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SPL Transducer

Speaker Emulator & Dummy Load
Published February 2008
By Paul White

If you want to capture the sound of your boutique valve amp for recording but can't turn it up loud, you need a power soak... and speaker emulation... and mic emulation... SPL's Transducer does it all.

SPL TransducerPhoto: Mike CameronThe Transducer is somewhat of a departure for SPL, who built their reputation on innovative outboard processing gear for studios, but this device is actually a collaborative enterprise between SPL and German guitar-amp specialists Tonehunter. As with the other similar devices described in the 'Alternatives' box, the Transducer is used instead of a guitar speaker cabinet and microphone. The aim is to provide a DI feed that recreates the sound of a guitar amplifier miked up, but without the speaker having to be belting away to achieve that. Speaker emulation devices rarely get the sound exactly right, but one or two do come very close, and I was intrigued to see what approach had been taken here.

Transducer Tour

The Transducer is active (whereas some well-known power-soak designs are passive), and it offers a choice of mic and cabinet setup emulation options, with the ability to change the distance of the virtual mic from the virtual speaker cabinet. All this is done using analogue circuitry rather than digital modelling, which means that there's no delay or latency. The advantages of a speaker emulator that actually works are pretty much self-evident: you can work at any time of day or night without causing noise problems or suffering spill onto other instruments, room acoustics won't compromise the sound, and you have more flexibility in changing the tone. The Transducer replaces a range of loudspeaker cabinets, two mics and their preamps using a dummy load (200W maximum) along with circuitry that mimics the reactive nature of a real loudspeaker. This is important, as the speaker's load affects the way in which the amplifier output stage behaves, and that in turn affects how the guitar feels to play. Additional filtering emulates the frequency response of the speaker cabinet and the microphones, taking into account the mic positions.

Everything is housed in a very impressive-looking 2U rack, with all the necessary connections located on the rear panel. There is a speaker input with an adjacent hard-wired thru socket (both on jacks) as well as an unbalanced line output, which comes after the attenuator but before the speaker emulation. The main output is available separately at both mic and line level on balanced XLRs, and there's a second line-level output with both jack and XLR connectors, with a phase-reverse button. Mains comes in on an IEC connector and there's a ground-lift button to avoid ground loops.

As with other SPL products, the designers select parts for their sonic integrity; having met the head designer some years ago, I can confirm that he's extremely fastidious when it comes to the audio performance of his circuits. For this particular device they've chosen high-quality foil condensers and custom-built German Lehle audio transformers. Overall, the build quality looks extremely good, and the front-panel design with its large metal knobs is reminiscent of SPL's high-end mastering products.

Controls

The Transducer is controlled using three seriously chunky knobs and four miniature toggle switches. In essence, the Speaker Action knob governs the amount of top-end coloration, simulating the distortions that occur when a speaker is driven hard. In reality, Speaker Action is also a type of level control, so if a low Speaker Action setting is needed, it must be combined with an increase in Miking Level or output gain. This is equivalent to a studio situation where turning the amp level down means you must turn the mic gain up. However, the Miking Level dial is not just a simple gain control: it is also designed to simulate the way a miked sound changes with volume, with higher settings making the sound seem more compressed and generally 'louder'. At lower levels the sound is brighter, with a less pronounced mid-range. A warning LED comes on 3dB before the microphone preamplifier circuitry starts to clip.

With legending repeated upside-down along the top, the Transducer should be perfect for those who prefer to peer at the back panel from in front and above!With legending repeated upside-down along the top, the Transducer should be perfect for those who prefer to peer at the back panel from in front and above!Photo: Mike CameronBoth capacitor and dynamic mics can be emulated, with a choice of close or ambient miking options. As a rule, the close-miking position pushes the guitar sound more towards the front of the mix. Output Gain sets the Line Output 1 and 2 levels, but doesn't affect the mic-level output. A signal-present LED lights when there's signal higher than -20dBu at the Transducer's input.

A Speaker Cabinet switch selects between an open and closed guitar cabinet tonality. The open-backed setting has more definition, while the closed-backed version has more punch but less presence. You can also adjust the character of the speaker within the cabinet using the Speaker Voicing switch: 'Sparky' emulates Alnico speakers, while 'Mellow' produces more of a ceramic-magnet speaker sound, more commonly associated with vintage British amplifiers. As the names imply, Alnico speakers tend to have a harder, brighter sound, while ceramic speakers are warmer and less aggressive-sounding.

Set Up And Go

Tube amplifiers behave differently according to how hard their output stages are driven, so relying on a master-volume amp to give you great tone at low levels doesn't always work out. With the Transducer, you can wind the amp up as loud as you need to. If you want the speaker to sound as though it is being pushed hard, you should choose a high Speaker Action setting, but otherwise the main decisions are down to combining the speaker, cabinet and miking options, all of which sound distinctly different. Taking a line-level feed into your DAW or recorder provides a suitable signal level for recording and, of course, any further effects or EQ can be added when mixing, if necessary.

I tried the Transducer using my all-tube Fender Champ amplifier and found that I could get very close to the sound of the same amp being miked, with a useful choice of alternative voicings available via the toggle switches. As expected, the open-backed, Alnico speaker combination came closest to how the amp actually sounds, but some of the other options were equally valid. I found the Speaker Action knob made less of a difference than I expected, but then the real-life effect it emulates is no doubt equally subtle.

Where this speaker emulator scores over most of the ones I've used before is in the way it creates a real impression of low-end cabinet thump. However, it could usefully have included a ribbon mic emulation, as with some overdriven sounds the high end can still sound a hint too raspy, and the smoothing effect of a ribbon mic would help overcome this. As it stands, sometimes you find yourself juggling compromises to avoid ending up with a sound that's either just a bit too soft-edged, or one that has adequate bite but sounds too hard or too raspy. Nevertheless, with just a little work you can get some really authentic sounds using this device.

Whether the Transducer is worth the asking price really depends on whether or not you work with fabulous-sounding tube amplifiers in an environment where miking them is impractical. You'll always get a better sound using the right microphone in the right room, but if you have neither and need to record some monster tube stack without being evicted by the noise police, or where spill is an issue, then the Transducer is one of the better solutions around. If, on the other hand, you don't have a great-sounding amplifier, you could buy one, plus a good microphone, for rather less than the cost of this unit, or buy one of the many modelling hardware or software solutions available today. What isn't in doubt is that the Transducer is built to the same impressive standard as other SPL processors, and it offers one of the best combined speaker emulator/power soak combinations on the market. Where a recording situation demands this type of approach, the Transducer certainly does the job well. 

Alternatives

The main direct competition for the Transducer probably comes from the Sequis Motherload (reviewed in SOS July 2005). An alternative would be to use a power soak (there are several manufacturers including Sequis, THD and Rockman) that lacks the speaker and mic emulation, and use software emulations such as Native Instruments' Guitar Rig 3 or Line 6's Amp Farm for this stage.

Published February 2008