OHM Acoustics "Walsh F" Speaker remakes

[Apogee]

Interesting project.

I'm curious how they sound with no toe-in?

45 degrees seems to be fairly extreme. How do they image when setup with no or very little toe-in?

Also, how far apart are your speakers and how far back is the listening area?

Thanks!

 

[mamboni]

The toe-in is critical to how they work. It focuses the bulk of the total acoustic output into the room and minimizes room reflections. The high dispersion provides for uniform frequency response to about 90 degree off axis. The directionality of the tweeter above 8 khz coupled with the 45 degree toe-in results in an elliptical energy/sound isoform ( a very wide sweetspot) such that when one is closer to one speaker, the high frequency output of the opposite speaker is greater as the latter is being heard more on axis vis-a-vis the speaker that is physically closer. The result is a very broad sweetspot and an extraordinary sense of presence and soundstage. If the speakers are no toed in, the result is an extremely oversize soundstage at the expense of image localization.

 

[c2cthomas]

Hi mamboni,

I have been following this thread with the intention of making a speaker like this. I would prefer the tweeter to be at ear height of 36" and that would require me to make a shorter sonotube base unit. If I follow your math correctly I figure a tube 28 inch H x 14 inch dia. should get me near your 2.5 cu. ft. target. I like your selection of mid-bass speaker and have been looking for a project that used them. I'm also interested in the "Walsh" traveling wave concept and want to see just what will happen. To complement the "open" radiation pattern of the Walsh I want to try a dipole tweeter such as a B&G Neo 8 or a Heil tweeter and cross over at 3.6 Khz with a 12 db slope - still driving the bass full range as you suggest. I would love to see any drawings or construction photo's you may have - as well any feedback.

Thanks,

 

[mamboni]

I humbly admonish you to exploit the Walsh principles at work - to utilize the much higher crossover point afforded by the driver as implemented in my design. The great advantage of the bending wave principle is the ability to reproduce virtually the entire audible bandwidth without the phase and time distorting crossover filter. With the 10" driver as illustrated in prior posts, excellent results have been obtained using a simple first order high pass filter (a capacitor) to the tweeter at 8-10 khz. The effortless and correct midrange that results from this alignment, wherein a 10" woofer lends it's copious radiating surface for the reproduction of the midrange up to the hihest partials of the strings and voices, must be heard to be appreciated. Also, any quality tweeter you choose will enjoy exceptional power handling and freedom from intermodulation distortion afforded by the high crossover frequency, one far above what is possible with conventional 2-way or 3-way designs.

 

[mamboni]

The design provides for time alignment of tweeter and woofer. The woofer is run full range to about 8-10 khz, where rolloff occurs secondary to voice coil inductance and mass. The tweeter uses a simple high pass filter, a capacitor and resistor in series:

 

[mamboni]

The woofer cone must be treated with felt damping to provide for proper wave termination and thus control cone breakup modes above 2 khz:

 

[c2cthomas]

Roger on the high x-over - I will comply with your recommendation. What are your thoughts on using a 28 inch high by 14 inch dia. tube?

 

[mamboni]

Those dimensions for the tube will work fine. As this is a sealed enclosure (acoustic suspension), the volume could be increased 10-20% to obtain a lower Q and somewhat lower Fc. Also, you might want to incorporate a variovent to extend bass response and improve impulse response. This approach has been used quite effectively by Dynaudio systems.

 

[rcavictim]

Electrohome Walsh idea satellite speakers

I found a pair of vintage Electrohome satellite speakers on chains designed to hang friom the ceiling. I`m guessing 60`s vintage. Inside they have a bending wave transducer with an all paper cone. These don`t go low but they sound pretty amazing.

3 pictures to follow....

 

[rcavictim]

View of the insides. The driver is about 5 inch diameter.

 

[rcavictim]

Well here is the sonic generator. Clearly this driver was made with an exagerated narrow cone angle to be used as a bending wave transducer. The cone is paper all the way and uniform as far as I can tell. I have not removed a driver from it`s cardboard tube cabinet yet to look at the underside of the cone.

I found another pair of these turn up exactly once on ebay so there must be a few out there to be had.

 

[c2cthomas]

mamboni,

Thank you for all of your hard work and your suggestions. I'm looking forward to building a project - but me being me - I've gotta put a bit of a twist in somewhere. What else is a hobby for!

I'm liking the virovent idea - I had considered a port of some type but was paying attention to your sealed enclosure specification, and was considering a Nelson Pass El PIPE-O variation for the really low base if needed. Heck - I wanna build one of those things just for the fun anyway!!

I'm using the Oscar Heil Kithara as a design target

 

[c2cthomas]

OOps!!

Inserted my file and posted at the same time. Need to discover how to attach more than one photo at a time.

The top unit will resemble a Ess Elite Tweeter and the entire unit should look something like this

 

[c2cthomas]

ESS Elite Photo

 

[mamboni]

Well here is the sonic generator. Clearly this driver was made with an exagerated narrow cone angle to be used as a bending wave transducer. The cone is paper all the way and uniform as far as I can tell. I have not removed a driver from it`s cardboard tube cabinet yet to look at the underside of the cone.

I found another pair of these turn up exactly once on ebay so there must be a few out there to be had.

