All you audio guys, impedance question

[jerrymrc]

Spikkers. About $150 to build these and I have to say they are still in my sitting room.

[Singlestack]

Beautiful, simply beautiful. Well done...

[PugnacAutMortem]

What is the exact amp and speaker models you will be getting ? (Point us to the specs/datasheet for them)

We need to make sure you are not confusing Wrms with Wp-p (peak-to-peak) or Wprog (program etc.)
There are also ways to protect your speakers from seeing too much power.

Well I know these are the speakers I'm looking at getting (one of each in both cabs):

http://www.eminence.com/pdf/Cannabis_Rex.pdf

http://www.eminence.com/pdf/Screamin_Eagle.pdf

And I'm almost positive this is the power amp I'm getting: http://www.musiciansfriend.com/ampli...rack-power-amp

Side note: What's with the dip between 1k and 2k on the EQ curve (or whatever the technical name for that chart is)? Is that all speakers or all guitar speakers or...?

[james_bond_007]

http://www.eminence.com/pdf/Cannabis_Rex.pdf ...

Side note: What's with the dip between 1k and 2k on the EQ curve (or whatever the technical name for that chart is)? Is that all speakers or all guitar speakers or...?

Speakers are essentially an electromechanical device. You put in an electrical signal, and the speaker mechanically "vibrates".

Ideally, one would like a flat response across all frequencies; that is, for say a single sine wave input of say 1V at any frequency, one would like the speaker to produce the same volume on its output. The graph (in your spec) shows the input frequency on the x-axis , and the output (in Sound Pressure Level) on the Y-Axis.
(Don't get too hung up on "dB" or "dBm or "SPL", just realize that it is a way to measure the output response of the speaker).

Like all mechanical systems, it has "sweet spots" and "dropouts" where it vibrates "better" or worse, depending on the frequency of the input.
So what you are seeing at 1.5KHz. is a frequency where it does not respond (aka a "bump" as well to frequencies (aka attenuates) in that range and produces a "softer" output than it does for signals in the range of 200-1KHz.

Likewise, it "likes" frequencies of just above 2KHz. and produces "louder" (aka amplifies) output for signals in that range (aka a "hump")

ALL speakers will have these, but better speakers are "flatter" (have fewer and not as dramatic "humps" and "bumps") than those of lesser quality.

Keep in mind that
1) the speaker response curve can be "corrected" by using a 31-band graphics equalizer (or "tone controls" ) to amplify/attenuate specific frequency ranges.
The sliders on the eq allows one to adjust the volume for only signals that fall into small frequency ranges, like 1K-to-1.3K etc.


So you can "flatten" the response from most speakers with an eq. (tone controls are also "eqs" , but cover a much wider range with a few knobs...they cannot address a narrow range like the eqs)

2) Speakers are typically measured in a "perfect" room...one that absorbs all the sound and does not allow it to bounce around (aka an anechoic chamber...a room that does not have any "echos")

Each room also has its dropouts and sweet spots across the frequency range, so a perfectly flat speaker will still need to be adjusted for frequency (aka tone) in a room. And each room will be different. So paying a lot for flat speakers that are going to be moved from room to room as your gigs move from bar to bar is not such a great idea. Paying a lot for speakers that will sit in one place/room is worthwhile (aka this is why "studio monitors" are often very pricey)

Sometimes when turning up an amp, you will hear feedback. If you listen carefully, the feedback has a certain "sound/freq range ". The feedback is the result of "certain" frequencies being amplified by the room more than the others. They get loud enough that they are picked up by the mic and re-amplified, along with the source signal until they keep growing and make the undesired sound. One way to fix this is "turn down the master volume" for all frequencies. Another way is to use an eq to only attenuate only the frequency range causing the feedback. That way you can get more volume out of your system, while sacrificing only a narrow band of frequencies, rather than ALL frequencies.

3) The ear is not a "linear" device. That is, if you double the power on a signal, your ear does not perceive it as "twice as loud". The ear works more on a logarithmic scale, such that is takes "about" 10x the input to make your ear perceive the sound as being "doubled".

I hope this helps fill in some of your questions ...If not, just ask. There are a lot of knowledgeable and friendly people on the forum.

Someone on here will help you.

[james_bond_007]

Well I know these are the speakers I'm looking at getting (one of each in both cabs): ...

So "I" have a few questions.

1) Why do you want to mix 2 different 12" speakers in the same cabinet?
From the specs, they don't seem to be too drastically different in response (Cannabis seems a bit better: humps/bumps not as pronounced, and flat part of output is at a higher SPL)

2) You have a "mono" guitar. Why do you want a stereo amp ?
Maybe...If you are using some effects, sometimes the effects can have a stereo output.
Maybe...If you need to separately control the volume of 2 cabinets, because they are located far apart.

But typically, the "guitar" speakers are stacked and located together.

3) Why not use bridged mono mode ?
Maybe...some amps invert the phase between the L half and the R half to their respective output jacks.

4) This amp has "2" output jacks for each channel (2xL and 2xR). Be careful.
The schematics show them wired in parallel. So if you plug "2" 4 ohm loads in the "2" L outputs, the amp sees a 2 ohm load...not good.

5) The amp is YOUR choice...I've not seen very good reviews on it so far. Seems the key selling point is that it tries to emulate a tube amp, but is reported to be VERY noisy.

6) Amp specs seem suspiciously lacking typical info.
Output power "type" is not listed (EX: RMS, peak, music, program etc.) but Input source IS spec'ed as RMS...hmmmmm.
No explanation for the 2 output jacks on each channel...I had to dig out the schematics to figure it out.
Input jacks on the rear panel...no issue, but typically they are on the front where one can plug in/out with ease.

7) What will you use for and how will you be using effects (as far as the signal chain goes) ? pedals ? another rack mounted unit ? etc.

8) Have you heard this amp ? Do the "tube simulations " really work well ? Do you need/want that ?
If not, consider using a solid/clean power amp, with a proven track record like a QSC.

[sellersm]

I used to have a set of Maggies! My all-time favorite speakers are the B&W 801 series! Could never afford them, but I used to love to listen to them, powered by Krell or Mark Levinson stuff. Just wow! Those are nice looking speakers there, Jerrymrc.

[james_bond_007]

Nice job, Jerry.

[jerrymrc]

Now that I think we have a direction I take it you are looking for pro-sound reinforcement as 007 is alluding to. I have only built a couple of pro-sound type stuff and that was long ago.