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Old 22nd May 2012, 04:14 AM   #1
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Location: Devonport, Tasmania
Default Tweeter power requirements???

Hello there and greetings from sunny, tropical Tassie.

My understanding is that woofers use heaps of power compared to tweeters. I imagine that the higher the crossover frequenccy the lower the tweeters demand for current.

Is there a book out there that simplifies the subject? or website calculator? Perhaps just a good old formula?

Specifically I want to know what the tweeter's power requirements are, as a PROPORTION (at any given frequency) of the available power.

Yours sincerely, Phil - aka farmerjack
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Old 22nd May 2012, 05:48 AM   #2
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Hi ,
the first time that I've read about power delivered to various drivers in a LS system was in a magazine many years ago ; it was an article about bi-amplification ( also tri-....)and it talked also about the necessity of putting a capacitor before the tweeter to prevent failures . I don't remember the exact percentages , maybe 70% for woofer and 30 % for a tweeter in a two way system ,and 50-30-20 for a three way .
Most tweeters usually have a usable power of 10 W ; I had a pair of Infinity speakers that had a PTC resistor on the tweeter section , and often it put them to 'mute' for some seconds ! nowadays you can find more powerful tweeters and with lower Fs so they can be less damaged by occasional power surges .
It depends on your listening habits and what music program is playing ; also
the amplifier mustn't distort , because the product of distortion on higher harmonics is likely to blow a tweeter's coil .
Ps. I have a 2 way system with a woofer claimed to be 150 W ( max ) and the tweeter....2 W !!!

Last edited by picowallspeaker; 22nd May 2012 at 05:50 AM.
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Old 22nd May 2012, 06:36 AM   #3
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There is not going to be a simple answer to this question as It will be very dependant on source material.

A couple of tips though:
- look at a tweeter voice coil. Even with ferro fluid the power handling is a few watts for domestic drivers.
- the efficiency of most tweeters is significantly greater than bass drivers
- the spectral content of typical music is way down in the frequencies at which tweeters operate. Ok this is more or less what you asked - the power handling of all "normal" tweeters is adequate.
- failures I have seen in tweeters have been because of -1- poor crossover design -2- clipping amplifier -3- running an oscillator into the system particularly in the form of an unstable amplifier


On failure mode -1- trying to push the crossover too low is a bad idea also running too close to resonance Is asking for problems. Your crossover will usually have bags of attenuation on the tweeter so this forms fair protection for the driver.

If you are sizing an amplifier for an active system, I have normally used a power amplifier for the tweeter that is in the region of 25 percent of the bass amp. I honestly think I could get away with less as in an active system there is no attenuation on the tweeter. You should put a dc blocking cap though.

Clipping amplifiers should not be such an issue unless you are a 16 year old or drunk. I am sometimes both at least in spirit ...

Oscillating amplifiers are a silent killer though are usually fatal to themselves too.

Hope this helpsn
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Old 22nd May 2012, 09:45 AM   #4
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Quote:
Originally Posted by picowallspeaker View Post
and the tweeter....2 W !!!
Awesome! Thanks Pico'. I have fitted an Adjustable L-Pad to the tweeters on this speaker & by trial and error I have found that;

Despite the woofer(s) and tweeter(s) identical effeciency rating of 95db/W/M the HF drivers have to be cut by a huge factor. My L-Pads are running on the 'power redline' because the Vifa BC25SC75-08 silkies don't seem to hack the pressure. The pdf datasheet said 50w for the drivers, but I think they will use about 5wrms tops.

A though just struck me... I can find the 'sweet spot' using the Adjustable L-Pad and then replace it with fixed high power golden coloured resistors - Or supplement the Adjustable one with a fixed pair of resistors - call it a 'pre-cut'.

My new speakers stand 1200 high x 450 wide x 320 deep, have two 12" redback $69 woofers in the bottom and two vifa $25 tweeters in the top. The box volume and portage (160litres volume minus the 3 x 90mm downpipes x 850mm ea). was designed on WinIsd speaker design software. I have only been running them for a few days but despite my tweeter connundrum, I am very very happily chuffed with the result.

