[matevana]

The Hestia-Forte represents the third incarnation in the Hestia line of low cost open back speakers.  Similar to the Original Hestia and Hestia-SL designs, it is designed to be bi-amplified, meaning that two channels of amplification are required for each of the left and right speaker units.
 
The Hestia-Forte project includes mods that address maximum SPL's, dynamics and refinement. It is easier to construct than the Hestia-SL and is more modular, allowing the enthusiast to model different low frequency enclosures, orient them vertically or horizontally, and allow for separate degrees of toe-in adjustment per top and bottom section. 

The Hestia Forte consists of a wide-range top section that employs three drivers summed together using passive components. The H-Frame bottom section is tasked to reproduce low frequency information with the help of a unique dual-slope passive crossover network. The dual-slope network makes use of a 12dB per octave passive line level crossover coupled with a 6dB per octave passive speaker level crossover which is dedicated to addressing dipole roll-off.

Careful driver sourcing along with crossover over/under lap and proper driver attenuation allow the Hestia-Forte to perform well without the need for additional active compensation (eq).
 
Revisions to the Hestia-Forte include:

Tandem H-Bomb (offset H-frame) bass enclosures sporting two Peerless 10" SLS drivers per side.

z-Board (Way Basics) cube construction allows for easy assembly and helps curb cabinet resonances

Can be positioned horizontally (maximum benefit from floor bounce) or vertically (enhanced vertical dispersion).

Hestia baffle re-purposed for table-top or separate bridge mounting.

Smooth Hemp Cone Lower Midrange Unit has no discernible break-up mode in its intended  band pass.

New minimalist passive crossover design features Mundorf, Clarity and Erse components and eliminates the Zobel circuit.

Unique LF passive crossover methodology combines low level and speaker level components for a cleaner bass to midrange transition.

Dome midrange option: ScanSpeak Discovery D7608/9200 in "open" or closed back version (easy swap)

Eminence Lil Buddy Hemp Cone Driver:
 
The Forte sees the introduction of a 10” hemp cone/paper former driver that has been tested as a substitute (*) for the original Dayton PA-255 that has been used as a lower midrange unit for both the Hestia-SL and original Hestia designs. This driver is extremely smooth with almost no breakup in its intended band pass.

Building the Hestia-Forte as designed herein will allow you to experience a high level of realism with no need for active compensation.  There is no driver “shout” to contend with and the transition from the top to bottom units are remarkably clean. I am extremely happy with the Hestia-Forte as an authentic 2 channel system.

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(*) While this driver is a physical "drop-in" replacement for the Dayton PA-255, there are three crossover component changes that must be made should one wish to try this with the previous Hestia-SL. The first is the substitution of a 27 ohm resistor for the existing 15 ohm resistor used to attenuate the Celestion upper mid driver. The second is the incorporation of a 2 resistor L-pad to attenuate the lower mid driver. I use a 6.8 ohm resister in series with a 2.7 ohm in parallel. I highly recommend the use of Mundorf MOX 10 watt metal oxide resistors in all three places. 

[matevana]

Assembly of the offset H-Frames using "soft" Way Basics modular cubes available from many retailers. The individual cubes are joined with mechanical fasteners, cleats, and MDF baffles. The z-Board construction is anti-resonant and helps dampen cabinet vibrations. They are also about half the weight of MDF and considered to be a green product. The standard cube from Way Basics was originally designed for home storage and is available in 9 finishes.  The basic structure assembles in less than 10 minutes, ready for a few quick modifications as detailed below.

[matevana]

Here's some detail showing the base which adapts the SL-top section to table mounting. The vertical panel is the same finished MDF material used in the H-frame baffles, which helps tie the design together aesthetically. I'm not a fan of spikes in an attempt to couple loudspeakers rigidly to the floor, particularly on anything other than carpeting. Conversely the zBoards are light and can theoretically "walk" due to woofer's excursion.  To address this I cut and glued carpet tile to the base of the H-frames and the base of the top baffle as well. There is also a rubber gasket that goes between the SL top and the new mounting plate.

Alternatively one could build a separate bridge ala Siegfred Linkwitz (LX-521) to minimize interaction with the H-frames and the top baffle. With the damping characteristics of the materials used I have not found this to be much of an issue. 




 

[matevana]

For anyone willing to forego aesthetics in place of an easier build, here's a rendering of how the main baffle would look as a finished 12" x 24" MDF board. I suspect there may be a slight degradation of performance off-axis, but the effect should be minimal. 

