Hi everyone, this is my first post here. I've got one of these tweeters wired into the front right speaker outputs on an amp that I got at Goodwill. The amp works fine when plugged into normal speakers, but when there's only a tweeter wired into the amp's right-speaker output, and I play a 1.5 kHz tone at about half volume, after a bit, the tweeter pops, smokes, and fades out.
The setup is:
* a laptop audio out going to the amp's CD inputs
* the laptop plays a 1.5 kHz sine wave
* amp volume dial is about 1/2. The left/right and forward/rear knobs are on the middle.
* the tweeter is impedance matched with the amp (8 Ohms)
* there's not a crossover in front of the tweeter
In trying to characterize the power that the amp is sending to the tweeter, the results were confusing. With a multimeter (or a scope) on the amp-tweeter leg of the circuit, in series it was seeing milliamps, and in parallel, it was seeing millivolts. Since the tweeter is popping and blowing, and the tweeter has a 300W rating, it would seem that the meter should be picking up way more than milliwatts.
Any ideas for measurements I can try, or any obvious thing I've missed here in the setup?
The setup is:
* a laptop audio out going to the amp's CD inputs
* the laptop plays a 1.5 kHz sine wave
* amp volume dial is about 1/2. The left/right and forward/rear knobs are on the middle.
* the tweeter is impedance matched with the amp (8 Ohms)
* there's not a crossover in front of the tweeter
In trying to characterize the power that the amp is sending to the tweeter, the results were confusing. With a multimeter (or a scope) on the amp-tweeter leg of the circuit, in series it was seeing milliamps, and in parallel, it was seeing millivolts. Since the tweeter is popping and blowing, and the tweeter has a 300W rating, it would seem that the meter should be picking up way more than milliwatts.
Any ideas for measurements I can try, or any obvious thing I've missed here in the setup?
You're playing it way too loud. A tweeter only plays the music overtones, and is not very loud in use.
It's easy to blow a tweeter with test tones. The 1.5kHz is below the tweeter's functional low frequency range limit, 2kHz. It sounds like the meter reading is wrong, and there are actually volts, not mV, on the tweeter. A 300W tweeter rating is not likely to say the least, perhaps 1W in its acceptable frequency range. Get the data sheet for the tweeter and check.
It's easy to blow a tweeter with test tones. The 1.5kHz is below the tweeter's functional low frequency range limit, 2kHz. It sounds like the meter reading is wrong, and there are actually volts, not mV, on the tweeter. A 300W tweeter rating is not likely to say the least, perhaps 1W in its acceptable frequency range. Get the data sheet for the tweeter and check.
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300W rating is a misnomer, read the fine print.
They claim 150W RMS ... of MUSIC (not continuous tones) ... applied to a full cabinet (not the tweeter alone) and of course with a crossover.
You are breaking all of the above rules.
The above tweeter can only handle some 5W RMS of pure tones.
An etra rule you broke: frequency response is stated >2000Hz ... which means crossover >3000Hz or so.
You are using 1500Hz .
They claim 150W RMS ... of MUSIC (not continuous tones) ... applied to a full cabinet (not the tweeter alone) and of course with a crossover.
You are breaking all of the above rules.
The above tweeter can only handle some 5W RMS of pure tones.
An etra rule you broke: frequency response is stated >2000Hz ... which means crossover >3000Hz or so.
You are using 1500Hz .
First of all, I find the name of the tweeters ironic. 300W is the max power and I'm sure that number is inflated (meaning it is way higher than the tweeter will actually handle). The RMS power is stated as 150W but again, I wouldn't test that limit. What are the specs of the amp? The response specs of the tweeter say 2k to 20k and you are sending a 1.5k signal to them so probably a bad idea. How long are you applying the test signal? These are $10 units so I wouldn't expect miracles but I think you are misusing them.
Edit: looks like most of my points were covered above...
Edit: looks like most of my points were covered above...
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Falcon10,
Check the amp's output for DC output, only takes a few volts to fry small voice coils. An amp leaking DC, (bad power supply capacitors or some such problem) will take out small woofers too.
A capacitor in series with the tweeter may have saved it, but the "Goodwill" amp is probably going to smoke other drivers soon enough.
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Thanks everyone for all the great replies. I'm a little overwhelmed by the quality of the replies here.
I should've originally stated that I'm relatively new to EE and audio hardware stuff (if that wasn't obvious!), so I don't have most of the common knowledge in this area, so please bear with me
I have a few naive follow-up comments and questions.
1. Doh, I shouldn't have been sending 1.5 kHz to a tweeter rated for 2-20 kHz.
2. Assuming I were actually sending (say) 3kHz to it, is there any reason I'd need a crossover if I'm only sending high frequencies to a tweeter?
3. JMFahey: You mentioned that this tweeter can only handle 5W RMS of pure tones. How did you arrive at that?
4. TBTL: Yeah, it does sound like I should be using a midrange driver with the kind of power I want to send it and the volume I want coming out. I'd like it to be as small as possible, though I really only care about the total diameter of the whole thing (not just the diaphragm, which seems to be what they mean when they say it's a 1" speaker).
5. The stated power rating of drivers is really confusing. I'm gathering that even if they tell you an RMS max wattage, it's assuming that a bunch of that power is actually going to a bunch of other drivers. So how are you supposed to know how much power you can send one particular one before it'll blow up (without blowing one up trying to find out)?
