Question on setting up speakers side by side.....

[55fmj]

Does the shape of the jbl MRX series speakers allow them to be set side by side without having too much "combing effect" ? Since the shape of the cabinets actually splay the speakers, I just wondered if it is enough, or should I splay them a little more ?

thanks

[Vinny D]

My guess is that 99.9% of the people won't even notice the combing effect...even if you explain it to them.

Try it and see if it works for you.

[KF650SB1000]

You'll need a wide splay, about 70 degrees on the centerline to centerline.

[Shaster]

Just a few short years ago I used to be worried about comb filtering and such. My theory now is that if it sounds good then generally it is good.

 

I'm guessing you're doing this for coverage and not for extra volume. If that is the case, then try splaying your cabinets to achieve your desired coverage - if it sounds good then you're done. If not, tweak until you get what you need.

 

My 2 cents.

[55fmj]

I actually did this on saturday for both coverage and volume. We normally run a pair of mrx515's and a pair of mrx518 subs, but this time we doubled the system. Two 515's and 2 subs per side. The subs we set facing straight on, but the tops were splayed a little because of the angles of the cabinets when you set them side by side.

 

I thought they sounded pretty good, but had someone mention ( they didn't hear it, just saw the picture ) that it could be a problem with combing. I didn't really hear a problem, but that got me wondering if I had them splayed enough, or should I spread them out a little more.

 

thanks

[mrcpro]

If it sounded good to you then it probably was. The guys who worry about comb filtering most run pink noise through their system in the afternoon when the venue is dead quiet, and then freak out if they hear the slightest bit of coloration when they walk slowly from side to side right in front of the mains.

 

I'll be honest - I must not have golden ears because once we're up and running in a noisy club, I've never noticed comb filtering if two identical cabs are splayed even at fairly shallow angles. There's too much other stuff going on for it to call attention to itself - if it's there at all.

 

But YMMV as always.

[trevcda]

Phase cancellation and interference happens where the the patterns from two cabinets (most noticably the horns) crosses each other and specific locations can vary by frequency. You won't hear it from stage and you most likely may not hear from a mix postions at front of house, but if you're not combining dispersion patterns correctly it's still there somewhere. If you working with a dynamic crowd that can randomly move about at will and is not packed into a confined space or has assigned seating, you can probably get away without putting much thought into it. Where it becomes an issue is when you start carving out a swath of audio issues in a fixed seating area where people are paying a premium for inner circle seating or a packed floor where they can't move away from the issues that you've created with the sound. In this instances it's unacceptable. At your Thursday night "Dentist and Lawyers in Leather" motorcyle gathering in the parking lot of your local watering hole? Probably not as critical, but why not strive for better sound, whatever the event? FWIW

[dboomer]

 

Phase cancellation and interference happens where the the patterns from two cabinets (most noticably the horns) crosses each other and specific locations can vary by frequency.

 

 

It's not so much an issue of "crossing". If you were to place a speaker at 12 o'clock and fire it towards 6 o'clock and at the same time one at 3 o'clock pointing towards 9 o'clock (therefore crossing each other) they basically act as if the other one isn't there.

 

The a notch/null comes when the listener hears a frequency from one speaker out of phase with the same frequency from another speaker. this can be from two different speaker cabinets of from two drivers in the same box ... even the horn and woofer if they are both reproducing the same frequency. This changes drastically because of location as some frequencies will arrive out of time causing them to be out of phase. When you get a bunch of these the pattern plots out like the teeth of a comb ... hence "comb filtering".

 

So it's a good thing to minimize it as much as possible. When is it too much? When it bothers you! So try it and then decide.

 

You can minimize it (in the horizontal plane ... which is probably what you are most interested in, unless you are sending sound to a balcony) by stacking the boxes one on top of the other with the horns as close together as possible. But now you will have to deal with the safety issues caused by stacking. Better bad sound than dead listeners;)

[trevcda]

It's not so much an issue of "crossing". If you were to place a speaker at 12 o'clock and fire it towards 6 o'clock and at the same time one at 3 o'clock pointing towards 9 o'clock (therefore crossing each other) they basically act as if the other one isn't there.

 

Would you not still get cancellation and comb filtering between the two cabinets, albeit in a much smaller space at twelve inches (completely impractical, I know!) in front of the two sets of drivers rather than at thirty feet into the audience? At least until you went completely deaf from listening to two cabs twelve inches away from your ears? "Point of interaction" may be a more accurate term.

[Bryan316]

If you can set up your subs in the center (underneath the front of the stage) you'll get the least amount of comb filtering and dead nodes in the room. Otherwise, angling the subs won't benefit much.

