World's Second Best Speakers!

hi we have posted a series of videos on sound [Music] about a year ago we put a couple of videos online covering our DML or distributed mode loudspeakers we've showed how you can use helium to inhibit the transmission of sound built an active noise reduction enclosure and constructed some sound absorbing panels that you can hang on the walls of your studio or your listening room today what I'm going to do is I'm going to go through the principals and the Assembly of more conventional speakers these are called void tubes and they were first described by Paul Voight in 1934 now you might say wow that's a pretty old design but keep in mind that was 17 years after Einstein released his theory of general relativity so just because something's been around for a while that doesn't mean it isn't a good idea to understand what makes this design so elegant we have to understand what's going on with a speaker a typical loudspeaker consists of two elements a thin membrane that's made out of either paper plastic bamboo metal and a voice coil a driver in the back and the driver essentially has a huge number of coils a very fine wire that are attached to your amplifier and by varying the polarity and the current flowing through those coils you vary the electric field and the magnet that's inside of that coil then moves in response to those changes and drives the movement of the membrane in front when the membrane moves forward it compresses a small sheet or a thin sheet of air and that air moves away from the speaker at the speed of sound about 300 meters a second when it moves backwards it produces a rare occasion node in that air and that also moves outward at the same speed and so as it vibrates back and forth it's producing repetitive high and low pressure zones that are moving outward and eventually they hit your ear and you hear sound that's simple that's straightforward work it's more interesting and more complicated is what's happening on the back of the speaker because of the scale of sound waves this membrane is effectively negligibly thick it's a two dimensional structure and so when the voice coil is moving the front of the membrane forward in producing a high pressure zone from the point of view of the back it's moving backwards and producing a low pressure zone when it moves backwards this way it's producing a high pressure zone here and a low pressure zone here so the sound waves are emanating from both surfaces of the speaker but they are a hundred and eighty degrees out of phase with each other now when the speaker is hanging in a room eventually the sound waves that are traveling backward from the rear surface are going to hit a wall or a surface and they will reflect off that surface and move forward toward the plane of the speaker now that distance can be measured in inches or centimeters or wavelengths and if that distance on that two-way trip back to this plane happens to be an integral number of wavelengths at any given frequency it's there's going to be certain frequencies where that is an integral number one wave two waves three waves it will arrive at that plane I would have phase with the front surface because it started out of phase with the front surface and those two wave fronts are going to be traveling toward your ear and eventually when they reach your ear they're going to be out of phase with each other and create a destructive interference and would create a lower amplitude of the sound that you would otherwise hear out of the speaker and conversely if the distance the two-way path distance is one half wavelength or one and a half or two and a half wavelengths that will create what's called a phase delay or effectively flip the phase so that when the wavefront reaches the plane of the speaker again it will then be in phase with the front surface and when those two in phase waves reach your ear you're going to get an increase of amplitude and as you scan through the entire frequency spectrum you will get points where you have increased amplitude and decrease amplitude and that creates what's called a frequency cone of spikes and troughs in the amplitude of the sound that's not a good thing because that's not part of the music it depends on where you put the speaker or how far the surface is from the wall and at what frequency it's putting out sound at that instant so you don't want that now you could modify that a little bit if you take say a ported design where effectively the rear surface sound is forced to travel a given length you won't eliminate the the comb it'll still be there but at least now you can control the frequencies at which that comb occurs so I want you to hold that thought for just a second now one way to deal with the bad effects of that rear surface phase interference is you could mount this on say a heavy box and then place a bunch of absorbent material in the box and effectively dump half the energy that the speaker is putting out which is kind of wasteful another idea that you might think you could use is you could simply mount the speaker on a heavy walled tube and run it all the way to the outside through a hole in your wall and let your neighbor listen to your music now first of all I don't think my neighbor has the same taste in music that I do but this also doesn't operate quite as effectively as you might think because this tube becomes what's called a transmission line it's a resonance structure and so when the sound bounces back and forth between the two surfaces there will be certain frequencies integral waves where this produces an increase in the amplitude above the mean and there'll be certain frequencies at which it causes destructive interference and you'll get a decrease in the intensity