Voigt pipe physics for Dummies!!

hi team this is janos this is real word audio and this is void pipe physics for dummies and today the operative words are simplicity and functionality and uh just for those of you who are new to my channel i've been building void pipes for more than 20 years i've built and designed a lot and i heard even more i researched the entire literature on uh void pipe transmission line and quarter wave pipe physics and uh tried out all of it and actually what my experience is that i just needed to throw it in the garbage and just go with my experiences when what they taught to me and uh here in this episode i'm going to summarize uh it for you i hope to make it relatively short and functional so basically what is a void pipe void pipe is a device like this you have a speaker cabinet which is triangular shape and there is around halfway there is a driver in it a single driver and down here there is a port and so that's it it's super simple super duper simple and all the fuss is about how how is this angle exactly how tall shall we make it how wide shall we make it what's the size of the loudspeaker we put in it uh shall we put in the loudspeaker exactly halfway a little higher a little lower what does that count what the material should be for the cabinet which is the best driver for it exactly and and in what sort of rooms will it work and to understand that let's just have a look at the physics i'm going to explain it in very very simple words with the practicality and applicability in mind not i'm not going to write a thesis on it so that's not the purpose of this video to give you a degree in your hand so you can hang it on your wall no for that you just go and research all the void by pre-twitcher and transmission line literature and get yourself a degree in mathematics if you need to understand it so what we need to understand here is that void pipes are basically pipes and what are pipes like an organ pipe so basically it's a tube and and the tube basically it has two places in it one place where you blow the air in it or if it's an organ there's a spot where you blow air into the organ pipe and there's another slot where the air can escape from the pipe and however between these two there's one spot where the air where the pressure enters and there's another spot where the air exits and uh and and the difference between two is that uh after we have like in this case the driver is creating the sound waves inside the cabinet and the sound waves start to bounce they will go up and down up and down they will start like a bouncy house so the pressure of a fluctuation is going down and as it goes down it widens up and then it goes up it narrows down widens narrows so it got does this ping-ponging effect and and as it does this up and down bouncing the uh basically the momentum and the directionality of the pressure change stabilizes and and because there is no set single dimension like in a box cabinet that we have the height width and depth but we have a constantly changing dimension there will not be a preferentially amplified single frequency that occurs during these pressure changes so that's the big genius thing in void pipes compared to regular box cabinet is that when the pressure bounces the pressure also bounces in your base reflex cabinet so let's say like right here this is like the box cabinet but when it bounces all the dimensions are the same so those frequencies which correspond to the specific dimensions of your cabinet they will be preferentially over amplified and they will excite the cabinet to resonate like crap now in a void pipe what happens is that as the pressure bounces up and down there is not a single frequency that's emphasized because the narrowness constantly changes so when then the pressure goes here there the the exact frequency which is preferential amplified changes at every instant so there will not be a single one that's over really preferred to excite the cabinet into resonances also the cabinet size is a triangle which is the most stable shape and it's the most rejecting resonance is while the rectangle is very very prone to be excited by mechanical resonances so we have two really big things going for the shape of this cabinet and now why are we doing a bouncy house inside the loudspeaker we are doing that because the sound waves that the driver that the cone can produce it can excite only those frequencies which are the size of the cone and that's basically down to about one kilohertz frequencies and and those sound waves which are longer than that they are basically too long for the driver to excite and it and it cannot doesn't have enough width enough uh enough flap basically enough surface to make uh to excite those low frequencies and uh and and when that happens in a base reflex cabinet basically we are creating a high pressure zone so that high pressure zone can be coupled to the air but when we create the high pressure zone we lose the ability to to have a dynamic resolution for the base it's going to get messed up congested things are going to get bouncing all around and you lose a lot of detail a lot of resolution however when you have a pipe when you have this bouncing up and down that's a uniform airflow basically in this direction alone while in a cabinet it's bouncing old everywhere with preferential frequencies coming out of it so here you have this bouncy house and there there's a big opening here which is not a port it looks like a