KLH Model Seven incl. stands, pair floor standing speakers KLH Model Seven speakers are a larger alternative to Model Five and Model Three that were inspired by the original Model Seven as introduced in 1960.

This improved version of Model Seven is a floorstanding, three way acoustic suspension design, with a 1” aluminium dome tweeter and a 5” midrange unit. The woofer is a 13” unit with a paper cone and a reverse roll rubber suspension.

The cabinets have a classic design and is made of 3/4” and 1” MDF. Additionally, there is a three position acoustic balance control. This new model Seven is available as a matched pair with mirrored drivers. A built in riser-stand tilts the speakers toward the listener.

Rugged enclosure
The Model Seven enclosure has been made more rugged than the KLH model 5. The baffle is made of 1” thick MDF. There is also a riser base that tilts the speaker up slightly. The internal bracing has been improved making this a heavy speaker.

Tweeters
Model Seven’s tweeter is a 1” aluminium domed unit with a soft rubber suspension. Metal domes are more rigid and lighter than silk dome tweeters. There is some debate around soft dome versus metal dome, but properly engineered metal dome tweeters can be as smooth as silk domed types. There are also other tweeter designs that are not based on a cone. These are known as ribbon tweeters and have a better dispersion pattern in the horizontal direction. Sometimes hybrid designs are used, with both a domed unit and a ribbon unit. In this case, the aluminium domed design is a perfect match for the woofers.

The crossover
Crossovers have also been improved using computer modelling for the best sound. A crossover is used to split the audio signal into bands, for feeding to each driver. The crossover frequency is set by creating filters using capacitors and inductors. The crossover needs careful design, to best match the drivers and is often done by computer modelling, as well as experimentation. The bass/midrange crossover frequency is usually in the range of 20 to 120Hz, while the mid/high crossover is in the range of 2 to 4KHz.

13” woofer and speaker design
The woofers are large 13” units with a pulp/paper cone and reverse roll rubber suspension. They feature a 2” diameter voice coil. These are made of several precision made components. The first is the basket – which holds the speaker cone and the magnet assembly.

Next comes the spider, which holds the cone and returns it to its original position. The surround also plays a part in this and Model Seven has a rubber surround that is more flexible than the paper part of the cone. This results in a faster response and better transient response. The magnet is usually a fixed type and made of iron. However, there are also more modern materials that have a better performance.

Finally comes the voice coil – this is wound around a circular former, at the end of the cone. This then sits inside a circular groove in the magnet. When an audio signal is applied the current causes the cone to move air and create sound. Finally, speaker coils have impedance ratings, usually 4 to 16 Ohms. This is not the same as DC resistance. Impedance is frequency dependent and made up of resistance, capacitance and inductance.

Model Seven Improved
The original Model Seven debuted in 1960 and was not produced in large numbers. The spacious sound was well liked however the price was a problem as was the large size. The large size gave good bass response but a more powerful amplifier was needed. This resulted in increased distortion. Finally, the two tweeters produced good high frequency dispersion.

The new version has been improved in all possible aspects and with an abundance of power amplifiers available today, matching is less of a concern. This latest design uses all new modern design paradigms for a full and smooth sound and is an excellent choice for a larger sound over the smaller Model Five.