below the mean and it's the same sort of frequency comb now you might say first of all we mean reflection this is an open end or dumping the sound outside you still do get reflection from the open em and the reason that happens is because the tube acts as sort of a protective wall and when this train of low and high pressure in this this train of alternating high and low pressure regions is sliding down the tube when a low-pressure zone gets to the end ambient air is able to flow into that low-pressure zone and so when the following high pressure wave gets there it will experience a little bit of reflection from the higher pressure that it experiences here than it did in the tube now most of the sound will will actually radiate out but some of it will reflect backwards and form a resonance between the membrane and between that open end and depending on the length of the tube it will occur at different frequencies depending on how you adjust the length of the tube the other thought you might think of is that this is a very heavy wall tube and we're dumping most of the sound outside how does the sound get out of the tube how does it affect the sound that you hear it does so through the front surface because if that speaker that's mounted on the front end of the tube is moving backwards into a region of air that happens to be at a low pressure because of the standing waves that we've created inside the tube it will move further back there's less air resistance and if it's a higher pressure zone it will move less far and so as a result you will modulate the movement of the front of the membrane and again modulate the sound that you hear with your ear now those two frequency combs caused by the resonance in the tube and caused by the distance that the sound is traveling do not have to correspond you can combine both of those to effectively negate them and the way you do that is if you create a structure like this where effectively you have a ported design and a transmission line effect a porta defect and a transmission line effect what effectively you can do is by adjusting the length of this element you can cause those two frequency combs not to line up peak to peak but essentially line up peak to trough and what you end up producing is more of an a ripple in the intensity modulation rather than deep peaks and troughs and effectively you negate the negatives of each of these different features now if you want to dig a little deeper down the rabbit hole understand that the reflection peaks and the the the transmission line Peaks aren't necessarily very sharp and the reason that occurs is because if the distance around this curve is say half a meter in the middle it might be say point four meters around the inner part of the curve and maybe point six meters around the outside of the curve so instead of getting a sharp peak you tend to get a broader hill and valley because of that differential distance around the 1/2 meter point now the transmission line as I've shown it here doesn't have quite that same broadening effect because we do have a shorter distance around the inside here and a longer distance around the outside here but because of the flat end here we end up getting less differential and less broadening of the peak now you could negate that or minimize that by simply taking a curve and mounting it to the end here like this and produce a transmission line that also had the same variability in length another way that you could accomplish the same thing is you can taper the transmission line tube here because what that does is it produces more variability in the length depending on where it hits the wall in the taper and that's why we tapered the transmission component of these speakers it's a little bit more compact than Tempah than creating the secondary Bend now all of this sounds good and it's pretty interesting but what I'd like to do is I would like to go ahead and prove that this system actually works and so what we're gonna do is I'm going to take these different components and we're gonna bring them upstairs into our new anechoic chamber and I'm gonna run some frequency sweeps on them and you're gonna see the effects of the porting the effects of the transmission line and also the effects of changing the lengths of the elements in these and show how we can move the frequency peaks and troughs around under our control so let's go upstairs and I'm going to show you what this what this looks like on the graph all right so I've got the speaker with the portrait design setup first and I'm going to go ahead and put this inside the anechoic chamber I'll go through the design of this chamber in a little more detail in an upcoming video but it's based on the schedule of the sound absorption panels that we covered a couple of months ago it's essentially a two sided box that allows us to close the two surfaces together and produce a cube that absorbs sound on all of its walls I've got a shelf back here with foam on it and it is supported on some adjustable ropes that allow us to bring the height of the speaker to the mid position inside the chamber I've got a couple of wires that lead in here and this allows me to hook up the test speaker to the amplifier that's on top of the box and then there's a microphone that's located on this surface or in this wall you'll see it better from the outside of the the box but effectively it's listening to the speakers and the technique for closing this is pretty straightforward I simply wheel the two surfaces together like this I just take a couple of clamps to bring the two parts tightly together to seal up the sound alright that's the back of the microphone and then both cables lead over to the other side of the room where we have the comp