Official Luthiers Forum!

I just got finished with my top bracing and was trying out the Chladni patterns. I couldn't find the 1 1/2 ring pattern and when i went above 200 hz. the speaker started to get pretty hot and I already burnt up one speaker. I did get a pattern up there but it didn't look anything like the 1 1/2 ring. But my bracing doesn't have a UTB so I'm wondering if that makes a difference. I'm guessing it does and I'm trying to open up the upper bout. I 'm using a adjustable neck joint and have buttresses to support the neck block.
The pattern i got at 194 hz. is in the picture and the next pic is the bracing that was mirrored to show how the pattern is in relationship to the bracing. And the 3rd. pic is a view of the bracing profile.
I like the even tap tone I'm getting across the lower bout.
From looking at the pattern it looks like to me that the body is vibrating pretty even around the body except for the node point and up to the neck block at the upper bout A bracing. The top was excited at the bridge plate by the speaker. I'm thinking that seems like a good thing and the bridge should do a good job moving the top. But what do I know. I'm interesting in some thoughts here as to whether my logic is correct or not? I also used CF in the X braces and the ends at the UB will be inlet and the LB ends not.

That's the 'ring' mode, the one that usually shows up just below the 'ring+' on most tops. It's got a better shape on yours than most, because the UTB stiffnes the bout so much that it just kills the vibration up there. Yours looks more like what you'd see on an archtop.

BTW, that's CHLADNI.

Thanks Alan. I guess I'll give it a go when the speaker cools down.
I have the hardess time remembering how to spell that. At least I spelled it right under the picture.

Here it is at 199-200 hz. Can that be the 1 1/2 with a 5-6 hz. difference? The next change is at 235 hz. and it's a strange looking pattern.

Chris, do you have a photo of 235? That is about where I would expect it after the ring one, although without the UTB who knows? Before it starts to close it can be really all over the place.

_________________
Burton
http://www.legeytinstruments.com
Brookline, MA.

Post the 235 Hz pattern. This one appears to be the same one as above. It can change slightly if the supports underneath are moved a little bit.

_________________
Formerly known as Adaboy.......

The 199 is definate different some from the 194 as it will go back and forth between them. I'll try and get the 234 pic up for you all to look at. Is it normal for the speasker to get as hot as mine is? I can't hold it bare handed and it seems to start to heat up over 200 hz.

234 Hz.

Hey Chris,

No, it is not normal for the speaker to get hot. I don't know why that is happening. Mine has never gotten hot to the touch. I don't recognize a shape I have seen in your 234 image, at least not that low. Sometimes there is one that is like 3 circle shapes in th lower bout but it is usually much higher, well over 300. It could be that everything is lower without the UTB, I really have no idea. If you are willing to give it a try, maybe you could double stick tape an UTB on your top? Maybe you could float it over the 2 braces you have there. I would be curious to see what changes. I did make one where I used flying buttresses and I had a very small and thin UTB. My results were low, but still resembled a normal guitar. Removing it completely may change it even more.

_________________
Burton
http://www.legeytinstruments.com
Brookline, MA.

Is that a lamintated X brace I see there Chris? Hardwood?

Chris - Sounds like you're getting too much current through your speaker which could be caused by an impedance mismatch. Are you using a 4 ohm speaker on an amp that is rated for 8 or 16 ohm output? The impedance on the speaker needs to match the output of the amp.

_________________
Steve Smith
"Music is what feelings sound like"

The 199 mode looks like it's trying to be a 'ring+', but without the UTB it's not quite making it. In your case, and assuming you use some sort of 'floating' fingerbaord extnesion, I'd be looking at the 'ring' modes rather than the 'ring+'. I tune the rings on archtops.

I use 'A' bracing like yours, plus a UTB, plus a 'chin' on the neck block. My transverse braces have gotten a lot lighter since I started using the A brace, but I still use them, and still think they're a good idea structurally. I'll be interested to see how your guiar without one turns out. I suspect the rest of the top is stiff enough even with the low mode frequencies. THe UTB would shift them up a bit, I think.

Yes Alan I will have a floating finger board as it's a Doolin adjustable neck joint. The extension will be supported by some CF rods next to the 1" neck tenon. That's one reason I wanted to loose the UTB because there will be be 2 or maybe 4 slots cut out to allow the CF rods to clear the top. On the last one I tapered the end of the CF rods so that the rods only cut the UTB about 1/4" deep.
When you tune to the ring what end result are you looking to get? Like I mentioned, when I tap pretty much around the inside of the ring area the tone seems to be pretty much the same and when I tap outside the ring the pitch gets higher which makes perfect sense to me since thats where the high tones are produced. Maybe when I tap on the edge the outside to the node line is more dominate and the tap energy is disapated by the time it reaches the center? I'm just thinking out loud here about some of the stuff I read in the Somogyi book.
The X braces are laminated with CF as per Mario's specs. and I have a Youtube on gluing them up that I believe is in the tut section here.
The speaker is 8 ohm and the amp is also.

"When you tune to the ring what end result are you looking to get? "

I nicely shaped mode, preferably 'closed'. You've pretty much got that. I can't say anything about the frequency, never having tried that.

