|Dayton SD215A-88 DVC 8″ Subwoofer
|First order of the day is to measure the T/S. They are not exactly the same as Dayton’s but at least, they are quite close, which is a relief ( see PDF SD215A-88 DVC ). The reason I bought this model is because according to the manufacturer’s specs, it models well in a compact 25L ported box.
Before I proceed further, note that this SD215A is a Dual Voice Coil (DVC). The measurements above were all made with the voice coils in parallel (ie. 4 ohms nominal). Using this driver with the voice coils in series or connecting the amplifier to one voice coil only will result in drastically inferior performance.
|Box modeling predicted an F3 of 43Hz for a 24 liters bass reflex.That is acceptable for music. I don’t need it to go down to 30Hz.
What I’m more interested in is the character of the bass.
How good are the dynamics? How detailed is the mid-bass?
Simulations can’t tell me that. The only way is to install it onto one of my test boxes and have a listen.
|24 Liters Bass Reflex
To test the SD215, I used a 24dB/oct electronic crossover and powered it with a 400 Watts/rms into 4 ohms amplifier. The active crossover offers me the convenience of setting different crossover frequencies.
After listening to the SD215 with different combinations of satellites, I feel it is not quite suitable for music. While there’s low bass, there’s not enough detail in the upper bass.
| 4th Order Bandpass
Having tested out the SD215 in a bass reflex, I’m curious to see whether it is any better in a bandpass.
In simulation, the Violet trace is the recommended optimum loading. High Pass F3 is 45Hz and Low Pass is 100Hz. It is a bit too narrow for my liking.
I opted for a wider bandwidth instead. In the Black trace, the HP is now 40Hz and LP is about 125Hz. Box has shrunk slightly, from 30 to 25 liters.
|25 Liters Bandpass Response
Bandpass subs have a bad rep for “one note bass”. There’s solely attributed to bad design. The thing with designing a bandpass sub is that it is extremely sensitive to the driver’s Thiele & Small Parameters. If you simply design without measuring the T/S yourself, you run the risk of having this “one note bass”.
The response above is from my 25 liters bandpass test box. In the plot, there is no sharp peak for that one note to manifest itself. In fact, it’s relatively flat from the predicted F3 of 40Hz to 125Hz.
Measurement made with the mic at the mouth of the port.
|Bandpass vs Bass Reflex
The SD215 in a Bandpass is everything the Bass Reflex is not. Dynamics and definition improved tremendously. This is the way I like my music to sound like.
In all fairness, the SD215 is a subwoofer and not a woofer. As such, it is designed more for low bass. In that respect, it is an excellent choice for a compact subwoofer for Home Theater. For music, especially for those who are very particular about the character of the bass, it is better to use the SD215 in a bandpass.
More information on crossing bandpass subs to satellites can be found at: Bandpass Subwoofer Crossovers
In my earlier attempt (25L), I traded efficiency for bandwidth. My next project will be at 30L. I think the higher SPL will be more practical.