[matevana]

The top section's passive crossover has been reduced by several components and refined. I am very pleased with this design. The quality of the components make for a fairly significant upgrade over "stock" pieces. The crossover is designed to compliment the new LF passive crossover that has been implemented in the H-frame section which must be biamped.  The tweeter and low drivers are wired mechanically in-phase and use 1st order electrical topology. Note that the mid coupler is wired with reverse polarity to avoid a phase tilt. The resulting sound is clear, detailed, and has no significant phase anomalies.



C1 = Mundorf EVO Oil 5.6uf

L1 =  Jantzen 0.33mh 15 AWG 
C2 = ClarityCap ESA 5.6uf
R1 =  Mundorf MOX 15 ohm       (Note 1)

L2  =  Erse Perfect Layer 4.0mh 18 AWG

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Drivers used:

Tweeter:           Vifa XT19TD00-4, 89dB 2.83v/1m 

Mid Coupler:      Celestion Neo 5" 8 ohm, 89dB 1w/1m (Note 2)

Mid Woofer:       Dayton 10" Prosound PA255-8,  95dB 1w/1m

      (or)

                          Eminence Lil Buddy 10" Hemp Cone, 99.1dB 1w/1m  (Note 3)



Notes:

(Note 1)      27 ohms when used with the Eminence Lil Buddy Upgrade

(Note 2)      mid is wired reverse polarity to avoid a slight phase tilt around the x/o point

(Note 3)      The Eminence Lil Buddy is more efficient than the Dayton PA-255 and will require a two resistor L-pad as follows:

                   R1 (series)   6.8 ohm Mundorf MOX 10 watt resistor     
                   R2 (parallel) 2.7 ohm Mundorf MOX 10 watt resistor

[matevana]

The H-frames are wired series/parallel to yield an 8 ohm load over the (4) Peerless SLS woofers in mono. After testing many new concepts, it became apparent that a two-pronged passive approach produced the best result in this design. The highs are attenuated at the line level by using a single 50 Hz F-mod passive inline crossover. The slope is further altered at the speaker level by using a 12 mH inductor which specifically addresses the 6dB per octave dipole roll-off. 

With this design, there are few sonic advantages in running separate left and right channel H-frames. There is however an advantage in my case  of being able to run (4) woofers at 8 ohms, instead of (2) per side at a 4 ohm load. Perhaps it's the amp's damping factor, but for whatever reason the low bass output was significantly more resolving. The dynamics were retained far more with this passive approach then with either my MiniDSP or DBX x/o mimicking a similar result.  My LF chain looks like this:

Benchmark DAC-1 -> Harrison Labs 50 Hz LP F-mod -> B&K Sonata Mono Power Amp -> 18mH inductor -> 4 x Peerless SLS 10" Woofers (mono)



Room placement is also simplified. It is possible to stack the Hestia-Forte top sections on each frame, or stack the frames in the center of the room with each Hestia off to the side. In my limited tests each produced similar results. This option may be beneficial though in dealing with a more difficult room.




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[matevana]

Lots of testing / tweaking / listening going on. What would we do without the Christmas/New Year break???

[OB_Newbie]

Congratulations Ed on what looks like another amazing build!  I really enjoy your builds and general approach to OB design.

I am (still) waiting on back ordered parts to build the original Hestia design.  Really looking forward to it and believe it is one of the value leaders in low cost open baffle designs.  Once I get the Hestia build I'll likely have the Forte in my sights next.

Thanks for another great design!

 

[matevana]

Thanks for the kind words!

[matevana]

For those who may have concerns over the continued availability of the Parts Express Celestion Neo 5" Buyout driver, I have tested an interesting "drop-in" replacement midrange. Albeit several times the cost of the buyout midrange, the ScanSpeak Discovery D7608/9200-10 is a very interesting driver all to itself.

The electrical and mechanical properties are similar to the Celestion, as are the baffle cutout and outside dimensions. As a result little or no modification to the design is required. But the similarities end there. The ScanSpeak is a 3" dome design, yielding excellent off-axis dispersion compared to the Celestion's 5" cone. It also maintains its clarity at very high levels. And unlike most domes that use a sealed back chamber, the ScanSpeak driver comes stock with a felt pad covering the rear of the assembly. As a result, there is ample rear radiation for OB, enough so that the manufacturer recommends enclosing the driver in its own chamber when used in a conventional box speaker. (Since I had the driver for testing purposes, I did not attempt to peel off the felt covering).

