In this blog post I test a new back loaded horn (BLH) cabinet that I designed and built. BLH No.2095 is part of a 3-way system I've developed. But this blog post focuses on the objective test data comparing two drivers...
15" Drivers Tested
- Beyma 15LX60V2 ($370 USD each)
- Supravox 380EXC Field Coil Woofer ($1,370 USD each)
Back Loaded Horn No.2095 Features
- 30mm thick birch plywood with birdseye maple veneer
- 15" bass driver
- 40Hz bass extension
- 580mm wide x 630mm deep x 960mm high
- Solid birdseye maple driver cover (decorative)
- Laser engrave brushed nicket rear decal terminal plate
Measurements
Below is the measured frequency response set to 2.83v (1w) at 1m on axis with the driver. This is with the speaker positioned in the middle of my test area. The Beyma is shown in green while the Supravox is shown in red.
I've overlaid the impedance sweep as well (blue) for the Beyma.
There is the expected cancellation dip at 80Hz with a summing peak at 140Hz. I should note that this exists only on-axis with a 1m mic distance. Changing the mic position only slightly will significantly alter the response in this region, as can be observed by the resulting responses shown in the distortion plots where I positioned the mic between the driver and horn mouth. Also worth noting is that the rear wall boundary reinforcement will bring up the bass frequencies which can be observed in the distortion response graphs, where the cabinet is positioned 1m from the back wall.
Distortion
For the distortion measurements I setup each cabinet side by side so that I could quickly change inputs as well as mic position. This reduced the risk of unexpected variables in my test setup. 
Intermodulation Distortion
Using a 12 band per octave test signal ranging from 50Hz to 2kHz, I positioned the mic between the driver and horn mouth to capture both outputs. The mic was positioned pointing upwards slightly (see photo above). The test SPL was set to 85dB at 1m and then repeated at 95dB SPL.
85dB Beyma
The Beyma provided -63dB IMD performance for the 150Hz region.
85dB Supravox
The Supravox provided -54dB IMD performance for the 150Hz region.
95dB Beyma
The Beyma provided -53dB IMD performance for the 150Hz region.
95dB Supravox
The Supravox provide -50dB IMD performance for the 150Hz region.
Harmonic
I tested harmonic distortion with the same method for IMD except I calibrated the test SPL to the 400Hz region and then ran the sweep.
Beyma 85dB
The Beyma remains below 0.10% for the 100Hz region rising slightly above 0.10% for the 200Hz region.
Supravox 85dB
The Supravox provides similar performance to the Beyma except for a bump in H2 centered around 80Hz where we see almost 1% distortion.
Beyma 95dB
For the higher test SPL we see the Beyma rising just slightly above the 0.10% mark for the bass region.
Supravox 95dB
Again, we see H2 pushing above 1% for the 80Hz region. Otherwise H3 and H4 remain low.
Conclusion
It's difficult to measure bass frequencies indoors due to all the reflections. It should be noted that the response would change significantly just by moving the mic position slightly. So I can only conclude certain things with my test data:
- Very generally, expect 100dB+ sensitivity from either the Beyma or the Supravox.
- The Beyma was flat to 40Hz while the Supravox was flat to 50Hz with a steeper roll-off
- The Beyma outperformed the Supravox in terms of low distortion
Subjective Sound Quality
Back loaded horn No.2095 provided excellent bass and mid-bass slam, unmatched by bass reflex or open baffle configurations. The ability of the cabinet to deliver shear power is unrivaled. I experimented with variety of amplification and found that even my Fosi TDA7498E 50w/channel could delivery concert level bass. Connected to the Hypex FA501 (500w/channel) I was easily able to achieve 114dB at 1m from a single bass cabinet.
On the more nuanced side, it was able to render the subtle undulations/modulations of instruments with ease.
I was worried that there would be a disconnect between the horn output and the direct sound from the driver due to the physical horn path length difference. I was careful with the design in keeping the horn path as short as possible, just enough to get a 50Hz bass response. In the end I am getting 40Hz and I did not detect any type of delay from the bass frequencies in relation to the mid-bass or midrange. In fact, it seemed more immediate than other cabinet types which may be attributed to the low diaphragm velocity benefited from horn loading.
Subjectively the Beyma sounded very similar to the Supravox. In the end it was hard to tell the difference between the two drivers especially when a 300Hz low pass filter was applied.