2.5" Driver Intermodulation Distortion Testing

[shrub0]

This is a comparison of Intermodulation Distortion (IMD) in 2.5" (70mm) drivers. This test will focus on the SB Acoustics SB65WBAC25-4, Tectonic TEBM54C30-8 and Wavecor FR070WA05. These are fun drivers to test and listen to, the absence of cone breakup where your ears are really sensitive (around 2k like from a 6" woofer) is pleasant to the ear.

I like all three drivers for different reasons. The SB acoustics has the most high frequency sparkle, the upper harmonics that come off of stringed instruments are accurately portrayed. SB acoustics is also the lowest price of the three. The SB has well engineered excursion as it kept up or outperformed the other drivers at 150hz while having a smaller cone area.

The Tectonic does very well in the midrange, the acoustics and ambiance of the recording room come through clear. The tectonic can also play louder than the other two with it's bigger 1.52" voice coil and higher sensitivity. However the tradeoff is less native bass response. The Tectonic projects high frequencies as advertised, I walked across my room while playing music with no discernable drop in the high frequencies.

The wavecor has a very low loss suspension and it can portray larger than life dynamics. The large impedence peak in my .5 liter test box boosts the efficiency from 105-215hz and drums and other instruments with fundamentals in this range sound excellent. This is interesting to me as many large woofers (6-10" for example) drop impedance in this 100-200hz range and sound rough. All three drivers can use some filtering or baffle step compensation, however if none is used the wavecor sounds the best to me as the native high frequency roll off blends well with the relative boost you see in the treble with baffle step.

I performed the 150hz-800hz IMD tests with the same measurement conditions as my other IMD tests (The microphone is on a stand 49"high with the base of the microphone 33" from the driver). But for the other tests since they contain higher frequencies I measured on-axis at 1meter away. All drivers were placed in a sealed enclosure of .5 liters.

Any feedback or drivers you would like to see?

 

[jaakkopetteri]

How does the TEBM54 compare to other BMRs? I think I remember you mentioning it has an improved motor.

SB65 seems a bit asymmetric in nonlinearities (and could be flatter too) but indeed not bad
https://audioxpress.com/article/Test-Bench-SB-Acoustics-SB65WBAC25-4-2-5-full-range-driver

I still wish you could get some Kartesian drivers 🙂

 

[Wik]

wondered how it compare to tg series from vifa

 

[shrub0]

According to Tectonic staff the TEBM54 has the most linear motor of all their BMR drivers. The other Tectonic drivers have lower efficiency and smaller voice coils. I haven't tried any of the other tectonic models but since an increase in current is one of the factors contributing to IMD and if two drivers are similar but one is more efficient (requiring less current) I would expect less IMD out of the more efficient driver. I've also been told larger voice coil diameters help prevent hysteresis but I don't know if the increase from 32 mm in the TEBM46C20N-4B to 38.6 mm in the TEBM54 is of much help.

The Kartesian WIB70_vPA-8 is the same size but has quite a bit higher fs than the three I tested. It is hard for me to get (out of stock at Solen).

Wik, is there a TG in this size, 70mm? I just see the TG9FD.

 

[tktran303]

Hi Mark,

Are you able to take high resolution eg. 10+ ms windowed polar measurements of the TEBM54?

Tectonic’s published data shows 1/3 octave smoothed power response measurement; which is fine and dandy for a single driver system, but for 2 or 3 way use, it’s a shame they don’t publish off axis charts.

Even a 30 and 60 degree line on a quasi IEC baffle or in your box would be super!

 

[shrub0]

Tktran303, here are .frd files from Parts Express.