Speaker No.1680

Speaker No.1680

In this blog post I feature speaker No.1680 which is a 2-way utilizing a SEAS 10" woofer and 1" compression driver. 



I custom designed and built speaker No.1680 after a build commission by a customer who was a turn-key build that offered reasonable sensitivity, deep bass, and outstanding sound quality. I came up with this design from my own inspiration. The project uses the SEAS CA26RFX 10" woofer which offers 90dB sensitivity and 30Hz bass extension. The high frequency is handled by the RCF ND350 1" compression driver using a 1.5kHz crossover point. The RCF uses a 1.7" diameter voice coil and polyester diaphragm. The front baffle is CNC machined from a solid stock piece of walnut hardwood and fully integrates the ES-800 biradial horn for a smooth frequency response. You can see the time lapse of the baffle being machined HERE. The rest of the enclosure is made from 1" solid walnut. 



Below is the frequency response measurement showing the overlay between the LF, MF, and port output. 

Below is the impedance sweep. The impedance minimum is 7.9ohm at 100Hz. The cabinet tuning frequency is 32Hz. 

Below is the burst decay and CSD plot. 

Below we see the step response which shows good physical time alignment between the woofer and tweeter. 

Below is the off-axis coloured polar map. We see a well behaved off-axis with good pattern control down to 1kHz. Coverage remains wide at 90 degrees right up to 16kHz. 

Looking at the same off-axis result but with the waterfall graph is shown below.


Below we see harmonic distortion at both 85dB and 95dB test signals. 

Distortion remain below 0.50% at 100Hz even at 95dB, a good result. 

Showing the same as above except in dB scale instead of percent is shown below. The SEAS CA26RFX 10" woofer offers great bass performance. 

Intermodulation Distortion

I test IMD at 85dB and 95dB test signal levels. I also tested low and high frequency bands. 

The low band at 85dB shows -60dB at 100Hz rising to -55dB at 500Hz. However distortion improves through the midrange at -73dB at 3.3kHz, an excellent result. 


At 95dB we see -53dB at 100Hz rising to -48dB at 500Hz. However distortion at 3.3kHz is unchanged at -73dB. 

Looking at the high frequency band we still keep the bass modulating tones in place. At 85dB we see the entire treble region at -70dB. 

Distortion in the treble region still remains low even at 95dB. 

Crossover Development 

The crossover ended up being a relatively simple affair. Below is the crossover schematic I ended up with after extensive listening. 

The high frequency was relatively easy to deal with since the raw frequency response was very well behaved as you can see below. 

The woofer was also pretty easy to deal with. It produced prodigous bass and was a pleasure to work with as you can see from the raw response below. 

Subjective Listening

I am completely thrilled with the sound coming from these speakers. The 10" woofer has all the dynamics and tactility of a good pro sound 10" or 12" woofer, but with more refinement, deeper bass, and much more musicality. It doesn't seem to struggle reproducing the midrange frequencies from 300Hz to 1.5kHz, instead it sound warm and full, with textured deep bass. The integration with the high frequency horn is completely seamless in terms of transient response and clarity. The speaker sounds extremely balanced with timbre being natural and authentic. The sound changes very little when you move off axis, with a natural falling of overall output across it's frequency range. Even if I walk out of the room it still sounds like there is a person singing in the next room, which means the overall power response into the room is quite even. Overall I am extremely pleased with the overall sound quality from these speakers. 


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