[P10]

First, thanks John Busch for posting this design. 

I've been looking for some time at these two drivers to attempt an open baffle design of my own, so when I came across this thread I thought that I might gain some insight into designing an OB passive crossover. 

I've always found that researching and reverse engineering on my own provides the greatest rewards in understanding. However, after spending hours with Edge and researching OB and crossovers, I have reluctantly come to the conclusion that I am not going to understand this particular crossover without help. In particular, I am completely baffled by the full-pass filter.  On first look, it appears to be a 1st order bandpass filter, but I don't understand why you would want to roll off the high frequencies in this application.

So, my questions are: 
1. What is the full-pass inductor and resister in parallel doing?
2. Is the full-pass capacitor and inductor in series a 1st order bandpass crossover, or is it something else entirely?
3. How are the resistor values used to calculate crossover points (i.e. sum both resister values plus the speaker impedance and Inductor DCR)? 
4. Are the resisters more then just attenuating the full-range driver?

Any help would be appreciated. Regards.

[JBspeakerman]

 

Hello P-10

Thank you for your interest in the Ultra!

Will try to answer your questions in order presented.

1. This is a simple trap that compensates for the rising response of the Vifa which begins around 5Khz.  Including the rear radiation, the overall rise is considerable.  The trap will yield a flat on axis response in most rooms with the Ultra 30"- 50" away from a wall.

2.  The large inductor does three things.  It corrects for the rising response created by the open baffle and the naturally rising response of the woofer.  It also help create a defacto 2nd order acoustic 700 Hz crossover point when it combines with the woofers natural upper roll off.    The cap in series with the Vifa combines with the Vifa's natural low end roll off to create a second order crossover, again acoustically at 700 Hz.  The calculated electrical values are god knows what.  You can reverse engineer if you want to, but with both drivers radiating both directions and adding in the diffraction effects and well as the comb - roll off effects of the large open baffle, standard calculations are not of much value.

3.  By ear and measurement.  Yes, in the initial design I considered the intrinsic efficiency of the drivers factoring in the anticipated rear radiation.  Plus series loses and driver dcr values.

4.  The pad resistor is general attenuation.  The trap resistor sets the amount of upper end frequency shaping.  Smaller values, less shaping, larger values more.  FYI, the trap inductor set the frequency at which shaping starts.  Larger value, lower start frequency.


Hope this info is helpful.


Best


John

[motosapien]

I have a pair of John's Manzanitas and once I tamed the newer Vifa's hotter upper end, they have been marvelous.  I listen to a lot of live recordings from large venues and the OB with the large woof really shines with this material.  So the Ultra's 15" woof is calling out to me.  A build seems unavoidable at this point.  And this thread needed a bump anyway......

[rbynon77]

motosapien-how did you tame your vifas? Just curious....

[motosapien]

John's original Manzanita design called for a 2 mh coil with a 5 ohm across it.  The latest run of these Vifa's was a bit brighter up top and needed a 2.5 mh with a 15 ohm across it.  Then 5 - 6 ohm for attenuation depending on the woofer.

[barryso]

Here are some shots of my Ultras to bump this thread.  The fronts are finished and look pretty good but the backs are still unfinished so there aren't any shots of the rears.

Overall it's been a great project.  They sound nicer than they have any right to sound for the money spent and they have a very pleasant sound signature.  Great recordings shine but you won't get ear bleeds from the poorly recorded stuff in the collection.

The only issue with the build was the quality of my woodworking.  The hole for the 3 1/2 inch driver was just a bit too big and there was a very slight gap between the driver and the wood.  This did reduce the quality of the midrange and high frequencies but a bit of rope caulk around the gap fixed the problem.

The bass was always good but with a few gear improvements the bass is now really amazing.  Tuneful, articulate and plentiful.  Folks ask if the subwoofer in the room is on but it's not.

They are a bit laid back sounding with the stock crossover and it's been fun making modest changes to suit the changes in audio gear and mood.  In my room I seem to like a bit more output from the high frequencies so there are a few resistors tweaked.

It's a good project.

[motosapien]

Those are handsome barry - you did good.  How are you liking the base response?  John's designs are somewhat unigue in that they do not require biamping.  This makes life easier, particularly for the entry level builder.  It also makes for a more commercially freindly product.

[barryso]

Thanks Motosapien.  They don't quite look that good in person but the light was hitting them just right the other day so it was time for some photos.

Bass is pretty amazing.  There is a lot of it and it has real texture.  Upright bass has the right tone and texture and the 15" drivers move enough air so you feel it.

There is enough bass that placing the Ultras in the room is sort of critical.  The bass can be very loose if the speakers aren't in the right spot so it can take some time to get them setup correctly.  Once you hit the right spot and the right toe in they'll really let you know.

Placement of the smaller Manzanitas was also pretty critical but there seemed to be a bit more wriggle room with them.  One or two spots would both sound good and it was just a question of personal preference on which spot was "best". 

Changing the crossover resistors will also change the bass output of the Ultras so they're easy to tweak.  I still haven't quite decided which settings are "best" but have been leaning pretty close to John's specs most of the time.

The Ultras are significantly better sounding than my Manzis but my Manzis are the original version with the 1st tweeter.  I suspect your Manzi build with the full range driver is up a few levels from mine.  So even though I've got both speakers I can't really do a good comparison between the two builds.  But based on my two builds, IMHO, the Ultras do put out more bass than the Manzis.

[Oktyabr]

I too am interested in these "Ultras".  While a strong emphasis on bass and mid bass has been made in these threads I have read very little about the upper end, other than for some it may seem "too hot" and for others, not enough.  Some of my experience with small, "full range" drivers, some costing several times more than the TC9FD, is that they tend to sound a bit muted above 15kHz, as if playing behind a veil or something.  I enjoy this upper end sparkle on strings, cymbals, bells, chimes and the like, and even the top octaves of a piano doesn't sound right if the driver can't swing those higher frequencies.

Is the TC9FD capable?  What sort of changes can be made to the XO to liven up the top end, if needed?

Last but not least this XO uses a lot of serial design, which I read (somewhere) might not be well liked by class "D" amps, which I have.  Should this design be pretty amp friendly to class "D"?

Thanks in advance!

[Phil A]

Barry - beautiful work!

[Slam]

Anybody still using these in 2018? They are intriguing.

[barryso]

Mine are still here.  Just feed them some power and they sound great.  A 5 watt amp isn't going to do it but a 50 or 100 watt amp probably will depending on your room and personal need for volume.

John and Pano have posted updates to the stand mounted Manzanitas on the DIY site so that's worth checking out, too.  It's also where you can get the latest version of the Ultra crossovers.