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first rig purchase - check my thinking

#61
Tusec said:
Why do you think doubling the speakers would double the power? All that happens is you divide the power between the speakers. You don't get more power.

If I'm in the back yard filling a bucket of water with a hose, the job doesn't go twice as fast if I connect one of those Y connector things to the end of the hose. All that happens is half the water goes down one branch of the Y and half down the other branch. You don't miraculously get twice the water.
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you double the speakers, you get 3dB more SENSITIVITY, that's 3dB more VOLUME with SAME POWER.
side effect: your amp will push out almost twice the power... near 3dB more.
 
#62
revroy said:
that isn't accurate... To make the analogy work, it is not like adding a Y to the hose but by using a hose that has twice the diameter and then adding the Y. When you change the load on the amp, the number of ohms, you change the amount of power the amp puts out. In general, if you drop from 8 ohms to 4, you more or less double the power in addition to adding more speaker surface area to move the area.
Click to expand...
even if you have a tube amp and don't double the power at different impedances, the extra boost is very noticeable. maybe not double, but it's certainly noticeable. and that's regardless of whatever instrument you play.
 
#63
@SurferJoe: I agree with what you're saying. I would also like to reiterate that this really doesn't matter to most people and, in order to play bass or use an amp one does not require any knowledge of any of this stuff.

However, ask and ye shall receive. [Invalid or Expired Link Removed] has a pretty good explanation of the way sound is measured, though it does not delve into any of the mutual coupling properties discussed here, in fact it does not touch on sound sources at all other than to mention how loud they usually are. In order to visualise the way we hear, this page (which is actually about programming a software volume control) has some good info and a diagram under the 'What is going wrong?' section.

@Tusec: Your hose analogy is a little misleading as sound pressure is not linear in the same way water or horsepower is. The effect is actually more analogous to having two smaller hosepipes filling a bucket more than twice as fast as one of them would have by itself. Speakers couple. That is to say when two of them are doing the same thing close enough together they reinforce what the other is doing. The output is more than the sum of it's parts. What happens is they begin to act as one larger radiator rather than two smaller sources. It's pretty common knowledge that your average 15" can go a little louder than your average 8",* the same principle applies here.

For a much more technical discussion, Rane have a massive [Invalid or Expired Link Removed], look under 'coupling or mutual coupling' in the bottom quarter of the page.

The JBL Sound System Design Reference Manual also (briefly) references the phenomenon when discussing subwoofer in section 7-7. It has an amazing section on frequencies and spl and all that jazz near the beginning too, in case anyone is interested beyond the other links provided here. The main section of the book can be downloaded here.


The 3db gain is very very subtle. You can get much bigger gains (or losses) by playing harder or softer or by placing your cab on a different part of the stage. But it is there.



* = Yes, ok, this isn't STRICTLY true. Some 8"s are wayyyy louder, especially at higher frequencies. But the basic principle holds.


EDIT - New posts in the time it took me to type this!

@Revroy: You situation of doubling the hose diameter is analogous to increasing power output from the amp. Whilst this usually happens with an SS amp when adding a second cab, it is not the effect me, Jimmy and ZolkoW are talking about. Doubling power gives you an extra 3dB. Doubling speaker surface area gives you an extra 3dB. Therefore, with a tube amp (same power at different impedances) moving from a perfect 4x10" to a perfect 8x10" will give you a 3dB increase in spl. On an SS amp you would expect a 6dB gain. 3 from the doubling of speakers, 3 from the extra power the amp is producing.
 
#64
Bass Junkie said:
I know this weighs a little more, but the Acoustic B200 is the best amp for the money for someone starting out. It's reasonably priced and it sounds good. Don't let the 200 watt rating fool you, it'll get louder than the 300 watt Shuttle. Read the reviews in the link below. This weekend they are 15% off with coupon code HEROES.

Invalid Link Removed
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NONONONONO

I have the B200 combo and it STINKS. You are doing yourself a HUGE HUGE favor if you spend the extra $50 and get the stack version. On the combo, the Notch knob CANNOT be disabled and it RUINS any pros the amp might have. It just sounds bad. With the separate components, it is easier to carry, you can turn that damned notch knob off, and you can choose between 1x15 and 4x10 for speakers, or both.

Biggest mistake of my life, getting the combo because it was cheaper.
 