set up with a roo program so what I'm going to do is I'm going to go ahead and bring up a test with checking the levels first to make sure that our amplifier is at a good setting and then we'll go ahead and we'll measure from 150 Hertz up to a maximum of 12000 Hertz and we'll see what kind of pattern we get what we'll do is I'll go ahead and smooth this a little bit just to make it a little easier to see and this represents the peaks and the troughs caused by that tube design now what we're going to do is I'll go ahead and I'll repeat the test but I'm going to change the lengths on that porter design and see what that does to the positions of these different peaks and troughs and try this test the other clamp all right let's see what we get okay we'll smooth this one too and then let's overlay them and see what happens there we go and as you can see the peaks and the troughs occur at different positions simply because the length of the tube has been adjusted now this is what the ported design what we're going to do next is try one of the transmission tubes [Music] it's again it will hook them up all right let's take a look at that we'll go ahead and smooth it and before I do a comparison let's change the lengths and do one more of these scans with different lengths tooms now as you can see you can obviously trim and cut and adjust if you've got one of these chambers in order to get the lengths just right so we don't get overlap it's obviously an iterative process and it might take you a lot of going back and forth and trimming but there's a neat trick with the Voigt tubes that allow you to simplify that process make it quick and easy you gotta love clamps alright so one more test alright let's go ahead and smooth that one and then let's overlay them now as you can see I will get rid of the first two for just now right now just for this comparison but this is the transmission line when it's adjusted in length and you'll see at certain points there's correspondence at certain points there aren't but effectively simply by changing the length of the tube we can adjust the position where these Peaks occur and that's what's useful in trying to get a complete overlap of the troughs and the peaks from the different techniques and by adjusting the lengths it's obvious that you could fine-tune this to the point where you get a zone where there's basically no peak and trough that occurs but that it requires a lot of adjustment and as I said the boy Voigt tube enables us to make these kinds of adjustments without any doing any additional work and that's what's so nice and elegant about the design there's one other property of the speakers that's very important and that is what's called the horn effect and it's the third property that we need to try to fine-tune in order to just to get the most out of speakers so what we're gonna do is are gonna go back downstairs and I'm going to show you a demonstration of what a horn does to a speaker element now a lot of speakers that you'll see commercial speakers he have cone elements and cone acts in an interesting way it acts to improve the impedance matching between the element that's moving and the air the element is very small and even if it's putting out a lot of watts it doesn't necessarily couple that sound into the air very well because the air is so thin it's so rarefied compared to the mass of the actuator it's a little like taking a hammer and slamming into a ping-pong ball no matter how hard you hit that ping-pong ball you're not going to transfer a lot of energy from that hammer and even if you were to take say that same hammer and pound it into a box of ping-pong balls you're still not going to couple a lot of energy into the end of those ping-pong balls because they can move sideways however if you were to take a long tube and fill it with a bunch of ping-pong balls and slam one end as long as you don't crush them you'll get better impedance matching because you're gonna move all of those balls all of that mass and it's gonna be more similar to what you get if you hit say a ball bearing a more dense item you can think of impedance matching a little bit like inertial match matching if you have something of equal mass to the actuator you're going to get more coupling of the energy now in this device the way that the cone works is that it keeps the air column within this this chamber and so there's a greater mass of air that's going to be moved then the small amount of air that would sort of shift away as soon as the actuator moves forward let me demonstrate and you'll hear how effective that is I'm going to turn on the signal generator the amplifier is powering this little driver now you can hear the volume with no cone in place look what happens when I add this cone substantially louder now you might think well that's because it's directing it upward but look at where I'm standing I'm over here I'm sideways and if anything the side of the cone is blocking some of that noise that would normally get to me but there's much more volume in the room from the effect of the cone now you might also thankful it's very important to have a very geometrically precise shape in order to get that cone effect and it does improve the performance but it's not really that critical as long as you can keep the air molecules within that walled space you're going to improve the impedance matching let me show you the simple PVC pipe it's not as effective but it does work you could even take something junky like these masking tapes line them up in a junkie looking tube it still works kind of neat now the directionality of a comb can be a problem because it can mean that there's a very sweet spot to listen to the stereo but as long as you don't overdo it you can