Warning…long post.

The title of this thread is a spoof on the speaker brand Pure Audio Project.  I heard their OB speakers at Axpona last year and liked them.  

http://www.pureaudioproject.com/trio15-open-baffle-speakers-pureaudioproject/

Then I heard ProggRob’s Hawthorne Trios with his UFO Zen and felt the quality bass they produced was something I wanted.  Then I heard Randy’s OBs at the fest with a Augie helper  http://www.caintuckaudio.com/ http://www.hawthorneaudio.com/catalogs/index.php?main_page=product_info&cPath=3&... and liked how musical it was.  Finally, ProggRob came over for a CDApS session and gave his honest opinion that bass was not a strength of my system.  He was right and that pushed me over the point of no return.

So, I had a little mad money at the end of the year and bought a single Augie from Hawthorne Audio along with a Dayton Audio 250W plate amp.  I figured if I liked it well enough I would get a nice baffle from Randy and be all set.  Little did I know…

Well, I got the Augie, stuck it in a 23.5W X 22H MDF baffle made from leftover wood , hooked it up and it was another wow moment for me - like when I heard my Rachael on a PS Audio power conditioner or when I got the Uptone Audio Regen.  But while it was great, I immediately wanted more.



So, I blew up my budget and ordered another Augie.  Stuck it in another MDF baffle made from leftover wood and set it up running off the plate amp in dual mono.  More goodness as the rabbit hole began to open wider and wider.

Then I thought why not get a couple Besty drivers.  Randy’s OBs at the Fest sounded good.  Those don’t cost much, right?  But then I did some research, exchanged notes with Randy and Maddog07 and started weighing out my options.  Betsy?  Audio Nirvana?  Or the Tang Band W8 1808 which was used in the Pure Audio Project?

I finally decided to take a chance on the Tang Band.  I had used a smaller Tang Band in the past in a simple OB I built pre-Decware days.  I figured that the Pure Audio speakers had received good reviews and they were at the core of that sound.   Steve also had a favorable opinion of them when he was looking for an OB driver.  Finally, I had a 20% off coupon from Parts Express so Tang Band it was.

I got the Tang Bands and cut some 23.5W X 13.5H baffles out of old wood and literally tacked them to the Augie MDF baffles with some leftover furring strip and some drywall screws.

The Tang Bands literally sounded like I was listening to music through a telephone hand set.  But, I was emotionally prepared for break in time, so I let them play for 24 hours.   Hmmmm…better.  Another 24 hours.  Better still.  Another day or so and I think we were there.

I played with the crossover frequency on the plate amp.  Originally, about 50hz.  Then full on (180hz), then backed it off to about 70hz.  That seemed about right.  Then I started playing with volume.  I started out with it about ¾.  But after much fiddling, I ended up about only ¼.  

Where these Augies help the most is in helping you feel the low end.  They provide a nice tight foundation.  If you have the crossover set too high, you can definitely hear the nice tight bass, but it starts to mess up and cloud the mid-range.  Same thing with volume.  It’s cool to rattle your walls, but it can overwhelm everything.

Something was still amiss.  Imaging seems off, so I decided to try an old honker Class D stereo amp that I had from pre-Decware days.  I pulled it out of the closet, and hooked it up to the line out from the plate amp, and rewired everything in stereo.

Wow.  Even tighter and more musical bass.   The plate amp wasn’t even close.  No crossover on the class D though, so I exchanged more notes with Randy and did some reading about how guys are powering the bottom end with Crown class D professional amps.  They have input sensitivity adjustment and a digital crossover (low pass/high pass).

In the meantime, I received a gift card from one of my employees for home depot, so I go there and get material to make a prototype of what I had in mind for the final OB.  A  Pure Audio Project style baffle, only without two bass drivers per side, just an Augie per side.