" Like I mentioned, when I tap pretty much around the inside of the ring area the tone seems to be pretty much the same and when I tap outside the ring the pitch gets higher which makes perfect sense to me since thats where the high tones are produced. Maybe when I tap on the edge the outside to the node line is more dominate and the tap energy is disapated by the time it reaches the center? I'm just thinking out loud here about some of the stuff I read in the Somogyi book. "

I haven't read Somogyi's book yet, so I'm not sure what he says. Basically, from my POV, when you tap inside the node line of the 'ring' you know that, whatever else you're activating, you're getting the 'ring' mode going. Tapping around the edge will activate a lot of other modes that are not as active in the middle as the 'ring', so you will hear them more.

What's the rated power of your speaker, and how does that compare with the amp output? Pure sine waves tend to have higher peak-to-peak voltages than the waveforms they usually use to rate speakers, so puuting 20W of sine wave thorugh a 20W speaker can overload it. Also, some pseaker manufacturers rate them for 'intermittant' power: the coil can take 40W for a little while, so they call it a '40W' speaker, but it's really only good for a steady diet of 20W. As a rule of thumb, for this application, try to get a speaker that's rated at twice the output of the amp.

Thanks again Alan.
Hrer's the speaker I'm using:
http://www.parts-express.com/pe/showdet ... er=290-372
And the reciever plate picture. But the right channel isn't working.

I would bet it's heating up because you are throwing straight tones at it. Most speakers don't really like that kind of tone. They are much more efficient when playing music. Throw a square wave or a simple wave at them, particularly in the low ranges, and they loose most of their efficiency. It'll probably burn up after a period of use, of this type.

_________________
Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Chris,

What Waddy said. I think most speakers are over rated. Also the amp is rated are 165 Watts and the speaker is rated at 40 watts. From that I would tend to believe that if you have the amp volume set to 15%-to 25% of max you maybe putting to much energy into the speaker. You may need a speaker rated at something more like 100 watts. Good luck.

_________________
Eddie Lee

It looks like that's a 16.5W speaker setup, but that could be the total for both speakers; so 8W @. Also, if that's a 'max' power for short term loads, the individual speaker might only be good for about 4W of sine wave. If that's the case, it's no wonder it's hot!

I've been using RadShack speakers rated at 20Wcontinuous/40Wpeak for years. I burn one out every three or four years. They've stoppped selling them, and I'm on the lookout for replacements.

I'm confused as to where the #'s are coming from? If the speaker says it's a 40w. with 70w max. at 8 ohm. then doesn't mean what it says? Wouldn't the reciever be 82.5 watt. per channel at 8 ohm.?
Like I said I'm confused, if I can't believe what the manufacturor has said then how do I know what to get?
I had this speaker first and it burnt up.
http://www.speakerex.com/5300.html

Part of the problem is that you are trying to use music speakers to do sine wave duty. Not really a good combination. Most amps throw pretty low current with high peak wattage out the wires. What you, most likely, should try to find is a guitar speaker that is designed to handle more single note traffic, rather than stereo speakers, which are designed for general music use. You can't use those music type speakers in guitar cabs either. They'll last about 15 minutes, tops, with guitar riffs coming through them. Car speakers are the worst, as they are really at the bottom end of the feeding chain, speaker wise. The difficulty may be in finding one that is small enough for your application. Most are 10 or 12", but there are probably some smaller ones. Check out some places that deal in guitar speakers. Torres Engineering comes to mind. www.torresengineering.com He used to have guitar speakers. I know he sells amp parts and tube amp kits, and stuff like that.

_________________
Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Looks like I might have to check out one of those small speakers in a Bose PA tower or rob one from my 901's.
Thanks for trying to explain this to me guys.
Well I guess it's time to go ahead and close the box then since the ring looks pretty good .
Maybe Alan will have located some speakers by my next top.

Don't rob anything from any kind of stereo system. You'd do much better to rob one out of a 4x10 guitar cabinet or out of a combo amp.

_________________
Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

I agree. But a 4x10" speaker cabinet on a 100 watt guitar amp is using 4 speakers to dissipate the 100 watts. So each speak only gets 25 watts. Here is a link to celestion bass speakers http://professional.celestion.com/bass/orange/index.asp . You can see that they are really beefy to handle the low in power.

As for as wattage, it is hard to tell without seeing the full data sheet but I think that stereo amps are rated per side. So a 100 watt amp is 100 watts per side. The 70 watt max on the speaker rating is for a short burst. A continuous sine wave is the worst scenario because it does not have any peaks and valleys to let the speaker cool down. That is why for your use the 40 watt RMS rating is probably optimistic.

_________________
Eddie Lee

As far as the amp. I'm pretty sure it's a total of 165 watts so it's probably only 40 watts a channel. I have a crown that is 75 watts per channel or 150 watts total and this fisher is no way as powerful as the Crown . The fisher also has 4 fuses, one for each channel.

I think the point is that you need a speaker with a different design than a "stereo" speaker. A guitar or bass speaker will, generally, have better power and sine wave capability, because of the difference in design. There are some out there, if you look around. They, are not, however, cheap. You can probably expect to pay somewhere in the $50 plus range for a speaker. I was just looking at the Carvin catalog, and they have some heavy duty 6" speakers with 200 watt power handling capability and 90 - 8K Hz, range with a 1 1/2" voice coil. They'd be better, but still not the best, as they are monitor speakers, not guitar speakers. The best would be if you could find a 100 watt rms, bass speaker with something like 50 - 3K Hz. I know there are some out there, you just have to find them. Check places like Speaker Doctor, where they repair and rebuild speakers. Sometimes they have used speakers, and they could direct you to the right speaker for the application.

_________________
Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars