BiB - responce ripple reduction ?

[Empee]

Hello all,


I've finally did it;
made a pair of BiB's using the Hemp FR8c

Great sound, really window shaking with techno and metal, BUT...


it seems lots of music hasn't got the <80hz bass mode so
most of the lower bass regions fall right into the responce ripple a BiB displays....

Is there any way to reduce the ripple ?


Cheers,

Empee

[pjanda1]

By "resonance ripple region", do you mean the midbass suckout on the graph? Are you hearing it, or just scared by the sight of the graph? When wall/ceiling/corner loaded, that suckout won't occur in the room to nearly the same extent it appears in the simulation. Do you have them against a wall or in corners?

pj

[Empee]

Hi !

Yes, I'm referring to the suck-out as you said, and I am really hearing it.

And when I run a frequency sweep from CD, the ripple is enormous (really not enjoyable......)

Too bad,
because on bassheavy tracks they produce really fine music

They are placed against the rear wall
(will post pictures later)


Cheers,

Empee

[GM]

Originally posted by Empee

I've finally did it;
made a pair of BiB's using the Hemp FR8c

Greets!

OK, which BIB? Seems there was more than one posted.

GM

[pjanda1]

Have you run a frequency sweep with other speakers in the room (or other rooms)? Nothing will be flat, most rooms are +/- 20db or more. Check out the inroom response measurements that Stereophile publishes with each big speaker review (available for free online). They usually look like enormous sawtooths, even with measurements averaged from 20 different mic positions. As they prove, it doesn't matter if you have $40,000 ruler flat speakers. If you want to to be able to play sweeps and have it sound flat, the BIB is the least of your problems. You'll need to get some digital EQ and some room treatments that make the BIBs look small.

You can flatten out the BIB with a little damping. I'm using 3lbs of polyfill in each mouth (top couple of feet), and it should reduct ripple.

pj

[Empee]

Hi!


Well,
I choose inner dimensions of:

364mm wide
464mm deep
1900mm high

inner plate terminating exactly in the middle,
232mm from bottom

Used 18mm birch plywood


Could you sim it?
I will set up some measument gear next weekend to check
the actual in-room responce


cheers,

Empee

[Scottmoose]

Where did you get those dimensions from? Did you use any of the math on the BIB site or the spreadsheets to calc. them?

This driver isn't a particularly good choice for a pipe-horn in that it needs a gigantic cabinet to perform optimally. Assuming it's tuned to the claimed 45Hz Fs of the driver, then it needs a Vb of nearly 21.5 cubic feet, or rather more than 607.5 litres if you prefer. That's a terminus CSA of 492in^2 (or 0.31753m^2). I'm not surprised you've got problems -that pipe, big as it is, really isn't large enough for the new FR8C.

Are they corner-loaded. If you've got a smaller than optimal pipe, then they really need to be pushed back as far as possible into corners to get as much help from the room as they can & fill in the dip at the 3rd harmonic. Without that, there will be a ~6db drop centred at 95Hz.

[Empee]

Darn!!

Really ?!
to small ?!!

I mean,
they are HUGE already !!


now what can I do ?

dampen it down to get the balance right,
try a notch filter, or just get another driver ??

What driver specs should I have for these pipes ?

[Scottmoose]

Yes, to be brutally honest, they're too small for the driver, unless you're corner-loading them (which is generally needed to mostly kill the 3rd harmonic dip anyway). Especially as the Hemp driver has an upward-tilting FR. Sorry. What method did you use for selecting these dimensions BTW? How far along the horn is the driver tapped in?

Most drivers can, in principle, be loaded in a pipe-horn, but its best if you design the box for the driver. If it's not possible to properly corner-load the enclosures, then I would be inclined to do something else with your drivers. In a fully sized pipe-horn they'll outperform many other speakers, but they will be very large -too much so for many people, so something mass-loaded will probably be the best bet.

FWIW, you can try damping things a bit & see how far you get. I don't know what you're doing at the moment, but try lightly stuffing the point above the driver & a layer on the internal base, and either line the terminus about 12in from the top down on all faces, or hang a pennant of damping material (carpet underlay or whatever) down the 2nd half of the flare.

[Empee]

Hi Scott !


I got them backed up against the wall,
but will try if things improve by shoving them in the corners...

Have some stuffing above the driver, carpet right behind the
driver, carpet on the base.

But if I was to buy a new set of drivers for these pipe's,
what would you suggest ?
I it possible to derrive the drivers specs from a given pipe ?

driver is 850mm from closed end

(btw, the dimensions are my own, and I derrived them from
the initial Hemp-BiB dimensions as in that HUGE BiB-thread,
in combination with the available space in my room, standard
sheet size, WAF... And there was this saying by one of the
participants in that thread stating "how forgiving these pipes are"

plus I didn't want to bother you and others asking for sims and all.....