Time-alignment of subwoofer

[Hyun]

Thanks to Lanett yesterday for lending me his beautiful enigma CD. donno if u're reading this, r u in the forum?

 

while meditating on it i kinda found out how to tune my sub. and since i dont think this topic was discussed much here, lemme start a post about it.

 

whoever knows how to TA subs please correct me or at least give ur ideas about this issue. i find that a great many subs are wrongly TA-ed, mine included. let's see if we can find a good method to TA.

 

1. select a nice bass track with sub response. it doesn't have to be too fast. but it should be repetitive cos u need to listen to many beats to get it right.

 

2. let's assume the TA of all your other speakers has been finalised.

 

3. as i played the bass track, i tried to time the beat of the music with the vibrations felt. u can feel vibrations especially on your seat and on your clothes.

 

4. TA is a relative thing. the timing of a speaker firing is with respect to the TA numbers of other speakers. so let's take the reference as the TA figure of your front right speaker. that, after all, is the closest to you, and probably is the anchor point from which u TA'ed your front left as well as rear speakers. let's pretend the front-right TA value is 50 cm.

 

5. start your sub TA at 50 cm as well. strangely, for my case, my correct TA value for my hatchback with "normal phase" for the sub is exactly the same as the TA value of my front right speaker. i.e. 50 cm in this example. this may not be true for cars of other designs, so start from 50 cm and experiment.

 

6. play the bass track, and change the TA 5 to 10 cm at a time. you will feel that the timing of the beat, and the vibrations, will start to close together or separate. e.g. u might find that u hear the music beat first, then the "buzz" of the vibration comes later, like it's slow, laggy, lazy.

 

7. as you change the sub TA value, u might find that the timing of the buzz gets closer and closer to the beat. the "correct" value might be the number that gives u the closest timing of music BEAT and vibrations BUZZING.

 

8. re: PHASE. TA value is different when you change your phase. some of u might be able to REVERSE phase (180 flip) at the head unit. others might have an amp dial that can turn phase from 0 to 180 degrees. try your sub with phase reversed. the TA value would be quite different. in my case, from 50 cm at normal phase, it became 270 cm in reverse phase.

 

9. compare the 2 phases at their respective "correct" TA values. see which sound you prefer. they don't sound the same to me, and i don't know enough physics to explain it. i chose "normal" phase in the end and set my "correct" TA value back to my normal phase value of 50 cm.

 

10. counter check with other genres of music - fast bass e.g. disco/trance tracks, and slow speed tracks. the effect should be retained.

 

next post: what is "correct" sub TA?

[Kermit]

Not bad...

 

To get sub SQ, there are some other types of tracks you can use. There are other things to listen out for too. Think about those big big traditional drums..you will get what I'm saying.

[Hyun]

so is my interpretation of "correct" sub TA the same as yours?

 

to illustrate, let's graphically represent the music beat like this:

 

....mmmMMMMMMMMMMmmmmmmmm.................

 

where the ... represents no sound, and capital M represents the moment you hear the loud beat. this is where your mind thinks the beat timing starts.

 

a sub might play something like this:

 

....sssSSSSSSSSSSSSSSSSSSSSSSSSsssssssss..

 

where capital S represents a strong vibration/buzzing, and smaller s a palpable but not so strong reverberation tailing the beat off.

 

should the timing of "M" and "S" occur exactly on the dot? that was how i tried to tune this "correct" TA value, by making the vibrations fit the timing of the music. as i went through all the values, a smaller TA value (telling the sub to fire later) or a bigger TA value (telling the sub to fire earlier) generates a sound whereby you feel the vibrations start later than the beat, and persist longer than the beat - giving you that "slow lazy" effect. it felt to me that the "correct" value was quite obvious, and that any other value just buzzed longer and at the wrong time and didn't feel right.

 

what if you make the TA number deviate by hundreds of cm? the timing of the sub wave shifts so much that you're at another point on the waveform - maybe effectively reversing the phase if my guess at physics is right.

 

e.g. at 50 cm, you feel it's the correct value with minimal "late" buzzing.

as you increase it to 270 cm in my case, you get yet ANOTHER coincident "correct" value, whereby the beat again coincides with the buzz. it sounds different from 50 cm, you might also notice that the sub wave resonates with your car parts e.g. doors in a different manner (more "noisy" in my case). i finally settled on the cleaner point of coincidence at 50 cm.

 

but is this the correct way to TA a sub? after listening so long to wrongly-TA'ed subs, you get so used to feeling the "buzz" at the wrong time, that when it seems to fire correctly, you feel something missing. at this "correct" value, you might feel that the buzzing is less obvious than at "wrong" values. you might feel that your sub seems to have less "kick". have we just done something like cancelling waves? what do you think?

 

at the next meet-up, i'll try to get some TA gurus to audit my TA and give feedback.

