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Old 29th March 2013, 04:13 AM   #1
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Default Add Highs to Cheap Guitar Speaker (wordy, but with pics)

I don't post much here, if I have at all, but there is a wealth of info that I digest on regular occasion. Lately it's been speaker treatments and phase plugs and all the cool things you guys are working on! Thank you very much for Doing It Yourself and telling us.

I build tube amps and effect pedals and play the guitar. So I've been on a ridiculous search for a guitar speaker that I love. The closest is an Eminence Private Jack, and I have that one and half a dozen other popular speakers on hand.

The following is perhaps a pointless quest in experimentation with no hope of success.

I bought a $15 1976 Eminence 12" (supposed to be) guitar speaker the other day to mess around with. It was terribly dirty, probably been wet (maybe the real cause of bad tone), and I read here and other places about cleaning it with a dry bristle brush. That made it look a little better. I then read about cleaning artwork with an eraser, so I tried that, and it worked a little more. The speaker sounds like the guitar tone knob is turned all the way down. It was probably built as a woofer in a cheap PA cab. I say that because it has an aluminum former, which hasn't ever been very popular with guitar speakers. I did contact Eminence and Anthony Lucas didn't have any info available about this driver.

So my first attempt at bringing some life to the cone was a 50/50 white glue and water mix, spread over the cone and dust cap (the dust cap paper is a little wooly on top, not sure if that's by design, but it has to suck treble). The glue made a very modest improvement in the high end, but not enough to bring it up into 'crappy guitar speaker' territory.

Next I decided to listen to the speaker without the wooly dust cap. And though I've read that it often improves tone, in this case it sounded almost exactly the same naked or with the dust cap. This brought my outlook to pessimistic.

So, then I read somewhere that a guy used a beer can for a dust cap. Hey, that's my style, so I cut the bottom off of a Diet Pepsi can. The original dust cap weighed 2 grams, and the Pepsi can was trimmed down to 2 grams. The glue is drying on this attempt right now.

So, before all the pictures, do you have any possible ideas to get more energy in the 2kHz-5kHz range? Maybe it's just not possible.

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Old 29th March 2013, 09:36 AM   #2
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is that cab closed or open backed? I can think of much except to try it in an open back cab, which would reduce the bass and change the tone emphasis to the mids and treble.

For the longest time, when i revamped an old cab with G10Rs, I was unhappy with the treble. After a lot to discussion here, I just roll the bass control to almost off. Apparently that isnt uncommon EQ on a valve head like mine (DM sig120) and high Q vintage or reissue drivers.
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Last edited by mondogenerator; 29th March 2013 at 09:43 AM.
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Old 29th March 2013, 12:51 PM   #3
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Originally Posted by mondogenerator View Post
is that cab closed or open backed? I can think of much except to try it in an open back cab, which would reduce the bass and change the tone emphasis to the mids and treble.

For the longest time, when i revamped an old cab with G10Rs, I was unhappy with the treble. After a lot to discussion here, I just roll the bass control to almost off. Apparently that isnt uncommon EQ on a valve head like mine (DM sig120) and high Q vintage or reissue drivers.

Open back. Yes, the EQ can get the tone better, but since you fellas here have refined your speaker modding abilities, I thought, perhaps there might be a trick in your bag that would help. If you've already gone through this quest, there's my answer. I thought that gluing the aluminum cap directly to the aluminum former would really brighten it up, but it only helped a little bit. (I had to hear it, so I cheated and played just a little bit at low volume 2 hours after attaching with CA glue.)

Can the magnet be re-magnetized, or 'more' magnetized via DIY methods?

Thanks,
CHAD
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Old 29th March 2013, 02:02 PM   #4
JMFahey is offline JMFahey  Argentina
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You have an excellent magnet structure there, and it certainly must be well magnetized.
Only way to weaken it would have been some idiot pulling those magnet bolts and separating the back plate, but he would have destroyed the VC on reinsertion, so it didn't happen.
The "22 rings" cone is very good too, your problem is a very heavy and damped voice coil.
Eminence (and many others) *did* use aluminum VC for some years (I still do for some models) because of high reliability and power handling but they had the dull sound you mention.
The aluminum dome helps a little, but since the VC itself does not move much, can't do miracles.

I suggest you either use it as a woofer , you can make a compact wedge monitor, with it and a piezo, or if you dare recone it with a proper Kapton VC.
Even better, try to get a Nomex one.
Less power handling (around 30W RMS) but much better sound.
Check Ted Weber for cones, VC, supplies, etc.
If you send them these pictures they will suggest proper replacement parts, also tell them the sound you like.
Use some type of loudspeaker specific Loctite or Hernon adhesive, the epoxy you have there is strong but too heavy.
Good luck.

PS: adding weight (coating with some kind of varnish, etc.) is what you do *not* want

PS2: magnetizing requires big mean expensive machines.
I have 2 magnetizers and am building the 3rd ... and suffering.
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Old 29th March 2013, 05:13 PM   #5
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PS: adding weight (coating with some kind of varnish, etc.) is what you do *not* want
Realizing that added mass lowers Fs, and as you say, is the wrong direction, I hoped that the added stiffness could brighten up. I have sound samples that show a very slight improvement. Not wanting any additional weight, I weighed the dust cap (together with the bits of dust cap) at 2 grams, and the aluminum replacement cap was trimmed to 2 grams.

When I saw that aluminum former I pretty much knew it was not going to do what I hoped. I can have it reconed locally for $55, and have to decide if that is money well spent.

CHAD
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Old 31st March 2013, 12:39 AM   #6
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if you make pedals what about a tunable treble boost? I dont know that eminence but if its such a vintage i would not have had the courage to cut the dustcap out!
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