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Summer 2009

Hawthorne Audio

Introduction To The Art And Science Of Open Baffle Speaker Building
Article By Darrel Hawthorne Of Hawthorne Audio

 

  I would like to welcome Enjoy the Music.com DIY magazine readers to the world of speaker building and outline the specifics of building a unique style of speaker we refer to as the Open Baffle Configuration. In this outline I hope to illustrate the various gradient steps and considerations involved in building an Open Baffle speakers. From Wikipedia we learn that an OB or Dipole speaker is:

A dipole enclosure in its simplest form is a driver located on a flat baffle panel. The baffle is sometimes folded to reduce its apparent size.

A rectangular cross-section is more common than a circular one since it is easier to fabricate in a folded form than a circular one. The baffle dimensions are typically chosen to obtain a particular low frequency response, with larger dimensions giving a lower frequency before the front and rear waves interfere with each other. A dipole enclosure has a "figure-of-eight" radiation pattern, which means that there is a reduction in sound pressure, or loudness, at the sides as compared to the front and rear. This is useful if it can be used to prevent the sound from being as loud in some places than in others.

 

That is a good start but for someone actually confronting building one we need just a bit more information. I would like to break this tutorial down into three gradient sections based on the progression from day one beginner through intermediate and then finally onto advanced concepts and theories. I would also like to mention that this tutorial has been written collectively by the contributing members of Hawthorne Audio's forum and as such will strongly focus on the use of the Silver Iris OB specific drivers. Much of this information will be of use regardless of the drivers used but performance may differ greatly when using none OB specific drivers.

 

Let's Begin
Most builders will want to use sheet goods to make their baffles from so we could start with a little discussion of what's commonly available and some basic shop tips for getting these sheets goods cut and holes made. A good material to use is 0.75-inch multi-ply, veneered plywood. Most larger home centers stock Birch Plywood and many find this close to ideal. Try to avoid plywood that may contain voids or small sections missing between these layers. This compromises the structural integrity and it's possible that a small fragment of broken off wood between layers may rattle and buzz when your music is playing. No fun and very hard to locate after the fact. Many home centers will do basic cuts for a small fee. You could have them rip (cut lengthwise) to the approximate width you want to start with. ( more on this a little bit later). Once ripped to width you could also have them cross cut to the desired length. It may be possible to purchase less than a full sheet (4 x 8 foot). and this may prove to be easier to work with as well as saving you some expense.
We have also used MDF and some guys like it and some do not. If you are considering using MDF remember that it is heavy and when cutting it produces a great deal of very fine dust. This dust is a irritant and many wood workers have issues with this. Actually most plywood are heavy, dusty and all require some level of caution when handling, cutting etc. If you plan to do your cuts at home these can be done with a table saw (preferred) or with hand held circular saws. Doing this entirely by hand with hand saws is possible but be forewarned of it's demand on your arms and patience.

I will now list some basic width and height ranges that are fine for a level one or study baffle. For width I would recommend going with a range from 17 to around 22 inches. We can explore side extensions or 'add ons' in section two Under "Tone shaping" Height you ask? We currently use 35 inches for our production Solo/Duet baffle. We add Oak trim pieces to the tops and also an Oak base or plinth. This gives us a total of approximately 37 inches for a combined height. Looking good is around 22 x 37 inches from a visual perspective and is large enough to add in the Augie at some future date. If one was building a Solo only they could reduce this height to as low as the width but preferably a bit taller to form a rectangle. For me personally, I would say about 24 inches minimum height and 35 inches seems about the maximum ever needed. Many of you have gone shorter so maybe 20 inches would be a good min?

Once we have our baffles cut to size we will need to make driver cutouts and this will be the next major portion of the project. A circle will need to be drawn onto your work surface and for this we can use a compass. Secure or make yourself a compass and draw out the desired circle size (driver location on baffle to be discussed in more detail in part II of this guide). The shipping carton for our Silver Iris has inside, a cardboard support that has a circular cutout that is near perfect for use as a template for these drivers. We can use a reciprocating jig saw to cut out this hole. Another popular tool to use for this is the handy router. If you own one, consider using it. If you plan to make a lot of speakers, consider getting one and a jig to make circles with. They are a major improvement over a hand held jig saw. The actual cutout diameter is driver specific. Check with the manufacture for this dimension. For our Silver Iris 15-inch coaxial use 13.875 inches for a relaxed fit and try 13.75 for a much snugger fit.

