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[Jose Peralta]

I have purchase and been using Smaart for a year now as a learning curve. Due to my schedule, going to a training may not be possible so on my own I have been learning how to use the software and the idea and concept behind it. Now comes my questions, when aligning subs, do I delay locate the tops first at any given position and use that for the subs or do I need to find IR of the subs since the wavelength of bass frequency are longer which make it hard to locate?  My other question is, if I were to use use indoor measurements, can I ground plane the measurements to reduce comb filtering?

[Tim Verhoeven]

I have purchase and been using Smaart for a year now as a learning curve. Due to my schedule, going to a training may not be possible so on my own I have been learning how to use the software and the idea and concept behind it. Now comes my questions, when aligning subs, do I delay locate the tops first at any given position and use that for the subs or do I need to find IR of the subs since the wavelength of bass frequency are longer which make it hard to locate?  My other question is, if I were to use use indoor measurements, can I ground plane the measurements to reduce comb filtering?

You can check out Michael Curtis his YouTube channel for some of the basics, also Rational Acoustics has a whole bunch of interesting video's online.

To answer your specific questions:

Main/Sub alignment: yes, you put your mic where you want to align the mains and subs, send audio through the mains, delay locate to the mains and take a measurement. Without changing the location of the mic and without touching the delay settings, you switch the audio to the subs. Then the goals is to make the phase trace of the subs overlap with the one of the mains around the acoustic crossover region (the frequency range where the magnitude of the mains and subs is close to equal), you do this by changing the delay on the sub output.

Measuring on the ground plane: yes, it is a good idea to put the mic on the floor for this process to avoid any floor bounces that cause comb filtering. It doesn't really matter if this is indoor or outdoor.

[Art Welter]

Now comes my questions, when aligning subs, do I delay locate the tops first at any given position and use that for the subs or do I need to find IR of the subs since the wavelength of bass frequency are longer which make it hard to locate?  My other question is, if I were to use use indoor measurements, can I ground plane the measurements to reduce comb filtering?

This article and it's links should answer your questions and give you a solid foundation for sub alignment:
https://www.merlijnvanveen.nl/en/study-hall/166-subwoofer-alignment-the-foolproof-relative-absolute-method

Generally, the output of the subwoofer lags in time behind the top cabinet, if delay is required the top cabinet, not the sub requires delay.

[Caleb Dueck]

Minor note - don't forget polarity.  If the phase traces cross sharply but not overlay, try polarity.  This is especially true with some tapped horn and other non-front-loaded/non-ported subs. 

[Jose Peralta]

Thank for the responses! I appreciate all the help. Art, good detail information on the link. Another thing I want to be aware is have the subs ahead of the tops for X reasons. I dont know if this true but the physics of the subs in relation to the tops, just the nature happens to have some sort of delay. Let just say I have to put the top about 3 feet behind the subs, does that mean I have to delay the subs plus the delay of the sub driver producing actual sound in time with the bass driver at the crossover frequency? I know their is a mathematical equation to this.

Caleb, I have gone through this situation especially when using various crossover slopes. I have a dbx driverack PA+ which does not have a polarity inversion but only delay.

[Michael Lawrence]

Minor note - don't forget polarity.  If the phase traces cross sharply but not overlay, try polarity.  This is especially true with some tapped horn and other non-front-loaded/non-ported subs.

Polarity doesn't change the slope of a phase trace (because it doesn't change timing), it just shifts it halfway across the phase plot. If they "cross sharply" before a polarity inversion they will still do so after.

I know their is a mathematical equation to this.

That's what the analyzer is for. Subwoofers are far more severely bandlimited systems than full range sources so they inherently have more group delay but it's not apples to apples. What you are comparing is the bottom end of the main's response against the top end of the subwoofer's response. The frequency range over which the two sources overlap is revealed in the magnitude traces, so start there.

do I need to find IR of the subs since the wavelength of bass frequency are longer which make it hard to locate?

This is not a function of wavelength, it's a function of bandwidth. Bandlimited systems have a less pronounced peak in the impulse response for a few reasons that have to do with the inherent mathematical reality of bandlimited systems.  https://www.merlijnvanveen.nl/en/study-hall/120-why-the-impulse-response-won-t-work-for-subwoofers
Since delay finder looks for the IR peak, it struggles with bandlimited sources particularly in reverberant environments. You can either use the Advanced Delay Finder to look for the peak energy at a given frequency range or simply adjust the measurement delay until the phase trace becomes helpfully readable. In a real world situation you can expect to have subwoofer energy arriving at the microphone position over a 50ms+ period of time so the idea of it having "one" arrival time is overly simplistic. A mile-long freight train passes through the station. What time does it pass through the station? Depends on what part of the train we're talking about. It can't arrive all at once.

if I were to use use indoor measurements, can I ground plane the measurements to reduce comb filtering?

You can, if the floor bounce is problematic. I usually just teach people to recognize it and ignore it, and I can't think of a real world situation where it's created an issue for me doing what I needed to do. I would advise against making any tonal decisions from the floor, as that's not where people listen from.

In my book I explain how the idea of main-sub alignment has been elevated to the point of a 'fetish' by some manufacturers and content creators because in most typical small and medium scale deployments it's probably the least critical decision to make in the alignment process, and the geometry prevents that timing decision from holding over the listening area to begin with.

https://www.prosoundweb.com/dont-fear-the-phase-gremlins-looking-further-into-alignment-between-mains-and-subs/

[Frank Koenig]

Here’s an approach for throw-and-go situations where a field measurement is impractical or small rooms where modes dominate and make measurement difficult.

Determine a “reference delay” for a given system configuration back at the shop. This can be done pretty effectively using near-field measurements. (While near-field magnitude is in general an inaccurate representation of far-field behavior the phase tends to be pretty close.) When you get to the gig estimate the distance difference between the subs and the mains at the desired spot and add the corresponding time difference to the reference delay. Easy-peasy. We’re dealing with large wavelengths here (14 ft at 80 Hz) so extreme precision is not required.

--Frank

[Art Welter]

I have a dbx driverack PA+ which does not have a polarity inversion but only delay.

The DriveRack PA inverts the polarity of all the outputs relative to the input, and I recall hearing someone tested the (early) DriveRack PA+ and it inverted the HF.

Good idea to check your DSP (and your XLR connectors..) independently from the speaker system.
XLR pin 2/3 swap adapters are useful if your DSP (or powered speakers) have no polarity switches.

If the system is properly time/phase aligned, a polarity reverse should result in a deep notch at the acoustic crossover when the mains and tops are equidistant and tested near field.

[Jose Peralta]

The DriveRack PA inverts the polarity of all the outputs relative to the input, and I recall hearing someone tested the (early) DriveRack PA+ and it inverted the HF.

Good idea to check your DSP (and your XLR connectors..) independently from the speaker system.
XLR pin 2/3 swap adapters are useful if your DSP (or powered speakers) have no polarity switches.

If the system is properly time/phase aligned, a polarity reverse should result in a deep notch at the acoustic crossover when the mains and tops are equidistant and tested near field.

I have not recall about this with the earlier driverack models.

[Caleb Dueck]

Polarity doesn't change the slope of a phase trace (because it doesn't change timing), it just shifts it halfway across the phase plot. If they "cross sharply" before a polarity inversion they will still do so after.

Correct, thank you for clarifying! 

And as Art said, if the DSP doesn't have polarity swap .... get a new DSP, er, XLR 2/3 pin swap adapters.  I didn't realize some DSPs don't have this, or automatically flip some output polarity.
 It's such a basic function, any DSP that can't get even this right isn't something I'd use. 

[ProSoundWeb Community]