Using new-ish surround speakers with old head unit?
October 23, 2011 9:09 AM   Subscribe

I have a Phillips DVD player/surround system. After making 15 seconds of horrible noise every time you started it up for the last six months, it finally died. How can I hook it up to the old Sony head unit that I had sitting in my basement?

I have a Phillips DVD player/surround system. After making 15 seconds of horrible noise every time you started it up for the last six months, it finally died. I took apart the amp/subwoofer to see if it was just a fuse; nope, plenty of crusty caps in there.

I have an old Sony head unit down in my basement, and figured, heck, I'll hook that up. Two problems: input and output to the head unit.

Input: the DVD player used a VGA cable (15 pin) to connect to the subwoofer (the sub in turn has a bunch of ports to the other speakers). There is no other means of outputting sound. I can't find a pinout for this. However, since we use an HTPC anyway (and had it outputted to the Philips unit), I could just bypass the damn DVD player, so this isn't really that much of a loss.

Output: here's where I'm stuck. The Sony head unit is from back in the days of giant 8 ohm speakers, even for surround. The surround speakers that came with the Philips unit are, according to the ports on the back of the sub, 4 and 2 ohm units. If I splice the speaker wires into the head unit, will I crash it? Is there a cheap way to hook up these speakers (bridging resistors...I know that's not how impedance works, but...)?

I'd buy a new unit like the Philips, but I'm kinda broke right now; thus the attempts at kludging something together. I can afford a couple electronic-component-wholesaler resistors if I have to.
posted by notsnot to Technology (10 answers total) 1 user marked this as a favorite
I think we can safely assume that Phillips isn't putting an exotic audiophile amp in their all-in-one units, so I'd expect a "real" receiver to be able to deal with the loads of those speakers in normal use.

Lower speaker impedance means higher current and higher temperatures. I would expect that you'd be fine as long as you don't play it loud, and as long as you keep a careful eye on how hot the receiver is getting.
posted by ROU_Xenophobe at 10:23 AM on October 23, 2011

I would recommend against using the Sony receiver to power the Philips speakers if they are, in fact, 2-4 ohm. Unless you find out that the receiver is 2-4 ohm stable, I would assume it is more likely 6-8 ohm stable. Powering speakers lower impedance speakers will not only create more heat, but could also fry the receiver.
Then again, you could always try it out and be sure to observe how hot the Sony gets.
If you choose to do this, keep it well ventilated. In other words, not stuck in a cabinet.

Note: Even some of the nicest quality receivers are not designed to handle 4 ohm loads. Home audio receivers and amplifiers are typically built to handle 6-8 ohm loads.
There are some mid-level to high end power amps that can handle lower impedences, but they require a separate pre-amp or sound processor. In many cases these are intended for custom installation and full-blown home theatre rooms.
posted by nickthetourist at 1:04 PM on October 23, 2011

Yeah, but my point was that if the Phillips engineers thought that whatever shitty commodity amp they included was sufficient to drive those speakers, it seems very improbable that the Sony wouldn't be able to handle it. At least not at un-loud sound levels.

I expect the deal is that being surrounds, those sound pressure those speakers are supposed to pump out is low enough that an unspectacular amp can drive them at 2-4 ohms, at the cost of making the consumer spend more money on electricity.
posted by ROU_Xenophobe at 1:41 PM on October 23, 2011

Response by poster: Just to clarify, if you're still reading: On the back of the Philips subwoofer, it says that the center is 2 ohm, and the others are 4. On the Sony, it's switchable to drive the fronts at 4 or 8, and the rest are 8 only. Does this make sense?

...and if I hook up the sub - sans amp guts - to the Sony, just be careful and don't let it over heat or is there some other consideration I have to take?
posted by notsnot at 2:00 PM on October 23, 2011

That's weird. You'd think that the center, which can be intended to produce more sound, wouldn't be 2 ohm.

How are you going to drive the sub sans amp? Are you thinking of cracking the case open and fishing some speaker wire into it? You'd want to do that before the crossover unless the receiver has a speaker-wire sub out that's managed by the receiver.

Anyway, cracking open the case and mucking around in its guts seems like Not Worth It to me. I think in your shoes, I'd just pick up a cheap pair of speakers, ideally used, and wait until I could get a new surround set. There are a bunch on your craigslist. Or just listen through the tv or headphones for a little while.

For sure if you do this research it ahead of time to make sure there isn't anything in there that might hold a charge when it's unplugged.
posted by ROU_Xenophobe at 8:53 AM on October 24, 2011

@notsnot - Since the front channels of the Sony can be switched to 4 ohm, I would do this and use the front L&R speakers for now. This will at least give you sound from about 80hz-20Khz, you just won't have the low frequency effects.
Without knowing more about this sub, and how it is designed (i.e. does it have an internal xover, etc.) I would not use it. If, however, you decide to experiment, do so carefully and be sure to check how much heat is coming off the Sony. If it's more than warm to the touch, it's probably best to unplug the sub.
Another possibility with the sub is that is may have its own internal amplifier. Do you know for certain that the sub receives power from the amp, or does it simply receive a signal?

@ROU_Xenophobe - most of my experience actually comes from car audio where I've had several different pieces of equipment in a couple different cars. Stepping up in quality with audio gear is more about gaining higher sound quality and performance than it is about being able to properly power a lower impedance speaker. In some cases the two go hand in hand, but unless the specs state that a receiver or amp can handle lower impedance, it is best to avoid them.
posted by nickthetourist at 11:56 AM on October 24, 2011

Best answer: Ok, so I just downloaded the user manual for the Philips system.
It appears to me, although I am not 100% certain, that the subwoofer actually house the amplifiers for the sub and the surround speakers.
Since the subwoofer appears to have a proprietary connection (i.e. not an RCA connection or speaker terminals) I don't see a way that it will work with the Sony receiver. It is likely designed to work only with the Philip DVD unit.
posted by nickthetourist at 12:05 PM on October 24, 2011

Response by poster: Yeah, I guess I wasn't clear. I was going to bypass the DVD unit completely (since my HTPC has a DVD player), output from the HTPC to the receiver directly, then just use the speakers from the Phillips system. When I took the "guts" out of the back of the sub/amp unit, I found the leads that go to the sub speaker; I can hook that up to the sub output on the receiver.

I guess the short answer is, I just have to watch it when I hook up the speakers, don't let the receiver overheat.
posted by notsnot at 6:31 PM on October 24, 2011

Best answer: I found the leads that go to the sub speaker; I can hook that up to the sub output on the receiver

Only if the sub output is an amplified, speaker-level connection. Most are just line-level RCA connectors that rely on self-powered subs to amplify the signal.
posted by ROU_Xenophobe at 6:38 PM on October 25, 2011

Response by poster: Well, I finally got around to wiring it up. Just unsnapped the connectors for all the speakers, put them in the terminals on the back of the receiver,'s really quiet. I guess the speakers are kinda rinky dink. Oh well, thanks guys.
posted by notsnot at 8:48 AM on November 23, 2011

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