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Old 12-28-2004, 04:36 PM   #41
Afroman
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Quote:
Originally posted by Bubonic Chronic
You only get a 3dB increase for a doubling of the power. That means 2X12 is only barely louder than 1X12. 2X4X12 is just a touch louder than 4X12...

That's why it's a good idea to buy good speakers in the first place.


good speakers are vital. I 100% agree with you there, that doubling the power doesent make a substantial volume difference. My only problem with that is i have always thought that decibles are on an exponential scale, like the richer scale for earthquakes. This contradicts what i noticed about more power not meaning tons more volume.
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Old 12-28-2004, 04:56 PM   #42
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Power is misleading with speakers. It's a grossly oversimplified figure, and doesn't really mean as much as people think it does. For example, if sound can actually impinge on the back of the speaker cone, you can feed them 500 watts of low frequency energy and get next to nothing in terms of dB.

Efficiency is really more of a factor than power handling. A speaker acts a lot like a light bulb; you've got coils of wire connected to a pair of charged leads. In fact, you can connect a light bulb to speaker wire and it will light up - don't try it, though. That situation gives you a lot of electromagnetic engergy, mostly in the form of heat. So as your cones heat up, that's wasted energy.

Better cones will give off less heat (coils are designed better, higher quality magnets, better wire, etc.)

Another reason wattage is misleading is that lower frequencies require more wattage. If you're putting out 3,000 Hertz, you could probably get 100 dB out of 5 watts or less. Alarms are quite loud, eh? NO power. Just high frequency speakers with a little 9V battery rigged up to 'em.

To put out 50 Hertz takes a lot of power. 40 Hertz, quite a bit more. Frequency response falls off sharply with most amps/speakers. That's why many bass amps are ~700 watts, while guitar amps are, like, 80 watts.

If you're designing something from scratch, it's good to look at something that's already been built. Pick up a broken cab and reverse engineer it. What looks like quality design? What looks like shit? A lot of that cab design goes into the efficiency, which is the main factor that will affect loudness. Good speakers will handle just about any amplifier.
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Old 12-28-2004, 05:34 PM   #43
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Dbs

As Bubonic says it takes power (watts) to produce high levels of sound at low frequencies.
Any body can build a 5000 watt speaker but if its only 90db at 1watt 1 metre its useless
That is why you should study the parametres of the speaker before you buy. Good manufacturers provide a graph of the individual speaker's performance these days.

Good speakers have venting for the voice coil to help with cooling and therefore reducing thermal compression, twenty plus years ago as the night whent at a gig you would have to keep turning the volume up on the PA. The following night at the next gig it would feedback if left at the same levels, this is the result of 'thermal compression' the hotter it gets the impedance curve rises.
As I said in an earlier answer wattage wise you have to times by ten to double the Dbs (accoustic power), Dbs are on a logarithmic scale not linear.

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Old 12-30-2004, 06:08 PM   #44
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Speaking of loudness, is there any scientific explanation as to why tubes make amps sound louder than the are?
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Old 12-30-2004, 06:34 PM   #45
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Originally posted by Afroman
Speaking of loudness, is there any scientific explanation as to why tubes make amps sound louder than the are?
Yes.

When you amplify something with a tube, you get a type of harmonic distortion that is pleasant to the ear. It's like adding a choir of voices to a vocal track (kind of), only the choir is singing octaves of the original.

So your tube amps sound louder for two reasons:

A) The harmonic distortion gives you more energy in the 2,500 Hz range, which is the frequency range to which we are most sensitive - it's also a range that doesn't require much power to amplify.

B) The effect of the "octave choir" thing (even harmonic distortion, I believe, but it's been a few years) is to make the sound louder psychoacoustically.

You see, the word "loudness" implies psychoacoustics, which is our perception of the sound, instead of acoustics, which is the actual physics of sound. If you say, "that's loud!", that doesn't necessarily mean it's a powerful signal - like your fire alarm. That's got very little power, but the sonofagun is loud, eh?

It is high dB, though.

But loudness is slightly different than dB. You can have 120 dB of 30 Hz and it will sound like 80 dB. (Just a rough guess, but not far from the truth.) We are less and less sensitive the lower you go. So the loudness is equivalent to, say 80 dB of 1000 Hz, hypothetically.

Kind of like wind chill or heat index vs. temperature.

When it's 80 and humid, if feels like 95, you know?

Or if it's 45 and windy, it'll feel like it's 29?

That's the idea.

So a tube amp is like heat index. You turn it up to 100 dB, it sounds like 105 because of those harmonics.

