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In Reply to: RE: tomservo - question on your small studio monitor posted by Edp on April 08, 2024 at 15:08:29
Hi
Well you have the way back machine on haha
The patents covers this concept;
An exponential horn has a fixed expansion rate and that governs where the "high pass" for the acoustic impedance transformation takes place. For example a 30Hz horn can only double it's cross sectional area every 2 feet but at 60Hz, it's 1 foot and so on up in frequency...
A conical horn has an expansion rate that changes from throat to mouth and while it has constant directivity (good when you have an audience vs a seat) , it also means the HF driver at the apex is poorly coupled as the frequency falls, the expansion is too rapid at the apex.
The patent for the Unity horn (my first try from back when you remember) covered the idea of coupling drivers appropriate for horn loading where the expansion rate was also appropriate.
This also meant that if drivers interacted, the sources must be 1/4 wavelength or less apart to couple into the horn seamlessly. This allowed the radiation to appear to be a single driver but still had all the phase response of the combined crossovers like a traditional mullti-way loudspeaker.
The later Synergy horns (about 20 years ago now) i found a way to have a high order passive crossover slopes without the phase shift /all pass phase response the named slopes cause. That way they radiate like a single source in time and space with the directivity of the CD horn. This is possible because the drivers are coupled together within the horn and the physical offset is incorporated to counteract the filter delay (something like a physical FIR filter perhaps)
The picture you linked is a typical configuration as a DIY project, the MEH name being a sub for the Synergy horn / Unity horn objective principals as the patent wasn't applied for in Australia.
One of the configurations in the patent is a way to use a coaxial driver that has a compression driver for the hf. This allows the cone output to combine with the HF again where the dimensions are less than 1/4 wl. That is what is in some of the smaller synergy horns like the small studio monitors in the video.
My interest is home audio, i like making big stuff for stadiums and large hifi out doors like for the mouse house but I like to listen sitting on the couch playing bass.
All along i have been making small speakers too at work for the fancy stadium suites and a couple customers started using them in studio's and then I made some big ones for larger rooms and then the ones you saw.
Those have a coax cone driver with a normal HF compression driver where the cone output is passed into the horn expansion where the dimensions are less than 1/4 wl so the combine coherently into a full range driver and the LF driver is close enough to be less than 1/4 wl apart.
They like them in the studio because they say they can hear everything, important in the creative / mix and mastering process..
The thing i love about these simple acoustic sources full range horns is they often disappear in the phantom image to where your not aware of them as sources, with eyes closed it's harder to tell how far away they are as single sources, they don't radiate many spatial clues that normally would become part of the stereo image.
My hope is the that the people with home studio's will see these recordings and embrace these for the same reasons, those musicians are the future of our program material.
Here are a couple songs from Albums that were recorded using them.
https://www.youtube.com/watch?v=d95WgaXjiBE&list=RDGMEMQ1dJ7wXfLlqCjwV0xfSNbA&start_radio=1&rv=auTP6NxfikA
https://www.youtube.com/watch?v=auTP6NxfikA&list=RDGMEMQ1dJ7wXfLlqCjwV0xfSNbA&index=3
I thought this one was cool as they made the video while recording the album and after i found they were very happy with the result. People sometimes wonder how recordings are made what it looks like and what a producer does.
https://www.youtube.com/watch?v=a1q25yLgRSc
I got to see these folks live, as good live as any band i have heard. Carl the guitar player gave me a big hug after they played.
https://www.youtube.com/watch?v=UzwKOI5Rcnw
As we are not a sales and marketing company, I think these are being sold to that market via a company called Sweetwater.
Hope that helps
Tom
Follow Ups:
Unity - that what it was called back then , remember that now. EDIT - 25 years ago was gathering and Lambda Acoustics was builder of the demonstrated Unity - End EDITAlthough not great in number but my interactions with this design were all either straight conical or a 2 flare conical.
**************************
EDIT - reread your post and see that exponential and conic geometries were discussed**************************
Have you found certain horn geometries work better than others?
**************************
Is your Paraline lens an offshoot or extension of the Unity "chamber" ( for lack of a better word) ?)The use of physical configurations of multiple separate drivers to combine wrt wavelengths for both Unity and Paraline.
Over last 20 years came across three other Lens implementations (Graham , VMPS and newform)
We builders spend 30 years fussin with removing any little bumps screw heads, flush mount drivers,etc and folks like you and others stick wood plank with holes and slots in front of drivers , it works well (. Have not heard Paraline). Leaves us home builders wonder what other " rules " ain't always to be followed.But I could ask dozens of questions, possible you could point me to additional docs and papers like the patents. I would understand a reminder if my questions or inquiries treaded to close to proprietary information.
