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post #1 of 8 Old 09-01-2019, 12:29 AM - Thread Starter
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Matching speakers to amplifier

Hi
New to this forum or any forum.
I have a question regarding a set of Goodman’s 212c speakers I sold. They are 15 watts rms 16 ohm, the buyer connected them to a 120watt class A amp with 4 ohm out puts.
I had made it clear that the speakers should be matched to amplifier before he received them.
He phoned me and told me one of the bass drivers were not working .they are triaxiom speakers.
He acknowledged to using the 120watt per channel amp but at low volume!!!

In my opinion this is a horrible mismatch .
Question is what will a GrandHigh A280 class amp do to these sensitive speakers that I have had for 13 or so years and he says he received as not working.
Thanks in advance ingo
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post #2 of 8 Old 09-01-2019, 07:03 AM
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Quote:
Originally Posted by ingo hildebrand View Post
Hi
New to this forum or any forum.
I have a question regarding a set of Goodman’s 212c speakers I sold. They are 15 watts rms 16 ohm, the buyer connected them to a 120watt class A amp with 4 ohm out puts.
I had made it clear that the speakers should be matched to amplifier before he received them.
He phoned me and told me one of the bass drivers were not working .they are triaxiom speakers.
He acknowledged to using the 120watt per channel amp but at low volume!!!

In my opinion this is a horrible mismatch .
Question is what will a GrandHigh A280 class amp do to these sensitive speakers that I have had for 13 or so years and he says he received as not working.
Thanks in advance ingo
A 4 ohm amp feeding 16 ohm speakers has to work harder and wont achieve 120 watt output. yes, at low volume the amp shouldnt have hurt the speakers, but you are taking his word for it that he didnt overdrive them.
heck, ive use a little one watt speaker just to test the output on a receiver i was playing with. no damage.
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post #3 of 8 Old 09-01-2019, 12:40 PM
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Quote:
Originally Posted by pgscubadiver View Post
A 4 ohm amp feeding 16 ohm speakers has to work harder and wont achieve 120 watt output. yes, at low volume the amp shouldnt have hurt the speakers, but you are taking his word for it that he didnt overdrive them.
heck, ive use a little one watt speaker just to test the output on a receiver i was playing with. no damage.
What?

The amp works far less driving a 16 Ohm load than a 4 Ohm load, and even with a 120W amp, odds of using more than a few watts are slim unless the volume control was turned up to stupid. Most of us have turned said knob to said level before, however.
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post #4 of 8 Old 09-01-2019, 01:18 PM
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Dynamic Power*
* IEC60268-Short-term maximum output power
240 W (3 Ω, Front)
210 W (4 Ω, Front)
120 W (8 Ω, Front)

ok. allow me to rephrase that using these specs from an onkyo manual.
the higher the resistance on the speakers the lower the power output on the amp.
that being said, i stand by my initial statement that you are taking the purchasers word for it that he didnt overdrive them.(or turn them up to stupid as you said).
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post #5 of 8 Old 09-01-2019, 02:16 PM
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paypal always sides with buyer if that means anything

Power: Marantz sr7008, NAD C 275Bee x 2, Video: Oppo 103, Samsung 75un6300 LG oled c9 77
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post #6 of 8 Old 09-06-2019, 05:12 PM
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Hey all, I'm the owner of the defective speaker.


I'd like to present my side of this for balance.


Some facts regarding the amplifier used to test the speakers:

The GrandHigh A280 power rating according to the user manual is as follows;

120W ( 1Khz 2% T.H.D. 4Ω )

I believe that's an EIA (Electronic Industries Association) rating of a single channel driven in short bursts (usually microseconds) at a mid-band frequency (in this case a 1Khz sine wave) to clipping at 2% THD on a 4Ω load.

That's pretty much the best an amp can perform under ideal conditions over a very short time. However, that rating is often and unfortunately used as a headline figure which manufacturers push to inflate an amp's power capability.

You'll never get that in the real world as an amp has to drive speakers (2 channels) across a bandwidth, usually 20Hz-20KHz, at much lower distortion (0.01%).

The latter is the FTC rating that gives you the average power (RMS) output for both channels running over a wide frequency range at lower distortion levels. A much more conservative and true rating with figures usually 10-30% lower than the EIA rating.

So the GrandHigh A280 rated at 120W under ideal conditions, would now realistically only put out about 100W per channel at full bandwidth into a 4Ω load.

