My open baffle project on ortho acoustic design ideas - 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 March 2013, 11:41 PM   #1
diyAudio Member
 
Join Date: Mar 2010
Location: Stockholm
Default My open baffle project on ortho acoustic design ideas

This project has been a long time coming, and I hope it can be of interest to some of you out there. I’m happy for all comments, views, questions and suggestions.

As long ago as back in 1984, I came across an article in Hifi News & Record Review about Wharfedale’s Option One research project. Their chief engineer G P Millard investigated the possibility to use dipolar speakers to increase the sweet spot area for stereo listening. This opened my curiosity towards dipolar speakers.

Click the image to open in full size.

Born and living in Sweden with a burning interest in sound reproduction, you will likely come across the late great speaker designer Stig Carlsson and his unconventional designs. He pioneered a lot of work on how the speakers should be designed in order to interact with a normal living room to create a believable lifelike reproduction of recorded sound, together with the likes like Roy Allison, Peter Snell, Jim Thiel, Harold Beverage and others.

He named his principals ortho acoustics and has been a huge inspiration to my own designs. And since the HNRR article in 1984 I have also been experimenting with dipolar applications to these ortho acoustic design ideas.

A number of incarnations have seen the surface since 1984, some realized and some just ending up as great ideas for the round archive. Then family and career came in between. Eventually this specific revision of my designs was initiated in 2009, when a faulty amplifier (my own modification) literary put the preceding version on fire in its premier listening session. A very sad day in my DIY life, but good things eventually came out of it (I think).

My vision for these speakers was to build a design which interacts positively with the acoustical attributes in a normal living room, in order to create a balanced and lifelike reproduction of a recorded sound - a believable gestalt of the original event. As in the article from 1984 I also wanted to use the dipolar directivity for time intensity trading in order to increase the sweet spot area for believable soundstage reproduction.

My aim was to create a speaker with an even frequency response both for the direct and reflected sound using conventional placement in a normal living room, with controlled directivity and integrated damping to suppress early reflections from influencing the direct sound but still to illuminate the room for a lifelike apparent source width and sensation of envelopment.

The design prerequisites:
- Dipolar speaker using dynamic drivers
- Should work as intended with conventional placement in a normal living space
- Discreet design, i.e. family acceptance

We eventually agreed on a design with approximate dimensions of 12x12x34 inches. Which created a lot of folding and puttering on my behalf, but in the end I had an idea of how they should look and how they should be built.

Click the image to open in full size.
Discreet external design.

Click the image to open in full size.

Click the image to open in full size.
The inside in cross-sections.

That gave me place for two 10” bass drivers in a W-baffle, one 8” midrange unit on an angled baffle with two 1” tweeters on top in dipolar fashion. My idea was to build the whole chassis in layers of routed MDF boards.

Click the image to open in full size.
Then you end up with a lot of details like this.

The original intention was to use a professional workshop CNC-cutting all these details, but that plan fell through. So I ended up working with my own hand router (a lot). In hindsight a bad idea. Plain too many hours spent and too much router dust for recommending to anyone else - you are warned. Next speaker will have to be of a different design.

Driver selection fell on:
- two Acoustic Elegance Dipole 10 for bass
- a Seas Excel W22NY001 as midrange
- the Scanspeak Illuminator D3004/660000 and D3004/602010 as tweeters

That would make it possible to reach 110 dB @ 1 meter within linear excursion limits for the intended crossover frequencies and given baffle dimensions.

To be continued.
  Reply With Quote
Old 8th March 2013, 12:05 AM   #2
guangui is offline guangui  Puerto Rico
diyAudio Member
 
Join Date: Feb 2013
I like where this is going...an eye pleasing OB...
  Reply With Quote
Old 8th March 2013, 02:07 AM   #3
PB2 is offline PB2  United States
diyAudio Member
 
PB2's Avatar
 
Join Date: Sep 2004
Location: North East
Blog Entries: 1
Have you seen this site on Stig's work:
CarlssonPlanet.com • Everything about the Carlsson loudspeakers

There was a decent paper covering his theories here:
CarlssonPlanet.com • Downloads
__________________
Pete Basel
http://www.linkedin.com/in/petebasel
  Reply With Quote
Old 8th March 2013, 08:15 AM   #4
diyAudio Member
 
Join Date: Mar 2010
Location: Stockholm
Pete,
Thanks for posting links to the Carlssonplanet site, and to the paper on some of his design ideas. Well known for all the Carlsson enthusiasts in Sweden.

The wealth of information and experiences on open baffle speakers applications found at the sites of Siegfried Linkwitz and John Krekovsky have also been of great support and inspiration for me in this endeavour.

