Mondie's speaker endgame: 4-way active, high efficiency horn system development

My first set of speakers were purchased at the ripe old age of 12 after saving months of paper round money. You could say I was bitten by a love of music and audio quite early, influenced as I was by my father’s audio system purchased with the windfall from a horse bet! Since that time I have been fortunate to own a varied and eclectic range of speakers in the pursuit of my audio nirvana over the last three decades. Everything from stacked active Quad ESL57’s, Tannoy D700’s, a TAD based 2-way system, Magneplanar IIb, Equinox Jupiters, VAF I-93 and most recently, ADAM Alpha 5-way actives. I have been fortunate to live with speakers of a wide range of characteristics and capabilities and heard many other systems in between, and so have developed a rather discerning ear as a result.

In 2006 I was fortunate to meet and spend an evening with a legend of the Australian Audio Industry, John Burnett of Lenard Audio. I sat quietly in Johns garden shed in awe at the sound of his 4-way active Sarabandes. The power, the immediacy, and realism was something that totally belied their humble looks and relative cost. I knew I was in the company of a true expert of audio design. Time spent reading Johns website and its education pages and learning about his various designs reaffirmed the impact the Sarabandes made on me that evening. This Experience inspired me in 2008, to build up a passive 2-way MTM system using TAD 1601a/4001, this gave me a real taste of what an endgame speaker was potentially capable of. The immediacy and realism that those 15" cones and a 4" compression driver could generate was exciting & intoxicating, but my meagre DIY skills were unable to address the many crossover related SQ issues that plagued the sound and so I eventually sold them on for something more conventional.

As I learnt more about Johns designs and his origins in valve amplifiers and high-efficiency systems and his schooling in classical audio science from the 60’s, back before marketing took precedence over SQ, I knew that I had to re-visit my unfinished business with high efficiency and TAD. Recently John and I discussed my requirements - superlative realism, uncompromising dynamic range and world class bass capability being three attributes I could not live with out. However, I wanted something that was relatively compact ie under 1.5m and 100kg as I wanted to live with these for decades to come. John told me about a design concept that he had been waiting to realise which had been bubbling away in the back of his mind for at least the last ten years that embodied the accumulation of his lifetime’s knowledge. A system that had the attributes I was seeking and the makings of being my endgame system which brings me to the point where I can finally step off the audio merry go round.

So, speakerless and determined to own a system approaching the very best, I have commissioned John to build me a 4-way active system based on this concept utilising TAD drivers and dubbed the Symphony. It will utilise 4 x 12" compound cavity loaded bass per side, TAD 1601a for mid bass, a TAD TD-4001 compression driver and the TAD ET-703 horn loaded tweeter. Amplification will be four channels of Johns hand built AB design with active crossovers. I was fortunate to hear an early prototype this last weekend whilst back in Australia and to state the SQ was astounding would barely be doing what I heard justice. I lack the vocabulary to describe the prototypes sound without slipping into the usual audio jargon but it goes without saying, I am super excited at the prospect of owning a system that is truly my endgame. The bass energy was huge and incredibly resolving, John explained that the Symphony bass system was equivalent to 2 x 15" drivers in a sealed 16 cuft box per side.

I will keep this thread updated as development work progresses but for now, here’s a few pics of the concept to date and some of Johns less WAF friendly work. All going to plan I will have these in time for Scalford, all going to plan.



The concept:

CAD (Medium)

A very rough proto sandwiched between a pair of active, full valve powered White Opals to one side, and Lenard Saranbandes on the other. These are what I heard.

20170901_191923 (Large)

An example of Johns more extreme work, no chance of seeing these at Scalford!

Canberra opals


Always good to see where folks who take things to the extreme are heading.

“Chumpy’s Duller Cousin” - very witty! I hope for your sake its not true :thinking:

I dont know if its taking it to an extreme, or just a logical conclusion.


Oh, I’m dull to the incider.

Hope that the tweeters come out at ear height, which doesn’t show from the pictures.

Nah tweeters will be above ear height but it makes no difference with the 703’s as they are horn loaded with controlled dispersion. I had that concern initially but once i heard them it was soon forgotten

Cool, would have to hear that to be convinced, but hope you might have a bake-off with them in place.

A bake-off is inevitable yes, hopefully you are not a million miles from Llandudno :slight_smile: On tweeter height, my previous ADAM speakers had the tweeter at about 1.3m, this makes no difference unless the tweeter has an odd dispersion/beaming problem IME. Too low is more of a potential issue than too high.

Sounds like fun! Can you explain more about the bass loading system? Is the crossover analogue or digital?

Yep, my tweets are 1100 above the floor with the mid horn above them. Makes for quite a high image, but now I’ve got used to it, wouldn’t have it any other way :+1:

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The crossovers and amps are all class AB with any necessary driver eq being done in the analogue domain. Lenard makes all his own amps with discrete electronics and I have specified these amps, rather than digital, so I can have them easily repaired in the future. I will get full circuit diagrams too for this reason.

On the bass, I am told it is of an isobaric hybrid nature and makes use of compounded pairs of drivers rather like the Kef 104/2’s and some other systems from the 90’s. The bass system achieves full spectral bass energy at full power, not just at one watt as most systems are specified. The system is highly tuneable and is currently tuned for full power down to 35hz free field. The bass is life changing but so utterly real and seamless that it doesn’t draw attention to itself like it would in many supposedly full range systems.


Progress :slight_smile: The skeleton of my pair is shown against the prototype I heard and I am happy to see the slightly reduced height and the funky foot incorporating the port for the compound bass. Coming up with an idea on the finish and colour/s however is proving to be a minor headfuck for unartistic me!


It’s time for a new year’s progress update on my final speaker system.

When the Symphony started development, the plan agreed with John was to use quad 12’s per side in a dual compound configuration for Fq < 90Hz. Back in October, John and Paul did a range of tests over a week to optimise the bass cavity design and volume using a test jig made to allow real time cabinet volume changes. Surprisingly, the testing showed that there was an audible difference between 2 x 12" single or 4 x 12" compounded configurations. This was totally unexpected as Paul explains:

“Johns work on the Sarabande many years ago revealed that using compounded drivers on the bass unit enabled the use of less expensive drivers with 100% reliability. (2 voice coils, double cone, improved stiffness, linear movement). The main reasons for planning to use compounded 12” drivers, two pairs/side in Symphony were:

  1. inexpensive, readily available drivers can be reliably used.
  2. We knew we would be throwing considerable power and some eq at the bottom end in this system.
  3. Marketing - People like the notion that system has 4 x 12” drivers inside it. (Regardless of the sound)

With only 4 x high power generic 12’s to start with and after testing the first prototype, we needed to test as a stereo pair. We ditched the compounding to be able to move on with testing and used only 2 drivers in each unit (non-compounded). An unexpected consequence was that an audible difference was detected in that the bass appeared to be deeper and flatter in response. (No Eq had been applied at this stage).

So, out came the testing Jigs and we experimented with different drivers, compound / non-compound, port lengths and chamber volumes. Critically listening in the bandpass was undertaken followed by FR measurements for confirmation. Our testing revealed that indeed there was a difference between compound / non-compound but only when using compound pairs and not in the smaller Sarabande single compound / non-compound unit. We have not yet identified the reason for this, but it’s kind of irrelevant given we simply use that which gives the best performance.

The results showed that chamber volumes/ratio, port length and area were in the ballpark. The compound pairs had a much larger peak in the FR whereas the single pair was flatter and went a little deeper. (Reasons yet to be confirmed with more testing). With some fine tuning to the port area and length we got to a point that was not expected from a cavity drive bass system, requiring much less Eq to stitch it to the 15”mid. The end result in this application is that the non-compound pair wins! John reckons, backed by his fifty years of experience designing bass, that the final Symphony cavity design delivers bass energy equivalent to 2 x 15” high-efficiency drivers in a 500 litre sealed box. And it does!"

I have decided to use the saving in 12" drivers required (8 down to 4) and utilise the ultimate drivers we could find for this application. ( it’s endgame remember :slight_smile: ) The non-compound design requires drivers with higher power handling & linearity, but offers more driver choice as they can be 8ohm, and not 4ohm as necessary for compounded pairs. The guys at Lenard had a long technical exchange with Acoustic Elegance, after which, we decided to go ahead and have them modify one of their 12" drivers specifically to suit this application. Around the same time, TAD let me down on the supply of 1601a’s so I decided to go all in with AE and also order a pair of TD15m’s with Apollo upgrade for the mid bass. My order of drivers arrived before Christmas, we now have all drivers in hand for the project with just the manufacture of the horns outstanding… Finally, the Lenard team are ready to make a start on building the finished design in the coming months with just the final aesthetics to be decided. Fortunately, work has me returning to Oz in Feb, where I get another chance to hear the protos and check on progress. I cannot wait​:bangbang:

For now I just have a few more driver pics from Paul to tide me over.


Sounds cool. But it looks like a 3-way, where is the lower mid driver going?

Edit: or is the bass just in the bottom bit?

The 12" drivers are inside the bottom half of the cabinet and exit through a downward facing port. You can see them in the CAD drawing, just ignore the compounding drivers shown.

How is this going now?

Hello AA,

Been ages since I have logged on to AA. I am now only about 2 months from receiving my new speakers. Fortunately, I have been back to Oz twice now and spent a lot of time with the prototypes, Paul & John are part way building mine now. \i will be back to Oz in about a month and will hear the production version with TAD and AE drivers before we pack them up and stick them on the slow boat back to the UK.

Will update with some pics once when I am in Oz.




Paul & John are closing in on completion of the first early production pair of Symphonies 18mths after we kicked this project off. Time has certainly got away from us due to several factors, the most significant being the time taken to finalise design decisions and then try and find suppliers who can meet the required engineering and quality expectations. This is not an insubstantial problem in Oz where traditional trade skills are now a scarce commodity! The good news is that the extra time has allowed additional experimental testing to fully resolve all aspects of the design where a small gain may have been possible. I am just back from a trip to Oz where I have been reminded again of the staggering performance an active hybrid 4-way horn system is truly capable of. It is not long now until my pair will finally be on the water to the UK. I cannot wait!

Here’s a pic of an early production ready pair dummied up with drivers fitted to show the final look. There has been much discussion over the horn colour, should it remain black and stealthy or would it look better painted, perhaps in deep gunmetal grey or very dark metallic green?

Interested to hear others comments and suggestions, nailing the aesthetics has been quite a challenge.

IMG-20190606-WA0008 by Simon Gee, on Flickr


Without other accents a colour might look a little out of place perhaps? Silver / grey or hammer tone might work or a mat textured black maybe? Certainly they look substantial. How thick is the ally? Bracing / damping?