Hi Nelson,

Thanks for jumping into the forum with your build results!  I've read your posts with some interest and look forward to the story as it continues.

If you're on the bright side of the holy grail, you may already be there.  It my experience just upgrading speaker wire can lead to another week of tube rolling with the final result being a completely different set of tubes.  That would indicate that a change as major as the speaker might demand the same type of system voicing.

Another thing I've noticed is that A) the DFR-8S (shielded version) has more bass than the DFR-8, and that some amps generate much more weight than others.  Our Torii MK II or MK III for example, has fooled me more than once into thinking I had bass augmentation on when in fact it was off.  

You've been trying different amplifiers so I expect you're already finding favorites.  I enjoyed your comment about being able to instantly hear how much better one amp was over another.  I use these type of speakers when I voice my amplifiers, as I know in 15 seconds what's up whereas if I used a normal pair of hi-fi speakers it takes 15 minutes and a fair amount of guessing.

Also, darkening the room a bit is a great way to pick up the low end.  Hang a couple moving blankets up over hard surfaces some night as an experiment...

It will be most interesting to hear what happens when you mic the chambers, but once you overcome the feedback none of what I've said above will be remembered.

Steve

I failed first attempt yesterday using a Behringer ECM-8000 and a mic preamp. Got acoustic feedback (boom boom) and too much noise from the preamp. I really need more gain (another preamp or a better mic preamp).

I also look forward to read Steves next article about the ZOBs.

I found the ZOB extremely detailed and open but to light/bright for my taste in the long run. I really nead more bass to balance the speakers for all my rock albums.

Though acoustic instruments and live recordings can sound absolutely life like. Stunning!  :)

Maybe the Tang Band W8-1808B 8" Neodymium Full Range Driver will fit? It does have a higher Q than the stock FE207E.

Who makes a good OB sub to use if you mic'd the chambers?

I was thinking if as Steve says the purest ,totally in snyc bass comes out of the chamber port, then using the chambered mic'd feed to some OB subs or even normal subs might be very interesting.

Break in period for the DFR-8's is 40 - 50 hours before they're even usable.  200-500 hours before they are completely done. Base fills out in the 40-100 hour window.

The resonant cavity is usually lightly stuffed.  The more stuffing you use, the wider the "Q" and the lower the gain.  

The chamber under the slider should be left clear to maximize air flow.





Installing mics in the chamber is an interesting journey.

Suspended just below the port opening pointing straight down into the fiber fill is one way.  Adjusting the height of the mic allows it to pick up some ambient information at higher frequencies that are originating from the rear of the driver.

Placed in the port opening so that the mic body touches the cabinet is another way that had good results.

There are no rules yet, after enough people get it to work and compare notes we'll have some usable information.

Feedback is the main issue.  Just about the time you get the mic turned up so you can hear some bass coming out of the broadcast speakers, you get boom.  No matter what, you have to find the level where it booms and back it off some.  The trick is to get the highest level possible.

A simple mixer is a starting point.  It will have the mic preamps and the line level outs you need.  Most will also have a bass, mid, and treble control for each channel.  This can help to reduce feedback.  

The microphones I used were Sure 57's (general purpose instrument mics) although I suspect some small drum mics would be worth trying.

With this simple arrangement, work on placement and type of broadcast speaker and what adjustments you have to get the least feedback possible.  Right now the feedback is helping you to find the best set up.

The tendency is to want to hear the broadcast system too loud.  It should be almost silent to where you have to get your head down by it to see if it's on.  This is usually the right amount ambience.  Remember, low frequency ambience is harder to hear than midrange ambience, so by the time it feeds back you're probably louder than you realize.

When you achieve somewhat usable results, you can either explore a better signal path, ie., mic preamp to replace the mixer, or go for more bass with less feedback.  It the latter is required, you can try a notch filter at the feedback frequency, or even a digital feedback destroyer.

The ideal set up would be a tube mic preamp with and adjustable notch filter.  I will eventually make one of these for myself and then probably for everyone else if enough of these speakers are built.

Steve

Yes, or the seas exotic which has better xmax, lower fs which should allow the magical Zen enclosure to do even more of its magic.
I am positively stunned by the openness and spaciousness the zen delivers and think with a slight increase in weight and depth it could truly be used stand alone with no subs or miking needed. I am about 100 hours into break-in and like others have found that tube changes, cable changes are clearly heard. If any others have experimented with alternative 8" fullrangers in Steves Magical ZEN enclosure, Please share!!

I am afraid to better the performance of Steves modified DFR-8S is not going to be cheap though, but am coming to the realization that the enclosure has gigantic potential and deserves the best fullrange 8" you can find.

Its more complicated by far than a normal box to make, but with minimal skills and tools and a lot of paying attention to the details, can be done.
What is truly amazing and magical is the spaciousness and clarity you would expect to hear out of a crossoverless open baffle along with real bass and fullness you NEVER would hear out of a 12" wide open baffle.
So Steve has done the seemingly impossible with the Zen OB. He gives you a beautiful high WAF speaker, the incredible open baffle openness,imaging, and lack of box coloration you want PLUS with his genius resonant enclosure below the driver, gives you the fullness and cleanest tuneful bass I honestly have ever heard. And he does all this with an ingeniously simple resonant chamber enclosure/open baffle design that allows you to eliminate all the crossover problems and use a single 8" driver driven directly by a tube amp.
This is what makes me think that using the best possible driver would yield a speaker that is literally untouchable. Even Steve admits that there may be better speakers out there than his heavily modded $300/pair DFR8-S's but none he knows of that are reasonable in cost.
For me personally, this design works so well in so many different areas that there is a gut feeling listening to them that a world class 8" fullrange would truly make the Zen OB the last pair of speakers you ever owned.  Still hoping Steve and others experiment and share their findings with other driver variants in this amazing design.