Not one person who I trust to actually understand how quarter wave resonance works, commented. I'm not sure if some of the commenters are disagreeing or if its just over their heads. If you have questions. Just ask 👍
my jargon is correct =) @paul7052 @TNT if you guys don't know why quarter resonance happens, just say that
Just read what I wrote and try to understand, if you are confused, just ask 👍
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You do understand that as long as the dimension of the room that "doorway" is connected to, allows it... this doorway will have a helmholtz resonance? Physics transcends your expectations. This "doorway" have a quarter wave length resonance two... There will be some type of resonance for every dimension matter of fact.
Lets say this corridor is 20ft long...
You: Transmission lines are bass enclosures that use the back-wave to create a quarter wave resonance, that boost bass efficiency
Physics: This corridor has a quarter wave resonance of 14hz
You: Impossible! this is not a transmission line enclosure made for a woofer!
Physics: Aww thats cute... well I'm going get going now...
The corridor: Hey guys.... I just resonated at 14hz....
You: What!? This is impossible!
Physics: You are overthinking it... I operate off of dimensions and the characteristics of the medium of air.... Not by the name you choose to call me.
Quarterwave resonance, Helmholtz resonance, will exist where ever physics allows. They care not about your names you use. The names are used to keep people from getting confused and to keep people organized. And from what I can tell, you need them.
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OK time for learning.
Quarterwave length explained in Camplo speak. Max amplitude is reached twice in a frequencies full cycle, 1/4th and 3/4th positions. Within a Line, it is the 1/4th position where max amplitude is reached for the first time and it is the catalyst to quarterwave resonance.... This is where the pressure antinode and velocity node is created. A pressure antinode is where maximum pressure difference occurs. In this case, max pressure and rarefication occurs here. A velocity node is where partical velocity is at a minimum. There is a characteristic of a wave traveling through a line, to reflect, if there is an immediate and large impedance differential. The cresting of the wave for the first time at 1/4WL causes the first peak in impedance that creates the conditions that allows a reflection to begin the creation of the standing waves that are responsible for the increase in pressure generated from the input signal, via constructive inference. Constructive interference; It's when overlapping waves add together, amplifying the resultant wave. It is also within the first antinode that coupling can occur. As long as the cross sectional dimension allows it... the driver will couple with an air column that gets cut off at the first antinode. Air within the first antinode, when coupling is possible, will reflect the same velocity as the diaphragm surface.
As I am still learning, I am looking for the experts here to correct and provide insight where deemed necessary.
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While you pretend that you actually ask questions or add to the expertise... I've been here asking all the questions, and am the catalyst to the conversation that inspires the experts here to open up and express themselves. The great advice is has been almost completely directed towards me... Because I am the one taking initiative, so you don't have to, apparently.
That websters is not being used properly
I like what I see by the way. If this is truly the result of my thread, then I can say that I have helped at least one person because yes, I benefit from this thread but I have long learned enough to create what it is I wanted to create. I continue on to ask question of the experts because of passion of knowledge. The conversation is available to the public and they can join in at anytime. So many topics have been covered in my thread. Long after I have left this earth, this thread will live on continue to be a gem of knowledge to the community. Generating content, That is my way of giving back. I have already seen, that If I don't ask questions... no one else does.. I mean we get to talk to Dr. Geddes!!!! How am I the only one asking all the questions!? Its as if I am the only one who appreciates the opportunity or If I am the only one who wants to learn. Why isn't anyone else taking advantage to access to such a profound individual? Not to mention all the other well meaning experts that have graced us with with their time! All I do really is ask questions or make statements and hope for correction. For 5 years straight this is what I have done. I will go to the well has ran dry. Its a passion.
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Hopefully to get back into some real discussion about science, here is what I am hoping to get a response on from the experts of the community.
OK time for learning.
