Marrying the Old with the New
The Sandpiper is based on one of my favorite horns, the Pioneer PD-40-4. This horn was originally used for the midrange in Pioneer’s CS-R700. The speaker was introduced in about 1972~1974. That makes my PD-40 close to 50 years. I’m sure some readers will be wondering why I’m wasting my time with a vintage horn when there’s such a wide variety nowadays. Well, for one, none of my horns can do what this PD-40 is capable of. It has a ridiculous effective bandwidth of 700Hz~14,000Hz. On top of that, the response is flat. And it’s a HiFi horn, not PA.
The original Pioneer CS-R700 is a 3-way with a 12″ woofer for the bass, the PD-40 horn for the mid/high and a super tweeter. I toyed with the idea of replicating the CS-R700 but I eventually decided against it. I’m not too comfortable with using a 12″ and crossing it at 700Hz to the PD-40. There’s also this issue with my weak back.
Since I bought some new drivers lately, it would be a good time to test out the DA215-8 with this PD-40. I loaded the DA215 into a fairly compact 24 liters bass reflex tuned to 36Hz. As with most metal cone woofers, the DA215 has a rather nasty breakup. Hopefully, it won’t cause any issues.
Fig 1 – Dayton DA215-8 RAW and Low Pass Responses. Baffle Width=13-1/2″
The Black plot in Fig 1 is the RAW response of the DA215. This woofer would be right at home in a 3-way but for this project, I will cross it at 700Hz. After testing out a few crossovers, I settled on a 3rd order (Blue plot). With its steep roll-off, the breakup peak at 5.5kHz is well suppressed and will not interfere with the treble. Due to limitations in my room, measurements below 500Hz are in Nearfield.
Fig 2 – Pioneer PD-40-4 RAW and High Pass Responses
Now comes the Pioneer PD-40. The Black plot in Fig 2 is the RAW response. It does go down to 700Hz. This is the horn cut-off frequency. The RED plot is with my High Pass filter.
Fig 3 – Dayton DA215 with Lo Pass and Pioneer PD-40 with High Pass
Fig 3 shows the acoustic crossover of the DA215 and the PD-40. On first glance, the roll-off slopes are not symmetrical. The PD-40 is much sharper than the DA215. That’s because I’m using the cut-off for the crossover.
Fig 4 – Crossover Summed Response
The Black plot in Fig 4 is the summed response in the passband. Note the dip at 700Hz. That’s caused by cancellation when the two acoustic centers are not well aligned. However, from 700Hz ~ 1.2kHz, the two drivers are summing well.
Fig 5 – Sandpiper Frequency Response
Fig 5 is the final frequency response of the Sandpiper. Apart from the light notch at 700Hz, the overall response is quite respectable. There is a slight treble emphasis at 4kHz~5kHz but I’ll leave that for the time being. It will add a bit of sparkle to the treble.
Fig 6 – Null Response
To check on the crossover, I reversed the the PD-40 wires. It resulted in a notch centering at 900Hz. The notch is symmetrical, which is good sign. I believe I can get a deep notch with a bit more tweaking. I’m almost there.
Fig 7 – Sandpiper Step Response
The Step response in Fig 7 shows the DA215 is leading the PD-40. The difference is not much, only about 100 microsec. It also shows that the DA215 and the PD-40 are both in phase even though I wired the PD-40 in reversed phase for proper summing. This is quite common with compression drivers.
Fig 8 – Sandpiper Waterfall
Fig 9 – Sandpiper Toneburst Energy Storage
The Waterfall (Fig 8) and Toneburst (Fig 9) plots show some artifacts at 2kHz and 5kHz. I doubt they are serious. The Spectrogram will reveal more.
Fig 10 – Sandpiper Spectrogram
As I had expected, there’s nothing much at 5kHz. It is below 2kHz that shows some ripples. None of them are serious enough because they dissipated by 6 msec.
Auditioning the Sandpiper
I am very pleased with the outcome of the Sandpiper. The Pioneer PD-40 midrange horn is fantastic. The vocals are crystal clear. No honking. No shrillness. Midrange projection is excellent. This is where horns beat cone drivers. The midrange is more focused and it projects.
In the treble, the PD-40 is devoid of harshness. One good reason is because there’s no crossover from 700Hz onwards. And since the response is flat, there’s nothing to pique the ears. What caught my attention is the incredible amount of detail in the highs. None of my dome tweeters come close.
Add to this the DA215 bass and the Sandpiper is a winner. It is loud enough and punchy. It is not as detailed or dynamic as some of my other woofers but that only enhances the retro appeal.
Crossover is available on request. Free for DIY. Not for Commercial use.
May 12, 2020Projects