Subwoofer - Phase Control & Freq Control - Help!

[oohsam]

Hi all,
Im somewhat confused as to what im meant to be doing with my Phase and Freq control. I've read so many articles and Im jsut more confused.
The specs of my speakers are in teh attachement. More details is available at
www.accusound.com.au.

What the hell do i do with these controls on the back of my sub. I dont konw what to set them too to get optimum settings.
I love bass, and love it to rumble, its an awsome sub, but i just dont know if I have it setup right?!

Plz help

Thanks

 

[Ethan Winer]

> What the hell do i do with these controls on the back of my sub. <

Unless you have a way to accurately measure the low frequncy response in your room, there really isn't much you can do. I suppose you could cross your fingers and fiddle with the knobs by ear. But the only viable way to set those control accurately is to measure the response to see how it changes.

--Ethan

 

[j_garcia]

Frequency is most likely your crossover point. If you are using a receiver with it's own crossover, you should set this to it's highest point or disable it if possible.

Phase - start with 0, but as Ethan mentioned, if you can't do measurements, adjusting this correctly will not be easy.

 

[ScottMayo]

Simple solution: Leave the phase at 0. Move the sub around to get the right mix of power and clarity; if you want maximum bass, put the sub in a corner. It won't be the clearest bass, but it will be the strongest.

Messing with phase causes different effects at different frequencies, in most rooms. You can probably get something good with enough experimenting, but leaving the phase alone usually results in the best sound, once the sub is placed properly. Phase gets more important if you have multiple speakers putting out bass; you probably don't.

Frequency contols how high pitched a note the sub will let itself handle. Usually the receiver is in charge of that decision, so dial this all the way up. If the receiver doesn't allow you to adjust the bass "crossover frequency", then turn the sub's frequency setting to 80Hz or so. That's usually recommended for movies and will give you plenty of rumble.

 

[oohsam]

Ok, Makes sense. I'll leave the phase at 0, Plus I probably wont be able to tell.
In relation to the Frequency however. If I set the amplifier to its maximum Hz for the subwoofer, do I leave the dial on the sub on the maximum? Or the Minimum? Or does it not matter as the amp will control it?

I've been doing heaps of reading, and have gotten a little confused about what to do...

I have floor standing speakers, but I want most of the bass to go to the sub. Would I still be setting my amp to 80Hz for the bass control?
I have an Onkyo TX-SR603...Really nice amp for what I want to do.

Thanks so much for ur help guys.

 

[ScottMayo]

Ok, Makes sense. I'll leave the phase at 0, Plus I probably wont be able to tell.
In relation to the Frequency however. If I set the amplifier to its maximum Hz for the subwoofer, do I leave the dial on the sub on the maximum? Or the Minimum? Or does it not matter as the amp will control it?

Max. Here's the way it usually works: in the receiver, the crossover setting is deciding at what frequency to divide the sound. Frequencies above the point you pick go to the main speakers, anything lower goes to the sub. (It's not quite that neat and clean, but that's the idea.)

In the sub, the frequency adjustment decides what the sub keeps and what it throws away. It throws away everything above the setting you give it.

Note - some systems may do all this differently, but that's usually the basic idea.

So if you set the receiver to "cross over" at 20Hz, the sub won't do much no matter how you set it, because you're sending pretty much everything to the main speakers. Not what you want.

If you set the receiver to cross at 100Hz and set the sub to 50Hz, you'll get a weird effect: the main speakers will get everything from 100Hz up, the sub will handle from 50Hz down, and you mostly throw away everything between 50-100Hz. Not what you want - although very occasionally this trick comes in useful for taming a very severe problem with room acoustics.

The simplest is to set the sub's frequency as high as possible (so it will handle pretty much anything it gets), and then use the receiver to divide things up as you like. A lot of movies are mixed on the assumpton that you'll divide at 80Hz, because that's a THX standard. That's at least a good place to start.

 

[cyberbri]

Ok, Makes sense. I'll leave the phase at 0, Plus I probably wont be able to tell.

