[markk]

Hello everyone in the Open Baffle Circle,

I would like to take the time to thank everyone here that have posted so much information on Open Baffle Loudspeakers.

I have been very lucky to learn from your knowledge so I could build my own loudspeakers.

My speakers consist of 2 Acoustic Elegance IB 15" subwoofers and one Hemptone 8" full range driver per side.

The Baffles are made from 1 and 1/4" Pine wood that has been stained and painted with clear urethane.

The crossover is taken care of by a DBX Driverack PX.  This matches the loudness of the low frequency and mid/high frequencies.  It also digitally corrects the speakers/room with a microphone that will listen to a pink noise signal.  It can make corrections from 20 Hz to 16 K HZ.

The 15" Drivers are driven by an old Krell KAV 300I, and the Hemptone Full range is driven by a Jolida JD 102B Tube Amp.

They are very fun to listen to and i think they sound better and more dynamic than my Magneplanar 1.6 speakers.

It is great to listen to all kinds of music with these but i really seem to like the sound of them with southern rock like Lynyrd Skynyrd or the Eagles. Also the Avatar and Pirates movie soundtracks can really show off the low frequency drivers.  Stereo Bass sounds better than one subwoofer put in the corner of the room any day.

I will try to post images of my loudspeakers and system for you to see.

Thanks again everyone for your help,

Sincerely,

Mark K.

[Brad]

Cool project Mark - thanks for sharing.

Love that OB bass!
How much space do you have behind the speakers?


I'm actually in the midst of something a bit similar - will post pics once I complete.

[markk]

Hi Brad,

I have the loudspeakers 3 feet from the back wall.

Peter Walker who invented the Quad Loudspeakers wanted at least 10 milliseconds of delay time for reflected sound from the room to reach the listener after the direct sound from the loudspeaker did.  So that would be closer to 5 feet away from the back wall.

I think the Cardas Website has a good planar speaker placement calculator that may be helpful for you to try also.

Thanks for your reply.

Mark K

[markk]

I was not able to upload a picture of the front of the Loudspeaker so i will give it another try.

Thanks for your patience.

Mark K

[MJK]

Hi Mark,

What are the crossover settings and the amount of boost or EQ applied to the woofers?

Martin

[markk]

Hello Martin,

I have set up these speakers with the DBX by setting it up for custom Stereo Subs and custom Mid/high stereo speakers.  That way it will start from scratch and not use any of the pre programmed loudspeaker settings like JBL or Yamaha, etc.

The DBX will correct the LF and MHF levels and will check the left and right channel balance automatically.

The Driverack Px lists the following on the LCD screen
20 Hz BW 6
100 Hz LR 12  (i think this is where the LF drivers start to cut out?)
100 Hz LR 12  (i think this is where the MHF driver goes down to?)

I think i turned off the 20 Hz filter and did another recalibration with the microphone and i was able to get the speakers flat down to 20 Hz.

None of the speakers seem to be suffering from large excursions but you can definitely see the LF drivers moving in and out during the eq calibration step.

It is very interesting to watch the Driverack screen during the Eq step. when one band like 100 Hz corrects its level to flat than it will affect several nearby octaves and then the Driverack will correct for these speaker/room changes.

I tried to make my own passive crossover first but I failed miserably. 

The Driverack is showing so many complex changes with the speakers/room interaction at the same time. I do not think a passive crossover could ever be built that can correct for the speakers,room and placement of the speakers in relation to the listener.

I know the DBX is thought of more as a Pro Audio piece of gear.  However it has worked quite well for me in this particular Bi amp configuration.

I suggest you would like it if you gave it a try for your speakers. 

Thanks for your reply,

Sincerely, Mark K

[MJK]

Hi Mark,

I built a very similar system and use about the same crossover settings on my older dBx Driverack PA.

http://www.quarter-wave.com/Project10/Project10.html

Low pass the woofers using a 6 dB/octave filter at 30 Hz and a high pass filter on the Lowther set to 12 dB/octave LR at 200 Hz. I ended up boosting the signal to the woofers by 18 to 20 dB so that their output matched the more efficient Lowther full range driver. I have not tried letting the dBx do the crossover work using the microphone, I guess I need to try that option. The dBx units are really nice but do not get a lot of mentions on the forums.

Very similar systems so I know your speaker must sound really good.

Martin

[mcgsxr]

Tasty build, thanks for sharing!

Some of my fav music when I ran my OB setup was using electric guitar or sax.  Those instruments just sang on that setup.

