Something stirs in the Undergrowth

[IslandPink]

I've just had my first listen to the horn with the phase plug assembly mounted, using the Fane Studio 8M driver. It definitely sounds better, not hugely, but it's moved in the right direction. I definitely get the impression that some of the HF energy beyond 2Khz has been curtailed, so the effect is not one of obviously extending the top-end, more one of getting a more 'correct' and graceful roll-off.
I'll do more listening and then try to get measurements in a couple of weeks time after I come back from holiday .

[waveguide]

You have to know that what you are listening to is what you attribute it to.
Is it the horn, the compression driver, the amplifier. Does not everybody gets good results that persists whether it is solid state or DHT direct or compression or horn

Yes, that goes without saying. Obviously only a fraction of the listening combinations you hear can be meaningful . Swapping in a controlled way can reveal 'deltas' if the some of the kit is a known quantity and the listening is done over a reasonable space of time. At our regular meetings I've often had the advantage of being able use my own phono and/or power amps in the system of interest .

I really like the benefits of random swopping as it is or maybe out side the normal other than with ones own kit but adds another dimension for discovery.

[IslandPink]

Yes, we get plenty of opportunity with our regular Yorkshire meetings. The other thing to remember is that if you make a change that sounds better, always try to go back again after about 2 weeks to see if you lost anything, as well as gained .

I'm off now for about 10 days, going to "de-assimilate from the cyber hive" as Ray Mears would put it - cheerio !

[IslandPink]

Managed to progress project 'Box' yesterday before going back to work -

[g3dahl]

Nice to see you back! Looks like a good start.

[IslandPink]

Thanks Gary .
I did some more last night and should be able to have a first listen over the weekend . The idea is to compare ( first ) the Fane Studio 8M as an unmounted driver vs. on the sealed box. It'll be obviously be different in its gross response, but hopefully I will be able to judge if there's much influence from box colouration, to my ears. If this is inconclusive I'll try the B&C 8PE21 which has a cleaner midrange, although ultimately it has too low a Qts ( on paper ) for this application.
It's really a test-bed to check which is the best way forward . I decided to put in the effort to make the box trapezoidal in section to get rid of the more obvious box modes , anyway .
I also want to hear how the low group-delay of the sealed box sounds, eg. if it can handle percussion nicely, in conjunction with the 288/AH425.

If it's a good result then I'll build another pair of boxes for something like GPA 414's or Supravox 215-2000 ( having sold some stuff to claw back some cash ! ) .

The horn with the phase-plug mod definitely sounds better, but listening last night it's still a mixed-bag, with some music sounding great and other things not that good .

[chris661]

I'd recommend you stuff the cabinet well, or add some bracing to break up the back-wall reflection.

You can use a "click" generator, a mic and a 'scope to find where the reflections are coming back through the cone.

It might be worth giving the B&C unit a try. IIRC, you're driving these from an amp with some output impedance, so that'd bring Qts up somewhat. You can, of course, check how it'll respond to a couple of ohms resistance using Hornresp. If you'd like a hand simulating some of this stuff, let me know and I'll see what I can do.

Chris

[IslandPink]

Thanks for the offer on analysis Chris, but I'm OK for using Hornresp and then doing some measurements to see how it differs. I'm interested to see how the low-end roll-off looks, as I debated about using 1-Pi or 2Pi on Hornresp when designing, since the box will be close to the floor, but not too far from a wall when you consider the wavelengths at 100Hz or so .
Good point about some series resistance to flatten-up the 8PE21 response - I will sim this and try if necessary on the real unit.

On the stuffing, I'm intending to start minimal and experiment to see what I need above that . I'll go by experience with the Ariels, which used 1/2" wool felt on some ( not all ) of the surfaces , and a very light filling of long-haired wool in a couple of places. I do not want to end up with that dull over-damped sound a lot of boxed speakers have . The advantage of my set-up is the box part will cross-over lower than a typical two-way ; 700Hz rather than 2 or 3kHz . Perhaps Gary can comment on what he did for the 416's .

[g3dahl]

I used Bonded Logic Ultratouch denim insulation inside my sealed 416 enclosures. The cabinets are full, but the material isn't compressed. They most definitely don't sound dull or overdamped.

With the Ultratouch in place, the Q value is lowered as expected, so the cabinet behaves as if the volume was somewhat higher. This should be accounted for when deciding upon the enclosure size. I might have liked the GPA 515-C's better if the enclosures were a bit smaller. Their lower Q didn't work as well in my system.

Below is the impedance curve of the 416's in the sealed cabinets, with and without the Bonded Logic Ultratouch stuffing:



Below is the effect of the Zobel network on the impedance curve:



Gary Dahl

[IslandPink]

Thanks for the detailed info Gary.
I must try some different options then ; then refine my ideas for the proper box. Can you link me ( or post ) to a frequency response for the 416 in your 3 cuft ( exactly how many litres is it ? ) so I can see how Hornresp differs from 'measured' - that would be very handy .
I will also look for suitable zobel components too .

Anyway - I've finished project 'Box' Mk.1 this afternoon.
First impressions are that it's a contender. It sounds tight and clean . Not much overhang on solo piano - definitely a differnt game to the Onken I built first. Tone seems good, within the limitations of the Fane driver ( ie. harsh higher-up ) . There may be a little bit of box resonance somewhere - will check with the sig.Gen tomorrow . At present I only have one brace ( dowel ) across the two big sides . I need to add one higher up, plus something from the back of the driver to the rear panel .

Pics of cabinet just before installation of driver, below :

[Paul Barker]

A lot of hard work there.

[ed]

Hi Mark

thought I was going bonkers, seeing double...that's exactly the box shape I'm using on my new sealed two way for the Seas Fa22. It's the only way to realistically get the volume down for a sealed enclosure....


I was going to say great minds...but honestly I couldn't find any other way....

I'm hoping that the sealed route lends to a cabinet that's a bit less room dependent

[IslandPink]

How about "great bonkers minds think alike" ?
I see you're trying to meet a specific height target as well as a volume . Makes sense to shrink the back panel then . I was trying to get a non-rectangular box . A bit of extra faff involved , but hopefully worth it.
For me the advantage of the sealed box is the low phase-change/group-delay at the low end, so I can run it right down into its low-end rolloff without a high-pass and get a good blend ( fingers crossed ) with a tapped horn run with a digital slope. That's the theory ....

[ed]

Phase, what's that?

The height thing is mainly to :

a) keep the driver focus at ear level
b) keep a fairly stable footprint with a floor mounted cab
c) keep the baffle size and height in line with other models I do

It's no biggy really because to maintain the required model height it's very easy just to take some volume by inserting something inside the cabinet..e.g expanded polystyrene.....I've always used builders foam moulded to the correct volume.

the six sided olney labyrinth that I used to make with a fostex driver was a cracking little speaker, but people didn't like the stand mounted format....I'm going to produce exactly the same speaker but in a floor standing format with redundant space inside...that's where the builders foam comes into it's own. Super stuff!

[IslandPink]

Ah yes, that's what I call "The Devil's Candy-floss" . Horrible stuff.