Quarterwave length explained in Camplo speak (inside joke). Max amplitude is reached twice in a frequencies full cycle, 1/4th and 3/4th positions. Within a Line, it is the 1/4th position where max amplitude is reached for the first time and it is the catalyst to quarterwave resonance.... This is where the pressure antinode and velocity node is created. A pressure antinode is where maximum pressure difference occurs. In this case, max pressure and rarefication occurs here. A velocity node is where particle velocity is at a minimum. There is a characteristic of a wave traveling through a line, to reflect, if there is an immediate and large impedance differential. The cresting of the wave for the first time at 1/4WL causes the first peak in impedance that creates the conditions that allows a reflection to begin the creation of the standing waves that are responsible for the increase in pressure generated from the input signal, via constructive inference. Constructive interference; It's when overlapping waves add together, amplifying the resultant wave. It is also within the first antinode that coupling can occur. As long as the cross sectional dimension allows it... the driver will couple with an air column that gets cut off at the first antinode. Air within the first antinode, when coupling is possible, will reflect the same velocity as the diaphragm surface.
As I am still learning, I am looking for the experts here to correct and provide insight where deemed necessary.
OK time for learning.
Quarterwave length explained in Camplo speak (inside joke). Max amplitude is reached twice in a frequencies full cycle, 1/4th and 3/4th positions. Within a Line, it is the 1/4th position where max amplitude is reached for the first time and it is the catalyst to quarterwave resonance.... This is where the pressure antinode and velocity node is created. A pressure antinode is where maximum pressure difference occurs. In this case, max pressure and rarefication occurs here. A velocity node is where particle velocity is at a minimum. There is a characteristic of a wave traveling through a line, to reflect, if there is an immediate and large impedance differential. The cresting of the wave for the first time at 1/4WL causes the first peak in impedance that creates the conditions that allows a reflection to begin the creation of the standing waves that are responsible for the increase in pressure generated from the input signal, via constructive inference. Constructive interference; It's when overlapping waves add together, amplifying the resultant wave. It is also within the first antinode that coupling can occur. As long as the cross sectional dimension allows it... the driver will couple with an air column that gets cut off at the first antinode. Air within the first antinode, when coupling is possible, will reflect the same velocity as the diaphragm surface.
As I am still learning, I am looking for the experts here to correct and provide insight where deemed necessary.
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I don't see anything wrong in what you say above. You've used the correct terms in the right places, except maybe when you are talking about waves and amplitude, all in the time domain, and then impedance and resonance which are concepts only in the frequency domain. You do tend to mix up your domains quite often which leads to confusion. And open pipe with a driver at one end (assuming the tube and driver are the same diameter as shown,) is the simplest 1/4 wave resonance which is also the lowest in frequency.
This fundamental resonance is very similar to a Helmholtz resonator since one can define simple mass and compliance values (lumped parameter simplifications) from this. But above the 1/4 wave point the two ideas differ substantially.
Some posts have been removed due to them crossing the line of Rule 1, and becoming personal. Infractions have been apportioned to the participants.
AT the very lowest frequencies a compression driver on a horn does act like a fourth order bandpass - in that region where lumped parameter assumption hold, but as the frequency goes up the wave propagation nature of the horn system makes it quite different. A fourth order bandpass is a lumped parameter concept - "order" tells you that. Continuous acoustics doesn't have "orders".
Just when I think I know ... ok for a simple transmission line where the diameter matches the driver, Does quarter wave resonation happen at every frequency until 1/4wl is longer than the line? With an exponential I would think the same... I mention this because I feel it may be related to whatever happens at the lowest frequency
The rest, I will research before I ask, lumped parameters, continuous acoustics, above my pay grade at this point, I'll have investigate these terms.
Maybe I can get your advice on the rear supports? The loops are to place rope, to suspend the rear of the horn. Is this an acoustical fail? I can easily create movable a cross brace out of metal... my fabricator started designing for himself instead sticking to the original plans (@docali) he also put holes every 2", and I quote "every inch, thats too many" lol... he did the work at a charitable cost so I did not complain. I can add the additional holes If I want them. I'm just not sure if the rope suspension in the back is acoustically detrimental or not.