#65
M0ses said:
NONONONONO

I have the B200 combo and it STINKS. You are doing yourself a HUGE HUGE favor if you spend the extra $50 and get the stack version. On the combo, the Notch knob CANNOT be disabled and it RUINS any pros the amp might have. It just sounds bad. With the separate components, it is easier to carry, you can turn that damned notch knob off, and you can choose between 1x15 and 4x10 for speakers, or both.

Biggest mistake of my life, getting the combo because it was cheaper.
Click to expand...


I agree almost totally - up to the 'stinks' part.

While I had bought the B-450 with the B-600H inside of it, I decided to keep it and just get another B-600H as a separate, stand-alone unit and plug it into whatever B-series cabs I wanted to use at the moment.

I like that a lot better - but the combo unit also has it's place and I can't give an A+ for that comment.

Now - where you DO make big points is in that the Notch Switch that cannot be turned off in the combo unit - although that was a revelation to me and I though ALL B-200s had that same design and didn't think it was just the combos that had that 'feature' if you will.

So - I learned something today (thanks to you for that) and I also think that a person with the B-200 combo gets a pretty nice entry-level unit all in all. Even with that bogus Notch Switch malfunction.

Wait a minute I just had another thought::

Is the B-200 combo designed with the same single T-R-S type jack that is supposed to operate the Notch and Standby?

If so - you may not be figuring the problem correctly. When I had the wrong footswitch installed on my B-450 I could not turn off my Notch Filter either. It defaulted "ON" and even though the Standby worked OK - the Notch was on all the time uncontrollably.

I finally got the right footswitch and even had to change some of the wiring in it to make it work correctly. BTW:: Don't even bother the Acoustic people - they don't care and find you an intrusion into their day of shipping units and ignoring any problems anyway.

If you want to - I can post the mods I made to the switch that finally works correctly - it might just be a wrong designed switch you are using - if you use one at all.

This MAY be the whole Notch Filter conflict/problem in the B-series combos!

<edit:: I posted those instructions here >
 
#66
revroy said:
that isn't accurate... To make the analogy work, it is not like adding a Y to the hose but by using a hose that has twice the diameter and then adding the Y. When you change the load on the amp, the number of ohms, you change the amount of power the amp puts out. In general, if you drop from 8 ohms to 4, you more or less double the power in addition to adding more speaker surface area to move the area. All things being equal (which they wouldn't be), double the power and you get 3db more volume. To have twice the volume you need to multiply the power by 10. Again, adding more speakers changes these numbers because you're also moving more air with the additional surface area.
Click to expand...

In my analogy water represents power, not current, and each speaker's impedance is doubled to keep the load constant and the power constant (yeah, I probably should've mentioned that!).

Keeping power constant puts the focus on the acoustical effect of adding more speakers, which I think is what we're trying to get at. We all agree that halving the load impedance will double the power, all things being equal. You don't even have to get into multiple speakers to demonstrate that. You could just replace your single 8 ohm speaker with a 4 ohm speaker. It's strictly a matter of impedance and voltage and current and power -- electrical stuff.

But that's not really what we're interested in, is it? It seems to me that the question is whether for a given power two speakers will be louder than one. And I think we're talking about more than 3dB stuff here, since 3dB is fairly subtle. We're talking about the ability of one versus two cabs to fill a room. This is another reason why I think we're interested less in the electronics/power side of this, and more in the acoustical physics side. Or at least I am, but maybe I'm just out of sync here.:o

My basic observation is that for guitar amps, for a given power, adding speakers doesn't have a strong effect on volume. But it does seem to have a strong effect for bass. I think that scooping up air molecules to create a pressure wave is kind of like herding cats at low frequencies, and that you have to have more surface area to do it, which equals more speakers/cabs. My basic point is that the argument for more cabs in order to increase volume should center on the acoustical issues unique to bass frequencies, and not so much on power/impedance, since that's really the core of it.

Or at least that's how it looks to me at the moment.
 
#67
JimmyM said:
even if you have a tube amp and don't double the power at different impedances, the extra boost is very noticeable. maybe not double, but it's certainly noticeable. and that's regardless of whatever instrument you play.
Click to expand...

Right, with a tube amp you'd keep the impedance matched so the power would stay the same. So no 3dB increase. And I still disagree that there's much difference in one speaker or two with guitar.

But you touch on an interesting point with regards to bass since you don't just hear bass, you also feel it. Even though a doubling in power might not impress your ears much (only 3dB volume change), to your chest cavity that might be a substantial boost.
 
