SPA8PAS -vs- SPG88
Teardown & Measurements of Two Inexpensive Passive 8" PA speakers.
LYX Pro SPA8PAS & Rockville SPG88
Both of these speakers can be had for well under $100, at the time of this review the LYX can be found for $50 off the LYX Pro website and the Rockville for $60 on Amazon, that's the economies of scale at work for you considering buying just an off the shelf 8" PA woofer and 1" compression driver gets year near those prices.
While there are obvious cosmetic differences the overall design between the two is quite similar, 8" woofer mated to a horn loaded compression driver in a rugged ABS cabinet with integrated pole mount. Both are also very similar is size and rated at 8 Ohms though the Rockville also comes in a 4 ohm variant.
-Quick Subjective Listening Impressions-
I did some quick listing of both, they are not good. It's about what you would expect from basically the cheapest 8" PA speakers on the web, terrible sound quality and tonal balance.
Both sounded very bright though the Rockville is more so, piercing treble would be a more accurate description for that one. The LYX treble sounded slightly more balanced but at the same time has a veiled quality, less clarity in the upper midrange and treble. Neither one had much bass extension to speak of, both also have a large rise to the response below 200hz which keeps them from sounding totally anemic but also gives them a bit of a boomy quality in the upper bass.
On first listen the Rockville sounds better, cleaner and clearer but the overwhelming treble quickly wears you out. The LYX while not as clean sounding does not lead to ear fatigue as quickly and is slightly more bearable.
Neither are good, maybe with some tone adjustments to bring down the top end they might be passable for light PA/announcement use when you just need a voice to be heard but definitely not even on the level of something I'd suggest for music or movies in the backyard if any semblance of audio quality is desired.
LYX SPA8PAS
Rockville SPG88
The LYX SPA8PAS has multiple inputs, 1/4", XLR (an odd choice) and SpeakON, along with a matching set of outputs for daisy chaining.
The Rockville SPG88 has just your standard SpeakON input/output.
-Measurements-
As not to clutter this main page and to give larger easier to read graphs I've moved the measurements for each speaker into separate pages which can be found below:
-Teardown-
Removing the grill:
Removing the grill:
Back panel removed, slightly more complex then the Rockville. Two seperate PCBs one for the inputs which just ties everything together and the other board is the crossover.
Back Panel removed to expose the very simple crossover and SpeakON connectors.
The SpeakON's are wired in parallel and the pairs of 1 and 2 pins are also tied in parallel (1+/2+ and 1-/2-), so don't connect to an amplifier that uses all four pins on a single speakON along with a 4 conductor cable or you may damage your amp. Using a two conductor cable is fine.
This crossover uses 6 different parts, two 20w size resistors (1 & 22 Ohm), a 2.2 and 1.5uF capacitors, a small air core inductor and a small polyswitch.
Closer look at the crossover, the small diode and resistor drive a blue LED (small white connector), the led seems to activate starting around 1w of input.
There are only three main components to the crossover, 2.2uF cap, 3 Ohm resistor and a 0.25mH inductor.
Back of the crossover PCB. Woofer is left to run fullrange tied directly to the inputs. The compression driver then gets a 3rd order highpass with some padding on the parallel inductor leg. The polyswtich is wired in parallel with the 22 Ohm resistor out in front of the crossover, so if the speaker is driven hard enough the switch will open causing the signal to flow through the 22 Ohm resistor reducing output of the tweeter/compression driver (~5dB) until the switch cools and resets.
Back side of the crossover PCB, if you have a close eye you may notice the woofer is left to run fullrange. So those three components form to give the compression driver a simple 2nd order highpass with a bit of padding.
SPA8PAS Crossover Schematic
Crossover Schematic
Response from the stock crossover showing the individual driver responses. With the woofer left unfiltered and it's own response extending to near 10khz with lots of breakup peaks the high frequency response is a mess. The tweeter is also left running 3-4dB hot with a rise in the 5-8 kHz range.
Response from the stock crossover showing the individual driver responses. The fullrange woofer wreaks havoc with the response especially its prominent breakup right in the the treble range. The tweeter does not have enough padding with a rising response towards 8-9khz running nearly 10dB hot there.
Here is the response when the polyswitch opens. The tweeter level drops about 5dB however the treble range is mostly dominated by the woofer and such the system response does not drop much except above 10kHz.
A closer look at the drivers:
A closer look at the drivers:
For those interested here are the woofer T/S specs I measured:
This data was exported from DATS the Dayton Audio Test System** Manufacturer: LYX Pro* Model: SPA8PAS Woofer* Piston Diameter = 167.6 mm* f(s)= 91.52 Hz* R(e)= 6.177 Ohms* Z(max)= 30.06 Ohms* Q(ms)= 6.597* Q(es)= 1.706* Q(ts)= 1.356* V(as)= 13.04 liters (0.4605 cubic feet)* L(e)= 0.9346 mH* n(0)= 0.5586 %* SPL= 89.57 1W/1m* M(ms)= 15.87 grams* C(ms)= 0.191 mm/N* BL= 5.748 * K(r)= 0.07486 * X(r)= 0.4888 * K(i)= 0.008788 * X(i)= 0.6981
For those interested here are the woofer T/S specs I measured:
Both of these speakers use very cheap parts but could be improved greatly with the use of a simple lowpass on the woofer and some minor tweaks to the existing highpass. This would give them a much more usable on axis response removing the hash where the tweeter and woofer overlap along with improving the off axis linearity immensely confining it to the radiation pattern of the horn rather the existing interference response between the horn and woofer.