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Author Topic: aux fed subs  (Read 9867 times)

Jerome Malsack

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Re: aux fed subs
« Reply #10 on: February 01, 2014, 12:55:06 pm »

Back in the day of Stereo Review they had some opinions on listening to various crossover slopes from sub to mains. 

The basic result was to give the sub a brick wall on the top to prevent it from going up, 12 or 24 db slope. 
The mains were aloud to have from no crossover and 3 to 12 db high pass.  Resulting in little audible or inaudible problems.

So for the Sub we should be trying to get the Sub low pass to 24 db.  Beyond that the question will be if the time or phase issues will be audible and where?   Add in the time to setup, test, adjust, test to satisfaction.  This will work well when outside at my place and setting up.  Not good usually at the show, along with each venues acoustics will be adding to the problems.

Having the flexibility to control the Subs output with out affecting the mains is the plus.  I still feel that a plosive coming from a 15 inch main is still going to be very audible and the correct filtering a processing on the channel strip helps and reduces the problem.  When this channel stip is removed from the sub it removes another part of the problem.

When the subs output is exaggerated to have a stronger punch and kick then the bass, organ, and keys will be exaggerated and the transition to the mains and tops will hear the audible difference at the transition if the channel strip to mains and the aux to the subs is not set accordingly.  When you adjust the sub out with the aux level you have changed the subs response to the keys or organ to the mains changing the balance and transition levels between the subs and mains.     
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Luke Geis

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Re: aux fed subs
« Reply #11 on: February 01, 2014, 10:29:56 pm »

I have tooled around with different PA's and have had some results that tend to make sense and improve perceived performance. It was mentioned above, simply letting the tops run full range ( Or at least with a gentle crossover slope ) while cutting the subs with a steep filter. The big fear from most in the FULL RANGE ( no aux fed subs ) camp, is that there is an acoustic gap between tops and subs for material that does not exist in the subs. For example: The vocals may not sound as full, or the guitar may sound weak? This can be an issue for the basic user who doesn't realize that you can still add those types of channels into the subs to fill it out......... BUT.......... The idea is to not have to do that since it defeats the purpose of running aux fed subs.

It's all in the acoustical crossover point. A well measured and tuned system will have proper acoustical crossover points anyway, so there should be no fear of a hole in the audio spectrum if that's the case. Now in the instance where you are running steep filters and a not so well tuned system, there is the possibility for a large hole to appear in an aux fed sub system. Since not all instruments could be getting full extension to below their fundamental notes. Vocals have fundamental notes down to 80hz, as well as guitar and several brass and stringed instruments. In a system where the tops are crossed over at 100hz or higher with a steep filter, you could be neutering the fundamental notes for several instruments! On the converse the subs could be over extending low end content into the fundamental not range too. Subs crossed over as high as 100HZ are really pouring out the fundamental notes of many instruments and vocals and if your like most people running subs 3-6db hotter than the tops, you can really have some heat in that area.

I feel that subs should be crossed over as low as practical in an attempt to keep the fundamental notes out of that part of the system. 80-100hz is a good starting point. You want to be careful not to go too low as you start to end up with too much low end build up in the tops and psychoacoustic effects start to take place where localization of the subs makes them be unable to be localized. The idea is to have a system that is concentric and melds together into one. If people can tell that there is sub bass in the system but have no idea where it's coming from, it can be confusing and it takes away from the impact of the system. The crossover slope should be determined by the desired system tuning. It may be better on paper to have steep slopes on the subs, but it may not add up in the systems entirety?

I have found that running 12" tops that don't have extended low range can work really well not crossed over at all with an aux fed sub that is tuned to work with the tops. Smaller speakers tend to have less low end extension and the natural drop off in them can work well. Larger 15" and other 12" speakers with extended low end do not fair as well with that approach. Most 15" speakers can extend to 50hz and lower ( pretty far into sub territory ) and some 12" speakers can get down to the 50-60hz area also. These types of speakers may not work well un-filtered, where as other more controlled tops that have smaller elements will. The acoustical crossover point is where it's at. there should be a smooth transition from the tops into the subs when instruments are either in, or out of each part of the system. If a hole emerges in the frequency spectrum of key instruments and vocals, you either have to fill it in by adding that instrument into the subs, or re-tune the system. 
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Bob Kidd

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Re: aux fed subs
« Reply #12 on: February 01, 2014, 11:00:57 pm »

Great advice Luke. To get a system correctly tuned in would you say a program such as Smaart is needed? Do not have program and not experienced at using it.
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Mark McFarlane

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Re: aux fed subs
« Reply #13 on: February 02, 2014, 08:48:13 am »

Great advice Luke. To get a system correctly tuned in would you say a program such as Smaart is needed? Do not have program and not experienced at using it.

