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Luigi

Tobacco Road,
North Carolina
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Reply with this quote Reply to this PostPosted:  Apr 6, 2007 12:11 AM
I figured I would start this topic and maybe pin it if it doesn't get trashed with 'get a so an so' crap - or noobs that think because they use a V30/Greenback - its the final word. Maybe this can be educational...

A couple of things about cabs - they are responsible for 35% to 45% of your sound, not many people realize this... take a crap cab and hook it to a decent amp, guess what? It will sound less than desirable - take a decent amp and hook it to a great cab and all of a sudden, it sounds like you just upgraded your amp.

A few things I'd like to touch on here, for discussion purposes:

+ Power matching - under/over powering a speaker cabs (watts)
+ Speaker sensitivity - what is is what does it do? (there is a standard measure for this)
+ Cabinet construction - joint types and materials
+ Speaker vendors - who makes them?
+ Cab makers - brand names, factory direct
+ Cabinet designs - porting, open closed back, and resonance
+ Impedance matching
+ Magnet sizes/types and frequency response.

For starters... I'll discuss one of the most copied cabinet designs ever - the 1962 Marhshall Bluesbreaker cabinet. Did you know that Bogner, Hartke, Germino and Avatar all copy that cabinets construction techniques? The reasons are many - durability and that big ass fat sound that so many people want. Curiously tho... (these cabs are exactly identical), there is a huge price differential from some of the makers though, using a the Bluesbreaker 2x12 'copy' with Vintage 30s as the example...

Avatar: $358.00 (factory direct)

Germino: $800.00 (msrp)


Bogner: $825.00 (msrp)


What makes these cabs so good? Dove/Dado joints, the finest quality glues and heavy 18mm 13 ply Baltic Birch wood used - no nails, joints are secured with both glue and screws.

Trivia tip... the Bluesbreaker Cab/Combo (JTM) - is what put Marshall on the map - the other most copied cabs are the Fender pre-CBS and Blackface designs.

Ever wonder why that Bogner sounds so good... in large part, its the speaker cabinet - the most overlooked part of buying an amp/combo - is the the speakers/cab you put it through... thats the first lesson here.

Armed with even that tidbit of information - should start telling you why some amp/cab rigs are some much more expensive than other - and those great 'cheap amp' deals? (Carvin, Line 6, Vox, Peavey, etc...) - The amps may be ok, but the cabs is where most of the skimping is done, to save the resell price - first order of anyone looking to improve their sound by leaps and bounds - check your cab, if its crap, this is the place to start looking into. Not your PUs, not your amp... start at the end of the signal chain and work your way back - thats how you build a 'tone machine' - this is also the downside to buying a cheap combo amp, although you can always throw another 2x12 bottom under the existing cab and don't bother using the original combo speaker cab, hey its a workaround.

I'll cover some more of the items listed, or anyone can... in future responses on this thread.
Eric Sopanen


PARK CITY,
Utah
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Reply with this quote Post a reply to this TopicPosted: Apr 6, 2007 12:52 AM
Cabinet construction is critical to tone. There are arguments that the cabinet should be inert, and not flex at all, which I believe is the principle behind some of the higher end open back 2x12 designs. Then there are those who like a solid pine baffle board (the board that the speakers are attached to) that is only bolted in at the 4 corners so it will flex and affect the low end. That is called a floating baffle, and that is how vintage tweed era Fenders were made, like the '59 Bassman 4x10. In a 4x12 generally you want some flex, but that doesn't mean you make it out of cheap thin plywood. The flex has to be by design, controlled and tuned. The best sounding 4x12's will also use a "sound post" that functions like the sound post in an upright bass, forcing the baffle board and the back board to vibrate in sympathy. Marshall traditionally uses 12 or 13 ply Baltic birch ply, I think, where Krank uses solid pine throughout, claiming improved low end response.
Most guitar speakers like Celestions and Jensens etc. don't respond that well below about 200 cycles or so, but what we like to hear as a low end "thump" occurs at about 100-150 cycles. A good cabinet design will "help" the speaker respond to these lower frequencies, without getting muddy or interfering with the speaker in other frequency ranges.
guitar czar


M/56
PARK CITY,
UTAH
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Reply with this quote Post a reply to this TopicPosted: Apr 6, 2007 1:48 AM
Rectified... wrote:
Why's my cheapy ashdown (120w, run at 16ohm, 412 vintage 30 copies (called ashdown classic)) cab so much louder than my (new, yey) Marshall 1960a 412 cab, i think rated at 280w (? not sure) with g12-t's at 160hm when they are both getting an 8ohm feed from the same 100w amp (simultaneously)?