#68
Jack said:
@Tusec: Your hose analogy is a little misleading as sound pressure is not linear in the same way water or horsepower is.
Click to expand...

You mentioned a 3dB change which seemed to indicate you were talking strictly about a doubling of power. I don't think the effects of mutual coupling and surface area reduce to such a neat and tidy number. If those are the kinds of things you had in mind that would make two cabs louder than one, then you're right, my analogy doesn't even attempt to take those into account. I was just using it to address power/impedance issues.

For a much more technical discussion, Rane have a massive [Invalid or Expired Link Removed], look under 'coupling or mutual coupling' in the bottom quarter of the page.
Click to expand...

Wow, lots of good stuff at that Rane site. Haven't looked at the JBL one yet.

@Revroy: You situation of doubling the hose diameter is analogous to increasing power output from the amp. Whilst this usually happens with an SS amp when adding a second cab, it is not the effect me, Jimmy and ZolkoW are talking about.
Click to expand...

Yeah, I didn't mention it but I was thinking tube amps in the analogy, so power would be kept constant.

Doubling speaker surface area gives you an extra 3dB.
Click to expand...

Okay this is getting to the heart of what I'm interested in.

Is this a known relationship -- 3dB for a doubling of surface area when power is kept constant? I can see this if excursion is kept constant, but not power. Also, is this true across all frequencies?

Do you have a citation for this?
Click to expand...
 
#69
Yes, the 3dB increase gained by doubling speakers is a known, and often cited fact here. And, though I'm no scientist, I can personally attest to the truth of it. 300 watts through a single 4 ohm 12" spkr, vs the same 300 watts through a 4 ohm 2x12 is noticeably louder, across the whole frequency spectrum.
 
#70
Tusec said:
Okay this is getting to the heart of what I'm interested in.

Is this a known relationship -- 3dB for a doubling of surface area when power is kept constant? I can see this if excursion is kept constant, but not power. Also, is this true across all frequencies?

Do you have a citation for this?
Click to expand...

Indeed, whilst other people have mentioned the 3dB gain from the doubling of output power I have tried to avoid this other to to state that it is not what I am talking about. This is the only point that I have been making, and it backs up comments that Jimmy, Rickenboogie and Zolko have made too.

As such, the Rane pro audio reference I linked to and the JBL book (section 7-7) cover this subject, usually called 'mutual acoustic coupling' or the like.

A quick Google has also brought up this and Invalid Link Removed. On TB, you could search for 'speaker coupling' or the like, look for posts from billfitzmaurice or other speaker gurus particularly. (Who's that dude with the GK Backline head an 1x12" cabinet? He's super smart but his name eludes me). Also check out Meyer Sound, Danley Labs or JBL. They all provide detailed papers on sound reinforcement and you'll find a few on this subject sooner or later.

There is a limit of sorts with coupling, namely that the two radiators have to be within a 1/2 wavelength in order to couple. Which means that the further apart two sources are the lower the boundary of coupling moves. In short, coupling affects low frequencies more in most practical situation as to couple a really high-frequency sound the driver really have to be in the same cabinet. Which means somebody else has done all of the work you already. The more drivers you attempt to couple also introduces negative interference and if you don't align them right you can screw with the directivity too.
 
#71
RickenBoogie said:
Yes, the 3dB increase gained by doubling speakers is a known, and often cited fact here.
Click to expand...

3 dB from halving the impedance or 3dB because of more surface area? The first is well known, the second is doubtful in my opinion (doubtful that it's a simple 3 dB relationship anyway). I'm asking about the second.

And, though I'm no scientist, I can personally attest to the truth of it. 300 watts through a single 4 ohm 12" spkr, vs the same 300 watts through a 4 ohm 2x12 is noticeably louder, across the whole frequency spectrum.
Click to expand...

Doesn't add up IMO. High frequencies could pretty much care less about driver area. They'll happily radiate at banshee volume from something the size of a quarter. I don't think 2x more speaker cone is going to have an effect on them. Low frequencies maybe, but not highs. Which makes me doubt that the difference would be noticeable across the whole spectrum. And since you've specified a constant 4 ohm load, there would be no increase due to doubling power.

Theorizing aside, my experience has been that one speaker has about the same volume as two. This is guitar amps. I have less experience with bass amps, and I do think there's reason to believe that more speakers/more surface area equals more volume for bass frequencies. But guitar frequencies, not so much, I don't think.
Click to expand...
 
