Improving Stereo Imaging & Off-Axis Response - 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 7th April 2010, 02:47 PM   #1
Loren42 is offline Loren42  United States
diyAudio Member
 
Join Date: Sep 2008
Location: "Space Coast" Florida, USA
Default Improving Stereo Imaging & Off-Axis Response

I have been a little dissatisfied with the limited sweet spot of my speakers and the mediocre stereo imaging I get.

My area of focus on my 3-way speaker is with the midrange and the tweeter.

Midrange is the Audax PR170M0
Tweeter is the Morel MDT-37
Crossover Point 2.7 kHz

My first thought was to check the off-axis response of the system and I have the following plot:

Click the image to open in full size.

Each line represents a 15° change in microphone position from zero (on-axis) to 60°.

Due to the room size the mic was 31" from the front of the speaker, aimed at the intersecting point between the Audax PR170M0 midrange and the Morel MDT-37 tweeter.

The driver pair are mounted so that they are 5.275" (134 mm) center to center. A small portion of the tweeter is carved out so that it fits close to the Audax midrange. The baffle size for the two drivers is 8" by 12", with the sides sloping backwards at about 30° to reduce the baffle diffraction step. The sloped sides appear to do just that and leave no ill traces of of a step.

My Observations:

The off-axis response looks pretty disappointing to me and may, in part, explain the sensitive sweet spot I get.

In the vertical direction I have these two plots that are in 7.5° increments along the azimuth axis and are plotted at the same distance of 31".

Click the image to open in full size.
This is going upwards in azimuth...

Click the image to open in full size.
This plot is going downwards in azimuth.

I would like to see a better performance from the Audax and Morel as far as off-axis response, but there seems little that I can do to coach better dispersion with these drivers.

The Audax has a lot of ripple on the frequency response, but that may be just the way it is with a paper cone. Most mids in this SPL range have this syndrome.

Your Opinions?

The question remains what can I do to improve the performance of the imaging and widen the sweet spot, if anything?

Errata:

The following is just information that some may find interesting or necessary...

Crossover Details

Now, the crossover was a design performed by Madisound and is available here: LEAP.pdf

For those of you with a sharp eye, the tweeter's polarity, if wired according to that schematic, produced a huge suckout at the upper crossover point at 2.7 kHz. It looked like this:

Click the image to open in full size.

So, before I began any actual measurements I reversed the tweeter polarity and every other plot here has the tweeter reversed from the schematic.

Cone Breakup

The gyrations in the plots from about 300 Hz to 1100 Hz (for those with questions) appear to be a combination of the woofer's cone break up and the Audax midrange. The crossover point is 400 Hz.

Click the image to open in full size.
This is the JBL 2235H:

Click the image to open in full size.
This is the Audax PR170M0
  Reply With Quote
Old 7th April 2010, 03:48 PM   #2
cuibono is offline cuibono  United States
diyAudio Member
 
cuibono's Avatar
 
Join Date: May 2006
Location: City of Angles
If you want more regular dispersion, you have to go with smaller drivers, and or drivers that can be crossed over lower. But looking at your first FR, it doesn't look too bad - the thing I look for in horizontal polars is that the lines are basically parallel, which they seem to be. It would be a pretty good idea to take your measurements outside where you can get longer gate times - you're pretty much only looking at the treble range, but the mids are almost more important - not in terms of polar response, but more for the overall FR of your system. I would highy recommend measureing at a greater distance too - like minimally 6 feet off the ground, and a speaker-mic distance of 5 feet. I do my best measurements 11 feet off the ground, and a mic distance of 6 feet.

What is your baffle dimensions/layout?

There isn't much you can do about your vertical polar response, unfortunately, besides get the drivers closer and cross lower.

Do you feel the treble is rolling off too soon, leading to a small sweetspot? Your tweeter is slightly on the large side, but not by much...

I'd guess that stereo imaging problems are more a function of differences between the two speakers FR, and their placement in your room. How much room do you leave between the speakers and large objects - I consider 3 feet about minimal.

Hopefully others will chime in too.
  Reply With Quote
Old 7th April 2010, 04:05 PM   #3
diyAudio Member
 
Robh3606's Avatar
 
Join Date: Nov 2002
Location: Destiny
Try switching to CD type waveguide or horn.

Rob
__________________
"I could be arguing in my spare time"
  Reply With Quote
Old 7th April 2010, 04:37 PM   #4
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Quote:
Originally Posted by Robh3606 View Post
Try switching to CD type waveguide or horn.

Rob
FWIW I agree.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 7th April 2010, 04:45 PM   #5
Loren42 is offline Loren42  United States
diyAudio Member
 
Join Date: Sep 2008
Location: "Space Coast" Florida, USA
Quote:
Originally Posted by cuibono View Post
If you want more regular dispersion, you have to go with smaller drivers, and or drivers that can be crossed over lower. But looking at your first FR, it doesn't look too bad - the thing I look for in horizontal polars is that the lines are basically parallel, which they seem to be. It would be a pretty good idea to take your measurements outside where you can get longer gate times - you're pretty much only looking at the treble range, but the mids are almost more important - not in terms of polar response, but more for the overall FR of your system. I would highy recommend measureing at a greater distance too - like minimally 6 feet off the ground, and a speaker-mic distance of 5 feet. I do my best measurements 11 feet off the ground, and a mic distance of 6 feet.