 

However... If you get a chance, try crossfiring your mains instead of angling them away. Your distance from edge of cone to edge of cone will be reduced and your higher frequencies won't be affected as much.

[dboomer]

 

"Point of interaction" may be a more accurate term.

 

 

Intersection is the wrong way to think about it.

 

If I asked a crowd "when you play 2 speakers together is it louder than a single speaker?" The answer would almost always be yes. That extra loudness occurs at the intersection of those 2 speakers. And that is pretty easy to picture.

 

But some frequencies get quieter ... that's the comb filtering part. Generally speaking these little notches of less signal are too narrow for your ear to integrate. Human ears tend to just connect the dots at the top of the frequency response and ignore the holes until they become pretty wide. Those frequencies that are notched out arrive at that same intersection but out of phase (out of time from a push-pull sense). Simply at some (any) distance the path of a given frequency will be moving in a negative direction compared to the same frequency from the other speaker. Depending on how much out of phase it could theoretically notch to infinity while those frequencies arriving perfectly in phase can double (but no more).

 

You have to setup a triangle with speaker 1 at one point, speaker 2 at a different point and the third point is the listener's ear. Got a listener in a different spot (yes you do) ? Then his comb nulls at at different frequencies than yours because the geometry has changed for him. Then factor in reflections and it gets pretty complicated pretty quickly.

[dboomer]

 

If you can set up your subs in the center (underneath the front of the stage) you'll get the least amount of comb filtering and dead nodes in the room.

 

 

Actually putting your subs together will produce stronger nodes than splitting them. Think about it ... a single speaker produces whatever nodes its gonna because of the interaction with the room. Now if you have a second speaker if a different spot, generally it's nodes will be in different places in that room and the phase of those two will likely be different where the phase of a second speaker right next to the first one will likely be more in phase. This may sound backwards to what I said in the post above but it depends on frequency. A few inches doesn't mean much to a speaker producing a low frequency who's wavelength is 11 feet long, but it means a bunch if that wavelength is 1 foot long (or shorter).

[Dogoth]

 

Then factor in reflections and it gets pretty complicated pretty quickly.

 

 

Agreed! Often acoustic issues in a very live room will cause much more comb filtering & nodes than overlapping horn patterns.

 

To add even more to the complication the dispersion pattern of any horn (F.I. 90 deg) is measured at some specific frequency and is not the same at all frequencies. In other words higher frequencies will almost always be narrower than 90 deg and lower freqs will be wider. It just depends on how the manufacturer measured the horn (good companies like JBL will usualy provide that info in their literature). There is really no exact dispersion specs for the entire audible bandwidth, it varies with frequency.

 

If you can walk the room and it sounds OK while playing some full bandwidth program music, you did good. Yup, if it sounds good it is good.

[Bryan316]

From the original post, didn't seem to differentiate between subs placement and mains placement. My comment was for mains. Subs, hell YEAH the combing effect can get terrible.

 

 

Then again, the room is a worse culprit to worry about anyway. There's a club in downtown Detroit, where you simply cannot sit/stand anywhere in the back right corner of the room. The low-mids just propagate there like you're standing inside the bell of a tuba. It magnifies so harshly it proves the ol' Brown Note myth, cuz after one song you wanna either puke or {censored} yourself.

[Bugzie]

I use the MRX 515's and 518's and 528's. The horns are 70 degree. If you're concerned about it follow Don's advice and stack the 515's on top of each other with the top one upside down so that the horns are closest to each other. I can hear the difference but rarely anyone else does. Side by side works best when you are trying to pound the dance floor. I do that a lot when doing a wedding DJ event. I attenuate the outside speaker amps so that the dance floor is louder than the area where people want to sit and talk.

[agedhorse]

 

If you can set up your subs in the center (underneath the front of the stage) you'll get the least amount of comb filtering and dead nodes in the room. Otherwise, angling the subs won't benefit much. However... If you get a chance, try crossfiring your mains instead of angling them away. Your distance from edge of cone to edge of cone will be reduced and your higher frequencies won't be affected as much.

 

 

Doesn't even apply within the context of the OP's question.

 

Your crossfiring comment just changes the location/physical position of the pattern. Another myth (typically)

[agedhorse]

The polar pattern of the MRX horns is quite uniform and the edges reasonably smooth, meaning that in practice the comb filtering effects will be much less noticeable. In practice, the issues are generally trivial compared with all the other more typical problems a sound provider at this level has to deal with.

 

Where comb filtering can become a real problem is in higher Q horns, where the increased directivity comes at the cost of polar uniformity. We don't see many of these horns anymore, but the myths continue.