[mcgsxr]

I have been listening to OB in my main system for 3+ years now, and am very happy to have found this particular alignment, and played around with optimization for it, in my room, for my ears etc.

This week, a fellow AC member has borrowed my Bolder modded SB3 in order to get a feel for the performance, in his own system, at his place.

He was also kind enough to lend me some gear to play with, while my transport/dac/pre is out of the system.  He lent my some PMC DB1 TL bookshelf speakers - http://www.soundonsound.com/sos/jan03/articles/pmcdb1.asp. 

Because I use the SB3 as my sole source for my system, I have had to remove the old Magnavox amp I use, and return to the use of my JVC EX A1 - http://www.jvc.com/presentations/exa1/features/index.html#unit.  This is a small format integrated/cd player that leverages JVC’s Hybrid Digital Amplification – for those of you that recall the JVC F-10 and the ES1SL that preceded it – my best friend still uses one of these in his HT system, with great results.

I did listen briefly to the PMC’s run by my Maggie tube amp, but with only 3-5 wpc on tap, and an efficiency in the mid 80’s there was not much volume on tap.  I am currently running them with the 20-30wpc that the JVC puts forward - I believe that more power would be better, but that is all I have - since making the move to high efficiency speakers, I don't really have powerful amps around anymore.  I did plug the PMC's into my Panny SAXR-10 receiver, and fed 100 wpc, they really start to sing.  They are darn good little speakers!

So, there has been a complete change in the system, while I have lent out my SB3.

The point of this post, is to try to get at the heart of what I am hearing, between the two types of speakers.  I find the PMC’s to be very good stereo speakers, with a very tight, defined soundstage.  The treble is engaging without being sharp or edgy, and the bass is very full and tuneful – my first exposure to TL bass – nice.

What I find about these, and most monopole speakers, is that although the stereo image is very defined side to side, the depth is not as satisfying as with OB speakers.  It is in no way a knock at the PMC’s, it is a comment about dipole vs monopole.

For me, the appeal of the OB sound is multi-fold, and being given the opportunity to hear some good "normal" speakers is helping me realize some of that appeal - depth of sound stage, room filling nature, timbre of real instruments truly represented etc.

What else have other people noticed, in coming from “normal” speakers, to OB?

[Graham Maynard]

Hi mcgsxr.

Monopoles excite room modes, and I can always hear the box or pipe behind the cabinet.
Tap the edge of the main cone and the side of the cabinet without music playing and the sounds you hear accompanies all your music. 
Once I recognise that, and especially if it excites a wall/floor/ceiling reflection mode I cannot enjoy the same !
The 'sound' of an artist comes from the front monopoles, whereas from bipoles or dipoles the 'artist' is in your room.

However monopoles are easier to site and can provide a better radiation pattern than dipoles, yet bipoles provide a better room 'fill' than both though with a well defined image from their front only.

Cheers ........ Graham.

[-Richard-]

Hi mcgsxr ~

Recently I found a dealer very close to me that sells Harbeth speakers right from his home.

I love Harbeth speakers... they originally came about as a challenge from the BBC for a "generic" speaker design that could reproduce the human voice broadcasted from BBC radio as faithfully as possible. So the Harbeth... like many British speakers... are "tuned" to the human voice... they have an addictive tonal "open" quality that I really like.

Deb and I went down and made ourselves comfortable in this rather nice chaps home in Ventura... only perhaps 20 minutes away from Ojai. He had 3 or 4 different Harbeth models on hand. I brought my own CD's that we were both quite familiar with from our OB listening.

I was amazed at how unappealing all the models sounded... "boxy" "closed-in" "mechanical" "artificial" "Hi-Fi'y."

The dealer even admitted that I was hearing the "box"... he had asked me my impressions... and from what I told him that was his response.

Soon after we left, Deborah made it clear that she thought the Harbeth's didn't even come close to the OB's for that real-in-the-room-palpable-visceral-tonally-rich sound. I agreed.

I am using my Korneff 45 SET with a Peppard Magic 5B preamp... with my OB's the combination goes beyond anything I ever imagined I would be able to enjoy... music is "alive" in my house.

