Open Baffle Fun with Cheap Goldmine Speakers

[wrenchone]

On a whim, I bought 36 Samsung 8 ohm 1.5W oval speakers from Electronic Goldmine at $0.99 each. They probably did duty in TV sets, and I figured I'd try them in an open baffle line array. I still had the box from my flat screen TV (lovely big piece of double thickness corrugated cardboard, couldn't bear to throw it away), so I chopped it up to make a pair of arrays 44" tall by 16" wide, each with a side brace. I used 16 speakers/side, each oriented with long axis horizontal. Mounting was simple, I lined them up on the cardboard, traced aound them, and cut the outlines with a box cutter. This allowed me to rear mount the drivers with a friction fit and a little help from some duct tape. Speakers were paralleled in groups of four, then connected in series, for 8 ohms total impedance. No crossover was used.

I'm driving the arrays with a 6W/channel SE ultralinear tube amp. Points for sensitivity and midrange presence. There is some high volume glare - whether it's the fault of the drivers or the baffle is not certain. Help will be needed for extreme highs and lows. So far, not bad for the investment of time and money. Right now they're handling an old Don Cherry CD. I should try a similar stunt with the cheapo 4" Pioneer full-ranges I have on hand for comparison - they are still sitting in the box they came in.

Electronic Goldmine also has some larger oval speakers for a little more money.

[Kensai]

You're high frequency problems come from comb filtering. With line arrays, the center to center distance of your fullrange drivers is the wavelength of the frequency at which comb filtering sets in. Its basically the treble of the drivers interfering with each other. You could EQ that out, but given that you're working on the cheap here, you might want to just make it into a "focused array" passively. First you'd want a high efficiency tweeter like a $2 peizo or something and put it at ear height, or in the middle of the line, whichever you like best. Just cap it off up high to avoid the issues of running a peizo too low. Then just put a single inductor in front of your fullrangers to keep them from reaching up into the comb filtering region (just look up the frequency that has the wavelength of your center to center distance and select an inductor to start rolling maybe an octave lower; then put your cap on the tweeter to where the rolloff curves overlap at around -3dB).

Cheap + OB + Line Array = FUN

Kensai

[wrenchone]

I doubt it's comb filtering, more like the driver basic frequency response - they're cheapo TV speakers after all. The glare at high volume is much, much more of a problem.

[pacificblue]

You might try an RC circuit in parallel with the voice coils. Voice coil impedance rises with the frequency. Tube amps have an output transformer. Transformer and speaker impedance form a voltage divider. As a consequence the rising impedance at high frequencies leads to higher voltage drop (= higher power = higher SPL) at the speakers.

To test that theory, connect a transistor amp instead of a tube amp. Transistor amps do not suffer that effect. The glare should be gone or at least reduced.

Here is a calculator for the RC circuit.

[wrenchone]

Unless it's the nasty little drivers resonating... Thanks, though, it's something to try. The tube amp has some negative feedback, so the output impedance may not be all that squirrely.