Klipsch Heresy IV Speaker Review

  • Wednesday, Nov 25, 2020


The Klipsch Heresy IV is a 3-way speaker with a classic look. The Heresy IV features a 12-inch midwoofer, K-702 midrange compression driver, and K-704 Tractrix horn for high frequencies. On the back of the speaker is Klipsch’s new element to this speaker lineup: the Klipsch Tractrix port. This speaker can be bi-amped if desired thanks to the links on the two sets of terminals above the rear port. The Heresy IV comes in a variety of finishes and features a tweed grille to hide the drive units. The model I tested is in the Cherry finish.

YouTube Video Review

I won’t get in to all the details of the speaker’s makeup as that can be found on the specification page here, or in the provided screenshot below. I would rather spend my time in this review discussing the performance.


BUT! I will provide some of my own photos…

grille on

grille off



Tweeter close-up:

tweeter close

Midrange close-up:

midrange close

Inside the cabinet, looking up toward the midrange and tweeter compression drivers. Note the extensive use of foam padding in the top half:

Inside Upwards

Inside the cabinet, looking toward the port. Notice there is little acoustic treatment here (some on the backwall and a small portion on the right side-wall):

Inside port

Close-up of the crossover:


Speaker terminals:


Grille with the Klipsch Heresy logo:

grille close up

Aesthetics are always a very personal thing. Some may not like the look of this speaker, but I do. I also fancy a lot of other designs that are flashier. This speaker is the opposite of flashy, though, yet I still appreciate its retro aesthetic.

Objective Data

Unless otherwise noted, all the data below was captured using Klippel Distortion Analyzer 2 and Klippel modules (TRF, DIS, LPM, ISC to name a few). Most of the data was exported to a text file and then graphed using my own MATLAB scripts in order to present the data in a specific way I prefer. However, some is given using Klippel’s graphing.

Foreword: Subjective Analysis vs Objective Data (click for more)
If you have seen my past reviews, you know that I am of the mindset that objective data is at least as important as someone's subjective evaluation of a speaker. If not more. Why? Because every room is different. Every listener is different. Some know what to listen for. Others know what they want to hear based on their own preference (i.e., some prefer extended bass, some prefer more midbass punch between 120-150Hz, some prefer a response with a dip around 4kHz, etc., etc.). What one person wants or expects may be opposite of another. Additionally, the room will impact the performance and therefore what the listener hears. This means when you read another's subjective-only review you are left to resolve those variables on your own. That's not likely to happen. Unless there is objective data you can use to get an idea of the performance. With objective data you can begin to understand why the subjective review turned out the way it did. Notably, objective data keeps reviewers honest. It's hard for a reviewer to legitimately bash one product but elevate another when the two measure practically the same in every regard. Not to say two similarly measuring speakers cannot subjectively sound different. Though, odds are if they do measure the same then a huge subjective difference is most likely attributed to other issues such as setup conditions, bias, etc. Objective data is the key to accountability. Simply put: if the measurements are taken with care and you understand them, you can rely on data to help paint a more accurate description of performance than a few adjectives from your favorite reviewer (myself included). As you will see, objective measurements can provide a lot of insight in to how the speaker will perform in your room.

However, when possible, it is always best to demo speakers in your own room. Not simply because of subjective performance. But because of other factors such as aesthetics, pride of ownership, etc. In my experience, all these factors play in to how the listener “connects” with the system. A good shop or manufacturer understands this and allows buyers to try items out at home before purchasing or they offer a reasonable return policy. If you question the performance and can demo the speakers in your own home, I suggest you take advantage of the opportunity.

For all the reasons listed above: What I provide here is objective-heavy analysis. I still provide my own subjective experience but with in-room measurements at my listening position(s) so we can understand why I heard what I heard. Is it the room, the actual speaker itself, my brain, or a combination?

Now that you understand my motives, let’s get started with the review.

Impedance Phase and Magnitude:

Impedance measurements are provided both at 0.10 volts RMS and 2.83 volts RMS. The low-level voltage version is standard because it ensures the speaker/driver is in linear operating range. The higher voltage is to see what happens when the output voltage is increased to the 2.83vRMS speaker sensitivity test.


Impedance vs FR

Frequency Response:

Notes about measurements (click for info)

Frequency response data (horizontal, vertical, “Spinorama”, polar, spectrograms, etc.) are all based on a 2.83 volts RMS logarithmic sweep at 1 meter to meet the standard sensitivity measurement spec. Depending on the speaker, I may measure at a further distance but the data is still referenced to 1 meter. These data are captured using Klippel’s TRF module and a mixture of ground-plane measurement and 4-pi free-field measurement. Klippel’s In-Situ Room Compensation (ISC) module is then used with the ground plane measurement to provide a ‘reference’ curve to the 4-pi measurement which then corrects for the room’s influence and allows me to generate a reflection-free far-field response from an indoors measurement. Note: This is not a standard merge of nearfield and farfield nor a merge of ground-plane and farfield. Typical merged responses still suffer low resolution in the midrange where the response is merged due to the necessity of windowing the impulse response to remove reflections. One major downside to “gating” or “windowing” the impulse response is this low-resolution does not show resonance in the midrange. For example, most free-field measurements are only reflection-free until approximately 3 milliseconds, or about 300Hz. That means a data point every 300Hz. If you have a high-Q resonance at 450Hz the 300Hz resolution data will not show this resonance because the frequency resolution only has a data point at 300Hz and 600Hz; skipping right over the 450Hz. You would need a resolution of at least a half the width of the Q-factor; generally, 20Hz is adequate. However, 20Hz resolution is roughly 50ms of window-free response. The only way to achieve this is in a large parking lot or open field. Ground plane measurements are perfect for this but are subject to aiming/ground absorption (grass) and related issues above 400Hz. The ISC module permits results with as-close-to-anechoic as one can achieve without being anechoic. Thanks to the ISC module, the data I am providing here is higher resolution (~30Hz resolution) than an average person can provide without access to an anechoic chamber or the like.

