A misgiving which could prove, in slightly different circumstances than yours, to be a costly and heavy mistake.
Indeed. A few dB difference in sensitivity can really wash out the increase. Growler, you really do "get" this and the headroom stuff.
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Double Bass Mixing speakers
- Thread starter klem.gote
- Start date
Indeed. A few dB difference in sensitivity can really wash out the increase. Growler, you really do "get" this and the headroom stuff.
- Feb 12, 2006
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Indeed. A few dB difference in sensitivity can really wash out the increase. Growler, you really do "get" this and the headroom stuff.
A few dB of sensitivity difference can reduce the appearant increase but it's still there (the basic formula would be (SPL1+SPL2/2), but you guys are also overlooking the effects of net increase of power, driver coupling as well as active baffle area increase which result in improved LF extension as well as total SPL.
This is not as simple as you guys are making it out to be. Even with a 2dB difference in gross sensitivity, the difference of adding the second cabinet will be clearly and plainly audible, and beneficial.
It is not an apparent increase. I'm discussing physical acoustics. I don't know from where you got that formula. If you are discussing power units, then powers add linearly when they are orthoginal. Because independent powers are additive, a pair of powers, P1 and P2 (in watts), simply add. Because you wrote "SPL," I assume you're talking about pressures. A pair of orthoginal pressures add as the square-root of the sums of their squares. Now, if we're dealing in decibels, the rules are different.
Returning to your formula, suppose SPL1 and SPL2 are both 10 units of pressure. Assuming you meant the division to apply to the sum, (10+10)/2 = 10. Essentially, you wind up with the average and have no change! If you meant the division to apply to a single one of the pressure untis, then you have 10 +10/2 = 15. That's not how pressures add. If they were orthoginal, the square-root of the sum of their squares would be 200^0.5 = 14.1. If the two pressures were not identical, then it would be arbitrary which values should be divided by 2.
In terms of decibels, let's take a look at the example I gave here. My example was two speaker cabs that differed in sensitivity by 10 dB. So, for a given input, one power is 1/10 the other. So, if we refer to the acoustic power output of one cab as 1.0 and the other as 0.1, then the increase acoustic output, relative to the cab with the greater sensitivity when they are added is 10*log(10)(1.1/1.0) = 0.413 dB. Let's assume the cab with the lower sensitivity is 3-dB less sensitive. Then, it's power will be half that of the cab with the greater sensitivity. The increase in that case will be: 10*log(10)(1.5/1.0) =1.76 dB.
It seems useful to keep in mind that human listeners require an increase of 10 dB or so in order to judge a sound as twice as loud.
Let's take your assertions one at a time. I always took into account the effect of net increase in power and SPL, as I did in my earlier comprehensive post. I have no idea what you mean by "driver coupling" in this context. I certainly do understand driver coupling in the engineering sense but don't see how it applies here. "Active baffle area?" I assume you mean baffle area which, in and of itself, when considering the other factors involved would have no substantial effect. Now, what could very well have an effect is the fact that using two drivers allows each to be fed half the power (if orthoginal) or 1/4 the power (if in-phase) in order to produce the same output. That might, in fact, extend the power-handling and low-frequency capability of the system as a whole. That, however, would not be likely to be achieved effectively at all with two different cabinets. It's best achieved by a cabinet design that incorporates two drivers.
As I see it, it's actually the reverse. I'm not suggesting that it's simple at all! Look right here.
Ah, so you want a 2-dB difference in sensitivity. Here goes:
10*log(10)(1.63/1.0)=2.13 dB
This assumes that you're using two cabs that have sensitivities within 2 dB of each other which would be pretty good and which would minimize the "different sensitivity" factor that I identified here and in my earlier post. That leaves you with the other problems. Would the difference be clearly and plainly audible as you say? Yes it would. Would it beneficial? It might be. It could make things worse. Even assuming it's beneficial, however, it may be an expensive and inconvenient way to achieve the benefit compared to more optimal approaches that could be employed by taking into account physical acoustics and electrical considerations.
Growler, you really do "get" this and the headroom stuff.
I wouldn't go anywhere near as far as to say that.
I do very much appreciate the thought and effort that goes into providing this kind of information. Now I just have to go back and try to digest this latest offering. See you in about a month
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Reading this thread and the linked thread, there is a discussion of phasing. I thought speakers were either in phase or out of phase (ie zero degrees or 180 degrees phase shift) and it just depended on which way you wired them up, but it seems it's not the simple. How do speakers get say a 90 degree phase shift?
Or have I totally misunderstood something?
Or have I totally misunderstood something?
The phase response (phase as a function of frequency) of a loudspeaker, electronic device, etc. derives from the details of the so-called reactive components of the impedance. Oh geez, that didn't help you, did it?
Okay, think of an electrical circuit or even the physical acoustic properties of a speaker in a cabinet as being made up of a combination of resistors, capacitors and inductors. Pure capacitors and inductors actually shift phase by 90 degrees. To simplify a rather complex topic, think of the influence of the various capacitors and inductors as varying as a function of frequency such that their combined effects, along with the resistors, can yield different total amounts of phase-shift at different frequencies. At one frequency, the phase may shift from some reference by, say, 35 degrees; at another the shift might be 63 degrees.
When people talk about waveforms being "out-of-phase," they typically mean that the polarity is inverted which is equivalent to shifting all of the component frequencies by 180 degrees. It's a special case of what can be a continuously variable function of phase shift.
Check this out.
The phase response (phase as a function of frequency) of a loudspeaker, electronic device, etc. derives from the details of the so-called reactive components of the impedance. Oh geez, that didn't help you, did it?
