my little speakers

[richie00boy]

As you have identified the issue is the volume taken up by the vents once experimenting is over. Other than that it doesn't matter if the vents poke inside or outside.

 

[baggins]

I went ahead and drilled another hole and cut some more breather tube and did some experiments with the tubes sticking out of the front

I observed the following :-

a: 2 open holes :- massive cone extensions, lots of 40hz
lots of I.M. on program CONCLUSION unusable

b: 2 130 MM long tubes :- cone under some control but still
doing most of the work not so much 40 hz but tubes
resonating quite well . Program sounded ok on short listen
if slightly muddled in the bass CONCLUSION prefer I.B.

c: 2 280 MM long tubes :- cone completley dominated by the
ports hardly moving for the same output as b @ 40hz i.e
agrees with calculations - but using the signal generator
the fall off in response sweeping down from 100 hz (there still
is a fall in output whatever!) wasn't as smooth as d:
Sounded tighter on program .
CONCLUSION maybe

d: 1 x 280MM and 1x 200mm long tube :- cone still under
control even less excursion @ 60Hz & 50 hz than above &
smooth transition when sweeping down from 100 hz.
Sounded the same as c: on program but I think the increased
cone control @ 60HZ & 50 Hz would pay benefits @ high
listening levels.
CONCLUSION its this or I.B.


I think I,ll probably try this for a while until Ive knocked up
some kind of active filter to drive a sub .I can always make another baffle then or just block up the tubes!

N.B. by definition these tests are very subjective but so's
listening to music--- great fun ,very interesting too

 

[richie00boy]

Nice work again, thanks for reporting your findings

You might find the following useful as it's a similar kind of thing.

http://www.diyaudio.com/forums/showthread.php?postid=93570#post93570

 

[baggins]

Is B.A.F. as good as fibre glass for tricking cabs into thinking they're larger ?

 

[richie00boy]

I never use loft insulation, always BAF wadding. Safer, nicer to work with and pretty much as effective.

 

[baggins]

Does pretty much as effective actually mean - not quite as effective?

I,m messing around with 0.16 cu ft here and every little helps!
sorry to be pedantic Richie but you see my point & ive got both available and due to the marginal nature of this tuning I,m scratching
around for all the advantage I can gain.
Needles to say your help on this build has been absolutely invaluable and I hope I,m not sounding churlish --- non intended!!

By the way the experimental setup using the spare drivers is producing enough bass now from this volume to shake my rib cage
on kick bass drum is this normal from such small enclosures?
Ive always had bigger speakers in the system before now and I,m amazed at the capabilities of these modern high compliance roll surrounds

 

[richie00boy]

I see your point in needing to maximise the effect, but the difference is pretty small and the effect will be quite negligible from the wadding anyway as being a vented box you would only be lining the walls not stuffing the box.

If you stuff the box it will very much reduce the airflow in the box and change the tuning characteristics more towards that of a sealed box. This could be desireable or an element of the design.

 

[sreten]

......
if they are more apart they start to function independently.
I heard somebody say that staggered tuning simply makes
an average single tuning no matter how far apart, but the
results I have seen did not indicate this.

Hi,

if far apart they do not average, they function independently.

The higher tuned port will prevent any air pressure in the
box for frequencies significantly below its tuning frequency.

Consequently the lower tuned port becomes next to pointless,
as does the whole far apart staggered tuning design idea.

/sreten.

 

[baggins]

Thanks for the replies folks, you seem to be dissagreeing slightly
,but for this particular box ,with these particular tube lengths my
observations regarding the cone movements at 60hz,50hz & 40hz
with the one tube fixed @ 280mm and the other being adjusted from
280mm down to 200mm were repeatable .though yet again thats not
to say this wouldnt cause problems elsewhere .I probably wont find out until Ive assembled them properly and retuned the "crossover"
and since I dont have a wealth of Bruel & kjaer @ my disposal
listening tests will be the final arbiter. wish me luck.

 

[quickshift]

Hello again

I don't know if it's helpful but I have measured the FR of the 5" wharfdale - literally just using room EQ wizard, free air from about 10cm away so thought I'd pop up the results in case they are of interest.

NB the mic isn't calibrated as such so the actual level is meaningless.

P.S. I have just got 24 of these for an experimental project because they are less than £2 each delivered... Can't really go too far wrong at that price.

 

[baggins]

Thanks quick!,

the graph confirms my opinion that the mid range reproduction is excellent i suspect the little peak @ 50hz was kidding me into
believing there was more low frequency extension than I thought but
hey, as youve found out, they're the bargain of the week !I think
I need some henries too ! the upper mids need taming methinks and
the piezos flat around there so Ill have a play (again!)
Bill.

 

[richie00boy]

Pretty good response there!

 

[baggins]

Richie,

what inductor would I need to cross to the tweeter @ 4000 hz
assuming 6 ohms .Ive gone and lost my Mullard audio circuit manual
in the house move and havnt got reactance tables .I am prepared to put a 6ohm wire wound across the piezo and sod the effeciency.

 

[richie00boy]

Xl = 2 * pi * F * L

so rearranging for L gives

L = Xl / (2 * pi * F) = 6 / (2 * 3.141 * 4000)

= 238.7uH

 

[baggins]

Thanks Richie' ,

Will a simple 6db job be enough to have the tweeter fill that chasm @ 8khz and do I use 1/2*Pi*4000*6 for the C value?.If I
need 12db /oct do I use 2sets of the same value?

 

[richie00boy]

The dip at 8k is so horrendous that I wonder if there's some other factor at play. I think a simple 1st-order crossover system at 4k is not a bad starting point, see how it sounds

To go 2nd-order the formulas are completely different.

 

[baggins]

an update :-

The tubes did not work when assembled properly - the loss of internal volume due to 2 thick wall tubes was just too much in this case.Maybe with a slightly bigger box the technique would enable port tuning where the length would be prohibitive normally. So Ive gone back to a single angled straight port using the tube out of kitchen foil
(nice thin cardboard wall) of about 130mm .Now here is something I discovered whilst re-checking the tuning of same (using the trombone
method) When one approaches the first piece of tube (fixed to the outside face of the baffle with plasticine) with the second tube of a
slihghtly larger diameter, just before you slide one over the other about 3mm gap there is a noticeable rise in bass output. once the gap closes this dissapears and the normal tuning phenomena occur.

Any Ideas ?

 

[quickshift]

It may be because the air in the second tube vibrates at it's tuning frequency when it's close to the end of the first tube because of the airflow from the first tube?

I wonder if you could line up loads of tubes with small air gaps between them and get them all to do the same? You could run a line of them round the walls

 

[baggins]

Stanger things happen :- someone said they were going to make a tweeter out of the flame on their cigarette lighter

I ASK YOU !! Crazy or what?

 

[baggins]

Just a note for all those who followed this old thread :-



I GOT MY MONEY BACK !!

(nil desperandum carborundum)