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Loudspeaker parameters and loudness

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property1:
Ok since you offered to expound! As a total newbie I recently read that you should build your cab with a "guitar" speaker and not one from the home audio system. What's the difference? How can you tell when you have a speaker in your hand? I now have 2 8" and 2 4" 8 ohm home audio speakers that I wanted to build into speakers for my amp. Any reason not to do it?

Dave

crystaltech56:
Yes, excellent reason is you will probably tear the cones off the rest of the speaker assembly the first time you play. Don't despair because inexpensive musical instrument grade speakers are available ( from, and I hate to use this word, RadioShack) and others ( on the web, cut out the middleman). I'll do some more research and get back to you personally, (unfortunately I've been away from the repair industry for so many years I don't know whose in Business still). The point is a hi-fi speaker cone and coil cannot handle the power( unless you want to sound like a cat chasing a mosquito both ductaped in a shoebox with holes). On the other hand, hang on to the cabinet that you have. It's a good staring point. CrystalTech56.

crystaltech56:
One good place to look is www.colomar/Shavano/speaker_design.html. In fact, the entire site is great. And on that particular page, there is another page you should download as well! These used to be called "musical Instrumment speakers", but now are called "musical instrument and Pro Audio speakers", (see how out of touch I am? I'm old enough to remember seeing the Grateful dead play at M.I.T. on May 5,1970 the day after 4 students were killed at Kent State(no I wasn't I student at either place). The guy who did there sound for a while was named Bob Heil ( of Heil Talk Box fame). He has his own site, is still in business, and has a book still in publication,I think it's "Professional Guide to Concert Sound". The book isn't on the site, but I e-mailed him and he sent a phone number(I'll post it later, can't afford to buy any toys this week) to call to order. It really is a great book. Do an Amazon search on it(it is available if you can't afford new) and also Goole "Bob Heil" I'm reluctant to post any of it because of copyright infingement and Bob desreves the money.  CrystalTech56

gavnook:
The sensitivity of guitar speakers typically blows away that of other types of speakers at the expense of accuracy. If a home audio speaker can handle 100 watts from your home stereo, it can handle 100 watts from your guitar amp. It just won't be as loud, and might not sound "right". If you hook up a guitar speaker to a home stereo, the music will sound awful.

Some speakers are rated at the power where they cross a certain distortion threshold even though they're capable of handling much more power before taking on damage. I've seen this with car subwoofers.

Anyway, as long as the speakers can handle the power and the amp can handle the impedance, nothing terrible will happen if you hook them up.

J M Fahey:
This is something I originally posted in an Orkut group, in Portuguese.
For those who understand it: http://www.orkut.com/Main#CommMsgs.aspx?cmm=144284&tid=5332929478380364898
For English speakers, here´s the translation:

How to "read " speaker curves.
I´m posting two widely different speakers , a "Premium" Guitar Speaker, the famous Celestion Vintage 30, and a "good" PA/DJ woofer, the Brazilian made (but easily available in the USA) Selenium 10PW3.
Both have big magnets (Celestion over 150mm , Selenium 147 mm) the same voice coil size (44mm, 1 3/4"), the same voice coil wire (round copper), same base material (Kapton), same adhesives (high temperature epoxy), etc. , yet they sound *very* different.
I´m posting their frequency curves.
They have "too much" information, and can be confusing for us guitar lovers.
To begin with, the classic HiFi range, 20Hz to 20kHz is "too much" for us.
We should be concerned with SPL: sound pressure levels (in this case, measured at 1 meter, with 1 Watt applied to the speaker) over 90dB, which is the minimum efficiency needed to "battle" successfully a drummer, who makes a lot of noise, doesn´t have a "volume control", and sets the minimum sound level we must achieve.
Any lower, will probably work (even be too much) in a bedroom, but not on stage or even the rehearsal room.
Besides, the SPL scale (the vertical scale) is not Linear but Logarithmic. Don´t worry too much about the Math, it simply means: a +3dB (deciBels) difference equals twice the measured sound volume.
Some useful values: +3 dB: twice the volume ; +6dB: 4 times as much; +10dB: 10 times as much.
I had some extra work to re-dimension the graphs, which usually are printed on a different scale, perhaps to make difficult their direct comparison.
I could not superimpose them, which is the best comparison method. I usually scale and print them on transparent paper but don´t know how to make it on a computer screen.
I did draw two green "boxes" showing the part of the graph that concerns us.
The left and right sides of the "boxes" show frequencies of 80Hz (Hertz or cycles-per-second), about the lowest guitar frequency, and 6KHz (6 Kilo-Hertz or 6000 "Cycles"), the practical highest harmonics of importance and anyway the practical higher limit of Guitar Speakers.
Top and bottom sides of the "boxes": 100dB (a very desirable efficiency) end 90dB (the absolute minimum acceptable for live work)
Now we can see that the V30 has no less than 97 dB from 150Hz to 350Hz (lower midrange) and practically 100dB from 450 Hz to almost 5000 Hz, with the added "gift" of almost 6dB extra (106 dB max.) from 1500 to 4500 Hz (brightness, attack).
An impressive speaker indeed, worth every extra cent it costs. As another extra, we should consider the exceptionally flat midrange response from 500 to 1200 Hz, the famous "V30 midrange". It´s unusual among guitar speakers, almost *all* of them have a response "dip" in that area anywhere from -3dB up to -9dB which usually produces "buzzy" sound, especially from SS gear.
Now on to the 10PW3.
The response is clearly less efficient and very irregular.
For example: from 120Hz and 2400 Hz (practically all the range of guitar strings) the response goes up and down, between 92 and 94 dB, with a small (98dB) peak at 1800Hz, a dip at 2400 Hz and a final 3800Hz peak.
All of that means a muffled, low efficiency speaker, which in most of the "guitar range" gives almost -6dB compared to the other speaker.
In practical means: a 5 or 6W Champ or AX84 tube amp, using a V30 or a good Eminence of similar specs will easily match a 30 to 50W SS amp driving a poor speaker.
That´s some of  the basis of the so-called "Tube superiority over SS". Truth is, usually Tube amps (expensive) have an expensive speaker; SS amps, perceived as "cheap" often use "cheap" speakers. The justly famous Lab Series often used very efficient EV speakers, or the best Eminences available. Same goes for JC120s and their impressive Pioneer made speakers.
What point am I trying to stress?: we SSGuitar fans, *must* use good speakers to make justice to our work.
Don´t need to break the bank: There are many reasonable priced Eminences and of course, the excellent Italian made Jensens to fill the bill, as well as good used speakers salvaged from dead amps or bought cheaply on EBay.
Try to design your own "green box" on any speaker curve you are interested in, to know how it will sound, even before actually hearing it.
Have fun.

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