A different tilt on things.

[VantheMan]

Just to provoke signs of life:
I recently spent a bit of time checking stability, levelness, distance from rear wall etc of my WD25TEx speakers. Mine are on improvised isolating plinths using screw-in rubber cone like bungs instead of spikes and thickish felt pads between marble slab and the boxes themselves. They wobble like a jelly if you touch them but I don’t touch them and they seem to work at least as well as spikes and I was tired of having a dartboard instead of a wooden hardwood floor due to conventional spikes. My tweeters have always been around ear height but this time I decided to inject a tilt-back factor by using thicker felt pads up front than those at the back. So much so that my tweeters now seem to aim a fair bit higher , more like at the top of my head or even over my head. This would seem to have levelled up the power output at higher frequencies and cymbal brushwork is much more obvious and easy to hear. Could it be that the fact that in these speakers the back tilt helps not because of where the tweeter aims but because the woofer has a fair bit more mids info than is usual due to the highish crossover point and is therefore also more directional than would be the case in a 3 way ? or does it seem to have improved by getting over the negative effects of my largish coffee table between me and my boxes. Has anyone else tried tilting their WD25ts back a bit ? Discuss

[bob orbell]

I think what is happening is because the HF travels at greater speed than LF's, you have now changed the time that the sound arrives at your ears, it is now most probably arriving at the same time, this is good and has been talked about a lot over the years. This is very much like a good RIAA stage and a bad one, the good one has more precise time Constance and the bad one, poor time Constance. Bob

[VantheMan]

Hi Bob,
So, inother words, so a layman canunderstand it, rather than speed up the arrival of mid frequencies from the woofer, I mayhave slowed down the arrival of the higher frequencies from the tweeter because my ears are nolonger in a straight line with the Millenniums. I had even thought of some strange lobing effect present caused by my coffeetable so that it is only now, with them pointing higher than my head, that hi frequency info is reaching me in time because it is curved downwards rather than feeding straight out.
Not to worry, it definitely sounds for the better.
Cheers,
Chris

[A Stuart]

Originally Posted by bob orbell

because the HF travels at greater speed than LF's

According to good old Wikipedia "In a non-dispersive medium, the speed of sound is independent of sound frequency, so the speeds of energy transport and sound propagation are the same for all frequencies. Air, a mixture of oxygen and nitrogen, constitutes a non-dispersive medium. However, air does contain a small amount of CO2 which is a dispersive medium, and causes dispersion to air at ultrasonic frequencies (> 28 kHz).",
and goes onto say
"The dependence on frequency and pressure are normally insignificant in practical applications. In dry air, the speed of sound increases by about 0.1 m/s as the frequency rises from 10 Hz to 100 Hz. For audible frequencies above 100 Hz it is relatively constant."

But apparently beer and hot chocolate cause weird effects. Is either of these a factor in your house, Bob?

Directional effects seems more down to earth explanation. Given that the wavelength at 3kHz is around 10cm, then altering the driver to ear distances by a few mm by tilting might just about be significant.

Alastair

[VantheMan]

I still think this has more or at least as much to do with tilting the mid-woofer and is not limited solely to the tweeter. In fact with my dodgy lugs, I’d guess a fair bit of what I hear comesvfrom that driver.

[VantheMan]

Of course, I meant to say “ a different slant on things”. I’ve been away too long.

[VantheMan]

I’ll carry onrambling about my wd25T experiences, if anyone is interested: After a forum member (Stefi) mentioned on here his idea that the main brace in these speakers might be a bit too close to the woofer and thereby unwanted rebound waves be affecting its linearity, I got in touch with him. His being much more experienced in building speakers and tuning crossovers than I am (not difficult) I have left the moretheoretical crossover work to him and after discovering that my aperiodic vent foam was non existent having crumbled away (as has Stefi’s) I set about the more menial task of drilling out 2 more 63mm diameter holes in my main brace on either side of the central hole prescribed in the original plans. Yes I didhold onto the discs I had cut out just in case they needed to be hastily glued back in place but it sounded quite promising and I decided togo ahead and so I set out sorting out the stuffing of my vent and boxes. My original stuffing was not as Peter had prescribed as I was late getting started and I never in fact bought a complete “kit”, having been given the Millennium tweeters and buying the woofers from Falcon. I used extra amounts of the Arboseal “gunge” to line the inner walls of my boxes and then acoustic felt on topand then some polyester stuff from Monacor here and there without any sort of direction. Bass had always seemed less than perfect regarding consistency so in for a penny…….. I had little to lose ……… to be continued.

[VantheMan]

So, spurred on by extra detail and resolution caused by the mere drilling of 2 holes to make the main brace more skeletal, I took out the polyester wool and relined the front face of the brace, cutting out the new holes, and the rear wall of the boxes with some motorbike exhaust wadding (recommendedelsewhere as being better than rockwool or polyester on another forum) and left no loose stuffing and all began to sound considerably better, smoother and in a weird way it was as if power output had improved both in the highs and the bass, there being more presence at the extremes. Maybe I had been overzealous withthe polyester.
I also went to the bother of drilling a 10cms hole in the base of my speakers so as to be able to reach inside the lower compartment and pull out the polyester, substituting it with a smaallish , loose roll of the wadding held in place by, but not blocking, the hole in the lower brace nd then resealing the lower chamber with the wooden disc surrounded by glue and Arboseal to ensure no leaks.
My enjoyment of music with WD25Tex boxes has increased no end, greater clarity, smoothness but startling piano and violin tone and more info in general and I haven’t yet touched the crossovers. Stefi ( the originator of the idea of “skeletising the brace more ) has tried loads of mods there but returns basically to Peter’s original crossover so far although he does favour increasing the value of the 2.2 ohm . resistor as Peter suggested . We shall see but for now this one-eared “luddite” is fair chuffed with his more “holey” brace.
I can understand people not wishing to commit this heresy of messing about with Peter’s design so fair enough but I would urge those that question their bass response to check the foam that covers their aperiodic vents just to see if theirs has also crumbled away as had mine and Stefi’s - no idea why. At present Ihave substituted mine with a half thickness piece of exhaust wadding and it seems to work fine I know that the original plans specified an 80 ppsi foam for this but given the difficulty in obtaining it and its crumbly nature, I think a substitute needs investigating, after all the original A25s used an old sock or whatever.

[Riggers]

Recently I decided that a recoat of the paintwork of my wd25t’s was in order but bugger me the butyl mastic that beds the 10inch woofer to the main brace you are talking about made it impossible for me to shift the woofer in the slightest. I guess I’ll have to take your word regards the benefits of modding the main brace!
Regards
Phil.

[VantheMan]

Mine were extremely difficult but with the aid of 6 fine metric thread bolts of the same diameter as the holes (M6 ? )in the driver rim and some nuts, I was able to push the driver out by screwing the bolts, a nut on each, in like an extractor or like when you tighten down a cylinder head, first at 12 oclock, then 6:, then 2 and 8, then 4 and 10, , say half turn at a time and tightening down the nut on each bolt to maintain a steady pressure and eventually the driver comes away from the box. The good thing is that the butyl mastic Arboseal never hardens so you can use it again after a bit/lot of kneading (or hairdryer) to warm it. Just take it slowly and let the stress dissipate bit by bit.
When it comes to refitting, just break a wooden matchstick in each hole to act as a rawlplug in the mdf and the retaining woodscrews bite again “in new wood”.