1 Woofer in front and 1 at backside (fiter)

Archived from groups: rec.audio.tech (More info?)

Consider a 3-way speaker system
---------------------------------------
In short: If 2 same woofers are used 600Hz and down, 1on front and 1 at the
the backside of the box... Will that simply reduce the 150-600range ~3db or
produce a strange sound /reflexions?
---------------------------------------

Ex.
Let's say whe want a speaker that goes low in base.

We use 2 budget woofers that combined get a sensitivity ~3db above the mid
range driver.
X-freq 600Hz.

Here is the idea... We put 1 woofer on front and 1 at the back of the box.

Now the sub base sound (<150Hz) will remain 3db above the mid sinse subbase
reflexts well. But, the Woofer (on the back) higher range (150-600) will be
strongly dampened.

Will this produce a strange sound or just smoth dampen the lower mid???


Morgan O.

Archived from groups: rec.audio.tech (More info?)

On Tue, 6 Sep 2005 20:25:54 -0400, James Lehman wrote:

> This is kind of a bipolar woofer idea. Such things do exist.
>
> A dipole speaker is one that allows the rear phase of the cone to radiate
> out from the back of the speaker. This sound field is out of phase with the
> front of the speaker.
>
> A bipolar speaker has active drivers on the front and the back of the
> cabinet that are driven in phase.
>
> I would say that this sort of thing is more common with mid ranges and
> tweeters. Your ideas are pretty much correct. You will be dumping a lot of
> mid frequency information behind your speakers, and that will either be
> absorbed or reflected based upon what sort of material is behind your
> speakers.
>
> I personally like direct radiators. The idea of having speakers pointing
> away from me seems like a lot of nonsense, except in the case of a real sub
> woofer crossed in at less than 120Hz.
>
> James. )
>
>
> "Morgan Ohlson" <morgan.ohlson@comhem.se> wrote in message
> news:yvyvvy8facao.yukzt8l70gh4.dlg@40tude.net...
>> Consider a 3-way speaker system
>> ---------------------------------------
>> In short: If 2 same woofers are used 600Hz and down, 1on front and 1 at
> the
>> the backside of the box... Will that simply reduce the 150-600range ~3db
> or
>> produce a strange sound /reflexions?
>> ---------------------------------------
>>
>> Ex.
>> Let's say whe want a speaker that goes low in base.
>>
>> We use 2 budget woofers that combined get a sensitivity ~3db above the mid
>> range driver.
>> X-freq 600Hz.
>>
>> Here is the idea... We put 1 woofer on front and 1 at the back of the box.
>>
>> Now the sub base sound (<150Hz) will remain 3db above the mid sinse
> subbase
>> reflexts well. But, the Woofer (on the back) higher range (150-600) will
> be
>> strongly dampened.
>>
>> Will this produce a strange sound or just smoth dampen the lower mid???
>>
>>
>> Morgan O.
>>

The idea... which you may have understould is that it that way would be
possible to use higher sensitivity to the wofers and gain that effect "only"
(?) in the lowest band (subwoofer area).

....which could generate the possiblity to build a loudspeaker with results
above what the used drivers otherwise would. (That is, very high Q/price
ratio)

Is it possible to tell how big the dampening of the "backwords driver" would
be, and aprox at which frequency it will occure?


Morgan O.

Archived from groups: rec.audio.tech (More info?)

> The idea... which you may have understould is that it that way would be
> possible to use higher sensitivity to the wofers and gain that effect
"only"
> (?) in the lowest band (subwoofer area).
>
> ...which could generate the possiblity to build a loudspeaker with results
> above what the used drivers otherwise would. (That is, very high Q/price
> ratio)
>
> Is it possible to tell how big the dampening of the "backwords driver"
would
> be, and aprox at which frequency it will occure?
>
>
> Morgan O.

A good speaker system is as flat as possible within its usable bandwidth.
You really do not want over exaggerated bass. Leave that up to the average
person who habitually turns the bass knob all the way up!

A more reasonable goal in speaker design is bass extension. In other words
you don't want the bass louder than the rest of the system. You want the
bass to extend as low as possible; while it is still well matched in volume
with the rest of the system.

Don't think louder. Think deeper. You won't get there with your idea.

To answer your question about how much sound will make it around to the
front of the box, that depends on many things. How big is the box? What
shape is it? What is behind the box? Even when you know all of these things,
the only real way to know the answer is to build it and try it!

Are you familiar with how to use the measured parameters of a woofer to
design the right box? That's really the only way to have any idea of what
kind of performance you can expect to get out of a speaker system. A ported
box, usually called "bass reflex", is most likely the best way to get the
best low end performance from a woofer.

James. )

Archived from groups: rec.audio.tech (More info?)

Morgan Ohlson wrote:

> What I wished /hoped for was that with 1 of them on box backside
> was that the upper base (dampened) would be just (lamost) in line
> with midrange.

IF you get a dual woofer system "just right" THEN the midrange increase
because of the baffle diffraction step will match the LF increase gained
by having the second woofer with its additional cross-over flank. It is
unavoidably required that both units should be on the front side of the
cabinet, otherwise a linear frequency response is plain impossible to
obtain.

> In this way... it was my hope that 10" drivers could be used (artificial
> 3½-way sys in Peter terms) to get a fast, attack bass

Fast is a term that has to be seen in the context of the frequency
range. It is conquently easy to see that it is a term that is at best
totally meaningless in this context. If a unit is "fast enough" then it
has a decent output in a range, if not, then it surely hasn't.

What most people think of when they misuse the term "fast" is that they
want a system with a low Q type response, ie. gently rolling off and
extended, rather than a system with a high Q type response, ie. peaky at
the lower limit and then rapidly rolling off.

That Q however is about the total Q of the constructions bass resonance
- for simplicity a closed box is assumed here, but similar
considerations do apply for choosing between the different bass reflex
tunings.

At the risk of geting some flak for atrociously and gravely
oversimplifiying this, here is an oversimplified guideline to what kind
of loudspeaker unit you should look for if you want to build:

a closed box design, then Qt 0.5 to 0.4 is good for ya
a bass reflex design, then Qt 0.4 to 0.3 is good for ya
a horn design, then Qt 0.3 to 0.2 is good for ya

this because low Qt type units tend to require very small cabinets for a
linear response in the passband and often also has an overall rising
frequency response. For a low Q box you need a high Q unit and for a
high Q unit you need a low Q box, all things equal the larger the box,
the lower the Q.

> and still deeper base
> than same 10" normaly would reach.

If you keep the box size constant, then you have to reduce the membrane
area to extend the frequency range downwards. Read it out loud 10 times.
It is always about the combination of unit and box!

> Morgan O


Kind regards

Peter Larsen

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