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post #1 of 29 Old 03-06-17, 02:23 PM Thread Starter
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Port Timing

Both my mains and the sub are ported. I remember reading a while back that ported speakers disrupt relative timing between speakers and subs. Is this true and if so, can it be easily taken care of with external delays provided by a miniDSP or equivalent?

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post #2 of 29 Old 03-06-17, 04:26 PM
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Re: Port Timing

Ported speakers just have a different SPL and phase response (different rolloff rates).
Ported or not, the objective is just to create close phase tracking between the SW and mains.

If the best timing alignment results in the phase crossing at the acoustic XO rather than tracking closely throughout the entire XO range it is possible to fine tune it by changing the SPL/phase rolloff rate of one of drivers:
> Plugging the mains ports will change the rolloff rate from 24 to 12 dB.
> Changing the relative filter settings (as from LR24/LR24 to LR24/But18) for the LPF and HPF XO filters may be an option.
> Changing the relative XO filter frequencies (HPF vs LPF settings) also has some effect.
> Possibly some the Phase control dials on some SWs will shift phase rate of the rolloff through the XO range. Others may just be adjusting the overall SW delay. I don't have any SW's with those controls to test.

It all depends on the setup controls available to the hobbyist. Most people don't have many, if any, options. Fine tuning like that is very complicated and time consuming. It's the playground of dedicated tweakers. It is very unlikely to be detectable in sound quality.

Just pick the best phase tracking for the XO settings you choose. There are better way to spend one's time.
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post #3 of 29 Old 03-06-17, 05:15 PM
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Re: Port Timing

Quote:
jtalden wrote: View Post
Ported speakers just have a different SPL and phase response (different rolloff rates).
Ported or not, the objective is just to create close phase tracking between the SW and mains.

If the best timing alignment results in the phase crossing at the acoustic XO rather than tracking closely throughout the entire XO range it is possible to fine tune it by changing the SPL/phase rolloff rate of one of drivers:
> Plugging the mains ports will change the rolloff rate from 24 to 12 dB.
> Changing the relative filter settings (as from LR24/LR24 to LR24/But18) for the LPF and HPF XO filters may be an option.
> Changing the relative XO filter frequencies (HPF vs LPF settings) also has some effect.
> Possibly some the Phase control dials on some SWs will shift phase rate of the rolloff through the XO range. Others may just be adjusting the overall SW delay. I don't have any SW's with those controls to test.

It all depends on the setup controls available to the hobbyist. Most people don't have many, if any, options. Fine tuning like that is very complicated and time consuming. It's the playground of dedicated tweakers. It is very unlikely to be detectable in sound quality.

Just pick the best phase tracking for the XO settings you choose. There are better way to spend one's time.
Yeah... you can spend a lifetime on this problem, and only hear the most minute of improvements. The big question is how dissatisfied you are with your current sound... if you're pretty happy at the moment, I wouldn't recommend going down that rabbit hole. Everything suggested above is spot-on, but also easier said than done in a lot of cases.
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post #4 of 29 Old 03-06-17, 11:32 PM
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Re: Port Timing

Quote:
Lumen wrote: View Post
Both my mains and the sub are ported. I remember reading a while back that ported speakers disrupt relative timing between speakers and subs. Is this true and if so, can it be easily taken care of with external delays provided by a miniDSP or equivalent?
I read the following article and his explanation made a lot of sense about this very topic.

It seemed worth the effort to give it a try and ended up following his advice for my 'music only' system. I'm amazed at how much better/clearer and how the sound is 'louder' on lower volume setting. Well worth the effort and I highly recommend it.

All my ports are sealed and my mains are crossed over @ 80hz as directed. I am using sub drivers designed for a sealed cabinet. (NHT)

BTW... an important part of the set up was using the subwoofer location in figure Fig 7. 'An asymmetrical layout.'