[markk]

Hello Martin,

Your Lowther and Acoustic Elegance system looks Amazing !!!

I have nowhere near your knowledge and skill with making and measuring my system.

I was able to have my DBX Driverack PX go through its own set up process first.  Then when it was done assigning the crossover points I noticed that in the crossover window it had given the low frequency roll off at 35 Hz.  During the Eq step the first time around I was not able to get the system to Eq out flat down to 20 Hz.  So i was able to manually change the low frequency cut off down to 20 Hz and re run the Eq step with pink noise again.  This time I was able to see the DBX Eq graph get the system flat down to 20 Hz in my room.  The Low frequency drivers will really be moving in and out to get down to this level so I only recommend using this setting for drivers with similar parameters as the AE IB 15s as far as QTS and X-Max measurements go.  3mm X-max woofers need not apply as I worry they may bottom out sooner.  I also recommend a strong amplifier as there will be a fair amount of low frequency boost going on in the DBX processor.

So you may try and let your DBX set itself up first and see how you like the sound.  Then you can go back to the first few windows and find the crossover settings it assigned.  You can manually change these crossover points and re run the Eq step again.  Then see if you like your crossover settings better.  Just remember to save the settings you like the most and have that be the setting that works best for your system/room.

The DBX company may have a software update to your unit if it is older and that may help you out as well.

By me using the Jolida and Krell integrated amps I can turn the volume up on the Krell for the LF and turn the Jolida volume down for the full range to get the drivers close to the same ballpark before the Driverack does the rest of the fine tuning.

Also I was wondering if you were able to try and vertically stack your AE H frames. If so could you turn your lowther baffle sideways or make a new baffle to adjust the lowther's vertical height in relation to the new vertically stacked LF drivers?

Visually it may look more appealing.

I know you kept the LF drivers close to the floor to increase efficiency but your drivers have so much surface area it might not be necessary.

I would be a bit concerned in seeing all of your H-Frames being the same depth.  Would you run into one big abrupt frequency change at the dipole cutoff frequency?
I wonder how your system would sound if you had half of your H frames at a different depth.  Would that help randomize the cutoff frequency roll off point more?
I am not sure I am explaining this correctly as my knowledge is more limited. However I made the wings on the side of my baffle taper from bottom to top based on the Visaton NoBox BB Loudspeaker Kit review and article by Dick Olsher.  It is on the Enjoy the Music website and it is very well written.  It gives lots of tips on OB speakers.

I also borrowed some of my look and shape of my speakers based on the expensive Jamo R909 which has lots of interesting reviews in the internet especially the 6 Moons website article on them. I could just not pull off a passive crossover design so i cheated and used the DBX in a bi amp configuration with very good results.

Thank you very much for contributing SO much to the field of Open Baffle Loudspeakers.

I am honored that a you would respond to my post.

Sincerely,

Mark K

[scorpion]

Very nice project !
I use AE IB15 for woofers now with B&G Neo10 and Neo3W with great sucess. As far as I can tell this combo is a bit better than Magnepan 1.7
which I had the opportunity to compare with. But I also liked the Magnepan 1.7 very well.

/Erling

[markk]

Hello Erling,

I have enjoyed your posts and find your builds to be very interesting.

Thanks for your feedback in your comparisons with the 1.7 Magneplanars.

I bet the 1.7s would sound really good with 2 AE IB 15s per side.

I always wanted my Magnepan 1.6s to sound a bit more dynamic.  Just turning the volume up louder did not seem to help them.  Some Open Baffle subs would be a good match for them and it would allow the magneplanars to not have to work as hard in the lowest frequencies.

I may however not have enough room to place four panels along the front wall of my living room.

Thanks for your reply,

Mark K

[MJK]

Hi Mark,

Also I was wondering if you were able to try and vertically stack your AE H frames. If so could you turn your lowther baffle sideways or make a new baffle to adjust the lowther's vertical height in relation to the new vertically stacked LF drivers?

Visually it may look more appealing.

I know you kept the LF drivers close to the floor to increase efficiency but your drivers have so much surface area it might not be necessary.

I switched my simulation around to model a stacked configuration, it gave pretty much the same results. So it appears to be a cosmetic issue, personal preference over which configuration looks better to the individual. If I were to stack the H frames I would build a new baffle for the full range driver, probably a tall narrow baffle to put the driver at ear level.