The A280 has a fairly robust power supply (a 1200W transformer) so it can be inferred that the power output would double as impedance halves, or vise versa. So the amp rated at 100W RMS into 4Ω would put an average of 25W into a 16Ω speaker - that again is with each channel driven to clipping.

Now the Goodmans Triaxiom 212C speakers are 16Ω and rated at 15W RMS, or 30W maximum. The speakers have an unpublished sensitivity rating but are generally thought to be around 100dB/1W/m.
¸¸¸¸¸¸¸¸¸¸


As it happened:

I received the speakers via a friend of the seller's (delivered for a fee) transported in a van and lying on their backs.

I placed them in the listening position and connected them to the amp via my existing speaker cables straight to the attenuator units (the cabinets have push fit and easily removable ARUs mounted below the triaxial drivers which gives access to the inside of the cabinets and to the hole in the back of the cabinets via which the speaker cable was fed through to the attenuators).

I switched the amp on with the volume down - as per good practice I always turn the volume down before powering any amp off. It has a soft start of about 10 seconds before coming on.

I cued up a vocal track which I thought would be a benign test, pressed play and slowly turned the volume up. I was less than 3 foot away from the speakers.

I'm confident I didn't exceed more than 65dB at that distance as my general listening position is 12 feet away and I listen at 80 dB most of the time - my party days are long gone. At that level I'm pretty certain that the amp was only putting out a couple of watts.

Almost instantly I noticed the imbalance in output - the 'left' speaker sounded weak so I put my ear right up to it and listened - I couldn't hear any bass at all - just the treble and mid units were working. I immediately checked the right speaker and that seemed just fine.

I removed the ARU from the left speaker and reached through the port and to the back of the driver to feel if the cone was vibrating - nothing.

All this took hardly any time - it was that obvious that the woofer was *dead.

I heard no thump, no scraping or rattling while the speakers were playing.

I turned the volume down and switched the amp off.

Disappointed, I called the seller to tell him.


*I have since removed the faulty driver from the cabinet and using a voltmeter measured across the driver's terminals. It measured 8.4Ω - it should be around 15-16Ω - which was confirmed by the working driver - it measured 14.9Ω. I then inspected the driver for any loose wiring - there was none.

I pushed down onto the cone to check the freedom of movement of the voice coil and was met with some resistance and a scraping sound. This all confirmed that the voice coil was blown.


Some questions:

The eBay ad stated that the speakers were "in good working condition". However, the speakers were run in conjunction with a set of Goodmans Triaxiom 301s (Impedance is unknown as they came in either 8Ω or 16Ω). Is it possible the seller didn't pick up on the faulty driver as the sound was masked by the other pair?

Is it possible the driver was damaged during transport - a mechanical failure due to shock? After all it was a 60 mile journey in the back of a van.

How likely is it to blow a woofer at low listening levels playing a program with limited peaks and particularly small low-level frequency information over a period of 5 or so minutes?

How much more likely is it that the speakers were overdriven by the seller's Quad 303 amp which is rated at 28W RMS - remember the 212C drivers are rated at 15W RMS?
This set-up was run "for many many years" at unknown output/listening levels. The seller has told me though that this is the second pair of Goodmans drivers he has installed in the cabinets as he "had damaged my first set on to(sic) many watts"

Sorry for the long-winded post but I feel it was necessary to get all the information out. Apologies also if this comes across as an eBay spat. I hope there's enough take-away to inform other members about the perils of buying untested speakers.


Looking forward to hearing your feedback. Thanks

TL;DR - Never buy second-hand speakers without a displayed impedance reading.

Last edited by leggoslave; 09-06-2019 at 05:30 PM.
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post #7 of 8 Old 09-06-2019, 06:13 PM
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Quote:
Originally Posted by leggoslave View Post
Hey all, I'm the owner of the defective speaker.


I'd like to present my side of this for balance.


Some facts regarding the amplifier used to test the speakers:

The GrandHigh A280 power rating according to the user manual is as follows;

120W ( 1Khz 2% T.H.D. 4Ω )

I believe that's an EIA (Electronic Industries Association) rating of a single channel driven in short bursts (usually microseconds) at a mid-band frequency (in this case a 1Khz sine wave) to clipping at 2% THD on a 4Ω load.

That's pretty much the best an amp can perform under ideal conditions over a very short time. However, that rating is often and unfortunately used as a headline figure which manufacturers push to inflate an amp's power capability.

You'll never get that in the real world as an amp has to drive speakers (2 channels) across a bandwidth, usually 20Hz-20KHz, at much lower distortion (0.01%).

