Fearful Cabs and Comb Filtering: Should I Mirror Baffles?

[Kaplan]

The large speakers are much more important than the tweeters! They need to be as close as possible. With two cabs, one tweeter can be switched off.

 

[agedhorse]

This is 100% the point of this thread. Do I bother asking Leland @ speakerhardware to mirror one of the baffles for me. If he's down to do it, and it's not a hassle, I'll 100% mirror one of the baffles.

Can the baffle be installed flipped over?

 

[fu22ba55]

Can the baffle be installed flipped over?

It does look like I could just flip one of the baffles... the 15s are NOT centered in either direction, but I think the only penalty would be if one side of the plywood were a nicer finish grade.

I can't recall whether the baffles have any biscuit holes or anything like that already routed out of the back. A question for Leland, but yes the thought crossed my mind to just flip one of the precut baffles.

 

[singlemalt]

The two pairs I built, 15/6/1’s and 12/6 cubes, I mirrored the baffles. I’m not sure it made much difference. With a pair running at 4 ohm and a healthy amp, it was overkill.

I ended up selling the big pair, and using a single 12/6 for most things.

I found a single 15/6 could carry a large room, and anything with FOH just a 12/6 for the stage. The 12/6 would do most small bar gigs. I don’t think I ever used the pair of 12/6 together at a gig.

Building them is half the fun.

It seems like you could just flip the baffle over, but there might be issues with biscuit cuts lining up.

I’ve never seen the cube version of the 15/6. The mid compartment looks like fun.

So, I don’t know if anyone could hear the difference. They sound great no matter what you bring.

 

[Wasnex]

Thanks Wasnex. I read your post more than once, and some of the maths actually did make it into my feeble caveman brain. This is why I purchase speaker cabs and don't design them.

@Wasnex please correct me if necessary in the conclusions I'm drawing from your post:

a) spacing drivers closer together produces LESS nulls between lobes, and the nulls/lobes produced occur higher frequencies
b) spacing drivers further apart does TWO things: produces MORE nulls and the nulls / lobes impact LOWER frequencies the further apart the drivers get?
c) the smaller the diameter of the driver, the less real-world wiggle room I have when spacing the drivers? (I've got more margin of error in real-world inches between two 15s than two 6s, simply because the 15s are larger?)

Are those three statements roughly correct?

So given the two images below: I (eye) and Iv2 (eye v2), are the following statements also true:

d) Option I (eye) is better since the mid drivers are closer together, and any nulls/lobing would occur at much higher frequencies than at Iv2 (eye v2)

e) The 3015LFs are actually 2" further apart in I (eye) than in Iv2, so technically, mathematically, there would be more nulls / lobing (for the 15s) but this is less of a concern because of the diameter of the drivers?

Is there any point where the drivers are far enough apart that the negative effects are mitigated?

So in Iv2... are the 6" drivers SO far apart that the effect is nullified, because the lobing would occur at frequencies LOWER than what the 6" driver can produce, because of the crossover?

View attachment 7434273

Not sure if you caught this. I believe the same cabs are used in option I and I V2. V2 simply switches the cabs from top to bottom. If you build the mirrored set, I suggest trying it both ways and deciding for yourself.

I believe A. and B. are approximately correct.

I believe your understanding of C is not quite right. Concern is on center to center spacing VS wavelength, rather than on driver size. The 6s operate in a higher frequency range so the wavelengths are shorter. The 15s operate in lower frequency range so the wavelengths are longer. Because the 6s work with shorter wavelengths, they need closer center to center spacing to avoid severe lobing

AFAIK the crossover is approximately 800hz, which has a wavelength a bit under 17". So the 15s will be dealing mostly with wavelengths longer than 17" and the 6s will be dealing mostly with wavelengths shorter than 17". The spacing for the 15s in your examples is 24.5" Therefore, the spacing to wavelength ratio at 800hz would be 24.5:17 which converted to decimal is 1.44

This is the pattern you get at 1.5

This is the pattern you get at 1

So at 800hz (worst case lobing for the woofers), the resulting pattern is closer to the top image. If the two woofers were placed on the same baffle you could probably get the spacing close to 17" (ratio of 1), so worst case would look like the bottom image. However since your dealing with two cabs, 24.5" is about the closest you can get the 15s unless you mess with the cab dimensions or choose to use wide spacing for the 6s.

If the 6s were spaced at 24.5" you would get exactly the same pattern at 800hz, and even more lobes would develop as the frequency goes higher. AFAIK close spacing of the 6's is more critical than the 15s. The lobing will be more severe and more audible in the range the 6s cover. So the preferred compromise is to place the 6s as close as possible.

Compare to the 1515/66 where the spacing for both the 6s and 15s is as close as possible.