6. A few people mentioned getting the datasheet for the tweeter. I'm not finding anything that looks like a datasheet (at least the datasheets I'm used to, that can be tens or hundreds of pages long). Bassrockers' own site (Bass Rockers 1" 300W 8-Ohm Super Tweeters Pair - BRT2D) doesn't say much more than Amazon does. Is there some specific place I should look for a datasheet, or does it just not exist for cheap consumer drivers like this?
7. I'm not sure anyone said this explicitly, but it sounds like playing a continuous tone is harder on the driver than playing music. Why is that?
8. paulys55 I don't have the amp specs. It's so old that there's not even a product manual for it online. But music does sound good with normal speakers on it, and it doesn't have any DC at its outputs.
9. phase_accurate and weltersys: Good suggestion. I checked for any DC output, and there isn't any.
Thanks again everyone. This is very educational.
I should've originally stated that I'm relatively new to EE and audio hardware stuff (if that wasn't obvious!), so I don't have most of the common knowledge in this area, so please bear with me
I have a few naive follow-up comments and questions.
1. Doh, I shouldn't have been sending 1.5 kHz to a tweeter rated for 2-20 kHz.
2. Assuming I were actually sending (say) 3kHz to it, is there any reason I'd need a crossover if I'm only sending high frequencies to a tweeter?
3. JMFahey: You mentioned that this tweeter can only handle 5W RMS of pure tones. How did you arrive at that?
4. TBTL: Yeah, it does sound like I should be using a midrange driver with the kind of power I want to send it and the volume I want coming out. I'd like it to be as small as possible, though I really only care about the total diameter of the whole thing (not just the diaphragm, which seems to be what they mean when they say it's a 1" speaker).
5. The stated power rating of drivers is really confusing. I'm gathering that even if they tell you an RMS max wattage, it's assuming that a bunch of that power is actually going to a bunch of other drivers. So how are you supposed to know how much power you can send one particular one before it'll blow up (without blowing one up trying to find out)?
6. A few people mentioned getting the datasheet for the tweeter. I'm not finding anything that looks like a datasheet (at least the datasheets I'm used to, that can be tens or hundreds of pages long). Bassrockers' own site (Bass Rockers 1" 300W 8-Ohm Super Tweeters Pair - BRT2D) doesn't say much more than Amazon does. Is there some specific place I should look for a datasheet, or does it just not exist for cheap consumer drivers like this?
7. I'm not sure anyone said this explicitly, but it sounds like playing a continuous tone is harder on the driver than playing music. Why is that?
8. paulys55 I don't have the amp specs. It's so old that there's not even a product manual for it online. But music does sound good with normal speakers on it, and it doesn't have any DC at its outputs.
9. phase_accurate and weltersys: Good suggestion. I checked for any DC output, and there isn't any.
Thanks again everyone. This is very educational.
Experience.
To be more preciseI have not even seen a picture of your actual voice coil, blueprints, or held it in my hands, so this is just an estimation, but I design and build speakers commercially, including winding my own voice coils, so I have practical eperience on what you can or can not achieve.
Your VC claims to be about 1"/25mm diameter , only parameter I know, but since it drives a dome/diaphragm its winding length is probably between 2 and 3 mm, not more.
It also must be very light (to reach high frequencies) which then implies very fine wire, light adhesive, so not strong/heavy Epoxy, rather some kind of light Cyanoacrilate or maybe "self adhesive wire", light former material: Nomex is very good for that although it easily bubbles when subject to higher power, very thin Kapton stands more temperature but is somewhat heavier, aluminum is almost unusably heavy so quite unlikely.
As you see, all design choices to make it a VC fit for a Tweeter conspire to make it weaker.
Just an estimation based on that, makes me suspect such a coil can be damaged with 10/12/15 W RMS, so for safety I´d rate it 5W RMS, maybe 8 W RMS tops, continuous tone applied straight to voice coil.
Now you put that very same tweeter in a cabinet together with matching Woofer and Midrange and a proper crossover, say 3000 or 3500Hz, good slope, at least second order - 12dB/oct or better, and you can drive that *cabinet* with Music (not continuous tones) from a 150W RMS amplifier.
And remember such Music will be listened at "clean", so given its dynamic range, (normal Humans do not like much clipping
) hardly above 10% , maybe 20% of said 150W RMS so in actual Musical use that tweeter will last a long time. All these numbers are estimations, but based on pretty standard ways of using Music related stuff, and in general being conservative.
If you read driver details from bigger/better companies they may give you the test conditions under which they test.
If you read the attached PDF you will see that the tweeter is rated at it's nominal 100Watt power handling under very specific conditions. One of which is a minimum second order crossover [ that is 2 components rolling off low frequencies at 12dB per octave ] and while it does note an ability to handle 450watts system power it is only for 1 second and only under the specific test crossover
If you read the attached PDF you will see that the tweeter is rated at it's nominal 100Watt power handling under very specific conditions. One of which is a minimum second order crossover [ that is 2 components rolling off low frequencies at 12dB per octave ] and while it does note an ability to handle 450watts system power it is only for 1 second and only under the specific test crossover
Yes and if it only has to produce a single tone, the horn can be replaced by a 1/4 wavelength resonator.
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