Cheers Pico. Phil

Last edited by farmerjack61; 22nd May 2012 at 09:54 AM. Reason: spelling
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Old 22nd May 2012, 10:05 AM   #5
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Quote:
Originally Posted by picowallspeaker View Post
and the tweeter....2 W !!!
Awesome! Thanks Pico'. I have fitted an Adjustable L-Pad to the tweeters on this speaker & by trial and error I have found that;

Despite the woofer(s) and tweeter(s) identical effeciency rating of 95db/W/M the HF drivers have to be cut by a huge factor. My L-Pads are running on the 'power redline' because the Vifa BC25SC75-08 silkies don't seem to hack the pressure. The pdf datasheet said 50w for the drivers, but I think they will use about 5wrms tops.

My new speakers stand 1200 high x 450 wide x 320 deep, have two 12" redback $69 woofers in the bottom and two vifa $25 tweeters in the top. The box volume and portage (160litres volume minus the 3 x 90mm downpipes x 850mm ea). was designed on WinIsd speaker design software. I have only been running them for a few days but despite my tweeter connundrum, I am very very happily chuffed with the result.

Cheers Pico. Phil
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Old 22nd May 2012, 10:53 AM   #6
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mmmh , Phil ?

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Old 22nd May 2012, 11:10 AM   #7
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Clipping amplifiers should not be such an issue unless you are a 16 year old or drunk. I am sometimes both at least in spirit ...

Hello googlyone, I have been building speakers for a few years now. In the beginning, I arrogantly assumed that it was an easy task - a 'no-brainer' as the kids would say. I was wrong again!!!

Speaking of kids, today I was playing air-guitar on my straw broom whilst listening to a good blues album and dancing the vegie stomp. Thank goodness the blinds were drawn cause I'm sure it was a hideous sight! - music is what it is all about for me.

Here are a couple of piccies of the speakers (black grilles yet to come for the woofers and a satellite enclosure for the sound dynamics horns also).
Thankyou for your response. Bye for now, Phil
Attached Images
File Type: jpg tweeter fz copy.jpg (66.8 KB, 84 views)
File Type: jpg Tweeter circuit.jpg (68.8 KB, 84 views)
File Type: jpg Woofer fz.jpg (97.3 KB, 81 views)
File Type: jpg Woofer circuit.jpg (43.2 KB, 81 views)
File Type: jpg photo of red spkrs.jpg (252.9 KB, 21 views)
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Old 22nd May 2012, 01:29 PM   #8
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Making noise is easy. Making good noise is a lot harder. Making loud and good noise is both had and expensive. It is a bit like cars = you can choose any two of:
- good quality sound
- high SPL
- cheap

That said, with some careful selection you can find a fair compromise on most of these.

An older pic of a few of my toys - though I am of late more into DSP and active systems. Linking back to the original thread - the power drive the top end compression drivers at in my PA based system is usually a few watts. JBL 2445 gets 150 watts MAX ever - and will tear your eardrums out at a dozen paces at that level. The super tweeters JBL 2402 get maybe 40 watts.

Phil
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Old 22nd May 2012, 05:48 PM   #9
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Quote:
Originally Posted by googlyone View Post
Making noise is easy. Making good noise is a lot harder. Making loud and good noise is both had and expensive. It is a bit like cars = you can choose any two of:
- good quality sound
- high SPL
- cheap
Maate, you look like the great Buddah himself perched up there!! I am a musician also, I play acoustic steel string guitar and love to sing blues although generally speaking people tell me I suck. I use open tuning (slide tuning) so that I can play with 4 fingers as I am a mutant.

It has been great talking, and by the way, My brother has a nice set of JBL's too, they are hifi speakers about the same size as mine with only one 12" golden coloured bass driver in a 3-way cabinet. They are the the smoothest warmest speakers I have ever heard in combination with his Harman Kardan 150W amp. Andy paid about 2000 dollars for his system.

I have another acquaintance who runs an old rotel of the same size with a pair of 2-way VAFs which use kevlar woofers and what appears to be a titanium bullett, These sound very good also but for my money the JBL's are way better sound and only cost about $1000 compared to the VAF's which I would guess cost twice that amount.

I've said it before and I'll confess again, I just love the sound of a largish paper cone!!!

Bye for now.

Last edited by farmerjack61; 22nd May 2012 at 06:12 PM. Reason: punctuation
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