Note: Follow the operation guidelines provided with the tool of choice and use all applicable safety equipment.

Once we have our holes made, we will then need to determine some method to keep these baffles in their upright position. In the next section of the tutorial we will explore tilting this baffle back to alter the resultant effect on our perceived soundstage, for now we will simply look at keeping it at a fixed 90 degree angle relative the floor. Some builders use shelf brackets, either store bought or shop made to keep their baffles upright. These work very well and are generally not visible from the front while listening. I make mention of this because aesthetics may or may not play a role in selecting materials for our baffles. Some builders will start out with a very basic "Study" (test) baffle (recommended) just to get a feel for how a particular design may work in their unique listening environment.

A second method of keeping our baffles upright is the use of a separate base or plinth. This base must be large enough and heavy enough to safely maintain our baffle and drivers I their upright position. The width should be the same or slightly wider than that of the baffle. The depth of this base should be such that our baffles will not tip over either forward or rearward should they be bumped into or while moving about your soundstage. That's about it for a basic, How to guide to baffle construction.

To recap then, we need a board (or similar) with a hole in it.
Somewhere between 17 and 22" wide by somewhere between 20 and 35 inches tall.
Keep it from falling over and make sure everything is securely mounted and rattle free.
Adjust the above as needed based on personal preference and room constraints.

Anything beyond this would fall into level 2, Intermediate and start to explore tone shaping and advanced sound stage considerations.

In the following sections of this tutorial we will explore in greater depth the baffles effects on tone, soundstage, soundscape, low frequency response. We will also look closer at baffle materials and construction considerations with regard to vibration management and sound wave interaction. The second section of this tutorial will be very useful for fine tuning our sound and aid us in getting more refinement than what we experienced with our study (test) baffles. For those of you continuing on to this next level we hope to offer to you a much greater understanding of your speakers, room and this illusion we call music. For those of you that are content with what you currently have created, I say "Well done and congratulations on completing your Open Baffle speaker project." May it bring you considerable enjoyment and help you better connect to the music we all love.

 

Section 2: Intermediate Level
In section two we can look deeper into this relationship between our drivers, baffles and the rooms we use to listen to our music . Because of the Dipole nature of our open baffle speakers, separating these front and rear waves is necessary to maintain good low frequency response. The opposite side of that coin is that we do not want to make our baffle any larger than what is truly necessary. I try to think of these baffles as tone shapers and their size, shape and the drivers location within the baffles can all influence our final sound. Generally speaking the larger the baffle the greater the separation we can realize between these in phase and out of phase front and rear waves. Bass potential can be considered to be the product of the driver itself and the degree of isolation of opposing waves. The Silver Iris drivers have very good low end potential and the baffle requirements would not be considered extensive. The concerns expressed by many with regard to having large baffles are many faceted and each worthy of investigation by the intermediate speaker builder. Let's take a look at some of the issues that may arise from the use of larger baffles.

First off, I would mention that we often desire our speakers to have the smallest physical size possible so that they occupy the least amount of room area as practical. This is a common goal as we often do not have an abundance of space in which to work with for our music playback systems. If on the other hand you are more fortunate and have plenty of space it may still be desirable to keep your baffle size small for these additional reasons.

Soundstage interaction: Everything that we locate within our soundstage has some effect on the final sound we hear. This of course would include the speakers themselves. Large baffles can also be viewed as simply large reflective surfaces and may influence to some degree how sounds are reflected about, in that critical area between, in front and to the rear of the speakers themselves. Here at Hawthorne Audio, we cover our baffles with felt and fabric in an attempt to help minimize this reflective quality of these wooden surfaces. Large baffles can effectively block sound waves that have been projected from the rear of the baffles and this is both helpful and can also be seen as a possible detriment. As the sound is projected from the rear of our drivers, it is free to travel into this area behind the speakers. This energy then reflects off the wall behind our speakers and makes it's way back out to us, the listener.