The key to the Pure Audio design is the metal that bolts into three pieces of wood and forms the triangle behind the baffles to give it a three point stance for stability.  I found some 48” aluminum slats at home depot for about $12each. [url= http://www.homedepot.com/p/Everbilt-1-1-2-in-x-48-in-Aluminum-Flat-Bar-with-1-8-...[/url]  

Using some foam board I modeled out the bends and length of each slat.  If I bent them just right, I could get three 16” aluminum bars out of each slat.   I cut them using a hack saw and then bent them using a vice.  

I also picked up some clear pine for the two six foot 1X2s for each side and one six foot 1X3 for the back pillar.  In hindsight, I should have grabbed cherry or oak, but I can always change that out later if I want to.

I cut the wood into 36” lengths, drilled the holes and bolted it together along with a baffle I cut out of cheap plywood for the Augie and used the same baffle I had cut for the Tang Band.  It all worked and was surprisingly stable. It all looked like it was going to work, so I bought some good Baltic Birch ply and made good baffles.







Unfortunately, I picked the coldest weekend of the year to apply the stain and finish to the wood, and royally screwed the baffles up rushing through the job.  When it warmed up, I took the sander to the baffle fronts and refinished them so at least they look pretty good.  



I then made the second frame and bolted everything together and it looked pretty decent.  I also had some adjustable feet that I put on so I could vary the angle.   They stand ~37” high and 23.5” wide.  The middle of the Tang Band is right about ear level for my listening chair.

I sanded down the aluminum bars and applied a rubber paint to make them black and maybe help with vibrations.  I also got some nice black socket head screws, washers and nyloc nuts off ebay and put those on in place of the cheap galvanized nuts and bolts from the prototype and it looks a little more professional.  I still need a few more bolts to completely secure the drivers, but otherwise, they are done.







So back to the Crown amp.  I found one cheap on eBay.  Since the
Crown only has line level inputs, I also bought a cheap high level to line level converter (used in car audio) so I could run the Crown straight off the Torii binding posts.  The el cheapo converter works, but I am going to build a “magic cable” designed by Dennis of Hornshoppe Horns fame that basically involves wiring in a 600 ohm resistor into your speaker wires to step down the juice from your amp to something the Crown can use.



So now I am tuning everything.  The Tang Band does have the typical single driver rising frequency response.  But I have found that playing with toe-in can impact this.  The more off axis you are, the less high end you get.  I am also playing with the treble shunt on the Torii III to help with this and mid-range shout.  The crown crossover point is now right about 100hz and I am running the input sensitivity up around ½ to ¾.  Some of this is due to the Crown requiring more input juice which I suspect the el cheapo line converter does not deliver.  I should be able to back it off again with the Magic Cable once I get it put together.

These speakers do some things amazingly well.  Soundstage, ambience, detail, tight, tight musical bass, real sound quality.   Imaging at first was not bad but not great, so I continue to play with positioning and toe in and it is getting much better.  They play a variety of music very well.   Jazz, light rock, classical, progressive, ambient, classic rock all sound good.   Uber complex stuff does give them a little trouble, but I don’t listen to listen to a lot of stuff like that.

I probably have them in too small a room.  Even though they are duos and not the trios as offered by Hawthorne and Pure Audio, they are a little physically imposing.   I ended up backing my listening chair up and I may move some of my room treatments to fine tune the sound.
I did some REW measurements and they are flatter than expected.  Also, I compared the FR of the OBs to the DIY monoliths and you can most clearly see the pickup between 25 and 100hz, which is kind of what I was after in the first place.  

It was a bit of a winding road getting here, but for now I am an OB guy.  It is a bit addictive.

Thanks to Randy, ProgRob, Darrel Hawthorne and maddog07 for your help.

Palomino, this appeared at exactly the right time for me. I have been researching OB's all of this weekend. Learning about QT's and excursion lengths and stuff like that.
Your report helps me a lot.
The fab part is the simple stuff for me. I have a whole crew of CAD designers and tool makers that work for me. The aluminum stuff will be cut out on our water jet. I might even have them jet out the baffle holes.
The Rest of the stuff needs to be thought out, but seeing that someone else has figured it out gives me insperation.
You have fired me up, thank you.

