Another thread on using different subs

Dick Rees

Dick Rees

Curmudgeonly Scandihoovian
Jan 11, 2011
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St Paul, MN
After reading yet another great column from Bennett on "throw and go subs", I'm wondering again about using different cabinets together. In this case my question is regarding the use of "subs under tops" on the sides of the stage (outdoor) combined with some subs in the center to be delayed for the most even coverage.

I have a job in September where I'll be using a Cobra II rig for the main PA but am wanting to smooth out the low end and get rid of the power alley. I have some Sb180's I can use in the center, either clustered or in a line. I can space and/or delay them as needed.

Are there any reasons NOT to attempt this with different subs?

Thanks.
 
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Re: Another thread on using different subs

no reason not to, perhaps try and model it on ease focus or the like, using similar designs of subs if the actual models are not available just to get an idea of what may happen. G
 
Re: Another thread on using different subs

Dick Rees said:
Are there any reasons NOT to attempt this with different subs?

Thanks.
Click to expand...

A reason to not try it is that if it doesn't work out to your satisfaction, you moved subs into place that you don't end up using.

Generally, not using matching gear is only a problem because the results are less predictable. On paper, the plan may look fine, but when you implement it, it might not work as well as expected. On the flip side, on paper, it could look odd, but actually provide the desired result you are seeking when put into practice. So, give it a shot and see what happens. If it sucks completely, you can always turn them off.
 
Re: Another thread on using different subs

Dick,

It can be done, and if you have Smaart or something like it you can even do it pretty well. Especially in a situation like this where the separate types of subs are in separate arrays. It helps a lot if they are similar types of cabinet with similar frequency response, or you can mess up your LF (it's easy to get it all right at the crossover point, all subs go high enough). Just be aware that the reason there are so many horror stories is that the people who are good at doing this are generally at a high enough level that they can demand their subwoofers match, or can be eccentric on purpose and pull it off.
 
Re: Another thread on using different subs

Thanks to you both for the replies. I'll look up the specs on the Cobra subs.

Can you give me a short list of the likely problems? I don't have any SMAART or other comparison programs, just my ears and a bit of time. And I'll add that the shows I do are not rock where there's a ton of critical low end. I just need some solid, smooth support for the mains.........

Edit:

Looking at the specs for the two boxes, the Cobra Sub (CS) and the 180 both use the same EVX 180B driver. The CS is a direct radiator, the 180 a folded horn. The 10dB down point is the same for both (30hz), but the CS tops out at 170 and the 180 at 250. Box tuning for the 180 is 38hz. I couldn't find that spec for the CS.

So I'd guess they'll probably play together fairly well.

Thoughts?
 
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Re: Another thread on using different subs

The problems you're going to run into will be additional frequency response peaks and dips as a result of differing phase between the two sets of subs. Sounds like in this case it's probably not a big deal, but with some crossover topologies you could be running the subs essentially out of polarity for their lowest octave.
 
Re: Another thread on using different subs

Thanks. I believe I'll be able to hear the polarity anomaly with simple A/B test by flipping the center subs. Any other phase issues I'll have to live with.
 
Re: Another thread on using different subs

Bennett Prescott said:
Except that it's actually a phase anomaly, not a polarity anomaly, so the cancellations will be frequency dependent. It may not be so obvious.
Click to expand...

and it will be different at every listening position.. so you'd have to stand in multiple places and listen to multiple frequencies with the polarity each way (the combinations are numerous)
and that only tells you which way is better, not if either of them is close to correct (both could be 90deg off of the sweet spot)

Jason
 
Re: Another thread on using different subs

Dick Rees said:
Better is good.......
Click to expand...

Just try it Dick, you'll likely be fine as long as you have some time to tinker and a bit of DSP available for delay etc. I used to be in the camp that would have discouraged this (particularly given the different loading of the 2 subs), but I'm getting LESS anal lately it seems. It won't be optimal, but will probably sound "good enough".

Longer term though, I'd encourage you to invest some time in a measurement system, it's worthwhile.
 
Re: Another thread on using different subs

I will soon be in a similar situation as Dick. One "solution" I am considering is essentially running a "dual sub on aux" setup- in other words, using one type of sub for kick and toms, while the other subs handle bass guitar and keys (or something similar to this). Has anyone tried this? In theory would this be a better approach than trying to wrestle with using both types for the same program material?
 
