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Sony str-de315 receiver 8ohm/16ohm, could 4ohm subs damage it?

post #1 of 5
Thread Starter 
Sony_STR-DE315_Receiver_Surround_stereo_audio_system_home_theater_.JPG

1. I have recently acquired a "sony str-de315" 5.1 audio receiver, I have some old but tough car subs that are in home theater boxes that are 4ohm. I used to run an old optimus "discontinued radio shack brand" receiver to these subs and it worked fine. that receiver too was rated to handle 8ohm speakers.

So I know that running 4ohm subs will make the amp run slightly hotter and push out more power, but having done this before with no ill side effects and reading the manual for the sony str-de315 in the user manual "found online" it actually lists 4ohm speaker output wattage!!!

on the back of the receiver above the inputs it says 8/16ohm.. but the manual clearly lists 4ohm output wattage and not 16...???


2. I have been told that you can use silicone grease to restore the suspension on older sub woofers (among other uses) anyone else try this with good or bad results?

I thought I would run this by the audio buffs on ocn to see what you have to say.
--Back in the day I also ran computer fans on top of my optimus receiver just as a precaution because I knew it generated more heat running 4ohm- something I will likely do with this sony if I ever decide to really push the volume to high levels for extended periods of time.
Edited by Killam0n - 1/31/11 at 8:30am
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post #2 of 5
About 1) If your amp can push its rated power on 8ohm, on 4 ohm if I remember correctly it can push the same power squared. Therfore the losses will be the normal 8ohm losses squared - so much more heat. You could mitigate this effect by never upping the amplification factor beyond one fourth of the scale.
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post #3 of 5
I've repaired torn paper cones with Permatex Form-a-Gasket, but never have repaired a surround, as that can go horribly wrong pretty easily.

An easy way to get the right impedance for your speakers...shoot for 8 ohm, as that seems the middle ground, and is assuredly what the amp can handle. To do that: put 2 4 ohm speakers in series..one after the other.

Basically you connect speaker 1's positive to the positive on the amp, then take speaker 2's positive and connect it to speaker 1's negative. Third, connect speaker 2's negative to the amp's negative. You will then have an 8 ohm load (assuming 2 4 ohm speakers are used), which the amp will handle.

Math behind series:

R1 + R2 = total load

Simple math behind lowering impedance by putting in parallel:

R1 x R2 / R1 + R2. You can add as many loads onto this. If both loads match, impedance is always half of whatever the original loads were (2x4ohm speakers in parallel makes 2 ohm).

If loads are mismatched (4 ohm and 8 ohm), use the above formula to balance it out. The total load will always be lower than the lowest partial impedance (lower than 4 ohms in this example).

So that makes:

4x8 / 4+8, or 32/10, or 3.2. So total load would be 3.2 ohms.

On a solid state amp, the lower the impedance, the higher the current passed through the transistor, hence more heat. Vacuum tubes do not work in that fashion however.

That's my experience with speakers and such. I highly recommend going with an 8 ohm load, and looking into pre-cut replacement surround, or having it professionally repaired.
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post #4 of 5
Thread Starter 
UnexplodedCow Thanks for the info, I know a little bit about ohm impedance I had to learn about it the hard way.. blowing voice coils on dual VC subs.. then I learned what i did wrong and how to wire DVC properly and get correct impedance.

knowing that 4ohm will push the receiver harder I think I might chance it and add some fans, why? 8ohm on a single output from the receiver pushing 2 200w subs with 80w will not achieve much volume, however at 4ohm on 2 outputs each sub should be getting somewhere around 150w- and I got this receiver cheap...

On question 2 I am actually referring to revitalizing the rubber, the surrounds are fine (no holes or tears), but are aging I have used silicone grease to revitalize rubber seals (like the ones on my car doors) and I am thinking it could bring more life out of the subs in the long run, first I am going to do a blotch test (small area) to make sure the silicone grease wont harm the rubber surrounds on the subs.

The car audio subs are actually good old: optimus pro series 10" 200w 4ohm (discontinued radio shack brand from the 90's)
Edited by Killam0n - 2/1/11 at 7:58am
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post #5 of 5
The cooling is only part of the issue, since more power is also used, which stresses other components (the power supply in the amp), and it may bring them out of spec. I've seen this happen, and had it happen years ago, before I had any idea about impedance mismatch. The amp's output stage might not blow, but somewhere along the line it will. In a high power application (1400 watt industrial power amp) the power transformer overheated, shorted, and kept blowing breakers, until it finally burnt up the amplifier board internally.
If the surrounds aren't shot, and they're rubber based, silicone may help a bit, but it will change the speaker's response and sound, mostly due to a mechanical change. Just putting a skin over things may help.

Also, the wattage isn't so much the issue as how the wattage is delivered. If the amp distorts, it will usually put out a square tooth wave (opposed to smooth sine wave..or cosine...pretty much the same only half a phase off each other). A square tooth wave will eat a speaker, even if it's below the wattage, due to mechanical failure typically, or overheating/shorting the voice coil.

Also, halving the impedance doesn't double the wattage. Industrial, MOSFET-based bass amplifiers will put out around 75% more power at best. T03 style transistors and circuitry don't respond so well, and only give about a 50% boost by halving the resistance.

I found a user manual from Sony online, and they rate the unit at an 8 ohm load...I still suggest that. Also, that model shows as 60W per channel @ 8 ohms, although there's a typo, calling the model a D315 in one place, and DE315 in another. It has a secondary rating of 145 watts @ 4 ohms, but I think that's pretty optimistic since pro power amps don't get a 100%+ gain by halving resistance. If you don't care about the receiver...no worries, then, but I don't suggest turning it up very much as a precaution if you have to use it that way. It's definitely not designed for pushing heavy bass.

http://www.docs.sony.com/release/STRDE515.PDF


Yes, I was long-winded.
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