Warmest Regards ~ Richard

[rajacat]

Richard,

Can the limitations of box speakers be overcome? What about AudioKinesis speakers that employ a box to contain the drivers? They seem to be garnering rave reviews including some fans of OB speakers. I haven't read  comments about their sound being constricted and colored. So I guess you can't speak in absolute terms regarding the superiority of the OB configuration. It all depends on a variety of design factors including the deadness of the box. From what I've read the Harbeth designers deliberately use the box to tune the sound therefor they are not a particularly appropriate box speaker to use for comparison.

-Roy

[Graham Maynard]

Hi Roy,

Put several pages of a newspaper over a driver cabinet or TL opening and tap it - the same returning entrapped energies you hear can never fail but to come back out and re-influence a LS cone after the music has already moved on.

By the time box characteristics are 'dulled' by damping so too is LS reproduction because the relationships of rear of cone pressures and inner wall reflections are merely modified, not removed.

Have those AudioKinesis loudspeakers been compared side by side with a decent open baffle ?

And if any cabinet is euphonically 'tuned', again the augmentation cannot arise until after the energising wavefront has moved on.

Whenever rear of cone energies are used to tune or augment front output, even with TLs, the energy which was subtracted from the original cone motion should already have contributed to the forward output.  Thus the leading edge or transient amplitude of forward radiating sound pressure wave has already suffered a subtraction, and this is why the 'hit' from say a snare drum can become reduced and muddied as soon as you put a driver in a cabinet; the rear of the cone is doing work against or generating a secondary trapped pressure wave within enclosed air.

Snare drum strikes are physically, as well as audibly, much more realistic from an open baffled driver.

Box loudspeakers might also do louder 'bass' without being large, and be much easier to position within a room than a dipole, but when it comes to immediacy and open reproduction from a kick drum the same stored energy aspects arise.  The initial kick from a boxed driver is less because rear of cone energy is being stored to augment front output later in the cycle, and thus the sound becomes more of a dull 'thud' than the pedal induced air flick.

At the same time however, the roll-off of a driver on a baffle can be just as severe below Fs as with a resonant cabinet, due to baffle and driver losses combining.  So in order to sound natural, the very low bass from a baffle will still need *additional* correction, or additional driver area to compensate for both phase change and displacement loss below driver Fs if a low Fs driver is not used.


Cheers ......... Graham.

[JLM]

I'd expect the PMC to sound as you've described Mark, after all they come from the Professional Monitor Company.  With a heritage born in the studio, depth of soundstage shouldn't be expected to be a high priority especially compared to speakers with the same energy levels front and back.  Glad you liked transmission lines, now you should try some fuller range TL's.   

Bipole design (like the AudioKinesis speakers) will provide a deeper/bigger but less defined soundstage compared to "normal" box speakers without the front and back sound being out of phase with bass cancellation of dipoles (like simple open baffles).  OTOH they require twice the number of drivers (that hopefully have been closely matched).  Either can provide a diffused, room filling sound.

There is no perfect speaker, but with the right extended range drivers a TL bipole could get pretty close IMO.

[rajacat]

Hi Roy,

Put several pages of a newspaper over a driver cabinet or TL opening and tap it - the same returning entrapped energies you hear can never fail but to come back out and re-influence a LS cone after the music has already moved on.

By the time box characteristics are 'dulled' by damping so too is LS reproduction because the relationships of rear of cone pressures and inner wall reflections are merely modified, not removed.

Have those AudioKinesis loudspeakers been compared side by side with a decent open baffle ?

And if any cabinet is euphonically 'tuned', again the augmentation cannot arise until after the energising wavefront has moved on.

Whenever rear of cone energies are used to tune or augment front output, even with TLs, the energy which was subtracted from the original cone motion should already have contributed to the forward output.  Thus the leading edge or transient amplitude of forward radiating sound pressure wave has already suffered a subtraction, and this is why the 'hit' from say a snare drum can become reduced and muddied as soon as you put a driver in a cabinet; the rear of the cone is doing work against or generating a secondary trapped pressure wave within enclosed air.

Snare drum strikes are physically, as well as audibly, much more realistic from an open baffled driver.

Box loudspeakers might also do louder 'bass' without being large, and be much easier to position within a room than a dipole, but when it comes to immediacy and open reproduction from a kick drum the same stored energy aspects arise.  The initial kick from a boxed driver is less because rear of cone energy is being stored to augment front output later in the cycle, and thus the sound becomes more of a dull 'thud' than the pedal induced air flick.