couple more energy out than you would otherwise if you just have the actuator moving in the air and it's part of the reason why you put a diaphragm on a speaker to help impedance match the motion of the little voice coil to a larger volume of air what makes the voice tubes so attractive is that it incorporates all three of those functions into one simple design there are no internal baffles inside of this tube it's effectively what you see it's a wedge shaped transmission line it is a port and it is cone now the reason for the wedge shape is that as I had described before the transmission line itself will have the tendency to produce peaks and troughs frequency combs and because of the fact that the flat ends of that resonator will tend to amplify and D amplify that frequency comb over a much narrower range because there aren't a variety of lengths within that that port that ducting shape by tapering one of the ends you improve the broadness of the spikes or the amplitude spikes and bring them out to a broadness that corresponds well to the broader peaks of a tube that also has variable lengths around its inner radius and its outer radius what's also kind of neat about the Voigt tubes is that as I was telling you upstairs it could be very problematic in order to try to adjust the port distance and the transmission line distance to get ad correspondence of those frequency Peaks but what you do is the upper end of these tubes are filled with a poly fill material or a fibrous material Paul void originally said that you need long hair wool but you can use any kind of a fibrous material even fiberglass and by putting that in the upper end of the tube you adjust the refractive index of air you make sound travel more slowly through it so you make the end of the tube up here appear longer so we've done as we filled up the top the top end of these tubes with a moderate amount of fiberfill and by just simply taking the back off and adjusting the amount of fiberfill you can really nail the D correspondence of the transmission line effect and the porting effect without having to go back to the table saw or cut different holes to try to adjust that you don't have to change the structure of the cabinet itself another thing you'll notice too is these curved plates in the bottom these are to send the sound out from the cone effect and they represent a an opening or they they effectively duct out of an opening that's about four times as large as the surface area of the back of the speaker so they're affecting they're producing a horn-like effect but without a flat surface they decrease the parasitic straight edge to straight edge modes that you would get within a speaker if you used a flat plate a curved plate works better now you might say metal it's kind of hard and it might ring well it doesn't it tends to be very easy to curve easier than say an organic product like wood it's also very hard so it tends to reflect the sound out very efficiently but it brings up a whole other issue of the building of the speakers and that has to do with what do you make them out of and so that's what we're gonna get into next now the vast majority of commercial speakers are manufactured using MDF or medium density fiberboard and it's basically a cellulose or paper powder that's placed in a resin matrix put into a press and then cured into large isotropic sheets isotropic simply means it has equal properties in all three dimensions as a result it tends to be very stable it doesn't warp or twist it is cheap it is easy to machine it's cheap it is relatively inexpensive and easy to obtain and it's cheap but the question is is it the best material to use for a speaker and if you're impatient the simple answer is no it is not but to understand why I make that statement what we have to do is understand what the panel's of the box is trying to do we don't want to absorb the sound within the speaker's we've spent a lot of effort in manipulating it so that we can get the best sound to be coming out where we want it to but we don't want it to just radiate from the sides of the box willy-nilly if we did we could just put this in a big cardboard shipping container what we want to do is we want to retain the sound inside and therefore we don't want it to create any sound that's coming from the box and the way that happens is the sound inside the air inside doesn't actually penetrate the box this isn't porous but the pressure waves create a distortion a bending or a movement of the panels and that then induces a secondary sound wave on the outside and that's what produces radiated sound and we don't want that we don't want the panels to move now there's two properties that will prevent that from happening one is stiffness and the other is mass now stiffness can be specified as as a specific stiffness and what that means is stiffness versus density steel and aluminium have a similar specific stiffness if you take two panels of equal thickness in aluminum and in steel the steel will be about three times as stiff but it's also about three times as dense or three times as heavy the aluminum however because it's lighter can take advantage of being thicker thickness is a related to the stiffness by the cube so if we were to double the thickness of the aluminum panel we would increase the stiffness Eightfold and because the aluminum is three times lighter than the steel an equal weight panel in aluminum could be three times as thick or twenty-seven times as stiff as an equal thickness of the steel and because the aluminum is inherently three times less stiff the net result is an equal weight aluminum panel would be nine times as stiff as a steel panel aluminum would be a better material if we're looking at weight and with heavy