They're both closed back cabs and the ashdown is a flimsy thing. In the mesa group, it was suggested that it's because the ahsdown has a stronger midrage and so appears louder, but im still not sure...

Also, are G12-T's the same as greenbacks? I thought they were two different things : S

Cheers.



Make sure all the speakers in the Marshall are firing. Take a speaker cable, plug one end into the jack of the Marshall cab, and take a 9 volt battery to the other end of the cable. Touch one snap to the tip of the plug, and the other snap to the sleeve. When you do this, you will hear a thump from the speakers. Don't worry, you won't hurt the speakers by doing this. Watch the speakers through the grill, and make sure all 4 are jumping in the same direction when you touch the battery to the plug. If any are not jumping, the wire to that speaker may have come off in shipping. I had this happen recently with an Orange 4x12. If any speaker is jumping the opposite direction from the others, it is hooked up backwards. In either of those cases, the cab will put out less sound than it should.

A G12T-75 is the Celestion that Marshall has been using for the last 10-15 years or so in their stock 1960A and B cabinet, 75 watts rated, fairly bright tone. A Greenback is basically a reissue of the original G12M used in the 60's. It is rated at 25 watts, and has a darker tone, and with the low wattage rating it is easy to overdrive (and blow). I think Marshall offers that speaker in the 1960AC and BC cabinets. I also think Marshall may have gone to a Chinese Celestion in the 1960A and B as of 2007, because it is one of the only products they make that the price went down instead of up. They still sound great though.
Luigi


Tobacco Road,
North Carolina
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Reply with this quote Post a reply to this TopicPosted: Apr 6, 2007 2:13 AM
Andy: Read above for the answer to your question.

RE: The G12T-75, while any speaker above 93dB of 'sensitivity' is considered a 'high-efficiency' speaker, that Celestion model is on the lower order of sensitivity when it comes to guitar speakers at 97dB. For each 3dB above 93dB of sensitivity, the speaker nearly doubles in volume/efficiency - given that the dB scale is logarithmic, I am pretty sure the V30s are rated at 100 dB of sensitivity... there in lies your answer, assuming that nothing is wrong with the G12T-75s. Using high sensitivity speakers is/was the old fashioned way of making smaller amps sound louder - side by side as you have them, they are unmatched and the higher sensitivity speakers are winning out.
Luigi


Tobacco Road,
North Carolina
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Reply with this quote Post a reply to this TopicPosted: Apr 7, 2007 3:15 PM
...cont...

Since the subject of sensitivity came up and is one of the items on the list, I'll delve into it a bit more...

Sensitivity translates into SPL (sound pressure level) and is a rating that can be found on just about any speaker spec sheet. Manufacturers have a standard measure for this - and it is: dB (decibels) at 1 Watt of power measured at 1 meter of distance from the speaker cone... note, this measurement does not take into account an speaker enclosure - since enclosures/cabs vary greatly - something we will get back to later on, for now, just think of this as a bare speaker suspended in the air.

With the formula above, here is an example using 3 speaker types:

For every increase of 3 dB, twice the power is required, so first... using a 97 dB rated speaker sensitivity:

1W of power = 97 dB of SPL
2W of power = 100 dB SPL
4W of power = 103 dB SPL
8W of power = 106 dB SPL
16W of power = 109 dB SPL
32W of power = 112 dB SPL
64W of power = 115 dB SPL
128W of power = 118 dB SPL
236W of power = 121 dB SPL

Using a speaker of 100 dB sensitivity:

1W of power = 100 dB of SPL
2W of power = 103 dB SPL
4W of power = 106 dB SPL
8W of power = 109 dB SPL
16W of power = 112 dB SPL
32W of power = 115 dB SPL
64W of power = 118 dB SPL
128W of power = 121 dB SPL

