Impedance Load Question

[DJ NiteFlite]

I'm hoping their are some audio experts here that can help me. I'm considering buying a Peavey xr 684 from a friend. It's rated at 200 watts rms @ 4 ohms stereo and 420 watts rms @ 8 ohms bridged. I want to run it in 8 ohms stereo. This should be safe correct? Is there a way I can calculate the wattage loss?

For now I don't want to wire it parallel and bring it down to 4 ohms because the amp doesn't have binding post outputs. I want to use my trs-trs 1/4" cables.

[DJ NiteFlite]

I ended up finding the answer myself. I thought I should post the answer for anyone searching the forums for the same reason in the future.

If an amp is stable down to 4 ohms, then it is also stable at 8 and 16. Running a 4 ohm stable amp at 8 ohms necessitates a wattage loss up to 50%. For example, an amp that delivers 200 watts at 4 ohms may only push out 130 at 8 ohms.

[PRECARIOUS]

Hey DJ NiteFlite,
Where did you find the info on Ohms and watts calculation?

I have an older Audiopipe 1500 amp that is trying to push 2 1000w floor speakers with 18s (using 1/4 inch mono cables). I'm only able to turn amp up to around 50% before clipping starts and sound deteriorates. I'm only a hobbyist and still learning but pretty sure something isn't right.

My configuration is:
Computer -> Mixer -> EQ -> Amp -> Speakers

Thanks!
Scott

[chefmix]

Can you post a picture of the amp? I can't seem to find any info on it

[PRECARIOUS]

Thanks Chef!
Here's what I could find about the Audiopipe APA-1500. I assumed by the model number that it was 1500 watts but perhaps that's not correct. I also assumed that my speakers could handle 1000w since I put 1000w 18s in the cabinet ...turns out that the cabinet has a label that states peak is 400w. I bought the speaker cabinets and amp from a reggae band. I had to replace one 18" because it was sounding blown (my first sign that maybe these items don't really go together as they were using them). Anyways... here's my mix-match of components, any help and suggestions would be greatly greatly appreciated:

Audiopipe APA-1500
input impedance: 10k ohms, unbalanced & balanced
input sensitivity: 1.15v
output power: 8ohms/ stereo 150 watt/channel
4 ohms/stereo 200 watt/channel
4 ohms/bridged 430 watt
frequency response: 25hz-25khz +0/-1db
total harmonic distortion <0.3%
signal to noise ration: 100db
weight: 33.7 (lbs)

These are the settings I currently have on back of Amp:
MODE Options: Parallel, Stereo, Bridged (Stereo selected - although Parallel might be better?)
SENSITIVITY Options: 1.44v, 1.0v, 0.7v (1.0v selected)
NORMAL or COMPRESSED: (Normal selected)
GROUND Options: Lift, GND (Lift selected)

Speakers:
They are large floor-speakers like you might see at a swap meet. In the cabinets are 1-18, 2-Horns, 4-Tweeters. They are heavy loads of crap but they sound better than the 12" name-brand portables that I occasionally rent. Here's the specs:

Zebra (brand) Pro XL Series Z-1832
Woofer: 18" with kapton voice coil
Tweeter: 4 Super Bullet 4x5 Tweeters
Horn: 2 4x10 Super Magnetic Horns
Frequency Response: 32Hz - 20.000Hz
Power: 400 Watts Peak
Impedance: 8 Ohm
Sensitivity: 101dB
Size: 35"(H) x 24"(W) x 17"(D)
Weight: approx. 78 lbs
Designed in UK

Link to amp:
http://www.savinglots.com/lotprod.asp?item=APA1500

Link to speaker:
http://www.ebay.com/itm/DJ-SPEAKER-B...-/370492091282

[deevey]

I have an older Audiopipe 1500 amp that is trying to push 2 1000w floor speakers with 18s (using 1/4 inch mono cables). I'm only able to turn amp up to around 50% before clipping starts and sound deteriorates. I'm only a hobbyist and still learning but pretty sure something isn't right.

