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Where should I put my speakers?
Can I beef-up my crossovers?
I’m not getting the 3-D sound imaging I expect from my system.
After listening to my system for a while, I get tired; not satisfying any more.
What Speaker cables do I need?
What is Bi-amping?
Are bass reflex speakers better than sealed or air suspension speakers?
where should I put my speakers?
The industry recommends that you set up your speakers as shown in the diagram below. This configuration does not show any walls or other structures and unless you are building a room to suit, there will most likely be problems with walls, speaker locations and room functionality.
The objective should be to place the speakers around the seating area with the tweeters at ear level. Try and get the distance between the center of the seating area and each speaker as close as possible to help balance the sound stage. Obviously, if there are many seats or they are spread evenly around the room you cannot get ideal sound stage in every seat. In these cases you have to settle for a “sweet spot” and dial the sound in for that seat.
Deviations from the ideal “surround” configuration can be improved using channel delay and level settings on your sound processor. For instance, if the left hand speaker is an extra 10 ft further away than the right hand speaker, a delay of 8-9ms applied to the right hand speaker signals would match the delay of the extra pathlength and align the stereo image. A small level adjustment ~1dB may be needed depending on room acoustics. Most high quality sound processors have individual channel settings for these parameters.
Some compromise will be needed for home theater vs music. When you’re watching a movie, you want the left and right speakers in tight against the screen whereas for music you typically want a wider separation. In most cases, however, the room will dictate the position of the speakers.
A word on speaker lobing. Most speakers tend to beam slightly downards, i.e. the peak in the directivity response points towards the floor. This is due to the acoustic center of the tweeter being slightly forward of the woofer. Certain types of crossover design can also cause this. You may notice an improvement in sound quality by tilting the speakers back a bit; a paperback under the front of the speaker will allow you to audition the effect, a little imagination may be needed for a more permanent solution. Take care that the speakers don't become unstable and topple off their stands!
Subwoofers are fairly flexible in their placement as there is little directional information in the bass frequencies. However, they are very sensitive to corners and you will find that the gain in radiation efficiency from pushing the subwoofer into a three-way corner (floor + 2 walls) can make the bass very boomy. Experiment with placement for your preferred sound and then tune with the level control.
Can I beef-up my crossovers?
Crossover design is the hardest part of loudspeaker design and generally. unless you can hear a problem with the speakers, they’re fine and you’d be best advised to leave them alone. That’s because the inductors and capacitors have an “effective series resistance” or ESR that is actually part of the crossover design. Upgrading to bigger and better components usually means reducing the ESR which most likely will degrade the crossover performance in some way either messing with the frequency response or spoiling the time alignment.
I’m not getting the 3-D sound imaging I expect from my system.
Stereophonic reproduction is capable of excellent sound imaging. In a well designed and installed system the sound will seem to come from thin air with individual instruments each having their own location. The sound stage can extend well outside the area between the speakers both horizontally and vertically. When this spaciousness or openess is missing it is usually due to phase distortion although room acoustics can also degrade the imaging and spaciousness of a sound system. If you think about how you localize sound, it is by two very subtle techniques. First, the difference in sound arrival time between the left and right ears is sensed and secondly, the high frequencies are heard differently between the two ears due to the folds and features of the ear pinna and masking of the head itself. Any error or distortion in the time alignment (i.e. phase response) or the high frequency response will cause the stereo image to collapse.
The top offenders in the phase distortion department are: graphic equalizers and crossovers.
In almost all cases a graphic equalizer should not be used in a music or home theater system. Their basic design of a bank of high Q filters means that each band will suffer considerable phase distortion and the final phase response of the reconstituted signal is completely uncontrolled. Phase can be considered as delay; a phase shift being equivalent to a time delay. When you delay different frequencies from a particular instrument by different amounts you will confuse the left-right ear locating mechanism and degrade the imaging. A lot of people add a graphic equalizer to try and fix a different problem usually with the speakers and the room and in the process end up making things worse. The best idea is to take all unnecssary sound processors out of the system, run all tone controls in their flat setting and see if the problems or inadequacies in the sound quality can be attributed to a particular speaker or room feature. Then you have a chance of fixing the problem rather than trying to cover it up.
Problems with speakers and crossovers are a little harder to remedy, usually because you need precision measurement and analysis equipment. Passive crossovers are very difficult to design well especially when trying to achieve linear phase over the crossover region. Typically, the higher the order of the crossover, the more phase error introduced into the sound. The components used in passive crosovers have their phase responses and frequency responses locked together and the design of a phase compensated high order filter is not for the feint of heart. A much better approach is through the use of active crossovers and in particular active digital crossovers.
After listening to my system for a while, I get tired; not satisfying any more.
Listener fatigue is very common and a lot of the time not even noticed. You just get tired of listening, blame it on your boring music collection and go and do something else. I have owned many mediocre sound systems in my past and they all suffered from this problem. Yet a really good sound system just begs to be listened to; you have to try just one more CD and before you know it, many hours have passed.
Listener fatigue is caused by distortion, poor frequency balance and over-bright room acoustics. In effect, the ear is working too hard to make sense of the sound; trying to hear the quiet sounds that are masked by the overly-loud ones and identify the instrument sound in a field of reverberation.
What Speaker cables do I need?
There is much advertising done on speaker cables and a lot of it is hype and bad science. In most cases, 16 gauge stranded copper is perfectly adequate for power levels up to 100Watts and cable runs of up to 50ft. If you have a very temperamental amplifier such as an esoteric tube amplifier or speakers with complex crossovers that present difficult loads to drive then you may hear some improvement from different types of cable. The variations in resistance are pretty small, 10’s to 100’s of milliohms, but the inductance of and the capacitance between the two conductors can interact with crossover function when used with a high output impedance amplifier.
I would start with 16 gauge twin and then audition other types of cable. I would only spend big bucks on expensive cables if they were demonstrably better. Personally, I think there is better value in spending the money elsewhere.
What is Bi-amping?
Bi-amping is when you use two amplifiers for each speaker. The idea is that you get rid of the passive crossover altogether and use an active one after the preamp and before the power amplifiers. While it is possible to bi-amp a three way speaker (woofer, mid & tweeter) the best approach for these speakers is tri-amping (three amplifiers per speaker.) One of the key advantages to bi/tri-amping is achieved through having a single driver wired to it’s individual amplifier.
Advantages include:
-Improved speaker damping.
-Eliminate interaction between drivers.
-Eliminate dynamic energy storage in crossover.
-Much easier load for the amplifier to drive, amplifier runs cooler.
-Ability to match amplifier power to requirements for each driver.
-Greater flexibility in crossover design.
When you implement the active crossover using a digital crossover you can also achieve these additional benefits:
-Perfect time alignment and phase linearity.
-Ability to correct imperections in driver response.
-Ability to tame room resonances.
Digital active crossovers used in conjunction with bi/tri-amping techniques offer the potential for previously unachievable sound quality.
Are bass reflex speakers better than sealed or air suspension speakers?
Bass reflex speaker designs incorporate a port to allow sound from the back of the speaker cone to mix with the sound from the front. The cabinet and port is tuned to a frequency below the low frequency roll off of the speaker driver and can extend the driver response by almost an octave. In this way a small bookshelf speaker with a driver roll off of 80Hz can be bass extended to match an equivalent 10” speaker in a sealed cabinet. This is not for free of course and the compromise is time coherency at low frequency and problems with turbulence in the port (sometimes called “huffing.)
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