Good question.
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Old 01-06-2005, 10:19 PM   #46
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Awesomely well explained. I am frightened by the fact that i understood that. My hat is off to you, Bubonic Chronic.
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Old 01-06-2005, 11:23 PM   #47
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You certainly know your stuff Bubonic

Valve amps are great but for bass they are also very heavy, the last valve amp that I used was an Orange 120 watt after that it was solid state for me.
as I said they sound great on bass but my days of lugging a valve amp around are long gone.

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Old 01-07-2005, 10:40 AM   #48
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^^ Props to you, too, on your knowledge of porting.

I studied room acoustics heavily, but only touched upon transducer design. What I know I have pieced together from theory and practice, it's good to have someone like you around with some real world experience.
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Old 01-07-2005, 05:02 PM   #49
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Hi Bubonic
Just thought that you and other Bassists would like to know about the light at the end of the tunnel regarding lighter speaker magnets.
I'm due to take delivery of a 15" Neodymium magnet speaker, Ive already got a 600 watt 18" with a Neodymium magnet which is smaller and lighter than the magnet on my 10"s..
Iv'e also been testing some lightweight panel speakers they are about 30"x 30" with what are called exciters on the back of the panel, the same sound comes out of the rear as comes out of the front, no tweeters but plenty of highs, they don't like too much bottom end so you need a sub bass unit, I've gigged with them on foldback.


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Old 01-08-2005, 08:02 AM   #50
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hye man, just the other day i had a ****load of quesrtions about building a cab. and you just answered al my questions. great work
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Old 01-10-2005, 10:42 AM   #51
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^^ Thx.

Speaker/cabinet design is probably the most important element to consider in your tone simply because this is the weakest part of the chain. Traditional speakers pale in comparison with amps, mics, effects, pretty much everything. Add the acoustics of the room in there, and you can get some unbelievably bad sound.

I just saw a show at a warehouse, and what a pile of crap! It's not even worth playing amplified music in there.

I'm currently thinking about frequency-specific phase cancelling speaker systems - manipulating room acoustics by adding energy from speakers. You could do something like that very cheap: a parametric EQ, delay box and an amp/speaker placed at the right location, simply wired backwards. Work with that EQ and the delay time, you could "tune" the room with unbelievable flexibility.

...ah, the thoughts of a lowly acoustician attending a very unpleasant concert.
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Old 01-13-2005, 10:27 PM   #52
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is it normal for a closed back bass cab to have cotton batting inside? Also, what are good ways of getting rid of tweeter his ( even if you have an L-pad)?
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Old 01-14-2005, 06:29 PM   #53
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is it normal for a closed back bass cab to have cotton batting inside? Also, what are good ways of getting rid of tweeter his ( even if you have an L-pad)?

Most manufacturers put some form of accoustic wadding inside bass & PA cabs. On bass it cuts down unwanted resonance, if you go too near a PA cab with a mike and the cab has no wadding inside you will notice bass boom /feedback.
If you fill a bass cab (without blocking the tuning ports) with accoustic wadding you theoretically increase the internal volume of the cab therefore lowering the resonant point, the only drawback is that you lose some effeciency.
Boosting high frequencies excessively can cause tweeter hiss having the master set too high can also make your rig noisy.
Just fine tune your settings, even the top range amps are noisy if used improperly.

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Old 01-16-2005, 08:37 AM   #54
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Hi Bubonic,

I loved reading your thread, there is some great information in here! I was just wondering if you could answer one question. I have a VOX AD30VT of the valvetronix series. I'm very happy with it, though the only thing I miss is the real bite, and the aggression. It all sounds a little bit to smooth, if you know what I mean. So I was wondering if I could change the speaker in my amp, but I decided I didn't want to fool around with my amp, since it's fairly new, and I didn't want to screw anything up.

So then I decided it might be cool to make my own cab, for under the combo. My amp doesn't have socket to connect with a cab, but it does have a line-out. So I thought I would connect the cab that I'm going to build, with my combo, by connecting the line-out of my combo and the line in of the cab, with an audiocable. Would this be possible?

I understand that the combo wouldnt't have enough power for the speaker in the combo itself AND the speaker(s) in my cab, so I thought that if I wanted a very smooth sound, I would unfasten the cable from the back of my combo, enabling the speaker in my combo to work. And when I would want a more aggresive tone, I would fasten the audiocable back, thus enabling only the speaker(s) in my cab to work. This way they wouldn't ever work simultaneously, os I wouldn't need a different amplifier.



Here is a picture I made to illustrate my idea. I would love to get some feedback on the plan, and to hear any critical points that I have missed in my idea.

Thanks,

Peter
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Old 01-16-2005, 06:08 PM   #55
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I dont think I saw this mentioned.. but if I did, im sorry. What about buying an unloaded cab off ebay? I see all sorts of unloaded marshall cabs there. Wouldn't it just be simpler to buy one unloaded, then put speakers in it?