Nice project!

My 2cents

A narrower baffle for the TB will help imaging.

Preferences vary, but I like less treatment on the wall behind the speakers and the speakers out 5' or more.
At 5.5' (or more) our ears can easily distinguish between direct and reflected sounds.

I have to rethink treatments.  It's a completely different ballgame now.  These speakers seem to want nothing behind them.  I will continue to experiment.  

4' from the front wall is about all I can do.  I am getting great depth right now.  Imaging is really dependent on toe in.  

These speakers seem to be easy to crank up too loud

Donnie,

16" should work well with an 8" driver; width is a trade off between imaging and how low the the wideband driver will play. I would offset the TB so that the distances from the driver to the top and both sides of the baffle are all different.
You can always make the bottom an H baffle for the Augies. Adding an 8" side panel + 16" = 24" total.


Palomino,

Shorter distances can work fine.
The 11' (5.5' x 2) target allows enough delay that ours brains don't work as hard to determine if a sound is direct or reflected.
I personally prefer an untreated wall as I feel it adds to the "live" sound. I've heard treated wall setups that made OB speakers sound more like monopole speakers.

I always ran my Visaton B200s with no (or a very slight) toe in.

BTW thanks for mentioning the Magic Cable.
I have been trying to figure out what to buy to connect my tube integrated to a line level only sub and completely forgot that I have a NOS Magic Cable.

Sorry I don't know.          Ed made mine.

Here is something I found while searching; reply 3:
http://www.audiocircle.com/index.php?topic=97456.0

Russound ADP-1.2
http://www.audiocircle.com/index.php?topic=139602.0

I agree Pal... rear reflections are a "good thing" for a dipole OB speaker.  That is precisely what is responsible for their characteristic "big" sound... some like it - some don't.  I think it makes for a more realistic sound myself.  I do not have any treatments behind mine, but I am considering messing around with some "diffusion".  I think absorption behind the speakers would be a bad thing in most cases, unless you have a really nasty response peak or something.

I was studying the magic cables to allow you to step down the speaker outputs of a power amp to drive the line level inputs of another amp.  Looks reasonable, but it would seem to me (and I'm not an electrical engineer) that 1/2 watt power rating on the resistor would be too small.  For example, if you were taking another speaker level feed off a Torii to drive the inputs of the Crown, and the Torii is rated for 24-25 watts - wouldn't the resistor need to be able to handle that much power?  Perhaps due to input impedance of the Crown (or any amp) only very little "power" is actually transmitted - I don't know.  

Can anybody explain this?

Pal, mighty impressive work!  I really want to stop by soon, I'm simply  not content just reading about it.  When I hear it, then I will post!

Maddog - you don't believe that bass trapping in the corners behind the speakers is a good idea?  Are you saying no absorption of any kind?

I'm saying don't install absorption "just because" - only install absorption if you need it.  I think in "most" cases diffusion is beneficial, but I think absorption is really, really room dependent.  Just my .02 ¢

Quote:


I did some investigation on this... google "speaker level to line level" and pay particular attention to the url:

http://www.epanorama.net/circuits/speaker_to_line.html

what we are talking about here is a voltage divider it looks like, and for amplifiers of average gain, a 10k ohm resistor in series on the + conductor and a 1k resistor in parallel across + and - gives us a 1,000 ohm output impedance and a 20db reduction (10:1) attenuation.  If we substitute a volume pot for the 1K resistor... we have a "variable" attenuator.... which could be quite useful.

I think its neat that we are sharing OB experiments.  I have been in touch with Randy for his insights.

Hopefully, others will weigh in or join the "brotherhood of the open baffle" (boob).

Every time I go to the hardwood lumber yard I see those big slabs with the bark still on and fantasize about doing a project with one.  Could make for some cool OBs.

