We are happy to announce that McKnight Guitars is now offering “Double Tops” as an option. What is a Double Top? It is what the name implies. The guitar actually has two very thin top plates that are separated by a Nomex honeycomb core. Nomex is made from Aramid paper and is extremely light in weight and was pioneered for the aerospace and aviation industries. The guitar Double Top technology was pioneered by two German luthiers about 10 years ago primarily for the classical guitar world in an effort to build a classical guitar that is more efficient and produces a LOT more volume and projection.

I have been doing my own R&D on Double Tops for about two years with excellent results. The sandwiched top is approximately 30% lighter than a solid top. What does this mean to the guitar player? A lighter top is more responsive and takes less energy to drive it. Many fingerstyle players [who use a light touch or string attack] love Cedar tops because of their responsiveness. Cedar is the lightest weight soundboard wood that is commonly used in guitar construction today. The light weight Double Top will respond much like a Cedar top in the hands of a player with a light string attack.

After the two thin tops have been joined and the bonding adhesive has cured, the completed top is not only 30% lighter than a solid top but it is extremely stiff. What does this mean for the player? A stiff top requires less brace mass. A stiff top has more headroom and can be played harder without the tone breaking up or distorting. Consider a top plate that is 30% lighter than a solid top AND has less brace mass than a standard solid top and you have a high performance top with an extremely wide dynamic range.

The complete top, after it has been braced and voiced for optimum performance is much stiffer and lighter than its solid counterpart top. Since the new Double Top is lighter and stiffer it is much more efficient since it takes less energy to drive it and the added stiffness (with less overall mass) offers the player the ultimate in headroom performance.

Double Top construction differs greatly from the standard solid top. It requires special equipment to sand the two tops to veneer thickness. It requires twice the material (2 tops instead of one) plus a special adhesive and unique application method. Special jigs and fixtures are required to position the tops during the bonding phase. It also requires a small internal pad to support the bridge and reinforce the sound hole & rosette. The Double Top requires a totally different brace design which is about 1/4 the mass of a standard solid top. When working in the construction phase there is no margin for error since the top plates are extremely thin. If a plate is dented there isn’t enough material to sand the dent out or it would be probable to sand through the top. Once the completed top is on the guitar there isn’t any concern for the player because the finished top is extremely rigid. The player will have to consider that the top is different and take precautions with their playing style.

Double Tops are an option that the player needs to consider this when ordering their McKnight Guitar. I have been extremely satisfied with the results of my research thus far. If it weren’t cost prohibitive EVERY guitar I build from this day forth would have a double top on it. Everyone who has played my Double Tops has been amazed at the sheer volume, power, projection and headroom the top has while still being extremely responsive to a light touch. These tops have the widest dynamic range that I have ever heard on any guitar. There is no discernable change to the overall tone of the guitar. There is a tremendous future for this top design so please consider your needs as a player and if there just might be a McKnight “Double Top” guitar in your future.

Inner Spruce top with a Nomex core on top of it & Redwood internal support pad

Outer Italian spruce top laying
on Nomex core

Wheat in Pernambuco on “The Tree” mahogany side

More information on tops:

The Guitar Top or Face : 80% or more of the sound that your guitar produces comes from the top or face of the instrument. There are many top tonewood choices to choose from and this process is sometimes quite intimidating to a player. Historically tops have usually been made of soft woods. Spruce or Cedar has been the most widely used woods. However hardwoods have been used successfully too and the most common include: Mahogany, Koa, Birch & Walnut.

I begin by asking my customers a series of questions that will help me narrow the field of choices down to about two or three wood options. These questions include what type of music will you be playing, how aggressive is your string attack, do you play mostly fingerstyle [either with fingertip flesh, nails or finger tip pics], do you play with a plectrum (pick), what gauge of pick to you prefer, do you play mostly rhythm, flat-pick or lead, what gauge of strings do you prefer and what type of sound do you like? Answers to these questions will focus our attention to just a few top species.

We can all make generalized statements about wood properties but the bottom line is each piece of wood is unique and one of a kind. Therefore I must approach building a guitar with this fact in the forefront of my design. After you and I have begun a dialog, in which I understand your needs in tone then it is in your best interest to allow me to guide you in your decisions by making suggestions that we both feel comfortable with at arriving with the tone that will please you.

