Fig 1 – Seas U18RNX/P RAW Response • Baffle Width=8-1/2″
When I measured the RAW frequency response of the Seas U18RNX/P, I couldn’t quite believe my eyes. I’ve never seen anything like this before. There’s a notch at 950Hz. Not a tiny one mind you. It’s -5dB deep and broad.
The notch is not from the U18RNX but from my box. But since I’m already setup, I’ll continue until a new box is made. Just imagine the notch is not there (see bottom of post for Notch Update).
First thing I did was to listen to the U18 without any crossover. If I can pick up something good about it, I can proceed with the crossover. Otherwise, it’s just a waste of time.
As expected. the midrange is hot. But that’s not a problem. I can correct it with the crossover. Most importantly, I cannot identify the notch. That’s a huge relief.
There’s treble but it’s brittle. That’s understandable. I think the highest it can cross without affecting the tweeter is maybe 3kHz. Even then it’s stretching it.
Fig 2 – Seas U18RNX with Low Pass Filter (LPF)
Now that I have an idea of what the U18RNX is capable of, I can proceed with the crossover. Since there’s no violent spikes in the cone breakup, the low pass is pretty much a standard 2nd order network. My targeted crossover frequency is 2kHz. This is a bit low but I want to avoid the frequencies above that. I suspect there are some cone ringing in the extension.
Fig 3 – Blue plot=U18RNX with LPF • Morel MDT29 with HPF
The Red plot in Fig 3 is the Morel MDT29 with a 3rd order network. I may need to adjust the tweeter crossover later because it’s crossing at 2.5kHz instead of 2kHz. For the time being, I’ll leave it as it is. What I’m eager to find out is how the Myna sounds like.
Fig 4 -Myna Passband
The Black plot in Fig 4 is the Myna’s crossover passband. There are no cancellations in the passband which is always a good sign. Another plus is the symmetry in the roll-off in the two drivers.
Fig 5 – Myna Frequency Response
Fig 5 is the final frequency response of the Myna. From 2kHz to 16kHz, the response is within +/- 2.5dB.
Fig 6 – Myna Step Response
Well, this is surprising. The Seas U18RNX is fast and clean. There are no breaks in the attack and it hits the apex at an astonishing 250 microsec.
Fig 7 – Myna Waterfall
Here’s another surprise. The Waterfall plot ( Fig 7) shows long decays from 2kHz to 5kHz.
Fig 8 – Myna Toneburst Energy Storage
The Toneburst plot in Fig 8 confirms what is seen in the Waterfall. There are excess energy from 2kHz to 6kHz. This may not be so harmful. It is those from 1kHz to 1.5kHz that may create some issues.
Fig 9 – Myna Spectrogram
The Spectrogram in Fig 9 shows slight hotness at about 1.2kHz. This will not smear the midrange because it disappeared by 6 msec. As I had suspected, there are signs of cone ringing. Look at the light blue spots along the 3 msec and 4 msec line. I wouldn’t be concerned with them because they vanished by 6 msec.
Fig 10 – Myna Harmonic Distortion
The Total Harmonic Distortion (THD) is about -50dB below the fundamental (Blue plot in Fig 10). The 2nd (Red plot) and 3rd harmonics (Violet plot) are about -55dB below.
Sound of Myna
The Myna is one of those speakers that doesn’t measure that well but sounds fantastic. Believe it or not, she beats the ER18RNX in the Starling-2020. No kidding. The vocals are on par. Where it makes all the difference is in the bass. The attack, dynamics and clarity sounds like in the Scanspeak 15WU. Excellent cone control.
Listening to “The Calling” (Santana-Supernatural) is wonderful and eerie at the same time. After the guitar intros, the bass comes on. I can make out clearly the bass texture. With lesser woofers, you get a one note bass. Not with the U18RNX.
The eerie part with this track is it’s trance-like nature. The bass is like an under-current that pushes a sea of believers towards the master who’s perched high up on a mountain. Visually very drama.
For voices, I played “Love is a Garden” (Jewel – Perfectly Clear). There’s no shrillness, no excessive sibilance, just well isolated, focused vocals. I can even hear her inhaling. She was obviously close miking.
Can the Myna be better? Yes certainly. Tighten up the crossover, maybe even time aligning the drivers. It will make the measurements prettier. Whether we can hear any significant improvement, it’s hard to say. For now, I want to enjoy the Myna before I move on to the next project.
Lastly, I’m sure there are readers wondering whether the Seas U18RNX/P is worth the price considering her less than stellar measurements. If you are really into sound quality, it is worth every penny. The Scanspeak 15WU cost more than $300. The U18RNX is one-third that but sounds just as good. This is High-End territory. $100 is cheap for this quality.
Update: Dec 8, 2020
Just as I suspected, the notch is not from the U18RNX. The Black plot is the U18 in my early 15 liters Starling box. No notch. I will have to investigate further why my 18 liters box caused the notch.
Crossover is available on request. Free for DIY. Not for Commercial use.