June 2009 - Posts
Crossover Features
• Optimized 3 ½ Way Crossover (low, mid, high)
• 4th Order Crossover for all sections
• High linearity air-core inductors
• Polypropylene capacitors (No electrolytic capacitors)
• Ultra low inductance power resistors
• Inductor layout optimized for minimal electromagnetic interference (EMI)
• Crossover physically isolated within enclosure to reduce sound coloration
• Crossover matched at factory within 1% tolerance
Through very accurate driver engineering, the system offers excellent performance without the need for corrections in the crossover network. The crossover should provide smooth transition between each drivers allowing for operation within a given bandwidth of the overall loudspeaker response. Thus, the network can be of straightforward design with extremely high quality parts. This also means the speaker will have a more direct and coherent character as compared with contemporary products that must employ more complex network circuits. High quality polypropylene capacitors are used along with air-core inductors in all circuit topologies to ensure the best performance and reliability. The network system produces a 4th order electro-acoustic filter when combined with the smooth, natural roll off of the drivers. The 4th order filters provide a rapid transition between drivers at a rate of 24dB/octave successfully meeting the criteria initially set forth in this design.
The crossover was designed for the woofers to operate up to 500 Hz, the horn loaded midrange from 500 Hz – 3.2 kHz, and the horn loaded tweeter 3.2 kHz to 30 kHz. The graph on page 16 shows the transition of each filter and the combined result of all of the filters.
The network is located within the speaker’s base plate which allows for the tri-wire input connectors to be conveniently located at floor level. This minimizes the length of speaker wire and produces a very clean finished look. The tri-wire input allows the end user to have a choice of amplifier/loudspeaker combinations, such as connecting a separate amplifier to each section of the loudspeaker providing individual amplification of the low, mid, and high frequency drive sections.
All network components are integrated into two separate high current printed circuit boards (PCB). Each PCB is a dual layer board made with a 2oz. copper on each side allowing for very high currents to be passed. All components are soldered into place and securely attached to the PCB to minimize component resonance. Each board is securely fastened to the bottom of the P-93F with special plastic isolation grommet mounted between the board and the enclosure.
A picture of each assembled crossover is shown below.
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Let's take a look at the un-equalized or raw response of each transducer now. In the graph above you will notice three discrete frequency responses for the LF, MF and HF sections of Palladium P-39F. These measurements are 3 meter mic distance with 2.83 Volts drive level to each section. To convert you would add almost 10 dB to give you a 1 watt / 1 meter reference level. So the design is quite sensitive with ranges in the pistonic region from 95 to 108 dB.
With considerations of the shape of the raw driver response and the roll off of each section, the crossover points and design can be considered. To define the best crossover frequency is not trivial. This will predict the power response of the speaker, the power capacity, the level of distortion at high drive level and the final sonic characteristic of the system.
Acoustic Power – Acoustic power out is a combination of the driver efficiency and dispersion of the components. Compression Phase Plugs will improve driver gain in the higher band of the driver and the angles of the walls on the horn will define the Di of the component.
Power Capacity and Fc – Defining the low cutoff frequency (Fc) of the component will define the amount of excursion a driver will exert. This will ultimately define the mechanical limitation of the component. Equalization will further determine the thermal capacity of the driver by steering the spectral density of power into the.
THD and IMD – Total Harmonic Distortion and Intermodulation Distortion will be affected greatly by the Fc of the xover.
SPL – Efficiency will be determined by the mix of the crossover and passive EQ.
So it is clear that the crossover pays a most important roll in the design of any good speaker system, and Palladium is no exception to this rule.
