Active filters for S9900

[Ian Mackenzie]

While the S9900 can be bi amped Harman never really supported or promoted bi amp of any of these statement systems.

Greg Timbers is an advocate of bi amping systems he was involved in developing at JBL. Greg told me he had a hard time getting Harman to provide any support information for bi amping. I think part of that is Harman not wanting to service customer enquires on setting up bi amp systems and Harman not wanting to rock the boat in the hifi consumer market where consumer amplifier manufacturers could react adversely to a push for bi amping passive loudspeakers.

Manufacturers like Elac and Dynaudio have walked a careful line with full active loudspeaker which have everything built into the loudspeaker. This is more of a convenience / connectivity benefit to consumers. Harman have a toe in the water with the 4305P self powered monitor.

The other jbl active monitors are a different market segment from Harman’s perspective seen as broadcast, home studio and pro recording.

The entry into full active consumer systems has been a learning curve for both manufacturers and the consumer. Some manufacturers are pursuing analogue active active systems while others like Dynaudio are streamlining their full active systems with more refined dsp engineering.

From my own perspective if your living in a condo and want a compact lifestyle music system an active loudspeaker is the way to go. A small active system punches far above its size and you don’t need to accommodate a whole bunch on hifi equipment.

For the traditional hifi consumer (a dying breed according to some) it’s sacrilege to loose control of what power amplifier drives the loudspeaker. More and more hi quality integrated amplifiers with digital connectivity are entering the market. This is creating preferences for an amplifier for modern times. The hifi customer gets to keep his/her trusted loudspeakers.

What some might be referred to as the audio amateur segment which is below the line in terms of marketing visibility continues to explore bi amp and full active amplification of pre determined loudspeakers and project loudspeakers. This group have been coined the thinking cap customer by Nelson Pass who has nurtured diy audio for decades.

The barrier to a performance improvement over the level of a pre determined passive loudspeaker is as the OP points out an understanding of how to execute bi amping a particular loudspeaker correctly. It’s not plug and play despite marketing claims by dsp equipment manufacturers. The acoustic performance of a loudspeaker designed for critical listening is a careful juggling act of numerous parameters which most audio enthusiasts are oblivious too. Transforming a passive loudspeaker to an equivalent or superior bi amped or Tri amp loudspeaker with external frequency dividing network and power amplifiers requires considerable technical insights, measurements and empirical adjustments. You can simply plug in an after market active frequency dividing network with one size fits all crossover slopes and crossover frequencies and it will go. But it’s unlikely to perform as well as the pre determined passive loudspeaker in all facets of subjective and measured performance.

Prior to the pandemic l invested in considerable research and development of tailored electronic frequency dividing networks with Greg Timbers and Nelson Pass. We were able to engineer, design and construct tailored analogue electronic frequency dividing networks for pre determined loudspeakers that performed extremely well. However, the segment that would benefit most is perhaps unlikely to embrace the cost of such specialised high quality electronics. This segment has been showered by low cost mass consumer and low quality offerings that have conditioned the user into the belief that it should be a cheap and easy thing to do.

So l am sitting on the fence and will probably supply such high quality equipment and the expertise to users who are seriously invested in this specialised area. That said l have seen Accuphase active crossover cards selling for US$500 a set on EBay.

Ian

[Robh3606]

Yeah not for the faint of heart, Take a look at page 12! Control Operation.

Rob

[Ian Mackenzie]

See below.

Technically
In this instance an internal switch bypasses the LF passive network and the passive HP filter but the passive EQ remains in circuit. On perusal of the voltage curves the woofer not only has a crossover filter but system optimisation applied to the woofer. The optimisation accounts for how the loudspeaker will sound in actual use in a variety of listening rooms and account to for complex electro mechanical characteristics of the woofer low frequency response where the dcr of inductors impact on the low frequency response. The absence of the inductor dcr effectively lowers the QTS’ of the woofer seen by the bass reflex tuning. So what you win on damping you loose on the enhanced LF extension which is often audible. The net woofer sensitivity is also reduced by the passive network.

