Rockin' it old school

[chatziva]

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?

 

[infinia]

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

 

[chatziva]

Hello Infinia! Nice to see you too!

What do you mean by "the gain is at operating at 4 ohms on the woofer"?

 

[infinia]

^
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.

 

[chatziva]

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?

 

[infinia]

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

 

[blue934]

Chatz, where did you find that crossover? I've never seen one posted for that design before. It does look like a decent low cost rocker project. That woofer is very popular.

David

 

[mikejennens]

These are very efficient speakers:

Pi Speaker Kits

Mike

 

[chatziva]

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.

 

[chatziva]

These are very efficient speakers:

Pi Speaker Kits

Mike

Very interesting!

 

[chatziva]

Chatz, where did you find that crossover? I've never seen one posted for that design before. It does look like a decent low cost rocker project. That woofer is very popular.

David

I just googled it before but seems can't find it now...sorry. I quite like how they look.

 

[infinia]

because of the sensitivity advantage I explained earlier above and to support BSC on speaker designs. E.g the woofer needs to be from 6 to 4 dB more sensitive to the upper drivers.

 

[chatziva]

^
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.

Okay I think I understand now. Because P=V^2/R right?

 

[chatziva]

Got it thanks! So going back to the original question, I think it's game over for these as they are not perhaps as efficient as I first thought.

 

[chatziva]

Other options i was thinking about:
-Restoring some JBL L100's
-Back loaded horn Fostex FE206En

 

[chatziva]

These are very efficient speakers:

Pi Speaker Kits

Mike

Now that's efficiency! The 4π kit particularly with the D&C DE250 & JBL 2226 drivers look sooooooo good!

The Eminence combo with Omega 15'' & PSD2002 also looks nice.

Another cheap combo could be PRV Audio D290PY & 15W800A 15"

I somehow feel that a midrange is needed though in all instances

 

[chatziva]

What about this El-cheapo 3-way Infinia? Is it well balanced? Worth exploring more?

-PRV Audio D290Py-B 1" / 8 ohm / 109 db + Horn + Lpad
-PRV Audio 6MB200 6.5" / 8 ohm / 93 db
-PRV Audio 15W800A 15" / 8 ohm / 97 db