Ohm Speakers, thoughts?

http://fullrangedriver.com/forum/viewtopic.php?pid=6485

If you read this thread, you'll find someone else commenting on the type of drivers used in newer production "Walsh" series. For the record, i never posted to this thread in any way, shape or form, even if one of the participants shares the same name.

As a side note, there's a "funny" story pertaining to the design motivations behind Decware's "Radial" speaker mentioned in this same thread.

John, the owner of Van L Speakerworks ( aka Chicago Speakerworks ) had previously verified to me that newer "Walsh series" used conventional design woofers firing face down into the cabinet. He has re-foamed many of these drivers over the years.

Yes, the F uses a spider. Sean
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Sean, I appreciate you sharing your knowledge, but there is something I don't understand after reading this quote from the German-Physiks files.

The transmission line type has commonly employed a steep, straight-sided cone and a fairly conventional voice coil and magnet assembly. But where it differs from an ordinary mass loaded cone is that the diaphragm is securely anchored at its mouth and flexed by the motions of the voice coil rather than pushed to and fro. Sound propagation is normal to the slope of the cone rather than parallel to the path of the voice coil in the gap as is the case with a mass loaded cone.

The diaphragm is securely anchored at its mouth. Wouldn't this mean that there is no spider employed ? And is sounds as though there is no surround employed ether.

What I am trying to get at is; the F's do employ a spider and a surround, and I am wondering if the sound emanating from the F's is a mix of conventional speaker sound and transmission line sound. What do you think? Am I missing something?

Sean,

Glad you are looking at this thread again.

Not being one to accept all claims, I decided to do some investigating. First, I wanted to find out just what constituted a Walsh loudspeaker. I looked up the Patent #3424873 (in case anyone is interested) and began my research.

The following is from the Abstract:

"Abstract of the Disclosure
The coherent-sound loudspeaker is a development derived from a theoretical concept of ideal sound reproduction by means of a conical diaphragm operating as a wave transmission line. Such a conical diaphragm will produce sound as it would be produced by a small cylinder pulsating radially with every portion of its area moving in and out simultaneously, and in phase with the input audio signal. This is coherent sound.
The requirements of the theoretical concept are closely approached by a sound producer of the following character:
(1) The angle of the conical diphragm, measured from a plane perpendicular to its axis is quite high, causing the speed of the mechanical vibratory waves in the diaphragm to be greater than the speed of sound in air, and to have a component in the desired direction of sound radiation equal to the speed of sound in air.
(2) Absorbing material absorbs the wave energy in the diaphragm to eliminate or minimize wave reflections from the non-driven end, so that a vibratory wave transverses the diaphragm substantially only once.
(3) Sound is radiated to the listener only from the convex side of a vertical conical diaphragm to obtain full frequency range, high quality sound omnidirectionally from a single radiator."

Four models are mentioned in the patent. Models B and J's diaphragm were made of felted fiber. Models L and M's diaphragm were made of aluminum. Other variations between the models are described. If you want to know more about them, lookup the patent (it's in file DImg-11.tiff).

Quoting from the results:

"The low end of the useful frequency range of all of these loudspeakers is approximately 40 cycles per second. The upper end was about 14,000 c.p.s for Models B and J, 16,000 c.p.s. for Model M and 34,000 c.p.s. for Model L. The frequency range of the Model L extending to 34,000 c.p.s., well beyond any person's audibility limit, confirms the theory that this new loudspeaker can be designed for any frequency range desired, although at some sacrifice of efficiency for wider ranges."

Throughout the patent, several items are mentioned to "fine tune" the design. One item is the basket for the driver. Normal drivers usually cover 30% to 100% of the convex side of the driver. A Walsh driver should be obstructed by less than 20%. The only other item I will mention is that the angle of the conical driver must be at least 50 degrees.

