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Annex Speaker Kit Development – Initial Thoughts and Transducer Selection

Initial Thoughts

Another 2 way bookshelf speaker kit? Not just another.

There is no shortage of speaker kits in the marketplace using this configuration. It seems to be considered the quintessential go-to kit for the new speaker builder. And that is precisely why I thought it was appropriate to begin my Make Audio journey targeting this configuration.

I wondered just how far I could take the performance of this speaker if I removed many of the limitations faced by DIY and professional speaker designers while choosing components that resulted in the highest performance to cost ratio.

Listed below are some of those typical limitations and how they were addressed.

  • Choosing transducers without being constrained to a single manufacturer.

You may notice that many speaker kits use transducers from the same manufacturer. There’s usually a reason for this and it typically has little to do with performance. Many kits merely exist as a platform to sell more transducers or crossover components for the manufacturer or retailer. Make Audio does not favour or benefit from using the transducers made from any one manufacturer.

 

  • Most speaker kits are designed by hobbyists.

My speaker building hobby began in 1992 and spanned 10 years. After 25 years as a professional loudspeaker designer, I am not embarrassed to admit that not one of my DIY builds was what I consider to be a competent design.  I vehemently believe that a DIY speaker design will drastically sound better if it is designed by a competent professional.

You make wonder why all speaker kits receive glowing accolades from their builders. The speaker kits are not objectively evaluated.

Renowned American acoustic expert and former MIT professor Leo Beranek wrote:

“It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else’s loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person’s opinion.”

( L.L. Beranek, Acoustics, McGraw-Hill, New York, 1954, p.208 )

I too was once guilty of this! Today, I take an objective approach to speaker design including extensive measurements, blind screen voicing and evaluation against well regarded professional speaker designs.

 

  • Crossover voicing time limitations.

The best speakers are never released into production after being conceived in a computer or evaluated with only measurements.  Objective voicing is always necessary to achieve the best result. Cycling between anechoic measurements and voicing in a controlled environment is time consuming. There are always time constraints in the professional voicing of HiFi loudspeakers. This was not a constraint in the Annex speaker development. I took the amount of time needed to perfect the design.

 

  • Size and appearance.

The Annex speaker prioritizes sound quality above all.  It won’t win any industrial design awards. Although the size is slightly larger than average, some builders may desire a smaller speaker (already on the Make Audio development roadmap).

A specific cabinet volume is required to achieve the optimal low frequency extension. The mechanical design is easy to assemble and yields the greatest flexibility with regard to finishing options. PVC, veneer, or paint finishes are all easy to apply to flat panels.

 

Choosing the Transducers

Tweeter

A high performance wide dispersion soft dome tweeter can offer exceptional performance with careful design. Metal dome tweeters may have some advantages but the audibility of those advantages is questionable. Some builders and audiophiles dislike metal dome tweeters because they describe their sound as harsh. This harshness is more of a product of the crossover design but I likely won’t be able to convince the critics. There is generally no such negative attribute associated with soft dome tweeters and speakers using them are found to be acceptable to a larger audience. The tweeters chosen for the Annex speaker are of the wide dispersion variety and do not utilize a horn or waveguide. I consider this to be the preferred target for the masses because room treatment and speaker position can be used to manipulate unwanted room reflections. Increasing the dispersion of a directional speaker is typically not an option.

Other important attributes are the resonant frequency, linear excursion, amplitude response linearity, dispersion linearity, impedance linearity, power handling, sensitivity, manufacturer quality assurance, materials, and of course cost to performance ratio.

 

Woofer

As it relates to low frequencies, I define “full range” as a speaker that generates bass sufficient for most music. It may not be able to reproduce the lowest organ notes or your car audio bass demo CD but you typically won’t notice any missing bass when listening to most of your music at a typical SPL.

I have found that a nominal 6.5” diameter woofer yields just about the best balance between low frequency extension, output capability and uniform dispersion for a 2 way speaker. A smaller woofer can result in a smoother off-axis amplitude response around the crossover frequency however the smaller woofer easily reaches its excursion limit when driven with music containing moderate bass content. If used with a subwoofer, the smaller diameter woofer is a better choice however this is a “full range” speaker designed to be used without a subwoofer.

Other important attributes include the T/S parameters, linear excursion, amplitude response linearity, dispersion linearity, power handling, sensitivity, voice coil diameter, overdrive behavior, spurious noise, manufacturer quality assurance, materials, and again, cost to performance ratio.

 

 

 

Transducer measurements, cabinet design considerations, and acoustic design goals to be discussed next…