speakers that's not an insignificant thing now the same property applies to organic materials medium density fiberboard plywood strand board they all have specific stiffnesses now MDF is inherently about half as stiff as plywood that's what it specified and specifies as and I've even tested the bending on it it's about half as stiff inherently when compared to plywood in addition MDF is heavier this MDF board weighs about 165 grams and an equal thickness plywood board weighs about 115 grams so we could effectively make a plywood panel one and a half times thicker than an MDF panel and it would weigh the same and because it's one and a half times thicker that's 1.5 cubed or about three and a half times stiffer because you can make it thicker and because it's inherently twice as stiff that means a panel that weighs the same in plywood as a panel in MDF will effectively be about seven times as stiff so on the stiffness front plywood winds out the second issue is mass if we were to take the panels of these speakers and not can edge connect them so effectively they're just sitting where they are based on inertia if we look at what happens when a sound wave a pressure wave hits the panel because of the very low impedance matching of the lightweight air and the the heavy panel we're not looking at kinetic energy conversion or m1f MV squared we're basically looking at a linear process if we have a doubly heavy panel it's going to be accelerated by the same load to half the velocity and so at any given frequency we have only so much time during which the pressure wave is pushing on the inside and then eventually it reverses and the pressure is greater on the outside and it decelerates it and moves it back in the heavier panel even if unrestrained is only going to move a lower velocity as a lightweight panel and so therefore it won't cover as much distance within that fixed period of time but because that's a linear effect if we were to take panels that are equal weight or say double the weight we would only decrease the movement by a factor of two by doubling the weight and effectively by making the plywood panel the same weight as the MDF panel we effectively negate the the effect of mass and so what we end up with is a panel that's superior and stiffness and a panel that's equal in mass as long as we make the plywood panel a little thicker now I intentionally used the cheapest plywood I could find I think these speakers look pretty nice but I used big box store construction grade plywood that costs about the same as the MDF panels actually a little bit less at about $33 a sheet and based on these dimensions you'll actually need to use 2 4 foot by 8 foot sheets of plywood but you'll only end up consuming about one and a half of those sheets so it's about 50 bucks worth of plywood now if I was going to build a high quality pair of speakers that really looked good I would probably use a higher grade of plywood than the construction grade plywood now you could use a furniture grade plywood or you could use a marine plywood I have a lot of experience with the marine ply woods and I would highly recommend them they're Lloyds rated for waterproof glue you can actually boil this plywood and it won't delaminate the glue will last forever in addition they have more plies per given thickness so they tend to be more stable in addition to that the plywood actually uses the same type of wood both on the surface as well as the filler wood they don't take big knotty defect Laden layers put them in between fill them with putty they use the exact same material on the surface is on the inner layers this is a panel of a Kumi which is a lightweight plywood it's similar to sort of a cedar plywood and this particular plywood here has probably been sitting on our shelves for about 20 years and you can see that it has no warp no twist it has a fairly nice appearance to the outside and it represents the less expensive version of some of these marine ply woods at about a hundred hundred and ten dollars a four by eight foot sheet now on the other extreme is Meranti which is a very dense plywood it's similar to a white oak or a spruce plywood it has the advantage of a harder surface so that you're less likely to ding it or dent it if you contact or do you bump it but also because of its greater density you can't take advantage of the specific stiffness issues because all of these plywood's have about the same specific stiffness but because this is lighter you could make it thicker for the same weight and you'd end up with a stiffer board but for cosmetic reasons you might decide to go with the Meranti if you want something that's a little bit more robust but my personal choice would be to go somewhat intermediate in terms of density and and sand hardness and that is to use one of the African mahogany plywood's this is sapele kaya is a little more expensive version of this but this is a beautiful plywood it not only has all the properties that I also told you about but take a little bit of alcohol and wet the surface like you might do if you say put a coat of varnish or polyurethane on this you can see that it produces a beautiful grain pattern and if I was building a pair of speakers like this you could probably put it in Merrell ago so this would be my choice if I was going to be using the marine plywood's and you'd probably spend about $200 a sheet for that material and so you're probably looking at about $300 of wood involved in the in the process now if stiffness was the only thing we'd be pretty much done but reputedly one of the advantages of MDF is the fact that it has a higher dampening coefficient it doesn't and I'll show the test to prove that but basically the reason you want damping be is because these