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Old 11th December 2006, 02:21 PM   #1
ijomojo is offline ijomojo  Austria
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Default F1 for open baffle?

hi there,

i need some advice for a pwr amp project suiting my latest (still under construction) diy loudspeakers: the phy-hp km 30 in open baffle configuration
first watt f1 would be my favourite, but im not shure if it goes well with open baffles
specs of the speakers:
KM 30
your advice is greatly appreciated

Joe
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Old 11th December 2006, 05:54 PM   #2
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It works quite well with open baffles.
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Old 11th December 2006, 06:31 PM   #3
lineup is offline lineup  Sweden
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Quote:
Originally posted by Nelson Pass
It works quite well with open baffles.
Click the image to open in full size.

That speaker unit is:
12" - 97dB - 16 Ohm

97dB is great for F1.
How about Z, impedance 16 Ohm?
Of course it would work, but how well?

One of the problems with proportional current amplifiers
is they can get problems when impedance gets too high,
because this needs more voltage to produce equal power
in accordance to input signal.

One solution here, if F1 is optimized for 4-8 Ohms speakers,
is paralleling two KM30.
This would give a speaker with:
SPL 100dB at 8 Ohm.
But this would not be sound coming from only one point at baffle.


Can you find some similar Unit that has got 8 Ohm impedance.
This would be best solution, in my opinion.
-----------------

16 Ohm speaker drivers are not too common these days.
But can be very interesting for some special amplifier projects
In my opinion, the control of driver and so possible Sound Quality
is getting better at higher impedance.
Most HiFi speakers are 8 Ohm ( or at least 6 Ohm ), you know.
Not 2/4 Ohm, usually.


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Old 11th December 2006, 06:59 PM   #4
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My presumption is that an F1 user will experiment with
loading in order to get the best response. While the F1 is
happy with any impedance, at the resonance of the speaker
the impedance might be high enough that you find yourself
running out of voltage. Some resistance in parallel with the
load will fix this and also adjust the Q of the speaker.

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Old 13th December 2006, 03:56 PM   #5
ijomojo is offline ijomojo  Austria
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Thank you for replies,

Though the impedance of the wide range unit will rise to 127 @ resonance, putting some resistance in parallel may do the trick.. I am not afraid of experimenting, so when Mr. Pass says it works well with open baffles, why dont give the F1 a try
I was just wondering about the impedance of the (inherently filtered) tweeter unit: Z=70 Ohm
I have never seen something like that but i guess it will not have any influence on the amp..
Btw, do you like the bronze baskets? I do

regards,


Joe
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Old 13th December 2006, 07:09 PM   #6
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Quote:
Originally posted by ijomojo
I was just wondering about the impedance of the (inherently filtered) tweeter unit: Z=70 Ohm
If it really is 70 ohms at the top end, you probably will want to
throw some resistance across it. I would start with 22 ohms
or so.
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Old 13th December 2006, 11:31 PM   #7
ijomojo is offline ijomojo  Austria
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Thanks again to The One and Only
Looking closer to the tweeter unit of the coax speaker, I see a rise of 20 ohm in impedance at operating frequency, going up to Z=90.
Please correct me if i am wrong: assuming that best matching to the F1 is only possible either with the wide range OR the tweeter unit, it would be the best to go bi-amping, as this would be posible with the same supply and (rather cheap) connectors. The costs for doubbling the output boards arent that high except of the larger heat sinks required to dissipate the doubbled amount of power.
Please let me know what you think about it

regards,

Joe
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Old 14th December 2006, 12:28 AM   #8
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by ijomojo
....................... The costs for doubbling the output boards arent that high except of the larger heat sinks required to dissipate the doubbled amount of power.
Please let me know what you think about it

regards,

Joe

tip:
you don't need same amount of Iq for tweeter amp as for bass amp
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