/Mats
  Reply With Quote
Old 8th March 2013, 08:48 AM   #5
Rudolf is offline Rudolf  Germany
diyAudio Member
 
Rudolf's Avatar
 
Join Date: Mar 2003
Location: Germany
I hope you know these papers:

http://decoy.iki.fi/dsound/ambisonic...Kates_1980.pdf

http://www.extra.research.philips.co...ers/aar03c.pdf

This is a comparison of radiation patterns at 1 kHz for my own dipole and Earl Geddes' Abbey WG loudspeaker:

polar comp wg-dipole.gif

Geddes is reporting a significantly larger sweet spot with his Abbey speakers while I can't report that for my dipoles in a comparable listening situation. "markus76" is missing this effect in his Nathan speakers (Abbey-like but smaller size) too.

It looks like you need a higher directivity for this effect than a pure dipole will achieve.

You will be interested in the software which Earl Geddes is developing for the control of sweet-spot-enlarging, documented in this thread:
New study on loudspeaker placement

Rudolf
__________________
www.dipolplus.de
  Reply With Quote
Old 8th March 2013, 09:10 AM   #6
Banned
 
Join Date: May 2008
Location: Switzerland
Quote:
Originally Posted by Rudolf View Post
I hope you know these papers:

http://decoy.iki.fi/dsound/ambisonic...Kates_1980.pdf

http://www.extra.research.philips.co...ers/aar03c.pdf

This is a comparison of radiation patterns at 1 kHz for my own dipole and Earl Geddes' Abbey WG loudspeaker:

Attachment 334702

Geddes is reporting a significantly larger sweet spot with his Abbey speakers while I can't report that for my dipoles in a comparable listening situation. "markus76" is missing this effect in his Nathan speakers (Abbey-like but smaller size) too.

It looks like you need a higher directivity for this effect than a pure dipole will achieve.

You will be interested in the software which Earl Geddes is developing for the control of sweet-spot-enlarging, documented in this thread:
New study on loudspeaker placement

Rudolf
I've tried it with an 8" full range driver too (Visaton B200). Didn't work either.

By the way, do you have more polars comparing your speaker to the Abbey at different frequencies?
  Reply With Quote
Old 8th March 2013, 09:29 AM   #7
diyAudio Member
 
Join Date: Mar 2010
Location: Stockholm
Rudolf,
Thanks for the links and your comments. Yes, the Kates paper is known and I have tracked the theory back to a AES paper by Bauer in 1960 on "Broadening the Area of Stereophonic Perception".

I also realise the dipolar directivity pattern is an approximation of the time intensity trading function investigated in these papers. Maybe you can achieve better correlation with a constant directivity waveguide, but I like to keep it simple and have found the dipolar pattern to be good enough for my aims. I'm reasonably satisfied with the stability in stereo perception through my speakers as I move around in the listening room.

And as Mr. Geddes mentions himself as an issue with waveguide solutions, I rather take advantage of the fair consistency in the polar response for a dipolar speaker throughout the full frequency range. Which helps an eveness in the perceived sound as you move around, as well as it enlightens the room with reflections for a balanced perception of apparent source width and envelopment. This has been very important for me in my designs, and I have prioritised this attribute over an improved match in the time intensity trading function in my speakers so far.

Rgds, Mats
  Reply With Quote
Old 8th March 2013, 04:37 PM   #8
zmyrna is offline zmyrna  United Kingdom
diyAudio Member
 
Join Date: Nov 2009
Location: London
My current project in progress is an OB similar to SL and JohnK designs.
I have 10" woofers, 8" mid, and Neo3 as tweeter.
I have been experimenting with waveguides on Neo3 as well.
I am also considering trying Neo8 as a mid too.
Lately, I have been seeing designs here with tilted mids like the Gradient.
It is interesting to me because my last commercial speaker was an Oskar Heil Syrinx.
So can you please explain to me the benefits of such a design?
Wouldn't it cause big problems when switching from a sitting to standing listening position?
And lets say I use neo8 as mid tilted 45 degrees backwards: would it have the same effect of reducing its height?
  Reply With Quote
Old 8th March 2013, 10:43 PM   #9
diyAudio Member
 
Join Date: Mar 2010
Location: Stockholm
As you tilt the driver from vertical towards horizontal mode you also tilt its polar response, from a forward beaming position to an upwards beaming position. And hence alsoto a more omnidirectional pattern in the horizontal plane. The goal with my tilt is to decrease the acoustical energy sent towards the floor by aiming the vertical null towards that direction, as well as sending some more energy upwards to enlighten the room with later reflections.