structures just like a cello body or a guitar body these structures resonate not the sounds that we're talking about bouncing inside the actual wood itself resonates and so at certain frequencies these boxes are going to move much more than they would at other frequencies because they're vibrating in step with the energy being fed in by the speaker and so as a result they'll produce a lot more radiated sound so you don't want them to resonate and all structures will resonate damping essentially eats up that resonant energy in frictional losses as the shear between the different particles inside the material produces frictional heat transfer conversion and therefore we get rid of some of that vibration and get rid of some of that that resonance now as I said reputedly MDF is better but I'm going to prove to you that it isn't and so what we're gonna do here is I've set up a little bit of a test jig here let me explain what's involved I have a vise a very massive structure and I'm gonna hold up these equal sized panels inside of the vise and then what we're gonna do is I'm going to put one of these accelerometers on here this is an 880 Excel 335 3 Access accelerometer you can get these from say digit key or eBay or any kind of electronic supplier for about fifteen to twenty dollars and effectively what they do is they produce an X Y Z accelerometer output in an analog voltage when you supply them with three volts and we're going to be just using the y axis here because we're just going to look at acceleration in the plane of the vibration what I'm gonna do is I'm going to lock this board in to the vise and then what I've got located behind here is a little fishing weight on a fishing line I'm going to bring it back a controlled distance and let it impact the surface and then what we'll see is we'll see the output from the accelerometer here and we're gonna see a few features that I'm going to describe to you so a little bit of double sticky tape to hold this in position I'm gonna step in front of the camera for just one sec and apply the tape then I'm going to adhere the accelerometer make sure this is centered and then what we're gonna do is we're going to produce an impact and you're gonna see what happens when I produce a controlled impact now this here the intensity or the amplitude represents the amount of acceleration it doesn't actually represent how much the panel is moving it's how vigorously it's accelerating back and forth these spikes are these Peaks they represent the frequency at which the vibrations are occurring which is continuous and the other property that you'll see is what's called damping the loss of the energy as the the energy of the vibration is being eaten up into friction now the MDF as you can see these are twenty milliseconds per grid within about a hundred hundred and twenty milliseconds it's getting down pretty close to nothing there's not much here now if I take a piece of plywood and put that in there same dimensions we're gonna take a look and see what the graph looks like when we do the same sort of impact okay now remember what this looked like about a hundred and twenty milliseconds going down to very little now this is the plywood as you can see not much longer you know maybe one hundred hundred and twenty milliseconds and we're pretty much down to zero so the resonance or the damping effect of the plywood is pretty similar to that of the MDF and so again plywood wins out over the MDF damping however we can do far better than that and it involves a process called constrained layer damping and effectively to demonstrate that what I'm going to do is get my little handy tool behind the cameraman here these are two identical strips of PVC foam board it's the same stuff that we built the freezer and the refrigerator rater out of it's relatively flexible and they've been clamped at one side and what I'm going to show you is I'm going to bend this and I want you to look mostly at this surface here of this end when I bend this like this watch what happens see how the side that's on the inside of the curve appears to get longer than the surface on the outside of the curve now they're not changing length but because you're on the inside of the curve you have a shorter radius and so therefore a smaller circumference and this length represents a larger arc in that in that circumference so it appears to get longer what's happening is we are getting friction across this interface point and that friction is good because it leads to damping but we can enhance the effect of that friction enormous ly if what we do is we use a very soft material that effectively can eat up some of that energy if we were to use something like say rubber sheet like this then sheet of rubber very stretchable you'll notice that this rubber is very elastic bounces back that's not very useful because when it stretches it stores up energy which it returns when we're making the other bend and so we don't actually eat up a lot of energy but if we use a material like this which is called Zorba Thane and it is a polymer that is visco elastic you notice when I stretch this it's more like gel it's gummy and so there's a lot more frictional loss when you use a material like this as opposed to say an elastic material I just plain urethane rubber now I can demonstrate how effective that is by placing in here a layer of the material this is the MDF I put a layer of the zorba thane between it and the constraining layer now the constraining layer doesn't have to be identical to the main layer it simply has to be much stiffer than the rubber in between to cause the shear forces and you can also use very inexpensive wood for that and it doesn't even have to cover the entire panel just most of it so