Beyma TPL-150H

 The package arrived!  Everybody was excited to get new speakers!






 I designed an enclosure to house the horn.  It stands 12" tall x 22" wide x 8" deep.  Construction is 18mm thick baltic birch plywood that is "skinned" in 3mm thick plywood that has been wrapped around the entire box.  I soaked the 3mm plywood in hot water for 5 minutes to make it pliable enough to wrap around the 4" radius.



 I did not glue the 3mm skin to but made it removable with screws so that I could test the effects of the rounded edges versus square.

Below is my test setup.  I used my rotary table to create full coloured polar maps of both designs (square versus rounded).



Below is the raw frequency response of the curved baffle.

On-Axis frequency response, distance 20", Dayton UMM-6, ARTA gated response.

As you can see below this does NOT match the manufacturer's published frequency response.  
Side Note:
The response requires that you use a 1500Hz crossover or higher.  I ended up with a 1500Hz 48dB slope crossover to the B&C 12PE32 woofer.  This combination sounds excellent.

Polar Response
I then conducted full polars which can be seen below. 

Beyma TPL-150H Polar Response on curved baffle

The response shows the typical coverage pattern for a constant directivity style horn.  The horn has a week off-axis response in the 2.5kHz region.  However it does provide broad coverage all the way up to 15kHz which is impressive.  Pattern control is maintained down to 1.8kHz.   I think these are respectable results.

I then removed the curved skin to reveal the square box.  This represents a more typical mounting baffle. 

Beyma TPL-150H Polar Response on Square baffle

The polar of the square baffle matches pretty close to the rounded baffle with the exception of some differences in the 2.5kHz region where it seems the narrowing is more pronounced.   There is also a little more energy off-axis in the 8kHz region but this is minor. 

Burst Decay Results
I then looked at the burst decay on-axis to see if there is more diffraction artifacts with the square baffle versus rounded.

Burst Decay (Spectrogram) for curved baffle, on-axis

I then tested with the square baffle.

 I was careful to gate the response to eliminate any room effects as can be seen from the solid blue area on the graph.


I was surprised that there was very little difference in the burst decay results.  In the past I've seen noticeable improvement with curved baffles however this is the first time I've tested a horn on a baffle.  There really isn't any difference which is useful information.  This means you can design with confidence using a regular square baffle.  Why is there no difference in the results this time versus my other experiments?  I believe it has to do with the horn coverage pattern.  There is very little energy a full 90 degrees off-axis to contribute to any energy on the face of the baffle.  In other words the horn does not "light up" the baffle like other direct radiating (non-horn) drivers. 

I then attempted to EQ the horn to get a flat response.  Using my MiniDSP DRC-DA8 I was able to get a relatively flat response with the following PEQ curve.


As you can see it requires some pretty aggressive EQ to get flat especially above 10kHz where the horn falls off sharply.   A full 15.6 dB of attenuation is required which would be pretty difficult to do with a passive crossover.   The frustrating thing is that you would never know this based on the manufacturer's published charts.

Subjective Impressions


The Beyma TPL-150H is able to produce a very clean ultra-transparent treble that is effortless.  Dynamic Range is on par with the best compression drivers.   I am thrilled to have this driver in my possession and I hope to further improve the sound by removing the rear plastic cover to allow the sound to vent to the enclosure.  I plan to fill the enclosure with acoustical damping material such as poly fill or other.  I suspect this is why the driver isn't producing much below 1500Hz. 

Other Horns 
Like I said earlier I'm working on a horn design for a client that wants better coverage above 5kHz.  I can't say much about the design on this new horn since I'm bound by a commercial agreement. 

Personal Life
Audio is certainly my passion and I love doing this type of stuff.  Over the years I've longed to do this as my profession and now I've finally got the chance.  I've made the difficult decision to quit my day job and do freelance audio engineering.  I've worked as a Manufacturing Engineer in the Automotive Industry for 16 years and it was finally time to throw in the towel.  I will be working from home and developing new and exciting designs and building custom speakers in my workshop.
So considering that I just put everything on the line if you have a special project that you would like me to support then please contact me at the email below...

Contact Email: 
Joseph_crowe(at symbol)josephcrowe.com

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Originally published at Crowe Audio.