How To- Perfect Subwoofer Integration

@avanti1960 you might want to get that mic calibrated then try it again.

@alex30
If you are starting from scratch, skip the free TrueRTA. Smoothing to 1 octave is not optimal. Go with REW (Room EQ Wizard). It's free and you can pick any smoothing level. It is also designed to work with the calibration files from Cross-Spectrum Labs if you buy one of their calibrated mics.

 

Can anyone explain what is happening with my sub setup? A few things bothered me so I took them out but would love to have been able to resolve the issues. First my preamp has two sets of RCA outs. One pair to my three way speakers then the other pair to my right and left subs. What I found was when the subs were added the volume decreased. I guess this is do to the additional load? The main disappointment however was the air and sound stage deminished. The subs were placed in line with the main speakers, maybe two inches back and to the outsides. If placed to the inside then they would have been almost on top of each other with maybe three feet of separation to the outside of their enclosures. The bass was never boomy, and it came from between the speakers and was well/realistically placed in the sound stage. The problem was a noticable amount of air around the instruments/vocals was removed and the depth of the sound stage didnt appear as deep. There still was air and sound stage just not as much. Maybe it was the phase adjustment but I never really heard much difference when turning/adjusting it. The subs are self powered, 500 watts, and tbe mains are run on tube mono blocks 38 watts per side. Any suggestions?

 

Thanks for the advice and yes, you are right,
I have noticed this but I did find that bungs reduced the boom I was getting. However, since then I have moved the sub and am getting much cleaner bass without bungs.So it is bungs out and I don't see this changing.
At the moment the only thing I may adjust is the gain but that would only be by a small amount and only after listening to a lot more music.
The problem with the gain is that I always feel that I want a bit more for movies than for music and as my sub has rear controls it is a pain to change so I want a good compromise.

 

Thanks for the info. I will grab that software and give it a whirl.

 

the microphone came with a cal file i could download and read into the truerta. it also came with a measured frequency response. the difference the cal file made was negligible- and only in the high frequencies.

 

apparently your speakers are active? regardless the volume level should not have dropped because all of the channels should have equal gain.
can you run the subs with high level speaker inputs in parallel with your main speakers? this is the preferred connection.

 

You have more knowledge than me, I am not sure I totally understand your questions. My main speakers are three way ported, not self powered. The main speakers are powered by two tube mono amps, 38 watts each. My preamp is tube and it has two sets of outputs. I run one set to my main speakers through the mono blocks, and the other directly to each sub. My subs are self powered by 500 watt internal amp. The sound does seem to become lower in volume when I am running both the mains and subs from my preamp. When I disconnect the subs the sound appears louder. There is definitely more air when the subs are not powered up, maybe this is what I am perceiving as louder. I would like to add the subs. I believe they give a bit more bottom end, they go lower than my main speaker's woofers, however I would like to keep the air that I have when they aren't in the chain. I was wondering if this might be effected by the Phase dial. Although I really don't hear much difference when I turn this dial form 0 to 180.

 

ok now i understand, when you said you connected preamp to speakers i thought they might be active powered speakers.
the best way to connect your subs is from the mono amps speaker connections- if your sub can accept a high level input.
what is the make and model of your subwoofers?

 

Same here, I often boost my sub for film and have to adjust it at the sub by hand. Next sub will have remote control.

 

Yes , a remote would be great but even better a sub that can be programmed for music and then also for movies so at the press of one button you could choose either profile.
It also doesn't seem beyond the realms of possibility that an add on box could be used so that any sub could have this function.
Does anyone know if anything along the lines I am thinking off exists ?

 

Most people I know love movie mode on their sub for music. Watch their faces when you turn it down to an even somewhat reasonable level.

 

Was the file for that specific mic or an average for the model?

 

Sorry for the double post. I missed the edit window.

Following the links provided by Cross Spectrum Labs. His discussion of the factory measurement comparison is old and may have changed. Also, his sample size was only two, so not enough basis for a trend believable trend. So feel free to write it off.

One thing he found was that the mic sensitivity was off by 1db. That isn't much but it does add 1db of error.
The other issue was that the factory cal file starts at 25hz. Anything below 25hz is not calibrated.