High-Frequency Driver (Tweeter) Design
Horn Loaded Tweeter Driver Features
• 90° x 60° Modified Tractrix Horn
• 10 to 1 high compression phase plug
• ¾” lightweight titanium diaphragm
• Ferro-fluid cooled voice coil
• High efficiency magnet structure containing 2 Neodymium magnets
• High Temperature N35SH Neodymium magnets
In order to deliver the dynamic range targeted in the design brief for this product it was necessary to develop a new tweeter from the ground up. Starting with a clean sheet of paper, the engineering team created a driver that is both sensitive and accurate. Low distortion, high sensitivity, wide bandwidth and neutral tonality were pushed beyond the standards for any previous Klipsch driver. A detailed exploded view of the tweeter is shown below.
The chamber behind the tweeter dome is resistively damped via a filled tube to reduce reflection of the back wave and thereby the distortion that would otherwise be produced. The phase plug that serves to put the dome into a compression mode also has a unique chamber within it that is designed to extend the upper frequency limit of the driver by more than 10 KHz. This proprietary technique offers numerous benefits including the elimination of undesirable standing waves in the high pressure layer between the phase plug and diaphragm.
This driver is inherently flat from 3 KHz to 30 KHz. In this application, this tweeter will operate from 3.5 kHz to 30 kHz. It has an inherent sensitivity some 10 dB greater than direct radiating designs, and distortion is reduced by a factor of 10 dB vs. conventional tweeters. A detailed cut-away of the horn loaded tweeter is shown below.
Built around a ¾” titanium dome, the tweeter makes use of two very large high temperature N35SH neodymium magnets.
As with all of the drivers used in the P-39F, the motor structure for the tweeter has been developed in house and optimized using FEA analysis. The below picture shows the tweeter motor structure magnetic FEA. This shows the high flux saturation in the steel around the voice coil which helps to reduce flux modulation thus reducing distortion.
Mid-Frequency Driver (Midrange)
Horn Loaded Midrange Driver Features
• 90° x 60° Modified Tractrix Horn
• 4 to 1 high compression phase plug
• 1” Diameter – High temp copper voice coil
• Aluminum cone w/ Aluminum dust cap
• High linearity magnet structure containing 3 different Neodymium magnets
• High Temperature N35SH Neodymium magnets
• One copper pole shorting cap
• Half-roll foamed rubber surround
• Low reflection die-cast aluminum basket
• Optimized rear midrange chamber
The inverted dome midrange driver used in the P-39F is a unique design not found on any previous Klipsch product. PWK is famous for saying, “The midrange is where we live”. A true high fidelity loudspeaker reproduces a flat midrange response, where the human ear is most sensitive. This particular midrange driver has been designed to operate from 500 Hz to 3.2 KHz. This preserves polar uniformity; avoiding assignment of information to drivers too large to deliver uniform dispersion. A detailed cut-away of the horn loaded midrange is shown below.
Special attention was given to heat management; ensuring full dynamics regardless of drive level unlike many dynamic designs where increased power leads to voice coil heating and a rising voice coil resistance. That change causes driver output to fall just when it should be at its peak. The heat generated by the voice coil is dealt with in two ways. The first, being through the low thermal resistance of the aluminum cone. The second, through the purpose-cast aluminum basket which acts as a heat sink for the motor parts attached to it. This basket is designed to have very narrow spokes avoiding reflection of rear wave driver output that might otherwise smear the sound. A detailed exploded view of the midrange is shown below.
The horn loaded midrange driver raw sensitivity is almost 110 dB allowing for minimal excursion at normal playback volume. When cone excursion is reduced, distortion is also reduced. The midrange is direct, detailed and clear without being forward or strident. High efficiency and a low moving mass are the best ingredients for maximum transient attack. It’s quite an achievement and one that will provide a great window into the subtle details of music.
Similar to the woofer the 4 ½” midrange follows the same design philosophy and is driven by a group of 3 high temperature N35SH neodymium magnets. As with the woofer this motor design maximizes magnetic field strength while optimizing the symmetry of the magnetic field surrounding the voice coil, ensuring linearity during high dynamic transients. The high strength magnets also allow for a minimum profile behind cone, reducing any unwanted reflections.
The midrange driver’s pole piece is topped by a copper cap whose purpose is essentially the same as the faraday rings used in the woofers. The end results also the same, reduced distortion and greater dynamic capabilities.
