Trans-Fi Audio

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Journey to No-Baffle Speaker System (and back)

My obsession with speakers took over my hifi life, and I am here to report on my journey where I think I may be at the end......after 15 years  

It all started when a client of mine sent me a picture of his set up . I noticed some unfinished speakers in the background, and jokingly asked him when was he going to box them in? He told me they were Bastanis and explained the concept of open baffle which was new to me. I ended up buying his old Prometheus baffles.

Like most of you, I went through many speakers in my lifetime......Wharfdale, Leaks, Kefs, Missions, Pioneer, Yamaha etc.........never found something to settle with long term. But I guess that could be applied to most components in my audio chain.

Not sure if I am getting less fussy or smarter, but the last 15 years have really solidified my system. Keeping away from mainstream, concentrating on products from the little guys with a passion for audio. My amplification is from Temple Audio, my turntable front end is my own, and digital is coming from Limetree Streamer + Chord Qutest. This sets the background for my current set up, but I really want to describe my speaker journey.

It wasn’t until I discovered the Bastanis that something psycho-acoustically switched in my brain. I suddenly started to listen to music rather than the hifi.

I contacted Robert Bastani & populated the baffles with appropriate drivers and made them my own:

I remember running them side by side with my Yamaha NS1000M’s and thought they did something special the Yamaha’s didnt do. I guess it was the live musical presentation that attracted me.

Of course, it wasn’t long before I wanted more. I noticed the 12" woofer (active, sealed box, plate amp) would bottom out playing Police......couldn’t live with that, so I upgraded to the Atlas units, 15” sealed woofers, twin widebands and Gemini tweeters!

This was a creative endeavour, so I had to sit down, calculate measurements and draw the baffles. I had to find a CNC guy to make them. Although I have a workshop and could do the work myself, I usually end up chopping bits off myself..........

A couple of years or so later, Bastanis released his Mandala, which retained the Altlas wideband/tweeter baffle, but added dipole bass in the form of an 18” S-frame. Back to the drawing board and the CNC shop and these were born!

You will notice the Bastanis used active bass, and I went from using built in plate amps to separate units, in this case XTZ (black boxes on floor)

Bass from the Dipole was more open & detailed, but there was a few things I didnt like. It was very fussy regarding room placement. I decided to ditch the S-frame and mount the 18” woofer on the baffle. I was also after a new 18” driver, eventually settling on the AE Dipole 18. My ‘Monster’ series of speakers was born.

These retained the Atlas baffle. Construction was also beefed up using 38mm MDF and painted white.

Before you ask, I have a loving understanding wife..........

I quite enjoyed these speakers, but looking at them I wondered if I could compact them & achieve the same..I fiddled with the format  (I was getting good with Microsoft Draw) and came up with the Mini Monster......back to the Prometheus single wideband arrangement.......

These actually worked very well and I didnt miss the extra wideband of the Atlas.

During this period of time, I expanded the permutation of this design with Selenium NEO 15" drivers. These suited the Open Baffle format and gave deep, clean detailed bass (Note: unfortunately no longer made). They were also lighter than dramatically heavy AE 18's!

My main issue now concentrated on the Gemini tweeter. I was noticing a lot of sibilance on some recordings, and originally I put it down to the recording. It was about this time I was helping my buddy build a set of Duet baffles for his Hawthornes. When they were completed I was stunned by how smooth they sounded! back to Draw. I wanted something bigger & better!

...and the Trios were born.

These were huge. The 15” at the top is a dual concentric unit with the tweeter positioned behind the magnet firing through the dustcap. Twin Augie woofers below....these things rocked & were smooth. Also, no need for sub-amp as the Hawthornes came with a Crossover.

I spent 6 months with these but I found myself playing my hifi less and less. Whereas my buddy loved his Duets, I was getting bored with my Trios. They were too smooth and laid back.

It was at this stage I sat down and pondered what direction to head in. I didnt like the Bastani tweeter, but really didnt have the electronic knowledge on how to fix it. I wanted to design my own speaker.....but something simple I could cope with.

Enter Full Range, but not in a an open baffle. After a lot of research, I settled on the Mark Audio Alpair 12P.  I had no idea how this would turn out....but what the hell......…

My experience from listening to FR speakers in the past was not good. Lack of treble was most noticeable, and the units with whizzer cones sounded brittle to me.

So, the Alpairs have a 500 hour run-in time, and they changed noticeably in the coming weeks. I became more and more impressed as they opened up. I thought to myself ......who needs a tweeter?

Also, before I designed this baffle I took note of what the experts were saying. I could increase my bass efficiency by adding a U baffle at the back.....which I did, and the bass increased. More on that later!

I spent a long time living with this format and exhausted all the permutations:

I did notice the narrower the baffle, the better the imaging, but something still not right.

I happen to listen to a lot of different music, and sometimes the music needs volume......lots of it. These just didnt deliver. Adding volume would cause the FR’s to flap like crazy with their compliant surrounds meant for a box. Actually, I didnt need this compliance as I wasn’t relying on them for bass....I had my woofers. I asked John at Temple Audio if there was a way to restrict the bass frequencies reaching the FR’s. He suggested an 80nF capacitor after the volume control but before the amps would work.

I duly installed this in my amp and the FR’s responded. No more flapping cones and the sound became cleaner with more detail. This was a revelation.

In case any of you are wondering, I am not into crossover design and had always driven the woofers actively  Behringer Ultracurve. Coincidentally around this time, they came out with the iNuke series, a powerful amp that had the Ultracurve built in. Not only that, but it was so simple to program even I could do it. They provided software that ran on my laptop and the amp connected via USB. I could dial in the crossover in real time and achieve perfect integration. After a while, I became quite adept.

I then started thinking about an alternative to the Mark Audio drivers. I wanted a Full Range driver, but without the bass and compliant surround. Scouring the web and different forums I came across a PRV thread which recommended the 5MR450-NDY.

This had the frequency range I wanted, no rubber surround, very high powered & efficient (unlike the Alpairs), Neodybnium magnets and cheap to boot. Great reviews on the forum.....what’s not to like? I ordered a pair, designed a baffle, which I made myself as the CNC shop was draining my resources  , and partnered  with my favourite 15 inchers, the Selenium NEOs.
Now this was more like it. The PRV’s sounded great out of the box. The Seleniums delivered bass and slam. The combination was fast & dynamic.
The PRV's had an uncanny ability to go LOUD very fast!

Still, I was not happy with the baffle design. The U-frame at the back promoted by all the OB gurus to increase bass also increased the room nodes by pressuring the waves. The bass I got from totally open baffles was more consistent and room friendly, although not as extended. I also felt the baffle was colouring the sound and introducing artifacts.

At about this time, I came across these:

Now, you can see where I’m heading........

Inspired by this design I came up with a way of taking the drive units out of the U-frame and mounting them on an open ladder frame, something like this.
A trip to my local Wickes procured the materials. I knocked the frames up pretty quick. The design was cheap, simple and fast....but would it work?

With some trepidation I fired them up...........

OMG. I was stunned. This combination never sounded so detailed and clean. Once I dialled in the crossover I was getting plenty of bass. I immediately thought I would never need to see the CNC guy again!

The next few days I was busy testing. I noticed the woofers dumped a huge amount of energy into the frames. This was being transferred into my wooden floor causing the house to shake . Also, I had mounted the PRV on a sub-baffle, and this was prone to vibrate with a nasty buzz at certain frequencies.

For my next design I thought of eliminating the PRV sub-baffle and also trying to compact the design. I came up with this, doubling up the woofers to save space:
This design was smaller, but still a lot of energy transferred to floor and frame. Vibes were so bad with Kraftwerk I thought the PRV would get torn from its mountings and shoot across the room. I added some braces, but still the design was flawed, altho it sounded great. Eliminating the sub baffle really opened up the imaging, so I was heading in the right direction.

