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Hoffman Amps Forum image Author Topic: best cab setup for small amplifier  (Read 5158 times)

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Offline fossilshark

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best cab setup for small amplifier
« on: August 02, 2016, 09:00:40 pm »
I'm building a small amplifier and I was wondering if it would be worth it to build a 2x6 or 4x6 cab or something like that. the amp will be around 5-15 watts and I'm already building a 1x12 cab with a 20 watt speaker in it. I was just wondering if there would be any advantage to more speakers on a low wattage amp (say use 1x12 for portability and a 4x8 cab for my playing room?) I'm a little new to this, this is my first (real) speaker cab.
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Offline jojokeo

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Re: best cab setup for small amplifier
« Reply #1 on: August 03, 2016, 03:46:45 pm »
It's really about personal preference. Two 8" speakers has more cone surface area than a single 12". And you "may" get better cone sensitivity/responsiveness? But you can get a low 15watt 12" speaker that can have  nice sensitivity but better efficiency than 8" speakers have and be nicely responsive for a 5-15watt amp. Also, a single 10" is plenty good for this range too.
On a 12" cab the wood and construction method used is important but for sure the overall size is equally or more so. This has been calc'd out to be appx 55 liters/l(dm^3) or 3350 in^3 internal dimensions but I've found a few cabs recently that sound really good at slightly less. There's a lot more to this that what I've just typed...as there's a whole host of considerations that goes into this.
« Last Edit: August 03, 2016, 03:57:48 pm by jojokeo »
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Offline drgonzonm

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Re: best cab setup for small amplifier
« Reply #2 on: August 03, 2016, 04:43:19 pm »
It's really about personal preference. Two 8" speakers has more cone surface area than a single 12".....
???   4 sqrtd times 2 =32: 6 sqrtd =36. (since pi is common to both calcs, not necessary to include pi in the ratio)

If technical info is avail review, the 12" speaker will probably have better low frequency response.  (I do have a 8 speaker, specifically designed for 30 Hz to 150 Hz, so there are exceptions).


Offline fossilshark

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Re: best cab setup for small amplifier
« Reply #3 on: August 03, 2016, 11:46:43 pm »
thanks for the help.
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Offline Ritchie200

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Re: best cab setup for small amplifier
« Reply #4 on: August 04, 2016, 10:31:12 pm »
It's really about personal preference. Two 8" speakers has more cone surface area than a single 12".....
???   4 sqrtd times 2 =32: 6 sqrtd =36. (since pi is common to both calcs, not necessary to include pi in the ratio)

Actually when you subtract the surround, most 8" speakers doubled up DO have more surface area than a single 12".  However, for what purpose did you bring that up as it has no bearing on your response? :dontknow:

Jojo, didn't you run through several brands before settling on a few that were really great performers?

Jim

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Offline jojokeo

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Re: best cab setup for small amplifier
« Reply #5 on: August 05, 2016, 12:32:54 am »
The issue of large verses small speakers. While a large speaker can and does move lots of air, the larger the speaker, the more compromises which are designed into the speaker. Larger speakers have less ability to reproduce higher frequencies, and it becomes harder for the larger speaker to control the mass of the cone. The magnetic motor (the coil and magnet structure) moves the cone back and forth, to produce sound waves from the cone surface. Ideally, the cone needs to have a mass of zero (but no cone has this characteristic) so that the motor part can start and stop the cone at will. Because of the mass of the cone and the coil structure, which is connected to the cone, raises the total mass, the cone therefore has inertia. Therefore, it does not start moving exactly when it is told to move, and it does not stop exactly when it is told to stop. With smaller speakers, there is better control over the cone movement by the coil and magnet structure. Also the cone needs to be relatively stiff and not flex over the surface area. This is the problem with large speakers (cone cry for example). In general, several smaller speakers will produce better quality sound than a single large speaker.

Could be I was using the circumference calc by mistake but even so it's close enough as Jim points out. One of the nice things about multiple speakers is the 3-D stereo type of effect you get verses a single speaker. 8" guitar speakers generally don't have the efficiency that a low watt Blue Celestion, S75 PVC & Scumnico Scumbacks, Blue Dog Weber, Red Fang Eminence, to name a few and many others have - but when you put smaller speakers together oftentimes good things happen. Also, if you use a poorly made & sized cab than you will be losing a lot of the low freq response even if the speaker is up to the task otherwise. IMHO, it cannot be overstated that the cab is at least as important as the speaker inside of it. Below doesn't get into open, ported, closed types, phase cancellations, low & high frequency roll off parameters, etc.. but a lot of info for wood choices alone.

Here is a little reference sheet that was built up a while ago showing the relative densities and elasticity of woods. The velocity of sound in a piece of wood is a function of it's modulus of elasticity to it's density. It effects how quickly the wood can react sympathetically to frequencies... it works kind of like capacitive reactance, in that it affects how much resistance there is at certain freq. The slower the wood, the more coloration generally, but you have to take into account thickness, grain of the cut and density too. Also the more porous the wood, the more frequency combing, and woods like Spruce or Swamp Ash that have internal chambers & a harder exoskeleton will act like two simultaneous different typed of woods, reacting differently. For cabinet purposes, MDF, and harder Oak, Rock Maple, Birch, White Ash, Teak, Zebrawood, Rosewood, etc will all sound pretty similar (unless they are thinner then they'll impart more character), and effect the tone of the cab minimally, which is why many audiophile speaker companies offer those woods as upgrades to MDF. Pine, Mahogany, Poplar, Alder, Spruce, Swamp Ash, Walnut, etc will all color the sound uniquely, and definitely make a noticeable difference, even if they are as thick as 3/4".
« Last Edit: August 05, 2016, 12:36:46 am by jojokeo »
To steal ideas from one person is plagiarism. To steal from many is research.

Offline drgonzonm

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Re: best cab setup for small amplifier
« Reply #6 on: August 05, 2016, 11:28:58 am »
Richie200, I won't disagree with your comment,  My post addressed two points, an assumption that two 8"
speakers have more surface area than a single 12".  I am still not sure if that assumption is correct.   And a general comment about frequency response.   

Nominal diameter was used to determine ratio, where a flat 12" dia has 9/8ths more surface area.  than two 8".
We can complicate the matter by looking at cone depth, and correcting for voice coil diameter.  The cone depth adjust adds more surface, while the voice coil diameter decreases surface.

What is a fair estimate of speaker diameter?  Overall diameter (favors the 8"), or baffle hole diameter (favors the 12") .  again this becomes nitpicking. 

after all fender did replace 15" speakers in its Bassman with 4 speakers.   Ampeg in its 8x10, svt cabinet, a favorite of bass players, starts to show significant db drop at 50 Hz, while the largest strings on bass typically vibrate about 40Hz, for a typical 4 string, and 30 Hz, for 5 string basses strung with a B0 string.

I mention bass amps, as some boutique manufacturers, believe bass amps need to provide a greater frequency response than a "regular guitar amp" 

If you are planning to play a guitar, where the low string vibrates about 80 Hz, then it is possible you may want to use multiple speakers, if you are adding pedals, a higher frequency response is more favorable.   IMO, a pair of speakers should be mounted vertical to minimize phase interference. 

 
Jojokeo, you make some very important points regarding speaker design. Afterall, fossilshark did not provide much info on his cabinet design. 

 


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