8 inch medium test, 18Sound vs B&C
The 8" Mid
We will test several 8/9.5" midrange drivers in this article:
- 18Sound 8NMB420
- B&C 8MBX51
Raw Response 2.84V/1m
Distortion
All measurements have been done at strictly the same SPL, 95 dB SPL, and with EQ flat across all the measured bandwidth.
For these cone drivers with similar emissive surfaces (Sd), the main source of distortion will be the breakup effect. Therefore, we should carefully examine H3 and H5.
H3
H5
All perform well in H3 but should no be cut so high even if they are midrange drivers.
There is a peak in the H5 measurement for the 18Sound unit, indicating an unwanted sound frequencies around 2500/2700Hz produced. It’s related to breakup, this H5 peak is a little bit too high.
Distortion with Air core inductor
We will measure distortion with and without a 1.2mH air core inductor, to reduce the driver breakup impact on distortions when possible, as seen in speaker breakup article.
In essence: We use Back Electromotive Force principle with an air core inductor that will increase gradually the impedance (affecting the voice coil) and linearize the woofer in the same time, it works very well if the woofer is already rising up in his final box and need linearisation.
It will reduce a lot H3 and H5 distortion related to breakup.
Distortion measurements are still done in the same condition, all drivers are EQ flat to be compared : The SPL is the same on all the bandwidth, for all drivers, with and without air core inductor, the difference with and without air core inductor is not due to SPL but to Back Electromotive Force principle, as explained in our dedicated article.
H3
H5
As these speakers exhibit a significant rise in their frequency response, they demonstrate a substantial improvement in H3, making them very suitable for ’true midrange’ applications. However, the H5 peak remains present in the 18S model.
Temporal measurement on woofer
All are perfect here, the only things that we can see is the breackup arround 2.7khz, but the distortion rise and directivity mismatch will dissuade you to getting close to this frequency.
Images are not published due to their limited usefulness.
Conclusion
The 8NMB420 exhibits some counter-performance due to its significant cone breakup, but this will likely be noticeable at very high SPL.
Considering its price the B&C is very interesting.
Important Note: All these drivers are considered as midrange-capable only. Even for the tests conducted, substantial low-end EQ was necessary to achieve a flat response. 200Hz already represents a very low frequency for these drivers.
These filters, implemented using linear-phase (IIR filters), will influence both Group Delay and phase, allowing for their linearization in the low-frequency range.