This second arrival of sounds should be sufficiently delayed and when set up correctly can result in a wonderful sense of ambiance, sound stage depth and 3D imaging. Anything coming between us and this second arrival can block or alter this in an undesirable way. One way to minimize this would of course be to utilize the smallest baffle size that would still yield us our desired tonal balance and low end response. We can cheat this rule to some degree by using a separate Bass Augmentation system and I will discuss this in later sections. Try to think of your baffles as crude tone controls. I mention this to new builders with the hope that the relationship between baffle size and shape is fully taken into consideration during the design and study (test) period.

Driver location within our baffles is also a consideration: More correctly stated, where our driver sits relative the objects it can be influenced by is a design tool to be used by the intermediate builder. One common question that often first comes to mind is "How high or low on our baffles should we place our drivers?" Lets explore this driver height question first.

Proximity to floor Vs. physical alignment of the tweeter to the ears of the seated listener. These are the two opposing concerns we face here. By locating our drivers closer to a boundary, in this case the floor, we can take advantage of something called "Boundary effect" and realize a noticeable reinforcement of our low end response. Boundary effect results in a perceived reinforcement of bass frequencies primarily because we are limiting the number of available directions this energy may travel resulting in an apparent increase in the amount of energy traveling to the remaining unimpeded areas. By placing our drivers low on the baffle and by having our baffles touch the floor we also create something closer to an Infinite baffle situation for this one edge. In an infinite baffle situation, no cancellation of the front and rear wave can occur and thus we realize the lowest possible low end response that the driver is intrinsically capable of.

The flip side to this is that whenever we lower our drivers we also must contend with the possibility of issues arising from our ears now being more off axis the tweeter and also the possibility of physically lowering the perceived sound stage height illusion. Many agree that ideally our drivers should be vertically oriented such that the tweeters align with our ears when seated in our favorite listening chairs. This seemingly sets us up with a built in compromise if we desire both the maximum low end response potential and also the un compromised imaging and high frequency potential of a driver located at ear level.

 

What To Do?
We could for example disregard boundary effect and floor loading and not concern ourselves with reinforcing these low frequencies. For many this option wins out as it preserves imaging and results in a high percentage of the total frequency response sounding it's best. Some will want this low end response reinforcement and are willing to sacrifice ultimate imaging rightness. One way we have discovered to approach "having our cake and eating it too" would be to tilt the driver such that while seated at our listening position the drivers are in fact pointing directly at ones own ears. This actually is a rather good compromise and for many a working solution. This tilt back angle is determined by your preferred listening distance and also the determined driver height on your baffle. Extreme example being a driver mounted as low as possible while having a very near field desired sitting distance. This would require the most severe tilt back angle and may introduce some ill side effects with regard to soundstage imaging. If you can locate yourself farther away you can reduce this angle accordingly and still maintain a proper sound stage height illusion.

I keep adding the word Illusion to these comments and it's important to remember that this is an illusion. While listening to our music we hear a phantom center image illusion and everything in the very long chain from performer to our ears may effect this illusion. I should even go further to include our brains in this as well. Personal bias's, cultural bias's, daily variances in health or mood all can theoretically effect what we perceive. Tone shaping and soundstage imaging are both very personal and both highly effected by our environments both physical and within the landscapes of our minds.

Vertical orientation of our drivers is important and for some the idea of how they are located horizontally with regard to a centerline may also prove important. The idea has been proposed and several finished speakers have been built with the drivers mounted such that we end up having differing distances to the edges both left/right and top/bottom. The theory suggests that at a certain distance from the edge, a driver will start it's out of phase roll off at a frequency determined in part by this distance the sound must travel before it reaches an edge and can then interact with the sound from the opposite side. This is known as the baffles roll off frequency and this frequency varies with distance traveled or baffle size in general. What we try to avoid is having the exact same distance to these edges so as to average out these roll off frequencies. The worst offender for having exactly the same distances would of course be a circle. This is the theory and I am sure that their exists mathematical formula that confirms that this is true.