What is your baffle dimensions/layout?

There isn't much you can do about your vertical polar response, unfortunately, besides get the drivers closer and cross lower.

Do you feel the treble is rolling off too soon, leading to a small sweetspot? Your tweeter is slightly on the large side, but not by much...

I'd guess that stereo imaging problems are more a function of differences between the two speakers FR, and their placement in your room. How much room do you leave between the speakers and large objects - I consider 3 feet about minimal.

Hopefully others will chime in too.
This is what the cabinet looks like:
Click the image to open in full size.

Front baffle layout:
Click the image to open in full size.

Note that the front baffle is raked backward at an angle of 3.8° as illustrated in this isometric view:
Click the image to open in full size.

Measurements were taken with the cabinet in the room center. Normally one speaker is closer to the wall, but the room layout will change in the future, so I am trying to get all the gremlins out of the beast first, then apply veneer.

Moving my head a few inches from the listening position does show some treble fall-off. Overall imaging is a little vague in my opinion. If you get into the sweet spot it is better. I am sure the room has enough to do with it, too.
  Reply With Quote
Old 7th April 2010, 04:48 PM   #6
Loren42 is offline Loren42  United States
diyAudio Member
 
Join Date: Sep 2008
Location: "Space Coast" Florida, USA
Quote:
Originally Posted by Robh3606 View Post
Try switching to CD type waveguide or horn.

Rob
Do you mean a full horn and compression driver?

I came up with this idea a few months back, but my girlfriend could not get the idea out of her mind that she was looking at two people mooning us all of the time.
Click the image to open in full size.

Last edited by Loren42; 7th April 2010 at 04:52 PM.
  Reply With Quote
Old 7th April 2010, 05:27 PM   #7
diyAudio Member
 
Robh3606's Avatar
 
Join Date: Nov 2002
Location: Destiny
Quote:
Do you mean a full horn and compression driver?
Something along those lines. There are option besides a 4430 clone. You could go with 1" or 1.5" PT waveguides or grab a set of Earls Waveguides. Just have to work out the compensation and driver integration if you strike out on your own.

With the improvements you seem to be looking for it's a good bet you could end up happy trying it out. One thing is for sure using horn/waveguide similar to a 2344 you don't have to worry all that much about a small sweet spot. Just toe them in a bit and go.

Rob
__________________
"I could be arguing in my spare time"
  Reply With Quote
Old 7th April 2010, 05:37 PM   #8
diyAudio Member
 
Join Date: Sep 2008
Would she feel better if you told her they can also be called "Dolly Parton" horn?
  Reply With Quote
Old 8th April 2010, 02:03 AM   #9
terry j is offline terry j  Australia
diyAudio Member
 
Join Date: Aug 2006
Room. I saw you later posted that the room could have something to do with it.

I noticed hard tile floors in your pic, not your listening room??

Anyway, I have never been an 'imaging freak', other things float my boat (or maybe I was not because I did not particularly have it??). Got bored one day (and had taken my speakers as far as they will go) and so just hung raw f/glass batts in my room....room treatment was always on my list and it just started that day.

Click the image to open in full size.

Click the image to open in full size.

Just to give you an idea of the rough and ready experiment!! They have been there for a year now.

My room is large and very solid (two foot solid brick walls), but that also made it very ringy.

I was staggered at the improvement getting rid of the slap echo made. Many improvements, but NOW I had imaging like never before. In fact, it rivalled the imaging I had only ever heard once before, and funnily enough that guy also had a well treated room.

Only a survey of two, but it seemed pretty conclusive to me!

Anyway, all I want to get across is that for an experiment (as you can see) it is very simple and cheap to do, and you can always put the batts in the ceiling after your experiment.
  Reply With Quote
Old 8th April 2010, 02:16 AM   #10
Loren42 is offline Loren42  United States
diyAudio Member
 
Join Date: Sep 2008
Location: "Space Coast" Florida, USA
Quote:
Originally Posted by terry j View Post
Room. I saw you later posted that the room could have something to do with it.

I noticed hard tile floors in your pic, not your listening room??
Yes, it is, but things will change at some point in a fairly major way.

My goal is to complete these speakers, but I have some things to do before I can veneer them. My list is:

1. Finish crossover tweaks and any other overt flaws in the system. So, I am trying to dial in the sound the best I can.
2. Fix cabinet resonances - there are a lot. Leaning toward constrained layer with green glue.
3. Fix flaws in the cabinets (nicks, dents, irregularities) so they are ready for veneer.
4. Room renovations. The room gets a new layout and the system moved or turned 90° so that the speakers fire down the long path of the room. This not only improves the seated listening position, but will play right into the attached kitchen. So casual listening will benefit as well.
5. Room treatments where possible.

Even with the room changes and treatments I expect that the room will be less than ideal, but I have limits there. I can accept that, but at least I want to make sure the bow and ribbon are done on the speakers so that they are not a source of inferiority.
  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
Improving off-axis response of a 15" alexclaber Multi-Way 24 20th July 2009 03:00 PM
On-axis vs. Power Response bunzinthesun Multi-Way 15 12th November 2007 06:12 PM
Phase response and imaging / resolution Branwell Multi-Way 9 25th October 2004 01:00 PM
Looking for Monacor freq response off-axis mgrzemow Multi-Way 0 20th October 2003 11:10 AM


New To Site? Need Help?

All times are GMT. The time now is 01:13 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