that we effectively tile the inside of our speakers with these constraining layers and this rubber to get much better damping so I'll place this in here and good we've got that still on storage and we'll go ahead and test this good now look at this you see what sort of the damping looks like it was fairly similar to the MDF the MDF was actually a little bit worse but notice the pattern here at about a hundred milliseconds it's pretty dead 120 even more dead now what we'll do is we'll do the test with the constraining layer one two three notice what happens here within less than half the time we've killed the vibration off and we reduced it to the point where we're not going to get a lot of resonance from our cavity from using very cheap wood and the sort of thing now problem with the Zorba Thane a better term for it would be exorbitant Thane this little half square foot piece costs about $25.00 and if you were to tile the whole inside of these speakers you'd spend about twice as much on your Zorba Thane as you do on the entire structure so mm-hmm not necessarily a really good idea but there is a much better idea let me show you what I used this is called decid amp and it is made by a company called pyro tech and we'll link to them this is a 10 kilogram bucket of two-part curing urethane goo and when you place this material on the panels it acts both as a constraining layer as well as an adhesive so basically you push the panels down put a little weight on them the stuff cures overnight and you have a constraining layer that costs a lot less that entire bucket costs about a hundred and fifty three dollars and you only need to use about a third to a half of it to coat the entire inside of the speakers and to prove that it works I made up a panel just like with the Zorba Thane and let's see how well it works so now what we're going to do is we'll go ahead and test the decid amp and see how it compares as you can see maybe a little bit more resonance than the Zorba Thane but still down at around 40 milliseconds we're pretty much down to zero so this stuff really does work now you might be tempted to think well boy this really works well what if I put a really thick layer of the stuff it's not that expensive it actually works better the thinner you make it and the reason that is is if you imagine this rubber band here is sort of a magnified cross-section through the rubber material if you make it very thick and you have a given amount of sheer motion you don't produce a lot of stretching in the rubber band but if you make the band very very thin very thin layer that same shear produces a lot more stretch in the material because it becomes even more effective the thinner you make it so about a one millimeter layer is all you need in order to make this this material work in addition we actually coated the metal plates these are not single plates but they're dual three millimeter thick aluminum curved plates and we put a layer of this decid amp in between the plates and it also kills vibrations from the metal it's dead so it reflects well but it doesn't resonate now for those of you who say yeah the numbers look okay maybe maybe I believe it let me show you a sort of a cruder but maybe more impressive demonstration of how well this stuff works over here I have three identical wooden panels plywood sized panels plywood MDF and then a plywood panel with the decid amp and the restraining layer take a listen to the sound I'm going to hit these [Music] mdf it's dead this stuff really does work and so what we're gonna do is I'm gonna go ahead and I'm going to clean up the table here put an amplifier down here we'll get the laptop and we'll play some music for you a mix of different kinds of sounds to give an idea of just how good these speakers actually do sound total cost probably about 650 dollars if you include the four hundred and ninety dollars that we spent on the drivers but you could Ness you don't necessarily need to use the high-performance full range speakers that we're using here these are tang band speakers and they're very good and very expensive but we're gonna be using these for a number of different speaker designs and so I thought we'll invest once in a pair of very good pair but you can get the equivalent sized speakers for maybe $80 a piece you don't have to go that that high in addition you don't necessarily have to build speakers this large you could build other kinds of designs now that you know a little bit about how to interact the the ported design how to interact the resonance of the transmission line how to use different kinds of materials gives you a lot of tools that you can use so we're gonna go ahead we'll put the amplifier down here we'll play these for you and you get to listen to just how good they sound in the description below this video we're going to put a link to our webpage where we're going to upload some PDFs and images as well as instructions so that we can show you what kind of materials you're going to need basically how to put this thing together as well as sources for some of the materials in the components that we used in this build so I'm going to start I'm going to finish with playing a little bit of music through these speakers and at the same time we'll give you a montage of my building of them the construction process so you get a better idea of what it took to put these things together finally I want to thank you very much for watching I really appreciate it if you would subscribe because we want to grow this channel huge and with your help we'll get there so I wish you a very good evening and we'll see you soon [Music] [Applause] [Applause] [Music] [Music] [Applause] [Music] [Music] [Music] [Music] [Music] [Music] [Music] [Music] you

