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Old 25th March 2008, 05:52 PM   #21
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Elbert

I'm planning to use these woofers for pure "sub-woofing" duty anyway!

Hi, what a waste ........ /sreten.

see : http://www.troelsgravesen.dk/33FWK.htm

Quote:
Forget about silver cables, golden binding posts, Mundorf Supreme and all that crap! Get an old 12-13" (good) paper cone and let it run up to 5-600 Hz. Give it 50-100 litres of volume or as much as your wife allows. Get a decent 5" paper mid and don't pay more than 50 $ for the tweeter! Get some electrolytic caps and - most importantly - make a good crossover and you're there.
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Old 25th March 2008, 07:10 PM   #22
Svante is offline Svante  Sweden
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Quote:
Originally posted by Elbert
Hei Svante!

Yes, my software actually plots a response curve, and so far I've been aiming for a flat response......

Your point about allowing for a slightly sloping response and to have it "compensated" by the room response is very interesting!

But then again, how does one predict the room response? And what might turn out to be right for my current living room might be completely wrong if (when) I move to another house.... that's the tough one with low frequency audio, the source and the room is really part of the same equation....

The best bet is perhaps to go for a reasonably flat response and use an equalizer for tuning to what ever room they might end up playing in?
Ah, ok. The questions on how to predict the room gain, and also how much of this one should compensate for is not easy to answer.

Even if the room gain of a room is possible to measure and/or calculate it is not necessarily so that it should be fully compensated for. Once we enter a room we get a feel for how much boost there is in the bass, and the brain compensates for this to some extent. This means that some of the bass lift should be left there.

There are several philosophies on how to do this, and what finally determines what is "right" is the monitors that are used in the recording studios. It is a pity that these are not standardised...
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Old 25th March 2008, 09:47 PM   #23
Elbert is offline Elbert  Norway
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Lots of more interresting input here!

Now first of all, I see that I have referenced the wrong data-sheet, my stupid!

This is the right one!http://www.seas.no/images/stories/vi...-wb_and_dd.pdf

I got hold of these drivers in a pair of SEAS kit speakers which I bought at a "loppemarked" for about 10£!

The foam surrounds were completely disintegrated, but i found a replacement set on e-bay, and now they look like new!

The speakers as such are very nice sounding, but with a cabinet volume of around only 60-70 L, I figured that I'd probably get much deeper bass response if I buildt some larger boxes. Of course i could then make the boxer much stiffer with bettrer bracing and better materials.

From there on, the idea of replacing the midrange and the tweeter with something 30 years newer followed quite easily.

So why the low x-over? Well, i figured it would be better having one midrange covering the entire critical midrange area rather than sharing this duty with a 30 year old 13" woofer...

I did some further box modelling, and it seems I can get away with a vented box in the 120-130 L range and stil obttain a F3 of around 35Hz with only a very moderate slope in response which could either be compensated by room effect or active equalizing..

definitive answers were never hoped for in the first place, but just bouncing some ball and getting some reality checks is great and much appreciated!
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Old 26th March 2008, 01:07 AM   #24
bjorno is offline bjorno  Sweden
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Quote:
…it seems I can get away with a vented box in the 120-130 L range…
Hi,

Yes you can, I designed a slightly larger box using this driver (Qt= 0.577 or Bessel) a long time ago that I remember performed very well and I believe so will yours likely do too.

b

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Old 26th March 2008, 01:09 AM   #25
bjorno is offline bjorno  Sweden
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Old 26th March 2008, 01:11 AM   #26
bjorno is offline bjorno  Sweden
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Old 26th March 2008, 01:12 AM   #27
bjorno is offline bjorno  Sweden
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Old 26th March 2008, 04:48 PM   #28
Elbert is offline Elbert  Norway
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Hi Again Bjorno,

Interesting to learn that you have had promising results with the same woofer, something which the plots you have posted seems to substantiate!

What sort of system did you use the woofer in?

I have enclosed an image of one of the loudspeakers I have..

Regrettably it hasn't got the DD version of the unit.
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Old 26th March 2008, 04:53 PM   #29
Elbert is offline Elbert  Norway
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Here's another image of the driver.

Allthough it is 30 years old (!), it still looks like a well buildt unit even by todays standards.

I discussed this driver with a guy at ELTEK, a Norwegian SEAS and DIY dealership, and he was of the opinion that the fundamental motor and driver technology hadn't really changed that much, and that fundamentally it was still a good unit, so that's why i have decided to use these drivers for a new project. After all, a pair of decent 12" woofers are not for free if I were to buy new ones!
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Old 26th March 2008, 06:10 PM   #30
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Elbert
Lots of more interresting input here!

........

From there on, the idea of replacing the midrange and the
tweeter with something 30 years newer followed quite easily.

So why the low x-over? Well, i figured it would be better having
one midrange covering the entire critical midrange area rather
than sharing this duty with a 30 year old 13" woofer...

I did some further box modelling, and it seems I can get away with
a vented box in the 120-130 L range and stil obtain a F3 of around
35Hz with only a very moderate slope in response which could
either be compensated by room effect or active equalizing..

Hi,

Err..... no to the low crossover point .... it means more BSC
(baffle step compensation) built into the mid driver and the
matching driver sensitivities go all over the place.

The curves for the bass driver are anechoic and in a box.
The baffle step is clearly shown, mainly from 200Hz to 500Hz.

My box modelling from the data sheet indicates 140L tuned ~ 26Hz.

I cannot find where Troels G discusses highish bass / mid crossover
points, but the general gist is do not run the midrange down into a
region where it needs BSC. A short coil dedicated midrange is by
design suited to this regimen, rather than trying to use a long coil
bass/mid as a midrange - generally for the latter sensitivity is not
high enough.

http://www.rjbaudio.com/Audiofiles/FRDtools.html
http://www.geocities.com/woove99/Spkrbldg/

May help. Seas midrange and treble seem to be the obvious choice,
though the best choice for the mid might be some older units, as
high efficiency pure midranges are very rare nowadays.

what other drivers were in the Seas kit ?

/sreten.
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