CD Player Output Vs. Preamp Output For A Sub. - diyAudio
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Old 9th April 2004, 05:50 PM   #1
kspv is offline kspv  India
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Question CD Player Output Vs. Preamp Output For A Sub.

I have a Yamaha AX-396 stereo integrated amplifier with 60W+60W continuous RMS output, without any subwoofer out, and without any preamp-out. I have been using this amplifier with a pair of high quality monitors to my satisfaction. Lately, I have set my eyes on a very good stereo music subwoofer. The music subwoofer demands that there has to be a "preamp-out, main-in loop" on my amplifier.

I have read from several postings on the net, including some on DIYaudio, that today's CD & DVD players can easily drive a power amplifier without requiring a preamp, as the output of CD players is generally around 2 Vrms, which is much higher when compared to a power amp's input sensitivity.

I believe that the same rule should apply to a subwoofer as well. If a subwoofer requires a preamp's line-level output as the input, then the working of a subwoofer should be satisfactory with a CD player's output as well. Why not I connect my CD player output to the subwoofer's input, and then connect the subwoofer's output to my stereo integrated amplifier, so that the bass portion is taken care of by my subwoofer, and the rest by my monitors.

Can the Gurus on DIYaudio throw some light on this issue,( for which I shall remain grateful)?
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Old 9th April 2004, 07:57 PM   #2
sreten is offline sreten  United Kingdom
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More than a slight problem with the lack of volume control I'm afraid.

Quote:
The music subwoofer demands that there has to be a "preamp-out, main-in loop" on my amplifier.
I you wan't to use line level filtering built into the sub then this is
the case, that is prevent low bass getting to your main speakers.

However if you don't have low bass upsetting your main speakers
issues then you can drive the subwoofer at speaker level.

sreten.
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Old 9th April 2004, 08:06 PM   #3
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The pre-amp out of a CD player is enough to drive a sub amp in most cases. As sreten says, the lack of a common volume control is annoying and not the best way to do it. Many CD players have A/B outs so one pair can go to the main amp and the other to the sub amp. Then (assuming there is one) you can adjust the crossover on the sub to better match the mains. This assumes that your mains don't mind having the full signal sent to them. Regardless, a better approach is having a common bass management system, but you know, sometimes you just have to make do.
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Old 16th April 2004, 10:45 AM   #4
kspv is offline kspv  India
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Since the Gurus have talked about using the variable crossover of the sub, and the speaker level inputs, I thought it appropriate to post some of the technical details of this sub. I can do with the slight annoyance of not having a common volume control, but would not like to opt out of this sub. If necessary, I would change my amplifier, and stick to my existing speakers and this sub. The following are details provided by the designer of this sub (whom I regard as a very experienced and knowledgeble sound engineer) on this piece of equipment ; the words in inverted quotes are from him. My thanks to Timn8ter and Sreten, and I request them to re-examine the issue in light of my preferences and technical specifications, and suggest whether I require an amplifier change.

".........The sub is built around 2x10" woofers, arranged internally inside a 16" cube cabinet in a complex push-pull system which is essentially a constant-pressure bandpass design!!!

To simplify - there are 2 internal 10" woofers, these are facing each other - suspended and separated by an internal panel inside the subwoofer cabinet. this configuration is unique anywhere in the world... and here are the advantages.

Firstly, this translates into a constant - pressure (isobaric) system. This configuration allows for halving the cabinet size without any drop in efficiency.

The second unique point of this cabinet design is that it is a push -pull system integrated in a bandpass design. - (a bandpass design is one where the speaker doesn't directly radiate into free air - it is mounted internally in the cabinet - and the air flows out through a properly designed port). With this configuration, 3rd harmonic distortion is completely eliminated at the output because - in a push - pull system - the odd order harmonic distortions are out of phase at the port interface.
Elimination of 3rd harmonic distortion is a large factor in elimination of ear fatigue.

The third unique part (and there are more)...is that a bandpass chamber internally compresses and de-activates excessive cone movements - because the woofers are actually working into a fixed mass of air - thus audible distortions due to overdriving are virtually eliminated. In any case, overpowering our dual 10" terra-150 is an effort in itself.

The terra150 subwoofer is once again unique in that it is a stereo
subwoofer - again a first in power subwoofer designs. In stereo mode (which can be changed to mono easily on the fly)...the electronics of the power module does not have to sum two channels of bass (the left and right channels) into mono. this process of summing has it's own inherent distortion and ambiguities - our terra150 allows cleaner sound - also a
stereo bass provides better integration and more control over music listening.

The bandpass design allows for it's own acoustical crossover at 125Hz - we prefer this over having expensive (and distortion causing) electronics to crossover the speaker. In any case, since you do have the studio1, the integration between the 2 (as also with the pro10) is perfect.

Finally - the electronic power module - is a separate black box - and is mounted as part of your equipment rack - this prevents excessive vibration of the subwoofers inside the cabinet and the constant air pressure from causing modulation distortions in your amp. Just imagine - would you like to keep your amplifier over your speakers? imagine what that would do to the internal parts in the long run? now think of those guys that keep their
power module inside their subwoofer!!! Now you know why all sub 35K subwoofers sound trashy!

Besides, having the power module in the equipment rack - is a practical and simple solution - allows ease of adjustment, easy maintenance and prevents water splashes on electronics when cleaning power subs _ especially in indian homes.

Now that's some subwoofer! - as always - at lithos we believe in one thing - do it the right way - no matter if the rest of the world does it different.

To answer your questions,

1) The subwoofer does not have a variable crossover - the crossover is a fixed internal - acoustic type

2) A 0-180 degree phase switch is possible - as simple as reversing the polarity of the speaker terminals of the subwoofer.

Remember- eliminating expensive electronics to do these things means cleaner sound at a better price...

3) The subwoofer can only be attached to - and here's the important part - a home theatre amp - or a stereo amp which has a pre-out-main-in loop. so do check the back of your amp if there is this pre-out-main-in system.........."
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