Starting my first project.

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#22
Hello all,
regarding bafle step...i was just thinking...will using two identical drivers (wired in serial or parallel) cancel out the effect of baffle diffraction in addition to increasing the power handling by 2.
also how abt if i use two midranges instead of one in the 3-way design...
like say in MTMWW config. is this feasible?what are the advantages and disadvantages of such a config...

regarding the Dayton drivers...i see that in a project that they have been used in say that they are not suited for vented enclosures...could anyone corroborate this view.
Cheers,
Sachi
 
#25
sachi said:
i was wondering if i can counter the baffle step by using two 10 inch drivers and would there be any logical sense in using two midranges(again here should i use them in MTM config).
also in the link given by Nappy the author uses 4mm 45degre pieces of wood to some efect which i did not understand.would u please take time and explain what those pieces are doing to the baffle step(if there is any ) and on the freq response.
Click to expand...

I'll get started on this, but the subject will likely run a few pages....

start here... read it, and follow the links too...

http://www.t-linespeakers.org/tech/bafflestep/intro-bds.html

When you get to John Murphy's pages you will see that he has posted graphs from Harry Olson's work on baffle diffraction.

baffle diffraction is a complex phenomenom... at high frequencies the edge of the cabinet creates reradiation that being a time-delayed signal will cause some comb-filtering... this is where shaping the cabinet edges, irregular cabinet edge distance to the driver, flush-mounting, and use of absobant surface treatment (ie wool-felt) play a role. At low frequency it exhibits as a step in respnse as the peaker has to load 4 pi space instead of 2 pi space. Inbetween we get ripple in FR at the transition. The shape of the cabinet plays a big role in the extent of the ripple.

Bipole drivers cancel baffle step by creating a mirror response that fills in the response as you transition from LF to HF. If used FR then some room behind the speaker is required, but if the cabinet is fore-aft symmetrcal it can approach perfect compensation. Everything else -- except placing the speaker "in the wall" -- is less perfect but can often be placed closer to a wall.

dave
 
#26
thanks Nappy, Navin, Planet10.

in fact am going thru ur site as i write this.i
actually have John L murphy's book and know what
baffle step is but did not know how to counter it
until i got to ur site.
Could anyone please give me links explaining in detail the
1.5(.5) brute force diffraction compensation
methodology(preferablby with pictures explainning the
mounting methods).
Cheers,
Sachi
 
#27
Okay here is the Baffle step simulation using Edge(i hope i did it right...)
 

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#28
and this is the baffle compensation
p.s the mic was kept at 1m and the baffle size is 297X837(in mm)

also the Dayton drivers are being burnt in at 20Hz even as i write this by my friend.
 

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#30
thank you Navin,
the thing is after looking at the Bipole idea...it will need a fair bit of woodworking skills and am not yet ready for it (and don't have the time..) i have decided to keep it a 3way(TMW) and am going to keep the crossovers outside the box so that later i can try out an active setup, as Nappy suggested.

now as i understand...the inductor in the baffle compensation circuit should not be an air cored one.

Why?

if so then the inductor is going to be expensive. what happens if i use an air cored one?
if not then
can any of the Bangalore guys help me in letting me know where i can get good inductors......... or

if i can make one on my own can anyone give me instrcutions as to how i calculte the inductance(like the one given on Rod Elliot's site for air cored inductors)..also the materials that i can use for the cores..

Cheers,
Sachi
 
#31
why does the bipole require more carpentry. you only need make a hole in the rear baffle.

the only reason to use iron core for baffle step ios that the inductor values are large. iron core is cheaper. only you must use soft iron.

i also find that air core inductors tend to soften the dynamics if they are too large. why i can only guess. over 1mh it might make sense to investigate iron core.

i wind my won inductors as i have access to 12 and 14 SWG wire and an impedance bridge.
 
#32
navin said:
why does the bipole require more carpentry. you only need make a hole in the rear baffle./B]
Click to expand...


But the moutnig is different..i mean it calls for the drivers to be mechanically coupled with either bolts running from the ront to the rear side baffle or with a solid aluminium rod or with a piece of wood pressing against them. ..and the price of getting another pair of drivers bears down heavily upon me. Please correct me if i am wrong abt any of this.

additionally i think i read that the bass is clean and tight but there is actually a little loss in the low frequency SPL because of the second driver facing the other way..and am building these speakers mainly for trance, hard rock and metal.

the only reason to use iron core for baffle step ios that the inductor values are large. iron core is cheaper. only you must use soft iron.
/B]
Click to expand...

thank you for correcting me. am sure i should be able to find 12 or 14 AWg wire in SP road.
Cheers,
Sachi
 
#33
You don't need a solid connection between the drivers if you add a rear driver.

If I understand you correctly, you fear that the rear-facing driver will lower bass lever. At low frequency, your drivers radiate in all directions.
This means that a forward-facing driver will radiate not only forward, but also "loose" some power radiating towards the rear below the baffle-step frequency. The rear facing driver will compensate this by also radiating to its own "rear-side", resulting in a compensation of the loss from the front driver.

Pheew... I hope all this makes sense. :xeye:

Jennice
 
#34
Thank you...
it definitely clears things up..
man am i glad u guys are there to correct me when i go astray...
But the cost is still a major concern...
I'll have to think abt it and and come to a head before the week is up.
Cheers,
Sachi
 
#35
I have an idea... It should work, elthough I have not tried it myself.

If you use two drivers (one to compensate for baffle-step), the enclosure should be 2 times the size of the enclosure for a single driver.
Therefore, you could start by making the speaker without the extra driver. If you decide you need it, then you could put the extra driver in a new enclosure (with seperate X-over) next to the "main" speaker.

You should be able to "simulate" the bass gain of the extra driver by placing the speaker with its back against the wall, so that the sound "lost" to the rear will be reflected by the walls.

Jennice
 
#36
Jennice said:

If you use two drivers (one to compensate for baffle-step), the enclosure should be 2 times the size of the enclosure for a single driver.

Jennice
Click to expand...


That's right.
The original design for a single driver takes arnd 2.87 cu.ft and to get the same response curve for 2 drivers at around the same tuning freq was arnd 4.8-5 cu.ft

The idea u have proposed is intriguing...i'll have to check my bank balance before i buy a second set of drivers....
i'll let u know...
Cheers,
Sachi
 
#39
Hey Navin,

I was just fooling around after u made that comment and actually ended up with a better enclosure..including a marginal improvement in the baffle step...
the group delay too has decreased to 18.25 ms from 21.05 with only the -3 db point shifting from 28.4Hz to 32.6Hz.

The volume is now 2.15 cubic feet.
maybe with a little more tweaking i can arrive at a better enclosure...
Sachi
 
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