8 ohms speakers to 4 ohms amp??

A

Andon

Junior Audioholic
Hi guys, I am wondering if I can full my amp (outlaw model 500) that the connected speakers are 4ohms insted of 8. I currently have polk RTI a7 with is 8 ohm speaker. The amp pumps much more power if connected to 4 ohm load. I think I saw a article or something that you can add resistor and make the load 4 insted of 8 ohms. Any ideas??
 
HTfreak2004

HTfreak2004

Senior Audioholic
From the outlaw website on your amp


The Model 5000 is our new high performance and affordable 5-channel amplifier. Rated at 5 x 120 watts into 8 ohms or 5 x 180 watts into 4 ohms (all channels driven), the 5000 is ideal for those who have moderate size living areas and desire a 5-channel home theater. Among the 5000 features:
 
R

Russdawg1

Full Audioholic
Hi guys, I am wondering if I can full my amp (outlaw model 500) that the connected speakers are 4ohms insted of 8. I currently have polk RTI a7 with is 8 ohm speaker. The amp pumps much more power if connected to 4 ohm load. I think I saw a article or something that you can add resistor and make the load 4 insted of 8 ohms. Any ideas??
If you add a resistor in parallel you don’t gain anything but wasted power in the form of heat lost by the resistor and not going to your speakers.

It also puts more stress on the amplifier having a lower ohm load.

Connect your speakers and don’t worry about it. An 8 ohm load is usually better anyways. And that possible doubling of wattage from 8 ohm to 4 ohm is only a gain of 3dB. But you wouldn’t get that gain of wattage because half of it would go through the resistor, effectively delivering the same amount of wattage but stressing the amplifier for no apparent reason.

Edit: Apparently your outlaw only gains 1.5 times the wattage when seeing a 4 ohm
load. This means that if you added a resistor, you would actually lower the amount of power delivered to your speakers and stress your amplifier. A double no. Enjoy your speakers and stop stressing :)

Also do you even need the extra wattage? Can the speakers even support it?
 
A

Andon

Junior Audioholic
Specs for the polk rtia7 is 20-300 wats. Dont know how if the "300" is peak or normal.
 
S

shadyJ

Speaker of the House
Specs for the polk rtia7 is 20-300 wats. Dont know how if the "300" is peak or normal.
I don't think that speaker would last long with a continuous 300 watts going through it.
 
lovinthehd

lovinthehd

Audioholic Slumlord
What others have said. FWIW the impedance of the speaker is only a nominal rating, many 8 ohm rated speakers can spend time in the 4ohm range. Your best protection for your speakers is judicious use of the volume control....
 
JerryLove

JerryLove

Audioholic Samurai
You may be right, I hust never had plugged them to 300w amp.
Though a 300W amp is *capable* of sending 300W; it only does so under its maximum load.

Most listening is closer to 3W.
 
B

Beave

Full Audioholic
To put it simply, the power that an amp supplies to speakers goes up as you turn up the volume.

The amount of power a speaker can handle is complex and depends on frequency and duration of the signal being fed to it.
 
Kvn_Walker

Kvn_Walker

Senior Audioholic
To put it simply, the power that an amp supplies to speakers goes up as you turn up the volume.

The amount of power a speaker can handle is complex and depends on frequency and duration of the signal being fed to it.
and many (if not most) manufacturers exaggerate those numbers, because of the "bigger number = better" consumer attitude.
 
HTfreak2004

HTfreak2004

Senior Audioholic
Looking at the specs on the manufacturer website for your speakers only gives a suggested suitable amplifier power range of 20-300 watts. I did not see a maximum input wattage rating for your speakers. If your amp is stable into 4 ohms it will work fine with your speakers if your using bass management. If your planning to run your speakers as full range then they could drop below 4 ohms at frequencies below 100 hz during peaks. Remember the 8 ohms rating for your speakers is an average over the frequency response stated as nominal impedance from the manufacturer specs. My Paradigm studio 100v3 can dip as low as 2.5 ohms at 104 hz according the sound and vision review. They also are 88 db 1 watt/1m anechoic measurements. My amp is rated stable 340 watts at 2 ohm load and the specs show its power rating for 8/4/2 ohm loads. I bass manage my speakers however because they are not true full range. Lastly although a peak input spec for a speaker may say 200 watts speakers are very conservatively rated so you don’t learn the hard way with a blowen driver. I read an article stating a 200 watt speaker driven with 600 watts of actual input. If The manufacturer designed their speaker and listed it with as 600 watts the consumer would assume that as an acceptable input literally and than destroy there equipment in no time. However if they specified a 200 watt max input rating the consumer would use some common sense increasing the life of their speakers. That is one of the reasons you can use 1000+ watt rms mono block amps to power each speaker individually. 1 amp for each speaker with its own power supply and dedicated wall outlet. It’s the peaks that drain amp reserves and leads to amp clipping. If the peaks were continuous without sufficient pause your speakers would be cooked in no time.
 
JerryLove

JerryLove

Audioholic Samurai
For most consumers: wattage is an almost useless number.

For one thing: real sound doesn't scale in a way that's intuitive (it takes double the wattage to increase SPL 3db, which is the smallest increment a human can hear in).

Then there's the issue of speaker efficiency; which is mostly ignored. Two speakers can have very different volumes at the same wattage.