After the top species has been selected then the choice of the top, from my inventory, is usually in my control. Occasionally, a customer will schedule an appointment and come to the shop to select his or her own pieces of wood but long distance clients generally leave this decision in my hands. The rough top is first analyzed visually to see if it meets my standards for an aesthetically pleasing piece of wood. A lot can be learned by first analyzing the rough sawn grain texture such as run out or grain abnormalities. The top plates are then tactilely inspected and flexed with my hands to get a feel for the general overall stiffness both across and with the length of the grain. The top is then “pinged” or tap tested to see if it has an exceptionally lively response that will result in a great guitar top. If the top has met all of these criteria then I measure the deflection of each top before I ever think about building with it. This gives me a baseline of the stiffness of the top based on a predetermined amount of flex. Based on the type of sound I want the guitar to eventually produce I will gradually thin and taper the top until I arrive at the correct stiffness based on the deflection measurement.

Top choices (currently in, my inventory) are arranged from the most flexible to [usually] the stiffest.

Tonewood grading systems – Unfortunately there are no standardized grading systems from ALL of the wood suppliers. When I purchase tops from a supplier what may be Supplier A’s master grade tops could be Supplier B’s A grade tops. Suppliers usually grade their woods based on visual qualities including the following: grain count, grain straightness, overall color, degree of cut (how close the end grain is to 90* perpendicular to the face), amount of run out. I generally purchase a large enough quantity that will allow me to sort through them and keep only the best quality tops in my inventory. The sub-standard tops are then sold.

When I look for a great top I am initially concentrating on two attributes:

• I want a very stiff top
• I want a top that is very light in weight. A top that has the highest stiffness to lowest weight ratio will always be a better choice of top to consider for use on your guitar. A light top is easier to move with the smallest amount of string energy and a stiff top requires less overall bracing mass which should be factored into the design process.

The following comments are generic grading guidelines for tops:

Grain Count The grains lines that are visible on the surface of the guitar top are the result of each year’s annual growth and are often referred to as annual growth rings. Wood that exhibits tight close grain tells me that the tree grew at a very slow even rate with little variation in the growing season and climate. Master grade tops typically have very fine, close and evenly spaced grain lines. I don’t put a lot of emphasis on tight grain spacing because often times these are not the stiffest tops.

Grain Visual Appearance – Suppliers will also grade their wood by the visual appearance of the grain and how consistent the grain lines are spaced apart. Even grain spacing is evidence that the tree grew in a very predictable and consistent manner. Grain coloration is also a factor to consider. Some tops have all the same color of grain lines; some have dark prominent grain lines while others have a mixture of light and dark grain lines within the same top.

Grain Straightness – Tops are also graded by how straight the grain lines run from the top to the bottom. Higher grade tops will have nearly perfectly straight lines which indicate the tree probably grew towards the middle of a forest stand and did not have to fight the wind or sun. Wavy grain is usually downgraded slightly from master grade. The waviness has no bearing on tone or structural integrity or stiffness.

Overall Color – The highest “visual” grade tops are the cleanest, purest, whitest of tops. Some tops have some naturally occurring coloration. This color is often a result of climatic changes and mineral deposits of the soil. Tops with some coloration are downgraded from master grade.

Degree of Cut – By looking at the end grain of the top you can quickly determine the accuracy of the mills quarter sawn or radial cut. The best processed tops have the end grain standing 90* perpendicular from the top’s face or surface. As the grains start to lean a few degrees off of perpendicular the top is downgraded proportionally from Master grade. Some of the very best tops are hand split from the log into billets. Then the billets are then hand split into wedges that are later milled into tops on a large band saw.

Run out – Is usually revealed by improper milling of the wood. Each tree has some degree of runout because of the twist that occurs naturally in a tree. Every log will have varying amounts of grain run out. Only the straightest logs are selected for musical grade wood. As the tree grows it constantly twists as it tries to follow the sun throughout the day. A tree is made up of billions of tube like cells that run from the roots of the tree to the leaves. Lets compare a rectangular board to a rectangular box of plastic drinking straws. Looking at the open ends of a box of straws would be comparable to the end grain view of a top. These cells run the entire length of the top. Now if you looked at the top’s surface in its longitudinal length you don’t see any [tube] ends or openings on the surface because each cell is laying parallel to the top’s surface. Each of these tubes are oriented in the direction of the grain. As the straws are lying parallel to one another along the entire length of the box so are the cells in a top. This is how a top with no run would look like.