That's fabulous that loudspeaker! The designer is running modified 5 inch paper cone woofer full range - a well designed 5 inch woofer (i.e. Pioneer) can reach up to near 18 khz and still have a reasonable Fs in the mid 50's, though the Xmax is compromised (~1mm). If this speaker is from the 60's it actually predates the pioneering work of Lincoln Walsh and precedes the US patent - this is very intruguing. The magnet looks like ceramic - I didn't think these were available in the 1960s.

Is there any chance of inducing you to open that little gem: I'd love to take a look at the cone surface and termination. Are there any markings of the driver that might give a clue as to who made it, where and when?

Please describe the sound: are there any audible resonances or colorations?

Amazing!

 

[mamboni]

OOps!!

Inserted my file and posted at the same time. Need to discover how to attach more than one photo at a time.

The top unit will resemble a Ess Elite Tweeter and the entire unit should look something like this

You choice of a super high quality ribbon tweeter like the Heil is inspired: I have been pondering building a Walsh two-way using a ribbon - I dont' think I'll find time enough till late spring.

But, your design is problematic. You are proposing to use a large and wide tweeter baffle - I must vociferously object to this. This baffle will defeat the fine imaging the ribbon is capable of. More importantly, the baffle will most certainly cause the ribbon to be directional, even at crossover, where the Walsh is radiating substantially omnidirectional (in the horizontal plane). Using this large baffle will obviate a smooth power transmission between the Walsh driver and the tweeter - they will not blend! The great advantge of the ribbon, outside of it's superior response because of it's low moving mass, is it's narrow width and long vertical dimension, which provide for omnidirectional (dipole) acoustic radiation in the horizontal plane but controlled directional radiation in the vertical plane (similar to the Walsh driver except for it being a monopole): at the 8 khz crossover frequency a 1/2 " wide ribbon will radiate as dipole with quasiomnidirectional forward radiation horizontally - it will blend seamlessly with the Walsh- if it has no baffle! To wit: my plan was to use a ribbon tweeter with minimal baffle - felt absorption applied to the baffle surface. This is what I would suggest.

Alternatively, you could use a sound-absorbing wide tweeter baffle. If the baffle is acoustically null, then the ribbon will behave as a quasi-omnidirectional driver as the phase cancelation (lobing ) of the dipole radiation is largely attenuated.

 

[rcavictim]

That's fabulous that loudspeaker! The designer is running modified 5 inch paper cone woofer full range - a well designed 5 inch woofer (i.e. Pioneer) can reach up to near 18 khz and still have a reasonable Fs in the mid 50's, though the Xmax is compromised (~1mm). If this speaker is from the 60's it actually predates the pioneering work of Lincoln Walsh and precedes the US patent - this is very intruguing. The magnet looks like ceramic - I didn't think these were available in the 1960s.

Is there any chance of inducing you to open that little gem: I'd love to take a look at the cone surface and termination. Are there any markings of the driver that might give a clue as to who made it, where and when?

Please describe the sound: are there any audible resonances or colorations?

Amazing!

I`d have to dig them out of the basement storage room. I don`t mind if you can be a bit patient. Yes the magnet certainly looks like a ceramic to me too. The soft iron end plates (pole pieces) are thicker than normal (if you use what`s common today as what is normal) for the thickness of the magnet itself. There is a 3 wire cable from the cabinet. It apparently has a built in crossover capacitor which you can use or go directly to the driver for full range by wire lead selection. It sounds better with the HP filter as there is reduced bass motion on the cone to muddy up the mids and highs. I remember that my initial feelings on the sound were of being impressed. I`ll have to fire them up again to listen for colorations.

Yes there are some markings on the back of the magnet I believe. That would be very interesting if this product predates the Walsh. patent. Electrohome is an Ontario, Canada company. they made home hi-fi combo radio record player consoles in the 60`s. Much later, until recently they made very good CRT video projectors.

 

[c2cthomas]

mamboni:

The Heil unit would not have a baffle on the back of the unit - the back of the tweeter is as open as the front and thus allows for the dipole radiation pattern of the audio signal. Also most likely I will not use a grill cloth front or back on the Heil tweeter (unless I choose to smooth things out a bit on the HF). I have a pair of old AMT2 tweeters that are left over from a pair damaged in shipping (the enclosures were dropped and it shattered the particle board base unit). The AMT2's are pretty much the same size as the AMT1's (6.5" h by 6.5" w By 4" d) but were crossed over higher (2Khz) and used a 10" woofer vs. the 12" used in the AMT1's. The point is that they are fairly deep because of the large magnet assembly (aprox. 4") - but the Heil diaphragm is located in the middle of the assembly and thus should position in the center of the magnet assembly of the woofer. The enclosure presented is primarily for attaching the tweeter to the base unit and allow for adjustment of tweeter height to sitting level via telescoping assembly.

Thank again for your feedback

 

[c2cthomas]

Duh - another Homer moment on my part

You mean THAT baffle!! I had to go back and reread things and then the lights came on!!

I can figure a way to trim that bad boy down to the size of the Heil to minimize the baffle effect (as much as possible considering the magnet configuration). 2nd generation might choose the B&G Neo 3 or 8 because they are a much slimmer device in all respects and still go dipole. I have the Heils on hand so I'll start with them.

Thanks again!!

 

[planet10]

Seems like Electrohome had at least a zillion similar designs... i have a set stashed that need new surrounds (3.5-4" driver)

dave