In this blog post I test the Peerless OC25SC65-04 with Horn No.1900.
The Peerless OC25SC65-04 is relatively affordable listing for only $13.67 USD each at Digikey and $22.49 at Parts Express.
Hifi Compass has done a full test of this tweeter mounted on a IEC baffle which can be found here.
There are a number of factors that drew me to the tweeter. Firstly, after seeing good test results of a similar looking tweeter, the Eminence SD28, I decided to keep my eyes peeled. Secondly, I wanted a tweeter that was reasonably affordable for use in an ultra small desktop speaker. More on that in a bit.
For this test, I custom designed a special 1.5kHz ES circular horn and had it 3D printed for the test.
The 3D printing quality is pretty crude, but is good enough for testing purposes. You can see my bass enclosure below so as to not falsely embellish the test.
I literally just tapped the driver in place for the test. 
Measurements
I begin by measuring the impedance sweep. We see the FS centered at 1.3kHz. The driver appears to be well damped with no visible resonances or breakup.
I then measured the raw frequency response. The horn loads down to 1.7kHz with a very linear falling response to 10kHz where we see a +4dB peak centered around 13kHz. Breakup starts at 20kHz with some extension out to 30kHz using a -20dB downpoint.
For further testing I decided to add a 3.3uF capacitor to flatten the response.
The response has now been flattened. Based on the resulting response graph we can go with a crossover point centered around 1.1kHz. So far so good.
I then measured the off-axis performance. I mounted the horn on top of a small bass enclosure so that any affect from the enclosure would be included in my result. This more closely replicates a real life application.
The same result is shown as a waterfall plot. This is a very well behaved.
Burst decay is also very well behaved. We see some stored energy in the 13kHz region but it is dead by 8 cycles so I don't consider this to be audible.
Even the CSD is exceptionally clean. The 13kHz region looks even more benign.
Harmonic at 85dB seems reasonably low.
Result 1kHz 85dB 1m:
H2: 0.03%
H3: 0.04%
Increasing the test SPL to 95dB is shown below.
H2: 0.10%
H3: 0.008%
Intermodulation is shown for 85dB test signal. We see distortion a full -73dB down in the 2kHz region. Distortion remains exceptionally low at 10kHz at -70dB. This is reference territory for a $13 tweeter!
Implementation into finished speaker.
This tweeter horn combo met my target for sound quality by a wide margin. Subjectively the tweeter is in the same category as the best I've heard regardless of cost. I decided that this tweeter/horn combo would be suitable for a small desktop speaker I have been working on.
The plans for this speaker can be found here. For the rest of this blog post I will focus on the more technical side of this finished speaker system.
I recently purchased the Markaudio Alpair 5.3 and based on a quick listening session I really like how it sounded. So I went with this driver for the bass enclosure. Below is the bass cabinet alignment results for a 2.2L enclosure tuned to 80Hz. I simulated a larger enclusure at 3.78L tuned to 75Hz but I found that it would quickly run out of xmax at only 5w of input power. Keeping the cabinet smaller at 2.2L allows a full 10w of power handling before running out of xmax on this small little 3" driver.
Below is the same results as above however with the input power increased from 1w to 10w.
We see this little baby enclosure pump out 95dB at 1m for 100Hz. If you are playing bass heavy content you will want to limit input power to 1w which produced about 85dB from one speaker. This is more than plenty for a desktop application where you will only feeding the speaker around 300 milliwatts.
Below is the step response for the system.
Subjective Listening
The little 3" Markaudio is a new driver that does not have any spider. The only feature holding the cone in place is the rubber surround. Subjectively this little driver has good clarity across it's bandwidth and actually produces real bass at moderate listening levels. Combined with Horn No.1900 using a 1.1kHz crossover point provides excellent clarity. Soundstage depth is excellent as well as overall smoothness. Dynamics are also very good compared to other soft dome tweeters I've heard. I feel as though the limit on sound quality will be your associated electronics, as distortion is well into the territory often reserved for electronics.