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Speaker A+B Clarification

S

stg5clinger

New Member
Picked up a pair of Wharfedale W60d's this weekend in pretty much mint condition. Hooked them up to my Sansui 2000A to do an A/B comparison with my DLK Model 3s. I didn't really have any expectation going in, but was almost disappointed when the Wharfs didn't seem to sound as good as the DLKs. The DLKs were recently recapped so that could have something to do with it. Long story short, both sets sound good individually. But running them A+B really packs a punch. Hitting up the experts here to get an opinion before I inadvertently blow up a perfectly good Sansui receiver. I can't seem to find any reliable specs on the Wharfs or the DLKs. From what I can see on the Wharfs they un at 4-8 ohms. I believe the DLKs are 8 ohm. If I am understanding the research I have done here, I can run 2 sets of speakers at the same time as long as they are both 8 ohm, correct? I think its the A*B/A+B needs to be greater than 4 ohm if I recall correctly. The novice question here is will I be putting my amp at risk by running these particular two sets of speakers in parallel (A+B). Thanks, in advance, for any responses here.
 
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I'll take a cut at an answer. Most receivers that accept two pair with an A+B, are designed for two pair of 8 ohm speakers, and they are running them in parallel, for a net of 4 ohm loading on the amp (evidenced usually by power ratings quoted for 4 ohms). You can measure the resistance in ohms with a cheap multi-meter. If they measure between 6-8 ohms, they are the proverbial 8 ohm speaker. If they measure under 4 ohm, they would be a 4 ohm meter, and so on.
 
Thanks for the reply. I guess it’s time to pick up a multi-meter so that I have the ability to measure resistance. In the meantime, hoping somebody out there that owns these speakers can provide some insight. Appreciate your info!
 
Disconnect one pair of speakers from the amp and listen to the pair still connected. Then engage A + B.

If the connected pair still plays, the amp is running two pair in parallel. That is a good indicator that it can handle a 4 ohm load. If the connected pair goes silent, the amp will run two pairs of speakers in series. Meaning the amp is not intended for a 4 ohm load. It wants to keep the impedence high.

Might not be totally accurate, but in simple terms, I used to explain to customers that the amp is protecting itself. Closer to the truth would be that the amp does not have the "balls" to drive low impedance speakers.
 
62vauxhall said:
Disconnect one pair of speakers from the amp and listen to the pair still connected. Then engage A + B.

If the connected pair still plays, the amp is running two pair in parallel. That is a good indicator that it can handle a 4 ohm load. If the connected pair goes silent, the amp will run two pairs of speakers in series. Meaning the amp is not intended for a 4 ohm load. It wants to keep the impedence high.

Might not be totally accurate, but in simple terms, I used to explain to customers that the amp is protecting itself. Closer to the truth would be that the amp does not have the "balls" to drive low impedance speakers.
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Good test. I know the oldest equipment wasn't 4 ohm-friendly. Good stuff to know.
 
Thanks for the suggestion. Just so i am clear on the test. If the connected pair plays using the A+B switch than I should be safe in adding the second pair of speakers? Or is it the other way around? Sorry for the ignorance just trying to educate myself on this stuff.
 
stg5clinger said:
Thanks for the suggestion. Just so i am clear on the test. If the connected pair plays using the A+B switch than I should be safe in adding the second pair of speakers?
Click to expand...

Correct. But knowing the impedance of both systems would be of value. I think those Wharfdales are nominal 6 ohms. If so and your other speakers are nominal 8 ohms, your Sansui will see a nominal impedance of 7 ohms. Provided that the one connected pair plays with speaker selector in A + B (parallel operation).

If that is not the case, and the connected pair goes silent with speaker switch at A + B (series operation), the receiver would see a nominal impedance if 14 ohms with both pairs connected and operating. Safer for the amp but a possible compromise in sound quality.

But it is not a cut and dried issue, there are variables.

Published speaker impedances are an average ie: nominal. During use, it will rise and fall from it's claimed figure. If each speaker enclosure dips to 4 ohms at certain frequencies, then the amp will see 2 ohms when those frequencies are reproduced.

It is low impedances that some amplifiers don't like. The less that number becomes, the closer it becomes to a dead short - 0 ohms.

I don't know the Sansui 2000A but it looks to have speaker fuses so one or both will or should blow if that number gets too low - "condition red". But it may be your unit will be fine driving a low impedance speaker load at least at moderate volume levels. Distress may not occur until high listening levels are attempted.

There is only one definitive way to find out.
 
62vauxhall said:
Correct. But knowing the impedance of both systems would be of value. I think those Wharfdales are nominal 6 ohms. If so and your other speakers are nominal 8 ohms, your Sansui will see a nominal impedance of 7 ohms. Provided that the one connected pair plays with speaker selector in A + B (parallel operation).
Click to expand...

oops. Math is off. A nominal 6 ohm speaker in parallel with an 8 ohm speaker is 3.4 ohms. Unless the amplifier is rated for 2 ohm loads, I would not run those two speakers in parallel because, if both speakers have an impedance dip at the same frequency, the amp will see a load much less than 3.4 ohms.

The manual for the Sansui 2000A says that the combined speaker load for A + B must be more than 4 ohms each and that two pairs of 4 ohm speakers must never be used at the same time. So, the Sansui can not handle 2 ohm loads and is happy with 4 ohm loads. You are gambling by attempting to power speakers with a load between 2 and 4 ohms.

edit: opnly bafld posted as I was writing my comment.
 
Thanks. I was assuming this combo would dip the impedence below 4, but was just a little confused because the Wharfs stated impedence at 4-8 ohms. I will play it safe it this point and avoid running in parallel. Thanks for the assistance.
 
DLK Specifications
Model Version Frequency Response Impedance Min Power Rating Max Power Rating
1/4's, 1, 150hz 13,000Hz +/- 4db, 200-12,000hz, 8ohm, 30watts Cont.
1/4's, 2, 80hz 12,000Hz +/- 4db, 80-12,000hz, 8ohm, 5watts RMS Channel 30watts Cont.
1/2's, 1, 50hz 20,000Hz +/- 4db, 50-18,000hz, 8ohm, 40watts Cont.
1/2's, 2
1's, 1, 35hz 22,000Hz +/- 4db, 48-20,000hz, 8ohm, 40watts Cont.
1's, 2, 45hz 18,5000Hz +/- 4db, 45-18,5000hz, 8ohm, 15watts RMS Channel 60watts Cont.
1.5's, 1, 30hz 20,000Hz +/- 3db, 35-20,000hz, 4ohm, 80watts Cont.
1.5's, 2
2's, 1, 35hz 20,000Hz +/- 3db, 40-18,000hz, 8ohm, 90watts Cont.
2's, 2, 35hz 20,000Hz +/- 3db, 35-20,000hz, 8ohm, 10watts RMS Channel 120watts Cont.
3's, 1, 30hz 24,000Hz +/- 3db, 35-20,000hz, 8ohm, 100watts Cont.
3's, 2, 30hz 20,000Hz +/- 3db, 30-20,000hz, 8ohm, 10watts RMS Channel 120watts Cont.
4's, 1, 30hz 24,000Hz +/- 3db, 30-20,000hz, 8ohm, 150watts Cont.
4's, 2, 30hz 24,000Hz +/- 3db, 30-20,000hz, 8ohm, 150watts Cont.
 
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