The measurement below provides the frequency response at the reference measurement axis - also known as the 0-degree axis or “on axis” plane - in this measurement condition was situated at the tweeter. I did reach out to Klipsch directly - both via email and twitter - to ask what the designed reference axis was but received no reply. Per my research it seems everyone listens to these speakers on the tweeter axis (typical) so I proceeded with my measurements in that fashion.

The speaker was measured without the grille in place. I did not have the time to measure with the grille in place.

fr horz

Below are both the horizontal and vertical response over a limited window (90° horizontal, ±40° vertical). I have provided a “normalized” set of data as well. The normalization simply means that I took the difference of the on-axis response and compared the other axes’ measurements to the on-axis response which gives the viewer a good idea of the speaker performance, relative to the on-axis response, as you move off-axis.

fr horz

fr horz norm

fr vert

fr vert norm

As I said above, the provided frequency response graphs were given with a limited set of data. I measured the response of the speaker’s vertical and horizontal axis in 10-degree steps over 360-degrees. Nearly 70 measurements in total are represented in my data. As you can imagine, providing all those data points in a single FR-type graphic below is a bit overwhelming and confusing for the viewer. A spectrogram is an alternate way to view this full set of data. This takes a 360-degree set of data and “collapses” it down to a rectangular representation of the various angles’ SPL. I have provided two sets of data: one set for horizontal and one for vertical. Each set consists of 2 graphics:

  1. Full response (20Hz - 20kHz with the angles from 0° to ±180°) with absolute SPL values
  2. Full, “normalized” response (20Hz - 20kHz with the angles from 0° to ±180°) with SPL values relative to the 0-degree axis

Normalized plots make it easier to compare how the speaker’s off-axis response behaves relative to the on-axis response curve.

spec horz

spec horz norm

spec vert

spec vert norm

The above spectrograms are the standard way of providing directivity graphics by most reviewers. Some prefer not to normalize the data. Some prefer to normalize the data. Either way, it’s a useful visual to get an idea of the directivity characteristics of a speaker or driver.

However, these “collapsed” representations of the sound field are not very intuitively viewed. At least not to me. So, I came up with a different way to view the speaker’s horizontal and vertical sound field by providing it across a 360° range in a globe plot below. I have provided both an absolute SPL version as well as a normalized version of both the horizontal and vertical sound fields.

Note the legend provided in the top left of each image which helps you understand speaker orientation provided in my global plots below.

360 horz polar

360 horz polar norm

360 vert polar

360 vert polar norm

CEA-2034 (aka: Spinorama):

The following set of data is populated via 360-degree, 10° stepped, “spins” from vertical and horizontal planes resulting in 70 unique measurements. Thus, this is sometimes referred to as “Spinorama” data. Audioholics has a great writeup on what these data mean (link here) and there is no sense in me trying to re-invent the wheel so I will reference you to them for further discussion. However, I will explain these curves lightly and provide my own spin on what they mean (pun totally intended). Sausalito Audio also has a good write-up on these curves here. Furthermore, you can find discussion in Dr. Floyd Toole’s book “Sound Reproduction”. Here’s my Amazon affiliate link if you want to purchase it and help me earn about 2% of the price. And, finally, here is a great video of Dr. Toole discussing the use of measurements to quantify in-room performance.

In short, the CEA-2034 graphic below takes all the response measurements (horizontal and vertical) and applies weighting and averaging to sub-sets and can help provide an (accurate) prediction of the response in a typical room. If there is a single set of data to use in your purchase decision, this is probably it.

