Aluminum vs Paper --- Dayton Audio RS100 vs RS100P

The drivers are basically the same in terms of parameters with only some minor variation. The biggest difference is the overall sensitivity, with the paper driver being +1.6dB more sensitive as a result of the lighter moving mass (mms).

Reviewing the published frequency response would lead one to potentially conclude that the paper has a flatter response. The aluminum version is showing a bump at 3kHz as well as the diaphragm breakup at 17kHz. The published data on the paper driver shows that the breakup is potentially at 10kHz but it is hard to tell as it seems very well damped. As a customer it would appear at least initially that the paper version performs better. 

The driver is mounted in a 15mm thick adapter plate measuring 20cm x 20cm.

The test baffle sits on my DIY rotary table incrementing every five degrees out to 90 degrees. 

The driver is mounted in a 9.4L sealed enclosure which is fille 100% will polyfill. 

I've spliced my response at 1.3kHz. Above this frequency I'm using a gated measurement using 1/24 octave smoothing using a 60cm mic distance. Below 1.3kHz I'm using an ungated nearfield measurement using 1/3 octave smoothing. My measurement setup consists of the Schiit Rekkr amp, Scarlett Solo Mic Pre with an ACO Pacific 7052PH reference measurement mic. 

Below is an overlay of the two drivers (Alum BLUE, Paper RED). The paper driver is 2dB more sensitive than the aluminum version. 

I then adjusted the graph result for the aluminum driver +2dB to align with the sensitivity of the paper driver to better visualize any response differences. As you can see below, the drivers are identical leading up to the first breakup mode. This is a surprise considering the differences we see in the published data, particularly at 2kHz. 

We can see that the paper driver does indeed have a sharp breakup mode centered at 10kHz. Treble extension continues to about 12kHz but falls steeply above this. In contrast, the aluminum driver has a flatter response through the treble region with breakup occurring at 17kHz. The breakup of the aluminum is higher Q (sharper) than the paper which one would expect. 

Below is the directivity index, in-room response, and listening window. 

• Both materials show very similar results for CSD (other than the breakup frequency)

The paper driver was a little more forgiving and offered the same resolution as the aluminum version. The aluminum version had some mild glare on electric guitar, but also resulted in slightly more perceived treble output. 

Overall I found the paper driver slightly more musical and enjoyable. 

I did not really notice the earlier breakup mode of the paper driver when listening to music. In fact, I found the aluminum driver to sound like the breakup mode was within the audible band, despite the measurements showing otherwise. 

It was easy to discern the unique sound that each driver offered, but the sound traits did not correlate to any of my measurements. 

Additional Remarks 

There is such a small difference between the two drivers both in terms of listening and measurement. Despite the earlier breakup of the paper version, the sound was still equal to that of the aluminum. As a result, scrutinizing differences in driver diaphragm material falls into the category of personal preference. There is no "right" or "wrong" here in terms of choice. 

In fact, the beginning stages of design development include careful observation of various driver attributes. This includes distortion performance, output capability, and directivity characteristics. All of these macro attributes are essential when determining the subjective sound quality goals. For example, a narrow directivity, such as what we see here, will result in a more forward sound character, and less spaciousness. Spaciousness is what we subjectively prefer based on Floyd Toole’s studies at the NRC, and is in alignment with my overall design requirements. 

Other critical aspects, for example, would be the maximum distortion limited output. This attribute directly affects sense of dynamics and resolution, particularly with bass and mid-bass frequencies. If a driver is approaching its threshold for distortion, it will not reproduce an "effortless" sound neither will it be authentic, accurate, or even enjoyable.

So in the context of overall great subjective sound quality, this format (ie. 10cm fullrange) has inherent limitations beyond simply looking at diaphragm material. It's important to highlight this context. In other words, changing or modifying this 10cm format will not miraculously provide wider coverage or lower distortion, and all the enjoyments that follow as a result (ie. spaciousness, nuanced mid-bass). It's simply an inherent limitation of the physical format.  

From a design standpoint, if would be much better to incorporate the RS100 or RS100P driver as a dedicated midrange. It could be taken even further by upgrading to a higher performing driver model. For example, if we look at the raw test data conducted on the SB Audience 5" Textreme midrange, we can see that it excels meaningfully over every performance metric. 

This is no surprise since the driver is slightly larger, large radiating area having no phase plug, lighter and stronger diaphragm material, and copper shorting rings in the motor structure, just to name a few. 

This is not to discredit what the RS100 and RS100P represent, but to highlight that it has a place in the audio food chain, and that design decisions made early on, should focus on the raw data that each driver offers, along with how it integrates into a final solution (ie. fullrange, multiway, horn loaded etc.) 

Not to labor the point, but this becomes clear when looking at very specific test data. For example, I've imported the ungated polar response data of the RS100 into VituixCAD. The on-axis response (RED) is in contrast to the in-room response (GREEN) which is completely shelved down starting at 5kHz. 

The core issue has to do with the directivity index performance shown in blue below. If the blue line is made flat, then the in-room becomes flat as well, improving spaciousness and timbrel accuracy. More on this can be found here. 

Contextualizing performance between macro and micro issues is important in the design development process. The macro issues (directivity, smooth linear response, low distortion) are core aspects of focus early on. Only then can a design progress towards micro changes...and in the case of this blog post and these specific drivers, diaphragm material is a perfect example.