At the same time however, the roll-off of a driver on a baffle can be just as severe below Fs as with a resonant cabinet, due to baffle and driver losses combining.  So in order to sound natural, the very low bass from a baffle will still need *additional* correction, or additional driver area to compensate for both phase change and displacement loss below driver Fs if a low Fs driver is not used.


Cheers ......... Graham.

Hi Graham,

Thanks for the detailed explanation of the acoustical merits of open baffle speakers. I've been toying with installing some Fostex 127Es that I have into some cheap plywood baffles just to get a hint of the OB experience although they may not be the optimum OB drivers.

It would be interesting to compare  AudioKinesis (the latest rage) to a competently designed OB. Of course there is the Emerald Physic OB speaker which is also garnering much recent publicity that would seem to be a natural competitor and a suitable match for the AudioKinesis. The Beringer DCX, required for the Emerald Physic, detracts from the elegant simplicity of OB but, I presume, there is no way to get it right without this complicated gizmo.

These are both relatively expensive speakers. It would be nice to come up with an OB for less than $1,000 able to compete with them on equal terms.

-Roy

[opnly bafld]

It would be nice to come up with an OB for less than $1,000 able to compete with them on equal terms.

-Roy

How about $1100?
http://www.hawthorneaudio.com/catalog/index.php?main_page=product_info&products_id=20

Lin

[rajacat]

If those have comparable sound quality to the AudioKinesis and/or Emerald Physic that would be fantastic. IMO that would be a tall order since both the AK and EP were raved about and have been considered among the best at some of the shows .....price no object.

-Roy

[opnly bafld]

If those have comparable sound quality to the AudioKinesis and/or Emerald Physic that would be fantastic.

 
EP=$3500
AK=$9000

[rajacat]

AK has a cheaper model @~$4500. Perhaps I could've have been clearer.  I meant that it would be great if an inexpensive, easily assembled homebrew OB could compete with these pricey speakers.

-Roy

[ttan98]

If those have comparable sound quality to the AudioKinesis and/or Emerald Physic that would be fantastic.

 
EP=$3500
AK=$9000

I thought CS2 from EP is about $2,500 with lastest price increase, I am building something similar CS2, the quality compression driver and horn I used is of better quality that that used by CS2.

I am >10,000km I don't how my system sounds like compared to CS2. That does not botther me as long I like it.

I will post here once take a few pictures.

cheers.

[rajacat]

Yeah, certainly would be interested in your super clone of the CS2. The CS2s are $3000 currently although I've heard that there will be an increase soon. Also there's all the mods, upgrades to the DSP to tempt you.

-Roy

[ttan98]

Yeah, certainly would be interested in your super clone of the CS2. The CS2s are $3000 currently although I've heard that there will be an increase soon. Also there's all the mods, upgrades to the DSP to tempt you.

-Roy

I am afraid it is not a clone, just using similar design concept as CS2(ie tweeter woofer woofer TWW that is all), differences are:

1. I use 2*12" woofers(I like to keep width narrower also my room size is small to medium size) instead of 15" used by CS2.

2. I use x-over at around 1.7khz, CS2 at 1.0 Khz very steep x-over, hence I can use less steep x-over. Currently using 3rd order Butterworth asymmetrical at around 1.7Khz.

3. I use square horn by RCF, CS2 uses circular PE horn which is inferior(I tried).

4. I use B&C compression driver whereas CS2 uses Selenium drivers(cheaper). So far no equalization reqd on my compression driver and horn combo. I think CS2 uses equalization on their compr. driver and horn combo provided by DCX2496.

5. My woofer is different from CS2. My woofer is inferior to CS2's. If I use better quality woofer the sound quality on my combo would improve further.

6. woofer mounted on U-frame no equalization is required, flat to 40-45Hz, CS2 uses straight open baffle, equalization performed by DCX2496.
   
Currently I use DCX2496 as x-over, in the longer term I will design passive to check whether it is really better than active x-over. Notice I don't use equalization hence designing x-over is much easier.

I believe the design concept is sound you can use this concept with success and the material costs are minimal, the compression driver and horn combo costs $130 per side, the 2*15" woofer about $160-$200 if you use Eminence drivers. DCX2496 about $250. parts alone cost about $910.