The midrange unit is housed in its own, acoustically tuned, sealed enclosure within the larger cabinet; this enclosure also serves to magnetically shield the unit. Furthermore, this sub-enclosure isolates the midrange driver from acoustic energy generated by the woofers. Every effort has been made to ensure great accuracy from this unique driver. From the choice of voice coil formers and coil wire to the mechanical design of the speaker frames; every part is evaluated not only for accuracy but also for long-term durability and the ability to produce all the information in the source. The Klipsch P-39F will accurately deliver all micro and macro dynamics found on today’s most advanced high definition media.
Transducer Design
Low Frequency Driver (Woofer)
LF Driver Features
• 1 ½” Diameter – Flat-wire “low mass” aluminum voice coil
• 0.72” (18mm) linear peak-to-peak high excursion design
• High linearity magnet structure containing 3 different Neodymium magnets
• High Temperature N35SH Neodymium magnets
• Two Faraday aluminum shorting rings – flux stabilizing rings on each side of the gap
• Reverse half-roll low density foamed rubber surrounds
• High air-flow – low restriction die-cast aluminum basket
• Hybrid Aluminum/ROHACELL® cone
The P-39F uses three 9” (225mm) diameter low frequency drivers. This custom woofer utilizes a low mass hybrid aluminum/ROHACELL®/Kevlar cone with an over hung voice coil design, ensuring there is always an equal amount of coil winding in the magnetic gap regardless of the excursion of the driver. Even during high excursion, the driver remains linear and low in distortion. A cut-away of the woofer is shown below.
The cone is constructed of an outer aluminum skin and inner Kevlar skin bonded to a lightweight rigid core of ROHACELL®. This material is commonly used in high performance vehicles and aircrafts. This unique closed cell polymethacrylimide (PMI) foamed plastic core adds increased rigidity to the cone while minimizing ringing and maintaining low mass. The sandwich constructions results in an extremely stiff but light cone allowing the woofer to operate as an ideal piston throughout the woofers pass band. This translates into much less coloration giving an incredibly natural and realistic sound. A three part high intensity neodymium N35SH magnet design is used in the 9” woofer with a main magnet plus two supplementary magnets, placed above and below the main magnet, to ensure linearity, reduce stray magnetic energy, and provide intense field strength in the voice coil gap. The field strength of the neodymium magnet structure has an equivalent magnetic field strength of an 80 ounce ceramic magnet, with only a combined weight of 13 ounces. A magnetic Finite Element Analysis (FEA) of the motor structure is show to the right. Additionally, dual aluminum Faraday rings are also located inside the motor structure and on the pole piece. Faraday rings, also known as shorting rings, are used for four reasons:
Minimize unwanted inductance.
Minimize inductance change with voice coil position.
Reduce flux modulation caused by the magnetic field generated by the voice coil.
Increase heat dissipation.
These all result in reduced distortion and compression and lead to improved dynamic capabilities. The effect of the aluminum rings can be seen in the graph below sowing the variation in electrical inductance with voice coil position.A superior motor structure is complemented by the design of an efficient voice coil. The 1 ½” voice coil is wound with a flat-profile low-mass copper clad aluminum wire. Flat-wire allows for efficient packing of the wire when layered on the voice coil resulting in an increase in the Bl. The Bl is the product of the magnetic flux density (B) and the length of the coil in the magnetic gap (l). This increased Bl directly correlates to an increase in the sensitivity of the woofer. The flat wire voice coil/motor structure provides 0.72” (18 mm) peak to peak linear excursion. Below is a graph showing the difference in BL(X) with and without the additional bucking magnets in the motor
Another unique feature about this woofer is the surround. The surround is made of half-roll low density foamed rubber and inverted to allow for minimum diffraction. The low density foamed rubber helps to reduce the moving mass while maintaining surround integrity under high excursion and box pressures. The flat-sided shape was created to maximize the linear excursion while increasing the radiating area. Special care has also been taken in the design of the driver suspension which, along with the surround supplies the restoring force to keep the driver moving linearly about the rest position. It is important that the restoring force is symmetrical in the forward and backward motion of the woofer cone. The graph shows the measured stiffness vs displacement for the P39-F 9”woofer compared to an inferior design.
