[D OB G]

Here are some photos of the latest incarnation of the "Audiosyncrasy".

I'll post each one in a new post, so I don't lose the lot like I just did!

David

[D OB G]

[D OB G]

[D OB G]

To start with, the things are golden because the curtains are (WAF ).

The baffle is laminated and radiused mdf (60 mm).  It is screwed and bolted to a base which the woofers are also bolted to.

The midrange is an 8" (promoted as wide/full range driver) PHY-HP H21 LB 15 SAG (phew!).
It has a very heavy cast bronze chassis and pole-piece, but is obviously very open at the back.  (They are promoted as OB speakers.  Qt of 0.6). Alnico magnet. Silver voice-coil.  98 dB. Very low moving mass M = 5.9 g, Ms = 9.4 g, which is bourne out by the incredible dynamics.

The tweeter is a B&C DE 250 compression driver, as favoured by Earl Geddes.  It certainly has excellent dynamics, but is not as detailed in the mid to upper treble as my Dynaudio Esotar, even though the freq response is ruler flat.  I'm thinking of trying the 18sound NSD1095N.  Anyone with any experience?

The constant directivity waveguide is an 18sound XT1086, with a foam plug, as innovated by the same Earl Geddes  (AES papers, patents, but OK for DIY use.  It is 35 ppi (pores per inch) open cell foam, glued in place.  No attenuation, but reduces HOMs apparently (higher order modes in horns).

Crossover is at 1600 Hz, handled by a DEQX HDP3.  This is the lowest freq the horn can maintain constant directivity, which has been chosen with the 8" driver, because this is where it starts to beam.  The DEQX time aligns, maintains linear phase, produces a flat on-axis freq response (the off-axis is determined by the physics of the speaker), and the crossover, and other things as well.

Woofers take over at 160 Hz.  Two Eminence EMI 1550s per side (Fs 24 Hz 96 dB).  Two subwoofers (sorry Graham!) double up from 40 Hz, which takes me below 20 Hz. The woofers are mounted in 10 mm steel plate laminated on both sides with 12 mm of cork (sort of the opposite of constrained layer damping).  Totally rigid and very well damped.

The "box of bits" is the "T" bass circuit as I used it for my last speaker, and I haven't adjusted it for this one yet.  (I strongly recommend following Graham's thread).

So they're not long out of the workshop, but long enough to do their stuff!

David

[NurEinTier]

Sweet.
I like the baffle shape.

[BrassEar]

Crossover is at 1600 Hz, handled by a DEQX HDP3.  This is the lowest freq the horn can maintain constant directivity, which has been chosen with the 8" driver, because this is where it starts to beam.  The DEQX time aligns, maintains linear phase, produces a flat on-axis freq response (the off-axis is determined by the physics of the speaker), and the crossover, and other things as well.

May I ask what slope/filter you are using with the DEQX?

[Badwater]

Very nice.     I will be very interested to read about your adventures as you tweek and optimize.

Bill

[D OB G]

Hi BrassEar,

48 dB per octave linear phase at both crossover points.

David

[panomaniac]

Nice looking rig!

That's an odd looking woofer baffle.  What's the idea behind it?

[D OB G]

The idea with the woofer baffle is to have it completely mechanically, acoustically isolated from the mid/tweeter baffle.
The woofers are placed as close to the floor as possible for maximum efficiency.

It is at 135 degrees so that there is no possibility of standing waves between the two baffles (not that there would be at that freq anyway).

DEQX time aligns it (which probably isn't really necessay at that freq anyway).

It also lets the three calibrated freq bands to be "hand" adjusted for subtle tuning (for example, when the speakers are not symmetrically placed in the room, the measurement function might show that some tweaking is necessary).

I discovered that what I thought was a lacking of treble detail was completely solved by a treble boost of 2 dB from the 2 m position, making it flat at the listening position.

[D OB G]

I emailed my DEQX file to Alan at DEQX to check out a few things.

Incidentally he noticed that changing the mid/tweeter crossover from 48 dB per octave to 60 dB per octave would reduce the group delay.  It did indeed improve the sound.

[scottw]

Wow, interesting.

That woofer baffle arrangement is fairly unique.

