Speakers: Dispersion vs Directionality?

  • Thread starter Thread starter cephus
  • Start date Start date
When I used to gig all the time with a soundman, He put a piece of duct tape on the grillcloth where the 57 was pointed at it.
 
cephus said:
When I used to gig all the time with a soundman, He put a piece of duct tape on the grillcloth where the 57 was pointed at it.

I've seen guys do that too when I was younger but didn't really understand the reason for it. I thought they must have had a tear in the grill cloth. :D
 
Piercing treble. Pretty much sounds like an ice pick going in your ears.
 
Add the single coil, stainless frets and nickle strings,...the stuff that tinnitus is made of. :D
 
In the bass forums and elsewhere, I've picked up the following:

Apart from the tendency of highs to beam and bass to be unidirectional, there *is* (caveat: on average) a directionality of a speaker that is a function of the speaker's diameter.

Bassists use anything from 5" to 18" speakers, with most falling in the 10"-15" range.

There is debate on this, but what I read in several posts was that the bigger (15+18) drivers are "beamier," while the tens radiate their sound more evenly and are better heard from either side and on the stage. I know, it sounds like the opposite of what we know about bass and treble, but this is what I've come across.

I can't find a link to one of these discussions, but speakers are not like microphones-- at least I've never seen a polar response graph for one. How would you measure it?

Your 12" speakers might well be doing some of this beaminess of the sound. Bass and low mids takes a little time to develop as they launch from the amp, too, so your proximity to the amp might seem to lessen the lows.

Hope there was something useful for you in this rambling post.

oh, and one slightly off topic fact is that larger diametered drivers do not necessarily make lower sounds (in bass cabs, at least.) here is a copy of part of a talkbass.com post from one of the Uberposters over there, Mujibunga:

QUOTE:"Here are Eden's specs on the D-210XST (which I recommend, and you know how many posts I have):


Speakers EC-1060XS Cast Frame
Tweeters E-2700 Cast Bell
Crossover 3.5KHz @ 18dB
Power Handling 500W RMS
Frequency Response 30Hz - 14KHz
Sensitivity 103dB SPL
Impedance 4Ω or 8Ω
Dimensions 23”w x 18”h x 18.5”d
Weight 59 LBS

Compare that frequency response with anything else they make, for instance, the D-215XLT:
Frequency Response 40Hz - 14KHz
Sensitivity 103dB SPL

Or the D-118XL:
Frequency Response 42Hz - 2.5KHz
Sensitivity 100dB SPL

Or the D-212XLT:
Frequency Response 40Hz - 14KHz
Sensitivity 103dB SPL

Or even the venerated D-410XLT:
Frequency Response 50Hz - 14KHz
Sensitivity 106dB SPL (this one is a little louder, but not lower)

Not to mention the D-410XST:
Frequency Response 36Hz - 14KHz
Sensitivity 104dB SPL

So you should be seeing a pattern here. Tens dominate when in the proper cabinet."END QUOTE


Cheers,

Obi-Wan cynjeoJ
 
Really? I've heard that...I've never had a chance to play through 10's.
 
Just call Ted Weber ya cheap fuck.

Long distance rates have come down a ton in recent years.

I'm tellin ya he will fix you right. ;)
 
c7sus said:
Just call Ted Weber ya cheap fuck.

Long distance rates have come down a ton in recent years.

I'm tellin ya he will fix you right. ;)

:D :D :D :D :D

If I had any rep left I'd give you sum.
 
Some of you have a pretty good grasp of some of the concepts, but I think that it's important that I review some basic laws of physics about how "real" speakers work in the "real" world.

I'll skip the math and techy stuff and try to present it in easy to understand terms. It all boils down to one basic axiom,and four smaller axioms:

1. The basic axiom: "Everything in designing a speaker is a trade off."
This can also be stated as:

"There no such thing as a free lunch.", or "You want something? What are you willing to give up to get it?"

These are the four smaller axioms:

2. "Small won't get you big, without some tricks."

3. "To get good bass response, you hafta move the air in the room - a lot of air."

4. "As the frequency goes up, the dispersion narrows."

5. "As the frequency goes down, the bass will roll off dramatically at some point, depending on basic axiom 1."

