Acoustic Audio GX-400 speakers

[momaka]

Part 1 - Acoustic Audio GX-400 build "quality"

Not going to lie – this will be another silly audio post/thread. If you thought the cheap Panasonic Thrusters speakers I posted about last time were bad enough, then you are about to explore some new depths in lo-fi audio here. Ladies and gentlemen, I present you the Acoustic Audio GX-400 speakers... or speaker (only pictured one for better details )


Before I continue any further, perhaps you might be asking why I even bother to post about such crap audio gear (let alone keep it). The answer is simple: I like to poke fun of gutless and badly-made things. In this case, I didn't buy the speakers nor spend a dime going anywhere to pick them up. They literally came to me – given by a former college roommate. Long story… long, as I moved in my college apartment, he saw me bringing my stuff (and mainly a lot of tools). So as we chatted, I mentioned that I fix electronics. Next day he presented these speakers to me and asked if I knew what was wrong with them. He said they just stopped working one day after he tried turning them up a bit so he could hear them in the shower (with an open bathroom door, he said. )

Upon seeing their build “quality”, I was pretty sure what to expect. Moreover, based on his description of what had happened to them, I was pretty sure they probably burned out. Pushing on the speaker cone confirmed this – both were hard as a rock.

But how could that be? They are rated for a whopping 600 Watts!! Wait, whaaat?? Per speaker? Sure the rating is “peak” power… but seriously? Watt, you don't believe it like me? Well, too bad – that's watt the specs say on most eBay pages if you were to look them up… and naturally where you can find such “100% brand new & high quality” products. Here's what one listing says:

Features:
Model: GX-400
Color: Black
1200 Watt Pair 2-Way 6.5” Speakers
1200 Watts Peak Power Handling (Total) / 600 Watts Peak Power Handling (Each)
600 Watts RMS Power Handling (Total) / 300 Watts RMS Power Handling (Each)
6.5" High Rigidity PVA Treated Cone Woofer
2-Way Design and Functionality
Extended Throw Drive Assembly
25mm Loaded Piezo Horn Tweeter
Digitally Tuned Front Firing Port System
Powder-Coated Steel Grille & Recessed Carrying Handle
Inputs: Standard Speaker Wire or Dual 1/4" Phono Style Jacks
Built-In Pole Socket for Stand

Specifications:
Minimum Power Requirement 10 Watts
Frequency Response: 28 Hz to 20 KHz ± 3 dB
Sensitivity: 95 dB @ 1 Watt/1 Meter
Coverage Pattern: 60° x 40°
Crossover Frequency: 1500 Hz
Nominal Impedance: 8 Ohm

… so yeah… these speakers are supposed to be capable of 300 Watts RMS each. Let's look into their fine build quality, shall we?

First, I want to make note of the extremely high quality “horn” driver:
https://www.badcaps.net/forum/attach...1&d=1552012822
It's top-notch really. Never mind the paint / hot glue drip.

Those edge protectors also look super-tough…
https://www.badcaps.net/forum/attach...1&d=1552012822
… just like the “Powder-Coated Steel Grille” (read: cheap cruddy plastic… probably the same as the edge “protectors”.)

But let's look at the most important detail: the speaker drivers!
https://www.badcaps.net/forum/attach...1&d=1552012822
Oh, what a mighty-big magnet that 6.5” driver has! It's almost 3 & 1/8 inches (8 cm) in diameter and ¾ inches (19 mm) thick (actually, that wouldn't have been so terrible if this was a mid-range driver only.) 300 W RMS? – No problems! Just bring marshmallows too!

And of course, such a mighty speaker driver shall only be housed in an equally matching sturdy enclosure – extra reinforced and built from the toughest wood particle board ever manufactured. (Note: give extra emphasis on the word “particle” here. )
https://www.badcaps.net/forum/attach...1&d=1552012822
https://www.badcaps.net/forum/attach...1&d=1552012822

Even the speaker inputs look very well-made:
https://www.badcaps.net/forum/attach...1&d=1552012822
Yes, durable plastic nuts are durable.

I think my sarcasm is getting silly now, right. So let's be be more direct then: the cabinets are a real piece of turd (calling it “sawdust” is an insult to sawdust), the horn driver is… not really a horn driver , and the 6.5” speaker driver is about as average and no-name as any cheap MIC speaker can get. On top of that, the cross-over “network” for the “horn” (I don't know why I even bother to call it that – it's not a real horn driver, damn it!) is simply just a 0.1 uF polypropylene cap in series with it. (But hey, at least they used a real polypropylene cap! Have to give them some credit, after all. ) Essentially, these speakers are nothing more than a cheesy 2-way system with a crappy 6.5” full-range driver that can't really do much below 60 Hz, and a tiny undersized tweeter that is barely audible. Low-range -3 dB response down to 28 Hz? Are you joking?! And 300 Watts RMS? -Not a chance! Even 30 (thirty) Watts RMS is probably too much… and my guess as to where these speakers released the magic smoke. After all, at least my roommate had a decent 100W/ch Sherwood stereo amp, which didn't look over-rated (late 90's / early 2000's amp with some weight to it).

Anyways. I pointed out the crappy build quality to my roommate, and he almost didn't want to believe me at first. He told me that he thought these speakers were a great deal when they were “on sale” on Black Friday, because they had a $300 price tag crossed out and slashed to $70… and FREE SHIPPING!!! Deal of the century, right?

How people could fall for such a scam is beyond my explanation. But it does happen, that's a fact - if you look up the model of the speakers on eBay or elsewhere online, you will still see that not only are they still available for sale and in stock, but also go for around the same price… which means someone out there is still getting scammed! These speakers clearly aren't worth anywhere near that! They are downright along the same alley as the various crap “white van speakers”. I personally wouldn't even pay $5 for any of this garbage (and I'm glad I didn't!):

With this said, it didn't take long to convince my roommate that I cannot fix these Acoustic crap speakers. Since he had a decent amp (the Sherwood), I told him to look for a used pair of tower/floor speakers on the local Craigslist or similar. After about a week, though, he asked me if I could help him with that. So I did: I asked for his budget and within the hour I found several worthwhile listings on CL. He didn't have much idea what to pick but decided to go with one of the more “pricey” options… and now that I look back at this, I think that was one of the better choices. The speakers he ended up with was a pair of Technics SB-CR77 for $50 in near mint condition - a pity, because my roommate isn't the type that cares for his stuff much and ended up trashing them pretty badly. But the fact that he didn't manage to kill them in 3 years says A LOT, IMO.

On a small tangent… the build and sound quality of the SB-CR77 speakers was pretty decent. While my roommate was moving in the summer, he asked me if I could keep them for him for a few weeks, along with a few of his other moving boxes, until he got a key to his new apartment. That's when I had time to test them… and snap a few pictures. So there's that:
https://www.badcaps.net/forum/attach...1&d=1552012822
https://www.badcaps.net/forum/attach...1&d=1552014159
The SB-CR77 is a typical average 3-way system with a 12” woofer. The woofer driver looked a bit cheap (and probably didn't have a very big magnet, much like most average mid-fi speakers), but it managed to pump decent lows, down to 35-40 Hz easily without much roll-off. And compared to the Acoustic Audio speakers… there's not even a comparison possible.

But how would I know that, right? After all, I got those AA craps in broken condition, so I was never able to hear how they sound. Or was I? Stay tuned.

[momaka]

Acoustic Audio GX-400 speakers - part 2

PART 2 – Acoustic Audio GX-400 driver repair.

Curiosity always gets the better part of me. I really wanted to hear how (bad) these speakers sounded. In particular, I was pretty sure those atrocious cabinets won't be any good. So I came up with an idea to put another set of 6.5” drivers in them from a pair of Kenwood LS-N451 speakers I had. After all, the Kenwood speakers sound quite alright themselves (for a small speaker in a small room, anyways.) Unfortunately, the screw size pattern and outer rim size of the two speakers was incompatible. So I couldn't try the GX-400 boxes with the LS-N451 drivers.

This gave me the idea - why not rewind/recoil the original Chinese generic crap Acoustic Audio GX-400 “woofers”. After all, I've never rewound a speaker driver prior to this (the 15” Eminence speaker repair I posted about awhile back was done many years after this.) Thus, I thought it would be some good practice… and allow me to say that at least I have some idea how these Acoustic crap drivers sounded like.

The first step in that process, as with any VC (voice-coil) driver repair, is removing the cone. One would think these crappy GX-400 drivers would be easy to take apart, because they are cheap - but nooo! If anything, the manufacturer of the drivers used a colorless, rubber-like glue that is actually very similar to the “snotty” adhesive found on some padded mail envelopes. It was impossible to pry/separate it without ripping out the foam edge surround. However, I found out that if I heat the metal parts of the driver basket from underneath to higher than 60-70°C, the glue would soften and come apart – at least until it cooled down again. It was a pain to do all that, though! (Literally, as I burned my hands so many times while heating the basket with my heat gun.) It took a lot of effort to pry the edge surround without damage, and I didn't really want to damage the old surround, because… let's just say there was no way in hell I'd consider investing any more money into new parts (surrounds) for these crappy speakers.

Anyways, here is what the speaker basket looked like with the cone removed:
https://www.badcaps.net/forum/attach...1&d=1552014685

And here is the cone:
https://www.badcaps.net/forum/attach...1&d=1552014685
https://www.badcaps.net/forum/attach...1&d=1552014685
Wire on the VC is gone because most of it was loose and stuck in the gap. I did manage to get it out and the gap clean, though. As you can see, we are dealing with a 1” (2.54 cm) diameter voice coil speaker here that has… what, 10-12 mm –long coil? The day I see a regular voice coil like that handle 300 Watts RMS without becoming a fire ball , I'd say humans have finally discovered a way to go beyond the physical laws of our universe.

As I wanted to match the original VC, I looked at the burned wire to get an idea for the thickness. It was quite thin though (not sure what size/gauge, as I didn't have any way to measure it.) Luckily, however, I did have a spool of very thin wire (also of unlabeled size/gauge) that looked similar in thickness. So I rewound the voice coil with that. Here is the first attempt:
https://www.badcaps.net/forum/attach...1&d=1552014685
Sharp eyes probably noticed I wound the VC only one layer along its length and not a second layer on top of it, as would be done normally. This is because after the first layer, I discovered the coil resistance was already around 12 Ohms! In fact, the picture above actually shows the second reversion of the “thin wire” attempt, after I removed a few turns from the beginning. This got the resistance down to ~10 Ohms. Probably close enough to call it an 8-Ohm driver, but I was also curious to see what kind of results I would get with thicker wire.

Thus, I dug through my junk boxes again and found some wire that I saved from the yoke/deflection coils of a scrapped/dumpster-picked CRT TV. This one was considerably ticker (28-32 AWG, maybe), but I decided to try it anyways as it still didn't seem that bad for a speaker.
https://www.badcaps.net/forum/attach...1&d=1552014685
Again, you can see I put only one layer on there. But this time, the reason I did this is because it possibly looked like there may not be enough space for a second layer on top without the VC rubbing inside the magnet gap. In retrospect, I found that there is enough space, but the tolerances would have been very tight and thus made it hard to center the VC, if not impossible. Moreover, both of these drivers had slightly deformed aluminum VC formers (which I had to straighten), so I wanted to leave a bit of extra space in the gap in case there were any irregularities with the VC formers.

Now this second VC above ended up being even further from spec than I expected – it showed only about 1 Ohm of resistance. Open-air inductance was quite low too: only roughly around 15 uH. In fact, my TT/ESR meter couldn't measure it alone, so I tested a bigger coil with the meter (that it could measure), and then added this VC in series to see how much of a change I would get… which varied between 10 and 20 uH, so probably around the 15 uH mark. Compare that to about 90 uH on the “thin wire” VC. Of course, I know that VC resistance and impedance are not quite the same thing. However, at low frequencies below Fs, the impedance essentially does become very close to the resistance. So obviously, the thick wire was a bit… too thick. Even if I was able to get a second layer of turns in there, the VC would have reached maybe 2 Ohms, which is still very low (except possibly for car audio - but I don't think there's ever a chance I will put this junk speaker in my car! )

With that said, I decided the “thick wire” VC will serve as an experiment/learning ground for the first speaker rebuild. I centered the cone (and VC) inside the speaker basket with pieces of paper for the VC shims.
https://www.badcaps.net/forum/attach...1&d=1552014685
Because I was pretty sure I would eventually need to re-do this VC, I decided to do things “the quick way” and resorted to using hot glue to hold both the spider and the speaker surround to the basket. ( I know.) Surprisingly, it looked OK!
https://www.badcaps.net/forum/attach...1&d=1552014685
But as you might imagine, hot glue is NOT a good idea, as it doesn't really stick well to metal surfaces (especially steel). Thus, the speaker ended up making a bit of mechanical noise at “stronger” bass notes. For my testing purposes, however, it still worked OK.

[momaka]

Acoustic Audio GX-400 speakers - Part 3

PART 3 – Sound Tests on the Repaired Driver

So how did the “thick wire VC” speaker sound?
One word: MEH! -Not much highs and certainly very weak low-end bass below 60 Hz. Mid-bass? Sort of, kind of, maybe something there?? But hey, the mid-range was OK.

Of course, part of the reason for this could also have been the fact that I didn't have any way to properly drive this rewound driver more “directly”. After all, the low resistance of 1-Ohm is a bit dangerous for most regular 8-Ohm (and probably even 4-Ohm) amps. If you think I'd risk connecting any of my decent (and even not-so-decent) amps to this crappy speaker – no way! So, to drive this speaker, I used a scrapped TV speaker amplifier board with a TA8216H amp IC (single-ended amp with 3A peak/Ch output, which I supplied with 30V). To make sure I didn't overload my amp IC, I connected a 220 uH, 2.4 Ohm large air-core inductor in series with the driver (same one that I used to measure the inductance of this rewound VC, in fact.) This increased the impedance to ~3.4 Ohms minimum. Obviously, the inductor would have some effect on the mid and high-range frequencies, but not much on the low end – which I was most curious about to hear from the crappy GX-400 cabinets, anyways. That said, another thing worth mentioning is that the TV amp board design also uses 2200 uF speaker output coupling capacitors. Thus, given the low impedance (3.4 Ohms with the series coil), the speaker-amplifier system low-frequency cut-off point was about 22 Hz - i.e. a bit high.

All in all, I was able to drive the speaker to maybe 4-6 mm of excursion while in its glorious “cabinet”. A properly-designed speaker system with 6.5” drivers and that amount of cone movement can typically produce decently loud sound, along with some bass to go with it (example: the Kenwood LS-N451 speakers.) But these Acoustic Audio craps? -Nope! The sound from my rewound speaker was incredibly weak! And from that weak sound, really only the mid-ranges stood out. The bass was “thumpy” at best. Highs were weak too (though, obviously the series coil contributed to the attenuation.) The strange part is that it looked like my repaired speaker driver was actually trying, but perhaps the crappy cabinets were holding it down to an extent.

To confirm (or disprove) my theories about what I heard above, I went back to the V2 “thin wire” VC. Before gluing it back in its basket, I decided to take a few measurements of the VC in open air again. The voice coil ended up having a static resistance of 9.6 Ohms and inductance of 90 uH (according to my TT/ESR meter.)

I proceeded to center the cone in the basket the same way as the first one. But this time, I didn't use hot glue for the spider and surround. Instead I used regular household silicone adhesive. This also isn't the ideal glue for speakers, but it is classes above hot glue.
https://www.badcaps.net/forum/attach...1&d=1552015356
https://www.badcaps.net/forum/attach...1&d=1552015356
Results (after the silicone dried): no mechanical noise with the cone movement at all.

Because the VC resistance (and thus impedance) was much higher on this “thin wire” VC, I could drive this speaker with any of my amps. Again though – not that I used any of my amps I care about. And for the sake of repeatability, I used the same TV audio board with the Toshiba TA8216H IC. Now this VC technically had some advantage: first, I didn't use the series 2.4 Ohm 220 uH coil and second, the 2200 uF output caps set the -3 dB low-frequency cutoff much lower: ~7.5 Hz for 9.6 Ohms. But the high impedance also had its toll on how high I could go on the output volume before running out of headroom. With 30V on the amp IC, that translates to roughly 10 Watts RMS as the max limit with the 9.6 Ohm speaker impedance (without distortion.)

That said, I don't think I managed to push even 5W into this second driver, most likely because the actual impedance was higher than the 9.6 Ohms I measured. According to my current meter when the speaker hit continuous bass notes (tested on pure sine tones between 10-80 Hz with Audacity generator), the current draw read 0.3 to maybe 0.4 Amps max (@ 30V). This translates to about 9-12 Watts of power draw for the speaker + amplifier dissipation, which means the speaker was getting, at best, only 65% of that, or ~6-8W RMS… and frankly, it just didn't sound like it did that much – no to me, at least. I don't know, perhaps these Acoustic Audio cabinets really are more horrible than one can imagine. Or perhaps the drivers themselves have really weak magnets, making the speaker very inefficient, as I heard with both speakers now.

So as another test, I ran the driver through 10-100 Hz sweep in open air (no speaker cabinet). From this test, it seemed like the speaker cone had the highest movement around 50-55 Hz (I got it to move maybe 1 cm total). Moreover, the current draw of the amplifier at around those frequencies was also considerably lower, suggesting the Fs for this driver is perhaps around 55 Hz somewhere. Considering the lack of low-end bass, I think that sounds about right (literally!)

On that note (silly pun again! ), I couldn't really tell there to be much difference between the “thick wire” and “thin wire” voice coils, in terms of how the speakers sounded. That is, they both sounded like utter crap, with no low-end bass, resonating mid-bass (thanks to their “awesome” enclosures), and hardly any highs (though the “thick wire” VC with the series coil has slightly lower highs still). Only the mid-range was somewhat OK.

As a final test, I decided to compare them against my Sony SS-MB215 speakers, which I use as bookshelf speakers in my room. They aren't known for being hi-fi speakers, or even great mid-fi for that matter. But the way I have them configured, they sound decent. So for this last test, I played music through my Sony speakers one at a time (that is, first through the left one then through the right one.) After that, I took these speakers down and placed the “thin wire” VC Acoustic Audio speaker in the same spots. In both spots, the Acoustic Audio speaker produced much weaker sound – especially bass. This, I think, rules out any room placement disadvantages. They are just crappy speakers.

Also, to rule out any impedance “disadvantages” (due to the “thin wire” GX-400 driver having much higher impedance and thus needing higher volume), I though it might be a more fair comparison if perhaps I connected my Kill-A-Watt meter to the power supply feeding the amplifier and set the output volume levels up so that in each case, the power consumption would be the same. So I did that… and still, the GX-400 driver sounded many times weaker than my Sony's.

Again, I just can't say if these GX-400 speakers are weak because of their terrible cabinets or because the drivers have weak magnets. And just for another test's sake, I also put the Kenwood LS-N451 speakers in the same spots. The Kenwood's also sounded a bit weaker than the Sony's, but were much closer to them than the crappy AA GX-400.

With all that said, my final words for the Acoustic Audio GX-400 speakers are this: Terrible! Avoid by all means! If you are not after the junk drivers in these speakers (and seriously, why would you be?), then there's even less of a reason to pick up a pair, as the cabinets/boxes (if we can call them that) are even less worthy. The only reason why kept these speakers/cabinets for so long is because I used one of them as a desktop PC stand and the other as a makeshift nightstand next to my bed (this was during my last year in college, where I found an unfurnished apartment by myself and didn't want to bring much furniture… so I used whatever I had on hand.) Yes, these speakers were more useful to me even as generic stands/tables/furniture than as speakers!

Anyways, I hope you enjoyed reading this one, folks. Have a nice day!

[Khron]

Re: Acoustic Audio GX-400 speakers

The "no bass" thing may well have been down to the too-high-tuned ported enclosure - that would also explain the no-bass-despite-large-excursion thing as well

Some might call you insane (if not even a "technological pervert") for endeavours like this, but then again... I'm sure we've all done that, at one level or another...

[momaka]

Re: Acoustic Audio GX-400 speakers

Some might call you insane (if not even a "technological pervert") for endeavours like this, but then again... I'm sure we've all done that, at one level or another...

Well, let's just say there were some days in college where I was simply tired of doing school work and needed something to "relax my mind". Generally, doing chores (cooking, cleaning, and etc.) was the normal stress reliever. But a few times, fixing useless stuff like I did above just felt the more "fun" thing to do, and so I did it. Hence some of the goofy/cheesy/pointless repairs I posted here.

And in the end, I've learned a great deal about glues, adhesives, and machining/fabricating stuff. So even "worthless" endeavors like this can be useful.

The "no bass" thing may well have been down to the too-high-tuned ported enclosure - that would also explain the no-bass-despite-large-excursion thing as well

Yeah, the two pipes for the "dual ports" are quite short, and I suspected that to be part of the problem too. But no matter which way you look at it, I think in the end just about everything about these speakers is bad/crap.

[Khron]

Re: Acoustic Audio GX-400 speakers

I didn't for a moment disagree

And like i said, i'm sure we've all done "pointless" stuff just for shits & giggles

One might argue, one big part of DIY is the learning experience. Anyone can just throw money at a problem (and sadly, "too"(?) many do), but us curious folk have this craving(?) or need to find out & understand how things work, etc. Or at least i know i do (to some extent)

[momaka]

Re: Acoustic Audio GX-400 speakers

I didn't for a moment disagree

I know.
But I still figured I should try to clarify my "logic" a little better.

...but us curious folk have this craving(?) or need to find out & understand how things work, etc.

Exactly!
It's like food for my mind - got to feed it every once in a while with something to make it happy.