Using a speaker of 103 dB sensitivity:

1W of power = 103 dB SPL
2W of power = 106 dB SPL
4W of power = 109 dB SPL
8W of power = 112 dB SPL
16W of power = 115 dB SPL
32W of power = 118 dB SPL
64W of power = 121 dB SPL

With that mapped out, you can plainly see how speaker sensitivity plays a HUGE part in delivering whatever wattage supplied from an amp. I stopped the scale at 121 dB because that is 1 dB above what is commonly equated to rock concert volume, very loud. Also notice that the delta between a 97 dB rated speaker and a 103 dB rated speaker, is pretty large when it comes to the amp needed to achieve 118 dB of SPL - 128W compared to 32W!

Note: All Watts are not equal, comparing between tube watts and solid state watts, there is a big difference in usable wattage, even if both are rated at the same total wattage - but this is for another response here later on.

So... what the heck is a dB anyway? - It is the measurement of sound pressure reaching your ears at a specific distance - in the case of this response - 1 meter, which is the acknowledged standard for measurement of SPL. Here is a common list that relates dBs to common sounds:

* Near total silence - 0 dB
* A whisper - 15 dB
* Normal conversation - 60 dB
* A lawnmower - 90 dB
* A car horn - 110 dB
* A rock concert or a jet engine - 120 dB
* A gunshot or firecracker - 140 dB

Notice that the jumps are huge, thats because decibel ratings are logarithmic, not linear - similar to the way earthquakes are measured using the Richter scale - in that a 6.1 magnitude earthquake is 10x more powerful than a 6.0 magnitude earthquake - the scales aren't relative to each other (between dBs and Richter), but this gives you an example of the scale being non-linear for those that may not have done so well in algebra.

So what is needed for a venue? - To fill a small club with sound, about 115 to 116 dBs, for larger venues, about 117 to 119 dBs - for outdoor venues or very large venues 120 to about 124 dBs - I'll stop there, since the sky is not the limit for a practical conversation here.

Why are there different ratings for speakers and how come some are louder than others? - Sensitivity is based on efficiency, since speakers vary in design, some are more efficient than others... whats that mean? - Power coming in from an amplifier has two directions to go, it can be used to move the voice coils that translate to sound waves or it can be dissipated as heat, the power must go somewhere - a higher sensitivity rating simply means the speaker design is more efficient, directing more energy to sound than heat.

Ok... enough for now :)
Luigi


Tobacco Road,
North Carolina
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Reply with this quote Post a reply to this TopicPosted: Apr 8, 2007 5:49 PM
Lets talk a little about speaker anatomy and cover a little ground on magnets, voice coils and power ratings... starting with a picture:



Probably the single most important part of a speaker is the driver assembly which consists of:

* Voice Coil Former
* Suspension or Spider
* Voice Coil
* Magnet
* Pole Plate

The former connects the voice coil to the cone, which vibrates and makes the sound you hear - many folks confuse the cone with the dust cap - the cone is the speaker paper. When charged with current, the voice coil becomes an electromagnet. The voice coil operates like a piston, with the incoming AC current from the amplifier causing a pulse due to the alternating polarity applied to the coil. This constant change in polarity moves the voice coil to/from the permanent magnet, creating the 'piston' effect. The voice coil creates a small can of compressed air pressure that reacts on the voice coil former, which transmits the changing frequency of vibration into sound - the spider or suspension keeps that 'can' of compressed air sealed as the voice coil moves.



So whats all that mean? Well... in general, more copper wire wound into the voice coil means it is capable of handling more power, but with a stronger electromagnet created by the additional windings - you also need a stronger permanent magnet to make it work correctly. Another method of increasing the power handling capability is to use different siize wire and keep the same or close to same siize permanent magnet... although the impedance or load of a speaker will change as a result.

Changes in the design of the driver assembly directly affects a speakers ability to handle power coming from an amplifier. Dynamics and frequency response come from the ability of the voice coil to travel its designed distance and impart the pulses to the coil former for output to the cone. With many speakers, if you read the specs... the diameter and/or length of the voice coil changes to enable the same siize magnet to be used, but vary the power handling capability. Also, all magnets are not the same and are made with different materials, ceramic being the most frequent these days - so unless you are aware of the materials when comparing magnets, its useless to compare weights.

