Ampless Speakers

[cotdt]

I want to be able to drive speakers straight out of an iPod, no amp. It should be small, and have reasonable bass. Doesn't need to be deep.

I tried this with my 87dB efficient speakers and it can play to medium levels, so maybe if I make a 100dB efficient speaker, I'll be set! I was surprised by how loud the inefficient speakers can get without an amp.

My question is, what drivers would be suitable? Remember I want the size to be reasonable, otherwise I would demand 120 dB efficiency!

[sreten]

Hi,

AFAIK power output of I-Pod's and similar is optimised into ~ 32 ohm loads.

For small speakers efficiency is usually low, to allow some semblance of bass.

You could consider Piezo tweeters - high output and high impedance.

Read the Wiki on Piezo's.

http://www.partsexpress.com/pe/showd...number=290-010

Possibly 2 or 3 of the above wired in series.

And some form of crossover / filtering for the bass mid unit.

/sreten.

[richie00boy]

You will probably find that using low impedance (lower than the 32 ohms of headphones) speakers on the i-pod or whatever will break the internal amp and/or power supply after a while.

Maybe you would wire a load of e.g. 3 inch or 2 inch speakers in series to get 32 ohms as well a a reasonable radiating area (=efficiency).

[Spasticteapot]

If I were you, I'd go for some high-efficiency drivers, with 4 wired in series for 32 ohms total.

[cotdt]

Originally posted by Spasticteapot
If I were you, I'd go for some high-efficiency drivers, with 4 wired in series for 32 ohms total.

you mean like 4 fullrangers? that sounds like a good idea.

[Spasticteapot]

Originally posted by cotdt



you mean like 4 fullrangers? that sounds like a good idea.

Yah. The problem is, though that small FR drivers are very inefficient as a rule of thumb, and four FE103's would be ridiculous.
I'd reccomend making a small, portable amplifier for your iPod, perhaps only a few watts. You'd be able to use only 2 drivers, though.

[ruerose]

if building an amp is too much, find a decent computer speaker set and cannibalize the amp out. Don't expect performance from such an amp, and watch the impedance it works at, a lot are 4 ohms

[cotdt]

Well I already have amps both small and big. The reason why I want to go ampless is to study the concept itself, as a way for people to save money and space. My real budget is nearly unlimited, rather I am studying new speaker design techniques.

[Spasticteapot]

Crazy.

However, it won't work: Most headphones use maybe 12mw of power per channel, at roughly .25 volts AC. Some can do up to .4 volts AC, if you really want to crank up your headphones, although the sound quality might degrade.
My advice? Use a low-power buffer, such as the OPA627, if you don't want anything else. That way, you can at least squeeze out a whopping 200 mw at 4v RMS. Not much, but something. (Alternately, use a LM1875 as a buffer, although you'd need more juice.)
That said, even at 100 db/w, you're looking at perhaps 90db at one meter, if you're lucky. And most speakers are'nt that efficient, and you'd be lucky if you can get them that small. On the other hand, you can use multiple drivers, and bi-amp them for a bit more power.

Perhaps tube-buffers might work, if used with output transformers.

[tomtt]

these work rather well-

http://www.lashen.com/vendors/bogen/...ansformers.asp