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Old 18th May 2004, 11:49 AM   #1
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Default Elf 1.0

Hi all, I recently ordered a 5 elf 1.0 kit and was wondering if I add a 100hz cap how much power will I be able to drive them with and how much audible low end will i loose?
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Old 18th May 2004, 12:52 PM   #2
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model the system in WinISD. It will show you teh maximum power handling based on your input of the driver parameters.

with a single capacitor in series with the system, response will roll off at 6 db/octave below the cutoff point. Actually, it starts rolling off above tehcutoff point and eventuallyhits a 6db/octave slope, but for this exercise, assume a sharp transition to the final slope. to get a 100 Hz crossover, you'll need almost 200 uf.

take your unfiltered response and subtract 6 db at 50 hz, 12 db at 25 Hz and connect the dots to give you an approximation of the filtered response.

check the maximum input power graph in winisd for the answer to your other question. overlay the filtered driving power curve (flat down to 100 hz, dropping 6 db (1/4 max power) at 50 Hz.) to verify that the filter has bought you the increased power handling you were looking for.

Win ISD may or other programs may be able to apply the filters to give you the answers drirectly, but I haven't figured it out and tend to go for the brute force solutions anyway.

Hope this helps
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Old 18th May 2004, 12:57 PM   #3
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The resonant frequency of that tangband is right around the 100hz region, so your 200uf isn't going to have anywhere near the behavior that you'd expect until you go beyond the resonance peak. It'll definately help power handling, but I would be careful that you don' t get too optimistic by assuming a linear 6dB/octave drop.
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Old 18th May 2004, 01:43 PM   #4
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Right, Jim. I ddin't realize that the resonance of teh ELF was so high.

WinISD's maximum input power curve takes into account resonant behavior and thermal limits - flat at Pd above resonance and excursion limited below.

so far so good, but at resonace the impedance rises considerably, so the 200 uf that was roughly 8 ohms reactance at 100 Hz is much smaller in relation to the 40 ohms (guesstimate) of the speaker. this means that the signal is attenuated much less than my original model would indicate.

The good news is that your amp delivers a voltage based on the signal and currrent based on that voltage and the speaker's impedance. So a ~28V RMS signal (100 watt RMS at 8 ohms) will only deliver 20 watts to the driver at resonance if the impedance rises to 40 ohms. below resonance the imedance falls again, so the capacitor would be more effective.

Of course, driving virtually any speaker to it's limits will mean hearing damage if done long enough. So I figure that this exercise is really about "will my speakers survive" comfort factor. A decent sub and a 24 db/ octave crossover (probably built into your reciever) to your ELFs would make this whole discussion moot.
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Old 18th May 2004, 03:27 PM   #5
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I will be using 3 elf's for HT, a center and 2 rears, the amp is a Nakamichi AV-2s with 80w rms per surround chanel...do I need to cap these? thx for your replies guys but you are all way ahead of me, may as well be chineese....me=n00b.....so a 200nf cap on the positive leed of each TB will do the trick of handeling more power without loosing the general sound and still have a bit of low end?....even so I would not blast them anyhow, on a side note I had a couple PSB bi-polar surround speakers or somthing like that they had 4 drivers opposed to each other out of phase....they were rated 80W rms and they blew on the Nak whatching a movie hehe
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Old 18th May 2004, 04:02 PM   #6
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I don't know your receiver, but it sounds like you are worried about having more amp power than your speakers are rated to take. if this is the case, forget the caps completely. Your receiver will take the deep bass power out of the Elfs and send it to the sub. Having too much power is not a problem unless you try to blast out a party.

For normal listening/movies, the average power is likely to be below a couple of watts. All that the extra amp power does is sit there in reserve waiting for transients. In this case it is better to have more power so that you are less likely to clip your amp. Tweeters I've blown by clipping a small amp, but I've never blown a woofer.

My daughter blew some woofers when she had friends over and drove her 6" woofers with both the loudness on and bass turned up full for hours. I guess the moral of the story is don't try to get too much deep bass out of your Elfs (or any small speaker), let the sub handle it. The Elfs will be happy driven directly from your receiver.

Quality capacitors that big are going to be expensive and may impact the top end of your Elfs, so spend the money on some good recordings instead.
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