PIC'S OF ICONIC'S DEMO ROOM @ GREAT PLAINS AUDIOFEST IN TULSA!

[homme_de_terre]

BobR,

thanks for your analysis. What is the audible impact of this flaw when you're on axis? How could that be cured? First thought was some kind of diffraction slot like on those old BBC monitors.

Manfred

[Todd W. White]

New of course!

[gearjammer]

So How much would the stonehenge V cost as a turn key ready to power up and take flight purchase as it sits there in the show room floor???
Cash and carry???

[Todd W. White]

It all depends on the finish. If you want them in the standard red oak with a standard stain and hand-rubbed tung oil finish (std also), that's one thing. If you want some exotic woods and/or finish, the price goes up.

E-mail me @ [email protected] for a quote on your specific needs.

[Jim D]

I would like to rspond to GM and Bob R about the horn/woofer issue of the 704s. Firstly, nothing we do in audio is perfect. The 704 has a far better HF diaphragn and phase plug assy than either the Tannoy or JBLs. We do know about the difference of directivity of the integral horn and the woofer cone, but, there is just not enough room within the cone to get in a much bigger horn, yes we do have plans for some changes in the future, but it will be a ways down the road. Using the cone as the HF horn, ala Tannoy, Radian, Eminence, etc, while it may (underline may) have a more like pattern near crossover, does nothing to keep the HF from beaming at higher frequencies. At extreme HF the pattern is no doubt about as wide as a pencil lead. The internal Manataray horn actually holds a 60 X 40 degree spread to over 16K, this is real usability. So nothing goes for nothing, the current Mantaray horn is the best of all the production horns as for being constant in pattern. The older 604B (larger) Multicell was next best and the performance of the small "eggcrate" horn of the C, D, E, and G was just plain awful. The Mantaray was an answer to the Urei horn and was intended to return the lower HF performance to be more like that of the earlier 604B horn. I have never heard a Manataray v/s a UREI horn, but I imagine being the UREI is a radial type horn, it will also beam at the extreme HF. At this time we consider the current 704, with our improvement to the LF driver, to be the best of any of the 15" CoAxials available today, all things considered. JIM

[joyspring]

Manfred:

"thanks for your analysis. What is the audible impact of this flaw when you're on axis?"

You're welcome. The audible impact of this flaw depends on the ratio of direct-to-reflected sound at the listening position; that is, the closer you listen to the driver, you'll receive a higher proportion of direct sound than reflected or reverberant sound.

It's quite obvious the direct sound ought to be `flat' (equal amplitude across the audible spectrum).

However, it has been shown that uneven amplitude vs. frequency of reflected sound imparts subjective `colouration'.

That is the whole point of `near-field' monitoring that is now ubiquitous; to remove (so much as practicable) the effects of room acoustics from the listening experience.

The issue at hand really is not on-axis response but power response...

Compression drivers have falling amplitude vs. frequency; their plane-wave tube response curves typically exhibit falling response above 5-8 kHz.

Horns that have increasing directivity vs. frequency (i.e. - radial horns) typically have flat response on-axis as the angular coverage shrinks as frequency rises. If you equalise to flatten response at one particular angle off-axis (and its mirror about the axis on the same plane), then the on-axis response will rise with frequency.

A constant-directivity horn (i.e. - the Mantaray) has flat power response that tracks the true acoustic energy output of the compression driver (the plane-wave tube response) and therefore requires equalisation to flatten its on-axis response. This also flattens off-axis response within its rated angular coverage as well.

So the Iconic 704 with its constant-directivity Mantaray(tm) horn assures even power response at crossover frequency and above.

However, it is the transition between LF and HF drivers where the problem lies...

The directivity of the LF and HF drivers at crossover frequency are not equal, and it is this difference that is detrimental to the overall system power response...

JBL's John Eargle has written a very useful, informative and simplified sound system design manual that is freely available at the JBL online technical library:

JBL Professional Sound System Design Manual - 1999 Edition (Pt.1)

JBL Professional Sound System Design Manual - 1999 Edition (Pt.2)

Perusing professional system design texts will answer a lot of queries that audiophiles seem to ask regularly.

Additionally, try using `near-field monitoring' and `power response' as strings in your favourite online search engines; you'll find plenty of other resources that cover this topic

"How could that be cured?"

As the aforementioned JBL folks (and JimD) have both mentioned, the limited physical space in a 15" coaxial driver precludes any type of solution.

There is a reason why you don't see Altec/UREI-type coaxial monitors in modern control rooms any longer...

"First thought was some kind of diffraction slot like on those old BBC monitors."

As JBL finally realised in the late 1970s, those diffraction lenses caused more polar response problems - and hence, colouration and uneven power response - then they solved...

JimD:

"Firstly, nothing we do in audio is perfect."

Definitely in the realm of electroacoustic transducers, yes

"The 704 has a far better HF diaphragn and phase plug assy than either the Tannoy or JBLs."

I'd agree with the former (despite the Tannoy having very good extended HF response), but unless the 704 HF section is much-improved over the 604-8K, I do know a couple transducer engineers (one of whom worked at 1515 Manchester) who would disagree with the latter...

"there is just not enough room within the cone to get in a much bigger horn, yes we do have plans for some changes in the future, but it will be a ways down the road."