So, the general rule of thumb is... match your speakers power handling capability to the power output of your amplifier, as closely as you can, if you want to experience the full dynamic range of of what the speaker has to offer. There are many different power ratings available for speakers, it should be relatively easy to accomplish that task - however, some folks have got it in their heads that bigger is always better - such as having a 300W cab (4-75W speakers) hooked up to a 50W amp.

Yes, it will work and yes, the more speaker paper, the greater the sound pressure levels - but if each speaker was designed to have a frequency range of 55-5000Hz, you will have narrowed that range considerably, not being able to supply all the power required to fully actuate the voice coils. Impedance is also derived for the driver assembly - in speakers, its a nominal value - as different frequencies create an ever changing load - but all the same, impedance of the load should always match the impedance of the supply - that is, if you have a 4 Ohm speaker load, you should be using the 4 Ohm supply from the amplifier.

For reference: On a standard tuned guitar, the low E (6th or fatty), will produce a nominal frequency of 82Hz.

I think that about covers the basics of speaker operation, aside from the basket or frame - not a whole lot else here, a speaker is a pretty simple device. But knowing how they work and an explanation of the driver assembly - gives you a better idea of how to go about power matching speakers to amps - also, the reverse can apply - the speakers match be mismatched power wise, specifically to narrow the frequency response - although if too heavily mismatched - say a 5W amp into a 300W cab, there will be a friction build up on the voice coils that will usually result in overheating and a melted voice coil.

One last thing about speakers... aside from the single speaker cab, you will usually find 2 or more speakers in a cab - the sum of each speakers rated power handling capability is the total power handling capability of a cabinet e.g. 2-25W speakers would make a 50W cab. Yes, you can mix speakers of different power ratings in the same cab - but a) keep the impedances matched and b) keep the sensitivities of the different speakers the same.
Eric Sopanen


PARK CITY,
Utah
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Reply with this quote Post a reply to this TopicPosted: Apr 10, 2007 2:51 PM
Jeff wrote:
When speaker swapping, will a well constructed 2x12 with only one speaker running give an accurate representation of the speakers capabilities? Or would buying a good 1X12 be the way to go?

If you have a 2x12 closed back cabinet with only 1 speaker in it, or with 2 speakers but only one connected, you will lose a lot of bass. When speaker #1 pushes out, if speaker #2 is connected it will also push outward, reinforcing # 1. If #2 is disconnected the air pressure in the box will cause #2 to pull inward in the opposite direction (out of phase) and cancel out the bass wave. Likewise if speaker #2 is not there, the motion of #1 will force air in and out of #2 hole also out of phase and cancelling the wave. In an open back 2x12 that won't really happen as the air pressure will go out the back, but a good 1x12 will still work better.
Luigi


Tobacco Road,
North Carolina
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Reply with this quote Post a reply to this TopicPosted: Apr 10, 2007 6:44 PM
Jeff wrote:
Eric Sopanen wrote:
Jeff wrote:
When speaker swapping, will a well constructed 2x12 with only one speaker running give an accurate representation of the speakers capabilities? Or would buying a good 1X12 be the way to go?

If you have a 2x12 closed back cabinet with only 1 speaker in it, or with 2 speakers but only one connected, you will lose a lot of bass. When speaker ..1 pushes out, if speaker ..2 is connected it will also push outward, reinforcing .. 1. If ..2 is disconnected the air pressure in the box will cause ..2 to pull inward in the opposite direction (out of phase) and cancel out the bass wave. Likewise if speaker ..2 is not there, the motion of ..1 will force air in and out of ..2 hole also out of phase and cancelling the wave. In an open back 2x12 that won't really happen as the air pressure will go out the back, but a good 1x12 will still work better.

Thanks. So I am wondering why the cab has such an effect on tone, is it vibrating like a speaker or do speakers just sound better when attached to a better constructed more solid piece of wood?

Think of an enclosure as a 'gun' - its main job is to project the sound waves forward, e.g focus the energy in a particular direction. The better built it is, the better it will accomplish that task. Yes, different woods thicknesses of woods for the cab affect tone. So does baffle design and porting - as well as back configurations.