If you are using vendor crossover presets for a good quality DSP, then you can probably get close with the presets.

If you are rolling your own crossovers, whether for subs or for 3 way or 4 way systems, a program that shows phase response is essential to 'do it right..  Smaart is one choice.  They are all expensive and take a bit of skill to use effectively.

An alternative is to hire someone to tune your system. Depending on where you live you may get a free volunteer.  This route is likely going to be cheaper than buying your own software. Buying your own software is a worthwhile investment if you plan to get into lots of measurements: e.g. making adjustments for venues, measuring latencies in your gear chain, testing mics,...
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Bob Kidd

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Re: aux fed subs
« Reply #14 on: February 02, 2014, 06:28:34 pm »

If you are using vendor crossover presets for a good quality DSP, then you can probably get close with the presets.

If you are rolling your own crossovers, whether for subs or for 3 way or 4 way systems, a program that shows phase response is essential to 'do it right..  Smaart is one choice.  They are all expensive and take a bit of skill to use effectively.

An alternative is to hire someone to tune your system. Depending on where you live you may get a free volunteer.  This route is likely going to be cheaper than buying your own software. Buying your own software is a worthwhile investment if you plan to get into lots of measurements: e.g. making adjustments for venues, measuring latencies in your gear chain, testing mics,...


Thanks Mark,

I currently use a dbx drive rack pa, and was going to dbx 260 but did not see a preset for qsc pl380 and 340 amps. Looking for one that would have presets for the srx's and qsc pl amps.
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Greg Cameron

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Re: aux fed subs
« Reply #15 on: February 03, 2014, 02:26:20 am »

I feel that subs should be crossed over as low as practical in an attempt to keep the fundamental notes out of that part of the system. 80-100hz is a good starting point. You want to be careful not to go too low as you start to end up with too much low end build up in the tops and psychoacoustic effects start to take place where localization of the subs makes them be unable to be localized. The idea is to have a system that is concentric and melds together into one. If people can tell that there is sub bass in the system but have no idea where it's coming from, it can be confusing and it takes away from the impact of the system.

I'm not sure what you mean here. I find the running the subs with a higher crossover point to where they can be "localized" isn't really a good thing. They can start sounding "boxy" at higher frequencies, so running them crossed lower tends to stave off that issue so long as your tops can handle reaching lower. My particular setup has the tops high passed at 60Hz (LR24) and the subs low passed ~50-55Hz. This prevents the subs from sounding boxy and makes localizing them more difficult which is a good thing since they're on the floor and the tops are flown. Since they're not really heard and more "felt," people don't bum when they're standing right in front of them when they're going full tilt boogie. Also having them crossed that low reduces the amount of combing with the tops since the wavelengths that are overlapping are relatively long. The higher you cross with separate tops and subs, the more frequencies are going comb due to the shorter wavelengths involved.

I don't like to run my tops down as low as they can go for 2 reasons: one is that you create even more unwanted overlap between the tops and subs which will result in more comb filtering of sources sent to both tops and subs; the other is that you're using up more woofer headroom in the tops which results in less overall output and more distortion. If you high pass the tops with a steeper filter, the woofer won't have to work as hard. I can get a lot more output out of my 15s high passing them at 60Hz than I can running them down to 45Hz. The subs are handling those frequencies anyway, so I want to save that headroom in the tops. A slow filter will also allow more headroom to be eaten up than I want to as well as allow for more negative interaction between the tops and subs from the larger overlap.

Anyhow, that's what works for me.
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Don Boomer

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Re: aux fed subs
« Reply #16 on: February 03, 2014, 02:41:51 pm »

Picking crossover points between tops and subs will depend on what you expect from your system.  There is no single answer that works in every system. It depends on your system of course and somewhat on the music you intend to run through them.  There's a lot of room for compromise here.

I typically choose higher crossover points that other folks as what I'd like to achieve is keeping as much vocal out of the sub as possible.  Here's where going with aux fed subs really is a benefit.

But you could also choose a crossover that gives your system the flattest (or some other of your choosing) response.  That could involve asymmetrical filters.

You might also be looking from a distortion standpoint.  Usually a high pass filter to the tops will cut back on distortion (especially inter mod distortion).

I suppose if you center cluster your subs and split your tops you could end up with a crossover that plays to this.
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Greg Cameron

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Re: aux fed subs
« Reply #17 on: February 03, 2014, 02:55:13 pm »

Picking crossover points between tops and subs will depend on what you expect from your system.  There is no single answer that works in every system. It depends on your system of course and somewhat on the music you intend to run through them.  There's a lot of room for compromise here.

Agreed. On systems with less capable tops, I'll vary the high pass based on the demand of the gig. When it's less demanding, I'll lower the low pass on the tops and subs. When I need the most possible clean output, I'll bump both up a bit.
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Luke Geis

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Re: aux fed subs
« Reply #18 on: February 03, 2014, 04:00:04 pm »

I'm not sure what you mean here. I find the running the subs with a higher crossover point to where they can be "localized" isn't really a good thing. They can start sounding "boxy" at higher frequencies, so running them crossed lower tends to stave off that issue so long as your tops can handle reaching lower. My particular setup has the tops high passed at 60Hz (LR24) and the subs low passed ~50-55Hz. This prevents the subs from sounding boxy and makes localizing them more difficult which is a good thing since they're on the floor and the tops are flown. Since they're not really heard and more "felt," people don't bum when they're standing right in front of them when they're going full tilt boogie. Also having them crossed that low reduces the amount of combing with the tops since the wavelengths that are overlapping are relatively long. The higher you cross with separate tops and subs, the more frequencies are going comb due to the shorter wavelengths involved.

I don't like to run my tops down as low as they can go for 2 reasons: one is that you create even more unwanted overlap between the tops and subs which will result in more comb filtering of sources sent to both tops and subs; the other is that you're using up more woofer headroom in the tops which results in less overall output and more distortion. If you high pass the tops with a steeper filter, the woofer won't have to work as hard. I can get a lot more output out of my 15s high passing them at 60Hz than I can running them down to 45Hz. The subs are handling those frequencies anyway, so I want to save that headroom in the tops. A slow filter will also allow more headroom to be eaten up than I want to as well as allow for more negative interaction between the tops and subs from the larger overlap.

Anyhow, that's what works for me.

I think you and I are saying the same thing. However with slightly different approaches? I like the subs crossed over closer to the 80hz area or lower, however in some cases they need to run up to near 100hz, or as low as 60-50hz. I do not like going any higher than that though. I don't mind running the tops out to low, but prefer to keep them right around 80-100hz. This is where most of the fundamental frequencies are for most of the important instruments and vocals. Any lower than that and you are  starting to waste energy in the tops. 80hz is where the beef of the bass guitar and the punch of the kick is. So too high of a crossover on the tops and you start to loose the impact, where as too low you start to simply waste the energy that the subs can utilize. Localization of subs is lost at around 55-50hz and 60hz is the power note for dance music ( edm at least anyway ). I alter my points based on what I hear and what smaart is telling me. I basically shot to have it sound like one big system. I have in some cases used a rather low crossover point on the subs with a more gentle slope to make that happen. I prefer center clustered subs too, so there is usually a small disconnect from the tops and subs. The subs get the most attention when working on the crossovers. I set the tops up to make them sound good throughout the venue and the subs are added in and altered based on the info and what I hear. If I can walk through any part of the venue and have no apparent separation from tops to subs, all is well.

Any system that has two sound sources producing the same thing will have comb filtering. Running tops out too low can really have some impact in areas of the venue. I like centered clustered subs for that reason. I can keep them near the 80hz area, fill the area with solid bass and reduce some of the combing in the frequency range that people tend to look for ( the kick in the chest and gut ). I prefer the higher crossovers on the tops if possible. Just depends on the venue. Sometimes it needs to be low to make it meld and sometimes it needs to be high to keep the low end junk out of them. It's all about playing with it until it's right.

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Jonathan Betts

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Re: aux fed subs
« Reply #19 on: February 03, 2014, 04:22:23 pm »

I have recently started running a system where the subs are Low passed at 100Hz and the tops HP  around 130Hz. Subs are boosted +6db or so. These were recommended settings given to me by  one of their engineers. With my SRX system I would low pass my subs at 80Hz and high pass my tops around 90Hz. The subs were normally run-on a group. The new system outperforms  my SRX in every way possible running just HPF's on most channels. I'm debating whether or not to try aux or group fed subs with the SM80/TH 118 setup. If anyone has tried this can you please chime in with some info?

Thanks!
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