PA subs crossover point?

[Walker]

I've just taken delivery of a pair of EV SB122 subs for our PA. They recommend a hi-pass filter at 40Hz.

They have a recommended crossover range of 80Hz-160Hz.

Can any wise PA experts out there offer any suggestion on where to set the x-over (or at least start trying things out)?

I've got a couple of Yammy P7000S amps and the tops are Yammy S115V's.

We are going to use them at a small gig on the Bank Hol weekend, so I don't have the luxury of spending hours trying out different points this week!

Thanks (again!),
Chris

[pietruszka]

Have a play around with it depending on the room. But I tend to have it at about 120hz.



Dan

[Walker]

Many thanks Dan. I'll start there!

[stevie]

You'll eventually have to spend a little time figuring out where the optimum crossover point is. I agree 120Hz is a good place to start. A lot will depend on how low your top boxes go. Don't forget the option of running the tops full range and just rolling off the subs. That can sometimes work.

[Walker]

[quote name='stevie' timestamp='1367241824' post='2063001']
Don't forget the option of running the tops full range and just rolling off the subs.
[/quote]

Sorry Stevie, can you explain what you mean here? Why should I need to run tops full range? I'm being thick!

[stevie]

Sorry if I didn't explain myself properly. The normal way to connect subs up is to use an active crossover to cut the high frequencies from the subs and cut the low frequencies from the tops. When you put the two together you get a nice flat frequency response with no overlap. In theory. However, sometimes it can sound better if you do have some overlap, especially if the tops have a relatively high built-in (acoustical) rolloff anyway.

So, what I meant was, connect the subs in the normal way but try running the tops flat (full range) without allowing the crossover to cut the low end.

[Walker]

Ah, I understand now, thanks for that Stevie - I'll try that too.

[Phil Starr]

Now I'm not really disagreeing with Stevie but it depends upon the size of the venue. When we play small places I often run our subs in parallel with no crossover for the subs but that's a bit lazy really.

You'll usually get a better sound if you keep the bass well away from your tops. Lots of bass pushes the speakers so that the coil starts to move out of the magnet and the speakers then distort, keeping the bass out avoids this. Your Yammie 115's will start to distort at less than 100W if the bass goes really low, with a 120Hz crossover they should handle peaks well in excess of 350W. If the venue is small there is less of an issue as your power levels will stay low. Unless you have an external crossover you'll have to use the crossovers built into your amps.

[mike257]

I'd agree with Phil. Just because your tops can't reproduce any audible bass below a certain frequency, doesn't mean the drivers aren't straining to try and do it!

Most decent manufacturers provide a frequency response graph for their cabs, I've just been looking at the ones for our newly acquired EV subs and tops. The subs start to steeply roll off above 100Hz and the tops are pretty happy to around the same point so that seems like a good starting point to work from for our system.

Take a look at the specs for your cabs and see if there's any pointers to be gleaned from that. What you don't want to end up with is a hole in the middle where neither your subs or tops are providing adequate reproduction. Taking the low bass out of your tops can only be good for the long term health of your PA though!

[Walker]

Thanks gents. I hooked everything up for the first time last night, just running some MP3's through the PA. I was amazed how little sound was coming out of the subs, compared to the tops but when I went closer, they were moving a helluva lot of air. Is that normal? Also, I was running the power amp practically full on - they soak up a lot of power, don't they?

The tops were sounding a little thin and tinny so I assume I have to try different crossover points.

More complicated that I thought!

[stevie]

All very sensible stuff so far. If the tops are sounding a bit thin you could also try overlapping the crossover frequencies if you are able to do that. Say, 120Hz for the subs and 80 Hz for the tops. And of course, you should also try swapping the phase of the subs or the tops and listening to the difference it makes. Use whatever connection gives you a 'fuller' bass sound. Measuring equipment makes all of this a lot easier, it has to be said.

[mdc]

[size=4][font=arial,helvetica,sans-serif]Chris, you don't say if you are using an external crossover or the ones built in to the amps - if you want to experiment with varying degrees of overlap between subs & tops then a single crossover point may not give you enough options unless you can try different filter slopes. A good starting point might be to use the filters in the amps which I think have fairly gentle slopes - on all amp channels which are driving subs set your filter switch to 'subwoofer' and all those driving tops to 'low cut' and you can adjust the frequency on each anywhere between 25 and 150Hz. If the tops sound thin just double-check you haven't got the low cut filter in and the freq control all the way up. Personally I hardly ever run subs up to 120Hz, with those 15" tops I'd be thinking around 90 to 100Hz but you need to find out what works best for you. Cheers, Mike. [/font][/size]

[bertbass]

So much useful information here. http://billfitzmaurice.info/forum/ Well worth a read of a few topics but it might take you a while.

[Walker]

Thanks gents, I'm going back to our rehearsal space this evening to try some of this stuff out. My x-over is a [url="http://www.dbxpro.com/en-US/products/223s"]DBX 223S[/url]. My amps have two filters on the back:

[i]SUBWOOFER: Use a low-pass filter. The amplifier outputs the frequencies that are lower than the cutoff set by the FREQUENCY adjustment knob.
LOW CUT: Use a high-pass filter. You can use this setting to filter out unneeded low or subsonic frequencies.
If you select SUBWOOFER or LOW CUT, you can then use the FREQUENCY adjustment knob to adjust the cutoff frequency.
The adjustment range is 25 Hz to 150 Hz.[/i]

Combining the amps filters and the x-over is going to be a bit of headwork, but I'll experiment!

[Walker]

[quote name='bertbass' timestamp='1367400855' post='2065057']
So much useful information here. [url="http://billfitzmaurice.info/forum/"]http://billfitzmaurice.info/forum/[/url] Well worth a read of a few topics but it might take you a while.
[/quote]

Nice, thank you!

[Gazm]

[quote name='Walker' timestamp='1367178014' post='2062259']
I've just taken delivery of a pair of EV SB122 subs for our PA. They recommend a hi-pass filter at 40Hz.
[/quote]

Don't forget this either, you don't want to stress your new subs with frequencies below what they can handle. It will mainly be converted to heat with little or no benefit in sonic output.

[Phil Starr]

Don't worry about the complications, once you have a system that works for you then you'll set up that way every time (well until you get bored enough to try something else) . When listening get well back from the speakers. If the subs are 1m from the tops you want to be at least 10m back,

Just to add one more possibility, probably to try later [url="http://totalproaudio.stevebunting.com/206/system-design/aux-fed-subs/"]http://totalproaudio.stevebunting.com/206/system-design/aux-fed-subs/[/url]

[mike257]

[quote name='Walker' timestamp='1367402381' post='2065077']
Combining the amps filters and the x-over is going to be a bit of headwork, but I'll experiment!
[/quote]

Since both are doing essentially the same job, it might simplify things for you to bypass one and concentrate on the other, at least for now. You'll end up with your head spinning trying to work out where the two relate to each other but ideally if your crossover is set correctly, your amp won't need to filter anything as it won't be receiving any signal outside the frequency range you've specified with the crossover.

Depending on the features available on your crossover, there might be benefits to running the filters on your amp too, but if you break things down step by step it'll be easier for you to both hear and understand the effect of any changes you make.