Real science, psychoacoustics, and the 2 Ohm load

**Chris Fitzgerald** · #1 10-03-2008, 09:33 PM

I've noticed something funny when running my Focus at 2 ohms with 2 Wizzy 10's. The sound is very different, much more bassy and tending toward boominess in live acoustic spaces. It also sounds much "hotter" than running a single speaker at 4 ohms. I'm trying to figure out how much of what I'm hearing is some physical principle at play, and how much is psychoacoustics.

Some random observations:

- The 2 ohm thing actually sounds wonderful for slab on those rare occasions when I play it. It kind of fattens up the sound and gives it a very charged presence that i like a lot. For DB, it's not so much that it's a bad sound as it is that it's a fundamentally *different* sound; Edgy, agressive, and more sonically opaque, if that makes any sense.

- I can't tell how much of the extra bass response is due to coupling with the floor. I'd try stacking the cabs on a chair, but they're tall enough that it would seem unstable somehow.

- Last, of course, is the fact that when you need to take 2 cabinets, you're probably just gonna be too damn loud for transparent sound (although the same rig sounds pretty good in deader rooms).

So, is there really any sonic difference between 4 and 2 ohms, or am I just imagining things? What's the science behind the sound?

T-Bal · #2 10-03-2008, 10:05 PM

Chris - I've never run two Wizzies, so I can't answer your specific question. However, I've noticed that with one Wizzy when the volume gets up there, it's kind of boomy, especially in live rooms. Dry rooms or outdoors, it's not an issue. Maybe you could try to achieve the same volume with one Wizzy that you get with two and see if the same situation occurs - anyway it seems like this would be a volume issue as opposed to how the Focus behaves with a 4 vs. 2 ohm load. Then again, what do I know?

T-Bal · #3 10-03-2008, 10:08 PM

Also, I think the Wizzy is inherently "thick" sounding, which may not be ideal in rooms with hard surfaces. YMMV!

bongomania · #4 10-03-2008, 10:13 PM

I won't pretend to know all the facts, but it seems reasonable to expect that two Wizzys will sound different than one, due to acoustic coupling and the use of more speaker surface area to transmit the same "information", as well if you stack them vertically then there is a pronounced effect in placing a cab nearer your head.

Also, any amp will have to work harder at 2 ohms than it does at 4, even when 2 ohms is given as a safe rating to use. Some amps may sound a bit different when they are working harder. Of course that will vary depending on how the amp was built, what the basic technology is, how the power is drawn and utilized, filtering, etc.

kb9wyz · #5 10-03-2008, 10:33 PM

I have a buddy who does a lot of car stero stuff and he insists that it makes a difference. He told me that the lower the impedance, the boomier it gets; the higher the impedance, the tighter & more accurate. I changed the way my sub was set up to go from 2 Ohms to 8 Ohms (parallel to series) and it did make a very noticable difference, just like he said it would. So I think that you're not just imagining the difference in the sound.

Beast

D McCartney · #6 10-03-2008, 10:42 PM

What Bongo said makes sense. Is one speaker sitting on top of the other?

robgrow · #7 10-03-2008, 10:45 PM

Using two identical cabinets increases sensitivity by 3 dB (or 2X). The two cabinets also couple, substantially increasing low frequency output. The 2 ohm load impedance increases the potential amount of power the amp can deliver. It all adds up.

There's nothing inherently magical about a 2 ohm load however.

mstclairmiller · #8 10-04-2008, 08:33 AM

I would have thought that shifting more air will increase the bottom end response - you have effectively got a cab twice as big as the tiny 10" cab that, on its own, will probably never sound boomy in any situation as it simply cannot shift enough low frequencies to boom.

Try using the high pass filter on the focus with the two cabs and see if you can get back to the sound of the single cab, only louder, but without the boom.

flatback · #9 10-04-2008, 09:15 AM

yea hey chris
i have that problem with 2 wizzies 10 and the FC especially if they are stacked against a wall. Split up with one as a wedge it is much less pronounced and with the Aptlex there isn't a problem. 2 wizzies 10 are a lot of sound. I have been using just one or most gigs, but 2 can sound so good if carfully placed. Thanks for bringing this up and let us know i you find a real solution.

**Francois Blais** · #10 10-04-2008, 09:47 AM

Quote:

Originally Posted by kb9wyz

I have a buddy who does a lot of car stero stuff and he insists that it makes a difference. He told me that the lower the impedance, the boomier it gets; the higher the impedance, the tighter & more accurate. I changed the way my sub was set up to go from 2 Ohms to 8 Ohms (parallel to series) and it did make a very noticable difference, just like he said it would. So I think that you're not just imagining the difference in the sound.

Beast

Series wiring?
Well, I just want to bring some science in.
A loudspeaker is not linear like a pure resistor.
The ohmage rating is an impedance rating in fact.
The impedance has two factors: resistance and reactance.
They are at 90º of each other, mathematically speaking.
The reactance can be of two kinds: inductive or capacitive.
They are at 180º of each other.
The impedance is the vectorial sum of the resistance and the reactance.

The resistance is fixed, and constant versus the frequency of the audio signal, but the reactance (inductance, in the case of a loudspeaker) varies with the frequency.
Furthermore, the loudspeaker is in a bafle, and this whole system has its influence (resonance frequency, and Q factor) on the impedance.

The impedance is therefore non-linear in the audio signal range.
At some frequencies, the impedance can be several times the rated impedance, or even go lower.

If you wire speakers in series, the resulting impedance can be pretty wild, and the power distribution between them too.

I don't recommend this, but if it works for you!

Best regards,
François

**Chris Fitzgerald** · #11 10-04-2008, 09:48 AM

I do use the HP filter, but there's still something else going on. I have been stacking them but will experiment with different configurations. One real obvious difference in the situations is that with one, I almost always get it off the floor. With two, they're so tall I don't bother, which adds a coupling issue.

