Rockin' it old school

chatziva

Member
2007-06-07 8:30 pm
I am in the process of building my first low wattage class A amp and so I thought it would be good to also build an efficient pair of speakers to go with it. It's been a long time since I've build speakers and its time to upgrade (really I am looking for any excuse to build stuff).

I came across this design which looks very interesting. Efficient and relatively inexpensive.

Speaker Project - Rockin' It Old School -- 12/31/2013

Other alternatives I've been thinking about:
-ZDT 3.5
-Something fullrange

-Has anyone built those speakers? Impressions?
-How might they compare to the other options?
 

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infinia

Member
2005-05-15 9:51 am
SoCal
Hi Chatziva good seeing you around!

I haven't studied your links but my 1st impression is that design is low to average eff. it's a numbers game thing! "the gain" is by operating at 4 ohms on the woofer see the resistor pads on the mid range killing real eff.
also investigate 4 ohms on Class A designs
 

infinia

Member
2005-05-15 9:51 am
SoCal
^
since most amplifiers hold voltage constant say at 2.8V RMS , when you attach a 4 ohm speaker the power increases by 3 dB over an 8 ohm speaker with equal efficiency. So when looking at speaker sensitivity make sure it is the power you are comparing otherwise its a false eff. gain.
 
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chatziva

Member
2007-06-07 8:30 pm
I see. The mid driver has 94db sensitivity and the woofer & tweet 92db so presumably the L-pad only drops 2 db to bring everything to 92db?

I will sim the xo/spk but I think it looks like a predominantly 4 ohm speaker. If so I will get that 3db gain you were talking about.

So overall I think it should be a pretty efficient pair at >92db, no?
 
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infinia

Member
2005-05-15 9:51 am
SoCal
sensitivity is changed by a voltage divider 20LOG(X/(X+Rpad))
where X= impedance of the speaker in parallel with any zobel

so looking at the mid X~8 ohms, 20LOG( 1/2) = - 6dB

so the whole speaker eff can be roughly estimated by reducing the midrange sensitivity downwards by 6 dB. or 94-6 ~88dB
which IMO is decent if the woofer gain is several dB higher for bass to appear. or good reasons for selecting a woofer @4 ohm!

BUT class A is limited by bias currents and may be unhappy to drive a 4 ohm woofer
 
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chatziva

Member
2007-06-07 8:30 pm
sensitivity is changed by a voltage divider 20LOG(X/(X+Rpad))
where X= impedance of the speaker in parallel with any zobel

so looking at the mid X~8 ohms, 20LOG( 1/2) = - 6dB

so the whole speaker eff can be roughly estimated by reducing the midrange sensitivity downwards by 6 dB. or 94-6 ~88dB
which IMO is decent if the woofer gain is several dB higher for bass to appear. or good reasons for selecting a woofer @4 ohm!

BUT class A is limited by bias currents and may be unhappy to drive a 4 ohm woofer

Thank you for the explanation. Just a question, so why would a 4 ohm woofer would be better than a 8 ohm one?

The amp I am building is an M2 clone from Nelson Pass. It should be happy driving 4 ohms.