The problem:

Think of the air in a room as a big bale of loosely packed cotton. You want to move the whole bale of cotton, but all you have is a small stick. (The "stick" is your speaker.) The stick won't move the whole bale; all it will do is poke into the bale and move the cotton near the stick. You need what's called "better coupling". Speakers are like small sticks; they don't do a good job of moving large objects. You need a better way to tie the speaker to the air in the room. You can:

Use a bigger stick: You can use a bigger cone, but there are limits to how big you can make it, and drawbacks start to outweigh benefits as the size goes up. if the stick is as big as the room, how do you move the stick? The bigger cone has to be heavier and stiffer, so that it doesn't flex as it moves. Heavier means sluggish. That limits the cone to slower starting notes like pipe organs. Stiffer, yet light cones means more exotic materials (i.e., expensive") like Kevlar, Aluminum, and Graphite Composites.

Move the stick more: This was the principle of the acoustic suspension speakers; make the speaker move longer distances to push more air. Unfortunately, it required a lot heavier cone and a long voice coil which dropped the efficiency way down and made the system sluggish as hell.

Use a lotta little sticks: The Bose/Hartke/Marshall approach, where you use multiple smaller drivers to approximate the cone area of a larger driver. The problem is still back to basic physics; even though you equal the area of a large speaker, the cone diameter of each speaker determines one of the low frequency cutoff points, and you pay for the bass boost with phase cancellations in the mid frequencies, and beaming at higher frequencies.

Taper the stick from small to large: It's called an acoustic transformer, and that's how horns work. They transform a high energy, large motion, speaker cone to to a lower energy, less motion, signal appearing at the horn mouth that couples better to the air in the room. The problem with low frequency horns is that the mouth of the horn has to be huge and (like every transformer), the throat of the horn (or the transformer's primary) can easily saturate when overdriven.

Tie a second stick to the first stick: This is what a Helmholz resonator does; it can either be done with a tuned hole in the box to move more air in a very small frequency range just below where the speaker starts to roll off (Axiom 5), or by using any tuned mass (like a passive radiator) to move air in that range. The efficiency of this port is tied to a lot of other factors, including cabinet volume.

Use eq to boost the bass and fix problems: That works ok, but only up to a point. You can't fix room nodes electronically, since those are caused by bass buildup over time, and they're different for each room. You can do some slight boost to help a steady dropoff, but you quickly run out of power (or speaker capacity) at very low frequencies.

A brief side trip about Axiom 4: High Frequency Dispersion: This dispersion problem is true of microphones as well as speakers. Even with a perfect omni measurement mic, you have a choice of flat response on-axis, but the high end will drop off as you move off axis, or you can have flat response off-axis, but the high end will increase as you move on axis.

With speakers it's the same thing; as you raise the frequency, the coil decouples from the cone and the bulk of the high end energy comes from the center of the speaker, while the sluggish cone works against the fast moving coil, further damping out the high end. The beam narrows and you lose highs as you move further off-axis.

So, what have we learned? Basically, just three things; that below a certain frequency, a speaker needs help to produce low end, and that bigger is generally better, but not without some compromises. And, we know that above a certain frequency, the high end dispersion begins to go down as the frequency goes up.

Hope this clears some things up. (I know that many people here consider me some kind of "mic guru", but my primary design experience is in loudspeakers, not mics.)
 
Harvey Gerst said:
Use a lotta little sticks: The Bose/Hartke/Marshall approach, where you use multiple smaller drivers to approximate the cone area of a larger driver.

I have an old 410 classic that I always thought had better low end, which seemed counter intuitive. I specifically held out for the 212 when I decided to buy a new one, thinking that the lows would be better than 410s (which are far more common).

I guess the board that the speakers are mounted to couple the 4 tens into a 40 and the 2 twelves are only 24. I am going to drill some holes and add four four-inch speakers and that should bring it back up to 40. thanks, Harvey.


I'm kidding.
 
I practice with a small 3-way speaker, and it sounds pretty cool... The highs are pretty even without being piercing... Too bad it's too small to have much oomph, though. Have you tried just hooking up 2 or 3 way PA speaker? It could work...
 
Harvey Gerst said:
Some of you have a pretty good grasp of some of the concepts, but I think that it's important that I review some basic laws of physics about how "real" speakers work in the "real" world.

...

Hi, Harvey. So, in light of all that, what is your take on the Weber Beam Blockers? I bought one for my Deluxe, just because 18 bucks wasn't too dear, but since there was an hour or so between listening without it and with it, a good A/B wasn't possible. I do know that I don't get as many complaints from my bandmates on the other side of my rehearsal space.

BTW, we got one of those Bose linear arrays, and it works great for rehearsals and as a live stage monitor.
 
Back
Top