We have not however, received sufficient anecdotal, real world evidence of this to say for certain that it's a real big consideration when using our Silver Iris drivers. Most of our builders (myself included) center our drivers on the baffle and achieve excellent performance. On the other hand it would seem unlikely to cause any performance reductions if done so. I would label this as an optional technique that should not cause any degradation of performance. The distance to the top of the baffle and also the shape of the baffle top, does seem to have a greater potential for effecting the final sound. This is a bit more involved with the soundstage illusion and will be covered more in the next section. For now I would say that it is generally considered prudent for this distance to not be our shortest. If the shortest distance to an edge is this top dimension, some suggest that the sound will interact in this area first and have ill effects on soundstage. We also have seen good results from making these top sections domed or sloped. Conversely we have countless examples that have perfectly flat tops who's builders are very pleased with their end results. Have fun with this and share you discoveries.

 

Section 3
Advanced Ideas and concepts in Open Baffle speaker construction. Now that we have a working foundation of information on how to build our OB's, we may now explore ways of making them even better. One popular way of making our baffles perform better is through the further reduction or elimination of distortions or coloration's. Whenever an object is set into motion it is plausible that this moving object can in fact create sound waves and be heard by the listener. This secondary sound is undesirable and advanced speaker builders strive to gain control and hopefully eliminate all traces of it from their playback systems. Improvements are usually described as our music becoming less congested, cleaner, less colored or having lower overall distortion. This, by the way is one of the primary reasons so many of us prefer our OB's in the first place. By eliminating our boxes we eliminate the potential for the coloration caused by the stored and released energy from the materials used to construct these boxes.

When looking at our OB speakers then, the last remnant of our former boxes is this front baffle. It would seem only natural that we finally focus on this one remaining surface with the same critical eye we did the other surfaces of this former prison. In this section we shall look into vibration management as a design tool for greater clarity. We will revisit our drivers themselves and look at damping the frames and basket assemblies. Once we have a good understanding of this mechanical tool called a speaker, we can also look at this tools presence within our rooms and soundstage. In this section we will look at the reflective or refractive properties of our baffles and discuss the improvement potential of surface treatments.

Not too unlike the sound boards and resonate chambers found in many acoustic instruments, our baffles have the same potential to be excited by the piston action of our dynamic drivers. How much sound our baffles can create varies with their construction and material selections as well as how much energy the drivers themselves are being asked to displace. Along with how loud we are asking them to play is also the consideration for how low in frequency we are trying to recreate. We will see that vibration management becomes much more of a consideration as we increase volume or when we include into our designs, bass augmentation. The first tool in the tweakers tool box that is useful for vibration management is decoupling. Not unlike the motor mounts in our vehicles we can decouple our drivers from our baffles and thus limit the transfer of energy from the drivers to the baffles. When building our production finished speakers we mount our drivers first to a plywood mounting plate. This plate is 16.5 x 16.5 inch and we bolt our drivers to this mount using 0.25-inch 20 bolts, washers and finally Nylock brand locking nuts. This seems to do a great job of arresting any ringing of the outer driver flange and stiffens everything up nicely. Very Rigid once mounted to these mounting plates. We then insert a thick, foam rubber gasket between these mounting plates and the back side of the baffle proper. We then bolt these plates to the baffle with this gasket serving to decouple the two pieces of wood. This does a good job of limiting the direct transfer of vibrations from the driver to the baffle.

Another approach to this which is rapidly gaining in popularity is to create a constrained layer baffle using visco-elastics damping products such as 'Green Glue'. By utilizing multiple layered baffles with this Green Glue in between these layers, significant reduction in vibration is possible. Perhaps the most interesting approach to this challenge of limiting transfer of energy from the driver to the baffles is to simply not use the baffle to mount the driver to, thus eliminating any direct contact. This is accomplished by mounting the driver by some part other than the outer rim. One common method is mounting the driver by it's motor assemble or what has been called "Magnet mounting".

By using some other part of the driver to mount to, we are now free to use a much wider variety of baffle construction materials. We can make the opening of the baffle such that the driver simply fires through this hole but makes no physical contact with any part of this baffle. When constructed such as was just described we could call this new baffle a "Facade" to differentiate it's function from that of a structural baffle. This facade may now be made from very light weight material and no longer needs high mass to help damp vibrations. This facade idea is slowly growing and we will soon see many study builds with this as a main feature. The ability to easily and very quickly change facades is seen as a major advantage over a structural baffle. Trial and study can happen very quickly as could also simply changing facades at will for visual interest or possibly for fine tuning for a performance change.

