Carverfest Sonorous Speaker Upgrade

[RobertR 847]

At the end of the 2017 Fest, Kevin gave me a pair of stripped AL-3 woofer cabinets he was through with. I installed a pair of spare drivers I had, one used, one unused.

 

Some months later Alex Sauter made me a pair of rear plates, to seal up the back, and we installed two pairs of speaker binding posts, but no crossovers or fuses. Then he cut several lengths of the original-type aluminum stock for upright supports. The original Sonorous Speaker stands use 47'' uprights, but these new ones are to be mounted atop the woofer cabinets, which are 24'' high, and listened to from my bed, with a somewhat lower head height than a normal chair. I was provided with lengths of 18, 20, and 22 inches; the 20'' turned out to be perfect. Also provided were new flanges for mounting to the woofer enclosures, into which Alex installed T-nuts for four machine screws. Pretty rugged, but I won't use it as a lifting handle.

 

Skip ahead to the 2018 Fest, where I took the woofers and Travis sold me a pair of CF speakers, so now I could complete this experimental project without poaching a pair from my living room three-channel system. But when I fired it up system it became evident that the older woofer was in need of a new surround. Just like magic, Harry produced one and installed it, like new. (Speaking of Harry, I should mention that the concept of bolting a CF speakers atop woofers was his idea, a year earlier.)

 

Travis had hard-wired the speakers to the feed wire that comes up through the stands, but for portability I wanted to restore the original-type plugs, so I did so. Then came some testing, and into an interesting learning curve.

 

It was a no-brainer to opt to use a MINI dsp 2x4 for integrating these units. The basic $100 model with the parametric (“advanced”) software. Three things for the dsp to do:

 

-Split the signal (crossover). This is easy, though I used the trick of setting the crossover-point a lot lower that -6dB, simply because I wanted a response cut in that area of frequency (turned out to be around 155Hz).

 

-Balance woofers to top unit. The CF units retain their original passive network, and have good deal less sensitivity than AL3 woofers running straight out of a power amp, so they need to be turned down a bit. I always have found that getting the right amount of bass is the easiest part of voicing a speaker system. [Good thing, too, because any change in speaker or listener position screws it all up.]

 

-Voicing/EQ-ing – Easier than for bi-amped AL3s, because, again, the CF speakers retain their original passive voicing. But still a fussy bit of tweaking, done over the course at least a month. This cheap Mini DSP is great – for the money nothing I know of can touch it – but there is a problem getting enough gain out of it without clipping the input (YUK!). Lots of playing with shelf filters before it's at its best. Each time I started over, some aspect sounded better.

 

I have to pause here – other things to do – more on this later.

 

RobertR

 

[loner_t 2,568]

Post a few pictures, please. I only saw the metal stands being waved like magic wands @CF2018. 

[RobertR 847]

Afraid  I'm without a camera at the moment - mine got stolen, along with my whole carry-on, when changing flights a year ago.  Keep thinking to get a new one, but don't know what to get, and shekels are a bit short...

 

RR

[RobertR 847]

Part 2

Back to the Carverfest speaker mod, but first I should take a minute (a page, actually) and mention that everyone should do some frequency glide testing. You will discover little problems, sometimes easily solved, that degrade the overall sound of your system. If you don't have a sine-wave generator, just feed your laptop audio output into an AUX input, get on line and go to any of a number of free sites, the type that lets you change the frequency in a continuous sweep, with a mouse-drag or whatever. The one I used is Synalski (their default output level is 75% - I find that just 5% is better).

 

Set things up so that you are in control at your usual listening position. First, do one channel at a time, and then repeat with both channels together. At a fairly high level, sweep at a moderate rate from as high as 2-3 KHz right down to the low bass; you will want to reduce the frequency more and more slowly as the frequency gets lower. Listen for increases or decreases in response – you will likely hear plenty of them. But also listen to the quality of the sine wave tone. If it gets to sounding 'buzzy' at some frequency, that's maybe distortion in the speaker.  Or perhaps a resonance in the room - those can be anything – a lamp, a picture on the wall, a wooden side panel in a chest of drawers, or something in one of its drawers. Maybe some loose object on a table, or a storm window, curtain rod, or even the cover on your amplifier – everything has a resonance frequency, where it will vibrate, and if it's not somehow damped, you may well hear it. Might have to make the tone louder to help run down the offending gremlin, as you may suddenly not hear it when you change your location -but keep hunting – it's there, at your sweet spot. If you can hear it now in this test, you hear it during louder music playback as well, but likely won't identify it, buried as it is within the complexity of the music. It will add to the sound, but almost certainly subtract from your listening enjoyment.

 

Some of the response dips you will hear are caused by the two speakers working against each other, right in the area of your listening. If you cut off one channel (or reverse the phase of just one speaker) and the sound gets louder, that is the case.  This is a problem of room acoustics, not part of this discussion, but maybe solvable with a well-placed tuned trap.

 

Also, at some frequencies there may be a peak or a dip just where you sit even if just one channel is playing. Peaks can be reduced with a notch filter, but dips – no so easy. If you move and the dip disappears (tone gets a lot louder), again, that's a room problem.