 

[fu22ba55]

The large speakers are much more important than the tweeters! They need to be as close as possible.

I am a bit concerned about how far apart the 15s are compared to my previous build. While it's not a scientific comparison because of the keystone-ing / distortion in the photograph... the 15s do seem much further apart, and they cabs seem... just... friggin HUGE.

 

[Wasnex]

Aside from the math, it's generally nowhere near as big of a deal as some folks make it out to be. Otherwise the classic 810 format would be a total bust!

I generally dislike the way an 810 sounds on stage, and yet a close mic on one of the 10s seems to sound really nice. I wonder why?

 

[Wasnex]

To tell you the truth, I never really cared for the sound of the stacked cabinets, I liked the sound of an individual cabinet with the mid/tweeter on top.

Exactly why I suggest @fu22ba55 try it both ways.

 

[fu22ba55]

Not sure if you caught this. I believe the same cabs are used in option I and I V2. V2 simply switches the cabs from top to bottom. If you build the mirrored set, I suggest trying it both ways and deciding for yourself.

Yes, same cabs, just different orientation.

If the 6s were spaced at 24.5" you would get exactly the same pattern at 800hz, and even more lobes would develop as the frequency goes higher. AFAIK close spacing of the 6's is more critical than the 15s. The lobing will be more severe and more audible in the range the 6s cover. So the preferred compromise is to place the 6s as close as possible.

Understood. Would still need to prioritize the 6"s

Compare to the 1515/66 where the spacing for both the 6s and 15s is as close as possible.

I love everything about the 1515/66 except the idea of moving it around. I made a promise to myself years ago to always go modular, and never again buy a cab that I couldn't lift by myself and carry up or down 3 flights of stairs.

I'm worried that my old config of two 15subs with a 2x6 headcase will sound BETTER than two 15/6 cabs stacked, no matter how I slice it.

 

[Passinwind]

I'm worried that my old config of two 15subs with a 2x6 headcase will sound BETTER than two 15/6 cabs stacked, no matter how I slice it.

I built four different headcases plus one duplicate and only did a single fEARful 12/6 to the original spec (as a single cab, and before Dave did any crossover designs) but I have heard and played through plenty of others, and suspect you’re right. Dave Green started out with a headcase build and IIRC he still had it the last time I talked to him, two years or so ago. But I doubt you’d find any differences to be deal breaking, probably. And FWIW, the 1515/66 is by far my least favorite of the lot…go figure!

 

[agedhorse]

I generally dislike the way an 810 sounds on stage, and yet a close mic on one of the 10s seems to sound really nice. I wonder why?

Yet there are plenty of top pro players who prefer the stage sound of the 810 even if it's not your personal cup of tea.

What I am getting at is that even if there may be some differences, there are players who prefer it the way that you don't. When multiple players who play large rigs in large venues consistently choose something that you don't care for, that doesn't make their choice and preference wrong... maybe they have a different perspective and taste or preferences than you do.

 

[Wasnex]

Yet there are plenty of top pro players who prefer the stage sound of the 810 even if it's not your personal cup of tea.

What I am getting at is that even if there may be some differences, there are players who prefer it the way that you don't. When multiple players who play large rigs in large venues consistently choose something that you don't care for, that doesn't make their choice and preference wrong... maybe they have a different perspective and taste or preferences than you do.

Yes many people think there is no better cab than the Ampeg 810. I totally respect their right to choose. It's obviously a respectable choice That's not what I was getting at.

As I mentioned, close mic'ing one of the 10s seem to sound nice. There seems to be some nice highs available from a single driver that are not possible to hear when listening to the cab as a whole. AFAIK the drivers play up to about 5k, but the cab sounds to me more like like it rolls off at about 3k

My understanding is this is due to the destructive interference that occurs between all of the drivers. IME no amount of EQ can make the full cab produce what I consider nice highs. Seem like boosting the high gets cancelled out.

 

[Wasnex]

Understood. Would still need to prioritize the 6"s

Providing a single 18 Sound 6NM410 can meet your volume requirements, I think the best solution would be to build a single 15/6 and a 15 Sub.

These details are in the plans:

Regarding the comments above. I think they are misleading. Doubling up on the woofers drops the impedance from 8 to 4 ohms, doubles the power handling, and adds 3dB to sensitivity. So basically you get +3dB from higher sensitivity and 3dB from doubling the power. This only applies to the frequency range of the woofers.


AFAIK, the 3dB crossover switch should allow a single mid to match the sensitivity of either 1 or 2 of the 3015LFs. The switch does not increase how much power the mid driver can handle or how loud it can play.