One obvious swap would be when shifting from 2 channel music to multi channel Home theater use. We could instantly alter our tonal balance and soundstaging signature with a simple swap of a couple alternate facades. Vibration management extends to the driver assembly as well as the baffle. In fact everything that comprises our speakers should be viewed with a critical eye towards controlling the byproducts (vibrations) from the creation of our music. This would include any base or plinth we may want to use. It could also be a consideration when we look towards mounting the filter network('s) or any on board electronics. The stamped frame of the Performance Grade 15 "Silver Iris Coaxial is made from heavy gauge metal and is shaped such that it is quite rigid and stiff. This alone however does not guaranty that it will not ring, sympathetically vibrate or reflect energy.

Many advanced builders are looking at these surfaces and asking the logical question. "How can we damp these surfaces and also keep them from being so reflective?" The answers coming back to us from our builders is that yes improvement can be realized if the driver is fully damped and several products have been suggested. The basic idea here is to add "soft mass" Soft Mass is something that lowers the resonant frequency through mass loading and yet stays soft and flexible. Modeling clays, duct seals, rope caulk and automotive damping sheet goods head up this list of products that damp well, and are readily available, inexpensive and removable. Many builders are also covering surfaces such as these with felt in an attempt at eliminating reflective surfaces. We like to cover the back side of our baffles with felt to help eliminate the possibility of these surfaces being the sources for these secondary reflections.

Some of you may now be asking the logical question, "Does all of this truly matter?" I think that if we look at any one of these ideas, isolated to stand on it's own, we may notice little overall improvement. I also think that if viewed collectively, that when all of these measures have been incorporated that yes, they do offer real gains in performance. One way to permanently reduce basket vibration issues is to upgrade to a cast frame design and this is exactly what we have done on our augmentation bass driver and the New Sterling Grade series of drivers. These heavy cast frames are the definition of rigid and are quite massive. They could still benefit from covering in some non reflective material. 

long these same lines of adding additional mass to help control vibrations we can look at adding mass (weight) to any section of our speakers needing additional management. Adding mass does not really remove vibrations but shifts the vibration to a lower resonant frequency. The basic idea here being that a heavy object needs greater external force to cause it to move. If insufficient external force is provided the material in question will not move significantly enough to possibly produce any secondary sound. This holds up well until we come along and supply it with enough external force to actually excite it into motion. This can happen from the creation of low bass information at higher volumes.

One way of adding mass that also does essentially eliminate vibration is the use of sand or metal shot. While strictly speaking sand cannot eliminate the energy content of vibration it can convert this to another form of energy called heat. That's right. Each little grain of sand/metal bouncing into it's neighbor converts these vibrations into thermal energy via friction and exchange. Some savvy builders are using sand to damp their baffles and especially the base or plinth that the speakers rest on. Draw backs to any of these mass loading ideas is the additional weight and additional effort required to reposition your speakers. For many the end result is worth the added inconvenience when it come time to move them.

One last topic we should mention here is the mounting of the passive filter networks. The Silver Iris Coaxial units passive filter networks are mounted to a block of solid Mahogany. Between the components and this wooden block is 100 percent Silicon adhesive which both holds them securely and also is intended to act as a decoupling medium. Locating them as far from vibration sources as practical is always prudent. Some builders go an additional measure and further shock mount their crossovers. Double sided foam tape under them may prove sufficient. Building an isolation platform using sand and or air bladders has also been suggested. Bass extension, bass weight, bass authority bass slam, boom, crunch and bass articulation. Seems we are not at a loss for terms when it comes to our beloved low frequencies. To many people, bass energy is the heart of any music system. That driving beat that everything rides on. Open Baffle speakers have been notoriously bass shy and until recently never thought of as being very desirable if powerful low end response was on ones wish list.