This made a huge difference in my small 13' x 15' room. I can actually balance the bass at the listening position by using the volume control on the two subwoofers. Very cool idea. I run the sub closest to the sofa at a low crossover and slightly lower volume so it's not detectable in the least. Both subs are firing aimed away from the listening position at the wall to cut down any localization. The bass is very tight and it really does "fatten up the base". So now the system plays louder on less volume. Helped with nulls also.

"A ported sub for home use is even more wrong than ported mains. Now you would be attempting to acoustically add together in the room at least SIX low frequency sources with differing phase and frequency slope conditions: the LF drivers in your two mains, their ports, the sub driver, and its port."


http://www.soundoctor.com/whitepapers/subs.htm
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post #5 of 29 Old 03-07-17, 06:33 AM
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Re: Port Timing

Quote:
Gdaddy wrote: View Post
"A ported sub for home use is even more wrong than ported mains. Now you would be attempting to acoustically add together in the room at least SIX low frequency sources with differing phase and frequency slope conditions: the LF drivers in your two mains, their ports, the sub driver, and its port."


http://www.soundoctor.com/whitepapers/subs.htm
This quote and some other comments in the linked article reflects a partial misunderstanding of the SW to mains XO setup issues in my opinion:
> I see no technical argument for a clear preference of a ported Vs sealed SW. They have slightly different advantages/disadvantages so for a given situation one may be a little better choice than the other. Pointing to 1 or 2 advantages/disadvantages without context to how it helps or hurts a particular situation is not helpful.
> We also cannot predict if ported Vs sealed mains will work more ideally for phase tracking in a given situation. It is the overall system acoustic XO characteristics that is main factor. This is a function of the room and SW placement as well as the electrical XO settings (including the important delay setting).
> The typical small listening room is often the primary actor in the success of the setup. Only careful measurements will determined the best setup from the various options available. Most often, due primarily to room acoustics of a given setup, it is a matter of choosing a compromise XO setting between several less than ideal solutions.
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post #6 of 29 Old 03-07-17, 08:46 AM Thread Starter
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Re: Port Timing

Quote:
jtalden wrote: View Post
Ported speakers just have a different SPL and phase response (different rolloff rates).
Ported or not, the objective is just to create close phase tracking between the SW and mains.

If the best timing alignment results in the phase crossing at the acoustic XO rather than tracking closely throughout the entire XO range it is possible to fine tune it by changing the SPL/phase rolloff rate of one of drivers:
> Plugging the mains ports will change the rolloff rate from 24 to 12 dB.
> Changing the relative filter settings (as from LR24/LR24 to LR24/But18) for the LPF and HPF XO filters may be an option.
> Changing the relative XO filter frequencies (HPF vs LPF settings) also has some effect.
> Possibly some the Phase control dials on some SWs will shift phase rate of the rolloff through the XO range. Others may just be adjusting the overall SW delay. I don't have any SW's with those controls to test.

It all depends on the setup controls available to the hobbyist. Most people don't have many, if any, options. Fine tuning like that is very complicated and time consuming. It's the playground of dedicated tweakers. It is very unlikely to be detectable in sound quality.

Just pick the best phase tracking for the XO settings you choose. There are better way to spend one's time.
Many thanks for your detailed response, and for saving me from a thousand deaths! Not being a dyed-in-the-wool tweaker, and having a processor with limited setup controls, I'm more than happy to take your advice to "settle" for phase tracking. Now to see if I understand correctly. Phase tracking uses FR measurements to verify a sub's phase control is set to provide good SPL support through the crossover region. Phase plot analysis is not needed, correct?


Quote:
DqMcClain wrote: View Post
Yeah... you can spend a lifetime on this problem, and only hear the most minute of improvements. The big question is how dissatisfied you are with your current sound... if you're pretty happy at the moment, I wouldn't recommend going down that rabbit hole. Everything suggested above is spot-on, but also easier said than done in a lot of cases.
Appreciate the confirmation! My OCD wouldn't stay under wraps very long under those conditions. To answer your question: I'm very dissatisfied right now. I'm in the early stages of renovating my HT room, and thought I had fine-tuned my speaker locations - until I brought in some room treatments, that is. I'll try starting over by introducing them individually. I was hoping to save some measurement time, but I now realize there are no shortcuts to doing it right (adding treatment without good reason can do more harm than good).

