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

+1 for measurements

+1 for Mini-DSP

Audiophiles make fun of the home theater crowd. The home theater crowd makes fun of audiophiles. Both groups can learn something from the other.

Subwoofers should be sized according to the room. I had Vandersteen 2ci speakers in a small room approximately 11x14 and they sounded great, I moved them to a much larger space and the magic disappeared. I did not need a subwoofer for the smaller room. I did need a subwoofer or more for the larger room.

Timing matters! I do not have automatic room correction. I use two JTR, S2 subwoofers in the basement. A friend familiar with free REW software came over to help dial them in. My room is 29 feet long. One subwoofer is in the front left corner. The other sub is located in the right rear of the room. The subs were level matched so they both played at the same volume at the major listening position. The subs were then individually measured and the individual measurements laid over one another via the program. The goal was to make two sign waves from two subs appear as one. The delays were made in the Mini-DSP until the sign waves were as close as possible.

My friend then proceeded to time align each speaker to the subs. Again the goal is to over-lay all individual measurements and have them appear as one sign wave. We did not get it exact. We gave my multi-channel system a tune up. Now instead of an 8 cylinder engine running on 6 cylinders I had a system working together as intended.

Prior to my friend coming over, I had pulled out a tape measure and set speaker distances. The distance measured by tape was different than the distance measured electronically. After timing alignment, I was able to reduce my listening volume by 10db and maintain the same enjoyment and listening intelligibility. I know many use automatic room correction and assume it is correct, you don’t know until you measure. You cannot just do the math to determine delays, the room and things in the room affect how sound travels. According to the math I should need 7-8 seconds of delay. Measuring with a mic resulted in 5.811 second delay.    

After alignment my system measured +/- 3 Db from 100Hz to 6Hz. I tried to listen to my flat system and did not enjoy it. I tried increasing the overall sub volume, but that resulted in bloated bass. I finally did some equalization in the Mini-DSP and the system came alive. I was able to reduce the overall sub volume back to where it initially measured flat. As someone mentioned earlier, we do not hear all frequencies at the same level. Lower frequencies must be louder to be heard evenly. Equalization helps accomplish this according to individual taste.  

My system produces great bass for movies but for music you may not know the subs are playing. After the changes, there have been a number of times I have really been surprised at the bass content while viewing non-action movies.

I use Innersound Eros speakers for two channel listening. The speaker is essentially two electrostatic panels on top of two ten inch transmission line subs. Bass is omnidirectional but there are recordings where two instruments that produce notes below 80 Hz are used. There are recordings where two pianos or two drum sets are used. A properly set up system can reveal that multiple pianos, drums, guitars are being used, just as a quality set of stereo speakers can reveal multiple singers harmonizing as one. In my humble opinion stereo subwoofers can help a listener detect the dual instruments in those recordings.  

           

In my humble opinion, from my humble experience

@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 😉