Fender Frontman 15B owners: Fart no more!
I finally found a way to get rid of the flabby huffing! Apparently, the cab is supposed to be sealed, but it had more gaps than the Titanic. The speaker is a floppy thing that really needs the pressure to help it retain it's shape. Now, on to my fixes...
First, remove the front panel and unhook the wires from the speaker, and set it aside. Pull the head out. Oh, and before someone sues me for lack of disclamers, UNPLUG THE AMP BEFORE DOING ANY OF THIS. There. Now, head's out, dangling, so set it to the side. Take a narrow thin strip of foam the width of the cab, and glue that to the top inside the cab, where the edge of the head sits. The next part I didn't do, but I reccommend it. Take the board off the head and put some hot glue around the bottom of each jack where it meets up with the pcb. Reassemble the head and put in back in the cab. Take a little glue (I used Elmer's school glue for all of this stuff), and smear it down into both sides of the head. Now while letting that dry, onto the front panel. The metal grill folds over the top of it, and on top of that is a strip of foam. Stupid design on Fender's part, as the diamond-shaped holes on the grill allow air to flow freely under the foam strip. Fill in under the strip with glue, and clean off the excess. Allow to dry, and pop it back it the cab. And for whatever reason, the white wire goes to speaker -, not the black one.
And there you have it! This mod took me maybe 45 mintutes, so not too time-consuming. All woofy huffing = gone, with just a tiny bit of distortion from the circuit, but only when cranked.
Let me know what you think!
Next mod I hope to do is find some substance that can coat the speaker cone to make it stiffer... If anyone has suggestions, feel free to post.
Actually, to stiffen the speaker, I was thinking of just coating it in glue and letting it dry upside down for an even coat. I have a piece of paper drying right now to test how stiff it'll be, but I was wondering if there's any reason I shouldn't do this. I'm not concerned about the glue soaking in, as that would further stiffen it, correct? And wrinkling won't be an issue because the cone holds its shape better than a plain piece of paper. Should I also run a test on contsruction, as that's closer in thickness to the cone? This'll be my first time doing this, so please correct me if need be.
First, it will add mass to the cone (changes the way the speaker operates/sounds in the cab). Second, the outer and inner suspension for the cone will be over-stressed due to the added mass and "stiffness". Will it be an improvement? Maybe/maybe not. To undo the changes will require a new speaker (doubt if recone kits will be available). The speaker may fail more spectacularly?
Some folks have used cyanoacrylate (Crazy glue) to stiffen old soft speaker cones. However, as B-string wrote, it will change the properties of the speaker. I suspect Fender did a fairly reasonable job of matching the speaker to the cab (while counting their pennies) so I'd be reluctant to recommend "treating" a new speaker.
Ok, but I thought adding mass was a good thing? To help drop the frequency response, right? And I was thinking stiffer meant better transients. As it is, if I do this (and knowing how stubborn I am sometimes, I probably will), I really am not impressed with the range as it is. I have another speaker I tested in it once, and it sounded so much punchier, with a smoother low end. It's a 4 ohm 15 watt, though, and the amp is 8 ohm 15 watt. But otherwise, I don't have crazy glue, so maybe I'll see what my mom has in her scrapbooking room to use. Further thoughts?
Adding mass is NOT a good thing. Stiffness is good, generally, but speaker manufacturers have a pretty good idea what they are doing.
It's your speaker though, feel free to mess it up.
The other speaker you tried may just be a better speaker overall. Since it presented a heavier load on the amp section it also changes how the amp responds (which would indicate that the amp section may have been in danger of overload).
A trick to preserve old speakers is to paint or spray on a thin layer of polyurethane lacquer diluted in thinner. It works well when you have an old paper speaker that is breaking down. People use all sorts of glues to do this.
There is a rubber based product called speaker service cement made by MG Chemicals that I use. It soaks into the paper and is used to repair surrounds and cones. Kind of like the dope that they apply around the edge of speakers.
It's gonna require some math on your part. You'll need to know the mass of glue or resin or epoxy you need. Or you could model the speaker with whatever added weight you feel gives you the response and use that amount of glue n stuff.
Of course you'll need the Thiele Small data for the speaker.
Sealing the cab was a good idea. Mass loading the driver, not so good.
Adding mass to the cone will lower fs, making more extended (deeper) bass from the driver possible. However, the mass loaded driver will need a substantially larger cabinet in order to avoid excessive peaking in the bass. This is due to the increased mass also increasing qts - the driver is less damped.
Stiffening the cone will improve pistonic motion, which is ok (in itself), provided that the driver is crossed over to a mid/high range driver an octave (or more) below the frequency range where the wavelength approaches the driver effective diameter. Otherwise the driver becomes highly directional.
Also, the stiffening agent decreases cone damping, and causes a mismatch between the cone and surround (which is designed to absorb waves traveling in the cone), producing a more peaky response.
One further effect is a loss of sensitivity.
Overall, a fun experiment and a good way to learn about drivers, but most likely resulting in the purchase of a new driver.
So, stiffening = good, increase mass = not good. Ok. Now, considering I don't have the thiele small data, nor do I have any way to simulate this, then I'd be basically going at this blind. I don't happen to have any lacquer, nor epoxy (besides jb weld, and I ain't using that), I'd just have to go slowly, and keep the glue as thin as possible... I'm not too worried about making the response peaky, as long as it doesn't affect approx. 1khz. I find the 1khz band gives quite a nasally tone, and not in a good way like 300 or 500hz does. Oh, and the other speaker is from a First Act 15 watt bass amp. Lemme find the model here... Ah, MA215. Cheap amp. Well, was a cheap amp. Now it's just a pile of parts.
I just want to thank you guys for all your comments, you saved me from just going ahead and slathering thick layers of glue all over, thus preventing me from possible disappointment. I will let the samples dry tonight, and see about getting the speaker done tomorrow morning. Hopefully, between this and sealing the cab, this amp will sound great Tuesday night for Christmas eve service. Gonna be doing CADG through it ^_^ .
Go by the seat of your pants, listen, and see how it goes. Whatever the outcome is, it isn't the end of the world. You can always buy a replacement speaker.
Google speaker preservation and speaker doping for more info.
The best substance for stiffening a cone (don't do the surround) is "acrylic mat medium" available in art stores and art supply sections. It is a prep for canvases. It has been used by hi-fi people for decades.
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