Early Measurements on ES-290 Biradial Horn

The ES-290 represents the largest format horn that I currently offer in a biradial format.  This is a new product that competes directly with the classic Yuichi A-290 Biradial.  Madera Handcrafted has decided to use the ES-290 Biradial in thier upcoming flagship speaker.  They decided to use this horn instead of the A-290 because of the measured performance of the smaller versions.  Even the smaller versions have outperformed basically any horn type in terms of off-axis performance by virtue of a well behaved consistent off-axis frequency response in relation to the on-axis response.  Off-axis performance is an excellent indicator of a horn's time domain perfomance.  This means the horn has very little stored energy, also known as acoustical resonance in various form.  Good time domain performance translates into a lower noise floor, better low level detail retreival, better dynamic range.  These are the virtues of a true audiophile sound which is the desired application.  The goal here is faithfully reproduce two channel music with absolute clarity and dynamics.  

The ES-290 represents the pinnacle of this biradial concept since it covers such an wide frequency bandwidth.  The horn is designed to cover 290Hz - 20kHz and so typically will require a very high performance driver such as those available from TAD, Radian, B&C, and RCF.  

Currently we await the best compression driver available from TAD Electronics in Japan, which won't arrive until February 2020.  In the interim I really wanted to get some off-axis polar measurements off the very first pair of horns which are now built.  Since I lacked a suitable compression driver I decided to use an unorthodox approach.  I found that the Scanspeak 5F (5cm, 2 inch) full range driver fit perfectly in the ES-290's 5cm throat.  Since this small fullrange is able to provide clean output up to 9kHz before it starts to see some breakup.  

Details on this little driver can be found here.

For some context I don't think I've ever seen anybody mount such a small driver into such a large horn.  Below is a video that shows the overal size of the horn.  In fact I've never seen a fullrange driver mounted in a biradial horn before either.  To me there is perfect rationale.  The ES Biradial horns are the best sounding horns that I make, so why not use them with full range drivers as well?  

 

 Continuing on with my measurements I decided to measure the frequency response and off-axis polars of the Scanspeak 5F in small Transmission Line cabinet.  

Measurements 

ScanSpeak 5F Mounted in Mini-Transmission Line

Below is the on-axis frequency response as measured in my studio.  

 Below is the off-axis coloured polar map of the ScanSpeak 5F mounted in my mini transmission line speaker.  The baffle width is 13cm. 

 ScanSpeak 5F mounted in ES-290 Biradial Horn 

I then mounted the driver in the horn and got the following frequency response.  (Black = ES-290 Gray= Non-horn direct radiating)

Based on this data we can make the following observations...

As you can see from the red arrows we have the following increases in sensitivity. 

+10dB @400-800HZ

+7dB @1.6kHz

+5dB @ 3kHz

The horn is effectively raising the sensitivity of this driver from 80dB@1watt to 90dB across the midrange.  For reference here is the published frequency response...

Below is the off-axis coloured polar map of the ES-290 horn with the 5F driver. 

 

As you can see from the polar map there is a much more consistent off-axis in comparison to the direct radiating counterpart. 

I would call this "near" constant directivity from 500HZ - 7kHz.  Above 7kHz I run into issue with the driver's breakup mode.  But it still seams to maintain wide coverage up to 10kHz where it quickly narrows down to a 50 degree coverage window.  

Taking it a step further I decided to extend the polar map to a full 90 degrees off-axis.  This is what I got.  

Looking at this we can see a nice strong constant directivity trend providing a 90 degree listening window from 300Hz-7kHz. 

And for comparison's sake let's look at the non-horn version (mini transmission line) extended out to 90 degrees off-axis. 

The above polar response looks like there is some strong midrange presence around 4.5kHz where it quickly narrows to only 70 degrees coverage at 7.5kHz.  Above 7.5kHZ we see some driver anomalies starting to effect our results.  Above 10kHz the driver only has 40 degrees of coverage which is quite poor in comparison to a regular 25mm dome tweeter. 

Conclusion 

This blog post represents an early glimpse into the performance of the ES-290 Biradial Horn.  These early results look promising especially in the critical midrange band.  It's unfortunate that the Scanspeak 5F has some anomalies starting at 7kHz which prevented me from seeing anything meaningful above this frequency.   This blog post also provides some insight into the effect of horn loading a fullrange driver and offers a comparison between a horn loaded and a non-horn loaded configuration.   I also have another project that I'm working on for a customer in Italy that wants to horn load a midrange driver.  This helps me confirm that the ES-biradial format is an excellent candidate for this type of application.  Here is a sneak peak of this midrange horn which I will be featuring in a future post.