Uniform Directivity - How important is it? - Page 75 - 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 9th October 2013, 02:04 PM   #741
Omholt is offline Omholt  Norway
diyAudio Member
 
Join Date: Jun 2009
Quote:
Originally Posted by gedlee View Post
Given the proper sized waveguide, I have not found any problems in home use. I wouldn't use a 1" driver down that low in a sound reinforcement situation - which is where the manufacturer issues a warning about going below 1 kHz. In home use you are never going to play a compression driver so loud that it would be a problem.
Seems reasonable.

What driver would you use with a 18" waveguide?
  Reply With Quote
Old 9th October 2013, 03:02 PM   #742
gedlee is online now gedlee  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Novi, Michigan
I use a de250. Its a great driver that I know well and have (mostly) had great success with. There are much more expensive drivers, but in all my testing I have not found any to be any better.

Back to beaming as not being a problem, it is if you toe-in your loudspeakers to widen the sweet spot. With a beaming device you have only one option and one seat in the sweet spot. OK for some, not OK with me. (There are other issues with beaming in reverberant rooms as well.)

It is simply not correct to say that constant directivity does not matter. Only a small few claim this, mostly because their designs are not CD. Kind of coincidence.
  Reply With Quote
Old 9th October 2013, 03:27 PM   #743
diyAudio Member
 
Wayne Parham's Avatar
 
Join Date: Feb 2004
Quote:
Originally Posted by AllenB View Post
As in bottoming the cone?
Yes, even when horn loaded, diaphragm excursion rises as frequency drops. And there's not a lot of room in a compression driver. So I don't like using them at low midrange frequencies (like under 400Hz). They're not made for that.
__________________
Visit the π Speakers website
High-quality audiophile loudspeakers and kits
  Reply With Quote
Old 23rd October 2013, 07:55 PM   #744
diyAudio Member
 
Wayne Parham's Avatar
 
Join Date: Feb 2004
We were talking about this on another thread, but we got sidetracked I guess.

As I see it, we have a handful of competing priorities in horn design.

One is to optimize acoustic loading, which provides smoother response and lower distortion. A second priority is the ability to create a desired beamwidth, to be able to create a radiation pattern that covers the intended listening area. A third priority is to optimize uniformity of beamwidth, which provides equal coverage throughout the listening area and a more spectrally balanced reverberent field. And a fourth is to optimize wavefront propogation, which improves both response smoothness and beamwidth uniformity.

You can see evidence of fractured wavefronts both in the polars and often even as amplitude response ripple on any single axis. Discontinuities in a horn almost always present as ripples in acoustic impedance, which also show up in the amplitude response. Sometimes in a highly fractured wavefront, the interactions are so dense that the polars seem relatively uniform but this is usually limited to cases like lenses. Single diffraction slots usually manifest themselves in the polars and amplitude response. In addition to all these measurable features, subjectively, it has been suggested that fractured wavefront propogation also damages suble acoustic clues, degrading imaging and lessening the illusion of acoustic reality.

One thing I've seen though, is a predisposition of some designers to optimize one trait so much they lose sight of others. I've never understood, for example, the choise to employ a horn with physical characteristics that make it impossible to design a loudspeaker with widely spaced vertical nulls. If the vertical nulls form less than about 20 apart (10 above and below the forward centerline), then I personally think the speaker is pretty worthless because the nulls are huge and audible, and they're basically straight in front of the loudspeaker. No mater how good the speaker is in other aspects, this one flaw is a deal breaker, because it is huge.

On the other hand, I've seen other designs that seek to reduce or even eliminate lobing, which I think is an excellent goal, but the strategies employed usually either require a highly compromised horn design, or they have a lot of internal reflections, or both. These kinds of approaches are maybe good in prosound, where coverage and arrayability are extremely important, but for home hifi - where arrayability isn't needed - I think it is better to use other optimizations that don't fracture the wavefront so badly.

I've also wondered why some of the newer waveguide designers have almost completely ignored acoustic loading, bringing the polarization of the horn versus waveguide methods. I realize that conical horns and the closely related waveguides have characteristically poor acoustic loading, particularly at low frequencies. But to me, this makes it all the more important that the modern waveguide designer do some modeling and testing of their device to ensure it provides smooth response.

Horn designers are able to enjoy smooth response, nearly ruler flat. I'm not just talking about the collapsing pattern providing on-axis rising response that counters faling response from mass rolloff. I'm talking about horn loading throughout the passband, from lower cutoff through midband and up. A conical horn or waveguide will not be able to match the low end smoothness of an exponential horn, for example. But it can be made close, if done properly, and it still can provide constant directivity. To me, this is an important balance to strike.
__________________
Visit the π Speakers website
High-quality audiophile loudspeakers and kits
  Reply With Quote
Old 23rd October 2013, 10:42 PM   #745
Rewind is offline Rewind  Sweden
diyAudio Member
 
Join Date: Jan 2009
Quote:
Originally Posted by pengesluk View Post
I have over a period of some four years now compared a wide selection of horns and drivers and as such found a reasonably absence of "free lunches" - as expected. First of all, in a high-end system I cannot see any two-way system as the optimum solution. The classical combo of a 15"/radial horn xoed at anywhere from 600 - 1.000 Hz does a pretty good job, but still, the compromises are far too big. IMO. Any 2" driver (or 1,4" for that matter) has no business over 7-8k regardless of what measurements etc. show. A substancial part of the output above this range will be breakups and distortion. Yes, some drivers/diaphragms work better than others but the laws of physics still apply.