Fortunately this is no longer the case. In fact powerful OB bass can be easily achieved and when done well is truly spectacular. Lack of enclosures and this dipole radiation pattern results in a very natural sound. Acoustic bass instruments radiate energy in a very similar pattern to that of our OB speakers. OB speakers fill our listening environments with direct and reflected sounds that have scale and ambiance clues that helps us imagine what size venue the original acoustic event originated from. Controlling all this energy potential should be high on the wish list of the advanced speaker builder. Everything that was mentioned in the previous section with regard vibration management need be ramped up and looked at with even greater attention to details. What could have passed unnoticed before will be glaringly obvious once we introduce these powerful low frequencies. Rattles that were never previously activated, now demand our full attention. Good mechanical practices here such as securely bolting everything down will go a long way towards ensuring success. Physical isolation of the Augmentation drivers may prove wise and mounting then to a separate baffle near ideal.

In our Duet style speakers that contain our full range coaxial and our Augmentation driver ( Augie) , we like to use two separate mounting plates, spaced well apart and decoupled from the main baffle and each other. This is done in hopes of reducing or eliminating any "cross contamination" that may come from mounting an Augie to the same speaker system that contains our full range coaxial. This Duet mounting style is very desirable for several good reasons but does expose the builder to the possible problems that come along with this pairing. We have many Duets, made by many different builders, all reporting very high performance. This should go a long ways towards instilling confidence that you too will succeed.

 

Soundstage And Soundscape
When someone mentions these words in the context of home audio they are generally talking about an illusion that is presented before us if certain conditions are sufficiently met. Soundstage, then is simply the illusion of a stage with performer('s) occupying space within or on this imaginary setting. It may be a real stage inside a studio, club, theater, performance hall, etc., or it may extend outside to include performances done in large outdoor settings. When seated in front of this illusion we can often perceive (imagine) Height, width, depth and distance to surrounding walls (ambiance clues). We may possibly even imagine the exact location of each performer relative each other and this illusion can be very convincing under the right conditions. This is what is being sought so intently by so many music lovers. We want to feel like we are sharing a space with the performers.
Some audiophiles focus their system on creating the illusion that while listening they are magically transported to the exact location that the original performance was originated from. " You are there" The idea of the sound fully encompassing this space is what we are talking about when we speak of our 'Soundscape'.

This is the landscape of our rooms both in front, to the sides and also to the rear of the listener. While it is perhaps easier to "surround" ourselves with sounds and paint a 3D soundscape with multiple speakers, it is also possible to experience a full soundscape using just the two front speakers. We obviously cannot recreate the rear channel effects of a true encoded surround system but we should be able to experience the illusion of the ambiance clues for hall size of a particular recording venue. Others seek a slightly different illusion and try to bring the performers into the listeners environment and imagine then right there in the room.

"They are Here": Both are fun and both can seem appropriate if certain conditions are first met by our systems.

In my main system for example, I like to try and create a listening environment that is conducive to bringing the artists directly into our home. Some recordings and some listening sessions align well enough that this illusion becomes intensely real, lucid and very persuading to experience. Open Baffle speaker systems seem to excel at this. Combined with the right mix of source and amplification we can approximate this illusion with some measure of repeatability. The real challenge with this is often found in the short comings of the listening environment and the speakers interaction with this space. In this section we shall look closer at our sound stages and soundscapes and see what our speakers have to do with all this.

When asked how to properly set up these OB speakers I like to start by going over a few preliminary guidelines for speakers in general and OB speakers in specific. Because of the intentional dipole projection of OB speakers we need to be mindful of this rear wave energy and try to utilize this energy source to it's maximum. One of the first considerations is distance off the "front" wall. I refer to the wall directly behind the speaker as the front wall. This is the wall we face while listening. I have seen this called the rear wall and it truly matters not what we call something so long as we are all on the same page. My "rear" wall then will be the wall behind the listeners head while facing forward at the front wall. Everything will be referenced from the listeners perspective.

In order for this rear wave to fully benefit our listening experience it needs to be delayed slightly so that it can be perceived as a separate sound contribution and is in fact different from the primary first arrival of sounds reaching our ears from the front of the speaker. It is generally agreed that this minimum delay should be no less than 6 MS or a spacing off this front wall of about three feet. We can reduce this some if we angle the speakers so that the energy wave strikes the front wall less directly on.