Alternatively, click this arrow, if you want my quick take on what these curves mean without going to another site.
  • On-Axis is simply the on-axis response. This is the 0-degree response curve.
  • Listening Window is an average of the 0° to ±30° horizontal and 0° to ±10° vertical response curves and is used to understand what listeners typically hear in a home at the sweet spot, or Main Listening Position (MLP). The reason for this extended window of sound is simply because your room makeup might differ from another’s. This curve is an attempt to quantify a speaker’s performance over a smaller window that is often the norm for listening angle differences in various homes. It is important for this curve to very closely mimic the on-axis response. Deviations of the Listening Window curve relative to the on-axis response curve indicates a compromise in the speaker; often caused by directivity changes (as a speaker transitions from one drive-unit to another a la midwoofer to tweeter, or as a tweeter’s response becomes highly directional).
  • Early Reflections is very useful because it helps us determine how the room’s influence will alter (corrupt, most of the time) the direct (on-axis) response. Ideally, the speaker radiates sound uniformly with no aberrations; no resonance, no directivity changes as the speaker transitions from the mid to the tweeter and so on. Because speakers often have these issues, however, what is reflected to us from the walls, ceiling and floor is not the same as what we hear from the on-axis, direct sound. And that’s a problem. Why is that a problem? As stated in Dr. Toole’s book “these are very influential in establishing timbral and spatial qualities”. Large deviations in this relative to the on-axis response also indicate areas where the room is of consequence. Also, it is important to understand the Early Reflections response is made up of rear-firing sounds. A speaker drive-unit is omnidirectional (radiating in all angles evenly) until the half-wavelength equals that of the drive-unit diameter. When the diameter is larger than the wavelength being played, the sound transitions from omnidirectional to directional; also known as “beaming”. Even tweeters beam. For example, a 1-inch dome tweeter will beam at approximately 6750Hz (speed of sound ÷ 2 ÷ diameter). In most speakers you have a single tweeter, firing forward. You can imagine that the high-frequency response in the front of the speaker would therefore be quite different than what is measured behind the speaker. So, being that the Early Reflections curve includes rear-hemisphere measurements you can understand that the high-frequency response would slope downward vs the on-axis response. This is understood and accepted.
  • Predicted In-Room Response curve has the benefit of showing directivity mismatches at the crossover as well as resonances easily by comparing them to the overlaid Target curve (further down).
  • Directivity Index (DI) curves are the difference in the Listening Window and the respective Early Reflections or Sound Power curves. My understanding, currently, is the Sound Power and Sound Power DI aren’t quite as useful for typical homes. However, there is emphasis placed on the Early Reflections DI curve. The right Y-Axis provides a value associated with the DI curves. The higher the number, the more directional the speaker. For example: a “0” DI curve - a curve which is completely flat - would be a speaker that is purely omnidirectional; radiating uniformly in all angles vertically and horizontally. A speaker that increases over frequency means that it is radiating in a tighter window as you increase in frequency. This is typical because, as I discussed above, even tweeters beam… and most speakers have a single tweeter facing the front and therefore, the speaker becomes directional at whatever the tweeter’s beaming frequency is. There isn’t necessarily a one-size-fits-all DI curve value. Though, it seems people (myself included) prefer a speaker with a wider soundstage which is found in lower directivity speakers (because more sound is bouncing off the side walls; which confuses the use of side-wall absorption but that’s for a later debate). However, what is important is that the curve, however tall you may prefer it to be, is smooth; almost linear. Dips and peaks mean that something, not good, is going on. But a linear curve indicates excellent transition through crossover regions, no resonance, etc. Since speakers are not perfect, though, linear DI curves are not the norm. Speakers become directional as they increase in frequency, around strong resonances, and as the sound transitions at the crossover from one drive-unit to another and you wind up with areas with peaks and/or dips whether they’re spread through a wide frequency range (low-Q) or very sharp/drastic (high-Q). But when you’re looking at the Early Reflections DI curve, look for this: smooth.

Below is a breakout of the typical room’s Early Reflections contributors (floor bounce, ceiling, rear wall, front wall and side wall reflections). From this you can determine how much absorption you need and where to place it to help remedy strong dips from the reflection(s). In this case, the listening room would benefit from having at least a carpeted floor and, if willing to do so, acoustic absorption on the ceiling between the listener and the speakers.

early reflections

And below is the Predicted In-Room response compared to a general target curve equaling -1dB/octave.

predicted vs target

You may ask just how useful the above prediction is. Well, I’d be remiss for not delving in to that a little bit here. Please see my Analysis section below for discussion on this.

Harmonic Distortion:

Measurements were conducted at 2 meters ground plane using Klippel’s TRF module. Multiple output levels were tested to provide the trend of distortion component profiles and to provide a comparison against other drive units I have tested. The SPL provided is relative to 1 meter distance, averaged in the noted bandpass region.


Maximum Long Term SPL:

The below data provides the metrics for how Maximum Long Term SPL is determined. This measurement follows the IEC 60268-21 Long Term SPL protocol, per Klippel’s template, as such:

  • Rated maximum sound pressure according IEC 60268-21 §18.4
  • Using broadband multi-tone stimulus according §8.4
  • Stimulus time = 60 s Excitation time + Preloops according §18.4.1

Each voltage test is 1 minute long (hence, the “Long Term” nomenclature).

The thresholds to determine the maximum SPL are:

  • -20dB Distortion relative to the fundamental
  • -3dB compression relative to the reference (1V) measurement

When the speaker has reached either or both of the above thresholds, the test is terminated and the SPL of the last test is the maximum SPL. In the below results I provide the summarized table as well as the data showing how/why this SPL was deemed to be the maximum.

This measurement is conducted once with a 20Hz to 20kHz multitone stimulus.

You can watch a demonstration of this testing via my YouTube channel: https://youtu.be/iCjJufvW0IA

Test 1: 20Hz to 20kHz

Multitone compression testing. The red line shows the final measurement where either distortion and/or compression failed. The voltage just before this is used to help determine the maximum SPL.


