A amplifiers with minimized number of amplifier stages sound so much better. The bottom line: it's all about higher order harmonics generation--which the human ear is much more sensitive to than lower-order amplifier harmonics. (6 Nov. 2012)

I also believe that there must be other IMD-related issues with multi-stage BJT amplifiers that haven't been uncovered yet. The reason why I say this is the "harshness" of BJT amplifiers indicates to me that there are higher-order transient FM effects going on based on the odd-order harmonic distortion of flat-topped amplifier clipping that is characteristic of BJT amplifiers. This is just like AM and FM distortion effects occurring with direct radiator bass bins that show up as "muddy bass" with respect to horn-loaded bass. But note: if the amplifier doesn't ever clip--because it has enough headroom to never clip--then you should never hear the difference between a high quality non-distorting tube amplifier and a BJT amplifier, unless something else is going on.

Chris

[russ69]

With a post this long somebody has to post an opposing position. Yes, widely spaced loudspeakers (cornerhorns) can have good imaging. However it's been my experience that planer speakers and line source speakers excel in creating a superior 3D space IMHO. I'm not knocking Klipsch, just relating my limited experience.

[Ski Bum]

Yeah, SETs suck to a dogmatic engineering mindset. My brain likes ambience, even if it is simply my SETs playing the room response back at me.

I auditioned a Pass amp. It was very, very nice. But I had to pass on the Pass. Way too expensive, and I'd rather take a ski trip to Verbier for that kind of dough. The Alps kick ***, if you ski.

For the price of that one amp, I could outfit several rooms of the house with used Cornwalls and SET amps.

[LarryC]

Only question: what does BJT stand for? Thanks.

Larry

[Chris A]

Only question: what does BJT stand for? Thanks.

Bipolar Junction Transistor, i.e., a "transistor amplifier". Field-Effect Transistors (FETs) have different characteristics than BJTs.

[to Ski Bum's comment...] By the way, Pass Labs is not the same company (or product line) as First Watt, even though Nelson Pass has a hand in both enterprises. Their pricing structure is much different.

Chris

Edited October 25, 2013 by Cask05

[davis419b]

Hey Chris,

Great infomation ! Answers alot questions I have had over the last 3 years of owning Khorns. I use class a tube monoblocks and just love the sound but I still have a long way to go. I really want to get into the room treatment thing but havent got a clue what to do. I sure wished you did housecalls. As I have told you before I sure would like to hear your Jubilees but am affraid I would get hooked but I may have to do it anyway. I am enjoying this info please keep it coming.

Thanks, Don

[Chris A]

Quote

However it's been my experience that planar speakers and line source speakers excel in creating a superior 3D space IMHO.

My intent was to raise the awareness of the sensitivity of corner horn speakers to room acoustics. Perhaps your experiences with Klipschorns and Jubilees were not as good from the standpoint of room acoustics, and source material?

 

EDIT: I find that artificial "depth perception" created by speakers, especially flat panel speakers, is the result of delayed reflections off of the front and side walls. This is due to the spilling of speaker acoustic midrange energy in the ~250 to ~5000 Hz range into the walls and placement of the speakers away from the walls. "Ambiance" is usually restricted to those even-more-delayed reflections off of the rear wall and multiple-bounce modes off two or more walls+ceiling+floor).

 

The problem with speakers spilling their energy into close acoustic reflectors in the room is that these strong early reflections are not representative of the original recorded material being played into the speakers by good electronics. This technique may bring an increase sense of depth to the recordings that wasn't put there by the recording engineers, but it also usually results in timbre shift of the speakers, and increased problems with low-frequency balancing of woofers and subwoofers to match phase at all crossover-band frequencies, which usually results in spotty and heavy bass reproduction in order to cover the bass weakness of the flat panels. [2 December 2011)

 

Dipole planar speakers have to stand out in the room away from any early reflectors, and really cannot be effectively toed-in. They have an extremely narrow "sweet spot" (you cannot be off-axis when listening) but they give the impression of a deep soundstage: this is probably due to the long delayed reflections from the front wall since these speakers have to be placed out into the room at least 6 feet (1.8 meters).

 

I truly wish that you could hear Jubs as I've set them up in-room with acoustic treatments. You might be very surprised at their imaging performance.

 

Chris

[russ69]

They have an extremely narrow "sweet spot" (you cannot be off-axis when listening) but they give the impression of a deep soundstage.

We use the term "head in a vice", the sweet spot is very narrow. It's a trade off, a very serious trade off. Maybe that's why my Klipsch systems get more play time?

[RRFL]

Thank you Chris.

[mark1101]

This was a fun read. Thanks for compiling.

[Chris A]

I sure wished you did housecalls.

I could be tempted... []

As I have told you before I sure would like to hear your Jubilees but am afraid I would get hooked...but I may have to do it anyway.

You could be tempted.

[LarryC]

Only question: what does BJT stand for? Thanks.

By the way, Pass Labs is not the same company (or product line) as First Watt, even though Nelson Pass has a hand in both enterprises. You might do a little checking before typing. Their pricing structure is much different.

I didn't post anything about Pass Labs or First Watt. Somebody else.

[davis419b]

I sure wished you did housecalls.

I could be tempted...

As I have told you before I sure would like to hear your Jubilees but am afraid I would get hooked...but I may have to do it anyway.

You could be tempted.

You tempt me and I will tempt you double ! Hows that for temptation ?

[Chris A]

Quote

I didn't post anything about Pass Labs or First Watt. Somebody else.

Sorry--I combined my responses for the sake of "economy of key-clicks"...

EDIT: I have edited my response to reflect this. (2 December 2011)

Chris