How do you get good imaging? - Page 5 - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 5th February 2009, 07:00 PM   #41
diyAudio Member
 
Wayne Parham's Avatar
 
Join Date: Feb 2004
Quote:
Originally posted by Patrick Bateman
Wayne,

I have my speakers set up in the manner described in your link. Being able to listen any where in the room is delightful. For instance, my listening room also doubles as my office, and I really appreciate being able to listen in the sweet spot, but also getting good sound at my desk which is a few behind the sweet spot. Highly recommended!

If I'm not mistaken this is also the setup described here:
http://www.gedlee.com/downloads/Cum%20laude.pdf
You're right. Earl recommends that same setup and so does Duke at AudioKinesis. We each have speakers that provide a constant 90 degree pattern, which is a requisite for this setup.

I learned about this by accident a long time ago, way back in the 1970's. The Pi cornerhorn always seemed to do something magical, even more than just boundary loading and constant directivity would explain. The imaging and room coverage was much better than anything else I had heard.

Back then, I guessed it was mostly due to the limited early reflections inherent in the design. It provides uniform coverage and the radiation angle is ultimately limited by its corner placement. The sound doesn't reflect from the side walls, rather, it is directed into the room by them, much like a very large horn. This is true down to the Schroeder frequency anyway, where room modes start to come into play.

What I didn't realize until later was how the geometry of having the forward axis cross in front of the listener tended to compensate stereo balance when the listener is offset one side or the other. Movement towards one speaker moves you further off axis from it, but more on-axis with the more distant speaker. This tends to compensate for stereo balance, making a larger area where the two speakers sound approximately equally loud.

You can walk around the room and you'll notice spectral balance everywhere, because the speakers are CD. But stereo imaging is best when you're equidistant from each speaker when you're at the place where the forward axis cross or ahead of it. As you move away from the speakers, past where the forward axis cross, the "sweet spot" becomes larger.

I displayed Pi cornerhorns at the Midwest Audiofest in 2003. Duke LeJeune was there and commented on the sound. He talked about how uniform the sound was througout the room and stated an interest in the approach. He has since then introduced speakers of his own that provide uniform directivity and he recommends that they be toed in 45 degrees.

Similarly, in 2005 at the Great Plains Audiofest, Earl Geddes unveiled his Summa loudspeakers. They provide uniform directivity using his oblate spheroidal waveguide and patent pending HOM reducing foam. His setup is just like mine, with 45 degree toe in.

I was very pleased because prior to Geddes and AudioKinesis' entry, my loudspeakers were somewhat alone in the market. The craze back then seemed to be tractrix round horns like Edgars and Avantgardes. When I would talk about constant directivity, tractrix horn lovers usually tended to be somewhat skeptical. In particular, the use of CD equalization in the tweeter circuit was seen as something "impure". To them, horn loudspeakers that provided constant directivity were for PA use only. To me, the most impure thing was using a non-CD horn that provided acoustic EQ at the expense of polar response.

Now days, I see Geddes, AudioKinesis and Pi Speakers as having a lot in common. All make speakers that are CD, all recommend the same placement and all suggest using multiple subs to smooth the response below the Schroeder frequency. We have minor differences, but the main things are the same. Geddes is the only one of us to use a foam insert to reduce internal reflections, for example. My first introduction to multi-subs was Welti's papers, and so that's what I initially adopted. Geddes proposed a slightly different arrangement. I think all of us agree that however the subs are arranged, using a number of them is better than using one. I use horns that limit vertical coverage, which in turn, limits ceiling reflection. It also allows the null angle to be placed outside the HF pattern. Geddes and AudioKinesis don't bother with that. But in general, we all three embrace the same principles, and this is very encouraging to me. I see it as corroboration between manufacturers, something rarely seen in the loudspeaker market.
  Reply With Quote
Old 5th February 2009, 07:04 PM   #42
HK26147 is offline HK26147  United States
diyAudio Member
 
Join Date: Jan 2008
Thank you Dr. Geddes:

I did indeed mean the Delta ( the difference added by the other 2 sides of the triangle ).

The ear appears designed for optimization around 3Khz - where the energy of consonants lie, perhaps since humans need to locate/communicate with other humans by vocalizations.
The ability to discriminate and focus and reject also seems to be adaptive: Being able to isolate 1 familiar voice in a crowd and isolate/locate.
Could part of what is attributed to listener fatigue, be due to the brain tiring having to focus and reject/discriminate out these delays...
The 170hz to 17khz window of preference ( Sept 2008 SB ) p 17 makes more sense in this context as well.
Because the binaural pattern of ears favor forward, If the reflections from behind create a problem Delta distance, how much does that come into play...
Thanks again
  Reply With Quote
Old 5th February 2009, 07:28 PM   #43
diyAudio Member
 
Lynn Olson's Avatar
 
Join Date: Jul 2004
Location: Northern Colorado
It may seem a little obvious, but one thing not mentioned is phase-match between the stereo pair. One technique for confirming good phase and level match is to place the pair close to each other, put the measurement microphone 1 meter away and on the exact centerline between the two, reverse the phase of one of the speakers, and measure the resulting spectra of the uncancelled residue.

This was a technique we used at Audionics for all of our speakers - we aimed for at least 25~30 dB of cancellation in the range from 100 Hz to 5 kHz. This degree of match isn't easy to do, by the way - most commercial speakers have more level and phase mismatch than this.