 

a final last word regarding TA, especially directed at those who find TA too artificial:

 

i suppose the car environment is quite different from home environment. at home, you don't have your sub located in your boot, separated from you by rear seats etc. therefore you might agree with me that the timing subsonic vibrations take to travel through the air in your home is probably going to be different than the time it takes within a car.

 

if we don't TA our subs, what might happen is, there might be a small discrepency in this wave timing with respect to the music beat felt in a non-TA system. without TA, we might not be able to correct this speed difference. (i might be wrong here. polyfill, box construction etc might change its speed, i don't know.)

 

but for those who prefer music non-TA'ed, headunits still have this feature whereby you can listen to front channels non-TA'ed, but yet leaving the sub still TA'ed correctly. you're simply just TA'ing one channel --> the sub. the TA of the fronts and rears can be totally off and you can enjoy the music neat. you just use the feature to correctly time sub response. this should be quite beneficial and not lead to any of the problems plaguing TA'ed music e.g. frequency losses, unnatural SQ etc.

 

that's all for now. i'd really appreciate some discussion on this. maybe next meet-up we can play a little, and i can re-do some of the members' sub-TAs i did in the last 2 weeks.

[Hyun]

thanks kermit. i'd like to audit my settings with some varied sub tracks e.g. the traditional drums you mentioned. but currently horrr.... i dun have backupssssss of traditional drums leh hehehehe .. *hint hint*

[Hyun]

Robin1_sg, don't mind if i cut and paste your comment here. trying to get more opinions in and see if we can help each other improve TA.

 

anyone knows of any web resource regarding TA?

 

--------- Robin1_sg wrote: -----------------

A correctly TA system will bring the music and vocals into cohesion without the diffused image. Same for subwoofer TA. Your write up on sub TA is basically right, but need to hear carefully the overall bass image. But bass TA is more forgiving, because basically lower frequencies are less directional. The first overlapping of wave will give u the image, but further adjusment can finely focus it making it sound in cohesion with the timing, and can bring the bass upfront without any sound coming from the back. After all these TA and EQ adjustments, can play around with the crossover frequencies, cut-off slopes, the gain. When all these are fine tuned, one can hear the depth, the image width and the clarity, the correct sound staging and coherent speed. It will be like looking thru a big open window with 3 dimensional effect like our home setups.

[Kermit]

A bit trying too hard to "technicalise" this...haha...

 

Sub TA and phasing and EQ affect each other. it is not easy...you need to spend a lot of time listening to the boom booms to get it to YOUR liking. Yes, it's personal. some people listen to say, R&B a lot, so it's a parculiar setting. Ochestra? Rock? Jazz? Hard to get into someone else's mind to understand. But, there should still be an acceptable tuning to cater to a variety of music. I admire your learning spirit!

[Hyun]

actually, having "realised" this, my current impression is that it does NOT depend on the music being played. the music played might interfere with your decision on how to equalise the curve at 80-100 hz, and 50-downwards.

 

the reason i say it doesn't affect, is because what we're doing is timing the wave, and determining the phase. it's like saying your tweeter timing (TA) should be this value. all music can use this value. it's just timing.

 

i tried my current config with 3 different kinds of tracks - enigma (new age, speed about 80-100 / min), some trance where bass fires faster and more repetitively droning, and vocals like golden ear. my conclusion is that when it's in time, it's in time. they all sound fine.

 

so different music MIGHT lead you to equalise or adjust sub level differently, but should not affect this timing at all. except, as i mentioned, not everyone plays "normal" phase. and yes, i agree one way is to listen to different booms and see which is more suitable ... but ....

 

.... my suspicion is that this thing about phase isn't just about gut feeling. i suspect to the audio engineer there is a CORRECT phase setting too. unfortunately i have no source of education on this subject matter. does anyone understand sub phasing?

[Twnll]

Hyun, full marks for your efforts We all can learn something here... Keep on booming!

[Fasthonda]

wow bro, you are simply amazing.

 

got a question, how you know the drummer is hitting the same spot consistently?

 

heng mine was simple, default ta and just adjust the x-over and slope can liao.

[Hyun]

we're tuning a sub beat which means it's not hitting a side/snare drum, but rather an acoustic bass drum or an electronic bass (synthesized). so the sound should be reasonably consistent, and VERY consistent for an electronic bass. that's why repetitive electronic music is best for tuning sub. but many trance tracks are too fast. just pick anything reasonably repetitive and about 80-100 beats per minute and it'll be quite easy.

 

> heng mine was simple, default ta and just adjust the x-over and slope can liao.

 

i.e. you did an auto TA, or the shop tuned for u? perhaps u wanna try this exercise to confirm whether the TA u have is accurate or not. remember to copy down your initial sub TA value in case u dun like, then u can reset it back.

[Fasthonda]

oh, haha thought you talking abt the usual drum.

