Axiom Home Page Forums General Discussion Stereo Powered Sub questions???

Long time Axiom owner, first time poster....

I have a pair of M2v2 bookshelves that are being powered by a tube amp with no sub output jack. I would like to add an EP125 powered sub to the system, but believe that any benefit of a tube amp might be lost if the speakers have to be run from the sub. In other words the quality of sound from the tube amp will be replaced with the transistor power of the sub. Is my assumption correct? Will the tube amp still be of benefit?

Also, not having used a sub before, if the powered sub has more output power than my amp, with the new output power of the whole system be greater (ie. the sub output rating) now that a sub has been added? In other words, if my amp is 50 watts output and the sub is 125 watts output, will the system now be more powerful, or will the lowest common denominator still be the 50 watts? A naive qustions I'm sure, but I've not used a sub before.


Thanks,

Kaz

I could be wrong here so anyone feel free to correct me... When you use the highpower input of your sub it's just to get input signal to route to the sub only. The main's speakers power source (tube amp) remain the same.

JaimeG is right. You then adjust your sub's power level to match your main speakers.

Thanks Jamie G and EFalardeau.

After I read you post I dowloaded the product manual for the EP125 off the Axiom site. I see from reading the instructions that the you attach both the wires from the receiver/amp and the wires from the sub to the front speakers, to the same High Input posts on the back of the sub. That makes sense given what you suggest in that there is still a direct connection from the receiver/amp to the front speakers. The connection at the High Input posts I would imagine just strips off the lower frequencies for the sub. I'm having a little difficulty imagining how this scenario works though, since there is still, in effect, a direct connection between the receiver/amp and the front speakers......do the low frequencies still not get to those speakers as well?

If anyone could explain this a little better, or direct me to an article or website on the issue, it would be greatly appreciated.

Thanks again,

Kaz

If your receiver (or processor) does not perform "bass separation", then both speakers and sub will receive the full spectrum. The sub is equipped with a cross-over that will filter-out all frequencies above the configured threshold (there is "slope" to allow blending with the main speakers).

The M2v2 are starting to curve down aroung 75hz. Setting the sub to 80hz would naturally blend nicely. Actually, the manual should be suggesting something.

Kaz, welcome. Even when the main speakers are connected through the sub, using the speaker level input and output terminals on the sub, this is simply a straight-through connection of the power and audio signals from your regular amplifier. The internal sub amplifier has nothing to do with the main speakers and only powers the sub driver itself.

There's no "stripping off" of any frequencies from the front speakers; they continue to get the full range of frequencies and the result is the same as it would be if you ran a separate wire from your amplifier terminals directly to the front speakers rather than running it through the sub terminals.

Even the audio signals that are directed to the sub amp itself by the branch of the wire from the input terminals are full-range, not with the bass "stripped-off". Since the impedance at the input of the internal sub amplifier is on the order of tens of thousands of ohms, essentially no power can get through, but the audio signal frequencies do. The low pass filter inside the sub(sometimes less accurately referred to as a "crossover")then rolls off those frequencies above the selected frequency on the control and only the lower frequencies are amplified by the sub amp and sent to the sub driver cone.

Thanks JohnK for the great explanation.

Just for clarification, if my amp did have a sub output jack, in that case would the front main speakers only be getting higher frequencies and the sub, only lower frequencies? It's my understanding based on everything you've all shared, that with no receiver sub jack, that the fronts get the whole frequency range, while the sub will play only the lower frequencies (as set on the crossover dial on the back of the sub)......however, if there was a crossover and sub jack on my receiver, there would be no redundancy between the frequencies the sub and/or the fronts were getting.

I apologize for any thick headedness here.....I just want to understand this before I order the sub.

Regards and thanks,

Kaz

It would depend on your preamp/integrated/reciever/whatever. Some sub output jacks are just that--full range outputs. If the preamp/integrated/receiver has no way to set the crossover, for the most part, there isn't one.

To further complicate things, some subs (eg. my previous PSB Subsonic 6i) have passive filters on the high level speaker lines, so speakers connected to the sub actually *do* have some of the bass content removed. In the case of the 6i you get a 6db/octave high pass filter on the speaker lines -- presumably just a series capacitor (eww !!).

I don't believe the Axiom subs have this passive filter, but IMO that is no loss. The passive crossover never sounded right to me anyways.

Kaz, that's right; if the receiver has a sub output and also has a crossover system built in(all modern multi-channel HT receivers do), then the sub would be rolled off above the frequency set and the speakers set "small" would be rolled off below the set frequency. As Ken pointed out, a sub output alone doesn't do this and a few stereo receivers(e.g. HK)have a sub out which is simply a convenience, but is full-range without any crossover to provide bass management.