From the patent, I have concluded that only the Ohm A and F meet these criteria. The Ohm G is a hybrid version and is therefore not a true Walsh loudspeaker. (as you have already said) All of the other models are not "true" Walsh loudspeakers.

However, a Walsh driver can be "designed for any frequency range desired". So the claim that Ohm's "Walsh" line of speakers use a Walsh driver could be true.

I had asked a question earlier (please see prior post) that if Ohm is not using a Walsh driver, how could they reproduce the midrange using a downward firing driver? (still looking for an answer) I went looking for any photos that would help verify Ohm's claim and I came across these Ohm FRS 11's (I think).

From Ohm's website:

"The FRS-11 is a tall square tower with each corner cut about 2''. One of the cut corners displays the Ohm logo near the top, just below the grill. The FRS-11 is a true Walsh speaker designed for small to medium sized rooms. They create a precise stereo image from a very wide Sweet-Sweep. We call the effect Full Room Stereo and we named it after this benefit."

Looking at the picture, if indeed this is an unmodified FRS 11 (except that the diffusion cans have been removed) there is no Walsh speaker/driver to be seen, and it is truly just a conventional woofer/tweeter combination.

My question now is, is it ethically, morally, politically... correct to keep calling the line a Walsh speaker?

Jamscience, thanks for the patent info. and picture.

One thing I would like to say, is that the cans are not diffusion cans, they are as transparent too sound as grill cloth is.

Jamscience: Thanks for all the research and leg-work. I have to agree with all of the points that you brought up. That's one of the reasons why i've "harped" so hard on the fact that these units are NOT actual Walsh drivers. This can be seen on the Ebay photo's that you provided for us. All i can say about that one is that if they had shown the other side of the speaker i.e. where the crossover network is attached, most people would be appalled.

As a side note, these drivers do appear to have some type of a "plastic" based cone material as Line described above. This would lead me to believe that they are the original equipment as supplied by the manufacturer.

As to the basket design, Ohm used two different baskets on the F's that i'm aware of. One has very "skinny" flat metal rails with wood glued to them to damp their resonance. The other has much wider "U" shaped metal channels with wood glued inside of the channel. Common sense would dictate that the thinner rails would cause fewer problems so long as resonance induced ringing was controlled. I have a set of each and to my ears, the thinner flat rails sound better than the wider "U" shaped channels.

As far as the Ohm G goes, i think that it is a Walsh driver by basic design, but i'm not sure about the flare rate on the cone. It obviously has a LOT less surface area than the Ohm A or Ohm F Walsh drivers. The "standard" cone driver that you see in the G cabinet is a passive radiator, not a driven woofer. I've never seen one of these in person though, so i'm kinda sorta guessing on this one based on photo's / technical info that i have.

As far as treble response goes, the internal factory wiring in the F's did a number on that. I would recommend plugging your speaker cables directly into the Walsh driver itself, which bypasses the internal wiring. I could NOT believe how much the 2 - 3 ft of internal wiring could demolish the sound after hearing the difference. I also have some Walsh "tweeters" that Infinity made, but i've never tinkered with them.

Once again, thanks for the legwork and sharing this info : )

Line: The info from the German Physiks website that you quoted sounds more like the design ideas behind the Manger driver than the Walsh design. How someone that manufactures a Walsh based product could confuse the design and description of operation is beyond me. Then again, they are a German based company and maybe something is getting lost in the translation.

As to your comment about the cans NOT acting as diffusors and being acoustically invisible, i almost had to laugh. Just placing a very thin layer of felt on the baffle around a midrange and / or a tweeter can cause major differences in reflections, diffraction and frequency response. This is VERY measurable in most cases and easily audible.

If you don't think that surrounding a driver with a perforated metal screen and placing it directly in the firing path between one's ears and the drivers would make any audible difference, you should think again and / or have your hearing checked. I don't mean this to be rude, but that screen also has grille cloth material in it, making an even bigger difference at high frequencies. Sean
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