Re: Another thread on using different subs

When you talk about phase cancellations it reminds me of an experiment I saw a number of years ago. They connected a mic near the tailpipe of a motorcycle and fed it into a preamp with a phase inverter and then to an amp feeding a speaker pointing towards the back of the cycle. Since the souind coming out of the speaker was 180 degrees out of phase with what was coming out of the muffler you could barely hear the cycle run. I suppose if you were off axis it would have been a different story but it was interesting none the less.
 
Re: Another thread on using different subs

Keith Billik said:
I will soon be in a similar situation as Dick. One "solution" I am considering is essentially running a "dual sub on aux" setup- in other words, using one type of sub for kick and toms, while the other subs handle bass guitar and keys (or something similar to this). Has anyone tried this? In theory would this be a better approach than trying to wrestle with using both types for the same program material?
Click to expand...

Keith,

This will essentially eliminate comb filtering between the two arrays as they will be reproducing different program material, but it will also result in a loss of output... and you may have wanted those additional subs for directional control. That said, it is not uncommon to build a full range l/r sub system flown or stacked with the mains that allows frequency response to the 30Hz range, and use high pass filters to control what gets into the subs. Then add an aux sub array just for kick and bass.
 
Re: Another thread on using different subs

Keith Billik said:
I will soon be in a similar situation as Dick. One "solution" I am considering is essentially running a "dual sub on aux" setup- in other words, using one type of sub for kick and toms, while the other subs handle bass guitar and keys (or something similar to this). Has anyone tried this? In theory would this be a better approach than trying to wrestle with using both types for the same program material?
Click to expand...

This wouldn't solve the original problem though, of wanting to direct the sound differently. The point of using 4 subs was to lessen the power alley effect. If you send different signal to different subs positioned differently, the mix is going to be drastically different in different parts of the room. I would say that this would be the worst possible scenario to pick from.
 
Re: Another thread on using different subs

Brian jojade said:
This wouldn't solve the original problem though, of wanting to direct the sound differently. The point of using 4 subs was to lessen the power alley effect. If you send different signal to different subs positioned differently, the mix is going to be drastically different in different parts of the room. I would say that this would be the worst possible scenario to pick from.
Click to expand...

I continue to think that the effect of the first reflections INDOORS far outweigh and render the power alley effect basically a nonconcern in deciding how to setup the subs. However, since Dick is considering this for an OUTDOOR show, then the power alley effect becomes one the most significant factor in determining possible cancelation nodes. It still needs to be balanced against the timing issues with the FOH mains. Which is more important to you or the client, performance at 65, or performance at or just above the crossover?

My instinctual answer is actually a combination of Bennett and Keith's. Treating the L/R +Cobra subs as one system, and the Sb subs as a separate center cluster. I would do my best to time align the L/R subs with the center cluster so you have all of them positively combining for the kick, and maybe the bass. Any full range keys, toms, and maybe the bass would just be sent to the L/R subs.
 
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Re: Another thread on using different subs

Here is some playing with the problem in Rayend. I have assumed that the outer stacks are approximately 30 feet apart, the tops are crossed over to the subs with a 2nd order L/R at 100 hz, and all of the subs are time aligned to the same base line. Of course this is also assuming (perhaps poorly?) that the Cobra system can be treated as a single source for the tops and subs, and that the levels of the L/R subs and the center subs are the same.

Here is the traditional power alley at 65 hz, 100hz, and 180 hz.

At 65 hz


power alley 65.png

At 100 hz
power alley 100.png

And 180 hz
power alley 180.png

Here is with the added subs centerfill
At 65 hz


center fill 65.png

At 100hz

center fill 100.png

And 180 hz


center fill 180.png

Here is just the tops at 180 hz for comparison

no subs 180.png

When changing the relative levels between the L/R and center subs, it appears that it is better to have the center subs stronger than the L/R. As you go up to 12db difference the patterns seems to smooth out. (In Rayend, it seems that the stronger the signal the less resolution the program shows, so I made the 12 db difference by raising the center 6 db and lowering the L/R by the same.)

At 65 hz

12db 65.png

At 100 hz

12db 100.png

At 180 hz

12db 180.png



From the models, it looks to me like it is possible to get the result desired if the center subs can simply be time aligned to the line through the L/R subs. Actually from playing with the models, it looks like having the center subs up to 30 ms behind the L/R subs does not make that big of a difference. I think it would be worth giving it a go and I would bet you can get something usable by ear.
 
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