But you are low passing the Phy at 1600?! Yikes, if I win the lottery and ever get to play with that fancy and pricey of drivers I think I'd let those puppies run up a couple more octaves. Of course I have no idea how that horned compression tweeter sounds but still........

With that electronic automagic  xover you must have tried a 8k to 10k xover point? Is 1600 Hz really better?

As far as 'beaming', I wonder if Graham's "foam finger" trick could help?



Scott

[D OB G]

Hi scottw,

Yes, the PHY is flat to 8 kHz.

And I've tried it crossed over at freqs between.

The overall speaker is better where its dispersion matches the horn (no discontinuities of off-axis response, as well as having a flat on-axis response).

Another thing is that the PHY is just going into break-up mode around 1600 Hz (just like any 8"driver- it's physics we can't avoid) i.e. non-pistonic above that.
The compression driver doesn't break up until 16 kHz.

Also, although the PHY has superb dynamic range, I would think that any compression driver in a horn (native 110 dB efficiency) will beat it (or any cone driver) for dynamic range (I'm a convert!!, and this from using Dynaudio Esotars).
And the B&C DE250 driver is really a mid range quality driver, the difference being it has a mylar diaphragm instead of some sort of metal.  It's advocates believe that gives it a smoother response.

I think Graham's foam fingers are partly because of the rising response of the B200.  I don't think they would improve the PHY, even if it was used up high, given that it would still need to be crossed over somewhere, unlike the B200s.

David

[JoshK]

The tweeter is a B&C DE 250 compression driver, as favoured by Earl Geddes.  It certainly has excellent dynamics, but is not as detailed in the mid to upper treble as my Dynaudio Esotar, even though the freq response is ruler flat.  I'm thinking of trying the 18sound NSD1095N.  Anyone with any experience?

The constant directivity waveguide is an 18sound XT1086, with a foam plug, as innovated by the same Earl Geddes  (AES papers, patents, but OK for DIY use.  It is 35 ppi (pores per inch) open cell foam, glued in place.  No attenuation, but reduces HOMs apparently (higher order modes in horns).

First off, nice speakers.  Looks like you thought through a lot of the gory details to execute a nice system.

If I could surmise, I think you might be blaming the lack of detail on the B&C CD driver, when it is in fact the waveguide that is at fault.  I have no proof of this, but the XT1086 has a diffraction slot at the throat.  This is good for what 18 sounds was going for, but I would guess it causes issues with the clarity of the treble.  I'd put my money on it being that, not the driver.

I've read some reports of those who've used that WG and driver and compared to other WG's and preferred the other WGs.  Unfortunately, there is a lack of available WGs on the market.

I'd probably hit up Geddes for a pair of his WGs.  He makes them to fit the exit angle of the B&C 250, so they is no discontinuity in contour. This is also very important. 

I've read a lot about the 18 Sound drivers too, and most have preferred the B&C, even on the 18 Sound WGs.  Don't fall for marketing hype.  Metal diaphragms aren't really always better than mylar, at least in a hi-fi situation.  Metal is for higher power pro-sound apps.  It allows for the wild break-up to be added to the natural freq response to boost the highs.  Not what I call a good solution.

[D OB G]

Hi JoshK,

I admit that Geddes' waveguide would be better overall, without a doubt. (Of course they wouldn't fit now!!!, and I'm hoping to make these my definitive speakers).

He does admit a vertical lobing problem (which he dimisses as of no importance), because of the large diameter, which is ameliorated with the elliptical 18sound horn.

I discovered that because I listen off-axis, and made the current measurements on-axis (for various reasons, and which I shouldn't have done), a 2 dB boost to the treble completely rectified the matter of detail.  i.e. I need to measure better next time (work in progress with DEQX- there really are so many variables).  (DEQX provides a confirmation measurement mode, which showed that the boost was effective, for now, on the listening axis).

Thanks for the advice about metal diaphragms (this is my first experience of compression drivers).  With the correction to the detail issue, and with further improvement to follow, I'll probably stick with the DE 250s now, although I'll double check with 18sound to see if their exit angle is a better match (I think the B&C is 6 degrees?).

If only I could do a side by side comparison. 

David

[D OB G]

P.S.