I'm doing good on finishing so far. Its not perfect, but its pretty good and by the time I'm done I should be happy. I want the gold ting inside the horn to be more silver/blueish. Everything else is black. The burnt then sanded exterior looks unique and took the 1part tung oil/black oil stain/turpentine, very well. The sprayer acts like a giant airbrush and it's very forgiving. 6mm tip for the interested. I used a camel hair brush to apply tung oil to the inner horn, something like 100 mL to a teaspoon of black stain and a teaspoon of turpentine. I'm not sure if the next inner coat will be was resin epoxy or with the highly recommended marine varnish that I have. The idea is to color the clear coat in order cause the desired colors to refract. The last layer of clear will be over that that's tinted sorta like tinted windows of a car. The in between layers will be strictly clear in order retain a good amount of reflective luminosity.
HI, and thank you for your dialog. I am trying to figure what exactly is going on
In my basement there is carpet with foam padding underneath, and the response changed. The dip 215hz is from having zero damping material in the enclosure. If I remove damping material from the simulation it appears in the sim. The stuff above the slot null, are not identical but such is a very complex thing to simulate as the simulation can only be as good as the simulator has been programed. There response below reflects a higher degree of damping, and shows that my main issue has to do with vertical reflections in the slot.
There are multiple options to fix the slot issues, the one that I am decided on is a rounded baffle to cup the outer dimension of the woofers frame. like in the picture below but I will place the segmented side facing the other way. I've played with the simulation enough to know that by decreasing the dimensions in any direction raises the resonate frequency and slot null... The above response is about good enough but I don't want to have to rely on carpet to fix the issue....I have a simulation showing where the new response might be but its not readily available as we are leaving out the door to see the new King Kong movie, I will report back later. =) in a nutshell I want to retain the 100% vibration cancellation, and honestly this way takes less reconstruction... Otherwise the V shape slot is an easy out.
@GM @gedlee I have yet to figure out how to separate the time domain from frequency domain. Frequency is a measure in time, so thats confusing, but in regards to impedance, I am referring to the density of air at the antinodes. Supposedly any time a wave meets a great change in acoustical impedance it will reflect. The antinodes meet those requirements
What I find interesting is the coupled air mass... if this column of air is coupled to the diaphragm it is moving back and forth with the diaphragm, along with the nodes and antinodes. it could seem the face of this coupled air mass would operate like a pseudo diaphragm and cause its own compressions and rarefactions... the more I think about it.... how is this coupled air staying in concert with the drivers surface and creating standing waves at the same time.
What I find interesting is the coupled air mass... if this column of air is coupled to the diaphragm it is moving back and forth with the diaphragm, along with the nodes and antinodes. it could seem the face of this coupled air mass would operate like a pseudo diaphragm and cause its own compressions and rarefactions... the more I think about it.... how is this coupled air staying in concert with the drivers surface and creating standing waves at the same time.
The word is resonance not resonation and resonance occurs when lambda equals 1/4wl. For longer wl there are no resonances and the wave emanating from the driver just damps out exponentially. For shorter wl there will be resonances at 1/4, 3/4, 5/4, etc.
These are critical concepts to understand so you should investigate them.
If the horn is a dead weight on the rope then its a good thing as the rope will isolate the horn from its support. If it is not dead weight then the tension in the rope will matter, but in no case is it detrimental.
The air must always stay in contact with the drivers surface unless the surface exceeds the speed of sound then the air appears more like a fluid - i.e. water, but that could never happen in reality for a driver. Only at the very lowest frequencies around 1/4wl does the air appear to move as a single mass. This is the region called "lumped parameter" where wave propagation is not a factor. At higher frequencies we have to consider the wave-like nature of sound which is why it gets more complicated.
it would seem that above cutoff, coupling would happen at 1/4wl of the frequency the driver is emitting, no matter which frequency... If that isn't true, then what a happens?
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