As you might imagine, phase spread between the stereo pair results in image-localization spread in the part of the spectrum where it occurs. One cause, not generally suspected, is mismatch of uncorrected peaks in the tweeter or midrange driver, or slightly out-of-tune notch filters in the crossover. This can result in very steep phase mismatches over narrow parts of the spectrum.

What the BBC called "detenting" is a separate issue. This isn't about image broadening, but asymmetries in the overall reverberant sound field - particularly when it "piles up" around the speakers, and is shallow or deficient elsewhere. This is mostly an artifact of diffraction and energy storage in the drivers (and horn, if applicable). The quicker the settling time, the less this is a problem.

As mentioned in the posts above, any reflections from nearby objects are very undesirable - a 10 mSec reflection is not a good thing, but a 5 mSec or shorter reflection is much worse. Reflections that are very close, 1-3 mSec, tend to merge with speaker artifacts, since many commercial speakers have substantial energy storage in this range.
  Reply With Quote
Old 5th February 2009, 07:45 PM   #44
pos is offline pos  Europe
diyAudio Member
 
pos's Avatar
 
Join Date: Feb 2008
Location: Paris
Quote:
Originally posted by Wayne Parham


I was very pleased because prior to Geddes and AudioKinesis' entry, my loudspeakers were somewhat alone in the market.
JBL did also use that principle in 1985 for the everest:
http://audioheritage.org/vbulletin/s...ead.php?t=5671
http://audioheritage.org/html/profiles/jbl/everest.htm

That horn has a builtin toe-in and is meant to achieve exactly what you describe.
  Reply With Quote
Old 5th February 2009, 07:53 PM   #45
pos is offline pos  Europe
diyAudio Member
 
pos's Avatar
 
Join Date: Feb 2008
Location: Paris
Quote:
Originally posted by Lynn Olson
One technique for confirming good phase and level match is to place the pair close to each other, put the measurement microphone 1 meter away and on the exact centerline between the two, reverse the phase of one of the speakers, and measure the resulting spectra of the uncancelled residue.
Great technique, thanks for sharing!
That would also be interesting to do with the speakers placed at their normal location in the room, so that the effect of the room and furnitures could also be taken into account for the EQ (preferably linear phase EQ I suppose).
  Reply With Quote
Old 5th February 2009, 07:55 PM   #46
diyAudio Member
 
Patrick Bateman's Avatar
 
Join Date: Oct 2006
Location: San Diego
Quote:
Originally posted by gedlee


John - not what I would expect, thats for sure. Maybe a smoother bass helps? I don't know. If what you say is true then the image should be level dependent. Is that true?
Well I had three subwoofers, each with a $25 MCM 55-2421 woofer. Paired with the Summas, it's a recipe for disaster, as these cheap little woofers can't keep up.

It's a GOOD woofer, but it's a cheap woofer, and there's only so much you can do with an eight.

When I played the subs by themselves, the distortion was obvious, and impossible to miss.

But once I fired up the Summas, the distortion was masked by the mains. But it was still there, and my hypothesis is that it was muddying the image.

Either way, it sounds a lot better with seven subs now. I should have the eighth finished soon.
  Reply With Quote
Old 5th February 2009, 07:55 PM   #47
gedlee is offline gedlee  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Novi, Michigan
It was the JBL concept that originally got me interested. It is a great idea and works well when properly implimented. Those older horns lack the "quality" of the newer ones however, which is why, I think, the idea never caught on. It makes perfect sense, but requires a waveguide to do it. Those have historically not had the best sound quality. I used to toe-in my 4430s, but always objected to the horn coloration from its diffraction device.
  Reply With Quote
Old 5th February 2009, 07:57 PM   #48
gedlee is offline gedlee  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Novi, Michigan
Quote:
Originally posted by Patrick Bateman

Either way, it sounds a lot better with seven subs now. I should have the eighth finished soon.

I can see your point now - it makes sense.
  Reply With Quote
Old 5th February 2009, 07:57 PM   #49
diyAudio Member
 
Patrick Bateman's Avatar
 
Join Date: Oct 2006
Location: San Diego
Quote:
Originally posted by pos


Great technique, thanks for sharing!
That would also be interesting to do with the speakers placed at their normal location in the room, so that the effect of the room and furnitures could also be taken into account for the EQ (preferably linear phase EQ I suppose).

I tried it that way for a day, out of curiosity.

It still sounds good, but the size of the soundstage narrows. Also, the image collapses to quite a degree when you move to the left or the right.

Set up in the way described above, the image is stable whether you move left or right.
  Reply With Quote
Old 5th February 2009, 08:02 PM   #50
pos is offline pos  Europe
diyAudio Member
 
pos's Avatar
 
Join Date: Feb 2008
Location: Paris
Quote:
Originally posted by Patrick Bateman



I tried it that way for a day, out of curiosity.

It still sounds good, but the size of the soundstage narrows. Also, the image collapses to quite a degree when you move to the left or the right.

Set up in the way described above, the image is stable whether you move left or right.
You mean the inversion phase rejection test or the 45° toe-in ?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
imaging jj Multi-Way 2 5th July 2009 12:30 PM
Imaging... retiredmxer Multi-Way 19 21st April 2007 04:12 AM
Horn Imaging gpsmithii Full Range 1 3rd June 2005 03:20 PM


New To Site? Need Help?

All times are GMT. The time now is 02:23 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2