Eminence Alpha-15A - 15" Woofer
Eminence Alpha-15A - 15" Woofer
The Eminence Alpha-15A is a 381 mm (15") diameter paper cone woofer. Eminence recommends the Alpha-15A driver for professional audio and bass guitar applications as a woofer in a vented or sealed enclosure. The woofer has a high Qts and works very well with open baffle speaker designs. We have found the Alpha-15A to be a cost effective and solid performing open baffle woofer. On a suitably sized open baffle the Eminence Alpha-15A woofer can produce excellent bass output down to about 40 Hz. The Alpha-15A woofer is available from Parts Express.
Photograph 1: Eminence Alpha-15A - High Sensitivity 15-inch Woofer Drivers
The Eminence Alpha-15A woofer driver utilizes a black paper cone and a solid composition paper dust cap. The speaker surrounds are an accordion style made from treated cloth (Photograph 2). This style of speaker suspension can have a very long service life. The nominal impedance is noted as 8 ohms and the measured DCR is about 6 ohms. The Alpha-15A voice coil diameter is 38 mm (1.5") with a vented core and the datasheet notes the woofer power rating at 200W. The weight of the small ferrite magnet is noted as 708 g (25 oz.) and the net weight of the Alpha-15A woofer driver is 3.04 kg (6.7 lbs). The 15" woofer is built around a black pressed steel basket. The woofer basket also features both a front and back sealing gaskets (Photographs 2 and 3) to facilitate front or rear mounting. From the datasheet the Eminence Alpha-15A woofer drivers have a noted usable frequency range of 46 Hz to 3.5 kHz. The woofer excursion is noted as Xmax = 3.8 mm. The overall build quality of the Alpha-15A woofer drivers appears to be very good.
Photograph 2: Eminence Alpha-15A - 15-inch (381 mm) Paper Cone Woofer
An Eminence Alpha-15A sticker covers the small rear motor structure of the woofer which features a vented pole piece. The Eminence sticker indicates that the Alpha-15A woofers are made in the USA. The woofer driver connectors are plain L-shaped spade / solder terminals. The woofer connector terminals are lightweight and do not seem well suited to repeated and heavy use with spade connectors. The Eminence Alpha-15A woofer driver comes neatly packaged in a split moulded styrofoam shell and snuggly inside a sturdy cardboard box.
Photograph 3: Eminence Alpha-15A Woofer - Pressed Steel Basket and Ferrite Magnet
Thiele/Small (T/S) Parameters - Eminence Alpha-15A Woofer
The Thiele/Small Parameters of the Eminence Alpha-15A Woofer have been measured using the Dayton Audio Test Systems (DATS). The T/S parameters derived from the small signal speaker testing as well as the parameters noted on the Eminence Alpha-15A Woofer datasheet are summarized below in Table 1. The measured Thiele/Small parameters of the tested woofer pair were close to the specifications noted on the Eminence Alpha-15A Woofer datasheet. The pair of Eminence Alpha-15A woofers measured very close to one another.
Table 1: Thiele/Small (T/S) Parameters - Eminence Alpha-15A Woofers
|Parameter||Eminence||Woofer 1||Woofer 2|
|Fs||41 Hz||42.39 Hz||43.07 Hz|
|Re||5.88 Ohms||6.04 Ohms||6.05 Ohms|
|Sensitivity||97.0 dB/1W/1m||92.5 dB/1W/1m||92.5 dB/1W/1m|
Eminence Alpha-15A Woofer Testing Notes:
- Temperature = 22.5 C, Relative Humidity = 42%.
- Sensitivity measured at 125 Hz.
Figure 1 shows the frequency and impedance response from the Eminence Alpha-15A woofer datasheet.
Figure 1: Frequency and Impedance Response - Eminence Alpha-15A Woofer (datasheet)
Figure 2 shows the superimposed impedance response of the measured pair of Eminence Alpha-15A woofers. The pair of Eminence Alpha-15A woofers were well matched to each other. The impedance measurements of the Alpha-15A woofer were made using the simple to use Dayton Audio Test System (DATS).
Figure 2: Impedance Response - Eminence Alpha-15A Woofers
Datasheet and Enclosure Notes - Eminence Alpha-15A Woofer
The official Eminence Alpha-15A datasheet is in the links below. The Eminence Alpha-15A Woofer Enclosure Notes for sealed a ported enclosures is also linked below. Note that because of the high Qts, the Alpha-15A woofer can also work well with an open baffle speaker system.
- Eminence Alpha-15A Woofer Datasheet Specifications - (PDF 492k)
- Eminence Alpha-15A Woofer Enclosure Notes - (PDF 410k)
Open Baffle Speakers with Eminence Alpha-15A Woofer
The Eminence Alpha-15A woofer has a small motor and a high Qts which makes the driver well suited for use with open baffle speaker systems. Martin J. King has done some excellent work with the Alpha-15A (see links at bottom of page) and found it to be a well performing open baffle woofer that can produce excellent bass output down to about 40 Hz. Because of the good OB performance and low cost for the Alpha-15A woofer, this is one of the more popular woofers for open baffle speaker configurations. The Eminence Alpha-15A woofer on an open baffle is quick, accurate, clean and musical. The woofer is an easy to drive 8 ohm load and will deliver tight bass provided the small motor is not over powered.
Photograph 4: Eminence Alpha-15A Woofer on 20" wide Open Baffle
In Photograph 4 an Eminence Alpha-15A woofer is shown on a 508 mm (20") wide open baffle speaker and paired with the 3" Fostex FF85K fullrange driver after the Eminence Alpha 15A Experimental Open Baffle Design by Martin J. King. In Photograph 5 the Alpha-15A woofer is used with a circular H-frame open baffle speaker coupled with a Audio Nirvana Classic 5 fullrange driver. Both open baffle speaker systems shown in the photographs were constructed by Keith Chappel of KickWood Audio.
Photograph 5: Eminence Alpha-15A Woofer on Circular H-Frame Open Baffle
Projects Links - Eminence Alpha-15A Woofer
- Eminence Alpha 15A Experimental Open Baffle Design - [External Link]
- H-Frame Open Baffle Speakers with Alpha 15A - [Forum Thread]
- Designing a Passive Two Way Open Baffle Speaker System - (PDF 354k)
- Comparison of the Bass Performance of Passive Open Baffle, U Frame, and H Frame Speakers - (PDF 117k)