Speaker watts same as electrical watts? - Page 1
Forum section: electronics / beginners

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: June 19, 2018, 04:36:41 pm
content: I am looking for a 230 to 110Vac converter / tranformer for thesehttps://www.monoprice.com/product?p_id=605800Speaker rating is given as total of 120W rms output power.How much input (electrical) power would these consume, would it be same as the 120W rms output power.Should I go in for a 110V, 250W transformer considering that each speaker would consume 120W, so a pair would consume a max of 240W (rms).

author: wraper
author_rank: Unknown
timestamp: June 19, 2018, 04:45:10 pm
content: Active speakers should have consumed power rating. Also amplifier efficiency and PSU power factor plays a big role.

author: wraper
author_rank: Unknown
timestamp: June 19, 2018, 04:49:30 pm
content: QuoteDo you need a transformer at all?

author: IanB
author_rank: Super Contributor
timestamp: June 19, 2018, 04:52:01 pm
content: Quote from: wraper on June 19, 2018, 04:49:30 pmSnap! I was just about to ask the same question.

author: wraper
author_rank: Unknown
timestamp: June 19, 2018, 04:56:34 pm
content: Actual speaker seem to have 100-120V written on it. In any case I could first take it apart and see if it has a transformer with multiple taps so could be reconfigured for 230V.

author: IanB
author_rank: Super Contributor
timestamp: June 19, 2018, 04:57:42 pm
content: Quote from: ZeroResistance on June 19, 2018, 04:36:41 pmI know this is a bit off topic and slightly pedantic, but it always puzzles me when I see this. You appear to live in the UK where the standard supply voltage is 240 V AC, 50 Hz. You are looking at a product for the USA market where the standard supply voltage is 120 V AC, 60 Hz. So why 230 V to 110 V? You would be better off looking for a 240 V to 120 V transformer (if indeed you need one at all).To the power question, amplifiers have an efficiency and may produce some waste heat. So the input power will be slightly higher than the output power. On the other hand, you are unlikely to be running the speakers at full volume, so they will not be running at full power. On the third hand, it is always good to have an operating margin on the power supply. So probably go with 300 W or more power rating on the transformer.

author: IDEngineer
author_rank: Super Contributor
timestamp: June 19, 2018, 05:07:31 pm
content: Given how the specs read on Monoprice's website, it's almost certain those speakers have a switch - likely integrated into the power cord socket - that allows you to select either ~120VAC or ~240VAC. That switch will reconfigure the primary side of the power transformer inside.If this were a smaller device that consumes less power, it would probably have a switching power supply and would take 90-250VAC with no manual switch at all. But for speakers like that it's likely cheaper to build a basic linear power supply with a transformer that has a tapped primary. The spec sheet makes it very clear that the speakers accept either of two voltage ranges.You're working too hard. You don't need an external transformer. All you need is a power cord that runs from the standardized cord socket to your choice of line plug. Be absolutely certain to confirm that the switch is set to your local AC voltage and you'll be just fine.

author: jdraughn
author_rank: Regular Contributor
timestamp: June 19, 2018, 05:33:34 pm
content: You can look at the picture on the website and see there is no switch.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 19, 2018, 05:46:18 pm
content: While the website says: "Power Requirements: 100 ~ 120 VAC, 60Hz or 200 ~ 240 VAC, 50Hz"The manual PDF says: "Power Requirements: 100-120 VAC 60 Hz"And it comes with a North American power cord: "IEC 60320 C13 to NEMA 5-15"https://downloads.monoprice.com/files/manuals/605800_Manual_130828.pdfIs Monoprice an international brand name? I went to monoprice.uk And while it has the same name and logo, it appears to be completely different products. Including no mention of speakers of any kind.

author: Brumby
author_rank: Unknown
timestamp: June 20, 2018, 01:15:58 am
content: Quote from: Richard Crowley on June 19, 2018, 05:46:18 pmI did the same tour.Might be a question for the manufacturer. It could be possible that they have two versions, one for each voltage. The specifications do not make this clear at all.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: June 20, 2018, 01:52:55 am
content: Thanks, Thanks and many thanks for all the answers.I can confirm and as jdraughn also rightly says there is no switch (voltage switchover) on the external panels of the enclosure.There could be one inside the speaker, interestingly the fuse is rated at 250V AC.The supply rating mentioned on the rear panel is 110 to 120VAC, 60Hz

author: IanB
author_rank: Super Contributor
timestamp: June 20, 2018, 01:54:59 am
content: Do you have the speakers in your possession? Have you opened one up to look inside it? Pictures would be interesting.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: June 20, 2018, 02:17:46 am
content: Quote from: IanB on June 20, 2018, 01:54:59 amI took them apart there is a transformer at the input with a power switch and fuse in series with the primary, there seems to be no extra tapping on the primary (just 2 wires). Unfortunately I reassembled them back without taking any pictures. And then I just read your post, I will surely post pictures the next time I dissasemble it.

author: IDEngineer
author_rank: Super Contributor
timestamp: June 20, 2018, 03:44:44 am
content: Bummer. Sounds like they have two different transformers for the two different markets. Someone probably just copied the generic spec sheet from the Chinese manufacturer without realizing that it's "one or the other", rather than "either".If you're still looking for a way to run these 120VAC units on 240VAC, and you have to find a suitable transformer anyway, I'd look for a replacement for the 120VAC unit already in the speaker. It might be a standard physical size, and if you can match the secondary this would be the cleanest solution.

author: Zero999
author_rank: Super Contributor
timestamp: June 20, 2018, 09:04:31 am
content: Quote from: IanB on June 19, 2018, 04:57:42 pmAvailability? 110VAC is a very common voltage on building sites, in the UK and transformers are widely available.QuoteManufacturers also exaggerate the power output of their amplifiers, so it's a tricky one.If the amplifier really is rated to 120V RMS, then I'd probably suggest a similar sized transformer, since the average power output, even at high volumes, will probably be around1/8of the maximum and the transformer will be able to withstand the surges.

author: Jwillis
author_rank: Super Contributor
timestamp: June 21, 2018, 04:25:32 am
content: According to the specs their are 2 amplifiers inside .A 40 watt for the tweeter and an 80 watt for the woofer .This seems to be where they get the 120 watts from .So really all you need to know is the VA of the secondary side of the existing transformer to match it for a 240V.Be on the safe side and get one with a bit higher VA

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 21, 2018, 05:03:04 am
content: A 250W transformer will likely be plenty for a pair of those speakers.You could probably even use a 200W transformer unless you are listening to head-banging acid rock or something.

author: Brumby
author_rank: Unknown
timestamp: June 21, 2018, 06:10:11 am
content: That's very likely going to be the case.120W RMS is a LOT of sound unless your speaker is 2 wires clipped to a piece of damp cardboard.