.
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post #7 of 29 Old 03-07-17, 09:59 AM
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Re: Port Timing

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Lumen wrote: View Post
Now to see if I understand correctly. Phase tracking uses FR measurements to verify a sub's phase control is set to provide good SPL support through the crossover region. Phase plot analysis is not needed, correct?
Yes, that is one method that provides good results.
> Set delays appropriate for the distances to speakers
> Increase the delay on the SW by 4.00 ms.
> Sweep (or RTA) measure SW+Lmain+Rmain 8 times reducing the SW delay by about 1.00 ms for each successive measurement.
> Choose the SW delay setting that provides the best XO range SPL support.

If you prefer that I confirm the settings I would need an mdat file:
> Acoustic timing activated on Left channel
> XO and delay settings activated
> Mic at LP
> Sweep:
  • FL
  • FR
  • SW (redirected bass from right or left channel, not an LFE channel)

REW analysis of those 3 measurements allows me to do essentially the same thing while also being mindful of the phase tracking.
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post #8 of 29 Old 03-07-17, 10:53 AM
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Re: Port Timing

Quote:
Gdaddy wrote: View Post



"A ported sub for home use is even more wrong than ported mains. Now you would be attempting to acoustically add together in the room at least SIX low frequency sources with differing phase and frequency slope conditions: the LF drivers in your two mains, their ports, the sub driver, and its port."





http://www.soundoctor.com/whitepapers/subs.htm

I completely agree with JT on this.
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post #9 of 29 Old 03-07-17, 12:21 PM Thread Starter
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Re: Port Timing

Quote:
jtalden wrote: View Post
This quote and some other comments in the linked article reflects a partial misunderstanding of the SW to mains XO setup issues in my opinion:
> I see no technical argument for a clear preference of a ported Vs sealed SW. They have slightly different advantages/disadvantages so for a given situation one may be a little better choice than the other. Pointing to 1 or 2 advantages/disadvantages without context to how it helps or hurts a particular situation is not helpful.
> We also cannot predict if ported Vs sealed mains will work more ideally for phase tracking in a given situation. It is the overall system acoustic XO characteristics that is main factor. This is a function of the room and SW placement as well as the electrical XO settings (including the important delay setting).
> The typical small listening room is often the primary actor in the success of the setup. Only careful measurements will determined the best setup from the various options available. Most often, due primarily to room acoustics of a given setup, it is a matter of choosing a compromise XO setting between several less than ideal solutions.
Quote:
willis7469 wrote: View Post
I completely agree with JT on this.
The word "guru" comes to mind.

.
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post #10 of 29 Old 03-07-17, 01:08 PM Thread Starter
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Re: Port Timing

Quote:
jtalden wrote: View Post
Yes, that is one method that provides good results.
> Set delays appropriate for the distances to speakers
> Increase the delay on the SW by 4.00 ms.
> Sweep (or RTA) measure SW+Lmain+Rmain 8 times reducing the SW delay by about 1.00 ms for each successive measurement.
> Choose the SW delay setting that provides the best XO range SPL support.

If you prefer that I confirm the settings I would need an mdat file:
> Acoustic timing activated on Left channel
> XO and delay settings activated
> Mic at LP
> Sweep:
  • FL
  • FR
  • SW (redirected bass from right or left channel, not an LFE channel)

REW analysis of those 3 measurements allows me to do essentially the same thing while also being mindful of the phase tracking.
Certainly a generous offer that's hard to refuse! How do you find the time?!

To try and provide robust data the first time, I have a few more questions:
  1. Delay can be converted to distance if multiplied by 1.125ft/msec, correct?
  2. Speaker distance is measured from LP to baffle (single plane for all distances). How do you measure from LP to sub, line-of-sight to the driver's center?
  3. Should I specify a 12 or 24dB/octave subwoofer LPF slope? Or does that warrant one set of measurements for each scenario?

.
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