board but it's not a port because it's a free opening so those frequencies which get excited like a bouncy house are free to propagate into your living room so basically we have this scenario and then we have the void pipe and the frequencies the low frequencies are excited within the cabinet and did that excitation goes out so this is the exact same process as uh creating waves so imagine the ocean and you see the ocean waves coming towards you so so the cabinet creates those ocean waves and they start coming out of the port and then once the wave is initiated it just continues its momentum and goes out into the room that's how a void pipe works and that's how it creates base so it does not create a high pressure base is just creates the wave and the wave is allowed to flow directly into your room now what are the limitations of the void pipe the limitation of the base is the the height of the pipe so basically the height defines the quarter wavelength of the lowest frequency that it has full energy for the output and half of that frequency is the absolute minimum output of the of the drive of the pipe so basically if the inside air column in your void pipe is 2 meters tall that's 200 centimeter that corresponds to the quarter wave of an 8 meter long wave that's approximately 42 hertz or so so it means that if you if the inside of your void pipe is two meters high then a 42 hertz wave can be formed by that void pipe with full energy full energy output and then the energy starts to roll off from there down to half of that down to a 16 meter wavelength which is 21 hertz so basically when you have a 2 meter tall void pipe it can put out down to 21 hertz clean base that's the limit in the frequency provided that the driver itself is is comfy working down to that range and you also need a second requirement is that as you see we do did not pressurize the room we are tagging on the waves so we are creating these pressure waves and and the pressure and these waves are created inside and they are propagating into the room now if your room is too short the length of the room where the pipe faces is not long enough then it cannot release those waves into the room if it if those waves which are the quarter wave is here inside the pipe and that needs to be extended to a full wave so it means that to have 21 hertz output from a 2 meter tall void pipe you need a 16 meter long room just like for an organ pipe you need a church right those big pipes there are not for joke and the size of the building is not for joke that's because of physics and that's the exact same physics that the void pipe uses and that's why you need a really long room for really low output now do not despair because if you have half of that size for your room let's say instead of 16 meters you have only 8 meters long wave there you can also have 21 hertz but because the room is sufficient to support half the wavelength now what that means is that you will have a clean 21 hertz there not as strong as in a full wave situation but if you want to go like a hertz or two higher then that will not be supported very well and the and the base will be choppy so there will be some notes over represented some underrepresented and and you will not have a nice even response to have a nice even response you need that 16 meters long room for a clean 21 hertz for a long void pipe now if you have half of that then usually in real life situation probably that's the best you can get because uh a 16 meter long room would require a very very high output level to sustain spl in there and realistically single drivers they will work for you up to about an eight meter long room so basically yes you can have a 20 hertz response from a void pipe in an 8 meter long provided that a driver is glued down to there usually i haven't met one yet that is that might do it actually the cube audio drivers are the ones that potentially could do it like uh the the the 10 f the 10 inch magnus that might be able to do this fit uh however they will be all very comfy to go to 30 hertz 25 hertz no problem and uh and for that basically you will need a room that's at least uh five six meters or or longer in a single dimension and basically the more you restrict the length of your room the more you restrict the lower end of your base response and if you have a like a four or five meters long room you can already have like like a 32 hertz pretty good in such a room so and and for that you need a void pipe that is the commensurately sized to allow the formation of that longest wave that you want to produce that lowest frequency now uh second thing people are wondering about the the shape and the build of the pipe so so why how come we see these triangular shaped uh are they better or not than the ones that are folded that look like a cabinet and on the inside they they have a baffle here so basically they are exactly this thing just the top one doesn't continue up but we just cut it down and we fold it back so the top part so the air has the same path it continues from the base and it gets narrower narrower and narrower but here turns 180 degrees and gets narrower and narrower and then then it widens up and done so it but the air bounces like this in a folded pipe while in a straight path pipe it bounces like this and almost exact same thing is happening and the same thing is true for a folded pipe uh basically you take the height of your pipe and multiply it by two because you need to add this height plus that height in the back and that adds up to the total inner height of your pipe that defines the quarter wave that is the full energy lowest output point and um so basically uh you can convert any any straight pipe to a folded pipe just using by keeping this total air column length the same and also the the total volume the same and they are roughly equivalent even though they look very very different on the outside now there are some differences though between the two is actually the one that's the triangle shaped it's this is mechanically uh far superior to the box shape because it's triangle shape so there's no mechanical excitations on the side that are stable that are constant because every height has a different width and here we have a box a flat panel on the side and it will resonate as a unity so that's not a good thing however as as a side effect because it resonates as a unity and it's like roughly one meter size in height it will also provide you a little extra boost for the mid base so every folded pipe i heard that is equivalent to a straight pipe using like similar driver similar size the folded one has stronger mid bays so if that's your priority pick the folded one now the straight pipe disappears better so if you want uh like a total 3d transparency the straight ones will give that a little it will give you an edge there because of the lack of that uniform cabinet resonance that's missing for the triangular shape and uh what else so basically uh the other question is the is the angle so do i make it like like a that big fat pipe a narrower or a very skinny so what shall this angle be for that and now the answer for that is uh defined by your driver look at the data sheet of the driver and look at the vas value the equivalent volume where that driver feels at home so if the vas says let's say 50 liter then it means that the volume the internal volume the free air volume of the cabinet has to be around 50 liter or more for this cabinet to have good base output to have strong low frequency output because it's the height of the air column that defines what will be the strongest frequency supported but it's the free air volume that defines whether your driver can maintain that frequency or it can maintain only shorter wavelengths so basically if you have a void pipe and you think it sounds great but you want a little more lower end extension let's say you already have a 2 meter tall void pipe so in theory it should get you down to 20 hertz and you are getting maybe down to 40 hertz then you can go about two ways to solve the problem one maybe your driver is totally insufficient for that and you need to look for another one or the internal volume the fear volume is not enough and then you need to increase this angle so instead of a narrower you need to widen it up to allow more freer volume inside the cabinet and based on my my experience you see that original shape i drew here this is kind of like like an optimal angle so if your void pipes has about this angle it has a potential to to sound very very good if it's that deep like this that's not the best choice it's going to get compromises there and if it's really skinny like like like like like this skinny almost like like a really tiny veg that's not going to get any bass either so one more thing truncated void pipes so what what on earth is a truncated void pipe maybe let's just draw it right here so this is when your it is the same thing so you have a void pipe but the top part like like here it's missing so basically it's chopped off and what this is going to do it's going to get get this nice and chubby cabinet with a lot of air volume you see because it's not skinny like this or skinny like that but it's it it's more of a fat saw right it has a fatty it has a belly to it so this design has the advantage to have bigger freer volume than a full height cabinet so your driver will be happier to work in it but because the top is cropped a shorter wavelength a shorter pressure zone can form in it so it will not be able to support as low frequencies as a full void pipe and for you to pick the one that works the best for you you need to be able to pick the right size for your driver and for your room that's because for example for the two meter length the theory is 20 hertz output but if your driver cannot support it maybe it it's good down to 30 hertz you do not need that two meter heights maybe 1.5 1.4 meter is enough and and then for example you look at the cube audio void pipe cabinet that's what they are doing they are truncating it and that that allows like an f8 frequency down to about 30 hertz to form and it gives that nice big free air volume to work in the uh room sizes that they recommend for you so that what the recommendations they have and the cabinet plans they give they are supported by physics and um i think i will make a video on that how how to break that down how to work it for now that's it i'm taking already too long have an amazing day i hope this helped everyone who wants to build their void pipe please like subscribe ciao

Channel: Real World Audio

Views: 13,342

Keywords: audiophiliac, steve guttenberg, andrew robinson, jbl horn, klipsch, schiit, focal, diy audio, loudspeaker design, vacuum tubes, real world audio, behind the scenes, audiophile education, snake oil audio, gr-research, ps audio, hans beekhuyzen, skifi audio, real hifi help, RMAF

Id: I1I7uSBCZUo

Length: 23min 31sec (1411 seconds)

Published: Tue Jul 26 2022