Eh hem!...Subwoofers... What do ya know?

@erik_squires 
Can you detail this thought please:
"Speaker level inputs are subject to the amp/speaker impedance matching"

My amp's Zout is much less than an ohm (according to Luxman the damping factor is around 700);
The Zin of the powered sub, according to JL's manual is about 4,500 ohms; 
The back EMF on the speaker cables should be super low, as the speaker "sees" a super low "load" across a very low DCR speaker cable;

If I was using an amp with high Zout (say 1ohm), then I could do some math and find, possibly in the 30-100hz region a reactive speaker impedance appearing to be "real" resistance of a similar magnitude to the zout of the amp, then causing a voltage drop the speaker sees, basically a frequency dependent voltage sag; 

But how would, even in a high output impedance amp, this affect the signal at the amps output eventually reaching the active subs 4.5K zin? 

My main concern about taking the signal to the sub from the amplifier output terminals, is the time delay that can never be made up by any adjustment in the subs crossover settings; I could delay phase by a full 360 degree to align the peaks, but i'm actually off a whole cycle. This seems bad for impulse response, bass drum hits, bass guitar lines, etc, might be perceived to be "fatter" but smeared. I don't know, maybe i'm going off in the weeds here and none of this actually amounts to a loss in perceived fidelity at the chair; I guess I will find out soon enough. I can see myself diving into the active crossover just because it seems so elegant and proper-- here we have total control over the timing latency and sub/main handoff;

Cheers

Hi @dpac996

So, if I understand correctly, you want to take an amplifier’s output as the input to the subwoofer, correct? And that this output would be shared beteen your main speaker and the subwoofer's input? If not, disregard all of this. :)


Now, onto theory and experience!

Measurements show that while the effect of an average speaker load on a solid state amplifier is small, it isn’t zero.

If you look at the Stereophile simulated speaker load,


https://www.stereophile.com/content/real-life-measurements-page-2

they estimate a minimum impedance in the bass of around 6 Ohms, while my experience says this is often in the 3 Ohm or less.

So, take a moderately solid integrated, like the Luxman 509, whose deviation from flat based on that load is here:

https://www.stereophile.com/content/luxman-l-509x-integrated-amplifier-measurements

The effect of the simulated speaker is very slight, honestly, around +- 0.1 dB. So lets say that at 3 Ohms that’s twice as much, +- 0.2 dB.


My experience has shown that this is sometimes audible, making speakers seem more demanding of an amplifier. For this reason, if you can take the signal from the preamp instead, which will have a flat impedance presented to it, you can avoid any such issues.

In other words, while I understand the math of output impedance, speaker impedance, voltage and current, my experience says that around 3 Ohms is enough to demonstrate a difference among a lot of amplifiers. I wouldn’t want to use that as a reference voltage for that reason.


PS - I own a Luxman 507ux myself. Very happy with it, but when I set up my sub, I’ll be taking the signal from the pre out. :)


Best,

E

Also ...

If your speaker is solidly above 6 Ohms across the bass, you can disregard my caution. :)

So far this turned out to be not another non sense poisoned discussion, seems subwoofers are "a thing to avoid" for the usual trolls,which is great

We are getting now into time alignment, dsp and such, keep it coming, I will take my minidsp mic and rew out of storage and do some measurements on my own system.

Thanks to the OP, I bet the short cryptic title is a deterrent 😉

@erik_squires thanks good info;

I agree the using a pre-out (or active crossover) the preferred way and so does JL audio, but in my case I am running my XLR only DAC directly into my Amp; I will need to play around in the speaker level input regime until I either get an active preamp or the JL CR-1 (preferred);

I actually sold my preamp because I found no real advantage using that vs DAC direct; So, with those funds I diverted into the JL subs and some cables (I digress); Now, it seems that plan was half baked and I would have been better off keeping the pre and stretching the budget to get the subs but I'm already way over my audio budget for the next 10 years, lol

Anyone: please take a look at my setup; do you think the subs should go on the inside or outside?

https://imgur.com/Paj46Ti

-Cheers