On Sat, 1 Mar 2008 13:56:58 -0800, jamesgangnc wrote
(in article <fqcjfa02enj@[EMAIL PROTECTED]
>):
> "bear" <bearlabs@[EMAIL PROTECTED]
> wrote in message
> news:fqc0ig01jv6@[EMAIL PROTECTED]
>> jamesgangnc wrote:
>>> I updated my setup to bi-amp last year. I was wondering if any others
>>> in the group is doing this now and what your set up and experiences
>>> were?
>>>
>>> I'm using a dbx 223 crossover usually at 700hz. I play around with it
>>> a bit but keep it between 500 and 1k. The lower end I'm running to an
>>> adcom 555 connected to 4 ten inch moderately priced woofers in closed
>>> cabinets, two woofers to a side wired in parallel. The high side I
>>> have going to an adcom 535 with a pair of 5 1/4 midwoofers and one
>>> ribbon tweeter on each side also in closed cabinets. The passive
>>> crossover on the high side is just a simple 6db centered at 5k. Of
>>> course it is subjective, but I feel like moving the bass out of the
>>> rest of the signal improved overall clarity. The two adcoms, when I
>>> experimented with them independently also seemed better suited to the
>>> separate tasks. Besides the obvious power difference the 535 seemed
>>> to have a better sound at mid and highs than the 555 when listening to
>>> them with a full signal range at about the same sound levels. Of
>>> course the 555 is obviously the choice for the low end anyway due to
>>> the power difference.
>>>
>>> For a signal source I'm using a technics sh-ac500d as a preamp and
>>> either xm radio or itunes acc ripped at 256k via a squeezebox. The
>>> setup doubles as part of my surround sound as well hence the ac500d.
>>> I mostly listen to old and new rock but occasionally anything else as
>>> well, except country. I'd like to take some measurements as well.
>>> I've got a signal generator and a scope but don't have a good high
>>> quality mic.
>>>
>>> As I suspect most of us are, I'm trying to decide what to change next
>>> as well :-)
>>
>> I'd get a higher order filter on your ribbons first.
>>
>> The distortion increases in typical ribbons when the excursion below
the
>> useful rolloff does not decrease substantially. A first order filter in
>> practical terms tends to make the excursion *remain the same* below the
>> inflection point of the "rolloff". That means that you've got excess
>> deflection/excursion. I'd consider a 24db/oct filter there... most
ribbons
>> can not handle a first order filter.
>>
>> Then use one of the various freeware FFT programs and a halfway decent
>> mic to measure the freq response of the mid/HF combo. Take note of the
>> off axis response and the waterfall as well. Look at the impulse
>> response of the two drivers together.
>>
>> You may need to adjust the xovers and do other things to arrive at a
>> best compromise response for the mid/tweeter combo.
>>
>> Then you can look at the relation****p between the woofs and the upper
>> range.
>>
>> After that I'd say that with the "average" sort of ripped music, it
>> probably won't make much difference what else you do. BUT, once you get
>> the speakers optimized you may start to hear larger differences in
terms
>> of source material - then it may make sense to think about upgrading
other
>> parts of your system.
>>
>> Btw, the difference you are now hearing is likely due to two things:
>> - different amplifier & load to the amp
>> - different crossover slope & Q
>>
>> Until then, enjoy the experimenting! :_)
>>
>> _-_-bear
>
> Thanks. Interesting. The low end on the ribbons is around 2k so I was
> thinking that I would get way with the 6db crossover because I was so
far
> above it. Given that would you still recomend the 24db crossover or
maybe a
> 12? Some of what I have read on the topic suggested keeping the
mid/high
> crossover simpler. In all honesty I'd probably think a little bit about
> switching to a three way active to get a 24db crossover rather than
using
> passive.
>
> I'm clueless in the mic world. But I would like to be able to really
test
> rather than rely on subjective listening. Can I hook the mic directly to
my
> scope or should I have a preamp on it? I realize I will have to power
the
> mic if I do not have a pre-amp involved. What mic brands tend to be
decent
> and what kind of dollar level should I be shopping at? tia
You can get a very nice condenser mike with a big 1-inch capsule and very
flat frequency response that outputs directly to USB for less than $100.
The
Samson C01U, for instance, is $89 from Zsounds and has 20-18KHz +/- 3db
frequency response. All you need with it is a USB cable, your computer and
the freeware sound capture and editing program "Audacity" (available for
Windows, MacOSX, Linux). Connect the Microphone to your computer via USB,
start Audacity, set the preferences to the USB input, and start capturing
audio, select a section and then then go into the "Analyze" menu and
select
"Plot Spectrum" It will even give you a cursor to look at any point on the
plot.
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