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| Speaker for frequency response testing http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=24879 |
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| Author: | SteveSmith [ Thu Dec 03, 2009 5:13 pm ] |
| Post subject: | Speaker for frequency response testing |
Did anyone ever come up with a good speaker for testing frequency response? I remember lots of discussion on possibilities and a discontinued Radio Shack part but don't recall if anyone finally found a good one. |
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| Author: | SteveSmith [ Fri Dec 04, 2009 2:27 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
Guess not. I remember a few that didn't work so I'll avoid those and go find something based on the guidelines we were discussing. |
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| Author: | Ken Franklin [ Sun Dec 06, 2009 4:56 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
bump |
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| Author: | JohnAbercrombie [ Sun Dec 06, 2009 6:10 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
SteveSmith wrote: Did anyone ever come up with a good speaker for testing frequency response? I remember lots of discussion on possibilities and a discontinued Radio Shack part but don't recall if anyone finally found a good one. Steve- Can you post a link to the original discussion? It's not clear what 'frequency response' you want to measure- is this getting the various Chaldni patterns on plates? HiFi is another of my interests- there's a lot of info on speakers out there, and some good (cheap) drivers available as well. Cheers John |
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| Author: | Pat Foster [ Sun Dec 06, 2009 6:44 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
I believe Chris Paulick found something suitable for a reasonable price. You could PM him. Pat |
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| Author: | SteveSmith [ Sun Dec 06, 2009 7:32 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
I think this is the last thread: http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=24325&st=0&sk=t&sd=a&hilit=chladni+pattern I've found some speakers (6" woofers) that look like they should work but wanted to see if anyone had found something that they liked before I order something. |
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| Author: | JohnAbercrombie [ Sun Dec 06, 2009 11:23 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
Steve- That speaker that Chris Paulick found http://www.parts-express.com/pe/showdetl.cfm?Partnumber=290-372 would be a good bet, in my opinion. Or if you can find some small cast-off car speakers with higher power ratings, they should work OK. Go cheap so you will not be upset if you burn something up.  I think Alan Carruth makes the point that smaller diameter speakers work better for Chladni (I got the spelling wrong in my last post) patterns, so 4" might be better than 6".. Cheers John |
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| Author: | SteveSmith [ Mon Dec 07, 2009 7:18 am ] |
| Post subject: | Re: Speaker for frequency response testing |
That one did work but it was heating up on him so I've been looking for one with better specs. |
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| Author: | Fred Tellier [ Mon Dec 07, 2009 9:33 am ] |
| Post subject: | Re: Speaker for frequency response testing |
I purchased a 75 watt peak 40 watt rms speaker and it also got hot them went dead, I think we are extremely hard on the speaker doing this testing. I think more rms watts than 40 would be better for us. Fred |
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| Author: | SteveSmith [ Mon Dec 07, 2009 11:28 am ] |
| Post subject: | Re: Speaker for frequency response testing |
I was wondering if these speakers might perform better if they were in some kind of small, sealed enclosure that would provide something to dampen the cone? Maybe we'll just have to stop and let them cool off? I looked at all the 4" woofers and couldn't find one with specs I liked so I ended up getting a 5" from these folks http://www.parts-express.com/pe/showdetl.cfm?Partnumber=295-360&FTR=RS125s-8&CFID=4578491&CFTOKEN=16924565. It's just real hard to find a speaker that small that can handle the power, I guess. I also ordered a 6 1/2" subwoofer that had pretty good specs and wasn't too expensive http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-064&FTR=WFR-06VB04B&CFID=4578491&CFTOKEN=16924565. It was the smallest sub-woofer I could find. I'll be trying both of these speakers over the holiday season and will report back. |
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| Author: | Alan Carruth [ Mon Dec 07, 2009 12:34 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
Steve Smith wrote: "I was wondering if these speakers might perform better if they were in some kind of small, sealed enclosure that would provide something to dampen the cone? " Another can of worms. Carleen knew a local (Montclair) fellow who made high-end speaker setups. He put together a cabinet for her, about the size of a kitchen counter, with the speaker in the center of the top. It was designed to have a 'flat' response (maybe a bass reflex?) and had the cone more or less isolated from the top, so that vibration of the surface would not drive the plates. The speaker was about a 10" one, iirc, and she had a plywood insert that cut the size of the hole down to about 6". There were basically two problems with it: overkill, and ease of use. You only really need to worry about flat response if you're measuring the Q values of the modes. Carleen used to do that when she was trimming bass bars, but so far I have not seen any convincing evidence that it helps a lot. Even so, most speakers won't have sharp dips or peaks in the output themselves, I think: the signal generatore might be another matter. Isolating the top from the speaker vibrations was also not something that was needed, IMO. It takes a fair amount of power to get things going, and the energy that can be delivered to the plate through the pads is limited. Remember, too, that the pads are at nodes: places where it's very hard to drive the mode in question in the first place: it's like pushing the see-saw at the fulcrum. With the speaker under the table like that it took a lot more power to get things moving in most cases that it does with a hand-held speaker. You can get the speaker within a quarter inch of so of the top if you want, and if you're not overlapping node lines that should get a wiggle out of things without massive amounts of power. The original units we made had 50W power amps, because Carleen needed that, but since then, with hand-held speakers, I find thirty to be more than sufficient. Finally, it was always a pain to get the speaker placement just right with the table top unit. With fiddles at least you have a pretty good idea what the modes will look like, but gutiars are a lot more variable. |