In the next iteration I placed the woofers facing each other, simply because they were easier to mount as previously the rear speaker required longe standoffs to clear the frame. In this configuration, BTW, I had to reverse the polarity on one of the woofers to keep them acoustically in phase:

Also, you may have noticed the Neos have been replaced. Since production of them ceased allegedly because the company was unable to get the ore required to make the magnets thanks to China buying it all up.
Looking for an alternative I decided again to depart from the Open Baffle Guru advice of light, efficient fabric surround woofers and went for heavy, high Xmax inefficient designs, in this case, Dayton 390’s. What the hell....watts are cheap nowadays using the Behringer iNukes. Tell you what.....this was a game changing decision and I have never looked back. I had REAL bass now, with deep slam and a weight behind coming from a combined cone mass of 1.2kg.....I never experienced it in a home environment. But If I thought this was bass.....wait till the end and all will be revealed!

So I was vexed by the amount of vibes being transferred to the floor with this arrangement and the rocking back and forth of the frames with subsonic frequencies I was working on a new design. One of my cycling mates was also a carpenter, and I asked for his help with my next project. I wanted to place the woofers low to the ground, but keep the PRV at ear height. We came up with this simple, T-frame arrangement:

The PRV’s were doubled up (why not) and mounted to a pair of 1” aluminium tubes using cable cleats. Substantial 3 x 3 wood was used for the frame make it strong and rigid. With this arrangement the frame did not move. The twin PRV’s projected better and had more depth. This was the best sounding iteration yet.

Still.....I wanted to simplify the design. Looking the the way the woofers were mounted I reasoned if I could join the woofers together, I could use a simpler frame. This was my next design.....a cradle frame:

Here, the woofers could be bolted together using aluminium stand-offs. This could then be treated as a single unit and be supported by the magnets on a wooden cradle with the PRV’s mounted on longer poles to the base:

I am envisaging this as a DIY project. So far, it still involves wood-working skills. Imagine if you could buy the frame off the shelf at minimal cost. The other issue with this design is the cradle still transmits vibrations to the floor and up the poles to the PRV’s. Could I kill 2 birds with one stone?

In my head I had a design to use metal poles and scaffold fittings. Building scaffolding was too big and bulky, but what if they made something smaller?

A bit of googling and I found exactly what I wanted at

Not only that, they would deliver free & cut to size. I designed a metal cradle using 34mm tubes & fittings. Here was the result, £99 delivered!

Another advantage with this ‘modular’ design was it came apart easy for transportation!

I should point out at this stage that our armchair engineers would say this will not work as there would be too much cancellation to get any meaningful bass. I would welcome any skeptics to come and have a listen, and if they don't hear any meaningful bass, I will pay for their petrol home.

It is true, this is not the most efficient way to get bass. It requires possibly double the number of woofers and power vs putting them in a box. However, there is no way I could go back to a boxed speaker arrangement after hearing dipole bass. No box could match the quality I was getting. The texture, purity and detail of this bass is difficult to describe until you experience it. Not only that, it extends deep with the woofers I have chosen which have a Fs of 19.5Hz. They are also very room friendly with bass distributed evenly throughout the nulls or nodes.

And fully assembled scaffold speaker:

The woofer assembly was now supported hammock style by a 2mm steel cable and is free to oscillate back and forth. I was concerned it might do this while listening to music, but it doesn’t. I tested with a frequency generator and oscillation does not occur until 5hz.

The effect of this is total isolation from the floor, in fact no vibes can be felt from the frame itself, nor in the poles supporting the PRV’s. This was the best sounding design bass with no reaction with the room or floor, and nothing to interfere with the PRV’s.

Cosmetically, of course, not to everyone's taste. They have an industrial look, but surprisingly my other half approves of the minimalist design. The eyes tend to be drawn to the woofers rather than the frame. Probably even less intrusive in black, but I love them as they are!

Another hifi buddy suggested a further modification to isolate the PRV’s by eliminating the cleats holding to the poles. After several protoypes, I worked out a method to hang the PRV’s using a cable similar to the woofers:

Eliminated one of the poles, joined the PRV’s together with a brass joining plate, and suspended by the top magnet on a cable. Very simple and this resulted in even better imaging and detail.

So I have been living with this system with over a year and got the itch again.............................

I alway wondered what would happen with 4 x 18” woofers rather than 15”? TBH, the way I play the system the woofers are on their limit in my room when producing deep bass, being rated @ 500Watts. The 18’s would take 1000Watts and have similar efficiency. I recently bit the bullet and went for the Dayton UM18’s. They were not cheap at a EU rip-off price of 1500EU vs US price of $1000  

A small frame adaptation allowed me to fit these:

Not sure exactly what I was expecting, but compared to the 15’s the system sounds like its been turbocharged. A huge increase in scale and dynamics with a doubling of everything! The bass can really be pushed now, but surprisingly, it stays in its place without overpowering the mid & highs. There is no muddying, just huge clean controlled bass that really slams with rock, but is also textured and detailed with jazz and acoustic music. I can achieve 110db concert  levels that leave my ears ringing with no signs of strains or distortion in the system.

What have I learned on this journey?

•   No baffle at all sounds best with fewer resonances  and better imaging. Bass is not as extended, but this doesn’t matter for upper frequencies using a bass assisted system.

•   You can get huge bass with no baffle, but you need heavy coned inefficent woofers with a large Xmax, low Fs and high wattage.

It took me 15 years to reach this point and I now feel I can relax and listen to a system that will deliver whatever I am in the mood to listen to. I think I now need to look elsewhere to direct my creativity.

BTW, if anyone is interested in any of the projects I made along the way, please contact me.............
Latest changes include replacement of the older Berhinger iNuke amps with the recently introduced NX series. I plumped for a pair of 6000's with the extra power to compfortably drive the UM's.

I  have been experimenting with finding an alternative to PRVs which are hard to beat with its efficiency and high SPL and are a waste in multiples of 4 in a domestic environment.

Thinking in terms of full range mini-arrays to make up SPL's, there are dozens of low watt drivers out there, which I figured used multiple configurations would make up for inefficiency and SPL.

They are also very cheap. These are what I put together to compare & test.

Faital 3FE's (20W each) cost £85 Blue Aran
8 Faital 4FE's (30W each) cost £145
8 PRVs .......over £800!
I chose Faitals mainly because of their efficiency/smoothness/cost & availability in UK.

My testing has revealed the Faitals to be superb drivers. As a general rule with full rangers, I would say smaller diameter drivers have a smoother and higher top end, compromising the low end. In this case, I am not concerned with low mid end as I am using in combination with the woofers. I have, however, rolled off the low end frequency (200hz) these drivers see to take the stress off them.

In brief they are very smooth with more extended treble than PRV's.
The 20Watt 3 inchers started to smell with high concert level SPL's, but weren't distorting.
The 30Watt 4 inchers handled the SPL no issues, and sounded fuller in the vocal range, but not as extended on top.

I experimented by combining  the 3+4" drivers together & eventually settled on a 334433 arrangement.. This array was superb  handling  concert levels with smoothness & air.....and retained the PRV's speed & dynamics. More testing to follow, but I think I have found a combo that will outperform the PRV's at a cut price!

If anyone is concerned about comb filtering, don't be. There is none!

Latest update (June 2020) is the trial of the Tang Band W8-2145. Experience of whizzer cones in the past put me off, but I decided to re-visit.

Glad I did, as the treble on these is very extended and liquid.

I need to also point out I was persuaded by a friend to buy a DEQX when it appeared second hand on ebay in February. I was dead against having something digital in the chain-line, but my friend said if I didn't like it, he would buy it off me. It was totally transparent, and even running completely flat it was cleaner & more dynamic than my passive its staying. Have to admit I have not been brave enough to set it up yet, but I have dabbled with the HPF and eq pages. I am finding now that any speaker can be made to sound great with this powerful tool....and all the characteristics that are uncomfortable to listen to can be tamed.