The latter is the FTC rating that gives you the average power (RMS) output for both channels running over a wide frequency range at lower distortion levels. A much more conservative and true rating with figures usually 10-30% lower than the EIA rating.

So the GrandHigh A280 rated at 120W under ideal conditions, would now realistically only put out about 100W per channel at full bandwidth into a 4Ω load.

The A280 has a fairly robust power supply (a 1200W transformer) so it can be inferred that the power output would double as impedance halves, or vise versa. So the amp rated at 100W RMS into 4Ω would put an average of 25W into a 16Ω speaker - that again is with each channel driven to clipping.

Now the Goodmans Triaxiom 212C speakers are 16Ω and rated at 15W RMS, or 30W maximum. The speakers have an unpublished sensitivity rating but are generally thought to be around 100dB/1W/m.
¸¸¸¸¸¸¸¸¸¸


As it happened:

I received the speakers via a friend of the seller's (delivered for a fee) transported in a van and lying on their backs.

I placed them in the listening position and connected them to the amp via my existing speaker cables straight to the attenuator units (the cabinets have push fit and easily removable ARUs mounted below the triaxial drivers which gives access to the inside of the cabinets and to the hole in the back of the cabinets via which the speaker cable was fed through to the attenuators).

I switched the amp on with the volume down - as per good practice I always turn the volume down before powering any amp off. It has a soft start of about 10 seconds before coming on.

I cued up a vocal track which I thought would be a benign test, pressed play and slowly turned the volume up. I was less than 3 foot away from the speakers.

I'm confident I didn't exceed more than 65dB at that distance as my general listening position is 12 feet away and I listen at 80 dB most of the time - my party days are long gone. At that level I'm pretty certain that the amp was only putting out a couple of watts.

Almost instantly I noticed the imbalance in output - the 'left' speaker sounded weak so I put my ear right up to it and listened - I couldn't hear any bass at all - just the treble and mid units were working. I immediately checked the right speaker and that seemed just fine.

I removed the ARU from the left speaker and reached through the port and to the back of the driver to feel if the cone was vibrating - nothing.

All this took hardly any time - it was that obvious that the woofer was *dead.

I heard no thump, no scraping or rattling while the speakers were playing.

I turned the volume down and switched the amp off.

Disappointed, I called the seller to tell him.


*I have since removed the faulty driver from the cabinet and using a voltmeter measured across the driver's terminals. It measured 8.4Ω - it should be around 15-16Ω - which was confirmed by the working driver - it measured 14.9Ω. I then inspected the driver for any loose wiring - there was none.

I pushed down onto the cone to check the freedom of movement of the voice coil and was met with some resistance and a scraping sound. This all confirmed that the voice coil was blown.


Some questions:

The eBay ad stated that the speakers were "in good working condition". However, the speakers were run in conjunction with a set of Goodmans Triaxiom 301s (Impedance is unknown as they came in either 8Ω or 16Ω). Is it possible the seller didn't pick up on the faulty driver as the sound was masked by the other pair?

Is it possible the driver was damaged during transport - a mechanical failure due to shock? After all it was a 60 mile journey in the back of a van.

How likely is it to blow a woofer at low listening levels playing a program with limited peaks and particularly small low-level frequency information over a period of 5 or so minutes?

How much more likely is it that the speakers were overdriven by the seller's Quad 303 amp which is rated at 28W RMS - remember the 212C drivers are rated at 15W RMS?
This set-up was run "for many many years" at unknown output/listening levels. The seller has told me though that this is the second pair of Goodmans drivers he has installed in the cabinets as he "had damaged my first set on to(sic) many watts"

Sorry for the long-winded post but I feel it was necessary to get all the information out. Apologies also if this comes across as an eBay spat. I hope there's enough take-away to inform other members about the perils of buying untested speakers.


Looking forward to hearing your feedback. Thanks

TL;DR - Never buy second-hand speakers without a displayed impedance reading.
that is an excellent other side of the story.
do i think they were damaged in transport- no.
does it sound like you tested them properly- yes.
i feel for both of you, tough situation to resolve.
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post #8 of 8 Old 09-06-2019, 06:27 PM
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Quote:
Originally Posted by pgscubadiver View Post
that is an excellent other side of the story.
do i think they were damaged in transport- no.
does it sound like you tested them properly- yes.
i feel for both of you, tough situation to resolve.

Thanks pgscubadiver for your response. Yes it's a terrible shame for both parties. Hopefully it gets resolved amicably.
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