How do I test amplifier speaker output polarity?

audioguru · May 16, 2022

In the good old days, every shopping mall had an audio equipment store and the salesmen always connected the speakers put-of-phase then turned up the bass to max to try to get some bass. I always fixed the phase and turned down the bass.

Hacdrag · May 16, 2022

audioguru said:
Your new recording is correct. The out-of-phase parts made me feel weird.
Some modern little speakers produce bass. I saw one on sale at Costco and I could not find their hidden subwoofer because the little speaker was doing it. It gave me goose bumps to hear the bass produced by the little speaker. It was expensive.

I found the order, and back in 2019, I spent less than $20.00 on this pair of 2.5-inch 8 Ohm speakers. Actually, my multimeter shows the speakers to be 7.2 Ohm.

https://www.amazon.com/Visaton-FRS7-8-2-5-Full-Range-Speaker/dp/B003EA03PK

I bought these on sale from another vendor.

Interestingly enough, the specs have the frequency range for 200 - 20,000 Hz, but if I play a YouTube Hz test through the pair at a listening distance of 9.5 feet, I hear the response all the way down to 62 Hz. Right in front of the speaker, I can hear the sound down to around 50 Hz, and with my ear to one of the speakers, I can hear the rumbling start even lower.

As I found out when frustratingly testing the phasing, the bass response when playing actual music is much worse than the pure bass signals.

In any event, I'm not complaining at all about the cheap speakers. They serve the purpose for some small electronic projects.

Solving the problem has been a learning experience.

I can't figure out how to undo my bad quotes, but Ramussons:

Not a bridged amplifier. I'm too tired to record my results now, but I'd like to reserve the right to continue the thread with my multimeter readings for your first test, as I'm having a hard time proving your theory with the first test. In a nutshell, with some multimeter settings where I get a reading for HOT-HOT, Hot-Cold just gives me -OL, regardless of where the positive and negative leads go.

I'm sure I can learn more with replies to my readings.

audioguru · May 16, 2022

Your speaker resistance of 7.2 ohms probably includes the 0.5 ohms of your multimeter leads.

A speaker should have a flat frequency response so that all frequencies are at the same sound level. The tiny Visaton FRS7 speaker sounds boomy at about 300Hz then its levels at lower frequencies drop a lot. At 100Hz its sound level is fairly low. Its sound level is much less at lower bass frequencies. It produces a squeaky shriek at 10kHz but only directly in front of it.

The bass levels of a speaker are greatly affected by its enclosure that should be made for the detailed specs of the speaker.

Hacdrag · May 16, 2022

audioguru said:
Your speaker resistance of 7.2 ohms probably includes the 0.5 ohms of your multimeter leads.

A speaker should have a flat frequency response so that all frequencies are at the same sound level. The tiny Visaton FRS7 speaker sounds boomy at about 300Hz then its levels at lower frequencies drop a lot. At 100Hz its sound level is fairly low. Its sound level is much less at lower bass frequencies. It produces a squeaky shriek at 10kHz but only directly in front of it.

The bass levels of a speaker are greatly affected by its enclosure that should be made for the detailed specs of the speaker.

Ty 4 the informative reply. I just looked up the data sheet for my speakers (https://www.visaton.de/en/products/drivers/fullrange-systems/frs-7-8-ohm) It lists nominal impedance Z (what the heck does the "Z" represent) as 8 Ohm, but it's rating for DC resistance matches my 7.2 Ohm reading. Some quick Google research sheds a little light on the difference between actual Ohms and DC resistance and how multimeters report the DC resistance, even with Ohms selected. I need to get to sleep and will look around some more tomorrow.

A friend of mine made the enclosures. He did a good job, but it looks like the fit could be a little tighter. Maybe if I stuffed them, I could get a little more bass response. Not that big of a deal and I'm not putting in the effort. I have other projects to work on, and I already have a good enough home theater system with a more powerful amp, bookshelf speakers, and a subwoofer. This was just something to play around with and to learn from.

I'm curious, how do you know what my speakers sound like? Have you heard them, or did you find another data sheet, or read some reviews?

Nigel Goodwin · May 16, 2022

Hacdrag said:
I found the order, and back in 2019, I spent less than $20.00 on this pair of 2.5-inch 8 Ohm speakers. Actually, my multimeter shows the speakers to be 7.2 Ohm.

https://www.amazon.com/Visaton-FRS7-8-2-5-Full-Range-Speaker/dp/B003EA03PK

I bought these on sale from another vendor.

Interestingly enough, the specs have the frequency range for 200 - 20,000 Hz, but if I play a YouTube Hz test through the pair at a listening distance of 9.5 feet, I hear the response all the way down to 62 Hz. Right in front of the speaker, I can hear the sound down to around 50 Hz, and with my ear to one of the speakers, I can hear the rumbling start even lower.

As I found out when frustratingly testing the phasing, the bass response when playing actual music is much worse than the pure bass signals.

In any event, I'm not complaining at all about the cheap speakers. They serve the purpose for some small electronic projects.

Solving the problem has been a learning experience.

I can't figure out how to undo my bad quotes, but Ramussons:

Not a bridged amplifier. I'm too tired to record my results now, but I'd like to reserve the right to continue the thread with my multimeter readings for your first test, as I'm having a hard time proving your theory with the first test. In a nutshell, with some multimeter settings where I get a reading for HOT-HOT, Hot-Cold just gives me -OL, regardless of where the positive and negative leads go.

I'm sure I can learn more with replies to my readings.

Speakers are rated in impedance, not resistance - and a resistance meter will always read low - an 8 ohm speaker usually reads about 6 ohms, and a 4 ohm speaker about 3 ohms. Your 7.2 includes the resistance of the meter leads and connections.

You should also bear in mind that speaker impedance varies wildly with frequency, and it's rated value is as much a guess as an average.

audioguru · May 17, 2022

The Visaton company is in Germany so maybe they spell impedance as "Impedanz".

The datasheet for the FRS7-8 tiny speaker shows a resonance at 220Hz without an enclosure that is increased when in a needed enclosure. The graph of frequency response shows a peak at 300Hz which would sound like a bongo drum and is about as high as I can sing. On another forum a guy uses that tiny speaker as the midrange in a portable speaker system.

The smallest woofer I have ever used is 5" in diameter. It resonates at 50Hz and with a tweeter and a crossover network it sounds pretty good. I have purchased speaker systems with 4" and 5" woofers that produce bass fairly well. Most of my woofers are 8" and I use a low frequencies boost circuit that make them sound like sub-woofers. I have a brand new never used 18" sub-woofer that I will sell.

How do I test amplifier speaker output polarity?

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