The speaker cone generates a back pressure as Eric mentioned. It moves in two directions - backwards creates a pressure level too - when trapped inside of a closed back can with little or no baffle porting - the cabinet has to absorb this pressure. Thats where cab resonance comes from - the more the speakers interact with the cab, the more resonance you generate - or 'bottom end'.

If you open a the back of a cab up, you let that back pressure out - less bottom end is the result.

But you have to be careful and not get a shotgun mentality about open vs closed back cabs either. Some speakers emit more bottom end than others, in that case you may want that back open because a closed back would rob all the highs and sound muddy. Likewise, speakers that operate more in the mid and high end ranges can be tuned somewhat for better bottom end by using a closed back cab if so desired.

The enclosure itself should be very rigid to withstand the vibration of low frequencies, so that the resonant lows don't a) just produce rattle or b) don't capture the sound pressure and transmit it to the outside too readily - causing a mushy effect.

Just like pretty much anything else in audio land - better materials and better construction techniques equate to a better end result, and cost is relative for the most part.
Riley³


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Reply with this quote Post a reply to this TopicPosted: Apr 18, 2007 2:02 AM
i have a question regarding speakers. if replacing speakers in a cab, is it essential to get guitar speakers, or would experimentation be a good idea? after making sure the impedance matched up, i tested out the 10" (4 ohm, 500w) subwoofer from my car, and it actually sounded a lot better than i was expecting. and from what i remember, it sure was a lot cheaper than any guitar speaker i've seen. is this a no-no, or would using a sub work out for guitar?
Eric Sopanen


PARK CITY,
Utah
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Reply with this quote Post a reply to this TopicPosted: Apr 18, 2007 3:25 AM
Riley³ wrote:
i have a question regarding speakers. if replacing speakers in a cab, is it essential to get guitar speakers, or would experimentation be a good idea? after making sure the impedance matched up, i tested out the 10" (4 ohm, 500w) subwoofer from my car, and it actually sounded a lot better than i was expecting. and from what i remember, it sure was a lot cheaper than any guitar speaker i've seen. is this a no-no, or would using a sub work out for guitar?


As long as the ohms are correct, and the power handling is OK, you won't hurt anything. Go for it, you might come up with something new.
Eric Sopanen


PARK CITY,
Utah
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Reply with this quote Post a reply to this TopicPosted: Apr 18, 2007 3:56 AM
Jeff wrote:
Another question about construction: how are baffle boards commonly connected to the rest of the cab? I have one that is screwed to the rest of the enclosure and I have one that appears to be glued to the face of the enclosure. The screwed in one is a mini bluesbreaker knockoff 1X12 and sounds clearer, bassier and louder than the 2X12 combo I have(even with one speaker against two). How are Bogner and Mesa copies constructed? What does flex do for a cab?


There is a lot more to know about cabinet construction than I know. There is a lot of engineering and physics in there that I know very little about. In hi-fi, PA, studio monitor, and other speaker cabinets where accurate reproduction is the goal, zero flex is what you want. You don't want the cabinet to color the sound at all in those applications. With guitar cabinets, the coloration is what we want, and cabinet makers are always trying to figure out ways to get these tones we want. Most players like the tone of a 4x12 closed back Marshall style cab, but few want to deal with the size and weight of them. So the better cabinet builders like Mesa and Bogner etc. try to come up with cabinet designs that sound like 4x12's but with only 2 or even 1 speaker. Since the air space is so much smaller, they use devices like tuned ports, or controlled flex to get the bass response of a 4x12. Flex can be a positive thing, if it is controlled and tuned. A cheap cab made with thin wood will have uncontrolled flex, and the lows will be muddy and ill-defined.

Your 1x12 might have a better speaker in it than your 2x12. If you look at Luigi's post about efficiency, you will see that makes a big difference. All other things being equal, doubling your speakers gives a 3db increase in sound, same as doubling power. But if your 1x12 speaker is 5 db more efficient than your 2x12's, the 1x12 will give more sound. Also I am betting that your 2x12 combo is open back, and your 1x12 is a ported closed back, giving more bass out the front. But even if your 1x12 is open back, the speaker difference can account for what you are hearing.
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