Raven-RST (Dayton RS180s-8 with RST28A-4)

Raven-RST
27L Bass Reflex Tower

The Raven-RST addresses the lack of bass when the Dayton RS180s-8 is loaded into a small bookshelf. In this project, I use a 27 liters bass reflex tower. This is much smaller than the 40 liters Raven-DCR. As with the DCR version, this Raven-RST is meant for Full Space (4 pi) environment. 

Fig 1 – Dayton RS180s RAW response in 27L Bass Reflex • Baffle Width=9-1/2″

Fig 1 is the RAW response of the RS180s-8 in a 27 liters bass reflex with a baffle width of 9-1/2″. Ignore the suck-out at 150Hz. It’s caused by a floor bounce in my setup. No smoothing is applied.

The baffle step is clearly seen at 500Hz. The midrange is +5dB higher than the bass (100Hz to 50Hz). If I leave it as it is, the midrange will sound too prominent. 

Fig 2 – Dayton RS180s with Low Pass Filter (LPF)

The Blue plot in Fig 2 is of the RS180s-8. This was made after I tuned the Raven-RST by ear. Meaning, I was listening with the tweeter connected and making adjustments along the way. When I got what I wanted, I disconnected the tweeter and did the measurement for the woofer.

Fig 3 – Dayton RST28A-4 Response with Surface Mounted

The Black plot in Fig 3 is the RAW response of the Dayton RST28A-4 that I am testing out for the first time. I couldn’t quite believe my eyes when I took this measurement. It doesn’t look anything like in Dayton’s spec sheet. My first thought was perhaps my unit is from a bad manufacturing batch. However, after checking the internet, I came across a test by AudioXpress and they got a similar result. Since it’s already installed in my box, I might as well continue and see what I can get out of it.

The Red plot is with a High Pass network for a crossover frequency of 2kHz. I’m rather concerned with the bite from 2kHz to 3kHz but there’s not much I can do about that because flush mounting it didn’t help at all. Maybe it’s a severe case of baffle edge diffraction.

One strange aspect with this RST28A-4 is the response is actually better with it surface mounted. That will save a lot of work in rebating the tweeter cutout.

Fig 4 – Dayton RS180s-8 Low Pass • RST28A-4 High Pass

Fig 4 are the plots of the RS180s-8 and the RST28A-4 with their respective networks. The two drivers are crossing at my target of 2kHz. I padded the tweeter to within 1dB, making sure it’s doesn’t end up too hot or too dull. Again, this was done by ear.

Fig 5 – Raven-RST Passband

The Black plot in Fig 5 is the summation of the crossover. It looks good. No cancellations are recorded in the passband.

Fig 6 – Raven-RST Frequency Response

The Raven-RST final frequency response (Fig 6) is relatively flat except for the dip at 3kHz. Maybe if I load the tweeter with a waveguide, the dip will vanish. Something to keep in mind.

Fig 7 – Raven-RST Null

The Raven-RST null centered at 2kHz when I flipped the tweeter wires. Surprisingly, the depth is quite deep. This indicates the two drivers are actually time-aligned.

Fig 8 – Raven-RST Step Response

I am bewildered by the Step response in Fig 8. I have no idea why the tip looks like this. The RS180s-8 is the same woofer I used in the DCR version. Maybe it has to do with the box stuffing. In this Raven-RST, I stuffed the box with Poly-Fil whereas the DCR was R13 Fiberglass wool.

Fig 9 – Raven-RST Waterfall

The Waterfall plot in Fig 9 shows some decay from 1kHz to 3kHz. They may be benign because the plot is highly magnified with a time window of 1.5 msec.

Fig 10 – Raven-RST Toneburst Energy Storage

The Toneburst plot (Fig 10) recorded some excess energy at 3kHz. They last for only 6 cycles, so I don’t think they will cause any issues.

Fig 11 – Raven-RST Spectrogram

The Spectrogram in Fig 11 doesn’t show any smearing. There are some delayed hot spots at 2.2kHz but they are dissipated by 6 msec. I may be wrong but it could well be diffraction at the edge of the front panel. As for the stored energy at 3kHz, it disappeared by 2 msec.  

Sound of Raven-RST

My initial version of the Raven-RST was dreadful. Measured well but was insipid. I then stopped using computer simulations and adjusted the crossover by ear. A little bit here, a little bit there and all of a sudden, the music jumps to life. I love it when a speaker does that.

The vocals now pop out. It’s not shouty. The clarity comes from cutting through the mix. The bass tightened up and the tempo improved vastly. As for the treble, I’m really surprised by the RST28A. Though it doesn’t measure that well, it’s actually a very sweet sounding tweeter. There’s no brightness nor does it sound plasticky.

The Raven-RST is one great sounding speaker. If the Raven-DCR is too large for your taste, this RST version is just as good. This is one speaker I can live with.

Crossover is available on request. Free for DIY. Not for Commercial use.
Unless otherwise stated, all measurements were made in Full Space (4 pi) with the mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied.