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Working out Sub delay??

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Shortrope View Drop Down
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    Posted: 27 March 2016 at 4:46pm
I know this has been loosely covered on here a few times but I can't remember which threads.
I've been told too but it just hasn't sunk in.
I've some Tham 15s and when I'm running them with some Reflex tops it's just not sounding right.
The Bass becomes mushy and unpronounced generally spoiling the whole sound.
I'm putting this down to there needing to be some time alignment but I'm not 100% clear on how to do it.
Any advice would be appreciated.
My Tinnitus is coming along nicely!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 27 March 2016 at 5:28pm
Originally posted by Shortrope Shortrope wrote:

I know this has been loosely covered on here a few times but I can't remember which threads.
I've been told too but it just hasn't sunk in.
I've some Tham 15s and when I'm running them with some Reflex tops it's just not sounding right.
The Bass becomes mushy and unpronounced generally spoiling the whole sound.
I'm putting this down to there needing to be some time alignment but I'm not 100% clear on how to do it.
Any advice would be appreciated.

Presuming you don't have SMAART or similar...

Play a sine wave sweep through your rig paying close attention to where the bass and mid-top are equal in level - this might not be exactly at the nominal crossover frequency you've input to your crossover, but hopefully won't be too far off. Find a generator that allows you to do the sweep manually so you can go back and forth a bit through what should be the crossover region to make sure.

Now, invert the polarity of your mid tops.

Play the sine wave again, just at the frequency you found from step one.

Add delay to the mid top until you get maximum cancellation.

As a reality check, if the applied delay is any longer than one wavelength of the frequency you're using, try again with one wavelength less delay - you should still get the cancellation.

Now, flip polarity back to normal - you should have reasonably good summation between the two passbands now with better timing.

HTH,
David.
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Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shortrope Quote  Post ReplyReply Direct Link To This Post Posted: 27 March 2016 at 5:42pm
Thanks David, that's very clear.
I'll give it a go and report back.
My Tinnitus is coming along nicely!!
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rish View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rish Quote  Post ReplyReply Direct Link To This Post Posted: 27 March 2016 at 6:34pm
I remember once Tony Wilkes saying delay the tops by 5ms.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 27 March 2016 at 6:47pm
Where are you crossing them? The group delay you're most likely to notice  from the THAM series is probably the big spike around 120-150Hz. Even if you cross them below that point you'll still be getting a lot of that in the signal, as in this plot from the THAM18 (Google images - too lazy to find a more specific sim) . 


Group delay <50Hz isn't an issue unless it's really high , but a 20-30ms spike at 150Hz will be very noticeable and sounds kind of like what you're describing. Best bet is to sim your driver in Hornresp and check the plot. If it is the upper spike causing problems you'd probably want to set the delay by ear, because it will be a balancing act at best. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2016 at 12:38am
So far I would totally ignore the posts apart from the one directly above. You need a measurement system really. If you don't have one, avoid using sine waves as you will only be aligned at one specific point which may well be worse than what you have already. At the very least use bandwidth limited pink noise to one octave either side of your ACOUSTICS crossover point (where the -6dB points of the boxes meet) or a Bink warble so that you have some broadband content to ensure you're at least in the right ballpark.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bitSmasher Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2016 at 1:27am
Room EQ Wizard, get a measurement mic and play around
https://www.instagram.com/batteryacidsoundsystem/
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2016 at 2:39am
If you do that, start with the mic on a soft thing on the floor at least 10 ft away from the stack. Start your measurement delay at the distance to the sub measured with a laser or tape measure, use at least 16 samples? 4 seconds or more. Ideally you'll get flat response in the sub region on the phase display but in reality it's rare. Don't change the measurement delay, save a trace of the subs, then measure the tops and save that trace. The trace with the gentlest slope from top to bottom from left to right is the one you need to add delay to. Let the live measurement run on that passband, and add delay until the slopes match (within 30 degrees for one octave either side of acoustic crossover ideally) if you can't make that work you will need to revisit your crossover points and filter choices and then start again.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2016 at 8:07am
Sorry but how is measuring on the floor relevant to whats going on on the ear height? 
Making the delay ideal is not possible. I mean it is, but for one exact point. So i find the DMorison advice completely correct. You do want to time match at the crossover frequency. The rest you can not match anyway because it varies with frequency and it is impossible.
Marjan Milosevic
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2016 at 8:33am
On the floor with a soft material helps counter the ground plane reflection. Aligning at a single point via sine wave means you have potentially octaves galore that sum or cancel in uncoordinated fashion. Aligning traces is not that hard apart from the occasional venue, you just need practice and to know what the data is telling you.

Perhaps watch the video and explanation here; https://www.merlijnvanveen.nl/en/study-hall/110-bink-audio-test-warbles

And if you can access and afford it I fully recommend attending on of Merlijn's courses. I'm due to do one myself just as a refresher and to meet the guy.

Edited by toastyghost - 28 March 2016 at 8:35am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shortrope Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2016 at 10:57am
This is very interesting if not a little confusing.
I have a measurement mic but the only software I have at the mo is Holmes response.
My Tinnitus is coming along nicely!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2016 at 6:24pm
If it can do a dual channel FFT transfer function you can use it. Or download the demo of SMAART or Systune.
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