The cast aluminum woofer frame made specifically for this model employs narrow spokes which are grooved to provide maximum surface area in their minimal profile. This assures maximum heat transfer without any reflection of the back wave of the driver that would otherwise color the sound. A Finite Element Analysis (FEA) of the heat transfer of the aluminum basket is shown below. The aluminum frame is designed to acct as a heat sink for the woofer motor, conducting heat generated by the voice coil away and thus reducing the effects of thermal compression, translating into greater dynamic capabilities.
Enclosure Design
Enclosure Features
• Non-parallel wall construction
• 1.06” (27mm) thick side wall – 1.2” (30mm) front baffle
• Triple Layer Laminated medium density fiberboard (MDF) and particle board
• Mid/High Horns combined into single bulk molding compound (BMC) structure
• Three flared rear facing port tubes
• Internal volume of the cabinet 4.2 ft3 (120L)
• Interlocking vertical and horizontal support braces
• Ultra high quality custom machined binding posts
• Optimized separate midrange enclosure
• All transducers are flush mounted for minimal baffle deflection
• Separate high mass machined base coupled to enclosure
• Four adjustable floor anchors for improved cabinet decoupling
When you first see the P-39F, the beauty of the cabinetry is apparent. The industrial design of the enclosure was guided by Design Works, a division of BMW Automotive. The P-39F is an artistic blend of beauty and functional performance. Functionally, the loudspeaker enclosure provides a mechanical placement of each transducer, a method for suppressing acoustical radiations, and a resonant chamber to extend low frequency performance.
Enclosures can also degrade the sound quality if they are not properly designed. Some of the most common problems are unwanted cabinet resonances. Enclosure resonances can be suppressed through the geometry of the enclosure and mass of the panels. This is why the P-39F enclosure contains nonparallel wall structures and thick, high mass walls. Nonparallel wall structures significantly decrease standing waves, which naturally occur because of constructive interference in the waveform. At the node of a standing wave, large sound pressure levels are generated potentially creating the enclosure walls to resonant uncontrollably. Cabinet wall thicknesses are a minimum of 1” thick with an even thicker front panel for a resonance-free platform to mount the drivers. Inner and outer laminated panels sandwich a middle layer of dissimilar material designed with a very different mechanical impedance to ensure the cabinet does not color the sound produced by the drivers.
Each of the curved cabinet side panels are comprised of multiple laminations of MDF and particle board that are formed in a proprietary process. A sample of the cross section of wall is shown below.
To further increase enclosure stiffness four “H” braces are strategically positioned in the enclosure to further reinforce the structure and control resonance. The inner surface of the panels therefore minimizes modal standing waves. Another feature is the high mass front panel key for the transducer mounting. The front baffle has also been designed to allow all woofers and the mid/high horn structure to mount flush the exterior edge. The width of the front baffle has also been minimized to decrease the total area. The overall enclosure was designed to extend the low frequency response of the three woofers to 39Hz (-3dB). This fourth-order vented enclosure contains three custom flared ports each of which is cleverly blended into the rear of the curved enclosure. The angle of the port flare helps to minimize the affect of standing waves developed inside the port tube.
Just below the ports, the high mass machined base is integrated into the rest of the enclosure. The base contains four adjustable floor spikes which anchor the speaker to all surfaces and also allow the speaker to be angled for fine tuning of the stereo sound stage. The base of the speaker also contains three sets of custom machined binding posts allowing the end user to have a superior connection. The front of the enclosure also contains integrated high intensity magnets allowing the two piece grill to seamlessly attach to the front of the enclosure. A detailed cutaway of the enclosure is depicted below.