Palomino,
   Can you attached the REW MDAT file? I would like to see whats going on. Do you do a REW when you make the Changes in position or equipment? I find it very interesting to see what the changes are doing to my FR, decay,....
JPV

I got the resistors and made up a couple of magic cables.  Big difference vs the el cheapo auto line converter.  Better volume, weight and slam.  But also a significant amount of buzz.  I had to go back to the el cheapo.

I resoldered everything and tried a couple configurations to no a avail. Something I am missing.

Worth a try. Let me see if I can measure anything between the two amps.

Yes everything is plugged into the powerplant.   No buzz on the car stereo line converter.   Only with the magic cable.

Just a note: I had a Rachel with a treble cut circuit installed, it can be added.

Yeah that's what had me concerned going in but the crown plus the augie is the best bass i have heard regardless of slicing and dicing of signal.  I am a horn guy who is not real crazy about crossovers to begin with.

I am open to trying the 15a's in a future build.  They are so inexpensive for what you get.  It's the driver the augies are based on I am pretty sure.  I see pure audio has their version of the augie now too.  I'm afraid I am hooked on bi amping though.

When the Treble Cut Circuit was new Steve told me that the circuit could be added to any amp. Then the ZMA came out and he told me it could not be added to the ZMA. I think it may depend on the year of the Zen amp. . . and Steve is really the only one who can definitively answer.

I gave the FRX2 a look.  Intriguing but a lot more expensive.

I am at a good spot with these speakers and intend to run them with the W8s via the Torii III.

It's only if I want to also run them via Rachael or some day a Zen that the W8 concerns me due to no treble shunt.  I do want some other ears on these to tell me if they feel the same way.

There is a possibility that you could also tame what I am hearing with tubes or other tweaks.  For example, ProgRob has a coax that provides a very even presentation.

Pal,
Do you have a link to the schematic (or representative drawing) of the magic cable?
With my background I might be able to help troubleshoot.

Last night I just accepted the buzz and listened to music.  Yes, it was there when I hit a quiet passage or between songs and yes it was annoying, but I have one word to describe the bass from this Crown/Augie setup:  sublime.  In fact its so addicting that I am going to live with the buzz rather than go back to the el cheapo line converter.

I have about 30 tracks in my collection that I like for testing bass and last night I listened to them all and was glued to my listening chair.  This morning I listened to Daft Punk Random Access Memories in 24/96.  I have to be in the right mood for this album, but it has great bass and again, it captivated me.

So, I am scanning the web for buzz solutions.  There is a fair amount out there on the Crown amp but no definitive solution yet.

So other facts that may help someone help with with this issue:

1.  I get the buzzing when the Crown amp is off.  It is amplified and changes tone once I turn it on.

2.  I have plugged the Crown into an entirely different circuit in my room and it is about 5X worse than when it is plugged into the Power Plant Premiere.

If I get a chance tonight, I will try a shielded cable and also see if I get the same buzz going through my plate amp to the Crown.

Looking at the connections I would suspect the ground of the Crown RCA jack is feeding back and creating a ground loop via the speaker connection. You could measure the RCA jack ground on the Crown to the chassis to see if it is a direct connection to your power amp.
I'm not that familiar with the Crown internals but if it is a direct chassis connection you could try adding a series 50 ohm resistor in the shield path back to the speaker negative instead of a straight wire (as part of your magic cable).
One thing for sure, be careful when isolating grounds between chassis that could be floating and then touching both at the same time.
You do not want to be the thing that completes the circuit!  :)

Dang. I have no way of adding a drawing here at work....
To measure, disconnect everything from the Crown, power cables, etc.
Then set the meter to Ohms and measure between the RCA input that the magic cable was plugged into, outer (shield) and the Crown chassis.
If it's not isolated you will get a pretty small #, like less than 5 ohms.
The 50 ohm, if you decide to try it, would be in series with the "other" wire going back to the speaker negative from the Crown RCA.