Channel: Tech Ingredients

Views: 2,289,318

Keywords: Speakers, Speaker, Sound, Voigt speakers, Tower speakers, Ported speakers, Transmission line speakers, Resonance, Damping, Constrained layer damping, Marine Plywood, Sorbothane, Anechoic chamber, Tang Band, audio, diy speakers, speaker build

Id: EEh01PX-q9I

Length: 52min 56sec (3176 seconds)

Published: Thu May 09 2019

Reddit Comments

[u/fasterbass]

I cant believe there are no comments! What an amazingly insightful and easy to follow video. Definitely inspired me to build a pair!

[u/BoogKnight]

Lol he leaves that annoying test tone on for like 5 minutes more than he needed to.

[u/Colonel_Mustard]

Man I feel dumb after watching that. Tons of great info

[u/Torg0]

Just watched this one last night and found it extremely informative. In fact, I ended up not being able to stop it and staying up too late. I have been thinking a lot about building the tritrix MTM TL and now I'm rethinking maybe working up my own design. His videos on the Dayton exciter based flat panel speakers were also very interesting.

Edit: Also - He really slays me sometimes and I often find myself wondering how much of it is intentional. Leaving the test tone on for fucking ever, talking about MDF: "It's cheap, it's cheap, it's inexpensive and most of all it's cheap" The varnished high grade plywood fitting in at maralago etc. The videos are so genuine, earnest, fact-based and unaware of themselves. They go for different camera angles and such but you wonder why. It's amazing content with that public access feel. That being said, just his workshop, not to mention all of the amazing things he does in it, is inspiring to me.

[u/soobrex1]

SUBSCRIBED! Damn that was awesome

[u/ArmchairArmchairist]

Wow, I'm no where near to being able to build things like this, but it's still inspiring.

[u/Area51Resident]

Wow, crash course in pros/cons of transmission line vs. ported, plywood vs. MDF and a whole lot more.

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Has anyone heard or built these? Construction seems simple enough but the dimensions of the taper in the cabinet are what makes/breaks this design.

[u/[deleted]]

Very informative video, but full range driver with whizzer cones? No thanks. Transmission line full ranges are cool, but treble distortion and comb filtering are always going to be a problem.

[u/LFX_za]

i'm more surprised by the fact that I understood like 95% of what he was saying...