Beyond the Ariel

[Pano]

Originally posted by Lynn Olson
[B]More than 90 degrees would be desirable./B]

Thanks Lynn. So much of what I read tells me that driver/speaker directivity needs to be controlled - certain patterns for cinema, other patterns for home use, PA use, etc. But so many of the systems that sounded very real to me had very wide -"too wide" dispersion patterns. 90 degrees or even much wider sounds best to me.

What's going on there?

[Magnetar]

Originally posted by Lynn Olson

Returning to loudspeakers, I was just corresponding with a horn designer, asking about a possible mid horn for the 18Sound 6NDA410 or Ciare 6.38 NdMR, and curious if it was possible to succesfully cover the range from 400 Hz to 3.2 kHz with a modern horn design.

I was under the cheerful impression that a modest bandwidth of 1:8 wouldn't be asking too much, but he replied the directivity of a 400 Hz-size horn with a 6" cone driver at 3.2 kHz would be extremely narrow - the last thing I want before crossing over to the double-high RAAL. Phooey. It was a good idea while it lasted.

Looks like a vertically stacked pair of 6" drivers on a moderate-sized OB is going to be the way to go. Unlike other correspondents, I want wide horizontal directivity, not PA or home-theater-style 60 or 90-degrees.

I'll dive in again.

It would be less narrow than one being driven by a compression driver. The horn wil be shorter with much more except able beam. It will be a magnitude less directional than single panel esl's including funny dispersion ones's such as esl63. It will be more directional than a stacked pair of 6"s by a little horizontally - I find mine open as opposed to closed in - I agree too narrow sucks. My room is only 13.5' wide. No I have not measured their di

A pair of stacked PR170MO Audax sound good if you don't like a horn but have their own set of problems. I like the horn loaded 6" better because it is less strained, more dynamic and easier to drive with 45's, 2A3 ect - IOW it sounds better in the first watt range and at all listening levels including a whisper

PS, you can adjust the ribbons radiation with foam to match the mid horn, I did that with the Auram Cantus G1

[dobias]

With my 12" full range speakers, I find that a 225 Hz low pass to the woofers is providing excessive reenforcement in the mid octaves. Rather than cutting off the lower registers from the full range, I'm planning to lower the low pass to the OB woofers & subs.
I've searched & can't find previous discussion about the benefits of stereo wired woofers.
At what frequency do open baffle woofers lose stereo effect?
dobias

[Magnetar]

Originally posted by dobias
With my 12" full range speakers, I find that a 225 Hz low pass to the woofers is providing excessive reenforcement in the mid octaves. Rather than cutting off the lower registers from the full range, I'm planning to lower the low pass to the OB woofers & subs.
I've searched & can't find previous discussion about the benefits of stereo wired woofers.
At what frequency do open baffle woofers lose stereo effect?
dobias

Open baffle bass has higher directionality and doesn't drive the room modes the same way a regular bass system (monopole) does so I say dipoles will have a little lower point where stereo directionality becomes detectable. I'd guess around 50-60 cycles. If you can get your stereo pair that low in your room you can hand off to single channel bass with little compromise.

It sounds like you need to measure your speakers then make decisions on the bass to 'fullrange' crossover.

[dobias]

When you're sure you have things adjusted, check them again!
I went back & checked evrything for a baseline....oops! I found I had set the receiver for +5.5 dB awhile ago.
Now, from 20 Hz to 10 kHz, I have an unbelieveable 68 dB plus or minus 5 dB using a test tone CD & my RS sound meter.

I need to add super tweeters to get more ambience (or whatever it's called now-a-days). The sound level drops off a cliff at 10 kHz. If I remember correctly, the cheap RS meter is partly to blame at that frequency.
dobias

[Lynn Olson]

Originally posted by panomaniac


Thanks Lynn. So much of what I read tells me that driver/speaker directivity needs to be controlled - certain patterns for cinema, other patterns for home use, PA use, etc. But so many of the systems that sounded very real to me had very wide -"too wide" dispersion patterns. 90 degrees or even much wider sounds best to me.