Multitone distortion testing. The dashed blue line represents the -20dB (10% distortion) threshold for failure. The dashed red line is for reference and shows the 1% distortion mark (but has no bearing on pass/fail). The green line shows the final measurement where either distortion and/or compression failed. The voltage just before this is used to help determine the maximum SPL.


The above data can be summed up by looking at the tables above but is provided here again:

  • Max SPL for 20Hz to 20kHz is approximately 110dB @ 1 meter. The compression threshold was exceeded above this SPL.

Extra Measurements:

Nearfield measurements.

Mic placed about 0.50 inches - relative to the baffle - from each drive unit and port. While I tried to make these as accurate in SPL as I could, I cannot guarantee the relative levels are absolutely correct so I caution you to use this data as a guide but not representative of actual levels (measuring in the nearfield makes this hard as a couple millimeters’ difference between measurements can alter the SPL level).



step response

Cumulative Spectral Decay (CSD).

I normally don’t provide CSD data but in this case, it’s a fine example of how the data (when presented correctly) can provide more insight into cabinet resonances. You can see in the below graphic a lingering resonance at both ~120Hz and in the 400-600Hz region.


Extra Measurements Revisited: Midwoofer Transducer Thiele-Small Parameters and Non-Linear Performance

Click here for additional testing. Currently hidden because it's very in-depth and some may have no interest in this level of analysis.

This speaker’s 12-inch midwoofer was removed from the enclosure and placed on my Klippel test stand (as shown below). Klippel’s LPM Module was used to provide the midwoofer’s T/S parameters provided in the table below. This is done simply to give us an idea of the woofer’s parameters before it goes into the enclosure. It doesn’t change the result. It does, however, satisfy some curiosities I know some of you will have.


Small Signal Testing (Thiele-Small Results)

Using Klippel’s Distortion Analyzer 2, Linear Lumped Parameter Measurement Module, Pro Driver Stand and provided Panasonic ANR12821 Laser along with Klippel’s Training 1 - Linear Lumped Parameter Measurement tutorial, I measured this drive unit’s impedance and small-signal parameters. Below are the results.

Electrical Parameters
Re 3.72 Ohm electrical voice coil resistance at DC
Le 0.420 mH frequency independent part of voice coil inductance
L2 0.739 mH para-inductance of voice coil
R2 10.70 Ohm electrical resistance due to eddy current losses
Cmes 470.24 µF electrical capacitance representing moving mass
Lces 31.23 mH electrical inductance representing driver compliance
Res 72.74 Ohm resistance due to mechanical losses
fs 41.5 Hz driver resonance frequency
Mechanical Parameters
(using laser)
Mms 49.807 g mechanical mass of driver diaphragm assembly including air load and voice coil
Mmd (Sd) 36.919 g mechanical mass of voice coil and diaphragm without air load
Rms 1.456 kg/s mechanical resistance of total-driver losses
Cms 0.295 mm/N mechanical compliance of driver suspension
Kms 3.39 N/mm mechanical stiffness of driver suspension
Bl 10.292 N/A force factor (Bl product)
Lambda s 0.010 suspension creep factor
Loss factors
Qtp 0.434 total Q-factor considering all losses
Qms 8.925 mechanical Q-factor of driver in free air considering Rms only
Qes 0.456 electrical Q-factor of driver in free air considering Re only
Qts 0.434 total Q-factor considering Re and Rms only
Other Parameters
Vas 107.1385 l equivalent air volume of suspension
n0 1.617 % reference efficiency (2 pi-radiation using Re)
Lm 94.29 dB characteristic sound pressure level (SPL at 1m for 1W @ Re)
Lnom 94.60 dB nominal sensitivity (SPL at 1m for 1W @ Zn)
Sd 506.71 cm² diaphragm area

Using Klippel’s Distortion Analyzer 2, Large Signal Identification Module, Pro Driver Stand and provided Panasonic ANR12821 Laser along with Klippel’s Training 3 - Loudspeaker Nonlinearities tutorial, I measured the linear, nonlinear and thermal parameters of this drive unit.

Large Signal Modeling (Linear Xmax Results)


Traditionally, Xmax has been defined in one of the following ways:

  • the physical overhang of the voice coil (height of the voice coil relative to height of the gap)
  • 115% times the physical overhang above
  • the point where displacement limit(s) is/are exceeded

The third option is where the Klippel LSI module comes in to play. It permits a more “apples to apples” approach of defining the displacement (Xmax) limits based on the XBL, XC, XL and Xd. The displacement limits XBL, XC, XL and Xd describe the limiting effect for the force factor Bl(x), compliance Cms(x), inductance Le(x) and Doppler effect, respectively, according to the threshold values Blmin, Cmin, Zmax and d2 used by the operator.

There are one of two sets of thresholds which can be used to define linear excursion:

  1. Non-Subwoofer Drivers: The thresholds Blmin= 82 %, Cmin=75 %, Zmax=10 % and d2=10% generate for a two-tone-signal (f1=fs, f2=8.5fs) 10 % total harmonic distortion and 10 % intermodulation distortion.
  2. Subwoofer Drivers: The thresholds Blmin= 70 %, Cmin=50 %, Zmax=17 % create 20 % total harmonic distortion which is becoming the standard for acceptable subwoofer distortion thresholds.