18 Sound 6NM410

• Power 180W
• Sensitivity 101.5dB
• Calculated SPL ~124dB
  • Calculated SPL of two drivers 130dB

3015LF

• Power 450W
• Sensitivity 98.4dB
• Calculated SPL ~125B
  • Calculated SPL of two drivers 131dB

 

[agedhorse]

Yes many people think there is no better cab than the Ampeg 810. I totally respect their right to choose. It's obviously a respectable choice That's not what I was getting at.

As I mentioned, close mic'ing one of the 10s seem to sound nice. There seems to be some nice highs available from a single driver that are not possible to hear when listening to the cab as a whole. AFAIK the drivers play up to about 5k, but the cab sounds to me more like like it rolls off at about 3k

My understanding is this is due to the destructive interference that occurs between all of the drivers. IME no amount of EQ can make the full cab produce what I consider nice highs. Seem like boosting the high gets cancelled out.

Can’t have destructive interference without constructive interference from multiple point sources.

If you are listening within a zone of constructive interference, your perspective might flip.

 

[Passinwind]

Providing a single 18 Sound 6NM410 can meet your volume requirements, I think the best solution would be to build a single 15/6 and a 15 Sub.

These details are in the plans:

View attachment 7434538
Regarding the comments above. I think they are misleading. Doubling up on the woofers drops the impedance from 8 to 4 ohms, doubles the power handling, and adds 3dB to sensitivity. So basically you get +3dB from higher sensitivity and 3dB from doubling the power. This only applies to the frequency range of the woofers.


AFAIK, the 3dB crossover switch should allow a single mid to match the sensitivity of either 1 or 2 of the 3015LFs. The switch does not increase how much power the mid driver can handle or how loud it can play.

18 Sound 6NM410

• Power 180W
• Sensitivity 101.5dB
• Calculated SPL ~124dB
  • Calculated SPL of two drivers 130dB

3015LF

• Power 450W
• Sensitivity 98.4dB
• Calculated SPL ~125B
  • Calculated SPL of two drivers 131dB

My personal take is that the original 3dB pad is too low, and at least a few of my builder friends always agreed with that. I’d leave it that way to play nicely with two 15s and knock it down to 6-8dB for a single woofer. But IME those values depend on where in the Fletcher-Munson curve you’re operating, and I am most definitely not a hard rocker.

FWIW, here’s a mic’ed recording of my old 12/6, which used an 8.5dB pad on the mid driver:



That’s slide bass over a looped regular bass and drums track.

 

[Wasnex]

If you are listening within a zone of constructive interference, your perspective might flip.

I have tried kneeling down in front an 810E and elevating an 810E to ear level. Never found any placement of my ears where the cab sounded like it had the nice highs I hear from close mic'ing one of the 10s.


I used think the dark tone was because the drivers did not play high enough, until I heard an examples of closing mic'ing one of the drivers.

 

[fu22ba55]

Providing a single 18 Sound 6NM410 can meet your volume requirements, I think the best solution would be to build a single 15/6 and a 15 Sub.

I have also thought about this solution. I don't dig the assymetry, but it might make the most sense.

In other news, there's a possibility I'll be able to get my old cabs back. The current owner is willing to part with them if we can sort out shipping, etc. He's being very generous and understanding, so that might work.

If that's the case, I might build one 15/6 tube anyway and play with a couple different configurations, including running EVERYTHING together for a 2.67 Ohm load.

 

[2thAche]

I have mirror-image F112s. At our gigs (the best sound we've had) we put them out next to the mains, on either side. The Fearless cabs IMO don't have a great horizontal spread stacked. On either side, they have a much better spread, they sound better then running the bass through the mains, and we use IEMs so I don't need something behind me. I move around out front with a wireless pack when we sound check, I've never heard any even slight instance of comb filtering. The best argument I can make for mirrored cabs is esthetics.

Another thing I'll say about two F112 is it's alot of high end. I pretty much turn the treble almost all the way down on the back of the cab.

 

[PeaveyPlayer]

Having the mid higher up closer to the ear I think would help with beaming

Allowing the user to hear more top end without as much roll off vs when of axis

 

[MikeBass]

I’m over here wondering in what band and/or gig situation does being this deep in the absolute fine details are you playing?

I completely understand working out these details, but at what point are you “listening with your eyes” (meaning what’s it look like on paper) and not your ears to determine what actually sounds good?

I’m not trying to be snarky. I’m just genuinely curious.
I’ve owned some ridiculously nice boutique gear, and never once did anyone, let alone other bass players ever say “you know, if you lined up the baffles you’d…” or “ya know there’s some serious comb filtering going on….”.
It either sounds good or it doesn’t. And that’s where your ears should be the final judge. Even if on paper it tells you it shouldn’t.