 

Anyway, I always do this sort of testing, and the current speaker project was no exception. I found a few room noises, plus a couple of fixable things that were emanating from the speakers themselves, and may well be emanating from yours, as well.

 

But today is a holiday for most, so I'll finish this post in another day or two. Meanwhile if you get a few minutes give the room de-buzzing sweep a try, and take a few notes on what you find.

 

RR

Edited December 25, 2018 by RobertR

[Magnaryder 757]

Robert, is James participating on this project with you? Just wondering if he's had any input. I do appreciate you pushing the envelope here

 

ray 

[RobertR 847]

5 hours ago, Magnaryder said:

Robert, is James participating on this project with you? Just wondering if he's had any input. I do appreciate you pushing the envelope here

 

ray 

 

Sauters were big help in the physical mounting of the little CF speakers on top of AL3 woofer cabinets.   Since that  I'm on my own. 

 

I have the results page just about finished, discussing  a couple of problems and how to deal with them.  But no rush  to post - I'm hoping those interested will find time to get into some 'room-debuzzing' sweeps, and note any frequencies where they hear problems from the speakers, not the room.

 

RR

 

 

[RobertR 847]

Part 3

Now to cover specifics for this pair of Sonorous.

 

A nasty sound in the neighborhood of 300 Hz could be a leaky end cap – you can find that by ear, or even by feeling the draft, when the tone is playing fairly loud. Travis sealed this pair very well, so I heard none of that.

But there was a nasty buzzing evident, mostly in the right channel, though if I cranked things up and listened for it there was some in the left as well - midway between 164 and 172 Hz. Turns out to be nothing in the room; it's from the speaker itself. Sounds like a bad side-driver, but on examination it's not – surrounds all good, no voice coil rubbing, and it's not loose driver-mounting screw. Besides, the rotten sound is the same from all four. Suspecting that it's maybe a wire hitting against the back of a cone, I finally pulled out the tweeter and got right in there, but the wires are in no danger of hitting anything live.

It turns out to be caused by sympathetic vibration of the power resistors in the crossover! There are five resistors in there and, being all the same physical size, they all vibrate at about the same frequency, sounding like a hornets' nest. Particularly if they are mounted slightly elevated off the board, at a certain volume they would scream their version of harmonic distortion whenever somebody hits the E below Middle C. The channel I had that was producing more of this garbage turned out to have its resistors mounted clearly looser, above the board (or above the coil in the case of the middle one).

My solution was to dismount the speaker, lay it on its back, and with the tweeter and the central wad of fiber-fill removed, dab some flowable silicone sealer below, beside, and between those resistors – enough to render them virtually motionless. I used the thin stuff because it's easier to get some of it underneath things with little clearance. I used Windshield Sealer -VersaChem 75009 (from O'Reilly's; other auto stores sell Permatex 81730). If you do this trick, avoid coating the tops of the resistors too heavily, as they need to be able to dissipate heat, though I must add that the wattage spec of these resistors is far into the overkill range – they rarely get even slightly warm (recall that the famous torture experiment at the 2015 Fest, which sautéed the side-drivers, did no harm to the crossovers).

A non-magnetic tool is almost mandatory for accurately applying this stuff among all those magnets. Wood works fine – I used a Popsicle stick; a throwaway chopstick would do the job as well.

I also glued the circuit board edges on two edges, just for luck. The vibration in there is amazing.

Did both channels the same way, of course, and let the silicone set a few hours, then replaced the fiber- fill and the ribbons. All done and seemingly ready to test, except there was another trick to play before remounting the speaker...

Louder frequency glide testing had disclosed another problem, centered sharply at 325 Hz, at which point the upright supports in my custom setup do a lot of sympathetic vibrating, producing some quite audible buzzing – pretty nasty. [Note: my custom uprights are just 20” long, as they're attached atop two-foot high (AL3) woofers, and sit just six feet from my ears; the stock supports are 47'', and would therefore doubtless resonate at a different frequency.] Anyhow, the cure was to take a long-enough dowel (could have used a yardstick) and use it to shove some everyday empty plastic grocery bags into the column, to damp it. I used just 3, but the much longer originals would want maybe 7 or 8. Obviously you want to have the feed-through wire held in place before stuffing the bags in there. Anyhow, this trick tamed that resonance down to where it's no longer audible. Kind of Mickey-Mouse, but it works, and you'll likely never see it again. [Be sure to use audiophile-grade bags, though - none of that Walmart crap!]

I put it all back together* and I revamped my response curve a bit, so now it's a bit flatter and simpler, for not having to reduce the gain at and around those lower midrange frequencies that sounded offensive before.

At this point I have no hesitation is stating that the CF speakers sound cleaner than any of my seven pairs of 48'' ribbons. And the sound-stage produced in my trinaural LR setup with three of these little wonders is unbelievably, staggeringly huge. It's kind of mind-boggling how such small speakers can create this immense acoustic envelope, and then sort of vanish into it. Now that I have both systems running with AL3 woofers plus subs to augment just the bottom octave, they are truly full-range, four-way reproducers.

