Axiom Home Page Forums General Discussion Technical Questions Understanding Specifications

I need some assistance in understanding the specs of the speakers in order to be able to do a more objective comparison between different sets of speakers. The part of the specs for M80's as mentioned below in RED needs better understanding........
Freq Resp +/-3dB (Hz): 34 Hz – 20 kHz
Freq Resp +3dB- 9dB (Hz): 25 Hz – 20 kHz
Impedance (Ohms): 4 Ohms Impedance Graph
X-Over 160 Hz & 2.3 kHz
Also, how does changes in the above specs change the performance of the speaker?
Thanks

The ±3 dB is the range where the speaker is considered audibly flat. Differences off less than 3 dB are hard to distinguish when at different frequencies.

The +3 dB to -9 dB covers the usable range of the speaker. The -9 is almost always on the bass end of things. While you'd be able to notice less output in the lower frequencies, there's still some usable output even 9 dB down.

Impedance is a lot more technical. It refers to how easily alternating current flows through the speaker at different frequencies. It's enough to say that you don't really need to worry about it, just get a good quality amp, and everything will be fine.

X-Over (or crossover) points are the points where each driver (or pair of drivers in the case of the M80) blends into the next. From the woofers to the midrange at 160 Hz, and the mids to the tweeters at 2.3 kHz. This doesn't change the performance of the speaker at all, it is just up to the designer to properly select these points for the drivers (and enclosure) being used.

Really, the only thing that tells you about the performance of the speaker is the frequency response range. 20 kHz is enough on the upper end, and as long as the bottom goes low enough for your taste, or can at least get down to where the sub is going to pick up (80 Hz typical), then it's good enough.

Sarang, the smaller the +/- db spec on the speaker, the more linear, or 'accurate' it is over the listed freq range....+/-3db is more linear than +/-6db for instance, but not as linear as +/-2db over the same range. So the +/- 3db is the variation from 34hz to 20khz(at 34hz it's down -3db) where at a lower 25hz starting point the speaker is down -9db....ie the freq response is quite flat down to 34hz then it tapers off at an increasing rate(that's where a sub is handy).

I wouldn't worry too much about the ohm ratings as long as you have one of the brands known to work well with a 4ohm load. Most modern mid level avr's should be fine. Keep in mind, a lot of speakers which are listed as being 8ohm speakers(considered easier to drive) actually have dips much, much lower into the 4 ohm region as well.

The X-over points are where each driver(woofer/mid/tweeter) takes over a certain set of freq's which they were designed for. The points where these drivers are crossed over, depends on a number of factors but mainly to do with the drivers themselves. For instance, some woofers are quite able to be crossed over at up to and over 2000khz, but you're asking the drivers to play a broad range that might be better played by two drivers covering different frequencies.

I hope that helps a little. Maybe one of the engineery guys can elaborate.

Freq Resp +/-3dB (Hz): 34 Hz – 20 kHz : The spec shows the range of frequencies a speaker can produce measured from 20Hz to 20kHz. 20Hz to 20kHz is regarded as the range of human hearing. This spec is taken in a anechoic chamber which basically removes any room interaction. +/- 3dB is a tolerance window. So basically the amplitude relative to the frequency does not deviate more than 3db from the center of the graph taken.

Freq Resp +3dB- 9dB (Hz): 25 Hz – 20 kHz: This is the same thing however instead of taken in a anechoic chamber, this is a "in room" response of the speaker noted by the +3db-9db. The specification takes into account room interactions and room gain. Personally, I do not pay much attention to "in room" specs as every room is different so it is not a very accurate measurement. You can take this spec as a "best case scenario" for performance in your room.

Impedance (Ohms): 4 Ohms Impedance Graph: Impedance is the speakers resistance to power or impeding the flow of power. 4 ohms is the nominal rating for this speaker and is rated to be no greater than 1.25 times the minimum impedance within the pass band. The minimum impedance is 3.2 ohms. Whether this is a hard 4 ohm speaker or easy 4 ohm would be determined by the phase angle which is not shown.

X-Over 160 Hz & 2.3 kHz: These are the two crossover points which separate what frequencies the bass, midrange and tweeters play. This spec tells us nothing about the performance of the speaker.

That's craziness there.

Thanks for the quick response Chris, Adrian and Dr. House.
I think I now understand the +/-dB theory. Based on the above, can we say that since in room response is +3dB- 9dB as compared to +/-3dB in the anechoic chamber, the reduction in dB in the lower frequencies is due to the absorption by the furniture and room treatments?

On the ohm rating, I read somewhere on this forum, that even though the M80's are rated 4 ohms, they should still be run at 8 ohms on the receiver. Is that true? If not, do you think the Yamaha RX-A3000 (140w x 7) can run the M80's and V180 on 4 ohms?

In case of X-over, I read certain speakers claiming that they crossover at a lower frequency (2.2kHz or lower) to the tweeter, thus reducing the load on the midrange. How does that affect the sound?
Thanks

Actually, the room causes a gain in low end, so the -9 is still supposed to be usable in room.

You should always leave the receiver set to it's highest (usually 8, but on some 6 Ohm) setting regardless of the speaker used. The lower setting is for a UL rating, and only causes the amp to have it's current limited, which is not a good thing.

Some midrange drivers start to break-up (non-uniform cone movements that cause distortion) at higher frequencies, so sometimes a lower crossover point is better. At the same time the lower point will place more load on the tweeter. Like most things in speaker design, there are trade offs. All of this is completely dependent on the driver selection, and thus up to the designer where to best place the point.

Any receiver can drive a pair of M80's. A lot will depend on your listening distance determined by room and its size and how loud you like to listen to music and movies. If you don't push the receiver to hard then you won't run into problems, push it hard and for a long period you can risk it overheating.

In terms of the crossover points they will be different from speaker to speaker, brand to brand based on the measured T/S parameters of the woofers and tweeters that is used in the design. Specific measurements are taken on drivers such as frequency response, impedance and cumulative spectral decay (waterfall plots) to find the break up/resonances of the specific drivers in question. You want to avoid this and this is where the crossover design and the selection of the crossover points are important. Crossing over the midrange lower depends on the driver parameters and where the driver begins to "break up".