Design 10" CoAxial (Apr 6, 2013)
High Frequency   Peavey RX14 1" Titanium Compression Driver  
Low Frequency Eminence Beta 10CX
Crossover Synergy (Bi-Amp - 18dB/oct)


The Osprey is an Eminence Beta 10CX Coaxial in a 52 Liters Bass Reflex.

For a 10" woofer, I would prefer to cross at 1,500Hz but I'm asking a bit much. Realistically, I'll be satisfied with 1,800Hz to 2,000Hz. The first step is therefore to ascertain the cut-off frequency of the horn.


Peavey RX14

After much contemplating, I eventually decided on the RX14, a 1" Exit Titanium Compression Driver from Peavey. Having worked with this driver before, I'm intimately familiar with it's sonic signature and performance. I was also hoping that the 10CX horn would, as a minimum, go as low as 2,000Hz. At this frequency, the RX14 will not sound strained. An often overlooked advantage with the RX14 is that it does not exhibit any resonant peak
(Fig 1), so should I decide to cross below 2,000Hz, I won't have the driver's resonance to contend with.


Fig 1 - Impedance Sweep of Peavey RX14 in Beta 10CX

Response of RX14

With the Synergy crossover set at 1,000Hz, a sweep was made with the OmniMic V2 (Red trace). It appears the horn can in fact be crossed as low as 1,300Hz.

The Blue trace is with the crossover at 2,000Hz. At one octave down (1,000Hz), attenuation is about -20dB. Interestingly, the bump at 1,500Hz has been largely suppressed. That would contribute greatly when crossing to the woofer.

Lastly, at 2,000Hz, EQ was added to flatten the response (Violet trace).

Fig 1 - Peavey RX14 Frequency Response

Beta 10CX 10" Woofer

Eminence's plot of the Beta 10CX (Fig 2) doesn't look very friendly. It is precisely this response that made me hesitant to purchase this coaxial. With a response like that, I would be forced to cross at 500Hz, which is not realistic for a 1" exit compression driver. Another option is to cross at about 1,500Hz, but that would entail a notch filter centering at 1,000Hz, a prospect I'm not too thrilled about.

Hopefully, it is not as bad as it looks.

Fig 2 - Beta 10CX Frequency Response


Beta 10CX Woofer Measured

The Black trace below (Fig 3) is the In-Room Response of the Beta 10CX woofer. Disregard the region below 500Hz as the reading is influenced by the room.

What a relief on seeing the Raw response. The sharp peak at 2,500Hz is not as bad as in the Eminence's plot. In fact, apart from the peak, it is surprisingly smooth.

The three other traces below are with the Synergy crossover at 2kHz, 1,750kHz and 1,500kHz.

Notice the attenuation of the peak at 2,500Hz. A crossover of 1,750Hz seems to be optimal where I can safely avoid using a notch filter for the 2,500Hz peak.

Fig 3 - In-Room Response of Beta 10CX Woofer


Tuning Osprey for Flat Response

Fig 4 is the Osprey tuned for Flat Response. Synergy crossover at 2,000Hz. The Grey trace is of the 10" woofer. The Red trace is of the RX14 with EQ.

For clarity, Fig 5 is the response without the woofer and compression driver overlays.

Fig 4 - Low Pass and High Pass of 10CX at 2,000Hz

Fig 5 - Osprey Frequency Response tuned for Flat


Tuning the Osprey for Music

For Musical reproduction, the Synergy crossover is re-adjusted for 1,750Hz (Fig 6). A Shelving filter is inserted for the woofer to lower the vocals slightly. This has the effect of boosting the Bass. The RX14 retains the same EQ network as before.

For clarity, Fig 7 is the response of the Osprey without the woofer and compression driver overlays.

Fig 6 - Low Pass and High Pass of 10CX at 1,750Hz

Fig 7 - Osprey Response for Music


OSPREY Hybrid Network

Fig 8 - Osprey Hybrid Network


Going Full Passive

Fig 9 below is the in-room response of the Osprey using Full Passive crossover.

Crossover frequency is 2,000Hz (18dB/oct for High and Low Pass).

Fig 10 is the response without the woofer and tweeter overlays.

Fig 9 - Osprey Woofer and Tweeter Frequency Response


Fig 10 - Osprey Frequency Response with Passive Crossover


Fig 11 - Osprey Passive Crossover


Component Recommendations

All Capacitors are Polypropylene.

All Inductors are Air-Core. Minimum 18 Awg.

All Resistors are rated 10 Watts minimum.

60 Downes Street | Calais | ME 04619 | USA