 

There is a further advantage to these speakers over Amazings, and the older I get the more I appreciate it – one can lift these more easily, and by removing a pair of screws in each channel the load can easily be divided into two pieces.

The CF speakers are not overly efficient, and, as has been observed by many, in a good-sized room a pretty powerful amp makes a noticeable improvement with them. Thus for example a TFM-45 is clearly preferable to a TFM-15. And I mean 'clearly' in a couple of senses...

 

RobertR

 

*Be sure you have the four little rubber feet between the bottom end cap of the speaker and the top of the mounting flange that it sits on. There is a lot of vibration, and they help quite a bit.

 

[PMAT 2,041]

Great post Robert. It has me juiced to play more with these great little speakers. Your protocol for finding specific frequency issues is such a cool idea. I also wanted to add a thumbs up to your assessment of the mini dsp. I have the newer 2x4 HD and have not found any clipping issues with its higher input of 2 or 4Vrms (switchable). These run $205 and are so worth it.  BTW I run my Sonorous with a TFM 45 and it’s a great match.

Carry on.

[RobertR 847]

PMAT - I hope you try the plastic bag trick. It's so easy - just two Allen screws and the speaker is off the column. Tape or tie the wires so they can't slip down out of reach (if yours have the rear binding post option, no need).  Then slide some bags in there – no need to tamp them in tightly; they just need to touch the walls at a number of places, all along.  Now remount the speaker,  take a knuckle or something and bang on the side of the support, near its center, and note the sound. Now bang on the other, unmodified channel. I'm betting you will notice quite a difference.

 

If you're living in a state where single-use plastic bags are banned and therefore aren't so handy, many other things would work just as well – smaller-gauge bubble wrap loosely wadded up, for example.

 

A small bonus is that when you take the speaker apart now, the wire is quite unlikely to slip down inside the support. And that wire can never vibrate in there, either.

 

 

I hope somebody figures out the resonance frequency of the stock 47'' uprights – I'd do it in a minute, but my own full-height ones are many miles away at present.

 

RR

[pindrop 330]

RobertR did you ever mount yours on the ALlll boxes?

Edited January 5, 2019 by pindrop
Sp

[RobertR 847]

1 minute ago, pindrop said:

RobertS did you ever mount yours on the ALlll boxes?

  Oh yeah.  Using a mini dsp with them, and that's what got me messing around with listening to various frequencies, looking for problems and trying solutions.

 

RobertR

[pindrop 330]

I forgot to ask you at the fest where the stands came from? Any more around?? My lll's ribbons are down until sea can regroup from his house. I know the bins work with them now, but I need the DSP and I'm wanting a xover anyway.

[sea 675]

1 hour ago, pindrop said:

I forgot to ask you at the fest where the stands came from? Any more around?? My lll's ribbons are down until sea can regroup from his house. I know the bins work with them now, but I need the DSP and I'm wanting a xover anyway.

 

Pindrop,,

 

I can help you with your ribbons anytime you are ready.  I will send you a PM.

 

Ed

[RobertR 847]

Hi pindrop - You can run the CF speakers on their original stands next to or in front of your AL3s and use the woofers only, bi-amped, using the original binding posts and fuse, but with the original crossovers bypassed.  Maybe just turn the AL3 units sideways 90^o so they don't present a big reflective surface, and see how good you can make them sound.  With two amps and a DSP you're in business, and if/when you get back to the ribbons nothing is destroyed.  I can send you some dsp settings that will get you started with pretty good sound; final tweaking for great sound is up to you -  rooms, and locations within any room, are quite variable.

 

If you want make it permanent,  remove the ribbon and the entire vertical structure that holds it (leaves about 20 little screw-holes per channel), and then you can do as I have done and mount the little speakers on top of the woofer enclosure.  The stands consist of your original flanges at the top end - two  shortened uprights, length 23'' (that's two feet shorter if you want the CF speakers at the same height as now) - plus a pair of custom flanges about 4''x4'' at the bottom, bolted through new holes in the top of the woofer cabinet into four T-nuts you add inside the box.  Speaker wire feeds from existing binding posts on the back plate, through the fuse (if you choose to use one), and bypassing the AL3 crossover, going right up through the upright support in the usual way to the little XLR plug for the speaker on top, where you use the original flange.

 

Alex Sauter made mine for me, and I'm guessing he'd do more for others, at a reasonable price. You'll need the upright, cut to the right length and tapped; the bottom flange, drilled;  and the flange mounting hardware bolts and  T-nuts.  You could have him get it powder coated for you if you like; I didn't bother. 

 

Or, you could shorten and re-tap you old upright yourself,  and then cut the original floor base plate down to use as your mounting flange.  Obviously those stands are now history- you can never use them again in their original configuration.  

 

The  black (plastic over MDF) woofer cabinet could be finished a number of ways, anything from stick-on tape to  rosewood veneer.  Or just leave it ugly, like mine...

 

RR