These parameters are defined in more detail in the (Klippel) papers:

  • “AN04 – Measurement of Peak Displacement Xmax”
  • “AN05 - Displacement Limits due to Driver Nonlinearities”
  • “AN17 - Credibility of Nonlinear Parameters”
  • “Prediction of Speaker Performance at High Amplitudes”
  • “Assessment of Voice Coil Peak Displacement Xmax”
  • “Assessing Large Signal Performance of Loudspeakers”

Below are the displacement limits’ results for this drive unit obtained from Klippel’s LSI module:

Displacement Limits
X Bl @ Bl min=82% >3.5 mm Displacement limit due to force factor variation
X C @ C min=75% 2.0 mm Displacement limit due to compliance variation
X L @ Z max=10 % 2.7 mm Displacement limit due to inductance variation
X d @ d2=10% 23.5 mm Displacement limit due to IM distortion (Doppler)
Asymmetry (IEC 62458)
Ak 74.10 % Stiffness asymmetry Ak(Xpeak)
Xsym -0.70 mm Symmetry point of Bl(x) at maximal excursion

Per the above table, this drive unit’s linear excursion is limited to 2.0mm due to exceeding the compliance variation displacement limit of 10% for the distortion limit of 10%.

We can break the above information down further. The below text is written by Patrick Turnmire of Red Rock Acoustics and used with his permission, substituting data from this drive unit’s test results where applicable.

Large Signal Modeling

At higher amplitudes, loudspeakers produce substantial distortion in the output signal, generated by nonlinear ties inherent in the transducer. The dominant nonlinear distortions are predictable and are closely related with the general principle, design, material properties and assembling techniques of the loudspeaker. The Klippel Distortion Analyzer combines nonlinear measurement techniques with computer simulation to explain the generation of the nonlinear distortions, to identify their physical causes and to give suggestion for constructional improvements. Better insight into the nonlinear mechanisms makes it possible to further optimize the transducer in respect with sound quality, weight, size and cost.

Nonlinear Characteristics

The dominant nonlinearities are modelled by variable parameters such as

Bl(x) instantaneous electro-dynamic coupling factor (force factor of the motor) defined by the integral of the magnetic flux density B over voice coil length l as a function of displacement
KMS(x) mechanical stiffness of driver suspension a function of displacement
LE(i) voice coil inductance as a function of input current (describes nonlinear permeability of the iron path)
LE(x) voice coil inductance as a function of displacement

Nonlinear Parameters

Bl change with excursion


The electrodynamic coupling factor, also called Bl-product or force factor Bl(x), is defined by the integral of the magnetic flux density B over voice coil length l and translates current into force. In traditional modeling this parameter is assumed to be constant. The force factor Bl(0) at the rest position corresponds with the Bl-product used in linear modeling. The red curve displays Bl over the entire displacement range covered during the measurement. You see the typical decay of Bl when the voice coil moves out of the gap. At the end of the measurement, the black curve shows the confidential range (interval where the voice coil displacement in this range occurred 99% of the measurement time). During the measurement, the black curve shows the current working range. The dashed curve displays Bl(x) mirrored at the rest position of the voice coil – this way, asymmetries can be quickly identified. Since a laser was connected during the measurement, a coil in / coil out marker is displayed on the bottom left / bottom right.

Suspension Stiffness change with excursion


The stiffness KMS(x) describes the mechanical properties of the suspension. Its inverse is the compliance CMS(x).

Inductance change with excursion



The inductance components Le (x) and Bl(i) of most drivers have a strong asymmetric characteristic. If the voice coil moves towards the back plate the inductance usually increases since the magnetic field generated by the current in the voice coil has a lower magnetic resistance due to the shorter air path. The nonlinear inductance Le(x) has two nonlinear effects. First the variation of the electrical impedance with voice coil displacement x affects the input current of the driver. Here the nonlinear source of distortion is the multiplication of displacement and current. The second effect is the generation of a reluctance force which may be interpreted as an electromagnetic motor force proportional to the squared input current.

The flux modulation Bl(i) has two effects too. On the electrical side the back EMF Bl(i)*v produces nonlinear distortion due to the multiplication of current i and velocity v. On the mechanical side the driving force F = Bl(i)*i comprises a nonlinear term due to the squared current i. This force produces similar effects as the variable term Le(x).

Asymmetrical Nonlinearities

Asymmetrical nonlinearities produce not only second- and higher-order distortions but also a dc-part in the displacement by rectifying low frequency components. For an asymmetric stiffness characteristic the dc-components moves the voice coil for any excitation signal in the direction of the stiffness minimum. For an asymmetric force factor characteristic the dc-component depends on the frequency of the excitation signal. A sinusoidal tone below resonance (f<fS) would generate or force moving the voice coil always in the force factor maximum. This effect is most welcome for stabilizing voice coil position. However, above the resonance frequency (f>fS) would generate a dc-component moving the voice coil in the force factor minimum and may cause severe stability problems. For an asymmetric inductance characteristic the dc-component moves the voice coil for any excitation signal in the direction of the inductance maximum. Please note that the dynamically generated DC-components cause interactions between the driver nonlinearities. An optimal rest position of the coil in the gap may be destroyed by an asymmetric compliance or inductance characteristic at higher amplitudes. The module Large Signal Simulation (SIM) allows systematic investigation of the complicated behavior.