If a top has run out then those cells or tubes would not be parallel to the top’s surface but would be lying at a some diagonal angle. You would then begin to see the ends of the tubes show up on these surfaces.

Have you ever seen a guitar top that appeared to have one side that was slightly darker or lighter in color than the opposite side of the center joint? This is a perfect example of a top with run-out. The cell or tube ends that are not laying parallel to the surface have their cell ends exposed on the top surface. When these ends of the cells are exposed to the light they will refract the light at different angles and make the top halves appear to be different colors.

A very small amount of runout can be acceptable but a considerable amount of run out is not a desirable characteristic for a top. Run out is visually distracting. More importantly it causes structural weakness in the top rendering it considerable less stiff compared to a top with very little detectable run out. The highest grade tops are hand split so the face of the top always follows any run out that may exist in the billet. Much of the soundboard wood today is not hand split, because it is a very labor intensive process which in turn drives the cost too high. Instead tops are rapidly sawn from planks at the mill. Improper sawing will usually reveal varying degrees of runout in the top.

 Medullar Rays or Silking – This is a visual sign that the top is of a high quality and was nearly perfectly quarter sawn. These rays or silking run at 90* to the grain lines on softwoods. Silking can be compared to re-bar used in concrete construction. This is the wood cells that lock or bond the longitudinal cells [or straws] together and they give the top extreme stiffness across the grain. Medullar Rays or Silking will only be visible in tops that have very little run out and were accurately quarter sawn.

Bear claw Figure – Is a naturally occurring figure that occasionally shows up in some spruces. The name was coined because the surface of the top appears as though a bear has left claw marks in the wood. No one knows for sure what causes this rare figure. The presence of bear claw used to downgrade the tops to B grade but in the last few years many luthier have discovered that these tops can be quite stiff and make strikingly beautiful and truly unique tops. With the recent swing towards the artsy look, bear claw tops are now even higher priced than master grade tops.

Volume: I am often asked why my guitars produce so much volume compared to other similar shaped guitars. Volume is largely controlled by the mono-pole action or mode of the guitar’s top AND the air coupling to the guitar’s back. This mono-pole mode is basically the up and down movement of the top and back. The freer or more flexible the top and back are then the more efficient the guitar will be at pumping air.

In its simplest form a guitar is a rather inefficient machine that pumps air. As a string is plucked, the vibrating energy is transferred to the bridge or the top’s point of centralized excitation. The bridge will then begin to vibrate or move in several different directions; up and down, side to side and top to bottom as well as transverse or crossways. The bridge energy then makes the top move in each one of these directions. The movement is very very small and not visible with the naked eye but is visible by using vibration accelerometers and computer modal modeling software. The top in turn is coupled to the back by a given volume of air inside the sound box or body of the guitar and then the air excites the back to move out of phase with the top. The end product is air that is emitted from the sound hole which reaches our ear in the [hopeful] form of music 😉

If you have an opportunity to visit a guitar store, and the manager will allow, try this experiment. Take each guitar and press in on the bridge with your thumb and try to feel how much you can depress the bridge or move the top on each guitar. If you can find a guitar or two that seem to be easier to depress the bridge, than the others, this will clue you in that the top is more flexible in the mono-pole mode. Now play this guitar against another a stiffer guitar. The more flexible guitar “should” be louder and probably have more bass response while the stiffer guitar will be less loud and brighter favoring the trebles or higher frequencies. Laminated guitar tops and backs are extremely rigid and therefore will have less volume than a “properly” thinned and braced solid wood guitar.

Most knowledgeable luthiers know how to control and manipulate the various modes of the top and back or to customize the volume and tone that the customer wants. By selecting the right piece of wood to start with, that has the correct stiffness [in the appropriate] direction(s), brace the top in such a way to control the top modes and tuning the back to work in [out of phase harmony with the top] all combine to provide the ultimate air pump that will bring joy and satisfaction to you, the new owner.

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