Edits: 04/10/24 04/10/24 04/10/24 04/10/24
Hi
There are (at least) two things going on, if you want / need constant directivity (where the highs extend to the edges of the lower frequency pattern), then you need to use a horn who's walls are more or less straight and obeys some other horn related guide lines.
The reason is for both the acoustic transformation and pattern control, the locations inside the horn that are in control all change with frequency, moving towards the throat with increasing frequency so a curved wall horn becomes narrower as the frequency climbs.
With the right driver and horn, this can have flat or pretty flat response. However, the power response of all hf horn drivers falls off around -6dB /oct 2 to 4Khz and if you have a CD horn, you get the shape of the power response which needs eq to be flat.
In a room, these two sound very different when off axis.
So far as two or more drivers combining into one source either inside (or outside) of a horn, they must be less than 1/4 wavelength apart at the highest frequency they interact.
This IS part of the stereo image. With separate sources, there is some distance one must be before the sources combine subjectively into one. However, "sounds like" isn't the whole story. With your eyes closed, listening to one speaker it's easy to point at where it is BUT you can also triangulate how far away it is thanks in part to the still separate radiations.
A single small source at significant distance has no distance clues to triangulate on, what reaches the right and left ears is identical. All you have to go on is the hf roll off and reflections as clues, It is the difference from one ear to another that allow triangulation in depth.
The cool / unexpected part developing these horns, about a single simple radiation is there is much less information radiated by the speaker about how far away it is and so with a good recording, the sources are not part of the stereo image.
This is something anyone can hear too.
Obtain and mount a pair of these drivers on a flat baffle at least 18 in square.
https://faitalpro.com/en/products/LF_Loudspeakers/product_details/index.php?id=401000160
Cover the baffle with 1/2 inch foam (super77), front mount the driver through the foam. Figure out a small sealed back box and set these up about 6 or 8 feet away pointed at you in normal stereo.
These drivers are an amazing little full range driver, small enough to radiate simply up to pretty high, no crossover phase and while they can't do low bass, they do a good job fading behind a phantom stereo image.
WE can hear things how sound is radiated in 3d, we measure in 1d even with the Klipple machine.
Tom
Bunch of DIY folks got in fury of making sets of those as it was purported to be a FOSTEX unit. It wasn't but bit of fun anyway.
Was doing a number of Open Baffle studie also at that time,, took that concept up to some Dynaudio 9" on 3 by 5 foot baffles. Not over great but still did single source bit of stereo illusion.
Bent your ear enough for now, but possibly in future can get some " lens" history and info.
No need to wait, a lens is easy to explain if one thinks in terms of time.
Imagine a convex lens (thick at the center, thin at the edges), the velocity of light in the glass is slightly less than in air and so if one imagines a flat plane of photons entering the glass (an optical plane wave) , the thicker the glass, the greater that photon is delayed relative to the outer edges.
The light that exits the glass that entered as a flat plane is now a converging wavefront (coming to a focal point) with the "F" number being the ratio of the diameter to focal length..
With Sound on the other hand the velocity of sound in air only changes with temperature so using different materials to cause a delay is out but one can use a longer / shorter path lengths for that purpose.
Consider the potato masher lens or a slanted plate lens. Both of these deal with a horn that has a very narrow pattern up high, the lens progressively delays the edges vs the center and this produces a more curved wavefront (wider dispersion angle) at the exit.
The Paraline is a reversed situation the driver radiation is radial 360 degrees but easier to imagine if one had say 20 equal length tubes attached to the driver exit who's exit ends are lined up in the straight line. This way the sound radiates from all the tubes at the same instant and arranged in a "line". Now, imagine that there are no tubes and it is the equal distribution of pressure that causes the distribution.
Hope that helps.
Tom
Appreciate the insight and explanation of the mechanisms involved.
Until you mentioned it I didn't think of horn lens like the JBL Hartsfield (2390 ?) relating to the examples of a lens applied to a direct radiator. Helps with grasping with mechanisms involved.
In his last few years Brian Cheney of VMPS was committing a number of his line source units with a lens. I never fully understood the mechanism he was working on, but the units he applied this method definitely "worked" as there was a difference with over without lens
Left no lens. Right with lens
In the link added for Graham Audio, I'm not sure, but it appears the vintage approach of slotting bass units is more of a directivity influence than what you describe for the lens
It's always an eye opener when I'm confronted with a design that "violates conventional guidelines" but actually works better.Possibly one day I'll stumble into an audio room and the Paraline can perform its eye opener. Did that with the Unity way back machine.
Edits: 04/12/24
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