Tweeters and crossover points
Martin Nieuwelaar
in part, of a Peerless 831709 8" mid/bass driver,
and Vifa D25 tweeter. I'm using some very cheap
12 dB/octave crossovers at present, until I get time to
build some active crossovers.
The present crossovers cross at approximately 3.5Khz (at least
they would if the tweeters were 8ohm - instead they're 6).
According to The Loudspeaker design cookbook, crossing an 8"
woofer at this frequency is not a great idea (the horizontal
polar response suffers). The 831709's response sort of goes
to mush above about 2000Hz anyway. I would like to
experiment with lowering the crossover point,
however the D25 fs is around 1500 Hz, so I
don't think it would be a good idea to try reducing the
crossover point too much. Instead, I have started looking for
more suitable tweeters. Ones that grab my attention, include:
Brand Model resonant freq. reccomended range
----- ----- -------------- -----------------
Morel MDT-28 fs = 700Hz 1.5-20KHz
Morel MDT-30 fs = 700Hz 1.5-20KHz
Focal T-120K fs = 600Hz 3-20Khz
Dynaudio D28-AF fs = 700Hz 2-20KHz
Seas H-400 fs = 600Hz 2-20KHz
(all from the Meniscus catalogue)
All these resonant frequencies seem quite suitable, though the
reccomended frequency ranges are different from what I would
expect. Why is the lower limit of the Focal suggested to be
3KHz, when the Morel drivers have a higher resonant frequency,
and have suggested lower limits of 1.5KHz? Does this simply
mean the Morel drivers can handle more power at lower frequency,
compared to the Focal driver?
Unless I hear otherwise, I will probably buy a pair of Morel
MDT-30s. From what little I have heard, these seem to be
reasonably good drivers. Then I could possibly get
away with a crossover point under 2000Hz.
I would be very interested in hearing from people who
have had experience with any of these tweeters,
or other ones that may be suitable.
Any help much appreciated.
Peter R. Tilton
>
>
> Focal T-120K fs = 600Hz 3-20Khz
>
>
> reccomended frequency ranges are different from what I would
> expect. Why is the lower limit of the Focal suggested to be
> 3KHz, when the Morel drivers have a higher resonant frequency,
> and have suggested lower limits of 1.5KHz?
>
the crossover point at 2 kHz; but to acheive this with an aspect of saftey
(the tweeters sake) a third order (18db) crossover point is required
or a second order at 2.5kHz will suffice with these tweeters.( There is actually
a rather expensive local made speaker that does just this - also with excellent
results)
I would be tempted to recommend you to try the Focal T90ti, as this has
a flatter response between 4 and 2 kHz (maybe this is why the 120 is recommended
to be crossed over at 3kHz - as it has quite a peak below this). You should
find that this will give you a better balanced sound, although the sparkle in
top octave is not as good as the 120's. If you want more information on
crossover data / design for these tweeters feel free to mail me.
One advantage these Focal tweeters have is their inverted dome design. They
still provide the clear open sound inherant in metal designs (ie on cymbals etc)
but I have personnally found them to be smoother and less metallic sounding than
Titanium tweeters due to the self dampening characteristics of this design.
I would also be interested if someone could give me the prices of the Focal
and Dynaudio tweeters in the states, for comparasion to what we are paying
down here in Oz.
Cheers,
Peter Tilton
Alex Mitaru
>
>I would also be interested if someone could give me the prices of the Focal
>and Dynaudio tweeters in the states, for comparasion to what we are paying
>down here in Oz.
>
>Cheers,
> Peter Tilton
>
Well, since I have Madisound catalog next to me, here they are:
DYNAUDIO FOCAL from Zalytron catalog
D-21AF $61.5 T90K $39
D-28 $62.0 T90Ti $40
D-28/2 $62.0 T90TiO2 $43
D-260 $87.0 T120K $60
T-330D $458.0/pair T120Ti $64
T120TiO2 $68
T122Ti $77
T130 $115
Cheers, Alex Mitaru
Dave Dal Farra
va...@tragula.equinox.gen.nz writes:
In article <vanz...@tragula.equinox.gen.nz> Martin Nieuwelaar,
va...@tragula.equinox.gen.nz writes:
>I have recently built a pair of loudspeakers, comprising
>in part, of a Peerless 831709 8" mid/bass driver,
>and Vifa D25 tweeter. I'm using some very cheap
>12 dB/octave crossovers at present, until I get time to
>build some active crossovers.
> I would like to
>experiment with lowering the crossover point,
>however the D25 fs is around 1500 Hz, so I
>don't think it would be a good idea to try reducing the
>crossover point too much.
[...]
>
>I would be very interested in hearing from people who
>have had experience with any of these tweeters,
>or other ones that may be suitable.
>
Your best bet is to probably go with the Vifa D35-AGsomething or other.
It is a 1" metal dome with an fs around 750 Hz. They also make a 1"
metal dome with an fs much higher, so be carefull to get the right one.
I've used this tweeter in several designs and it is very easy
to integrate into a system. I've measured its response using MLSSA and
it is VERY flat. It's impedance is well behaved and very easy to
equalize. I've had nothing but positive feedback from those who've heard
it used in my systems.
I know there are better tweeters out there, but not at anywhere near
it's price (at least that I know of, and I've looked).
It is an amazingly good deal at $29 Canadian. Theil uses a modified
version in some of their speakers, and I beleive the NEAR's also use it.
It allows a low crossover point, but be very carefull. You can not go
below 2kHz with it. One company tried and this resulted in the return
of blown tweeters. Vifa wrote an article to Audio stating that the
loudspeaker design company screwed up by using a 1.5kHz x-over which
resulted in the cooked drivers.
One final warning: USE IMPEDANCE EQUALIZATION. If you are going to
use low x-over frequencies, you MUST impedance equalize the tweeter
imdepance rise at resonance. Why? If you don't, the increasing
impedance at resonance will result in more effeicient power transfer
to your tweeter around resonance. The result? The high-pass x-over
won't behave correctly and may even stop rolling off over the region
around tweeter resonance. The result will be cooked tweeters and a poor
frequency response through x-over.
The impedance EQ cct is simply a series combo of an inductor, a
capacitor and a resistor, placed in parallel with the tweeter.
The cookbook should contain the necessary formula's.
Also, before you design another x-over, try and obtain frequency
response measurements for your drivers, including the time offset
incorporated in the phase.
Designing just from formulas with idealized drivers will not give you the
results you're expecting on paper.
My typing is too slow. I'll let Dick explain the above 8:)
Dave D.F.
"It's true they say that money talks. When mine spoke it said
'Buy me a Drink!'."