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Old 16th February 2012, 11:47 AM   #1
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Default 4ohm amp running into 8ohm drivers?

Check out my plan below, in particular the sub amps.

So the dayton apa150 amps run 2x75watts at 4ohm... the Emi 15's are 8ohm speakers. So 3 questions:
  1. Will this amp be damaged if I run it like this or will it adjust fine you think?
  2. Would running all 4 subs from one amp (2 being parallel) be a better route?
  3. Anyone know how much power these Alpha's need in general since they're so efficient?

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Old 16th February 2012, 11:51 AM   #2
AndrewT is offline AndrewT  Scotland
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Tube/valve output stages do not tolerate open circuit loading.
Sold state in general only complains when the loading is too low.
Normally all SS perform better with a higher impedance loading.

An amplifier specified as suitable for driving a 4ohms speaker, will more than likely play better when driving an 8ohms speaker.
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Old 16th February 2012, 12:18 PM   #3
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1. The Zaph ZA5 design is designed around a sealed/ported box with a certain front baffle width. If you go to an open baffle design with a much wider baffle the design will not perform as intended by zaph. ie. YMMV, and it is no longer a proven design. The ZA5's will run out of midbass potential very quickly in free air with no high pass filter.

2. If the Emininence 15"s are 8ohms each, you'll have to wire them in parallel (for 4ohms total) or series (16ohms). Before running them in parallel make sure the dayton can handle a 4ohm bridged load. My guess is it won't. 3rd option is run one woofer off each channel, which is what I would do. You won't need much power, because like I said above, the 5" midbass will limit you with no high pass filter.
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Old 16th February 2012, 04:56 PM   #4
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The APA150 is a two channel amp.
Each channel is 75W for a 4 Ohm driver.
It can be use bridged. Then you have one channel.
This channel is 150W for a 8 Ohm driver.

You only need one APA150, to get 2 x 75W
Each channel running a pair of EMI15 wired in parallelle.
Two 8 Ohm driver wired in parallelle is a 4 Ohm load.

Using bridged mode you can get 2 x 300W.
With 4 APA150 one for each of the 4 EMI15.
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Old 16th February 2012, 05:04 PM   #5
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So andrew, you think this may be ok then?

Storm, you bring up some good points. I chose the in-wall Zaph's which according to this would be a good candidate. This is from Madisound when I inquired about performance on an open baffle:
Click the image to open in full size. I wonder if there's some mods to the c/o that could fill in those low-mids better?

McChambin, do you think 2 x 75 will be enough to power 4 Alphas?
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Old 16th February 2012, 05:17 PM   #6
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Quote:
do you think 2 x 75 will be enough to power 4 Alphas
No idea.
I don't know how efficient these drivers are and what is your taste about sound level.
Look at the sound pressure to know about driver efficiency.
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Old 16th February 2012, 05:49 PM   #7
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" ... Will this amp be damaged if I run it like this or will it adjust fine you think? ..."

Damage is extremely unlikely with a Sold State amp driving a higher load than recommended. You are effectively increasing, not decreasing, the safety margin.

Could affect frequency response, not usually a big effect if the amp isn't transformer-coupled (and few SS amps are, some classic units mostly) but it's possible.

Damping factor will increase. In theory that means tighter control of the driver, but my own personal experience is damping factor isn't an issue for or against in most cases, even with a transformer-coupled amp. There are those who disagree, though, and say it does matter.

Output power in watts may fall. Not a safety issue, though, unless you end up really overdriving the amp.

Bottom line: it's not a problem.

As an aside, it is technically not a "4-ohm amp". That's just the recommended load; the actual output impedance of the amp will be (far) below 1 ohm.
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Old 16th February 2012, 06:08 PM   #8
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Quote:
do you think 2 x 75 will be enough to power 4 Alphas?
Going about SPL in the case of two drivers run together is not obvious.
A channel has two paralleled EMIs.
Each driver is run at 37.5 Watt. However the two drivers will give more SPL than a single driver run at 75Watt.
I think there is a 3dB gain, not sure ( I saw this long ago ), please check with driver guys.
So you would get the same sound level as 2 x 150W.
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Old 16th February 2012, 06:13 PM   #9
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That makes sense Johnny! The answer I was hoping for actually. I've read that Open Baffles work well with increased damping. I listen to a lot of alt-country, singer-songwriter stuff.... mostly music that would be in the sonic genre of Jazz. I like to hear a tight pluck of the bass string and a thump from the kick drum. I don't do a lot of metal or punk these days so a nice tight bass would be perfect.
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