Sure tilting the baffle can cause problems if you don't balance the directional characteristics of your design. But that can happen with a conventional vertical position just as well.

As speaker unit's directional characteristics is set by the size of the active membrane in relation to the reproduced wavelength. Tilting does not affect the size of the membrane, just the direction of the beam as the membrane gets large compared to the reproduced wavelength.

Be sure to check the Neo 8 excursion requirements in your application depending on choosen crossover topology, baffle size and desired maximum sound level. There is a Neo 10 also, which might fit the bill better as a midrange driver in your project.

/Mats
  Reply With Quote
Old 9th March 2013, 11:45 AM   #10
diyAudio Member
 
Join Date: Mar 2010
Location: Stockholm
Some experience from the build. To cut the basic MDF boards in the local property market was easy enough. Loading the trunk of my car with all the bits and pieces I could sense these beasts would be heavyweights by the end of it. Final speaker weights in at roughly 150 pounds each. Huge drawback when you are curious to test and try them out in various surroundings... Next model will have to be lighter.

Click the image to open in full size.Click the image to open in full size.Click the image to open in full size.
And piling them up to get a first impression of the expected result was smooth. In the pictures I have also cut and routed the first mid baffle.

Click the image to open in full size.Click the image to open in full size.
60 routed boards later – phew... Lots of plugs, glue and screws later the result looked like this, the finished raw chassis.

Click the image to open in full size.
Time to get the drivers in place. The midrange is magnet mounted and this is when I used ferrules to tighten the driver just enough towards the baffle.

Click the image to open in full size.Click the image to open in full size.
Looks like a huge motor to a diminutive cone on those AE Dipole 10’s. Should be able to keep the bass in control.

Click the image to open in full size.Click the image to open in full size.
Assembling first the lower and then upper bass driver. The chassis now has some protective paint as well.

Click the image to open in full size.
There we go, bass chassis ready with drivers and plinth in place, including one version of a passive crossover.

Click the image to open in full size.Click the image to open in full size.Click the image to open in full size.
Assembled speakers positioned as intended in the living room.

Click the image to open in full size.Click the image to open in full size.
Details on the mid baffle, with damping and an acoustic lens added to the forward Illuminator controlling dispersion.

After my router marathon it was time to focus on the crossover. First I wanted to try out a fully passive solution, but I wasn’t sure I could find a satisfying compromise.

Click the image to open in full size.
Before you know how it will end up it can look like this…

I made a decision early on to aim for rather steep slopes in the crossover, to ensure the drivers didn’t work outside their linear territory all the way up to anticipated maximum sound level. For the passive version I ended up with LR4 filters at around 300 and 2000 Hz, using the bass drivers all the way up towards the cavity resonance in the W-baffle to avoid burning more than minimum energy in the coil compensating the dipole cancellation. The Seas Excel 8” unit has good dispersion and behaves well enough up to around 2000 Hz, where the tweeters could take over and still manage intended maximum sound levels within their linear region.

Click the image to open in full size.Click the image to open in full size.
Finished passive filters, for bass and midrange in the plinth and the tweeter filters on a detachable tab of the mid baffle.

But I was never fully satisfied with a passive only solution. It would probably have been necessary to filter away a couple of additional decibel sensitivity in order to get the balance just right, and that felt like the wrong way forward. Already as it was, the speakers required a couple of hundred watts to reach maximum intended sound level.

So by now I have turned to a hybrid solution, with active filters between bass and midrange. But keeping the passive filter between midrange and tweeters. The active filter manages compensation for the dipole cancellation and crosses over to the midrange at 150 Hz. I have also rebuilt the passive filters for improved phase correlation in the crossover region. The active filters are based on Linkwitz ASP solution, adapted to my needs.

Click the image to open in full size.Click the image to open in full size.
Final filter solution.

Next up – some listening impressions and measurements.
  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
open baffle project sqrivi Full Range 58 25th July 2014 03:25 PM
FS: Acoustic Elegance 12 Dipole one of the best open baffle mid bass drivers hum4god Swap Meet 5 24th March 2012 01:52 AM
Acoustic Elegance TD15LO Dipole Best Driver for open baffle NEW!! hum4god Swap Meet 3 22nd September 2011 01:57 AM
FS: Acoustic Elegance 12 Dipole one of the best open baffle mid bass drivers hum4god Swap Meet 0 10th September 2011 03:43 AM
Vented / Open baffle hybrid design and ideas Spike415 Multi-Way 2 23rd September 2010 05:53 PM


New To Site? Need Help?

All times are GMT. The time now is 04:08 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