It occurs to me that Earl's speaker is radiating (constant directivity) at 15" at 1600 Hz versus an 8" driver (is it?). i.e. which scenario has the most even power response?

He claims the 10" Nathan is not as good as the 15" Summa?  Is this power handling?, dynamic range?, directivity?, higher crossover point?, integration at the crossover point?, in spite of vertical lobing? (which might be similar in character anyway?)

BTW, looking at the published graphs, the 18sound titanium diaphragm with nitride coating appears to start having small wobbles in the impedance curve from about 15 kHz, but the main break-up seems to be above the graph's 20 kHz limit, whereas the DE 250 has it, complete drop off, at about 16 kHz.  It is that 18sound driver that I wonder about.

[BrassEar]

Very impressive attention to details David.  Please describe their sound if possible.

I would not give up on the DE250. I am using that unit with the DDS waveguide and going back between passive and active. Right now I am listening to it actively crossed (LR24) at 1500 Hz which is also about where the DDS horn breaks up. I am currently playing with the active analog Behringer CX3400 which has a CD horn lift EQ at 3.5 KHz.

Have you listened with the mids/horns crossing slightly in front of your listening position? Most CD setups sound better that way.

The more I read about Geddes, the better my system sounds.

[D OB G]

Yes, I do have them crossed in front of the listening position.

Sound?

I suppose one DE 250 sounds like another.  I presume the foam is helpful, because their is no sense of "colouration", even if it is on a XT1086.  The baffle shape and roundover should contribute minimum diffraction.

They have superb dynamics and detail, for which I have no doubt the PHY is justified.

They throw a large yet precise soundstage (depending on recording.  Isn't it funny when a piano has been recorded spanning the speakers, making it three times bigger than in real life ), which would be better if I had a bigger room and more spacing.

The bass is interesting.  Typical OB clarity .  The eminences are flat to 1600 Hz, with no break-up peak at all, just to give some idea of the smoothness of the driver.  The OB doubles up with four 8" XLS Peerless woofers in boxes below 40 Hz, using two Rythmik 350W amps, (24 dB per octave) which to me seems to give the best of both worlds.  I do find that last 18-30 Hz does help with the ambience of classical recordings. Even though a contra-bass basoon only goes down to 28 Hz, drum and hall reverberation does benefit.

They have this sense that the sound is bullet-proof.  They're not going to fall apart.  Nothing fazes them.

They might be on the warm side (could be the amplification).

We all know how hard it is to describe the sound of speakers, especially when they're our speakers.  Cellar palate and all that!!!

 

[Graham Maynard]

Hi David,

I have followed your thread with interest, but been time limited for comment.

Digital EQ with appropriate time delay sounds ideal for separately driving low and med-high drivers, but I have no direct experience, so could not comment.

Re the LF, you appear to have one driver covering all, then a second below 40Hz.

My choice when using T-bass was for one driver (15") covering all LF, with a larger (18") second driver in parallel having lower Fs and much earlier roll off in order to take energy from the (15") driver without need for either any additional amplification or crossover circuitry.

It appears to work too, for this is better than two of either type in simple parallel, BUT, it would not work when the same drivers a conventionally parallel connected to a single SS amplifier due to its very low output impedance preventing energy sharing between the drivers, or one driver and a crossover plus driver.

In some regards a tube amp can be better for LF reproduction than NFB SS, that is as long as the phase and amplitude responses can be genuinely maintained to low frequency.

Cheers ......... Graham.

[D OB G]

Hi Graham,

You must be on the right track with the two woofers as you have them, since Gilbert Briggs of Wharfedale fame did something similar with a 12" and 15" (I think), or was it 10 and 12, on his OB competitor for the Quad ESLs.  Are both drivers run with the "T" bass?  I intend to run only the Eminiences obviously.

The way I have the woofers, as you say one running all the way down, allows me to apportion the contributions of the subbie and the OB with the Rythmik vol control, before using DEQX each time (which is amongst the reasons why there are so many permutations and combinations) was an attempt to,  ???maybe??? create some sort of a cardioid response.  The output certainly sums in front of the baffle, but I'm not entirely sure what it does behind-  I haven't got Praxis out yet.

David,