Dude you are only getting 150 watts into those boxes .. you need a bigger amp.

I also assumed that my speakers could handle 1000w since I put 1000w 18s in the cabinet

Since you have changed the rating on the box, so the stickers mean jack shit :P

You might need to change the crossovers to handle the different drivers.

Depending on the speakers you replaced them with your resistance may have changed to something odd (e.g. 6ohm).

[PRECARIOUS]

Thank you deevey,
If you read my last post (below) it might make more sense ...but your volume settings comment brings up another question. What is the optimum (volume) to set each component in the string? My configuration and output levels typically look like this:

iMac Computer (volume max)
-to-
Small 2ch Mixer -not amplified- used as master volume (usually around 25% - higher makes amp clip)
-to-
Equalizer (set at 0 gain)
-to-
Amp (maxes out at 60% before clipping)
-to-
Speakers

Is my configuration correct? Please read below for specs on Amp and Speakers. Forgive my ignorance and THANK YOU !!!

Amp:
Audiopipe APA-1500
input impedance: 10k ohms, unbalanced & balanced
input sensitivity: 1.15v
output power: 8ohms/ stereo 150 watt/channel
4 ohms/stereo 200 watt/channel
4 ohms/bridged 430 watt
frequency response: 25hz-25khz +0/-1db
total harmonic distortion <0.3%
signal to noise ration: 100db
weight: 33.7 (lbs)

Settings on back of Amp:
MODE Options: Parallel, Stereo, Bridged (Stereo selected - although Parallel might be better?)
SENSITIVITY Options: 1.44v, 1.0v, 0.7v (1.0v selected)
NORMAL or COMPRESSED: (Normal selected)
GROUND Options: Lift, GND (Lift selected)

Speakers:
They are large floor-speakers like you might see at a swap meet. In the cabinets are 1-18, 2-Horns, 4-Tweeters. They are heavy loads of crap but they sound better than the 12" name-brand portables that I occasionally rent. Here's the specs:

Zebra (brand) Pro XL Series Z-1832
Woofer: 18" with kapton voice coil
Tweeter: 4 Super Bullet 4x5 Tweeters
Horn: 2 4x10 Super Magnetic Horns
Frequency Response: 32Hz - 20.000Hz
Power: 400 Watts Peak
Impedance: 8 Ohm
Sensitivity: 101dB
Size: 35"(H) x 24"(W) x 17"(D)
Weight: approx. 78 lbs
Designed in UK

Link to amp:
http://www.savinglots.com/lotprod.asp?item=APA1500

Link to speaker:
http://www.ebay.com/itm/DJ-SPEAKER-B...-/370492091282

[DJ Aaron]

Impedance is actually variable and changes with frequency. The curve is not linear but it typically dips in the low frequencies. An impedance rating on a speAker is a nominal rating not an absolute rating so a 8 ohm speaker can dip to 4 ohms or lower at 40 hz which is why you need an amp can that get as close to doubling down as possible. Ideally if an amp can do 100 watts in to 8 ohms you'll want it to do 200 watts in to 4 ohms. This wil enshure your amp won't clip with intense bass.

Look for high current amps. Current is way more important than wattage. High current and lower wattage is much better than high wattage and low current.

[manchild]

Your underpowering the heck out of those speakers. I would suggest getting a bigger amp. In the meantime be careful

[DJ Aaron]

Absolutely you are under powering those speakers. If a speaker can handle 400w, use a 600 watt amp. You'll typically be driving the speakers with only 200-300 watts but the bass transients will require more juice. Remember low frequency = low impedance. Low impedance = more power needed.

Speakers can handle much more CLEAN power, that they denote on the speaker typically. They can also handle big transients for small instances of time. If you can be careful and not do anything reckless you should always over power your speakers and adjust the gain structure so you don't blow anything.

I've fixed a lot of speakers in my day and you blow speakers with distortion (under powering) way more than too much power.