Does speaker-level input to sub by pass its electronics?

Bob, I'm embarrassed to admit I didn't see the post was a quote and when I checked out the link I discovered the extensive coverage of using an A7e with high-level inputs.  Also I was sorry to learn that Al is no longer with us.  I have valued his advice in the past.

db

Um, uhh, Al is no longer with us. Though even residing in the beyond, he continues to help us mortals.
Al, you are missed.
Bob

Al, I think you warned me about that once before but I forgot. Given I mostly listen to jazz and baroque in the living room, and the unaided LS50s do a nice job of the bass, I’ll satisfy my lust for pipe organ music and Mahler in the media room where the Reference 1s are supplemented by a pair of HGS-15s with SMS-1 acoustic room correction  -- I don't notice the subs until a pedal note or explosion draws my attention.

Again, thanks.
db

 To the contrary, I was concerned that speaker-level input might treat the subs as ordinary 15" speakers, but the high input impedance of subs is always stressed as the reason it doesn't stress the amp.

That would be a very odd design!

It's a lot easier on everyone if the speaker input presented even a normal 8 Ohm load as that would require large, and expensive parts, and completely different crossover components.

As Duke points out, it's usually a high impedance input with a voltage divider.  Your amp will see a parallel 1,000 Ohm load or so, and the subwoofer's electronics will see a vastly reduced voltage swing (Say from 50V to 2).

It's a question of where the crossover is. 

My current Velodyne 12" servo self powered sub: full range l/r line out to Carver Amp. Speaker wires from Carver Amp to sub speaker wires in. Sub's crossover sends low bass only to it's internal amp. Then Sub speaker wires out to front l/r. 

This method: the Carver Amp is amplifying all frequencies, no relief to it's job; however the primary l/r no longer try to make low bass, an advantage to them. Their highs/mids/upper bass are not in a cloud of self-imposed distorted low bass they had no business trying to handle.

IF you go to a crossover first, i.e. line out to self powered sub, then sub sends line out (no low bass included) to the Amp. Now the amp gets a break, it no longer has to make low bass, and it sends upper bass/mids/highs only to primary l/r. speakers also get the break of not trying to make low bass.

Reducing the low bass load from both the amp and the primary l/r is important when trying to keep amp power needs down, especially tube amps.

I’ll ask Ayre if they see a problem with high-level input from the A7e to a sub, but now I doubt they will.

https://forum.audiogon.com/discussions/subwoofer-for-ayre-ax-7e?sort_order=asc

almarg9,670 posts04-01-2018 10:13am
In addition to the fact that the AX-7e doesn’t provide volume-controlled outputs from its preamp section, there are significant potential issues if its speaker-level outputs are connected to a sub. Note the following statement in its manual:

The Ayre AX-7e drives the loudspeakers with balanced outputs. Since none of the output terminals are grounded, connecting any of them to ground may result in damage to the amplifier. Do not connect the loudspeaker outputs to any speaker switch-box, accessory, or test equipment that has a common ground connection.

The negative speaker-level input terminal of many and probably most powered subs which provide speaker-level inputs is connected to AC safety ground through a low impedance, or in some cases perhaps even directly. In those cases connecting the negative speaker-level input terminal of the sub to the negative output terminal of the amp risks damage to both the amp and the sub, depending on how circuit ground and AC safety ground are interconnected within both the sub and the amp.

And what would probably be a much worse possibility is that if you were to use just one sub, and if that sub provides inputs for two channels, if you were to connect the sub’s two negative input terminals to the two negative output terminals of the amp the result would most likely be a direct short between the amp’s two negative output terminals.

An approach that would probably work ok, which REL recommends for use in such cases, would be to connect the sub’s negative input terminal(s) to a chassis screw on the amp. Although it is possible that hum could result with that approach, depending on the specific designs that are involved. An even better approach, IMO, would be to solder the wire from the sub’s negative input terminal(s) to the ground shell of an RCA plug, leaving the center pin unconnected, and inserting that plug into an unused RCA connector on the amp.

Regards,
-- Al

Duke, thanks for the explanation.  It gives me much more understanding of high-level input to a sub, and confidence in using it.

Erik, I have no interest in bypassing the amp or HGS function.  To the contrary, I was concerned that speaker-level input might treat the subs as ordinary 15" speakers, but the high input impedance of subs is always stressed as the reason it doesn't stress the amp.

I'll ask Ayre if they see a problem with high-level input from the A7e to a sub, but now I doubt they will.

db

The "speaker level input" on a subwoofer goes into a "voltage divider network", which derives a line-level signal from the speaker-level signal.  This line-level signal then goes into the subwoofer's electronics, including the gain control, low-pass frequency control, and any others, before going to the power amp section and being amplified to actually drive the woofer.  

If you use the "line level input", there would be no need for the voltage divider network, but everything else would be in the signal path.  

Some subwoofers have an "LFE input", which is designed to accept the LFE channel output from a processor.  In this case the gain and frequency and EQ (if any) have already been set by the processor, and all that's left is for the subwoofer's amplifier section to amplify the signal and drive the woofer.  

Given that the motion feedback feature is part the amplifier section, it would be active in any of the above scenarios.   

Duke

There’s no part of that amp you want to bypass.

If you want to start modding or DIY'ing a sub, consider making your own from scratch.

no

I've used HGS-15s & 10s for years, but not with high-level input.  It's the high-gain servo function I want to preserve.  I'm not familiar with how high-level input functions.  A local is selling an HGS-15 that I might use with the Ayre A7e to supplement KEF LS50s.  I assume I just add a second pair of speaker leads.  The other possibility is a REL T/5i or T/7i.

My primary setup has a pair of HGS-15s that supplement KEF Reference 1s, and use a pair of SMS-1s for acoustic room correction.  I also have a pair of HGS-10s that I hope to try in a distributed bass setup.

db

Can't you run the sub using the speaker output?
And use the subs high/low pass functions?
B

Um, no, and if you did bypass them you'd end up with no signal.

Besides, the servo itself acts to reduce distortion, so no idea what it is you are trying to accomplish here.

Best,

E