The initial CS2 price of $2000 is not really expensive, infact a fair price.

cheers.

[Graham Maynard]

Hi Roy,

More discussion thoughts.

I went right off multi-way monopoles, and blamed their distinctly audible sound characteristics upon electrical crossovers disturbing the waveform coherence.
But maybe there was more - the separate 'crossover' plus rear of cone energy 'storage' mechanisms acting separately and differently in music time, yet being coincidentally and electro-mechanically in series !

Most OBs start out with a widerange driver in order to reproduce voices and the tonal character of instruments in a way I have not heard via any crossovered or enclosed driver design.
These are then augmented at LF and HF if necessary to encompass everything which should be audible.

There is then compromise due to that main driver, for if the voice coil is underhung to ensure definition, and the cone is large enough to cover lower frequency voice fundamentals, it starts beaming due to the centre and edge of cone radiating simultaneously and causing a lens-like focussing effect at higher frequencies.

The beaming is however very easy to cure using fingers of light foam coming in from the edge of the baffle towards the centre of the driver.  This disperses/reduces the edge of cone output and stops the beam from becoming so intense, and, the response is entirely adjustable to suit personal preference.
One finger say coming up vertically from below and very close to, though X.lim clear of, the cone can cover the lower edges of a centre dust-cap and horizontally disperse the high frequencies too !
http://server6.theimagehosting.com/image.php?img=Fingers.a9d.jpg
I have used more fingers as necessary.

Thus the 'esses' of voices and the wispy brushing of cymbals can be returned to proper level relationships with the rest of the normally radiating forward AF.
I use foam off 4" (10cm) paint rollers soaked in boiling water to soften the adhesive, and then peel the foam back off the rotating shaft.

So beaming is quite curable *without* introducing series impedance circuits which will separately store and release electrical waveform energies in music time.

One of the reasons a tweeter usually makes listening worse with a widerange driver is due to that main driver beaming.  
The tweeter cannot approximate a level/phase coherent crossover point once the beaming has started, and yet crossing over at say 2 to 5 kHz to overcome beaming is for me what ruins the normal OB advantage.
However, once the beaming has been managed it is then possible to add a supertweeter above maybe 10 to 12kH if desired, to add that last bit of reproduction fluidity on voices, etc.

Bass can be a problem with widerange drivers which have limited X-max, whereupon augmentation is a simple matter of adding a large coned driver as per Eminence, Hawthorne etc., or this example;-

http://www.enjoythemusic.com/magazine/equipment/0606/visation_nobox_bb_loudspeaker.htm

Note in this article that the bass response was further extended by using a tube amplifier, though it would take a fair bit of 'bottle' to have sufficient output at higher impedance due to the voltage headroom which is necessary to generate the series impedance.  
Also, *ALL* output voltage developed across the amplifier-output/loudspeaker-input terminals - mid drive too - would be modified in *music time* by the fractionally delayed phase and amplitude shifts induced in the amplifier output by the bass loudspeaker's electro-mechanical characteristics. 

Either drivers do not generate back-EMF in response to voltage drive until after the voice coil has moved, or, where the amplifier output is purely current, the voice coil simply cannot start the cone moving with the same force as from voltage drive, and thus is less able to counter cone mass inertia and suspension stiffness though will allow mass/compliance induced fundamental resonance because there is no electrical damping.  Resonance might sound euphonic, but beyond a critical combined electrical-mechanical damping is most certainly not a desirable reproduction characteristic.

!!!  This aspect should always be borne in mind !!!  

Current source amplifiers might help increase LF and HF amplitude responses, but this does not happen without overall leading edge waveform coherence being modified in music time, and thus transient responses become degraded.  Might suit classical music, but not percussion and electronic instruments.

It was for this reason I made the completely separate passive 'T'-bass transformer driven circuit to provide the same tube like boost from a SS amplifier output, without the co-connected amplifier drive to a widerange driver or tweeter being simultaneously affected;-
http://www.audiocircle.com/index.php?topic=53322.0

For me it is the widerange driver which is the whole point of going OB in the first place, not coaxials, not bass/mid/tweeter or mid-bass/tweeter, but as wide a range of reproduction as is possible with a good driver, then augmentation as necessary and if desired.

Cheers ........... Graham.

