B&C 10" Mid-Bass Comparison

In this blog post I compare two 10" woofers from B&C.  The 10NW76 and 10HPL64 are very similar with a few exceptions. 

B&C 10NW76

B&C 10HPL64

Differences:

  • The 10NW76 has a 76mm voice coil diameter versus the 64mm on the 10HPL64
  • The 10NW76 has an aluminum demodulating ring to achieve "very low distortion" according to B&C.  General information on this feature can be found here.

Why compare these two? 

As I test various drivers I've started to see a consistent pattern where any driver that uses copper shorting rings, aluminum demodulating rings, or a copper cap on the pole piece, consistently outperform drivers without these features in terms of sound quality both subjectively and with test data.  This is regardless of listening level (SPL) and seems to benefit the entire frequency bandwidth of the driver.  My goal is to establish a robust test method that highlights the difference between drivers in terms of the benefits demodulating features provide. 

Applications

These drivers can be mounted in large 2-way stand mount speakers with subwoofer support or in larger 3-way or 4-way floor standing speakers.  An example of this would be Troels Gravesen's  'The Loudspeaker' found here

A note on testing

Like all my blog posts they are always in the context of home stereo listening.  This means I focus on sound quality related to listening levels of around 80dB SPL at the listening position.  

Test Setup

For this test I built a test enclosure out of 24mm thick baltic birch plywood.  I decided to go with a sealed enclosure to best represent the intended configuration.  The test baffle was made 60cm x 60cm wide to represent the speaker's baffle.  

The internal volume of 7 liters created the following simulated parameters for the 10NW76.

Once built I ran an impedance sweep on the 10NW76 to confirm alignment.  The resulting impedance sweep is shown below.  

With the exception of the driver mounted in a sealed enclosure, the impedance matches closely with B&C's published data shown below.  Notice how the small impedance imperfections match my results closely.  

 

Measurements 

Frequency Response

I began by running a frequency response test measured at 1 meter.  The 10NW76 shows a ±3dB variation with a gentle falling response and providing a frequency range from 120Hz – 3kHz.   Developing a passive crossover on the 10NW76 would not be too difficult.  My 60cm wide test baffle seems to be providing excellent reinforcement up to 500Hz.  This should provide a nice 'full' sound especially on male vocals. 

The 10HPL64 shows ±4dB variation and a 230Hz – 4.2kHz response.

Harmonic Distortion 

Generally the 10NW76 has about 35-40% less harmonic distortion as can be seen below. 

Step Response

Step response from both drivers see a near vertical rise profile.  

Burst Decay 

Burst decay sees clean results from both drivers. The 10NW76 is cleaner a little higher up (3kHz) versus the 2kHz on the 10HPL64. 

Off-Axis Frequency Response (Polar Map) 

I conducted an off-axis measurement in 5 degree increments to establish my coloured polar map.  This shows the the driver has the following polar characteristics:

Gradual narrowing starting at 1kHz with an 80-degree listening window at 2kHz, narrowing to 40 degrees at 4kHz.

This means you could potentially use the 10NW64 up to around 1.5kHz before the off-axis coverage starts to narrow too much.  Alternatively you could horn load the driver or mount the driver behind a vertical slot opening to increase dispersion and potentially cross at 2.5 or 3kHz. 

Intermodulation Distortion

I measured intermodulation distortion for both drivers and compared them against each other below.  The 10NW76 outperforms the 10HPL64 in overall clarity.  My reference target for IMD is <0.50%IMD (-46dB) for audiophile sound quality.  Anything better than this is a bonus and is audible from my subjective listening.  The 10NW76 is a full -70dB down at 225Hz representing extreme clarity.  

To add some context, here is how the Seas FA22RCZ 8" full range driver performs (Grey line below).  While the Seas also achieves my target for low distortion, both B&C drivers excel against the Seas.  I even tested the new SB Acoustics SB15NRX2C30-4 5" Woofer and it achieved similar results as the Seas (not shown). 

Conclusion 

If you are looking to achieve ultra low distortion mid-bass, the B&C 10NW76 is a good choice. 

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