Can concentrics ever be as seamless as FR?

[freddi]

what's opinions on coaxial and Unity types' subjective coherency possibiiities vs fullrange/wideband?

with some FR, how do "helper" LF and woofer fit into the spatial picture as are usually non-concentric?

most coax woofer are larger diameter than what might be prefered for FR so this alone may make comparsions difficult.

[Geoff H]

I think the dual concentric types fit the full range bill. They still provide the point source effect.

Even a single cone wide or full range has a mechanical crossover in the way of ribs, bi-cone or a curviliner cone. As the freq goes up, decoupling occurs, and you get a smaller piston.

If the helper lf is filtered well above 100hz, the source appears to be where the harmonics are. It used to be regarded that 180Hz was the point where directional sensitivity became unknown.

Since trying a common bass helper, I think that figure needs to be lower, ie 100 Hz or even lower, or better still 2 helpers.

Cheers,
Geoff.

[freddi]

Hi Geoff - regarding helper woofer, would two woofers suggest "D'appolito configuration?

I don't like spatial jumps - is it good practice to place a helper tweeter concentrically with a bracket?

coaxial (if woofer is good) aren't too bad a tradeoff

Best,
Freddy

[Geoff H]

Hi Freddi.

The two helpers I referred to was one for each channel, rather than a common one. And best to exploit all avenues of obtaining the best bass from the full range as I am doing here:
Aperiodic enclosures

If the tweeter can be mounted inside the main, go for it. My concern here is to provide a rigid bracket or mount, and some sort of rear cover to direct the sound from the apex of the main cone around the tweeter. That then becomes a phasing plug or wave guide rather than a brick wall for the top end of the main.

With anything in that direction, it's a good idea to keep drivers like Tannoy DCs and Altec 604s in mind.

Where I think a lot of dual cones have gone wrong, is the whizzer is too small. Probably in aiming for 20Kz.

If you look at my Wharfedales in other posts, you'll see the dust cap is 3" in diameter. The guy that did these explained two options. Leave the woven cap alone, and allow all the energy from the voice coil former out into the open, or coat it, so it becomes a radiator, and phase corrector. I have gone the later.

Cheers,
Geoff.

[freddi]

ha Geoff - see an aperiodic box - 40+ years ago I used 5 cubic foot and 12 -3/4" holes for a Knight 12.

perhaps you can give some advice on a musical box for Beyma 12CX. IIRC, Beyma suggests 50L tuned ~50Hz and I'd like it not boomy. (Karlson used de-Q-ing holes in one coupler)

Freddy

Beyma 12CX specs - its woofer is fairly extended on-axis

http://www.diyparadiso.com/datasheet...beyma/12cx.pdf

[Geoff H]

Hi Freddi,

The specs do look good. In fact I think a good candidate for aperiodic.

Looking at the z plot, if the rise could be flattened from about 100 Hz down, it should extend the lower end down to 30 Hz in a 30 litre cab, may even go lower.

It's actually close to my system (overlooking power!!) which is still under development - enlarged the vent holes last night, no measurements yet.

From other posts of yours, you are chasing accurate phase response. I don't know if TL or BR would provide that. It's either sealed or aperiodic. And if space is restricted, go with the latter.

Most importantly, try to have a listen to the Beymas, in any cabinet. Figures and graphs are one thing. Sound is another.

Regards,
Geoff.

[freddi]

Hi Geoff -

are you measuring impedance amoung other things? would (should) the curve be double-humped or lose most of the first Z peak?

what happened to sound and Z when you enlarged holes?

Best,
Freddy

[Geoff H]

Hi Freddi,

I have since posted z readings with the larger holes.

With the aperiodic, the double peak gets flattened. You'll notice the peak in z on my system down to 13 ohms at 63 Hz. As the z peak goes down, the bass comes up, as the load on the amp is more constant.

But you don't have the phase issues you get with a resonant system.
It's not just the bottom end that gets improved, the lower mid gets a lot more clarity. Bass drums have that initial "kick" and if it's on the recording, a nice mellow reverberant decay. The rest of the kit is as sharp as you could want it.

One thing I have noticed, that's important, is cone excursion. As the aperiodic is closer to a sealed enclosure than a BR, I figured it may increase, which isn't a problem on my drivers, but could be on others.

I have watched the cones on walking bass at high levels. About +/- 2mm. That could be the limiter with the 12BX. I wish I had one here to try.

There maybe a slight trade-off in sensitivity too.

Cheers,
Geoff.

[freddi]

Hi Geoff - I think some aperiodic will lose ability to play sine and sound less resonant on electronic/synth bass than verted box but make up with drums and upright bass - whadya think?

Karlson added 3/4" diameter holes around the main port to the llittle 1960's "x15" system and even one hole opened de-Q's things a bit.

re:12CX Beyma - do you think fs at ~50 is too high to benfit or OK?

Freddy

[Geoff H]

Hi Freddy. Bass and percussion like that on Ultravox do sound hard and non reverberant, almost sterile. That gets into a tricky area. I have seen keyboard players go nuts at recording engineers because each has an opinion, and the player is listening via his amp, but what goes to the track is DIed to the console.

So what do we compare it to?

As for the 12CX. I am certain the right combination of bv and AP resistance would get it down to 40. I'll have a better idea when I can "tune" some 8" drivers that fo about 60Hz.

We have to keep in mind there was a bit of luck in my first attempt.

There are others keen to get their hands dirty on APs. When we get to comparing notes we may be better equipped to recommend combinations.

There was a swag of 10 and 12" Beymas on fleabay today. They went for a little more than I was prepared to pay.

Cheers,
Geoff