>150 ohm impedance speaker to plug directly into headphone jack - Page 1
Forum section: electronics / general

author: dcarr
author_rank: Regular Contributor
timestamp: February 16, 2018, 05:14:00 am
content: Hi there,I'm looking for a passive speaker solution that could plug directly into a jack intended to drive headphones. Audio quality is not a priority.The headphone output is rated for a minimum 150 ohm load impedance which is higher than most small speakers I can find. I guess a transformer would be another option if such a speaker isn't available.Any ideas out there? I've struck out so far at Digikey, etc.Thanks!

author: helius
author_rank: Super Contributor
timestamp: February 16, 2018, 05:32:02 am
content: Most headphones are higher impedance than full-size speakers (although some are not: low-impedance cans have been tried, like the Sony MDR-F1). But the more important factor is probably power output. Just 50mW into a set of headphones can be incredibly loud, but will be barely audible in most full size speakers. They are not even close.Speakers with higher efficiency used to be made about 50 years ago for tube amplifiers, but for a long time they were unavailable. Since there is a renewed interest in low-output tube amplifiers now, there may be "boutique" drivers made to suit them, but I expect they come with a high price premium.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 16, 2018, 07:27:23 am
content: Quote from: helius on February 16, 2018, 05:32:02 am50mW (17dBm) into a pair of headphones would be deafening - on the order of 117dBA output. Typical listening levels for headphones are more like -30dBm. That said, 20dBm or more peak is easily achieved by most headphone outputs and hence the problem of kids who think it's cool to listen with the volume turned all the way up.That said, passive 3.5mm jack speakers do exist and work OK when volume is not a high requirement. It used to be that the cheapest computer speakers worked that way, but nowadays most have some sort of amplifier. Maybe you can find something similar at the dollar store.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 16, 2018, 07:56:58 am
content: As others have mentioned, the power output available from a typical headphone output is unlikely to be sufficient to drive even a speaker of the matching impedance. The available power is a much larger factor than a matching impedance. Certainly it is easy enough find a 150 ohm transformer to whatever matches your speaker driver. But I wouldn't expect to hear much unless you hold you ear against the speaker.

author: helius
author_rank: Super Contributor
timestamp: February 16, 2018, 08:38:36 am
content: Speaker drivers have lower output efficiency (dB/W) than they used to, because they use heavier cone materials and are tuned for better bass response, both of which reduce efficiency. A maximally efficient speaker would be very large, have a high bass rolloff, and use the lightest possible cone material. Since the move to compact/bookshelf speakers on the low end of the market, and stiff sandwich/fibre cone materials at the high end, they are now scarce.

author: BrianHG
author_rank: Super Contributor
timestamp: February 16, 2018, 09:04:27 am
content: 150 ohm will have such low volume unless it's right in your ear, and still then, the volume will be less than a 32 ohm headphone. On the other side, I've actually got some ok volume within a room by wiring some normal Paradigm 8 ohm loudspeakers directly onto the headphone out of both my laptop and portable CD player.