Just to illustrate phase, I've uploaded a screenshot of a chart with two graphs. I just upgraded my speakers and sub, and I now have a HSU VTF-3 Mk2 subwoofer. I did some quick measurements tonight at 1/3 octave, playing tones off my HTPC. The sound is coming from the left/right speakers and sub combined, with a crossover at 80Hz.

My left/right speakers are about 3' from the back wall and about 2' from the side walls. The sub is along the right wall in front of the right speaker, with about a foot or so of clearance behind it.

In the attached picture, you can see a big dip with the blue line. The blue line represents a 0 degree phase setting on the sub, and the pink line represents a setting of 180 degrees. With the speakers out of phase with the sub, that would give me a 15-20dB dip from about 75-130Hz or so. Definitely noticeable with music. And this is with the sub right up front with the speakers. Of course it may not be this drastic for your situation, but you never know.

My room is about 26 feet deep and 14 feet wide, with the TV/speakers on one 14' end. With my previous subwoofer (Acoustech H100 - great sub for the $) in my previous residence (room shape was very different), I also found that with the sub near the front right corner 180-deg phase was much better.

An easy way to test phase is with an SPL meter using the phase tones on Avia (a very worthwhile investment). You play the phase tones (per channel) and measure SPL with different phase settings - most of the time the proper setting will be the one that gives more SPL on the meter. Running frequency sweeps and even plotting out the response by measuring with individual tones (like I did to make the graph) will get you more data to work with.

 

[j_garcia]

If you set the receiver to cross at 100Hz and set the sub to 50Hz, you'll get a weird effect: the main speakers will get everything from 100Hz up, the sub will handle from 50Hz down, and you mostly throw away everything between 50-100Hz. Not what you want - although very occasionally this trick comes in useful for taming a very severe problem with room acoustics.

Not exactly. The sub's x-over works the same way the receiver's does - there is a slope associated with both the sub's and receiver's x-overs. NO subs have a x-over with such a steep slope that there is no sound above the x-over point and all receivers have a slope associated with their x-overs. The sound is slowly reduced as you move further away from the x-over point, but there will still be sound for quite a bit above (or below) the x-over point to allow the sub and speakers to blend with each other. The sounds above or below the x-over point are not simply "discarded".

Now, if you set the receiver's x-over to 80Hz AND the sub's x-over to 80Hz, you will combine those two crossovers creating a very steep slope which is not always desirable. By setting the sub's x-over to the highest point, you are effectively "removing" it from the equation. Some subs have the ability to disable the sub's internal x-over completely.

 

[ScottMayo]

Not exactly. The sub's x-over works the same way the receiver's does - there is a slope associated with both the sub's and receiver's x-overs. NO subs have a x-over with such a steep slope that there is no sound above the x-over point and all receivers have a slope associated with their x-overs.

I was simplifying. My old Earthquake sub, though, had more of a slope than I would have expected. My current VMPS sub (passive, not adjustable) throws away very little. It varies by manufacturer. You're right that no one uses brick wall filters, but the slopes are sometiems steep enough to be useful. I've had customers who took advantage of an aggressive filter to carve an artificial dip in their bass output, to combat a room mode. Not a perfect solution, but a useful trick while you're waiting for bass traps or better equalization.

 

[j_garcia]

For low pass, most subs and receivers tend to use a 18dB/octave and it is the odd unit that uses a 24dB/octave for a quicker roll off, but they are out there. Most receivers use a 12dB/octave high pass which allows the mains to be able to play just a bit lower and blend more easily with the sub. I've seen people use the cascaded x-over to deal with room modes too, and it can be a useful trick if your room issue happens to be at the right point.

 

[SackoHammers]

They way I understood all of this is that you leave the crossover on your Sub set as high as it will go. Let your receiver handle the crossover between your main speakers and your sub.

However, if you have your main speakers plugged into your sub (instead of your receiver), and you are using your sub's crossover, then you will want to make sure your receiver is sending everything to the sub, and then use the sub's crossover to determine what it uses, and what the speakers use. IE, this second paragraph is not what you would want to do since you've got a good receiver.