At an early stage I had high hopes for a combination of JMLC-200T and Altec/GPA 288 - that combination worked like a charm all the way down to 350 Hz with 24 dB LR cutoff. The grunt and growl was fabulous, but above 7k approx. the beaming was far too big and above 10 k nothing much happened.
I am looking for a replacement for a Goto replica that plays down to 200Hz. Seems I will only be needing 350Hz. Was the JMLC-200T good enough to keep?
  Reply With Quote
Old 25th October 2013, 03:04 PM   #746
diyAudio Member
 
Wayne Parham's Avatar
 
Join Date: Feb 2004
I personally prefer cone drivers in midhorns for use down to 200Hz.
__________________
Visit the π Speakers website
High-quality audiophile loudspeakers and kits
  Reply With Quote
Old 26th October 2013, 09:58 AM   #747
diyAudio Member
 
Join Date: Jan 2008
Wayne,

Your take on uniform directivity is strictly from horn perspective. Your designs illuminate one side wall and rear wall. Virtual mono source located between speakers would illuminate both side walls if it were real. True uniform directivity is 360 degrees.

Exploring true 360 degree coverage reveals misnomers about early reflections. With 360 degree coverage, room response uniformly equals speaker direct response. Imaging is detailed and remains so in much wider and deeper listening area. Such speakers can be placed in room or against boundaries and retain spectral balance. No room treatments or changes in equalization are needed.

Sensitivity of 90 degree waveguides/horns to room placement and toe in and the highly limited sweet spot show failure to uniformly cover listening area.
  Reply With Quote
Old 26th October 2013, 03:19 PM   #748
diyAudio Member
 
Wayne Parham's Avatar
 
Join Date: Feb 2004
I would agree that DI-matched two-way speakers definitely have the problems you're describing. I recommend flanking subs or some kind of helper woofer blended with the mains to mitigate those problems. But that approach is a compromise done to allow a sort of "generic loudspeaker" to be built, one that works in most rooms.

A constant directivity cornerhorn, on the other hand, is a no-compromise solution that has none of those problems. In a sense, it is an omnidirectional source placed at the apex of the room's corner. So there is no self-interference from the "back wall" or the ipsilateral "side wall" because the sound source lies upon those boundaries.

As for the waveguide/horns used to build these loudspeakers, to me, the holy grail is a horn that provides constant directivity with the smoothness of a an exponential or LeCleach horn.

What I've found works very well is an OS/PS/EC device, any of which have the same flare profile as an OS waveguide/horn. But it is very important that the area expansion be chosen that provides smooth response. This can be done with mouth dimensions, e.g. aspect ratio and/or beamwidth. It should also have some mouth roundover, using something like an iterative expansion technique just like LeCleach uses. Not so much that the device has to sacrifice too much of its OS/PS/EC flare though.

Many if not most of the common 90 OS and EOS horns are too shallow for their mouth area, and response is lumpy as a result. Common wisdom is the larger the mouth, the better the response, but this overlooks the flare profile. In the case of the OS/PS/EC flare used to create these devices - especially those with secondary flares or mouth radiusing - the overall dimensions have a great influence on response smoothness. This is demonstrated in the response chart comparison on the first post of this thread.

Again, many OS and EOS horns have 5dB or greater ripple, which the loudspeaker designer seeks to mitigate with notch filters. To me, that approach is not much better than the 1970s CD horns. Diffraction is better, but the internal standing waves are horrendous. What they have is a highly resonant horn.

So again, to me, the holy grail is smoothness of an exponential or LeCleach and the directivity of a OS, PS or EC flare. I have found this can be done with an OS/EC waveguide/horn with the right choices of area expansion and aspect ratio.
__________________
Visit the π Speakers website
High-quality audiophile loudspeakers and kits
  Reply With Quote
Old 26th October 2013, 06:37 PM   #749
diyAudio Member
 
Join Date: Jan 2008
What is width and depth of sweetspot with corner horns? They lock listen to center line to get balance from ipsilateral reflections.
  Reply With Quote
Old 27th October 2013, 11:31 AM   #750
Banned
 
Join Date: May 2008
Location: Switzerland
Quote:
Originally Posted by Barleywater View Post
Wayne,

Your take on uniform directivity is strictly from horn perspective. Your designs illuminate one side wall and rear wall. Virtual mono source located between speakers would illuminate both side walls if it were real. True uniform directivity is 360 degrees.

Exploring true 360 degree coverage reveals misnomers about early reflections. With 360 degree coverage, room response uniformly equals speaker direct response. Imaging is detailed and remains so in much wider and deeper listening area. Such speakers can be placed in room or against boundaries and retain spectral balance. No room treatments or changes in equalization are needed.
With "virtual" you mean a real source instead of a phantom source? Such a source also wouldn't illuminate the room the way a stereo configuration with two omni speakers would. How does that fit in your (Linkwitz's?) hypothesis about reflection perception?

Last edited by markus76; 27th October 2013 at 11:37 AM.
  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
Dumb Directivity Question Patrick Bateman Multi-Way 2 23rd April 2013 02:02 AM
My S13 OB. Uniform polar response to tweeters at last! gainphile Multi-Way 12 24th February 2010 08:03 AM
A question on directivity swak Multi-Way 18 31st July 2005 03:03 PM
Improving on the LCY uniform dispersion ribbon Audiophilenoob Planars & Exotics 34 22nd July 2005 12:01 AM
where is short wiring in an amp important/ not important ? sandro600 Solid State 5 4th April 2004 03:10 AM


New To Site? Need Help?

All times are GMT. The time now is 01:48 PM.


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