Vertical cab stacking---the only way to play

[asad137]

I have a problem with vertical stacking.
From what i remember from physics and math, the power levels drop 4 times as the distance doubles (from a point source).

Yes, this is true.

That certainly can't be good. Vertical stacking might work in some situations, it certainly isn't the be-all-end-all.

You're going to have the same problem with any configuration unless the dimensions of your speaker system are comparable to the wavelengths of interest and you're in the near field radiation pattern. At 100 Hz, the wavelength is about 11 feet! For a 4x10 cab which has dimensions of about 2' x 2' square, you're in the far field when you're about a foot away from the speaker cabinet at 100 Hz. Further than that, the cabinet acts as a point source as far as intensity is concerned, and the SPL drops as 1/r2​.

Asad

 

[billfitzmaurice]

comb filtering ... occurs when the drivers/cabinets are reproducing the same frequencies.

Which is exactly what 99.9% of commercial electric bass cabs do.

In a vertical 212 for example, how come you don't get comb filtering then? When standing eight feet away the drivers are still at different lengths away from my ears.

Because those different lengths remain at a constant value as you move across the soundfield. Combing occurs when those distances shift as you move about.

Vertical stacking might work in some situations, it certainly isn't the be-all-end-all.

Vertical arrays are not perfect, to be sure. But they are better than everything else.

From what i remember from physics and math, the power levels drop 4 times as the distance doubles (from a point source). What this means is also that as the distance is halved, power increases 4 times. What is perfect for a guy in the crowd 50 ft away sounds nearly 3 times as loud for someone at the front of the stage, 12 ft from the rig, with 16 times the sound energy.

This is true of all sources, stacked vertically or otherwise, unless they are high enough to operate as line sources. As far as electric bass is concerned even a six foot high cab array operates as a point source.

 

[MikeyD]

Personally I think the comb filtering thing is a non issue with musical instrument cabs, but I'm sure it will be beaten to death here for many years to come.

I agree. You'd notice it more along with beaming at higher frequencies from larger woofers or arrays of woofers AND with steady, held notes. With typical bass guitar notes that are changing all the time and don't have a lot of steady high-frequency content, it's usually a very tiny (negligible) aspect of the acoustic quality perceived, especially at the audience position. You also have to keep in mind all the zillions of other things going on - particularly reflections from walls - that tend to mash out these effects.

Indeed, if comb filtering were a significant issue, guitarists would be a lot more likely to shun their 2x12, 4x12, or 4x10 cabinets. I don't see that happening. Amps like the Fender Twin Reverb and Marshall 4x12's have been eminently popular for eons - and you *would* notice some comb filtering on held out high notes or heavily overdriven notes with these cabinets.

Comb filtering is much more of an issue for hi-fi systems in which the listener remains at one static position and the speakers are producing a lot of higher-frequency content. In this case, the listener would readily hear a lot of artifacts of constructive and destructive interference from horizontal arrays or drivers that were too large in relation to the wavelengths they were generating.

- Mike

 

[JimmyM]

I have a problem with vertical stacking.

I know how comb filtering and power alleys come about. And i do know that vertical stacking eliminates most of these things. However, having all your power emanating from what is essentially a point source puts out huge amounts of power at that location.

From what i remember from physics and math, the power levels drop 4 times as the distance doubles (from a point source). What this means is also that as the distance is halved, power increases 4 times. What is perfect for a guy in the crowd 50 ft away sounds nearly 3 times as loud for someone at the front of the stage, 12 ft from the rig, with 16 times the sound energy.

That certainly can't be good. Vertical stacking might work in some situations, it certainly isn't the be-all-end-all.

Let's assume this is true...not that I believe it is, but let's assume. Wouldn't it be the same thing regardless of where the speakers are or how they're stacked? And wouldn't you WANT the point source to have more power since you're standing in front of it most of the time?

Sorry, VS'ing is still the be all and end all for me

 

[ModestCargo]

Indeed, if comb filtering were a significant issue, guitarists would be a lot more likely to shun their 2x12, 4x12, or 4x10 cabinets. I don't see that happening. Amps like the Fender Twin Reverb and Marshall 4x12's have been eminently popular for eons - and you *would* notice some comb filtering on held out high notes or heavily overdriven notes with these cabinets.

No, because comb filtering is a much bigger issue with lower frequencies.

Comb filtering is much more of an issue for hi-fi systems in which the listener remains at one static position and the speakers are producing a lot of higher-frequency content. In this case, the listener would readily hear a lot of artifacts of constructive and destructive interference from horizontal arrays or drivers that were too large in relation to the wavelengths they were generating.

- Mike

No, because the listener is in one static position - usually directly in the middle of the speakers, and if there are two subwoofers, they are on either side as well. Little to no comb filtering there as the listener is in the prime location and as you say not moving around the room.

 

[getonup]

i have a 2 Aguilar 112s I stack them so they are vertically the tallest -

Link Removed

I like it cause they are ear level but --

i feel like they might sound less loud in general on the stage though - dues to less contact with the stage.


Any thoughts?

 

[billfitzmaurice]

No, because comb filtering is a much bigger issue with lower frequencies.

Comb filtering is more of an issue at high frequencies. The degree of filtering present is dependant on the wavelengths involved and the distance between the sources. To prevent comb filtering drivers must be within one wavelength center-to-center. At 3kHz that's 4.5 inches. At 100 Hz that's 11.3 feet. It's impossible to prevent combing at 3kHz unless the drivers are no more than fours, while at 100 Hz combing is almost never a problem unless you spread the sources.

The other issue overlooked by most, and understandably so since audio engineering isn't even offered as a course in most colleges, let along high schools, is horizontal dispersion.A speaker's angle of dispersion is inversely proportional to the size of the radiating plane. Assuming drivers small enough and close enough together so that they form a single source with no comb filtering having them horizontally mounted will still result in narrower dispersion, having them vertically mounted will give wider dispersion.

 

[billfitzmaurice]

i feel like they might sound less loud in general on the stage though - dues to less contact with the stage.


Any thoughts?

Myth.

 

[pedro]

This isn't about vertical stacking but as long as all the Talkbass professors are gathered hope nobody minds - do casters on a cabinet have any effect on the sound either way?

 

[A9X]

This isn't about vertical stacking but as long as all the Talkbass professors are gathered hope nobody minds - do casters on a cabinet have any effect on the sound either way?

No.

 

[pedro]

Excellent!

 

[69nites]

No.

unless there's a squeaky wheel

/cheesy joke

 

[billfitzmaurice]

unless there's a squeaky wheel

/cheesy joke

Or the caster is two feet high.

 

[pedro]

Actually 'Greasey Wheel' was a name I had suggested for our band. Nobody liked it except me. Hmmm.

 

[brredstik]

In the 60s many bass players would set their 2x12 cab edgeways...helped them hear it better.

I don't have that problem...

 

[Blues Cat]

I don't have that problem...

Comb filter city.

 

[greenboy]

Here - let me help:

BTW, the reason you don't hear the bottom cab when you're standing close to it is because it takes a good 8-10 ft for bass waves to even develop fully.

Myth.

If you aren't hearing your bottom cab it's a combination of elements:

(1) Its contribution in this example has to travel further to your ear. Therefore by inverse square law it'll seem less loud even if the two sources are equally sensitive.

(2) Your knees can't hear its midrange and treble. And for the most part neither can your ears, because midrnage and trele are more directional and youre ears are off axis/above axis. That makes its contribution harder to track and make sense of.

(3) Your positioning relative to the bottom cab's cab positioning is being affected by room modes, which are caused by long waveform reflections arriving [partially] out of phase with the source. Thus, lower frequencies are being [partially] cancelled in that particular spot.

But I should think you've played at least a few gigs where standing next to your cab bathes you in low frequency goodness. That should make you wonder how this bit about "low frequency waves taking x feet to develop" ever got started. If they did, headphones would have to be 56 ffet wide to hear a low E fundamental, and we all know that isn't true.

Like MF and HF content LF content typically is loudest at the source, and as the waves travel outwards the loudness drops off inversely - [room] boundary effects withstanding.

 

[greenboy]

Also noticing people talking about comb filtering as if you have to move around to hear it. Well, when you travel across the soundfield you can hear what it causes, sure enough: frequency response smears that vary widely from place to place. But any one of those positions has a widely different frequency response from another, whether you are moving or not.

This makes for different tonal/mix details being obscured for some listeners, and all too brash for others, a spot to spot variance that affects a seated audience as well as a dancing one. Add it to other room variables that make mixing tough and you can end up with a garble in a lot of the room.

Not that it matters to many, but I thought you should know ; }

 

[pedro]

But I should think you've played at least a few gigs where standing next to your cab bathes you in low frequency goodness.

(pedro suddenly feels tingly and good all over.)

 

[Johnny Mack]

I have never done this, but am just curious. a few questions:

while i agree my two 112s sound great stacked on axis, is it really not practical to split them approx. 6 feet apart at the drums in a small club or at a club while going FOH?

I think i would gain volume on the other end of the stage for monitoring and possibly give the group more of a "full" sound.

I also know comb filtering will take place, but is this really a concern in real life applications for medium sized gigs?

what if the two cabs were slightly angled out?

other than loss of bass response due to decoupling, what real disadvantages are there to this method?

sorry for the hijack, but its still fairly on topic i think.
if the set-up was 300 watts into a total of 4 ohm load, would it be acting as two individual 150w rigs due to the separation or does it still act as a 300w rig with separated cabs?

thanks TB!