Then there's the issue that wattage tolerance isn't consistent throughout the audio spectrum.

And, of course, that the wattage/spl relationship also isn't consistant as resistance changes.

That's how you get people looking at wattage numbers on the amps and speakers rather than looking at max SPL the speaker can handle and the room.

If someone new really wants to understand what they should get.
1) Figure out your listening position.
2) Figure out the max SPL you want to hear at that position.
3) Factor in your distance to figure out the 1m SPL
4) Check if the speaker can output that SPL at that distance without hitting XMax or melting.
5) Determine the amount of wattage needed to support that:
5a) Do the maths to figure out the power needed at 8ohm
5b) Take the lowest spot on the ohm curve and figure out the new number
6) Get an amp that provides that much power.

So. If you want 105db peaks @2m; you'll need 108 @1m.
If the speaker is 92db sensitive (1w@8ohm) you need 16db of gain.
That means you need 40w assuming the speaker is 8ohm.
If the speaker dips to 2ohm then you'll actually need 160w power to hit the peaks at the most demanding frequency.

So: make sure you get an amp capable of 160W into 2ohm.
Also: check the speaker spec and make sure it can handle 160W (or better still: someone with the max sustained and transient SPL)
 
B

Beave

Full Audioholic
For most consumers: wattage is an almost useless number.

For one thing: real sound doesn't scale in a way that's intuitive (it takes double the wattage to increase SPL 3db, which is the smallest increment a human can hear in).
Errr?
 
JerryLove

JerryLove

Audioholic Samurai
Hrm. With a tone I managed to pull off a 99% confidence.

OK fine. 3db is about the smallest change in SPL that you are really going to notice unless you are listening to some constant test tone and attempting to identify the change.
 
HTfreak2004

HTfreak2004

Senior Audioholic
Keep in mind the inverse square law only applies to open space measurements. A speakers in room spl response is amplified by boundary gain. When using an spl meter I found it best to use a tripod and with the mic at tweeter level 3.3 feet away for 85db reference level calibration on my system. After I move the mic with stand to the main seat position which will show what my spl loss is from original reference 1m from the speaker. In my room I lose 3 db at the main seat positioned 8.5 feet(2.58m) from the speakers tweeter. I angle my mains from back to front about 5 degrees to aim the tweeter towards my ear level which allows me to maintain the spl otherwise I will lose another 1.5 db from sitting 1 foot below tweeter height of my towers. Now when both main speakers are performing together the spl at my main seat should hit 85 db average reference level without 20+ db peaks or troughs at 0.0 max volume setting. Each speaker is only contributing 82 db however two speakers are twice the power hence the 3db gain overall nets 85 db. You can use double the amp power for 3 db gain or double the speakers. Stereo Sound is a blended image and sound has a decay time. This reinforces the spl off boundaries hence the reason people choose ported subs over sealed for heigher spl. Ported subs/speakers usually are less accurate than sealed ones but they give a louder bang over a certain frequency range than sealed speakers/subs with a bit more LFE extension from port tuning/room interaction. With all the sound information being blended in home theatre sound tracks and special effects the accuracy of reproduction is less important at high listening levels since the room boundaries interfere with accurate location of the sound source. At low to moderate listening levels source of sound is more accurate since the boundaries of the room are not being stressed as much. Accuracy of sound is another reason why sealed speakers/subs cost more. It is important to remember that when watching a movie all of the speakers/subs + boundaries of the room are being amplified to produce the total spl output. The likelihood that any one speaker is at or near reference level is highly unlikely. A lot of calculations would have to be considered to define how much amp power is truly being used to produce the speaker playback level. No one listens to only one speaker while watching a movie and no one removes all the boundaries of their room just to hear the speaker in open space. The room should interact with movies as part of the overall effect. In fact the room is the most exciting special effect during the movie. Big explosions that shake the room and house put a smile on my face every time adding to the visceral impact experience. During music that is fun at times but obviously no one wants to hear the room and everything else rattling apart when enjoying Hans Zimmer live or Pink Floyd in HD. Too many people stress about being able to hit reference play back but soon find it not a desirable listening level for movies anyway. If your planning on being 3 floors away from your system while vacuuming your master bedroom I guess concert level play back volume is important but your neighbors most definitely won’t agree nor will your pets, family, or your long term hearing! True reference peaks could exceed 130 dbs in a room with boundarary gain. I’m talking about all speakers hitting reference at the same time which is 120 db + up to 18 db from the room is 130-138 db. Get out the gauze for your bleeding eardrums!
 
67-79

67-79

Audioholic Intern
IT's been 4 time i changed my speakers position in my listening room since 2 months, the experience is different each time.
 
HTfreak2004

HTfreak2004

Senior Audioholic
Absolutely. The way your speakers interact with your room can make or brake overall quality. Speaker placement is part of the hobby tweaks. If music is your fancy the speaker will sound more natural away from the boundaries to create an imaged soundstage from behind your speakers. For home theatre the room becomes more involved to increase/reinforce low frequencies and maximize the SPL, yet for a blend of movie/music it’s more what sounds optimal to you with the hope your friends and family will agree with your setup. Keep in mind the optimal location isn’t always the ideal location for room traffic. It’s a give and take scenario so the room can still maintain some functionality unless you have a dedicated theatre or studio!
 

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