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Author Topic: Seeking speaker advice for "Ruby" LM386 based amp.  (Read 7480 times)

Jack.Straw

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Seeking speaker advice for "Ruby" LM386 based amp.
« on: April 29, 2009, 09:31:08 AM »
Hello everyone.  I've just finished building my second Ruby circuit (http://runoffgroove.com/ruby.html).  On my first amp i used a little 8ohm 5" speaker out of an old stereo.  It works fine, but for my second project i need to balance function with  size.  I know almost nothing about speakers, so i was hoping someone here could make a recommendation.  When selecting a speaker what sort of things should I look out for? (other than a total impedance of 8ohms)  Is the size of the magnet something to look at?  Do certain speakers respond better to guitar frequencies?  What would you say the smallest diameter speaker i could use and still produce a strong sound & good tone?

Thanks for your time,
-Scott

iTzALLgoOD

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Re: Seeking speaker advice for "Ruby" LM386 based amp.
« Reply #1 on: April 30, 2009, 09:37:02 AM »
I just usually use salvaged stuff from old radios.  I don't expect to much from the 386 tone wise so I don't put a lot of effort into the speaker. I have bought a few 50mm speakers and put the circuit in pop cans and they sounded pretty much like the salvaged radio speakers.  I am also not very picky when it comes to tone from these little 0.5 watt amps.

phatt

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Re: Seeking speaker advice for "Ruby" LM386 based amp.
« Reply #2 on: May 03, 2009, 04:45:14 AM »
Hello everyone.  I've just finished building my second Ruby circuit (http://runoffgroove.com/ruby.html).  On my first amp i used a little 8ohm 5" speaker out of an old stereo.  It works fine, but for my second project i need to balance function with  size.  I know almost nothing about speakers, so i was hoping someone here could make a recommendation.  When selecting a speaker what sort of things should I look out for? (other than a total impedance of 8ohms)  Is the size of the magnet something to look at?  Do certain speakers respond better to guitar frequencies?  What would you say the smallest diameter speaker i could use and still produce a strong sound & good tone?

Thanks for your time,
-Scott

Hi,
   If you are trying to get your head around speakers then I find the easiest way to explain it is thus;
There are only really two types worth understanding, those being "Low Complience" (musical instrumet/voice/guitar)
and "High Compliance", (Hifi, woofers for reproduced music).
Bass drones for cars and disco stuff.

For guitar you want LC.
What's the diff?   Easy HC wobble easy and  LC are stiff as a board.

How to tell?  HC, Woffers have a loose rolled edge (called the spider) and a rather long loose travel (easy to move with light force). These need to be in a box that is tuned to match the driver paramiters otherwise they sound crap.
This is not what you want for guitar.

LC on the other hand are very rigid with very little movement. They can be used without great need to *Comply* with box design.
In the really old days this is all that was used and I've seen early PA's with a 12" driver mounted on a 1 metre flat square board (no side or back), For voice reproduction this is all that is needed anyway.

Magnetic guitar PU's have masses of bass output and you really don't need much low freq help. Try plugin' a modern guitar and Amp through a wooffer and I doubt you will like what you hear.

The early celestion company was commissioned by the mines to make a speaker for a siren and the design called for high output at 1kHz too 3kHz.
Greenbacks as they are now called where not designed for guitar at all. :o

Just so happens, that these are the frequencies where the magnetic PU guitar needed a boost and so the rest is kinda obvious history and many folk probably don't realise that all the treble for Guitar is from 1kHz to 3KHz.
For hard driven OD rock anymore bandwidth just destroys the sound and it is no longer sweet.  (listern to Carlos Santana and I doubt there is much above 3kHZ)

These days speaker makers are going crazy making all sorts of claims about extended freq response but I have heard enough of these to say I have my doubts as to the benifits of such claims.
Unless you are wanting pristine clean then more bandwidth will just get in the way of good tone.

Good speaker effeciency (High SPL) is a bonus and worth some merit but as long as you realise the drawbacks that can come from that. I doubt that many Amp designs adjust their circuits to suit the drivers that are used.
Brand name Amps use high SPL (sound pressure level) Drivers simply because it makes there product Louder than the competion of the same wattage.
An old wise man once said to me that it would be better to design an amplifier from the speaker first and work your way back from there.    interesting thought?

I just recently pulled the very harsh Speaker from a Trademark 60 (Teck21 stuff)
and replaced it with a less efficient driver and the owner was amazed
at the difference. Yes slightly less percieved power but now a joy to play. 8|

I don't think you need a degree in sound enginering to get an idea of what works as
It really just comes down to balance,, Just think of a hifi speaker where you have bass, midrange and tweeter.
If you have one super high SPL output driver and the others only average then
it will likely sound off. It is better to have all the drivers balanced even
if they are not top of the range drivers you still get a balanced good quality tone.

You mentioned magnets.
This is another of those things that tends to just end up as a dog chase tail affiar
as the bigger the magnet the more energy required to move the darn voice coil and cone.
So pick a magnet and keep in mind that some small older types sound better than those big mag one's.
Anyway You would be better to look at the Voice coil as it's more important and
can make a big difference to the tone.

Understand that regardless of magnet size any given cone diameter can only handle about 3 octaves efficiantly and smaller VC's for same dia cone will sound more peaky at some ugly freq.
Some small speakers sound quite good if they have a decent sized VC.
(sadly a lot don't)
A larger VC for given size cone will keep the cone more stable over a broarder freq range, hence a flatter better perfomance.

Some 12 guitar speakers can sound very honky because they have a VC that is to small for the cone dia. That said some may like the peaky nature of lesser drivers found in really old Amps.  Pick a flavor?

For guitar The rule of thumb seems to be 12" cone with a 1-1/2" VC.
(Celestions had 1-7/8" VC).  So anything around that is going to be good.

Even if you only want 6 inch speaker at least now you have some idea of what to look out for :tu:
Well this turned into a marathon so I hope it helps you in your pursuit of great tone.
Phil.
   


Jack.Straw

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Re: Seeking speaker advice for "Ruby" LM386 based amp.
« Reply #3 on: May 05, 2009, 08:18:48 AM »
Phil, thank you so much for taking the time to type all that.  Very helpful and informative!!!  Thank you!!

pelanj

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Re: Seeking speaker advice for "Ruby" LM386 based amp.
« Reply #4 on: June 05, 2009, 03:07:01 PM »
Hello, I have recently tried one trick with small speakers, that really helped the distorted tone. I have used a 2nd order lowpass as found in HiFi speaker crossovers with the rolloff frequency around 4-5 kHz. That really takes away the buzziness assiciated with small speakers which have a wider frequency response that usual guitar speakers. I wonder why this is not very often used in small practice combos. It sounded more natural to me than using a line level lowpass. Maybe it is due to reduced damping and also it can smooth out power amp clipping in Ruby sized amps.