EV HT94 Horn with Peavey RX14

about the EV HT94

The HT94 is another vintage horn from mid-80s to early 90s. They were extensively used in EV speakers like the T series. This horn is different from the JBLs in my previous posts. The HT94 is what is called a Constant Directivity horn with a Beamwidth of 90°Hx40°V.  According to EV specs, the Constant Directivity crossover frequency is at 3kHz.

Let’s take a closer look at this horn. One of the many EV speakers that used it is the EV T52+. 

The T52+ is a 15″ 2-way with the HT94 horn crossing over at 2.2kHz. It is not a particularly big speaker for a 15″ woofer. 4 cu ft is about 113 liters. That helps with setting up. Now let’s see what the Frequency Response looks like.

This is the very reason why some people find Pro speakers sound terrible. There’s too much treble. But bear in mind that this response is at 1 meter. When used outdoors and you are 60ft away from the speakers, the treble will be less. Perhaps even leveling to a flat response. We must not forget that pro speakers are normally used with a mixer. Almost all mixers are equipped with EQs so that the soundman can adjust for the best tonal balance. It’s a very different world from domestic HiFi.

The crossover above is that of the T52+. This schematic gives us an idea of what the designer was trying to achieve. We’ll first examine the High Pass filter for the horn.

Basically, it’s a 12dB/oct network, a 1.5uF followed by a 1.0mH to ground. The resistors after that are to attenuate the output. What’s interesting is the use of a PTC in parallel with the 10Ω resistors. This is to safeguard the compression driver in the event of it being over-driven. When the power exceeds the safe limit, the PTC will open forcing the amplifier’s power to pass through the 10Ω. It is crude by today’s standards but during that time, electronic limiters or compressors were expensive.

The woofer has only a 0.83mH inductor to roll-off the highs. My guess is they are trying to use the woofer for the maximum extension. This is a 15″ after all. Crossing it at 2.2kHz is stretching it. 

Now that we have a bit of history of the HT94, I shall proceed to the post in hand – finding the right compression driver for the HT94.

HT94 with Peavey RX14

Having tested it out with my collection of compression drivers, I am pleased to find a few mated well. They are not perfect but usable. The first driver I’m presenting is one of my favorites, the RX14 from Peavey.

Fig 1 – EV HT94 with Peavey RX14 RAW Frequency Response.

Fig 1 is the RAW response of the HT94 horn with the Peavey RX14 compression driver. The microphone was on axis with the horn at a distance of 2 FT. No smoothing was applied.

This compression driver gave the smoothest response. An important point to note is how linear the download slope is starting from 2.5kHz. This is important for a Constant Directivity horn. Once EQed flat, you’ll have Constant Directivity. 

There are a few notches in the upper treble, one at 7.5kHz, next at 13kHz and the last one at 18kHz. This is a small price to pay in exchange for a smooth response.

Fig 2 – EV HT94 with Peavey RX14 Impedance

Fig 2 is the impedance of the HT94 with Peavey’s RX14. The RX14 impedance is very unusual. There’s hardly any peak at resonance. It is actually more resistive. Reminds me somewhat of planar tweeters. This will save cost as no conjugate network is required to flatten the Fs.

Fig 3 – Spectrograms of HT94 + Peavey RX14

The Spectrograms in Fig 3 shows a bit of hotness at 2.5kHz. We see this as a peak in the frequency response in Fig 1. However, the energy is dissipated by 3msec. There’s a very slight peak at 4kHz, followed by another at 7kHz.

Fig 4 – Waterfall of HT94 + Peavey RX14

The Waterfall plot in Fig 4 shows the 7kHz and 15kHz artifacts in 3D. I believe those from 15kHz ~20kHz originates from the cone breakup. They will not degrade the sound quality as they don’t last even 2msec.

Fig 5 – ToneBurst Energy Storage of HT94 + Peavey RX14

The ToneBurst Energy Storage (TES) in Fig 5 shows a very clean HT94+RX14. Whatever stored energy is there doesn’t last long enough to interfere with the sound.

Fig 6 –  Harmonic Distortion of HT94 + Peavey RX14

The 2nd Harmonic in Fig 6 is at 0.143% whereas the 3rd is at 0.243%. THD from 2nd~9th harmonics came in at 0.751%. Generally, they are 40dB~50dB below the fundamental. I don’t hear anything that low down.

The Peavey RX14 in Use

Like I mentioned earlier, the RX14 is one of my favorites. Mainly because of the sound quality. Not as sweet as the Radians though but it’s a lot cheaper. Definitely suitable for domestic HiFi.

According to Peavey’s specs, the recommended crossover is 2kHz (12dB/oct). I’m a bit apprehensive even at 2.2kHz. This driver is small compared to the Selenium D220Ti. Looks more like a tweeter to me. In fact, the PV115 crossover for the RX14 is at 2.8kHz.

If it’s not robust enough to withstand pro use at 2.2kHz, I will not hesitate to use a 24dB/oct electronic crossover. That should improve the robustness of the RX14. If I have to resort to limiters, so be it. Electronics is cheap nowadays.

As for the speaker, I’m not keen to do a 15″ 2-way like in the T52+ or the Peavey PV115. For that, I will use either a 1.4″ or 2″ compression driver and cross it as low as possible. With the HT94 coupled to the RX14, I prefer using a 12″ or a 10″. I wouldn’t even mind using two 8″ in a MTM.  That’ll be fun.

Unless otherwise stated, all measurements were made in Full Space (4 pi) with the mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied.