I have not seen much information about endfire sub arrays on the forum. So to fill in any possible gaps read the article below.
Phase Wavelengths: The End Fire Cardioid Array made visible | Bob McCarthy's Blog
Thanks to this forum and other resources around the internet I have learned some horn theory.
i.e. An increase in mouth area will decrease cut off frequency.
Now for the question. Lets say we have 4 TH's side by side. Our mouth area is 4x that of a single TH.
If we take the same 4 TH's and place them in a properly configured endfire array, do we still have the same 4x increase in mouth area?
Phase Wavelengths: The End Fire Cardioid Array made visible | Bob McCarthy's Blog
Thanks to this forum and other resources around the internet I have learned some horn theory.
i.e. An increase in mouth area will decrease cut off frequency.
Now for the question. Lets say we have 4 TH's side by side. Our mouth area is 4x that of a single TH.
If we take the same 4 TH's and place them in a properly configured endfire array, do we still have the same 4x increase in mouth area?
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Mouth area is increased in multiples regardless of the array implemented.
An increase in mouth area does not appreciably lower Fc even in regular horns, and hardly at all in TH.
Mutually coupled drivers do have a lowered Fs, but the horn's Fc remains the same regardless of driver Fs.
FLH with "too small" mouths LF response does "fill in" and become closer to flat as the mouth areas are mutually coupled.
Forward directivity will increase in a large horn array, reducing the rear output relative to front output. The additional directivity will result in more output than the 12 dB gain from one to four cabinets, but the gain will be more at upper frequencies which are more directional than lower frequencies.
The 12 dB gain from one to four cabinets is often mistaken for a lower Fc, as our ears interpret a 5 dB increase at 20 Hz to be twice as loud, while it takes a 10 dB increase around 1000 Hz to sound twice as loud.
An end fire array using TH will reduce rear output compared to a side by side array, but will have slightly less forward output than a side by side array.
End fire arrays can put more sub sound where you want it, which is a good thing, but may not sound as loud or punchy as a stacked TH array with the mouths placed together.
Art
Thank you Art for your response.
The reason for me using an endfire has to do with keeping a good horizontal coverage pattern and also limiting spl levels behind the array.
I don't think I have ever noticed the decrease in SPL or 'punch' compared to the two configurations... maybe because it is usually a toss up between a large distributed array or an endfire. Distributed array usually spaced enough some noticeable cancellation happens. At the end of the day I notice more punch from an endfire, I guess it has to do with it being more point source like.
A thing of interest is the 5db at 20hz vs 10 at 1k, never heard of it, figured our perception of 'loudness' was linear over the frequency range, but as I write this I visualize that one frequency response of the ear curve thing.... not sure what it is called.
Ahh thank you.
Now though I am forced to wonder about TH mouth area in relation to lower frequency response.
Am I right about mouth area and a decreased cut off frequency? Or is that just some bs?
Art do you Have any links to studies that show that kind of perception to LF?
Obviously I'm not doubting you, I just haven't seen it and would like to read up on it!
Although the fact that a 5 dB level change sounds twice as loud at 20 Hz while it takes 10 dB at 1000 Hz was always right in front of us looking at the various equal loudness contours published through the years, the first time it really "sank in" was reading about VLF noise generated by wind turbines.
The way people's hearing works, those VLF rotor noises may be undetectable below a certain threshold, but since sound drops off at 6 db per doubling of distance, may be intolerable for someone half the distance to the wind turbines, leading to "not in my backyard" arguments.
Actual ground transmitted noise can be less predictable than the inverse square law would predict, different soil and rock have different transmission values.
Fortunately, turbine design has evolved and rotor noise on the current generations of turbines are way less, allowing them to be placed fairly close to populated areas without the dreadful oppressive feelings VLF can "generate".
Green energy without feeling "green"
.Art
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Although the fact that a 5 dB level change sounds twice as loud at 20 Hz while it takes 10 dB at 1000 Hz was always right in front of us looking at the various equal loudness contours published through the years, the first time it really "sank in" was reading about VLF noise generated by wind turbines.
The way people's hearing works, those VLF rotor noises may be undetectable below a certain threshold, but since sound drops off at 6 db per doubling of distance, may be intolerable for someone half the distance to the wind turbines, leading to "not in my backyard" arguments.
Actual ground transmitted noise can be less predictable than the inverse square law would predict, different soil and rock have different transmission values.
Fortunately, turbine design has evolved and rotor noise on the current generations of turbines are way less, allowing them to be placed fairly close to populated areas without the dreadful oppressive feelings VLF can "generate".
Green energy without feeling "green"
Art
In 2001 I lived about 40 meters from a set of railroad tracks. The sound of the train didn't bug me too much.
In 2008 I bought a house that's 150 meters from a set of railroad tracks. At that distance, the sound was *much* more noticeable.
IMHO, I think the second distance seemed louder than the first because of the difference between near field and far field.
For instance, if the transition from nearfield to farfield occurs at five wavelengths*, then all frequencies above 43hz were in the farfield when I lived at the first home. (which was closer.)
But at the second home, all frequencies above 11.3hz were in the farfield.
Long story short:
At the second home, the very low frequencies generated by a passing train were in the farfield, and because they were in the farfield, they summed constructively.
To my ears, the difference was that the sound of the train at the second house was much deeper in pitch, the kind of roar that you could feel in your body. Whereas the first house the roar of the train was higher in pitch. (It was actually the same train in both situations, just different homes near the same set of train tracks.)
Anyways, if you're ever looking at buying a house near a set of train tracks, it might be easier on the ears to live *closer* to the tracks than 150 meters from the tracks.
* I know there's a formula for determining the nearfield to farfield transition but I am too lazy to do it. I generally use a 'rule of thumb' of five wavelengths. With a choo choo train it's massively complicated by the fact that the length of the train will affect the nearfield to farfield transition because the entire train is generating sound, and even the curvature of the track will have an impact.
The train is akin to a long line array.
The longer the line, and the lower the frequency of concern, the closer the distance to the line the low frequency is in the far field.
JBL :: Technical Library
You were likely hearing more (annoying) summed upper frequencies at the greater distance.
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