Maybe its simpler for me, because I dont like to have to measure things, then I get confused and the thing comes out in the wrong shape.
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Old 01-17-2005, 07:30 PM   #56
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About the VOX, you will have to hook up a speaker output.

The important thing is to get the same wattage, but most importantly the same ohms speaker as the one in there.

To hook up a speaker out, you're correct, you need to disconnect the existing speaker. Understand, though, that any alteration to your current cab is a deviation from its original design and the original sound - and VOX is very sought after - will not be available anymore.

What I would recommend is to install a speaker out after disconnecting the current speaker. Then, install a standard 1/4" connector to the speaker so you can plug it back in if you want and have option of using the original cabinet very close to its original design. Unplug that speaker, plug the new one in, etc.

Don't worry about porting or anything on the guitar cab. There are some ways to work with resonance to boost the low end, etc., but they are very tricky, and I doubt you'll need them. Just buy a nice 12". 12"s are good all-around speakers for attack.

The main thing about this job, though, is that you will probably never get the kind of attack you want out of a VOX amp because they just are not designed to give you that kind of sound. Can you improve the sound for attack by using different speakers? Definitely. Will it sound like a Marshall, or better yet, a Mesa/Boogie? No.

The nice thing is, though, you can always just pick up a head later, Marshall, Peavey 5150, Mesa, Laney, whatever you want and hook it up to your speaker. I give you my blessing in doing this, but warn you in advance that modifying the speakers will only get you so far. The amp itself has the biggest influence on the attack.
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Old 01-18-2005, 11:13 PM   #57
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hey, great article its sparked my imagination for building a cab. I was just wondering, since i love Cerwin Vega's speakers so much, why aren't Cerwin Vega's used in cabinets. I would like to try and would love input on how good they woud sound. thanks
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Old 01-19-2005, 11:04 AM   #58
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hey, great article its sparked my imagination for building a cab. I was just wondering, since i love Cerwin Vega's speakers so much, why aren't Cerwin Vega's used in cabinets. I would like to try and would love input on how good they woud sound. thanks
They are not designed for instrument use.

They are designed (if I'm not mistaken) to be used for music that is already produced, meaning there are no sudden impulses of high decibel sound coming through.

It's kind of like the difference between a pickup truck and a sports car. A Cerwin Vega is kind of like a sports car, but if you need to haul 1,500 lbs of junk, you're pretty much screwed. The pickup truck is not as fast or comfy, but when you need to move your shit, you're glad you have it.

Know what I mean?

Two different kinds of speakers for different kinds of tasks.

Instruments put out a lot of juice, and it's really hard on speakers. That's why you need something that's specifically designed to be rugged, that can handle funk bass, or heavy metal chunk. You would probably tear your CV's to pieces in an instrument cab.
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Old 01-19-2005, 06:18 PM   #59
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hey thanks alot for the Cerwin Vega explanation you saved me like 400$$ but ive got another 2 questions concerning speakers. Why do so many speakers (guitar) cut off the frequency at about 5khz when our hearing goes up to almost 20khz for some people? As well, what does it mean when a speaker has 100db sensitivity? thanks in advance, and keep up the great work=D
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Old 01-19-2005, 10:21 PM   #60
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hey thanks alot for the Cerwin Vega explanation you saved me like 400$$ but ive got another 2 questions concerning speakers. Why do so many speakers (guitar) cut off the frequency at about 5khz when our hearing goes up to almost 20khz for some people? As well, what does it mean when a speaker has 100db sensitivity? thanks in advance, and keep up the great work=D

There are speakers around that go up to 20khz, these are co-axial speakers that take an added HF unit as well as the basic speaker, also available are 'Dual Concentric' or twin cone speakers, these speakers have a tapered cone fitted where the dust cover goes in the centre of the speaker cone, they can extend response up 14/15khz.
The above mentioned speakers are very rarely used on instrument amplification they are normaly used for public address (PA). The twin cone speakers aren't much more expensive than standard speakers
The 100db sensitivity figure is very often a waste of time as it usualy is '100db @ 1 watt @ 1khz @ 1metre, the point that I am making is that 1khz has little meaning for guitars bass or vocals.
Many manufacturers now give a performance graph printout which is much more relevant to requirements. Bubonic actualy wrote earlier in this thread about higher frequncies, look it up and you will see what I mean.
As an after thought why don't you start experimenting with add on HF units yourself, I was using horns in my bass cabs way back in the 70s, you can experiment by altering the value of the capacitors and getting attenuation by using high power handling resistors.

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Last edited by John Swift : 01-19-2005 at 10:24 PM.
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