Now THIS is excellent news down the line and DEFINITELY what we ought to be hearing from Iconic; can't wait to see the proposed solutions

"Using the cone as the HF horn, ala Tannoy, Radian, Eminence, etc, while it may (underline may) have a more like pattern near crossover, does nothing to keep the HF from beaming at higher frequencies. At extreme HF the pattern is no doubt about as wide as a pencil lead. The internal Manataray horn actually holds a 60 X 40 degree spread to over 16K, this is real usability."

No doubt that the Tannoys, et al. do exhibit the rising directivity index... however, the Tannoy and to a lesser degree the Radian cone-horn coaxials that have a smoother LF/HF directivity transition are STILL being used for professional critical listening despite the rising HF DI (now whether I _agree_ with this is another issue).

Perhaps end-users felt the smoother transition was more important than a rough transition with smooth HF power response?

"So nothing goes for nothing"

Agreed. It would be preferable to have both the smooth LF/HF DI transition AND flat HF power response... and the highly-successful JBL 4430/4435 monitor series eventually accomplished just that. Unfortunately, they could not utilise a coaxial driver to accomplish it.

"the current Mantaray horn is the best of all the production horns as for being constant in pattern."

But the pattern of the LF is appreciably different below the crossover frequency in the 704, which is the issue at hand.

"...but I imagine being the UREI is a radial type horn, it will also beam at the extreme HF."

Yes the UREI does exhibit rising DI, and that's one of its major shortcomings.

In summary, we must evaluate these systems in their historical context: when the 604 and UREIs were initially designed and used, the notion of even power response and smooth directivity index at crossover really were not important design considerations; heck, a lot of companies were still attempting to achieve flat on-axis response at that time!

So when I mention that subsequent monitor designs (a la JBL 4435 and nearly every professional monitor afterwards) did not have these failings, that's because these issues were considered in the design phase.

Now that Iconic is attempting to market a current, modern product whose design predates some 20-odd years of research, eventually these failings will rear their ugly heads as competent reviewers in the media (DB Keele, Dr. Rich and P Aczel at The Audio Critic immediately come to mind) will take note of them straight away.

All I'm stressing is that we Altec advocates have to be prepared and willing to accept that while the Duplex was state-of-the-art in its heyday, its performance has been surpassed in terms of subsequent psychoacoustic research.

Let's stress what's good about these drivers and be forthright about their problems as well. Todd's assertion that measured data (i.e. - frequency response, polar response, etc.) will be published, `warts and all', is reassuring.

What I'm hoping is that we as a group don't become unreasonably defensive, much like those folks owning vintage 1940's hot rods regaling other enthusiasts with incredible (or rather, not credible) tales about outhandling modern Porsche Carreras on winding mountain roads, and such.

Anyhow, I will be purchasing a brand-new pair of 704-8As sometime this year; my father is retiring next summer (at 71) and I want to build a nice tri-amped system (704s + sub) for him so he can enjoy his 2000+ classical LPs, CDs and open-reel recordings of 1950s-60s FM broadcasts. A nice way to repay him for the Altec 605A he gave me as a child which introduced me to a lifetime interest and eventually a career in engineering and teaching audio.

BobR

[klausesser]

Hi Bob!

After using Tannoys at home (12") and as main-monitors (15") i agree to your saying about more even pattern at crossover.
BUT: when i went across a pair of 604E two years ago and having them near-finished now and knowig their weak points i nevertheless prefer them for home-listening after redoing the crossovers.
They?re more transparent and "light" in bass/mid-bass than the Tannoys, which are in my ears a bit too warm and "boxy". I?m speaking of ClassicMonitors with HPD385 passive or active amped.

I stopped using Tannoys 14 years ago and am using an active Manger-MSW now for work but am listening to the 604E at home and like their directness and easyness (i couldn?t describe it better in English, sorry) along with ?50s and ?60s jazz recordings from vinyl and tape.

Never thought i would say something like that one or two years ago - and they?re not even finished . . . .

best, Klaus

[Adhoc]

BobR,
Thanks for those links to the JBL manuals! Interesting and reccomended reading, as "tricky things" are explained in easy language.

[homme_de_terre]

BobR,

thanks again for your excellent remarks. Now I've understood what the deal is about dispersion. Gonna read the JBL papers later. Isn't it so much easier to obtain information today than,say, 20 years ago?
I love the information age.

Let's see if I got this straight:
At the crossover frequency of 1500 Hz, the LF section beams more than the HF section. If I interpret the polar plots on the 604-8Ks data sheet right, a more appropriate crossover frequency would be around 1kHz. What if I were fearless and extend the MR horn or replace it by a bigger one that's suitable at 1kHz? I wouldn't care about a protrusion within the range of a couple of inches.
Kinda brings the "Engine" design to my mind.

Manfred

[Steve Mac]

Looks like I have acquired the original showcase Stonehenge Vs from this show. A buddy of mine carted them back from Oklahoma at Bill's shop.
Here's a pic:
Stonehenge V

I will say the bass response of these cabinets is the fantastic. I put on some test frequencies and while it was down at 30Hz...there was a lot still there. I've also got a set of Bill's new replacement passive crossovers that are basically the stock Altec design. Don't have a lot of opinions yet...need to listen more. I need to do an A/B after I'm really familiar with what I'm hearing and then switch over to a bi-amplified sound. That should be interesting. The speakers are built well...but the finish leaves quite a bit to be desired. Oak veneer is not easy and it needs to match to work. I know, I built clock cases in a factory for a year. A mahogany deep red veneer would work. Especially if I use the big black grill cloth. If I could find a round black grill cloth cap that would cover just the speaker I could try some lighter designs.