In short, the PRVs. Faitals & Tang Bang can all be made to sound great with eq, but I am noticing something special with the TB's. Watch this space & will report back once fully run in.


First let me say, I am well pleased with the UM18 /Behringer combination. This gives me everything I want in the bass department and I have not even thought about a replacement.
The Full Ranger, on the other hand, is something I believe can be improved. So I spent most of the summer living with and testing different units.
I went through these 8" whizzer drivers:

The Tang Band W8-1772 was a more refined version of the 2145 with Neodymium magnets and greater efficiency. This was an impressive unit with a full, sparkly lush treble. However, it needed eq with a rising treble rate and a few peaks that needed controlling.

Around this time, one of my buddies with similar system to mine was waxing lyrical about the EMS Field Coils he had running in his system. I had been curious about this technique so ordered a pair of EMS LB8EX MkII. I also needed to order power supplies to drive the coils.

For sure, once run in, these were the best drivers I ever had in my system. My friend hearing them called them 'immersive'. A good description because they totally immerse you in the music without drawing attention to themselves.

They are large heavy units with same efficiency as the 1772's.

Initially treble was quite hard, but this softened with run-in and became similar to the 1772.

The main thing I noticed with run-in, though, was the lower mid. Running these drivers in a baffless configuration really doesn't do anything for lower mid, and this has to be compensated for by the woofers, but with time I noticed this frequency range getting thicker & thicker, so much so I had to reduce my crossover. This is the first time I have had to do this.....but the EMS were outputting so much lower mid, the sound was getting muddy!

Now, the caveat is I still had to apply some eq to tame the 1-4k frequency range, although much less than the Tang Bangs. I am thinking as these run in they may need less & less eq. My buddy is running them without, although he has a baffle.

This seems to be a characteristic of all these full range whizzer drivers I have tried....maybe because I am not using a baffle, or maybe the synergy with the rest of my system. Either way, I cant really recommend any of these drivers if you cant use eq.

Possibly, the best sounding drivers without eq I have tested so far would be the Faital array.

Which brings me to my next update!

So, this is a total departure for me. I have left the design & acoustics to another this case Anthony Gallo. I managed to source a refurbished pair of Strada 2's and incorporate them into my system. 

I fired these up with some trepidation.

Initially I thought I had made a mistake. They sounded really dull & subdued :(  Then I remembered I was running them with eq. I removed the eq & ran them flat....they came to life!

Before I pulled the trigger on these, I read all the reviews I could. All very positive, especially with the imaging they produced. This was the first thing that hit me too....and actually, because the are 'baffle-less' the soundstage is very deep taking place behind the speakers....similar to open baffle.

I can detect no boxiness, and if you knock the metal chassis, it sounds totally solid. There is no crossover inside, only an impedance matching transformer and capacitor. They are efficient @ 90db, have huge dynamics and maintain their integrity at volume.

With 50 hours on them, they are still changing. I notice treble becoming more extended, but also lower mid which is huge, I guess effectively due to the sealed box loading. My crossover now has gone from 275hz to 150hz, and I may have to reduce further.

At some point, I will swap with the EMS's to see how they compare, but at the moment, I am really enjoying the Stadas!

New Update Feb 2021

This latest update and direction my journey is taking me in has been a surprise. After doing the whole Open Baffle no cross-over thing, and having formulated certain beliefs along the way,  am now back into sealed boxes & cross-overs  

Trying to follow the purest path of using a single full range driver with a direct connection of voice coil to amp did not work in this type of box-less, no-baffle configuration. All the FR’s I tried all tended to break up around 1-4k which subconsciously was forcing me away from my rock roots, and into softer more acoustic type of music.

My experience with the Gallos has demonstrated a box can be totally inert.....maybe it needs to be made of metal and a funny shape. At least the Gallos conformed to the no electronic cross-over in the way sapping power & detail from the amp belief as they only used a capacitor to protect the tweeter. The Gallo being a no-baffle design retains and openness that is in keeping with Open Baffle I have not moved away from that.