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| Author: | JohnAbercrombie [ Mon Dec 07, 2009 1:22 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
SteveSmith wrote: Maybe we'll just have to stop and let them cool off? ...................................(snip) I'll be trying both of these speakers over the holiday season and will report back. I just started watching Alan Carruth's Plate Tuning DVD and he definitely does turn off the sound when re-arranging supports, etc. That may be because (for the video) he's explaining what he's doing and working more slowly than usual. My guess is that if the top is way too thick/bracing too heavy it will take a lot more energy ie 'volume' to get a pattern- perhaps it get's 'easier' as you get things closer to the final 'tuning' ??? If I get some time this week, I'll dig into my 'junk' speaker collection, do some testing and report back. It will warm up the basement, at worst. Cheers John |
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| Author: | SteveSmith [ Mon Dec 07, 2009 1:30 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
What I was thinking may not work, could just be a silly idea. What triggered my thought about using an enclosure was a dim memory (quite possibly invalid) about some speaker cones doing better if they had a 'load' to work against. The load being a fixed volume of air that the cone would have to compress/expand as it worked and, perhaps, provide some damping to the system. I was thinking a sealed enclosure of the same outer diameter as the speaker and maybe only 4 or 5 " long. Close off the end with a plywood plug and put a handle on it. Maybe use a piece of that cardboard tubing they use to roll carpets on. Don't know what this would do to the frequency response of the speaker and have no idea if this would help or not. For sure I'll just try holding the speaker first, not at all recommending anyone try this; this is just the kind of thing that happens to me when I try to sit quietly 
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| Author: | JohnAbercrombie [ Mon Dec 07, 2009 1:51 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
Steve- You are correct in your recollections. I think the problem was finding a way to control cone 'excursion' without spending the cash for large magnets, thus the 'acoustic suspension' speaker and the sealed cabinet. (Prevented the bass from becoming 'flabby' - I believe that's the reason why electric bass cabs are often sealed or ported boxes??) Not sure that it would help in this situation- it sounds like there is just too much (hopefully AC) current flowing in the speaker voice coil, causing heating?? Putting this in an insulated box might make the situation worse re heat buildup.... Voice coils are pretty tough- people take the coils from speakers and use them in attenuators for guitar amps, etc....but that's music, not sine waves. Enough theory- down to the basement!! Cheers John |
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| Author: | dunwell [ Mon Dec 07, 2009 4:56 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
Hmmm, I'm not sure why folks are getting heating of the speaker coil. If you - match your speaker power to the max of your driver - make sure you have an impedance match (watch your 4ohm/8ohm ) between the speaker and driver then you should be able to turn up your driver and not overheat the speaker. I'm running with either a 4" or 6" 40watt/25peak speaker with a 20 watt amp. This is enough for the free plates but a bit wimpy for driving the completed box. I can still get the first three modes which is what I'm mostly interested in. It will get warm after a session but never more than just a handwarmer. Alan D. |
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| Author: | Pat Foster [ Mon Dec 07, 2009 5:20 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
One thing to watch out for when choosing speakers and amps. It's true you can overdrive a speaker and blow it out with a powerful amp. But you can fry a speaker with an amp that's too weak; excessive clipping can happen due to low amp output. the signal to the speaker becomes more like DC, which can fry coils. Pat |
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| Author: | JohnAbercrombie [ Mon Dec 07, 2009 6:53 pm ] |
| Post subject: | Re: Speaker for frequency response testing |
Pat Foster wrote: One thing to watch out for when choosing speakers and amps. It's true you can overdrive a speaker and blow it out with a powerful amp. But you can fry a speaker with an amp that's too weak; excessive clipping can happen due to low amp output. the signal to the speaker becomes more like DC, which can fry coils. Pat As we all know, you can also introduce clipping by giving 'too hot' an input signal to the amp (overdrive pedal in guitar world) so adjusting the input level from the tone/audio generator to the correct drive level for the amp input is also important. So we should be looking at <2 volts into the CD/AUX input of a typical stereo amp, way less into phono or guitar inputs. John |
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| Author: | JohnAbercrombie [ Mon Dec 07, 2009 6:57 pm ] |
| Post subject: | Re: Speaker specs and choice |
When shopping, it's a good idea to keep an eye on the speaker SPL rating in dB- higher # means 'louder' for the same power, so you may be able to get away with a smaller amp and lower W rating for the speaker... and still get that glitter moving. John |
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