Billbobboy42 Loc: Center of Delmarva

I am using a 1982 Harman Kardon amplifier to drive a pair of equally vintage Polk bookshelf size speakers. Still sounds good after all these years, but I would like to enrich the base output. The amp has hookups for two speaker sets. Each set can be active separately or played simultaneously. Since I am using just one set of speakers , is there a way to effectively connect a powered subwoofer? Thinking of a Klipsch or similar model.

bpulv Loc: Buena Park, CA

As long as the impedance of the amplifier's output is the same as the impedance of the loudspeaker it will work. Most of the older systems were low impedance (8 ohms the most common, 4 or 16 ohms less common) newer systems have higher impedance.

Longshadow Loc: Audubon, PA, United States

Just don't hook up only one speaker to the second set of speaker connections unless you know the design of the amp.
Some amps do not bode well without a speaker connected unless the speaker is fed from a transformer.
Some units rely on the impedance and current flow in speakers as part of the output circuitry.

Dave327 Loc: Duluth, GA. USA

Well yes, but you need a powered unit with the connections to connect to your old amp. Basically with inputs (L & R). A quick check on Amazon showed a Monoprice 8” powered (79.99) unit that safely does what you want to do. Most units today have only a single coaxial input for subwoofer out on newer amps.

Najataagihe

Do NOT hook up the inputs of a powered speaker to the speaker outputs of ANY amp!

You either need to use Monitor Out connections or tap into the INPUT jacks going into the amp.

A powered speaker has its own amp and is expecting line level (Subwoofer) or mic level (PA) inputs.

Pumping an amplified signal into another amp is a good way to let the smoke out of the circuits.

TriX Loc: Raleigh, NC

If it’s a powered subwoofer, it has a built in amplifier as mentioned above. Just hook the input of the subwoofer to the tape monitor output of your amplifier. If your amplifier doesn’t have a tape monitor output, reply, and we can advise further.

RGreenway Loc: Morristown, New Jersey

I would add a subwoofer to the main speaker outputs and use the sub's built in circuitry to send only the mid and upper frequencies to the bookshelf speakers (in other words, use a non-powered sub with a built in crossover). Some powered subs may also have built in crossover and would also work I guess.

OlinBost Loc: Marietta, Ga.

Just be sure that the new speaker can handle the power output of the amp.

Rhl0630

You need the type subwoofer that two inputs and outputs. You run both outputs to the sub. Then the outputs to the so Polk speakers the subwoofer has a built in adjustable crossover. I have several of those somewhere in my basement. This system works fine with your amp

Billbobboy42 Loc: Center of Delmarva

I do have a tape deck hookup on back of amp (left & right input/output, RCA jacks) and a tape monitor on/off button on front panel. The amp`s power is 30 watts/channel "both channels driven into 8 Ohms, 20-20,000 Hz". "Power bandwidth @ half rated output into 8 Ohms". The typical power output of most 8" subwoofers I have looked at on eBay are rated @ 200 watts, but don't remember what the rated Ohms are or how to determine compatibility in that regard. This amp has hookups for record changer/turntable, cassette deck, and CD player.

TriX Loc: Raleigh, NC

Now that you’ve provided more information, let me add some detail. I don’t want to make this complicated, but here are the considerations:

1) if the subwoofer is powered by its own amp and has low level inputs, then you need a low level signal to drive it. That signal level must vary with the volume setting. If you have a separate amp and preamp or your amp/receiver has a variable signal level output, then you can drive it directly from that output. You can’t use the tape monitor output because it’s a fixed level which doesn’t vary with the volume control.

2) some powered subs have speaker level inputs. In that case, you can simply use the “B” speaker outputs from your amp and select both “A” (to drive the Polks) and “B” to drive the sub. Since that type of sub has a high impedance input, there are no problems with the load on the amp being of too low impedance.

3) some subs, as mentioned above have built in crossovers. Those are typically designed to be used with small satellite speakers with no or limited low frequency response, not like your Polks, which have decent, if not overwhelming low frequency response. While that type of configuration is often used with computers and has been used for some speaker systems, there are real audio compromises involved

I suggest the following: first, you can maximize your bass response by the placement of your Polks. Every surface you place next to the speaker doubles the bass. For example, placing them on stands, away from the floor and walls results in the lowest bass. Placing them against a wall increases the bass. Placing them against a wall and on the floor (2 surfaces) increases the bass more. Finally placing them in a corner on the floor (3 surfaces) produces the maximum bass. If this is practical, you may find the bass is adequate without a sub woofer. Remember that only a small percentage of music has really low bass, and MP3 sources are always lacking the bottom octave.

If you go ahead with a sub, I would suggest avoiding the type with the built-in crossover that sends no or limited bass to the Polks. You may find that the lack of mid bass from the “satellite” Polks to be unsatisfactory. I would pick a sub that can accommodate speaker level inputs and run it off the “B” speaker outputs.

Fotoartist Loc: Detroit, Michigan

Nice equipment you have.

BBurns Loc: South Bay, California

Trix, Keep in mind that on most vintage gear 'Tape Out' was ahead of the volume control.

TriX Loc: Raleigh, NC

Absolutely correct and I mentioned this in my later post.

BBurns Loc: South Bay, California

Missed it!