Bl symmetry xb(x)

This curve shows the symmetry point in the nonlinear Bl-curve where a negative and positive displacement x=xpeak will produce the same force factor Bl(xb(x) + x) = Bl(xb(x) – x).

If the shift xb(x) is independent on the displacement amplitude x then the force factor asymmetry is caused by an offset of the voice coil position and can be simply compensated.

If the optimal shift xb(x) varies with the displacement amplitude x then the force factor asymmetry is caused by an asymmetrical geometry of the magnetic field and cannot completely be compensated by coil shifting.


Kms Symmetry xc(x)

This curve shows the symmetry point in the nonlinear compliance curve where a negative and positive displacement x=xpeak will produce the same compliance value kms(xc(x) + x) = kms(xc(x) – x).

A high value of the symmetry point xc(x) at small displacement amplitudes x » 0 indicates that the rest position does not agree with the minimum of the stiffness characteristic. This may be caused by an asymmetry in the geometry of the spider (cup form) or surround (half wave). A high value of the symmetry point xc(x) at maximal displacement x» xmax may be caused by asymmetric limiting of the surround.


Objective Data Analysis/Evaluation:

Frequency Response:

  • The mean SPL, approximately 94dB at 2.83v/1m, is calculated over the frequency range of 300Hz to 3,000Hz.
  • The on-axis frequency response is extremely non-linear, measuring +3dB/-4dB above 74Hz.
  • The speaker’s F3 point (the frequency at which the response has fallen 3dB relative to the calculated mean SPL) is 74Hz.
  • The F10 (the frequency at which the response has fallen by 10dB relative to the mean SPL) is 47Hz.
  • The nearfield responses show many issues which turn up as resonances in the frequency response. For example, the port has significant resonance above 200Hz over multiple octaves that contributes to peaks/dips from 300Hz to 1kHz. The woofer shows breakup at ~1.3kHz and again at ~6.5kHz which affect the frequency response measurements and drive the uneven tonal balance of this speaker. Multiple diffraction effects appear to be borne from the termination point of the horn/compression driver throat.

Impedance/Amplifier Requirements:

  • There are a couple areas that show up as resonance in the impedance/frequency response measurements. ~120Hz and ~400-600Hz both show signs of resonance (the former being very audible in my listening evaluations).
  • The tuning frequency of the enclosure is approximately 35Hz.
  • The minimum impedance dips to about 3.6 Ohms below 5Hz so keep this in mind. But, realistically, this speaker is closer to a 5 Ohm nominal load. Thanks to their higher sensitivity, a standard AVR should be able to drive these to nominal playback levels but make sure to check the specs of the AVR and use an online calculator to determine if it has enough power to drive the speaker to the level you need at your listening position.

Distortion/Max SPL:

  • At 100dB at 1 meter (which is equivalent to 88dB at 4 meters), the low frequency distortion increases but is still respectably low between 1-3% THD from 50Hz to 200Hz.
  • There is a glaring HD profile increase around 800Hz. I presume this to be the midrange compression driver. This distortion level reaches 8% THD at 100dB at 1 meter and increases to as much as 14% at 104dB.
  • The max SPL measured is 110dB (mean) at 1 meter. So far, this is the highest max SPL achieved by any of my test subjects, besting the previous winner by about 4dB. Keep in mind that these speakers can play louder than 110dB. The test setup and conditions are described in the appropriate section above. This simply gives me a way to provide an apples-to-apples comparison against other test subjects.

Dispersion and Off-Axis Response:

  • Horizontal dispersion varies by frequency thanks to resonance and directivity mismatches. Though, the mean horizontal dispersion window is about ±50° below 10kHz .
  • Vertical dispersion varies by frequency thanks to resonance and directivity mismatches. Though, the mean horizontal dispersion window is about ±30° below 10kHz.
  • This unevenness tends to cause the soundstage to behave quite erratically causing some instruments to be placed throughout the soundstage differently from the fundamental to the harmonics, driving imaging inaccuracies as well.
  • Some DSP can be used to smooth out these problem areas (wherever the Directivity is relatively flat is a good candiate for DSP correction). For example, a portion of the 300-500Hz resonance can be tamed. But there are many directivity mismatches that would make this task more challenging. If not for the resonances, however, this task would be much easier.

Spinorama and Predicted In-Room Response:

  • No way to sugarcoat this: the SPIN data results in a very uneven response riddled with mismatches in driver-to-driver directivity as well as numerous resonances. From on-axis to listening window to predicted in-room response.
  • The midwoofer to midrange crossover region indicates a directivity mismatch.
  • Though, the midrange to tweeter crossover region looks relatively benign and indicates a fair match in their directivity profiles.
  • The port resonance discussed above shows up clearly in this SPIN data in the 500Hz region and tended to make voices sound boxy. In combination with the 200-500Hz dip in response this resonance was even more pronounced.
  • The predicted in-room response indicates a peaky 1-2kHz region (which results in a “forward” sound; verified in my listening evaluations). I’m mentioning this specifically because this area was the most bothersome to my ears.