[jkelly]

I am also building a CS2 clone.  The drivers are now mounted and ready for testing.
More to come.






Jeff

[opnly bafld]

http://www.emeraldphysics.com/pricing.htm

Considering the CS2's are sold through dealers I think the price is very fair.

I compared the CS2 ($3500) to AK's Dream Maker ($9000) because it is a bipole speaker which IMO comes closer to the OB sound than monopoles.
I liked both speakers a lot when I heard them at RMAF. 

IMO it is hard to beat OB (done right) with no box bass.

Lin

[mcgsxr]

An interesting series of posts, as I expected it would be, given the typical constituency of the OB Circle!

JLM - indeed, the PMC is my first cut at TL bass, and I can definitely understand the appeal of this alignment - even this baby bookshelf implementation shows well the abilities of TL - tuneful bass, in line with the rest of the presentation - not boomy, and not sloppy.

Rajacat - not sure that Richard meant specifically to call out the Harbeth's, I think he was just reporting on what he heard, and preferred.  So too, my careful discussion of the PMC - an excellent little speaker, better by memory than the Totem Rokk's I owned for 10 years, and clearly a great choice where video shielding is not a concern, and there are watts on hand - I think they would sing with 100wpc or so if SS power.

I simply find that boxed speakers, in general, fail to deliver what I find entrancing about OB - but, I am not saying that they are not as good.  I think it comes down to what each person prioritizes around reproduction, and there are tons of threads here about the best technology etc - and tons of different opinion.

I started the thread to see what folks who enjoy OB feel is what attracts them to the sound - it does seem different from other driver implementations, and as well documented, relates to a specific series of trade offs - but, it attracts people, and I am interested to know why.  Especially since I am currently able to hear some good boxed speakers at the moment, and recognize their abilities, but in the end prefer my less attractive speakers.

I am interested to follow the experiments of those building other OB speakers, and appreciate that all would share their efforts and results here!

[Bob in St. Louis]

Hi Mark,
For me, open baffle gives a sense of clarity and presentation I've not heard from a box.....yet.
The term "openness" comes to mind regarding sound quality, no pun intended. With your eyes closed, OB makes your room larger and gives the audible impression that vocals and instruments are coming from places in the room that couldn't physically be possible as they appear to originate beyond your walls. This despite the point source origin. The sound is superbly clean and revealing given well recorded content. The snap of a plucked guitar string seem to have no location what so ever. It's just 'there', like the artist really is in your room.
Regarding OB bass, well, what can I say? it's like no other. There's rumble without the boom. There's bang without the mud. Given enough cone area, your pants can be felt on your legs and you can have that kick in the chest tactile feeling without the slightest bit of distortion, mud, or boom typical of a box.

Clean........

Boxless Bob

[Dmason]

I think it would be easy to improve on one, and less likely on the other. THe AK stuff is using ultra high quality TAD, and Beyma drivers, a state of the art waveguide whose geometry was developed by Earl Geddes, so that would need to be taken into consideration. Good parts begets good results, and Duke's inventions are THE best monkey coffin speakers, I personally have ever heard. I would like to hear the DreamMakers actively crossed over, and use of SET amp on top, and something else on the 10 inch TAD's. Active XO always improves things, usually in no small way, either.

While I wish the AudioPhysic people all the continued success they clearly deserve, I see it as an essentially flawed design, with large cones mated to small format compression drivers, each driver working outside of its optimum  operating band, and worse yet, crossing over right smack dab in the middle of the presence zone is a no no. It would have been easy to include one compatible wideband for the mids, and be a much more successful design. I can think of several 6-8 inch midband drivers that would sound wonderful.

Using one really good bass driver seems acceptable, depending on your SPL requirements, two seems to be better, and Bob in St Louis likes lots of them. There are no rules. Now I see Graham has his bass enhancement circuit which is a good thing, and allows baffle widths of no more than 18 inches.

If I were to start a new OB project I might use the new AE Lamda IB15 ,or the Auggie, which enjoys success, possibly a Tone Tubby of some type, hemp in the mids is fabulous, and crossover to a compression driver/horn-waveguide around 2.7-4kHz. This way you could easily and inexpensively bi amp the bass speakers with BASH plate amps, and use low powered tube amps for the mains, and avoid crossovers anywhere between say 150-4kHz. Just thinking out loud