I would be a bit concerned in seeing all of your H-Frames being the same depth.  Would you run into one big abrupt frequency change at the dipole cutoff frequency?
I wonder how your system would sound if you had half of your H frames at a different depth.  Would that help randomize the cutoff frequency roll off point more?
I am not sure i am explaining this correctly as my knowledge is more limited. However I made the wings on the side of my baffle taper from bottom to top based on the Visaton NoBox BB Loudspeaker Kit review and article by Dick Olsher.  It is on the Enjoy the Music website and it is very well written.  It gives lots of tips on OB speakers.

The lowest H frame resonance is very predictable and I use it in the acoustic crossover design. Having both the H frames the same is intentional. Making them different lengths does not seem like such a good idea to me, just my opinion. My intent in building things this way was to be able to remove one of the H frames per side to match up with a less efficient smaller full range driver or a more conventional midrange and tweeter (maybe the Neo 8 or 10 and the 3 at some point).

I also borrowed some of my look and shape of my speakers based on the expensive Jamo R909 which has lots of interesting reviews in the internet especially the 6 Moons website article on them. I could just not pull off a passive crossover design so i cheated and used the DBX in a bi amp configuration with very good results.

The dBx is a nice unit, not cheating at all just making more things work better together.

Thank you very much for contributing SO much to the field of Open Baffle Loudspeakers.

I am honored that a you would respond to my post.

Thanks for the positive feedback, I am just a dabbler like everybody else. It just so happens that my hobby plays off my engineering background of 30+ years as a vibration and structural analyst and tester. I do the same stuff 8+ hours per day on much more expensive hardware and get paid for it.

Martin

[markk]

Hi Martin,

Thanks for explaining your horizontal H frame layout in more detail. I am glad it works for you. 

I was also thinking that a vertical placement would change the amount of floor bounce artifact that may be present by changing the height of some of your LF drivers.

I want to build another Open Baffle in the future a little like the Kef Blade concept that has all of the LF drivers mounted up higher away from any floors.

I want to have the LF drivers work on their own merit not use a floor or wall or corner as a way to make them more efficient.  I have a feeling that if I can get them to sound good away from any boundaries the bass will sound even better.

I am trying to start this project soon so someday I hope to post my project in the future. My goal with this project is a full frequency Dipole that can measure 20Hz to 20K HZ on both the front and back of the Baffle.

I definitely recommend you try to set up your DBX with the microphone hooked up and located at the ear height and location where you sit.  Your system will sound better by leaps and bounds. It will also help boost your Lowther in the high frequencies and will even out the system quite well.  My DBX also has 2-3 other target curves built in that you may want to try.  However the flat curve setting has worked the best for me.

Thanks for your reply,

Mark K.

[MJK]

Hi Mark,

I was also thinking that a vertical placement would change the amount of floor bounce artifact that may be present by changing the height of some of your LF drivers.

I want to build another Open Baffle in the future a little like the Kef Blade concept that has all of the LF drivers mounted up higher away from any floors.

I want to have the LF drivers work on their own merit not use a floor or wall or corner as a way to make them more efficient.  I have a feeling that if I can get them to sound good away from any boundaries the bass will sound even better.

I placed the woofers close to the floor for both bass reinforcement and to avoid the floor bounce. The higher you place the woofer above the floor the lower the frequency where floor bounce will become an issue, woofers near the floor and a low crossover frequency will mitigate the floor reflection. In my simulations and measurements you do not see any floor bounce artifact in the woofer response, you do see it as the small ripple in the Lowther SPL response.

I do not think you can avoid interactions between the dipole speaker (any speaker for that matter) and room boundaries, use them to your advantage by placing drivers carefully on the baffle, designing the speaker to work well at a prescribed distance from the room boundaries (the floor will always be there so include it in any design calculations), and rotating the system to not be parallel with the rear wall as mentioned in another thread.

Martin

[markk]

Hi Martin,

Thanks for explaining this to me.

I have read articles that the closer the woofer is to the floor, then the floor surface starts to look or act like an acoustic mirror.

You must have added quite a bit of efficiency by having all of your LF drivers positioned so close to the floor.

It also seems that it is important to couple the open baffle frame or panel all the way down to the floor and not leave any space. This then will also create a mirror image of the baffle itself allowing the overall baffle width to be reduced.

I think this was also mentioned in the Enjoy the Music article by Dick Olsher on the Visation NoBox BB loudspeaker kit.

As I see by your images your Lf woofers are about as close to the ground as they can get.

Thanks for explaining your design choices to avoid floor bounce artifact.

Mark K