Re: Connecting subwoofer with speaker wire

In article <lajslvdg36l.fsf@xxxxxxxxxxxxxxxxxxxx>, Tomi Holger Engdahl <then@xxxxxxxxxxxxxxxxxxxx> wrote:
>szekeres@xxxxxxxx (GregS) writes:
>
>> In article <1128564660.757571.140190@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
> mhkatz@xxxxxxxxxxx wrote:
>> >Sorry if I wasn't specific enough. It is a powered subwoofer and the
>> >speaker wire would be carrying a signal, not driving the speaker. I
>> >called Yamaha (it is a Yamaha receiver) and their tech support guy told
>> >me that my solution might possibly work if I get some kind of line
>> >conditioner to remove any noise from the signal. He could not give me
>> >any more detail on what I would need. Can you tell me more about what
>> >you mean by "balanced conversion" if that still makes sense now that
>> >I've described the situation more completely.
>>
>> Radio Shack part number 273-1374 is a 600 ohm isolation transformer. You
>> attach the input to the drive, normally a speaker output. A line level output
> is probably not
>> going to have a low enough impedance to drive it.
>
>True.
>
>> So you get another maybe 10 watt
>> amp and attach the amp input to your sub out. The amp will attach to the
> transformer input.
>> Its better to have the transformer near the sub. The output will feed the
> sub.
>
>True for the idea. The problem could be that the technical specifications
>of that Radio Shack transformer do not look very good for subwoofer application
>
>>From http://support.radioshack.com/support_supplies/doc9/9888.htm
>
>1:1 Audio Transformer (273-1374) Specifications Faxback Doc. # 9888
>
>Coil Turns Ratio:......................................................1:1
>DC Resistance:
> Secondary:..............................................60 Ohms +/- 10%
>Impedance:....................................................600-900 Ohms
>Frequency Response:........................................300 Hz to 5 kHz
>Insulation Resistance:.....................More than 100 megohms at 250VDC
>
>The frequency response is specified from 300 Hz to 5 kHz.
>That transformer is not expected to work well with subwoofer
>frequencies (20 Hz to 100-150 Hz typically).
>Attenuation of the lowest frequencoes and with strong input signals
>(amplified line signals) I would expect serious distortions at lowest
>frequencies.
>
>Ttransformer approach works as descrubed above, but I would look
>for a better transformer with more suitable specifications.
>
>> The gain on the
>> auxilarry amp may have to be fiddled with, and will otherwise have no bass
>> or treble boost. The polarity may also have to be reversed if the aux
> amplifier iverted the
>> signal.
>
>> Since the 600 ohm transformer feeds a higher impedance input, its response
> will be
>> much better than its specs indicate. This will give noise free performance.
>
>
>The specifications on frequiency response would be with high
>inpedance load on output and low impedance input better than
>listed on the specs. That's true. But still might not be adequate
>for hifi subwoofer. And then there is that risk of transformer
>satutation at low frequencies at high signal levels.
>This is quite tiny transformer, it can't handle high signal
>levels at low frequencies.


I feel the specs would be using a 600 ohm output load.

Like I say, I have used this type of setup on a few systems. I have not
measured the response. On my TV setup, the audio sounds pretty good.
I tapped off the speaker leads, to feed the receiver. I did this because
it was the only easy wasy to control the volume with the remote.
Plenty of bass, but I would predict some low frequency rolloff at some point.
Expecting to get no reduction at 20 Hz would be asking too much.
I ran about 80 feet of line in a bar to drive a remote system. Worked well.

greg

>> I have used this system,
>
>Do you have any specifications to give how well it worked.
>Especially at lowest frequencies.
>
>> however you might want to check out part # 270-054
>> which is a RCA ground loop isolator from Radio Shack. I have never used this,
> but
>> if you connect the ends of the wires to the RCA input, it will feed directly
> into
>> your sub. There are several products for car stereo which you can adapt to
> your situation
>> if you do a little searching.
>
>I have never used this particular products. But I have used
>similar devices from several manufacturers (some look pretty much the
>same as the one in the Radio Shack web page picture).
>
>This kind of RCA isolators generally work much better than
>those small 600:600 ohm transformers in audio applications.
>When connected to normal RCA line level sources, they typically
>attenuate the lowest frequencies somewhat, but not very much.
>You can get frequency rensponse from 40 Hz and up wery well
>on units I have worked with... with very low impedance signal
>source and not too stong signals lower than that to 20 Hz or so.
>
>
.

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