Okay, think of an electrical circuit or even the physical acoustic properties of a speaker in a cabinet as being made up of a combination of resistors, capacitors and inductors. Pure capacitors and inductors actually shift phase by 90 degrees. To simplify a rather complex topic, think of the influence of the various capacitors and inductors as varying as a function of frequency such that their combined effects, along with the resistors, can yield different total amounts of phase-shift at different frequencies. At one frequency, the phase may shift from some reference by, say, 35 degrees; at another the shift might be 63 degrees.
When people talk about waveforms being "out-of-phase," they typically mean that the polarity is inverted which is equivalent to shifting all of the component frequencies by 180 degrees. It's a special case of what can be a continuously variable function of phase shift.
Check this out.
OK, that makes some sense
The logic being that these phase shifts at different frequencies are a product of the specific speaker design and box design, and therefore two of the same box will have the same quirks and not cancel each other out, yes?
If I take two different speakers with the same Thiele-Small parameters, the speakers themselves won't have this issue, right? Can I engineer enclosures for them that will also not have these issues?
OK, that makes some sense
The logic being that these phase shifts at different frequencies are a product of the specific speaker design and box design, and therefore two of the same box will have the same quirks and not cancel each other out, yes?
Essentially, yes.
Actually, the raw driver, being a reactive load (there is a coil in there), will be subject to these issues.
I'm not sure what you mean. All speaker/cab combinations can be thought of as "filters" that have particular phase responses. You really couldn't build a practical speaker/cab in the real world that had a flat phase response. Actually, there would really be no good reason to do that.
i know all the theory and stuff says you shouldn't but when all is mixed together and the whole bands is rocking not sure more than 2% of the crowd would hear any difference. Solo i would agree, but in real life gigs there is a lot more stuff to effect the sound...IMHO. that being said i try and use same brands and sizes but more because that is what the majority says.
JAE used different heads and speaker sizes and we all love his sound, ditto with Victor and his 15 and 4 10 setup..
JAE used different heads and speaker sizes and we all love his sound, ditto with Victor and his 15 and 4 10 setup..
As I've mentioned before, stacking different cabs is a different situation than using them at different locations to gain broader coverage. It's not just "theory." Constructive and destructive interference are very real. As I said in post #18:
So the phasing issue is electrical in nature and not sonic? As an electrical designer I can understand that better.
I'm considering adding a 15" ampeg cab (PF115) to my 2x10" ampeg cab (PF210), both are the same made/model with this difference only. I think that given the simliar speaker area neither should drown the other out and, given same cabinet otherwise, they have the best chance possible not to have phasing issues. I can see its more complicated than that but I am trying to keep things intuitive where possible.
I've heard good things about the combination. My objective is a "more full" sound with a bit more high and low than each speaker size would get independently.
I'm still waffling a bit because of my concern is that my sound quality will actually go down (since my goal is opposite), but I think I've mitigated this chance as much as possible.
edit: should add I'm planning to put the 15" on the bottom of stack, 210 on top. 15" wont be heard as well therefore, partly I want it for the "thump", but hoping my clarity doesnt suffer.
I'm considering adding a 15" ampeg cab (PF115) to my 2x10" ampeg cab (PF210), both are the same made/model with this difference only. I think that given the simliar speaker area neither should drown the other out and, given same cabinet otherwise, they have the best chance possible not to have phasing issues. I can see its more complicated than that but I am trying to keep things intuitive where possible.
I've heard good things about the combination. My objective is a "more full" sound with a bit more high and low than each speaker size would get independently.
I'm still waffling a bit because of my concern is that my sound quality will actually go down (since my goal is opposite), but I think I've mitigated this chance as much as possible.
edit: should add I'm planning to put the 15" on the bottom of stack, 210 on top. 15" wont be heard as well therefore, partly I want it for the "thump", but hoping my clarity doesnt suffer.
stevemac said:
I'm not an expert in this but I am following it for similar reasons to you.
Phasing issues are definitely more than electronic. One simple example . If your cabs are ported the ports are out of phase. In my case my 15 relies on the port to get below 50 hz so if I combine it with a 210 that goes below 50 hz I should expect to lose frequencies below 50hz due to phase cancellations.
I'm not sure if you can figure this stuff by intuition. Just gotta look for discussions of it and learn.
Probably in most cases, adding almost any second cabinet will sound better than either cabinet alone -- as drurb has noted earlier, the gains can be infinitesimal, but are often there, especially if you're standing in the right spot! I imagine this is why many players assert that they love their particular combination of furniture, and more power to them for that.
However, unless you are very lucky with your combination, it will sound better still with a pair of the same cabinet (that is, identical, not just any two 115s or 210s or whatever). If you can try the mismatched pair and the matched pair(s) side-by-side, including in various off-axis positions, you can make an informed decision between them. If this is not possible, then your chances of achieving the best possible result are far better with the matched set.
Sure but it was just an example that was clearly not electric. Like I said, I don't fully get this stuff, but the text book answer is two identical cabs will sound best.
Indeed! Relative phase shifts result both from the electrical and acoustical/mechanical properties.
For an excessively geeky discussion of exactly how the electrical / mechanical properties work, check out my little web page. One interesting observation is that two cabs with similar frequency response graphs will also have similar phase response, at lower frequencies.
M'Kay, now my brain (and my eyes) really hurts. But it does appear to explain in principle how some cabs, mismatched to the eye, are well-matched sonically (I'm thinking of the various fEARful iterations here). Good resource, and thanks for making it public
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