subwoofers question

[whaleboat]

I did have a digital signal processor with a crossover that handled this problem , but it's toast now . I have a fair size sound system including FOH mains , two rows of fill speakers in the house , monitors above the stage , and subwoofers FOH . Right now I'm running the FOH mains off the left side of the board , through a graphic EQ and to the mains amp . I'm running the overhead stage monitors off the right side of the board , through a graphic EQ and to the monitors amp . I have some equipment I'm not using laying around and would like to hook up my subs . My board has left and right matrix sends feeding off the main mix . Can I use one of these sends to feed a graphic EQ and place a crossover between the Eq and the amp for the subs ? I guess what I'm asking is , if I send a signal to a crossover can I only hook up the low end to an amp , and just leave the highs output unwired ?

[museav]

Originally Posted by whaleboat

I did have a digital signal processor with a crossover that handled this problem , but it's toast now.

Keep in mind that a crossover between subs and mains is typically both low passing the subs and high passing the mains as well as possibly applying some delay to one or the other. And how you are handling functions such as delay for the fills, limiting, etc, that the DSP probably handled? Have you considered repairing or replacing the DSP?

You could use a matrix send for a subwoofer, effectively very similar to an aux fed subwoofer arrangement, but by feeding it only the main mix it would result in many the negatives and few of the positives of such an arrangement. For example, you could not take advantage of not sending particular inputs to the subs, one of the primary reasons for using aux fed subs.

Also consider how such an arrangement potentially affects the interaction between the subs and mains. Think of a line coming from the upper left to the lower right, that line represents the slope of your low pass crossover for the sub. A line from the lower left to upper right represents the high pass for the mains (or say a roughly straight line if you have no high pass for the mains). Where those two line cross depends not only upon the slope of the lines and where the lines start (the filter corner frequencies), but also the amplitude (height) of the lines. Turn the mains or sub signal up or down and the point where the related lines cross shifts both up and down and left and right, equating to the actual crossover point shifting up and down in relative level and frequency. It makes operating the system that much more complex.

I'm also curious as to the left/house and right/OH stage monitor arrangement since as you pan something the level in either output would change. Perhaps even more of an issue, any changes to a fader would affect both outputs. Have you thought about using a pre-fader aux send for the monitors?

[jkowtko]

(I'll withdraw my earlier comments and respond to your question directly)

I checked a couple of user manuals for crossovers and found no mention that you must have all outputs connected in order for the crossover to work properly. Input impedances for amps are generally pretty high, so I would think there is no issue here.

[whaleboat]

You're right , the left/house and right/monitor mix all fader movements affect both outputs . For theatre and choir I don't pan either way , the monitors are smaller speakers on a smaller amp than the FOH amp and speakers , and so the volumne on stage is lower than in the house . So I just leave the pan straight up as both theatre and choir like alot of monitor . For different performers such as a soloist with guitar ,I use floor wedges off a post fade aux . Right now I'm using the EQ's off the floor wedges on the mains and overhead stage monitors to keep going . I don't have any delay on the fills and it's noticeable but performances are still acceptable . I'm thinking If I got 3 Samson D 2500 digital EQ's I could Run FOH and overhead monitors off one with no delay , row two fill and row three fill off another with corresponding delay , and use the third for the subs . I didn't really like the DSP I had and would like to try something different . I haven't thought about compression yet . But I believe the D 2500's have peak stop limiters on them .

[mixmaster]

Originally Posted by whaleboat

I did have a digital signal processor with a crossover that handled this problem , but it's toast now . I have a fair size sound system including FOH mains , two rows of fill speakers in the house , monitors above the stage , and subwoofers FOH . Right now I'm running the FOH mains off the left side of the board , through a graphic EQ and to the mains amp . I'm running the overhead stage monitors off the right side of the board , through a graphic EQ and to the monitors amp . I have some equipment I'm not using laying around and would like to hook up my subs . My board has left and right matrix sends feeding off the main mix . Can I use one of these sends to feed a graphic EQ and place a crossover between the Eq and the amp for the subs ? I guess what I'm asking is , if I send a signal to a crossover can I only hook up the low end to an amp , and just leave the highs output unwired ?

The quick answer to your question is yes, it will work electrically. The right answer is that you're going the long way around and probably still not getting to where you need to be.

Running your stage overheads off the mix buss leave you open to a variety of potoential problems, but if you want to feed those overheads the same mix as the house, I might recommend driving the stage overheads off the matrix so you can at least turn them up, down, or off independantly of the house.

You don't say wheather you crossover is a stereo unit but if it is, I would then run your (currently mono?) house feed from one channel of the board to one channel of the crossover. set your crossover frequency and only send the high output to the main amp. Wire your subs from an aux to the second channel of the crossover, same crossover frequency, only use the low output to drive the sub amp. With the subs on an aux you can choose the sources you send to the subs, thereby only sending material to the subs that has sub frequencies. Search for sub on aux for more info on that. Delays can be run off the other matrix or a group depending on what exactly you want in them.

[theatremowat]

I agree with a lot of whats been said, you can set it up just about any way you want and it will work, its just how good of a sound quality you want.

The whole purpose of a crossover is to send only specific sets of frequencies to specific speakers (ie high to high, low to subs), and to control these. If you do not use a cross over and just plug in your subs through a matrix your bass frequencies are going to overlap, you'll have too much and it'll either sound like crap (being unbalanced signals), or be too much and cancel out. The purpose of using subs is not only to achieve more base, but to take the stress of producing low frequencies off of your other speakers. So i would seriously consider it rather destructive to run this in any manner not involving a crossover, and their really easy to setup and use too.

[Attreui]

Originally Posted by whaleboat

if I send a signal to a crossover can I only hook up the low end to an amp , and just leave the highs output unwired ?

Wait I am confused. a crossover is exactly what you need. You say you have one... I am confused about the problem. if you take your mains (mono left is fine at this point, running a mono PA is common) from the board to an EQ and into a crossover, High output to your FOH low to your subs, that's precisely what you should be doing. It's a simple 2 ways crossover. The DSP does it with greater flair but it's still doing the same thing. Am I missing a problem? Why would you prefer to run your subs separate at all?