But now, I have gone for sealed box & full blown crossover. The pain & sacrilege!

Let me explain. Going for a single FR driver I was after a point source. Didn’t work out too well, but using a mid & tweeter in dual concentric arrangement would achieve the same thing. I had lived with the Hawthorne Iris in the past....but it was too laid back for me. Having cut my hi-fi teeth on Kef in the 70’s (didn’t we all?) I kept abreast of their developments and was always curious about their Uni-Q driver. I dismissed them because they used a crossover and came in a box.....but now using the Gallos, I was half way there.

I wanted to try something cheap....just to get a taste. Aware of the Home Theatre pods Kef were famous for, I studied the range.
I homed in on the HTS-3001.....3rd Generation pods from 2006.

The Uni-Q driver was using a Neo magnet, a sophisticated crossover & was 88db efficient. The box was cast aluminium and a funny shape. So, we are in Gallo territory, and down 2db on efficiency. I could pick up a pair of these from eBay for £ hifi terms.....a steal, so I pulled the trigger.

I made a simple right angle bracket and mounted the units to the pole above my UM’s. These things were light....2kg compared to my 6kg Gallos!
I fired them up and adjusted the bass to compensate for the lower efficiency and sat down for a listen. Initial impressions were good. Treble was smooth and extended, detail and dynamics were there.......but....ugh....they were boxy and they had a lower mid characteristic I could only describe as ‘tubby’.
I realised I wasn’t going anywhere with these, so replaced the Gallos. This helped me to re-assess and confirm how good they were!

However.....I am a tinkerer by nature, and don’t give up easy. The 3001 pods were reflex loaded with a long plastic port. What if I turned them into sealed units? I don’t need the bass extension anyway.

So next day, I performed some surgery and split the eggs open. I was pleased with the build quality, Kef went through a lot of trouble to make sure nothing rattled internally and everything was properly sealed. They were a bit stingy with the damping foam though with only a 6” square of that white felty stuff.

Anyway, proceeded with the plan of removing the port and sealing the hole. I am lucky to have a small lath so could easily turn an aluminium plug and used some hot melt glue to seal in place. I then proceeded to line the shell with 2mm car sound proofing panels, stuffed the cavity with some denser foam and sealed the unit back together.
Replaced the modified pods and fired up.

Well.....what can I say. My jaw dropped. The box was gone and so was the tubbiness. The presentation was as clean & clear as the Gallos. Now I could hear the Uni-Q driver unhindered by the colouration of the port. This was certainly something I could live with. The point source imaging was on a par with the Gallos, if not better.

Been living with them for 2 days now. I been throwing everything at them to trip them up. They do scale, volume, hard, soft, rock, jazz......I am totally stunned. I have not had a single inkling to put the Gallos back....and I think I know why:

The Kefs are more musical & immersive than the Gallos which are clinical & analytical in comparison.

I have more listening to do and maybe I will come across a flaw. Need to point out that I restrict the bass frequencies going to all my non-bass drivers. This allows them to play cleaner & louder when they are relieved of bass duties.
Will report back in due time!
Well....the single pod update didnt last long! Even though the single pod gave me SPL level of 105db, I couldnt resist doubling them up!

This has resulted in a 6db gain in efficiency (+3db adding extra driver, +3db halving ohms in parallel). Have had to boost subs to keep up!

Cant get over how good this combination sounds in my setup. Kefs are very musical and integrate flawlessly with subs. Crossing still at 120hz, same as Gallos. 

The twin Kefs  now are much fuller in lower mids than Gallo's were, so some recordings of female vocal can sound a bit 'chesty'. I had to compromise and increase roll-off of the Kefs from 100hz to 200hz. That has nailed it now. Hopefully done with updates for a while & I can sit back to enjoy!

KEF Center channel pod update March 2021

Being so impressed with the HTS3001 Satellites, I decided to invest in a pair of 3001 Center channel pods. Unusually, these were dedicated units.....not just a satellite pod turned on its is the usual practice!