Subjective Evaluation:

Now that we have gotten through all the data, let’s talk about what I heard!

I listen to speakers in two different rooms: my home theater room and my living room. I have provided a layout of the home theater below. And below that is a picture of the speakers set up in my living room. This gives you an idea of the actual environments these were auditioned in.

Home Theater layout:

room layout

Per the illustration, I built a false wall and used an acoustically transparent screen with speakers behind it. The wall is only 2x4's; no panels of wood or anything. Just a skeleton of a wall to give me something to attach the screen and acoustic treatment to. There is 2-inch wedge foam affixed to the 2x4 studs and between the false wall and back of the room are the front speakers (L/C/R & 18-inch subwoofers).

Living Room setup:

No pictures this time. The house is a mess and if my wife found out I shared photos of our living room in total disarray I might not live to write another review.

Subjective Analysis Setup:

  • The speaker was aimed on-axis with the vertical listening axis on the tweeter axis.
  • I used Room EQ Wizard (REW) and my calibrated MiniDSP UMIK-1 to get the volume at the seated position between 85-90dB on average. In a poll I found most listen to music in this range. Though, I often listened at higher and lower volumes.
  • All speakers are provided a relatively high level of Pseudo Pink-Noise for a day or two - with breaks in between - in order to calm any “break-in” concerns.
  • I demoed these speakers without a high-pass crossover. I did not use room correction on these speakers.
  • Components: Oppo BDP-103, AppleTV 4k, Adcom GFA-545 II, Crown XLS 1002, Denon X4000 AVR.
  • Speaker placed on the floor (as Klipsch marketing implies is ideal) as well as on stands. Near and far from walls (see notes for more info).

I initially listened to these speakers and made my subjective notes before I started measuring objectively. I did not want my knowledge of the measurements to influence my subjective opinion. This is important because I want to try to correlate the objective data with what I hear in my listening space in order to determine the validity of the measurement process. I try to do a few listening sessions over a couple days so I can give my ears a break and come back “fresh”.

My demo music:

I auditioned these speakers numerous times over the span of a few weeks. While the list below is my primary auditioning music, I ultimately listened to many, many more tracks spanning various genres.

Title Artist Album
Enjoy The Silence Depeche Mode Best Of Depeche Mode, Vol. 1
Higher Love Steve Winwood Back In The High Life (MFSL UDCD-611)
24K Magic Bruno Mars 24K Magic
Magic The Cars Heartbeat City (MFSL)
Everlasting Love Howard Jones The Best of Howard Jones
Kodachrome Paul Simon There Goes Rhymin’ Simon
Everybody Wants To Rule The World Tears for Fears Songs from the Big Chair (2014 Deluxe Edition - Disc 1)
Know Your Enemy Rage Against The Machine Rage Against The Machine (Hybrid SACD)
Doo Wop (That Thing) Lauryn Hill The Miseducation of Lauryn Hill
Tell Yer Mama Norah Jones The Fall
Don’t Save Me HAIM Days Are Gone
He Mele No Lilo Mark Keali’i Ho’omalu and Kamehameha Schools Children’s Chorus Lilo And Stitch
Wrapped Around Your Finger The Police Synchronicity
Sledgehammer Peter Gabriel So
Feel It Still Portugal. The Man Woodstock
Free Fallin John Mayer Where The Light Is
Whiplash The Swampers Muscle Shoals Has Got The Swampers

Note: I don’t generally audition speakers with the typical “audiophile” music. I have a copious number of high-quality albums ranging from pop to metal to jazz and all around. I don’t typically listen to “audiophile” music because I just don’t enjoy it, personally. It is far more important that your evaluation music be something you are familiar with than it is to be esoteric for the sake of being esoteric. You also want to listen to music you enjoy because auditioning a stereo system shouldn’t feel like a chore. Besides, my subjective evaluation is purely to help tie to the objective data and make sense of what I am hearing to help you all get an understanding of how relevant the data is.

Below is the measured in-room response at the main listening position (MLP) of my Home Theater (HT) in red and my Living Room (LR) in blue both compared against the predicted in-room response (purple). These were taken via the moving microphone average, covering the space of about 1 cubic foot in the MLP. The measurements/prediction below do not have EQ applied.