To account for these factors we provide some focused tweaking specific the woofer. It’s not trivial and adds to the complexity and cost of implementation. Unless these intricate details are taken care of your better off staying passive. If done thoroughly and to a very high standard the results can be stellar. Precise level matching of the electronic crossover left and right low and high frequency outputs is required.

The results
This results in a remarkable improvement in pin point sound staging, sharper more visceral bass dynamics, spine tingling dynamic headroom and simplify a more effortless lifelike sound reproduction. It brings you closer to the emotional impact of the original live recording.

Specific acoustic treatments of your listening room can then be investigated to manage reverberation and other audible problems your ears are sensitive too.

This is not snake oil or marketing hype. It’s engineering a systematic approach to the mitigation of a number of product compromises that collectively impact on your listening experience.

The implementation
Implementation of an electronic frequency dividing network would require measurement of the volt drives at the driver terminals and or simulations. Furthermore an inbuilt LF low frequency shelf filter to fine tune the low frequency performance. To ensure you obtain the absolute pinnacle of straight wire transparency we use simple but elegant electronics circuits without the limitations of conventional mass production opamps. These circuits have over 100 x the value of key performance parameters such residual noise and class A sink and source current swing found in mass market audio op amps. This is to ensure the audio signal is never influenced by inherent design compromises in mass produced audio equipment.

An analogy is once you own a really sharp very high quality carving knife for thanksgiving your never going to go back to a cheap knife! Not ever. What you don’t know won’t hurt you but once you have it you can’t live with out it. It’s a sad fact but true!

The fun part
The power amplifiers can be selected and optimised specifically for the low and high frequency duties. For example select a high performance digital amplifier such as a PS Audio power amp for powering the woofers. You then can focus on your own personal choice of high frequency power amplifiers to match to the rest of your system. You can literally sculpt the finer subjective characteristics of the overall system to suit your preferences.

Ian

[Ian Mackenzie]

Some of the design work in an electronic frequency dividing network for a pre determined loudspeaker system.

See images below.

Some of the design work in an electronic frequency dividing network for a pre determined loudspeaker system.

See images below.


1& 3. The top and bottom image is a modelled acoustic simulation of the Tri amp Everest DD67000. The in room response is well extended with the LF shelf filter we designed. The helper woofer signal is derived from cascading an additional low pass filter from the main woofer which is carefully designed so both woofers sum flat in the pass band.

Greg Timbers designed the Everest DD67000 for tri amp operation should the user wish to explore tri amp mode of operation. Greg is at the top of his field when it comes to unique solutions for loudspeaker systems. Greg also has outstanding communication skills which enables other members of the team to pick up the solution and implement it correctly. Even so bringing this project together was a lot of painstaking hard work. The tri amp project was quite successful and a significant subjective advancement on the passive Everest DD67000.

2. The second image is one of several prototype pcbs designed by Nelson Pass following detailed conversations with myself. The most recent iteration (image not shown) has a transversal design layout which mirrors how the user visualises the functional configuration of the crossover chassis The daughter boards are larger and are a consolidation of several of the smaller daughter boards with on board switching. This concept allows the user flexibility to either expand from bi amp to tri amp or quad amp mode while also offering flexibility to use different woofers and compression drivers subject to availability and performance criteria. The crossover slopes and crossover points are optimised ready for use with some tweaking room in the final implementation. Yes figuring that out did do my head in.

3. In the third image down shows an actual measurement (not a simulation) the hump in the voltage to the woofer in a bass reflex system. Large woofers are often difficult to model accurately from T/L parameters and impedance measurements because the models rely on assumptions. So when we make real measurements we often find clues to why something sounds different. This problem exists with many pre determined bass reflex loudspeaker systems because the swings in the complex motional impedance cause a voltage drop across the inductor.

4. The fourth image is a simulation of the vertical polar response of a two way loudspeaker in crossover region. This requires a number of off axis measurements of each driver. This representation allow selection of the best crossover topology for a particular woofer and horn.

My understanding is that Greg has since come up with other approaches to tri amp of the Everest.