Many loudspeaker designers – passionates – attempt to construct a time coherent speaker at some point in their lives. After a fiasco of such attempts – most designers consider such speakers to have more disadvantages than assets. Sometimes in-depth, but very theoretical, studies on this topic appeared, for example in AES materials. However nobody provided a “recipe” for proper, non-compromised, construction of such a loudspeaker. Today the sense of this design is many times questioned, both by engineers as well as people judging based on listening to speakers. Our response to the engineers is as follows: Measurements means not only frequency response, impedance curve but also voltage impulse response. It cannot be claimed in any way, that if a speaker responding to voltage impulse in no way related to the actual signal provided “measures well”. The response for the second group is also easy: Place our speakers next to others (where the designer believed in high order filters) attach them to a class hardware and put some well recorded acoustic music.
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The Time Coherent is our solution to the creating a time coherent speaker problem. Designing it we based on our long-term experience, when we came to the following conclusions about time coherent speakers:
1. A loudspeaker where the speakers are mounted on one plane tilted by about 10 degrees has the following shortcomings related to the need of the individual speakers to cooperate in a wide range at the cross-over frequencies:
- While listening from a distance smaller than 3.5m downfalls in the frequency response reaching -10dB at a range of 1.5m
- Bad frequency response characteristics when listening above the tweeter axis
- Increased distortion due to the too large cross-over overlap of the speakers
- Too low impedance at cross-over frequencies
2. A loudspeaker which has its drivers mounted on a plane tilted by about 20 degrees has one major disadvantage: The frequencies above 15kHz are lowered at the main axis even by 10dB.
3. Using an electrically second order cross-over in the high frequency part causes a substantial degradation of the treble. Our solution is free from such disadvantages:
- The tweeter is placed vertically
- The acoustic centers of the speakers are exactly at the places they should be
- Inclining the midrange driver by 30 degrees makes the frequency range where the membrane resonances exist to be significantly less audible at typical listening height
- High quality of the midrange driver in the 2000-4000Hz allows to make the cross-over cut at higher frequency and alleviation of the tweeter load
- The design of the SEAS tweeter (among others the low resonance frequency, the setup of the ultra-short coil and long slot) guarantees, that the increase of distortion while using a first order filter will not exist, although it is present in many, even very expensive, tweeters.
Closed or bass-reflex enclosure?
The Time Coherent series is designed to work in both settings, bass-reflex or with closed vent (vents).
In general we think, that a bass-reflex speaker, in a professionally prepared room and with proper positioning will give better results than a closed enclosure. The advantage of a closed enclosure is in many cases (especially in larger rooms) is illusory, although in a small room, near the corners, this type of enclosure might give better results.
Closing the bass-reflex vents we achieve:
1. Less bass in the range provided by many recordings
2. More of the extremely low bass (very rarely present in disc recordings)
3. Improvement of impulse characteristics in the bass range
4. Increase of speaker movement amplitude in the range typical for many recordings, thus increasing non-linear distortion
Connecting to the amplifier:
The loudspeakers should not be connected to amplifiers not working in a stable way with 4 Ohm load (Marcus, Keith, Dobermann Grand) or 6 Ohm (Dobermann). In case of amplifiers with separate terminals for various loads the speakers should be connected to 4 or 2 Ohm terminals.
Bi-wiring:
We encourage experiments. With proper system configuration positive effects can be achieved.
In our speakers the tweeter and midrange is connected to the upper terminals, and the woofer to the lower ones. The cross-over frequency between the sections lies at about 500Hz.
The following rules should be obeyed:
1. The cables to the upper and lower terminals can be of different manufacture and length.
2. The cables right and left in the pair should be exactly the same.
3. The cramp between the terminals should be removed
4. The upper section requires a higher quality cable (may be with lower diameter)
5. A low diameter cable should not be used for the lower section.
Bi-amping:
Let us distinguish two cases:
1. Two identical power amplifiers (set-up identically) – we encourage experimenting. In most cases the results are promising.
2. Two different amplifiers (eg. Tube for the upper section and a transistor for the lower section). Without proper technical knowledge and at least the simplest measurement equipment we HIGHLY DISCOURAGE EXPERIMENTING in that case.
Different power amplifiers have different sensitivity, some can also invert phase. Proper set-up of such a system requires measurements.
CAUTION! While bi-amping the clamps should be removed in any case!
Listening room:
In general we dissuade over-dampening of the room with the aid of sponge “pyramids” or curtains. We also do not recommend any resonance structures (especially without measurements and acoustic project).
We also do not recommend digital acoustical corrections with analog or digital devices.
We do recommend the usage of large amounts of dispersive elements, diffusers, thick carpet on the floor, dampening the treble as well as the midrange.
In rooms used not only for listening to music book shelves can be used (with uneven spines)
Features
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Toroidal coil in the bass circuit
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Tape coil in the midrange circuit
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Tin SCR capacitor in the treble circuit
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Mills resistor in the treble circuit
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Polypropylene capacitors used for impedance linearity in the bass circuit
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Tape conductors in the bass/midrange circuits
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Bitumen covered cabinet interior
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Dampening with polyuretchane molders
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Bi-wiring, bi-amping
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Internat reinforcements of the enclosure
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Cross-over in a seperate chamber
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Printed circuit covered with silver in the midrange/treble PCB
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Kimber TC wires in the treble circuit
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4 Mills resistors in the midrange circuit
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Massive supports under the stainless steel spikes
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