'bi-amp' the cheap way

[colterphoto1]

I volunteered to provide sound for a youth ministry conference last weekend. Wanting to take a smaller but full sounding Klipsch system, I was thinking of ways to incorporate a small sub with two KP250 'speakers on a stick'. This event was to be mainly people speaking, but at times we wanted to get the crowd of 18-25 year olds really energized with music and also to play jams between speeches. Here's what I came up with.

I have only one KP115 'stubby sub' (as it's called in Klipsch tech literature) so my first thought was to use a bi-amp processor and second amp in my main rack. Recall that my main rack has Mackie board, single Crown PS200 amp, and multiple processing. It usually included Quadraverb for vocals, dual 15eq for mains, DBX 166 compressor that I patch into troublesome channels). I took out my Lexicon and ART FX so had only two slots open.

I could have stolen the Rane AC23 from my amp rack and used a single space amp like BGW150 or Crown D75, but that would have the rack totally full and the amps would not get proper cooling.

Here's what I configured. I'd installed a passive crossover in the KP115 earlier in the week and had tried using it attached to one channel, but then I only had one channel with a sub. And frankly, that 115 just doens't produce enough bass to really augment a KP250, let alone a pair of them. Realizing that the Mackie 1604VLZ board had not only main L/R outputs, but a MONO output with it's own volume control (on the back panel), I knew I could do a 'poor mans biamp'.

I hooked up the main L/R to a BGW 150 single space amp (attached between two spaces for adequate airflow) for the KP250's, providing them with good clean 100 watts or so, running full range down to their rated 50 hz.

Then I used the mono output of the Mackie into the bridged PS400, yielding 280 clean Crown watts for the KP115. Having a passive network in the sub caused it to reduce output at the upper limit of 150. I had some overlap of frequencies which wasn't too harmful and I pulled the 120 Hz slider down on the master eq to flatten the mix. Now I had a thumpin sub with plenty of power to augment the Kp250's. This system easily fit in my pickup bed and with a single dolly for speakers and main rack on wheels I had only two carts to push through the hotel hallways.

This system did a great job in a hotel conference center holding about 200 people. With a little channel eq and the Ultimate speaker stands positioned just forward of the stage/speaker table I was able to tweak the system for great sensitivity and no feedback. Even the most pipsqueak little girl who spoke was clearly heard in the room. Another trick is to use a mic on boom stand, positioned at the front and one side of slanted lecturn. Use the mini-boom to force the mic into the face of the speaker, angle mic upward at 45 degrees or so- when the speaker tilts head down to read their notes they are right in the mic.

While playing at ballrooms of this type, SECURE ALL GEAR every night. The movable partitions at most hotels are not really lockable, and staff can get into your stuff. In this case, I left all cableing in place for the next day and just rolled the speakers, rack and stands to a guest room for the night.

[bhendrix]

Nicely done there, Michel!!

Thanks for the write-up. More of your PA "tips" will be most appreciated!!