These pods are larger & heavier that the satellite pods as they need to accommodate a pair of tiny woofers. From what I can gather, these liberate the Uni-Q Driver from bass duties, allegedly producing a sonic midrange advantage. The pod is also a sealed reflex port.

Internally, the pod is divided into 3 sealed compartments by clever use of the crossover circuit boards. I did beef these up with the usual car dampening material, as well as applying to the inside of the pods. I also inserted more foam.

Auditioning these pods was a revelation. They are voiced slightly differently from the satellite pods. Immediately obvious was more emphasis in upper treble seemingly giving more detail. There was also none of the 'tubby-ness' associated with the satellites.....presumably because this is a sealed unit.

The other thing I notice is more lower mid/upper bass detail. Very delicate, and something I am not used to. Hmm....I think I will like these....more listening. Also, a couple of db more efficient than satellite pods.

Just mounting is a bit awkward as they are long & deep. Off center solution mounting to side of pole seems to have worked.

Hear them in action: 3001 / UM18 hybrids


Been living with these CCP's (Center Channel Pods) for a week now and something interesting has come to light that has caused me to re-assess my beliefs on OB.

OB is fine for treble & upper mid. From my experience, I have unfortunately not found a full ranger that will reproduce this frequency range to my satisfaction with all types of music, but splitting the range between different drivers (mid/treble) will work fine, especially if you have expertise in designing crossovers. However, in this short wavelength frequency range I am questioning the benefit of Open Baffle. Certainly, with the design of the  metal pods I have been using in the Gallos & Kefs, the colouration and boxiness associated with many wooden enclosures is non-existent. Also, these designs being 'baffless' allow a wide spread of the sound waves emanating from the front to reach the back and create an openess associated with open baffle. I am certainly not missing the OB presentation.

Regarding the bass frequencies, I think this is where OB is of great value, especially in the configuration and drivers I am using. The face to face -push/pull arrangement gives great control and directionality of the longer wavelengths and  creates fewer room modes.....a problem that has always plagued me with boxed speakers.

The issue with OB bass is getting to the low frequencies with sufficient SPL. So, you can increase the baffle size and achieve lower frequencies & higher SPL's.....but there is a cost. Increasing the baffle size
or incorporating fancy U-frames, W-frames, H-frames etc., also increases the room modes. Damn. I have had situations where my U-framed Dipole 18's totally cancelled the bass in my listening position. What is the point of that?

So, with my face to face naked arrangement how do I get any bass? The secret is choosing the right driver. This needs to have a large heavy cone with big Xmax, and be capable of taking a lot of watts! The UM18's suit this application perfectly. I have been using this arrangement the last 3 years, and have never thought about using anything else. They totally satisfy me reaching seismic depths and power when required, but without inciting any room modes. These will reach 20hz, and the highest I have crossed at was 275hz.

.......but where the bass meets the mid creates an issue that these latest pods have brought to light. I have discovered a frequency range that has  been missing detail in my system, one that these CCP's excel at....the 80-300hz region. Previously, my woofers would be delegated to  produce these frequencies, but the detail the KEFs produce are  a revelation.  I never realised how important this frequency range is, and usually just assumed the woofer would fill it in. In fact, this range includes leading bass edges and lower vocal registers. I was missing, for instance, the fine detail and impact of a plucked bass string and the detail & clarity of deep vocals. I guess this is something the multi-driver guys knew all along, but something I was ignorant of.

My Bastanis used a 12" driver in OB configuration to get down to 80hz. The CCP's use a pair of 3" drivers in a box. Which do you think sounds better? Not sure how you can get an OB driver to produce this frequency that is as detailed & fast as the KEFs. A small, nimble driver used in OB will start to roll off at 500hz. Maybe using a bigger baffle it could be lowered to 300hz. Then you start compromising imaging and baffle effects. 

I had been using my UM's to fill the gap up to 275Hz. Its quite common for woofers to be used in this way.....and you can tailor the crossover via DSP to make a seamless transition. But you can hardly expect a driver that produces 20hz to be very detailed & nimble @ 300hz. Well.....I thought I was faithfully reproducing this frequency.....but the CCP's have showed me clearly not! Perhaps using a lighter coned more efficient fabric surround  woofer would be more nimble? Well. perhaps.....but it would miss out the bottom octave I have become used to, and would not match the attack and detail of the 3" boxed woofers. Dont forget, I have tried!

Its one of those things I never knew was a problem until I heard it. I have been living with OB for years, doing what I thought was a great job crossing between the bass & mid. You don't really know what you're missing until you hear it. It was a similar experience going from a belt drive to direct rim drive.

By the way, the Satellite pods (or the Gallos) I was using previously don't produce detail at this frequency either. This was left to the UniQ driver to produce. With the CCP's, the 3" drivers cross with the UniQ @ 500hz. Something funny going on with the Satellites below 500hz. I reported they were 'tubby' in their stock state, and blocking the reflex port helped. Even so, they still bloated on some material, and I found it was best to roll them off around 150hz.

Here you can see a bigger bass hump in the CCP, yet there is no bloat while listening.... and these will produce useful output to 70hz where I set the HPF to protect the drivers from deep bass excursions. I have dialled in the crossover from the UM18's to the point where they just start to encroach the 3" drivers.

In contrast, the Satellites need to be rolled off higher, between 150-200hz. If I let them extend lower, they sound tubby & muffled.

In summary, this speaker journey has taken me from conventional boxed speakers to a no-baffle, no-crossover woofer assisted full range design to a hybrid no-baffle woofer assisted multiple driver boxed design with crossovers! Nutz...............

..........more listening............

Update end of May 2021: 

My curiosity got the better of me. As I am now back in bookshelf territory I decided to try one of the many formats on offer. Q Acoustics,  Elac, Wharfdale etc., all get acclaim. In the end I got attracted to the Klipsch with its Tractrix horn & seemingly high efficiency which made it stand out from the rest.

Quite enjoying the RP-500M's at the moment. Music seems to flow from them in an unrestricted way. They are slightly more efficient than the Kefs, but image in a similar way....I guess the Tractrix horn acting as a point source. Most noticeable difference is the upper bass slam.

Been living with this setup for a month now....still loving what it does and no desire to change anything.

I have had a few enthusiasts email me to point out I have it the wrong way around....the woofers should be boxed, and the mid/tweeters should be open. Indeed, if you search the I'net, there are many examples of this type of arrangement. But I think I have this right.....I will explain.

Using a boxed speaker for the top, and restricting the bass being fed to it, the quality of the box becomes less relevant. Its the bass frequencies that suffer with resonant boxes, so the more expensive the speaker, the more the manufacturer puts into the box in terms of materials, shape, bracing & isolation in an attempt to render it inert. Restrict the bass the speaker needs to reproduce and this becomes much less of a problem, so you will get away with a cheaper box.

Conversely, I shudder to think of the box that would be necessary to neutralise the resonances emanating from the UM18's, which would be seismic. I don't event want to go there, but have seen the lengths people will go to attempting to create an inert box! Letting them operate in free air surely drastically reduces the loudness of the bass they can produce, but the quality remains unmatched by any boxed speaker I have ever heard.

My experience with open baffle is the problem creating upper bass/lower mid frequencies...say from 100-300hz.
Typically, the drivers I tried roll-off would begin @500hz ( a bit less with a baffle). To fill this gap, the woofer crossover would need to be raised, or a larger (12") driver needs to be used (Bastani).

My experience has shown the woofers or 12" driver will not produce this upper bass frequency with the detail, slam & fidelity of a boxed speaker. Like I often say, you don't know its missing until you hear it. Indeed, I spent years with such a setup without realising!

I think the combination of open woofers and boxed mid/highs is a winner so will be sticking to this.....unless proved otherwise. would be easy for me to change the 'flavour' I am getting from the Klipsch by simply substituting another boxed speaker. I have been digesting many reviews, but so far I am not tempted.