I will now go over wall treatments later in this section but for now we are focusing on arrival times of both this front and rear wave. Because of the stereoscopic nature of our two ear based hearing system we can hear a pretty convincing illusion of what is called a center phantom image. This then is when we falsely perceive a sound emanating from a mid point between our left and right loudspeaker. I refer to this as a false perception because we do not actually have a sound source setting between our speakers, although it sure can sound like we must. This center phantom image is best perceived when sitting equal distance for the right and left speaker. This is often called the sweet spot and with some speaker systems this optimum listening position is very small and one needs to remain very focused on keeping one's head in proper alignment and facing forward. We seem to need be far less critical of listener positioning when enjoying our OB speakers.

The distance apart from each other that we set up our speakers is also part of this initial setup consideration and the thing to keep in mind here is that this distance helps to establish the illusion of soundstage width. If for example you were listening to a Solo performer setting directly in front of you in real life, their sonic footprint would only be a few feet wide. If we add in a second performer we would need to allow for greater distance between them. This is basically how it works for our speakers. We need to space them far enough apart to help us create this illusion of their being physically enough room for all the performers we are enjoying. Fortunately we do not need to replicate a real stage 1:1 as far as width goes. Generally speaking we will find that a spacing of four to eight feet apart will work very well for most music, most of the time.

Listening distance is how far we set away from the front plane of our speakers. Near field listening is when we set quite close to our speakers. Far field listening of course would be a noticeably greater listening distance. I hesitate to give actual measurements because of the wide variance we see in the usage of these terms in audio articles. To me, near field is when you could easily reach out and within a step or so touch your speakers. Your setting 4-6 feet away, possible even closer. I have seen extreme examples that looked as if the listener were almost wearing the speakers like a giant pair of headphones. This can produce an amazing illusion and there are many benefits to a near field listening setup, especially in smaller rooms. I will touch on these in greater detail a little later on.

Far field listening then would be the polar opposite to this and would yield a totally different perspective and illusion. We see this distance being preferred whenever we try and recreate a large soundstage. If for example you wanted to recreate the energy of a large scale performance that was seemingly true to scale, we would want the greatest distance possible to all surrounding walls. We would also desire a wide spacing between our speakers and we would locate ourselves in a very far field listening position.

As you can easily guess, this style of listening is very demanding both of available listening room size and also equipment performance standards. The reward for providing these prerequisites will be a Grand Illusion indeed. The difference being similar to the difference between watching a small TV screen Vs. the Cinematic experience of watching a projected image on a comparatively huge screen. Between these two extremes we would find the majority of serious audiophile listening spaces. If we can position ourselves approximately the same distance from our speakers as the speakers themselves are from each other, we would be at a great starting position for further exploration.

Lets recap and pin this down to some real numbers. These following 'recommendations' are simply that and never to be considered mandatory for the enjoyment of music in our homes.
Speakers a few feet ( approximately three feet minimum) from the front wall.
Speakers several feet apart (wider = better).
Note: It is possible to get too far apart and thus experience imaging/soundstage issues.
Listener distance would be this width above, away from the front plane of the left/right pair.

Start with the speakers pointed directly forward. Listen to the overall sound and move them forward/rearward, wider/narrower until your soundstage illusion seems strongest. Think of this as one would think of the focusing of an optical lens. Make small and symmetrical moves and stop and truly listen before moving on. It is important to note here that every recording will produce a slight to widely varying illusion depending on how it was recorded. Some recordings produce a very holographic illusion and some do not. Take an average from several different recordings into consideration as you set up your speakers. Pay close attention to musicality or simply put, pay close attention to getting everything to sound real, as if the instrument was real and being played by a real person in a real acoustic environment.

First arrivals, second arrivals, reflections and their effects on clarity of illusion. In a real acoustic event we hear the sound that travels directly to our ears from the instrument. Same is true with our speakers. In a real acoustic event we also hear the sounds as they are first reflected off a surface in the room in which the sonic event took place and them subsequently we hear this same sound a multiple of additional times as it reverberates throughout the room.