You can see the prediction follows reasonably to what is measured in the seated position in both rooms, notably in the trends. Two completely different listening setups yielded a similar response that both match the predicted in-room response borne from the Spinorama data. This proves that the anechoic data and means to provide a predicted room response result in an accurate prediction for this speaker.

measured vs predicted

Here are my key notes and takeaways from my audition:

  • The Heresy IV has a very uneven tonal balance. The high frequency tends to be a bit forward (thanks to the 1-2kHz being a bit higher in output level vs the mean). The bass is punchy but “dull” thanks to the ~100Hz “knee” where the response falls off rapidly below this point and trails off to be -3dB at 300Hz.
  • There was no low bass in my demo sessions. Even with room gain, I often found a lot lacking below 70/80Hz and I would definitely recommend a subwoofer if you want low frequency content. In my home theater the speakers were out from the walls. In my living room the speaker was placed both next to the cabinets (about 1/2 foot) and also demoed at about 2 feet from the cabinets. The former helped shore up the bass a little bit but still left me underwhelmed and confirmed my notion that a subwoofer would be needed. Maybe if you corner load them you can get some more low end but there’s nothing you can do to change the Fs (or Fb/Fc) of the speaker and it will rolloff above 70Hz so if you’re comparing to other speakers in the same placement position, keep this in mind.
  • These speakers get very loud. I measured about 110dB at my listening position (~12 feet from the speakers) when demoing them. I couldn’t take this output level for too long and had to turn the volume down.
  • Soundstage width was a bit slapdash, if I am being honest. Some notes tended to go a few feet outside of the physical location of the speaker while other notes did not. I attribute this “slapdash” aspect to the uneven response (caused by resonances and directivity mismatches between drive units). If you look back at the objective notes, particularly the horizontal dispersion, you can understand why this is the case.
  • Soundstage depth is an odd bird here. Again, thanks to the unevenness of the response, there are bits about this speaker that have a “forward” presentation (the 1-2kHz region, notably) while others have a more “recessed” presentation (the midrange). This causes the soundstage depth as well as the “depth to stage” to vary depending on the frequency in a way that I would deem inaccurate.
  • Numerous times I heard a resonance in the cabinet that was quite annoying. I mentioned this in the objective section above but I wanted to point out that it is quite audible; notably on male voices.
  • While the majority of my demo was with the speaker placed directly on the floor, I tried these lifted off the ground, placed on a stand as well. I preferred the coupling of the bass to the floor when placed directly to on the floor. I have read others who preferred them on stands. To each his own.
  • As for horizontal toe-in, most of my session was with the tweeter aimed directly at me. However, I did find that (in some cases) I preferred the speaker toed-in about 20°. But, again thanks to the wild variation in horizontal response there really wasn’t a “best”. I’d recommended trying toe-in but no more than 20°. Once you go beyond that angle the dip in the 2-4kHz region is more pronounced relative to the 1-2kHz region and results in a considerably more unpleasant sound. At least to my ears.

Bottom Line

Klipsch has a very strong following in the audiophile community. Klipsch fans generally know what they are getting and they enjoy it. What do they know they are getting? Well, consider this: Klipsch’s literal marketing line is (and I quote) “Pissing off the neighbors since 1946”. Here’s the background art supplied on their own site. I know I am not alone in thinking this tagline translates to “loud and bright”. That is what Klipsch has given you in the Heresy IV. You have a 94dB (2.83v @ 1m) sensitivity speaker with an upward trend in the HF response. The newly implemented rear port may help the bass response compared to the Heresy III model but you’ll find it hard to get much below the 70-80Hz region out of these and you’ll need a subwoofer if you want good kick-drum (50/60Hz region) and definitely need a subwoofer if you want LFE content (if you choose to watch movies with these speakers).

With the above said, Klipsch also says this about these speakers: “The Heresy IV offers unparalleled sound quality from a relatively small speaker”. While this may be true relative to the Heresy III, let me make it clear: the Heresy IV speaker is not the quintessence of hi-fi. These are not an accurate speaker. I do not believe others expect that to be the case. I just want to make that clear up front. They may very well play your favorite rock n’ roll album with the zest you love, but they are not a reference speaker. Their response is too unbalanced for that task (both subjectively and certainly objectively). In my opinion, these are party speakers. They are show-off speakers when your neighbor comes over bragging about his Bose setup. The Heresy IV is what I would call a Jekyll/Hyde speaker. Sometimes they make your music fun and sometimes they make it boring. Heck, sometimes they make it aggravating. It’s a grab bag depending on what track you come across and your mood at the time.

As an aside, I am not biased against “horns” or compression drivers. My home theater system is made up of JBL Pro 2447j CD, 2380 horn and 2035HPL midwoofers. They literally came from the old Cinemark in town when they closed down about 8 years ago. They are ran actively off a Rane RPM88 DSP and some Crown amplifiers. So, while I prefer a different radiation pattern for general music listening, I do enjoy “horn speakers” assuming they are designed and implemented well.

Acoustics aside, let’s not ignore the “retro” look of these. They are quite appealing in their own way. A simple box with a throwback-look that appeals to many generations (myself included). It’s not a work of art. It’s a box. But, in its own way, it’s pretty cool. And, again, this is something Klipsch is known for and fans come to expect.

Ultimately, aside from looks, this is not the kind of speaker I would personally purchase. The tonal balance is much too varied for me to enjoy. But whether I enjoy them or not is of little consequence to your listening tastes. I’ve established that these have that “Klipsch sound” and it’s evident many prefer it regardless of how inaccurate it is. Therefore, I can merely only provide you the data and my thoughts on the performance and let you decide what works best for you. If you are interested in the Heresy IV and plan to purchase a pair to try on your own, please consider using my Amazon affiliate link below. I get a small commission (at no additional cost to you) and it helps me keep doing what I’m doing here.


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