In wall versus standard speakers

    I was prompted to write this little essay by finding many sites had a similar essay that was simply copied from the Crutchfield Advisor. The way I could tell the information was copied was that they repeated the same wrong information. Basing your speaker buying on wrong information can lead to a choice of speakers that is less than satisfying.

    Now Crutchfield is a big company, and you are probably wondering what they are wrong about and how I know. This will have to get a little technical, but has a direct bearing on whether to choose in wall or standard speakers.

    The first issue we will deal with is efficiency. The fact is, for the best bass response out of a particular driver size, a speaker in a correctly designed box will always be the winner (this does include speakers placed in wall in a box, provided the box is designed for the exact make and model of speaker used). Here is where Crutchfield is flat out wrong. If you wish to skip the somewhat technical discussion about why, and get on to the meat and potatoes of the comparison, skip down to the next section.

Somewhat Technical Discussion

    One reason that an in wall driver usually can not compare in bass response to a properly designed box system is one of system efficiency compared to a ported cabinet design. An in wall speaker is an example of what is termed an infinite baffle enclosure, which may approach an acoustic suspension type depending on the wall it is going in, etc. What this means is that the energy from the back of the driver is absorbed and lost. In a bass reflex system, one of the very common enclosures for box speakers, the back wave from the rear of the speaker cone is ported out in such a way as to reinforce the energy from the front of the cone. This results in a large increase in efficiency, and also makes more usable bass at the lower frequency's. No, you can't simply drill a hole in your wall to get the same effect! A ported system is very carefully designed to resonate at a particular frequency that also damps a peak at approximately the free air resonance frequency of the driver. This results in decreased distortion from the driver. The variables include the mass of air in the enclosure, port length and width, and the Theile Small driver parameters of the particular driver. For more information on enclosure types see our basic discussion paper:

    Theile Small parameters and their application are the other reason in wall speakers can never outperform a correctly designed box speaker, even if the box speaker itself is acoustic suspension, tuned labyrinth, waveguide or one of the other numerous designs. The parameters developed by Theile and Small correctly predict the performance of a particular speaker driver based on several mechanical and electromagnetic factors of the driver construction. These include the magnetic field strength of the magnet, mass of the cone material, resistance of the spider construction, resistance of the voice coil, resistance to motion of the surround on the cone and other factors. The amount of variables make the Theile Small parameters unique for each driver. THese parameters will  even vary between supposedly identical drivers of the same make and model.

    What these calculations add up to is that for each type of enclosure (I:E: bass reflex, acoustic suspension, etc), there is an exact internal volume where the driver will perform the best. Too large of an enclosure and you lose power handling capability and the bass becomes flabby and loose. This is because in most box enclosure designs a precisely calculated volume of air provides additional damping to the driver element. This helps prevent inertia from having it's way with the cone, since the cone wants to continue moving forward (or backward) after the electrical signal tells it to reverse direction.

    Conversely, too small of a box makes a bass peak at a higher bass frequency, and it will become boomy sounding, as if the driver was in a barrel. You will also lose low bass response.

    ALL speakers, even in wall, have the Theile Small parameters and (if used enclosed and not in free air as a dipole design, which requires precise bass equalization) would respond best in an exactly tuned enclosure. This implies a known volume of air, in addition to a known and precisely tuned amount of damping insulation, and a known construction. I should add at this point that some dipole designs are boxless and work very well. In addition some manufacturers such as Polk Audio make an in-wall box that is tuned correctly for the particular speakers to be used in it. These work well, providing they are matched to a specific speaker and not a generic version. Another wild card with in wall construction is the vibration of the wall around the speaker. The more rigid a speaker enclosure, the better the sound, for various reasons we will not delve too deeply into. The fact is, the wall vibrates, and the speaker designer of an in wall speaker has no way to accurately predict how much wall motion there will be, and so can not compensate in the design of the speaker. Let me add that this is not all theory, but is borne out in practice. We have years of experience in performing custom installations of in wall and standard speaker systems to draw on. One last factor I should not omit concerns diffraction effects. These effects are due to a large baffle (the wall) surrounding the speaker. To oversimplify the issue, reflections from the wall around the speaker cause peaks and dips in the frequency response. (A closer analogy would probably be the way light bends when it meets water.) This is diminished in box speakers nowdays by using a small front surface surrounding the driver, and chamfering (rounding) the cabinet edges, among other things.

    The bottom line is that the designers of in wall speakers can never accurately predict the environment or the placement of the speakers, so can not optimize the design to perform at it's best. All they can do is take their best guess at the environment, and try to compromise to get the best overall average response. In the design of box speakers, at least one of these factors, the enclosure environment is under their control and can result in a precisely optimized system. They can even voice the speakers for certain types of placement, for example near a wall, and recommend that in their instructions. If you have read our guide on speaker placement you know that the proximity to a corner or another wall (or ceiling) for in wall speakers affect the sound quality by a startling amount.

    All that said, in wall speakers can sound very good.

Some advantages are:

• You don't have to pay for the box surrounding the speaker, so the driver and crossover quality can be better for the same price.

• All the wires are hidden in the wall.

• Increase the resale value of your house.

• No large speakers to clutter up your living room.

• Grilles can be painted to match your walls. This makes the speakers unobtrusive and almost invisible.

Some Disadvantages

• As described above, less overall performance is possible.

• You can't easily move them if you want your entertainment system elsewhere.

• If you want to upgrade speakers to a better model you may end up doing some drywall work.

• You can't easily upgrade to better speaker cable.

• You can't easily take them with you when you move.

• You don't know for sure how they will sound in their location until holes are cut and they are installed.