Bassamatic · #12 10-04-2008, 10:31 AM

In addition to the great comments above - when you stack speakers vertically, there is a change is the dispersion pattern. You can see this in column speakers where this is taken to an extreme. The vertical column spreads the sound wider with less to the top and bottom. With only 2 speakers this is minimal, but it is still there. Because of the spacing, this is liable to be in the upper bass or lower midrange and could be easily audible.

drurb · #13 10-04-2008, 12:21 PM

Quote:

Originally Posted by Chris Fitzgerald

I've noticed something funny when running my Focus at 2 ohms with 2 Wizzy 10's. The sound is very different, much more bassy and tending toward boominess in live acoustic spaces. It also sounds much "hotter" than running a single speaker at 4 ohms. I'm trying to figure out how much of what I'm hearing is some physical principle at play, and how much is psychoacoustics.

Physical principles and psychoacoustics are not orthoginal in the sense that one is physics and one is "perception." Psychoacoustics is a branch of psychophysics that seeks to understand the relation between perception and the physical stimuli. In this case, when you hear (perceive) a difference, it is BECAUSE you have changed the physics. The mapping between the two is the domain of psychoacoustics.

In the case you cite, I would venture a very educated guess and say that it has little, if anything, to do with loading the Focus with two or four ohms, per se, and everything (or almost everything) to do with the change in the radiation pattern, interaction, and coupling difference between two and one cabinet.

drurb · #14 10-04-2008, 12:25 PM

Quote:

Originally Posted by kb9wyz

I have a buddy who does a lot of car stero stuff and he insists that it makes a difference. He told me that the lower the impedance, the boomier it gets; the higher the impedance, the tighter & more accurate.

Hmm. I can imaging ways in which this would be the case for poorly designed circuits. The lower the impedance of the load, the smaller the damping factor. This is usually not an issue because the internal impedance of most solid-stae amps are a fraction of an ohm so that changing from 4 to 2 ohms still usually leaves the damping factor (calculated as the ratio of load to internal impedance) very high.

drurb · #15 10-04-2008, 12:28 PM

Quote:

Originally Posted by robgrow

Using two identical cabinets increases sensitivity by 3 dB (or 2X).

True enough, especially in the technical sense that for a given voltage at the cabinets, twice the power will be delivered (as long as the amp can handle the current). This effect, however, is only one of level.

Quote:

Originally Posted by robgrow

The two cabinets also couple, substantially increasing low frequency output. The 2 ohm load impedance increases the potential amount of power the amp can deliver. It all adds up.

Now, we're talkin'! Yup, the changes in "boominess" etc. are, I suspect, almost entirely the result of the coupling/radiating effects.

Quote:

Originally Posted by robgrow

There's nothing inherently magical about a 2 ohm load however.

Absolutely true!

Thangfish · #16 10-04-2008, 12:45 PM

Quote:

Originally Posted by Chris Fitzgerald

[snip]
One real obvious difference in the situations is that with one, I almost always get it off the floor. With two, they're so tall I don't bother, [snip]

I suspect that this is the exact issue here.

jsbarber · #17 10-04-2008, 01:03 PM

Chris:

You might try a simple experiment. First play with both speakers in the room. Then, keeping both speakers connected to the amp, move one out of the room; preferably down the hall and in another room with both dorrs closed, while keeping the other in the room you're playing in. This is to keep the load on the amp the same, but trying to remove the acoustic contribution of the second speaker. You may want to do this both with and without adjusting the volume to achieve the same loudness.

Just a thought...

Jim

Another approach, in principle, woud be to find a 4 ohm load to connect to the amp in parallel with one speaker; and then compare the sound with and without this dummy load. However, as Francois mentioned above - Impedance is a complex thing, literally, and is also frequency dependent. So finding a dummy load that is similar to your Wizzy is not so simple. (Plus, a 4 ohm, 200w resistor is not likely to be available at Radio Shack.)

Ric Vice · #18 10-05-2008, 09:45 AM

Chris,
About two years ago I was considering changing the two 8" speakers in my VL 208 to 8 Ohm's . John Dong of EA said that they could do that but the cabinet would sound significantly "darker" at 4 ohms than it did ad 8 so I abandoned the idea.

I also tried using two VL 108's, and when you couple them they are indeed very loud and it increases the bass response to a point where it's far more difficult to control feedback. I actually prefer using a single larger cabinet to using smaller cabs if I need more volume. It seems to work better, at least for me. That sort of throws portability out the window though.

Ric

**Chris Fitzgerald** · #19 10-05-2008, 09:54 AM

No matter what the real answer to the question is scientifically, I obviously need to spend some time with the 2 cab setup and come up with a default baseline of settings for it, as well as experimenting with different cab placement. Basically, I need to think of it as essentially a different rig altogether, and go into it with different expectations. Part of the problem, I'm pretty sure, is that I use the 2 cab setup so infrequently that I'm always a little off balance when faced with the differences in sound. I'm pretty sure that if I worked with it more, the proper way to handle these issues would emerge.

Everything is a learning curve, nicht war?

**Adrian Cho** · #20 10-05-2008, 12:37 PM

Coupling issues aside, it seems to me that the things you mention - the aggressiveness, edginess, sonic opacity and the bassiness are all basic characteristics of that cab. Those are all the things I dislike about the cab although there are times when those characteristics can be useful. I would fully expect that two of them would be "more of the same." That little cab is a marvel for what it delivers given its size and weight but it is definitely not the most sonically transparent cab. Also, as you point out, when you have more amplified sound, the ratio of acoustic sound is consequently lower so the overall effect will be less transparent.