 

My subwoofers are SVS SB-2000: 500 Watts. They appear to only have an RCA connections in the rear. These subs with 12 inch woofers that are powered by a Sledge STA-500D, which is a Class D amp rated at 500 watts RMS power and 1,100 watts peak power. The follow is the tech info on the frequency response:

Frequency Response
19 to 188 Hz ±3 dB

Crossover Low-Pass Rolloff
-24 dB/octave

Max Output CEA-2010A Traditional
(1M peak) (2M RMS)
40-63 Hz avg 117.8 dB 108.8 dB
63 Hz 118.2 dB L 109.2 dB L
50 Hz 117.8 dB L 108.9 dB L
40 Hz 117.3 dB L 108.3 dB L
20-31.5 Hz avg 107.4 dB 98.4 dB
31.5 Hz 111.8 dB 102.8 dB
25 Hz 106.1 dB 97.1 dB
20 Hz 101.1 dB 92.1 dB

My main speakers frequency response is +-2.5 dB: 50 to 20,000 Hz and -10dB: 30 to 24,000 Hz, with a 91 dB SPL 1w @ 1m sensitivity.

The crossover data is:

Frequency: 900, 4,500 Hz
Slope: Asymmetrical 18 dB per octave
Type: Third Order Equalized

I hope this gives enough tech info. I'd really love to put these back into my system and maintain the air and get those low frequencies again.

 

Thinking about the mic some more.
The sensitivity difference shouldn't make a difference because the sweep should be continuous from a reference point.
And looking at the curves, the factory isn't that far off as long as the factory mic is only used for bass, 25hz and above, into the midrange.

Being an analyst and numbers geek it would still bug me though.

 

OK, you are correct, no high level inputs for these subs. We'll make the cables work. I am not sure of the cables you have from pre to monoblocks and pre to sub- you want really low loss shielded cable.
I highly recommend these interconnects- they are used for long runs in car audio with remote amps and sound amazing, get the lengths you need- these are very reasonable- unless you are certain your interconnects are really good quality.
http://www.amazon.com/JL-Audio-XD-CLRAIC2-6-Twisted-Pair-Interconnect/dp/B003YUR7JU

Unfortunately your subs do not have a reverse polarity switch either. I believe what might be happening is that the subs are cancelling frequencies with your main speakers (possibly) therefore the reduced volume level. I tried searching for reverse polarity interconnects but couldn't find any. You could DIY some but maybe you won't need to.
Set the phase control knob full over to 180.
Set the crossover filter to ~ 60Hz.
play some deep bass music and adjust each sub so that you can hear them approximately the same volume but deeper as you stand next to each side.
I would also recommend you get this CD that has pink noise tracks-
http://www.elusivedisc.com/My-Disc-The-Sheffield-A2TB-Test-Disc-CD/productinfo/SHECD10508/

play tracks 47 and 48 repeatedly and adjust the level until they sound relatively at the same volume. If some are high of low (especially 47-3 and 48- 1,2,3 and 49-1.
Adjust the crossover slightly up and slightly down until you get the most even response.
Now adjust the phase knob slightly to see what effect it has on the levels of each track.
keep doing it until you are happy that all of those tracks appear to have the same level.
List each track e.g. 47-1, 2 and 3 etc. on a note pad and write down the levels after each adjustment.
This should get you very close.
Then give it the music test and adjust only the level of the sub from then on.
good luck!

 

MDS-


Hold on, I just thought of something- reverse the polarity on your main speakers- connect the plus from the amp to the minus on the speaker for each speaker- this will not hurt anything.
Now add in the sub but start with the phase control at 90-degrees, same crossover (~ 60Hz) and follow the rest of the instructions above. I guarantee this will sound its best with the sub and main speakers wired out of polarity. It is the same as having the switch on the sub but you are doing it to your main speakers manually.