 

"i.e. you did an auto TA, or the shop tuned for u? perhaps u wanna try this exercise to confirm whether the TA u have is accurate or not. remember to copy down your initial sub TA value in case u dun like, then u can reset it back."

 

auto ta? neh, i never trust auto ta or auto eq cos never accurate. shop never tune for me also. me tune myself. my initial value is 0.0cm

[Kermit]

Yes, you're right on some things. The Sub level and EQ really depends on your preference. The TA and phase should have a correct setting. I think phase affects TA too. Oh did I foreget to say...TA affects EQ and vice versa? How then can you not be affected by the type of music you listen to when you TA? Interesting? I have no answer now...

[Robin1_sg]

actually, having "realised" this, my current impression is that it does NOT depend on the music being played. the music played might interfere with your decision on how to equalise the curve at 80-100 hz, and 50-downwards.

 

the reason i say it doesn't affect, is because what we're doing is timing the wave, and determining the phase. it's like saying your tweeter timing (TA) should be this value. all music can use this value. it's just timing.

 

i tried my current config with 3 different kinds of tracks - enigma (new age, speed about 80-100 / min), some trance where bass fires faster and more repetitively droning, and vocals like golden ear. my conclusion is that when it's in time, it's in time. they all sound fine.

 

so different music MIGHT lead you to equalise or adjust sub level differently, but should not affect this timing at all. except, as i mentioned, not everyone plays "normal" phase. and yes, i agree one way is to listen to different booms and see which is more suitable ... but ....

 

.... my suspicion is that this thing about phase isn't just about gut feeling. i suspect to the audio engineer there is a CORRECT phase setting too. unfortunately i have no source of education on this subject matter. does anyone understand sub phasing?

 

Time alignment makes use of time delay for the low, mid and highs to arrive at the same timing to achieve the correct sound stage for off centre sitting in car environment and distant woofer. EQ affect tonality but does not affect TA, only phase reversal does. Hope this helps.

[Lionheart7004]

Hyun,

 

Thanks for the compliments.. but one thing to note..

 

You got to note that where did the Sound Engineer placed their mic..esp for percussions.

[Sarong1]

Yes, miking does affect how we perceive the sound or the music should be reproduced. But in a market where commercial CDs dominate that of audiophile, there is really no means to determine how the miking was done. In any case, not all audiophile CDs indicate how was the miking done.

 

One such record that I know of do indicated how it was recorded, and it is the "Drum and Track Record" produced by Sheffield Lab, where a brief illustration was included to inform the listener that two mics were placed above the drum set and how another mic was placed at the kick drum. In this case, how are we going to differentiate the height of the percussion set? Are we not confused further and tune our EQ wrongly? Remember, this was with illustration, what about those without?

 

So, this is very much left to our experiences (be it thru listening to live performance or tuning) and our perception. Besides using measuring tape to determine the correct distance and thereafter fine-tuning it to suit our car environment, the end state of how we "feel" for the sub takes precedent.

 

Thereafter, we can move on to determine the correct and accurate rendition of the sub ranges.

[Kermit]

"Time alignment makes use of time delay for the low, mid and highs to arrive at the same timing to achieve the correct sound stage for off centre sitting in car environment and distant woofer. EQ affect tonality but does not affect TA, only phase reversal does. Hope this helps."

 

Let's put the sub issue aside first.

 

I kinda agree that in theory, EQ affects tonality and does not affect TA. But in my limited experience and practice, i find that because of imbalances in tones, the focus of each instrument in the soundstage is very hard to achieve given that the TA is set, because certain frequencies get played more on either side of the speakers, causing drifts of shifts in focus.

 

Now, back to the sub.

 

Sub range, as many of us would do, would try to Low Pass it to at least 63hz, if not lower, so as to keep it non-directional. Suppose your sub level and EQ boosts those sub ranges. In relation to the other parts of the low/mid bass, sub is supposed to give you that "feel" of bass resonnance/vibration. Now that also means...the sub normally kicks in later in relation to that punch, something like PSsss (pardon me for using Hyun's idea of representing it), where the P is the initial punch and the S/s stands for sub and their levels, in a typical big drum beat. Ok, if because you EQ and boost it such that it becomes PSSSs. In theory you cannot say that the TA is wrong, because it comes just nice after the punch, tappering out. But in practice, can the human ear discern if the extra louder SS is the cause of TA or EQ? i.e. sub appears nearer than ideal or louder than ideal? Or is the drum a bigger drum? Again, preference and perception differences also come in and complicate.

 

I kinda think that at the end of the day, you like and think it's correct can liao....no one can really say what is really correct or wrong.

[Sarong1]

So Bro, was it suppose to be a high Chinese drum on that disc?

[Kermit]

haha...maybe it is...the strikes seemed to be at head level, and the sticks droped from head level to the floor level....wah lao...tell me what's written on the CD leh