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Understanding Loudspeaker Power Ratings

Tech Talk With Big Tony

Speaker power handling must be the most misunderstood specification in our industry.  Knowing the power handling of a speaker is rather useless without considering other specs and details.  It’s like knowing the “what” without the “when” or “where.”

Eminence uses an industry standard method (EIA 426A) for establishing power ratings. A speaker is tested in free-air with a continuous noise signal with a 6dB crest factor.  This continuous average power rating (or “watts” rating) is basically a thermal limit.  Eminence does not associate a watts rating with “RMS.”  RMS pertains to voltage or current, but “RMS watts” is an erroneous term.  The music program rating is always twice the continuous rating.  It is a higher rating because music has many peaks and dips and is not as abusive as a continuous signal.  This is a good rating to select amplifier power for proper headroom in a pro audio application.  Eminence does not publish a peak rating, but we accept it as four times the continuous rating.  Peak is higher because the shorter duration of a burst of sound is less abusive than a music signal or a continuous signal.

Power testing is performed on all Eminence branded speakers offered on our website.  We also manufacture products for OEM (original equipment manufacturer) companies, which may or may not carry the “Eminence” name.  These products are custom designed to a manufacturer’s specifications and are not power tested or rated by Eminence.  It is at the discretion of our customer to test and rate their amp or cabinet, but rating the speaker may not be a concern for them.  For instance, if a certain speaker works to the satisfaction of a manufacturer in a 300 watt product, it’s insignificant if the speaker can actually handle 500 watts.  The cabinet or amp containing the speaker will get the 300 watt rating.  The more important concerns of the cabinet or amp manufacturer are how well the speaker performs mechanically and sonically.  The mechanical performance involves how well the T/S parameters of a speaker align with the enclosure.

Mechanical power handling becomes the real issue when you consider a speaker for a specific cabinet.  Keep in mind, it can never exceed the thermal power handling because the speaker would fail first.  A speaker’s mechanical power handling will vary in different cabinets and is dependent on the cabinet volume and the tuning frequency (if ported). Larger cabinets and lower tunings, for example, are both more abusive conditions and will decrease the mechanical power handling of a speaker.  Woofers (a speaker designed to produce lower frequencies) are particularly more cabinet dependent because bass frequencies are more abusive. Lower frequencies require the woofer to move more air.  In applications where low frequency reproduction is a requirement, it might actually take a 500 watt woofer to handle 300 watts of amplifier power.  This is common in bass guitar and pro audio subwoofer applications

T/S parameters will help you ensure whether or not a speaker is suitable for your cabinet and amp power. They can also help you determine the mechanical power handling of a speaker in your cabinet.  Xmax and sensitivity (or SPL) are a couple of parameters that are so often overlooked.  Xmax is especially important for pro audio and bass guitar applications.  This parameter represents the maximum linear excursion, or in simple terms, how far the speaker can travel before reaching harmful levels of distortion.  A speaker with more Xmax has greater excursion capability (or travel), which basically means it can produce lower bass at higher volumes.  Xmax is crucial to a speaker’s mechanical power handling when the application requires low frequency reproduction.

SPL represents how loud a speaker is and provides another means to compare speakers.  A speaker with a higher SPL will not require as much amp power to achieve a certain volume.  We have found that many people use the high SPL of our pro audio speakers to their benefit for applications such as bass guitar, car audio, and home hi-fi.  The demanding low frequency bandwidth of these applications may often limit a speaker’s mechanical power handling significantly, but the higher SPL can be a huge advantage in several ways.

One example is a pro audio woofer used as a car audio or home hi-fi subwoofer.  A 500 watt woofer may be reduced to a 100 watt woofer if asked to produce a signal anywhere from 20-40Hz.  However, this could be an effective approach if the woofer can produce this signal at 96dB with one watt of power.  In another example, it is often more beneficial to use a high SPL, full range type woofer over a true low frequency woofer for a bass guitar application.  The true low frequency woofer would provide better mechanical power handling in the cabinet, but could be too narrow in bandwidth, resulting in a lack of mids and highs.  It may also require more amplifier power to achieve a desirable volume.  A higher SPL, more full range type of woofer will produce better mids and highs and the overall output is higher per watt.  As previously described, it may take a 500 watt rated speaker to handle 300 watts of amplifier power.

Mechanical versus thermal power handling is not a significant topic for open or closed back, lead/rhythm guitar applications.  The standard guitar frequencies are not that abusive on a speaker, so guitar speakers are not as cabinet dependent as pro audio or bass guitar speakers.  The important factors for selecting a guitar cabinet are based more on how the size and materials affect or add to the tone.

At this point, you might be thinking why Eminence would publish such a useless rating?  Well, a thermal power rating gives you an idea of a speaker’s potential and a way to compare to other speakers.  Most of our speakers are multi-purpose and we don’t know how or where they might be used.  End users often use our speakers effectively in ways that we never thought about, and we encourage it!

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