For those who prefer a less diffuse mid range sound, (or are forced to run their OB speakers closer to the wall than ideal) the ScanSpeak driver may be sectioned-off with the use of a Seas K2851 1.7L enclosure cup.  This will effectively eliminate the rear wave and produce a more direct sound. Doing so also causes the driver's SPL's to increase slightly from the front, which may necessitate a tweak of the 15 ohm padding resister used in the design.

I had the opportunity to listen to the ScanSpeak mids for a weekend in the Hestia-forte design and was truly impressed, particularly while listening off-axis. Is it worth the difference in cost? Perhaps not, but it does present an interesting alternative. Additionally, I spent several hours listening with and without the Seas enclosure cup. There is definitely a difference in presentation, with the enclosed version having slightly less OB character (but not quite to a fault). This can be a good thing when your speakers are too close to room boundaries, in cases where aesthetics are a factor in determining speaker location.



ScanSpeak Discovery D7608/9200-10 Midrange Driver



Seas 1.7L Enclosure
   

[jonasz]

Very interesting design Matevana. Is it made all by ear or do you have any measurements to share?

It makes me wanna try something similar but I don't have any high sensitivity bassdrivers available. I do have have 4 10" normal sensitivity drivers though, maybe I should try a WMTMW top?
How would you describe the sound of this passive design compared to John K's NaO RS, SL's LX521 or similar active systems? I realize you use cheaper drivers but do the sound end up in the same ballpark as the aforementioned? 

[matevana]

My go-to process is a bit odd. I use a digital SPL meter along with reference tones to get me about 80% there. The next 10% comes from listening to a number of reference recordings, mostly individual instruments and voice. Strings are perhaps the easiest to get right. Well recorded solo Piano is another story. When it approximates the proper weight and heft of the instrument, I feel like I'm getting close. The final 10% comes from swapping small increments of about a hundred caps, coils and resistors I keep on hand, and making any baffle tweaks that may be needed, I then revisit it over several weeks to adjust for mechanical changes as the drivers settle-in, repeating the last 10% of the process.

I have not had the opportunity to listen to the designs you mentioned but I would love to. I did get to hear the older Nao II RS and the 3rd generation Orions, along with many original OB designs at the local audio meets. . Many of the amateur designs had some serious flaws, at least in my mind. I really liked both the Nao II and the Orion and have a lot of respect for their designers.

My recollection is that the Hestia forte comes close to the earlier Nao II which is significant since my design relies on proper matching and voicing, minus all the active compensation. I consider myself an audio minimalist, relying on things like high quality passive volume pots, power amps and low capacitance (short) interconnects, so the thought of yards of additional signal path in an active rig is a bit unsettling. I've always liked the idea of passively crossed dipoles, albeit a bit of a challenge. I firmly believe the "make or break" part of the design occurs at driver selection, since there is little opportunity to address incompatibilities when you are not using analog or digital correction. I also believe that errors of omission are better than those of commission in the often compromising world of passive speaker design. 

[Poultrygeist]

Are the Peerless SLS woofers now discontinued?

If so what other woofers would you suggest for the H-bombs?

[matevana]

Are the Peerless SLS woofers now discontinued?

If so what other woofers would you suggest for the H-bombs?

Not to my knowledge. Both PE and Madisound have ample stock. I also like the Usher 1001B but they are a little pricey. I bought a pair used and they have the lowest motor noise of the 10" drivers I've tested. I also like SB Acoustics and Scanspeak. Not a big fan of Seas woofers, however the L26ROY looks nice if you can afford them.

[matevana]

One of the nice aspects of the Forte design is the ability to toe-in the top unit independently from the bottom. This can be very effective in maximizing the speakers ability to throw a realistic 3D image. I've been playing with this lately and the ability to change each axis is not insignificant.



In my listening space each Hestia Forte are placed 7 feet apart, center-to-center. The listening position is 9 feet back, again from the center of the H-Frame. Each Forte is also 38" from the rear wall.

After some trial and error, the best stereo image in my listening position occurred when the top section was toed-in 15 degrees relative to the H-Frame and then the entire unit was toed-in an additional 5 degrees. This also  has the relative effect of increasing the distance to the rear wall and altering the reflected sound to a degree. In my room the final geometry looked something like this: