Tuesday, March 14, 2017

It Sounded Good at the Time

Oh gosh, it has been far too long between posts, yet I don’t feel guilty about it this time. Too many things have been going on in too many parts of my life so something had to give… and this wasn’t the only thing.

Multiple rounds of illness involving whatever upper respiratory virus of the moment circulating amongst the local population robbed me of days then weeks. Sudden developments with Dad’s paralyzed stomach suddenly showing motility led to a highly irritating pair of fiascoes last week added to the woes. Even the weather decided to take a turn for the worst after flirting with Spring like temperatures.

My sole consolation during the past month or so has been getting into audio theory and execution more deeply. Curiosity about crossovers, frequency charts, and clearance drivers has led to a lot of mad scientist behavior on my part not always wisely executed (see multiple rounds of illness above).

Fortunately, end results have been promising with stunning increases in performance for my newly rigged up 5.1 setup in my bedroom to make the PC much more of a hifi platform. It all started with a lucky win on eBay luring me down the rabbit hole.

An old Sony STR-K740P home theater receiver had an unserious low bid put on it which actually won. Smaller than most units it would fit perfectly on one of the desk shelves next to my monitor and had the optical in jack needed to accept Dolby Digital Live and DTS Connect from my Sound Blaster Z soundcard.

Once I got it, I ended up ordering an Acoustic Audio PSW-8 8” subwoofer that once had been highly regarded in the budget audiophile community for a more musical deep bass. The company had gotten a bad rap from a run of inferior amplifier plates and never quite recovered their reputation despite having fixing the production run in recent years. They claim to go all the way down to 26Hz and I can verify the plucky little sub really does. It favorably compares to the BIC America V1020 in the living room much to my pleasant surprise.

The beloved Insignia NS-SP213 bookshelf speakers were employed as fronts and the old Monoprice 8247 center with two surrounds completed the 5.1 arrangement. Or so I thought.

Taking apart a spare satellite to see how it was wired was my first mistake. Seeing a primitive scheme of using a capacitor to filter the signal to the tweeter from the full range mid-woofer got me thinking that an audio grade capacitor would improve the sound. Then came researching the crossover between the speakers and realizing more could be done cheaply while learning proper wiring and soldering.

Using online sound tests revealed a bigger problem, however. The subwoofer could only reach a high of 140Hz, the Sony receiver crossed the satellites on small mode at a fixed 120Hz up, and the Monoprice speakers started making sounds at around 160Hz. There was a gap in covered frequencies, an actual hole.

So much for using what I had on hand, or so I initially thought. But what if I could rebuild the speakers?

After much travail (never measure things while sick and/or using a flexible ruler), a perfect drop in replacement 3” full range driver that wasn’t insanely expensive was found at Parts Express. Fountek FE87 full range drivers promised to get down to around 118Hz in a sealed cabinet plugging the aforementioned hole better than a little Dutch boy. While they are fine for highs, the decision was made to keep the tweeters and cross them over at 6400Hz as the capacitor they used indicated.

During all the sick time, research tended to drift off in fascinating tangents including finding out the favored mid-tweeter-mid (MTM) layout for center speakers tended to be self defeating in creating accurate sound. Vertically it works beautifully, but centers are laid out horizontally with a consequence of colliding wave propagation or some such oddness. Search on it and maybe you’ll understand it better than I.

Anyway, between that revelation and finding a pair of 3” passive woofers on eBay simplified the project by omitting one driver in the center and placing the passive radiator there. Some insist that a passive has to be at least half again as big as the speaker it complements, yet I’ve seen many designs from reputable manufacturers that went with the same size so hey, worth a shot.

Omitting the nightmares of learning to solder properly and getting hot glue guns to function, the replacement drivers fit in perfectly and so did the passive on the center speaker. An exceedingly simple first order two way crossover was glued directly to the back of each cabinet. Consisting of a capacitor to the tweeter and an inductor coil to the mid-woofer for a -6db crossover it dramatically increased the soundstage as well as the clarity.

Having no specs on the tweeter, no resister was used as an L-pad.

Frequency tests showed the satellites now were able to make sounds at well below 120Hz and the center closer to 60hz. Yet there was fuzziness in that center that kept me from being satisfied until a very simple fix changed its tonality completely. Examination of the spare passive showed that there was no mass attached to the cone so the air movement powering it was allowed to go into the dust cap area to create unwanted resonance.

Looking up the MMS of the speaker indicated that 2.1g of weight was needed. A lack of a scale that can go that low and only spare change on hand meant some Web sleuthing was required. As it turns out, the slightly smaller than a dime opening matched the weight of a dime, which is slightly more than 2.2g.

Hot glue gun time!

Testing with matrixed music (SBX rather than Dolby Pro Logic or DTS Music Mode) the center sounded amazing so I changed the receiver setting to large for it. Oh my, I can’t believe a 3” speaker can sound so good especially for vocals. Sinatra was just incredible as was Annie Lennox.  For the purpose of gaming and watching movies/streaming on my PC, this is overkill!

Yeah, I’m a purist when it comes to playback of music. If it was recorded in stereo or mono, it should be played over stereo speakers and not artificially manipulated to multiple surround speakers. The Sound Blaster Z soundcard is set up so that it pipes out stereo from its front speakers 3.5mm jack to the Sony receiver’s RCA jacks meant for a CD player with 116db signal to noise ratio, which is very clean.

With the stereo fronts aided by the subwoofer, music can be heard as it is intended to be. Of course the bargain Insignia NS-SP213 speakers were weak and not terribly capable below 80hz, but still a smashing bargain at $50.

Then I ran into a clearance item at Parts Express, the Peerless HDS 835024 5 1/4” aluminum cone speaker. For nearly the price of the Insignia’s I could put in what looked like a drop fit that would give me much better mid frequencies, a flatter response, and more low end.

Having lost my mind, I ordered them and waited eagerly for them to arrive from Ohio. Once in hand, the drop fit turned out to be off – while the outer diameter and shape was close enough, the inner baffle cutout was way off. At least a quarter of an inch had to be ground off with a Dremel, which is a very messy business given the black plastic it was molded from.

A small shop vac had to be purchased to clean up the mess, it was that bad.

Once hooked up to the lovely little crossover in the Insignia cabinet, each speaker was put back into service with the plan being to burn them in through everyday usage. There was an immediate improvement in lows despite my concern about the port being tuned specifically for 80Hz and the original woofers. 60Hz was good and significant sound could be heard below that without any noticeable “chuffing.”

While a relief, the sound was even more recessed than the lightly V-shaped performance native to the Insignia’s. Of course aluminum cones are like other metal cones in that they take longer to burn in and achieve their normal elasticity. My eagerness to keep the setup running meant patience was needed.

Slowly they opened up and as I type right now, they are nothing short of beautiful sounding. A wide open soundstage, smooth mids, tight but strong bass, and a whole lot presence make them delightful no matter what kind of music is played. The effect is holographic with no equalization, matrixing, or spacialization being employed. Good speakers require none of that and simply perform.

Sigh. I will soon be grinding plastic again, because the Peerless drivers are going to be transferred to the modified Insignia’s in the living room home theater setup. Those cabinets house vintage Boston Acoustic Lynnfield tweeters so it will be interesting to have my favorite tweeter of all time paired with these lovelies.

Not exactly an onerous task given the reason behind it. A shocking turn of events in winning yet another eBay listing has netted me something I’d thought was completely beyond my reach: a pair of Boston Acoustics VR-460 tower speakers in good condition. They were meant to pair with the VR-10 center already owned, so the modified faux Boston Acoustics bookshelves will be redundant.

Hopefully they will arrive intact.

Dayton B652-AIR bookshelf speakers are the new workout/hobby room speakers and a crossover for them will most likely be my next speaker project, though a 4” speaker rebuild from the Sony mini receiver cabinets might be.

Another project will assist in either endeavor, a large helping hands made from a 20lb rectangle of aluminum, ball & socket coolant hoses, alligator clips, and vinyl tubing. With four extra hands, a magnifying glass and the option to add another arm, soldering will be much easier than before. If I can get back into scale modeling, it will be a great asset there too.

Enough rambling for now, time to pay more attention to the beautiful sounds.

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