#72
 
#73
Jack said:
Indeed, whilst other people have mentioned the 3dB gain from the doubling of output power I have tried to avoid this other to to state that it is not what I am talking about. This is the only point that I have been making, and it backs up comments that Jimmy, Rickenboogie and Zolko have made too.

As such, the Rane pro audio reference I linked to and the JBL book (section 7-7) cover this subject, usually called 'mutual acoustic coupling' or the like.

A quick Google has also brought up this and Invalid Link Removed. On TB, you could search for 'speaker coupling' or the like, look for posts from billfitzmaurice or other speaker gurus particularly. (Who's that dude with the GK Backline head an 1x12" cabinet? He's super smart but his name eludes me). Also check out Meyer Sound, Danley Labs or JBL. They all provide detailed papers on sound reinforcement and you'll find a few on this subject sooner or later.

There is a limit of sorts with coupling, namely that the two radiators have to be within a 1/2 wavelength in order to couple. Which means that the further apart two sources are the lower the boundary of coupling moves. In short, coupling affects low frequencies more in most practical situation as to couple a really high-frequency sound the driver really have to be in the same cabinet. Which means somebody else has done all of the work you already. The more drivers you attempt to couple also introduces negative interference and if you don't align them right you can screw with the directivity too.
Click to expand...

Okay, yeah, I took a look at the links and you're right about the acoustical coupling giving a tidy 3 dB bump (and 6 and 9 and so on as you keep doubling the speakers). Of course like you say, the limitation is that it really only works at low frequencies, where the wavelengths are long enough for the driver centers to be within a quarter wavelength apart.

So that explains why more speakers = more volume for bass for a given power but not so much for guitar.

Which is what I thought was the case when I made my comment at the beginning of the thread, and now I get the reason why.
 
#75
SurferJoe46 said:
I agree almost totally - up to the 'stinks' part.

While I had bought the B-450 with the B-600H inside of it, I decided to keep it and just get another B-600H as a separate, stand-alone unit and plug it into whatever B-series cabs I wanted to use at the moment.

I like that a lot better - but the combo unit also has it's place and I can't give an A+ for that comment.

Now - where you DO make big points is in that the Notch Switch that cannot be turned off in the combo unit - although that was a revelation to me and I though ALL B-200s had that same design and didn't think it was just the combos that had that 'feature' if you will.

So - I learned something today (thanks to you for that) and I also think that a person with the B-200 combo gets a pretty nice entry-level unit all in all. Even with that bogus Notch Switch malfunction.

Wait a minute I just had another thought::

Is the B-200 combo designed with the same single T-R-S type jack that is supposed to operate the Notch and Standby?

If so - you may not be figuring the problem correctly. When I had the wrong footswitch installed on my B-450 I could not turn off my Notch Filter either. It defaulted "ON" and even though the Standby worked OK - the Notch was on all the time uncontrollably.

I finally got the right footswitch and even had to change some of the wiring in it to make it work correctly. BTW:: Don't even bother the Acoustic people - they don't care and find you an intrusion into their day of shipping units and ignoring any problems anyway.

If you want to - I can post the mods I made to the switch that finally works correctly - it might just be a wrong designed switch you are using - if you use one at all.

This MAY be the whole Notch Filter conflict/problem in the B-series combos!

<edit:: I posted those instructions here >
Click to expand...

Thanks for the advice. I like how we're having our own little conversation in someone else's thread. But here's the problem. I think you're talking about the B200H, stand-alone head. I don't have a problem with that, it's probably fairly nice. I'm talking about the B200 combo. The combo does not have any sort of footswitch capability whatsoever. There's just the knobs on the front, and a DI and speaker out in the back. No way to turn the notch knob off.

Drives me absolutely crazy. I am 100% disappointed with the tone I get from it. I can have either mids or lows, but never both.
Like I said, spend the extra $50 to get the separate B200H head, which I believe DOES have a switch / footswitch on the back.
 
#76
acoustic coupling works at all frequency

as the frequency goes up the distance between the center of transducer need to be closer to have the coupling effect

same power with double amount of transducer = +3db
double power with the same amount of transducer = +3db

often time when you double the amount of speakers, you half the impedance, which in turn allows a SS amp to generate 2x power, thus +6db






.... yeah, and the earth is flat, because we all know that we are not walking of a ball, at least I don't feel like it ... ha
 

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