Same is true of our speakers. Box speakers project their sound forward and having only one direction of projection can be called "Mono"-pole. Mono pole speakers have been used successfully for many decades and can provide a very accurate first arrival simulation. OB speakers project their sound forward and rearward and having two directions of projection can be called Di-pole. Dipole speakers have been used successfully for several decades and can provide a very accurate first arrival of sound and can also provide us with the energy needed to recreate the second arrival of sounds that normally arrive the listener via reflection off the front/side wall of the performance venue. This Dual pole projection, when well executed, has an uncanny ability to provide us with the clues necessary to fully engage our imaginations into this illusion of real performers right there in our rooms with us.

In the first part of this section we talked about the need to delay the reflected sound energy coming to us from the front wall. This delay allows our brains to be tricked into thinking that we just heard the real delay that would have been present in a real acoustic event. Throughout our lives we train ourselves through repetition of experience, what this delayed second arrival of sound, sounds like. We use this memory to help us judge how large a space or room we are experiencing when listening to a recording on our systems. Given the proper clues it is easy then to be tricked into thinking that what we are hearing from our speakers is somehow real. This illusion can be enhanced through proper focus and can conversely be diminished by careless execution of room layout or system setup. The energy coming off the rear of our speakers needs to be delayed and it would often be of further benefit to diffuse this reflected energy. Through diffusion we take the total energy and break it up into many, many smaller energy reversals. This, when done well further enhances the 3D quality of our soundstage illusion and balances out this reflected energy.

Coming forward we can also look at the reflected energy produced when the sounds coming to us from the front of our speakers interacts with objects between the speakers and listeners. This would be our rooms side walls, floor and to some degree the ceilings and rear walls. Try and imagine what happens to the sound as it is displaced and projected off your speakers. It travels outward and interacts with everything in our rooms.

The major areas to address in your speaker setup are the following areas:
Directly In front your speakers
Directly behind your speakers
Directly between your speaker

The secondary, yet still very important areas to address in your speaker setup are:
Side wall in front of your speakers.
Floors in front of your speakers
Phantom center image area both in front and also to the rear of the speakers
The speakers themselves.

We could spend considerable time going over the above areas and look at each one individually and would gain considerable insights with this study. Much of this has already been written and can be found easily by anyone seeking additional information on the subject. I would like to take just a brief look at the last item on our list above. The speakers themselves reside in our soundstage area and can effect the movement of energy throughout this area. If we think about this for a moment we can see the need to take baffle size and composition into consideration. We would, for example wish to avoid overly large baffles as they can block or shadow the program energy arriving from the reflections off our front wall. (Large baffles in above average size listening rooms being a possible exception from the rule). The baffles can also be a source of reflected energy and it would be prudent to study this as a potential upgrade path. If we could limit the amount of reflected energy coming off our baffles we would as a result hear more of the primary sound projected by our drivers and less sounds from other sources such as the other speaker, reflected sounds off side wall, front wall, rear wall, floors etc.

When hearing more than one sound, coming from the same general area, we often find this composite of sounds slightly confusing. We are being asked to split our attention between two or more sounds and this can also cause some fatigue. This is most noticeable in the upper mid range and treble frequencies. Because of the nature of our hearing we can pinpoint sources of these sounds fairly accurately. That is, until we hear two or more competing sounds from the same source. Composite sounds require greater focus and concentration to mentally disassemble and this can lessen the enjoyment of the experience. Much in the same way we deal with these reflections from our listening room walls, so to could we treat our baffles. We cover our production baffles with felt and finally speaker grill cloth in hopes of lessening any reflected secondary sounds. We do this on both the fronts and rears of our baffles. I realize that to many speaker builders, the desire to showcase our woodworking trumps any benefits gained from the reduction of reflected secondary energies. I mention this here to complete our overview of soundstage considerations and share our design insights on our production speakers.

I hope you have found this information helpful and also serving as inspiration. For many, the desire to own a high fidelity speaker system is often held at arms reach because of the resource demand these systems often represent. By building our own Open Baffle speakers we can experience very good performance and also experience the personal satisfaction from having created something of considerable reward.

You can do this,

Darrel Hawthorne Of Hawthorne Audio

 

Reviewed!
Hawthorne Audio Sterling Silver Iris Duet Loudspeaker
A hand-crafted easy DIY speaker project... or assembled!
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