What's going on there?

It's not that complicated. My background in commercial audio started with patenting a dynamic-matrix specifically designed to leave ambience information intact and undistorted - there would be instantaneous changes in image resolution, but the level or ambient information at any location in the room stays constant. This principle is currently used in Dolby Pro-Logic II in Music mode, designed by Jim Fosgate, and licensed to Dolby Labs. (Pro-Logic I had quite poor ambience retrieval and was prone to noticeable "detenting" at the speaker locations.)

In the quadraphonics era, classical music, as reproduced in the home, was the gold standard for realistic ambience retrieval. The reference source was discrete quadraphonic mastertapes, ideally with no Dolby A processing to muck up the imaging.

A decade later, one man at Dolby Labs, Tomlinson Holman, was able to dictate to the audio industry how multichannel would be implemented in the home, and was in a position to enforce it with the secret, and Dolby-proprietary, THX licensing system. I see no evidence in Holman's writing he is familiar with the prior work of Peter Scheiber or Michael Gerzon of Ambisonics, or if he was, he consciously chose to ignore a decade of extensive research in spatial perception.

As a result of THX licensing, multichannel became associated with intentionally asymmetric LR, Center, and Rear speakers, "constant directivity" design techniques to minimize room interaction, lossy digital compression techniques that also discard ambient information as "useless bits", and sound systems optimized for shock value (dinosaur thuds, car crashes, and explosions) - in other words, sound optimized for the teenage gamer demographic. (I'm not making this up - check out the target demographic for big-budget movies - it's boys aged 12 to 16 years old. If this demographic is not satisfied, the big-budget movie doesn't get made.)

All of these things are grossly antithetical to musical values. In particular, what are the consequences of using 10:1 lossy digital compression and then re-designing the speaker to optimize voice intelligibility (to compensate for the lost bits, of course). You end up with raucous, harsh speakers with narrow directivity, but they do have the required ability to cut through the crowd noise and overcome the poor quality of the transmission chain (peaked-up microphones, "de-essers", lossy digital compression, and frequency-but-not-time equalization in the theatre playback chain).

It should be kept in mind that theatres cannot reproduce phantom images due to Haas-effect problems. In the home, people can sit within a metre or so of the centerline, and experience small enough Haas localization shifts that phantom images are preserved - they may be distorted for off-axis listeners, but they don't fall apart completely. In a theatre, very few people are on the exact centerline where they could experience intact phantom images.

This is the reason theatres have used Center speakers since the early Fifties, when multichannel sound was first introduced. Along with the picture, dialog is the most important element of the movie, and it is essential it seems to come from the center of the screen, regardless of where the movie-goer is sitting. If most people hear Left, Center, and Right, that's good enough for movies. The only people who are going to hear any phantoms at all will be sitting within a metre of the centerline.

It also goes without saying the acoustics in movie theatres are not concert halls - far from it. They are simple boxes optimized for voice intelligibility and little else.

This is why playback in the home is so different. Any halfway competent domestic loudspeaker can create phantom images, and loudspeakers with smooth dispersion patterns and rapid-decaying time response can generate extremely realistic phantom images and complete phantom acoustic environments. In a movie theatre, none of this is possible - a pan in depth (moving away from the listener) is going to be lost unless the effect is extremely exaggerated. A subtle pan-in-depth is a common effect for vocalists on rock recordings, and is also used in classical music, where the composer can intentionally "bounce" the pulse and rhythm of the sound off the hall reflections. Ask any musician - classical music in a "dry" environment is difficult to play in ensemble, and for the listener, a travesty of what the composer and conductor intended.

There are some things in the pro and movie-theatre worlds that are useful for home hifi - low IM distortion, wide dynamics, freedom from hum and noise, etc. but copying the spatial properties of theatre speakers isn't one of them.

