Monitors.....

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getuhgrip

getuhgrip

Bring Back Transfat!
Nobody got back to the thread about inpedence......

Searching for monitors I started to notice that ohm ratings seem to vary quite a bit. 4,6, and 8 seem predominant.
My amp's rated for 4 ohms at a meger 70watts, so prudence (and volume) dictates that I find a 4 ohm speaker.

I'm curious:
What physically determeines the impedence of a speaker?
What's the reason for varied ratings?
Is the impedence of a speaker alterable by a guy with a soldering iron and a Radio Shack catalog? :D
 
Mainly with a moving coil loudspeaker it is Thermal. The voice coil gets heated to very high temperatures and if this is excessive they either melt or the adhesives that are used in the construction fail.
Also the voice coil can be forced out of its normal working zone (x max) which can cause physical damage to it.

One of the reasons that PA speakers can take more abuse is centred around the design of the voice coil and its suspension, not just thicker wire and a great big magnet.

The subject of amplifier suitability based on just output power and impedences is just not possible as many other things have to be taken into acount. In general a well designed amplifier will drive a well designed speaker period.
 
Thanks for the insight, guys.
So much for modifying monitors.

Anybody want to recommend a 4 ohm monitor in the $300-$400 price range?
 
Come on guys......

Who makes a 4 ohm monitor???!!!:eek:
 
How about skipping the whole passive monitor / small amp / impedance thing and going with a pair of powered monitors? 8th street has the M-Audio monitors for about $300 / pair. Event PS6 seem to be running about $600 / pair. Both are biamped with enough power to be heard. The PS6s are really sweet.
 
Just a little circuits note:

Ohm's Law:
Voltage = Current * Impedence

As the impedence goes down, the amp needs to supply more current.
 
Lower impedance drivers tend to be more efficient. They also tend to rely more heavily on electrical damping rather than mechanical to control their motion. These are generally desirable properties, but they lay more of the burden on the amplifier.

An ideal amplifier would also be an ideal voltage source, which can supply whatever current is required for a given voltage swing. In other words, it's power rating for various speaker loads might look like this:
Code: 
Load(Ohms) Power(Watts)
8          100
4          200
2          400
1          800
0.5        1600
Unfortunately, real amplifiers can't do this. Their ability to deliver current poops out when the load impedence drops too low. And with dynamic loudspeakers impedence is not just as simple as Ohm's Law. The resistive (static) impedence component can often be 30% lower than the rated impedence. It's complicated, and I can go into a more technical explanation, but sometimes the amplifier can be "chasing" the dynamic part of the speaker load. It's sort of like running on top of a circus ball. You're always just 1 meter off the ground, but the ball is rolling out from under you, making you work that much harder. And the faster you run, the harder it is to stop.

Anyhow, where was I going with this? Oh, well designed low impedence speakers can have advantages over higher impedence speakers, but they tend to be more picky about the amplifier.

barefoot
 
I copy every bit of tech info I ask about. Every couple months I print several pages and enter them into a folder. I'm not thinking of compiling a book, but the folder's becoming quite large!

In any case, I do want to use this amp at least for experience sake until summer. What I was really hoping to see at this point are recommendations or comments on monitors in this range.
The only thing I'm seeing in 4 ohms is Alesis' Mk2.

How 'bout it? :cool:
 
Ok, let's take this from another angle. Is there a defined reduction rate when going from a fixed power induction at a certain ohms level up and down? For example: 70watts @ 4 ohms, ? watts @ 6 ohms.


Oh yeah! Anybody got a set of 4 ohm passives that they like? Cool, what are they? :D
 
The penalty is half the distance to the goal; 35 watts @ 8 ohms. 8 ohms works best.
 
35 Watts low?

You should be fine with whatever passive speaker you get. I know that 35 watts doesn't sound like much (and in terms of PA's, guitar amps, etc, it isn't), but I would bet that you'll be surprised how loud that 35 watt amp would be into 8 ohms. Because, while you've been focusing on that loss of 35 watts (going from 4 ohms to 8), don't forget that it's LOUDNESS that you're interested in. And to double apparent loudness, you need to increase (radiated) power by 10 times!

Put slightly differently, let's take the Mackie HR824's (one of the more powerful biamped speakers out there). The're rated at 250 watts per speaker cabinet. Ignoring for a minute that fact that your Mk2's or Tannoys are going to have different drivers/ efficiency, even if you only ran your amp at 25 watts, it would only seem half as loud! Not a bad deal, all things considered.

The biggest problem is going to be the quality of that amp. If it's a good-quality 70 watt amp, it may actually work better for you than a cheapo- 150 watt-jobby. In short, don't worry about impedance. If you can, bring your amp to your local (or not-so-local) music shop and try it with all their passive speakers, and buy the ones that your ears trust most.

Also, I think someone else mentioned this, but be careful until you do get a bigger amp. If you overdrive the amp trying to make the speakers sound like a 15" sub, you can distort the amp which can damage the speakers. You'll know it as soon as the speakers get that "loud concert" sound. It's all the upper-harmonics from the distorted power amp. Anyway, try out some speakers and have fun! :)
 
getuhgrip said:
Come on guys......

Who makes a 4 ohm monitor???!!!:eek:
Click to expand...
the tannoy reveals are 4 ohm impedance.

btw: speakers are rated in impedance and not in resistance because their 'resistance' is virtual (meaning there is a phase shifted part j). This is cause the speaker itself is mainly a coil plus the frequency switch also consists of coils and capacitives being a resonance circuit. Thus gives the speaker a impedance that varies over the frequency. The nominal is the lowest impedance over the frequency.
Most of the pro amps (Hafler, Crest,...) can drive speakers down to 1 ohm, but i had big troubles with a usual homie amp driving my Infinity Kappa until i got my mosfet power horse ;)
 
The specs on my Reveals say 6 ohm (nominal) and recommended amp power is 50 - 100 watts into 8 ohms.

:cool:
 
struberg said:
btw: speakers are rated in impedance and not in resistance because their 'resistance' is virtual (meaning there is a phase shifted part j).
Click to expand...
Not exactly. Dynamic loudspeaker voice coils have a DC resistance which is usually about 2/3 to 3/4 the nominal rated impedence.

Ztotal = R + Zfreq
Originally posted by getuhgrip
Is there a defined reduction rate when going from a fixed power induction at a certain ohms level up and down? For example: 70watts @ 4 ohms, ? watts @ 6 ohms.
Click to expand...
No. This depends on the output impedence and maximum voltage swing which differ from amp to amp.

Don't worry about it. Your amp should have plenty of power for monitoring. The more important questions relate to internal nonlinearities and how the amp deals with the complex part of the speaker load - i.e. how well the amp was designed and constructed. All this discussion of power rating tells you nothing of this.

barefoot
 
Well, the Tannoys are rated at 6 ohms and recommended power is 50 to 100 watts.

How does this play out with my 70watts @ 4 ohm amp? If there is a reduced wattage supplied to the 6 ohm speaker, will it be enough to get good performance from the speaker?

I always thought that more power meant not just louder volume, but better sound at low volume.
 
Correct me if I'm wrong but wont he get more power using 8 ohm speakers, not less?
 
getuhgrip,
Let's forget about any frequency (time) dependence and assume our speaker are resistors.

Power=Current*Voltage=I*V
and
V=I*R
so
P=I^2*R
or
I=sqrt(P/R)

This shows you that for a given speaker load (R) the current (I) the amp must be able to deliver goes up by the square root of power(P). More powerful amps, therefore, must have higher current capacity. This can sometimes translate into better performance and sound quality but it's no guaranty. Better to have an excellently designed lower power amp than a poorly designed high power amp.

TexRoadkill,
The power equation above can also be rewritten as:

P=Vrms^2/R

The maximum voltage swing is fixed in an amplifier (40V for a 100W\8Ohm amp). So the maximum power output decreases as the load increases.

barefoot
 
>Come on guys......

Who makes a 4 ohm monitor???!!!

The Event 20/20 is 4 ohms.
 
I went with the Tannoy Reveal based on name and a half dozen positive reveiws from actual users.

If the Samson amp won't drive them I'll buy a little more amp.

I'll let ya'll know how they sound when I get them.
 
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