 

Don't think so.
Your preamp has two sets of RCA style outputs, correct? One set going to the mono blocks (left to left, right to right) and the other set going to the subwoofers?
If so, don't change anything with the RCA interconnects unless they are cheap cables and then you should consider the JL audio cables mentioned previously.
For your main speaker wiring, try to reverse the polarity of the wiring for each speaker from amplifier to speaker.
You do this by reversing the wiring at the speaker terminals plus to minus for each speaker.
This now puts the subwoofers completely out of phase with your speakers which is the same as having a reverse polarity switch on the subwoofers- I have found this switch to be a necessity and is included on the subs that have great reputation for integrating- JL audio and REL for example.
Then set the crossover to 60 Hz and the phase dial to 90-degrees and proceed as recommended.

 

Got you. This makes sense, however to throw another curve ball your way, and which begins to makes even more sense about my issue is my preamp is a CJ unit and its output signal is out of phase. For this reason I already reverse the main speakers cables to out of phase to counter this. With this in mind I believe this is what is why I'm having a possible phase issue. With this new info should I then wire the main speakers typically, not out of phase?

 

Interesting. If you have had trouble integrating the subwoofers with the current speaker connections definitely try reversing them back to conventional and then experiment with crossover and phase degree.

 

Will do. You've been a great help giving me sound advice and a good starting point. Thanks.

 

no problem. it's only through help on a DIYMA forum (do it yourself mobile audio) that I learned how to integrate a subwoofer in my car so that it actually sounded like music should sound.
the same principles apply to home audio. you just have to work at it. unfortunately the sound is never really that good (or acceptable) until you get it right.

 

Very interesting thread, it convinced myself to look into subwoofers and share my experience.

First of all, my apologies for the clarity of my writing, english is my second language.

My setup: I own a beautiful pair of Opera Grand Mezza loudspeakers coupled with a Preludio integrated amp from Unison research. The source is either my RP40 for records or a Rotel RDD-06 DAC for digital music. I was very happy with the sound signature of my system (beautiful midrange, detailed highs but not harsh), but it was lacking a bit of punch in the bottom end. So, after getting some advice from my local dealer, I had two options: spending a lot of money on new speakers, or getting a subwoofer. I decided to invest in a subwoofer , the REL T9.

For the calibration process, I bought a cheap calibrated mic on Ebay for AU$40, the Dayton Audio IMM6.



It is only supposed to work with iOS devices (and Android), but I decided to give it a try. I managed to make it work with my Apogee Jam (used for guitar recording), and my macBook Air with the free software "Room EQ Wizard" or "REW". I suppose it would work with any USB soundcard with a mic input.

First, I calibrated the signal coming from the Apogee Jam. To do so, I used a minijack to minijack connector, and connected the macbook Air headphone output to the Jam. REW then plays a sweep from 20Hz to 20KHz through the headphone output and gets the feedback from the preamp. Then I loaded the microphone calibration file (obtained from the website using the provided serial number) in REW.


Continuous line: Mic calibration
Dashed line: Preamp calibration

It was quite interesting to observe that, as I turn up the adjustable gain of the Jam, I loose the bottom end (20Hz to 200Hz). It also shows that microphone and soundcard calibration should not be overlooked.

I found the website Free Online Audio Tests, Test Tones and Tone Generators » very useful to determine the correct phase.

Now, for the RTA process, I used the free version of “Mobile Tools” on my Iphone. I skipped the calibration process, as it’s already done by REW on the macbook. The minijack goes from the monitor output of the mic to the preamp, and I let REW do the rest with a sweep from 20Hz to 20kHz through my USB DAC. For an unknown reason, the 20-22Hz range is not shown, but that's not a big deal.


Red: Without sub
Blue: With sub
As you can see, there's already a bump at around 50Hz, and no matter the volume and crossover settings, I couldn't get rid of it. I suspect it's room resonance but my listening room is not ideal and there's nothing I can do about it at the moment. The result is not perfect, but at least I tried to do it right.

Now, it all comes down to the enjoyment of listening to the music I love, and all I can say is that the sub blends in perfectly with the speakers. I turned it down a bit because I leave in an apartment, and I want to stay in good terms with my neighbours . It's a subtle addition, it provides that deep and beautiful "kick" on bass drums and bass lines, with clarity and definition. A big improvement for a "small" price!

 

You might want to start your own thread on this. Also, much help can be found on the forum where you found REW.

For starters, I'd limit the graphs to the sub's range, like 20hz to 200hz. Then view the graphs unsmoothed.