[Nielsio]

Hi Lynn,


I personally use a high quality full-rangers (Supravox 215 SB, high qts) on a large open baffle, in combination with a digital equalizer. The idea is to keep as much of the low frequencies as possible through the large baffle, and the driver has to have a high linear excursion. That way, you can equalize the whole range while keeping the driver with enough headroom for a high quality of sound. With a smart use of room acoustics you can actually create a very natural and powerful sound.

http://my.hifi.nl/index.php?user=1088

Have you ever heard/tried something like that?


Equalizing correctly is something not many people accomplish btw.

[Magnetar]

Originally posted by Lynn Olson


It's not that complicated. My background in commercial audio started with patenting a dynamic-matrix specifically designed to leave ambience information intact and undistorted - there would be instantaneous changes in image resolution, but the level or ambient information at any location in the room stays constant. This principle is currently used in Dolby Pro-Logic II in Music mode, designed by Jim Fosgate, and licensed to Dolby Labs. (Pro-Logic I had quite poor ambience retrieval and was prone to noticeable "detenting" at the speaker locations.)

In the quadraphonics era, classical music, as reproduced in the home, was the gold standard for realistic ambience retrieval. .........

The Rocktron Circle Surround circuit is excellent for home music systems. I have one here pretty tweaked out. What I like is omni directional upper rear speakers ( I use Tannoy dual concentrics in spherical enclosures firing up into a 360 degree reflector) and upper side firing Tannoys for more natural and delayed reflection points. No center speaker is really needed. It helps most with the tone and believability of the 'whole' - much prefer it on to flawed two channel one dimensional flatness.

[swak]

Magnetar.

what horn have you used with the Audax mid? What is the range you have use them that way (with horn) and as a pair? What do you reckon is the approximate directivity of the mid in horn in the upper end?

For use in a waveguide/horn, how do you consider the maxfidelity 6"er (which I think you have tested)?


Regarding using foam on *dome* tweeters for more directivity: how is it done? I have been thinking using fiberglass (which has a higher absorption coef. as foam) in the form of thick rings (1-2") around the dome tweeter, perhaps with a slanted profile of around 50-70 degrees. I would recess the tweeter in such a way on the baffle, that the fiberglass ring would be flush/on level with the baffle, and covered with black polyester fabric over the surface of the fiberglass ring.

I reckon the material used around the tweeter should be as little reflective as possible at high frequencies. The problem with the raw fiberglass rings could be the fibers ending up all over the dome.

regards,

sebastian

[Magnetar]

Originally posted by swak
Magnetar.

what horn have you used with the Audax mid? What is the range you have use them that way (with horn) and as a pair? What do you reckon is the approximate directivity of the mid in horn in the upper end?

For use in a waveguide/horn, how do you consider the maxfidelity 6"er (which I think you have tested)?


Regarding using foam on *dome* tweeters for more directivity: how is it done? I have been thinking using fiberglass (which has a higher absorption coef. as foam) in the form of thick rings (1-2") around the dome tweeter, perhaps with a slanted profile of around 50-70 degrees. I would recess the tweeter in such a way on the baffle, that the fiberglass ring would be flush/on level with the baffle, and covered with black polyester fabric over the surface of the fiberglass ring.

I reckon the material used around the tweeter should be as little reflective as possible at high frequencies. The problem with the raw fiberglass rings could be the fibers ending up all over the dome.

regards,

sebastian

Hello,

The Audax PR170MO is a terrible horn driver. It has a rolloff of about 800 cycles. The B&C I use in the same horn in my 'sensitive open baffle ' post is much better going to 3K+ Use the Audax as a direct rediator dipole and you will be much better off - it's really sweet.

I have not bought the max fidelity. I tried to get it from the factory and they ignored me. I don't think it would be any better than the B&C in a horn but better than the Audax.

Open cell foam or loose felt placed in the direction you want to control around the dome will change the dispersion. I agree, fiberglass could get messy