It really is, thanks. I really wonder why there are so few commercially available OB speakers
SAF. Nowdays the skinny tall multi way is in fashion or just the little home theater cubes. OBs and big horns are on the outside of the loop. Myself i find the 10" sub on my Pioneer HT a bit flabby and overblown single note sounding. But HAY , i bought it.
ron
As an added thought, if i was going with a line OB array, it would be focused.
SAF. Nowdays the skinny tall multi way is in fashion or just the little home theater cubes. OBs and big horns are on the outside of the loop. Myself i find the 10" sub on my Pioneer HT a bit flabby and overblown single note sounding. But HAY , i bought it.
ron
As an added thought, if i was going with a line OB array, it would be focused.
MisterTwister said:
Another little update. I added more PVA to the bottom cone, coated the top cone lightly too and reshaped the acorn phase plugs with some sand paper so they fit better.
The difference is night and day to the untreated speakers and they are actually now very respectable (although they REQUIRE EQ to provide bass and to tame those ugly response bums, though the PVA treatment has definitely evened them out a lot). I was expecting these to be an experiment that ended up leaving me with some amp testing speakers, what I actually have is a pair of speakers that I can really enjoy, are exceptionally good value and shouldn't take more than a few hours to build.
I'll finish with a question... I have the 2 drivers connected in series. As I understand, adding series resistance alters the drivers TS paramaters (increases Qts?..) so I assume I'm correct in thinking that connecting 2 drivers in series would also have this effect. We then also have the effect of the voice coil inductance of the first speaker which I assume would roll off the response of the second driver. In this case these effects dont seem detrimental but are they generally factors that need to be taken into consideration?
valleyman said:
Hi,
seems you get really involved while playing with your OB ...
fine !
When connecting two equal drivers ins series, there is no
change in TSP. Of cause your drivers are not equal anymore ...
While connecting them in parallel maybe could improve bass
response in your design, there is an interesting option with the
currently applied series wiring.
You can boost the highs of the upper driver and damp the highs
of the lower driver when bypassing the lower driver with a small
capacitor or RC series circuit.
This will cause presence to brillance range to be radiated
predominantly from one driver and add some air and brillance
at the top end. If chosen carefully this may push your design
a further step forward ... additionally this way you may
circumvent some of the nastyness in some fullrangers
mid to presence region.
Cheers
OK. Can you explain why this is the case. In my last post I referred to the first and second drivers but I'll stop that as since we are talking about AC signals it's fairly meaningless.
The spec sheet gives Le as 0.28mH @ 1kHz. I was not aware that inductance was a function of frequency (I am aware that inductive reactance is a function of frequency), so would I be right to conclude the frequency dependence of the voice coil inductance is due to the fact that it is moving?
If a constant inductance of 0.28mH were to be assumed I would expect this to act as a low pass filter with -3dB at around 4.5kHz.
I'm clearly missing sometihng here and I'd be grateful if someone would enlighten me.
Thanks
The spec sheet gives Le as 0.28mH @ 1kHz. I was not aware that inductance was a function of frequency (I am aware that inductive reactance is a function of frequency), so would I be right to conclude the frequency dependence of the voice coil inductance is due to the fact that it is moving?
If a constant inductance of 0.28mH were to be assumed I would expect this to act as a low pass filter with -3dB at around 4.5kHz.
I'm clearly missing sometihng here and I'd be grateful if someone would enlighten me.
Thanks
Hi,
i am not well prepared to discuss all reasons of
VC inductance and frequency dependency ...
Maybe someone else wants to enter discussion here ...
But to reduce inductivity and flux modulation a
copper pole piece is usually applied.
If your drivers miss that you could glue some copper
on the pole piece or use a copper phase plug ...
But the effect of the series wiring is not that evil
as you may fear, because the relation between
inductive reactance and VC resistance stays the same
when connected in series compared to the single driver.
The relation stays also the same when wired parallel.
Since the relation between inductive reactance and resistance
is independent from wiring, there is no -additional-
Lowpass effect introduced from series wiring ...
The RC bypass i suggested reduces impedance of the
whole speaker at HF, thereby driving more current through the
upper VC. Interference between drivers will be reduced,
FR will get significantly smoother.
Much quicker effect than milling copper plugs ... and solves
more problems in one single step.
Cheers
i am not well prepared to discuss all reasons of
VC inductance and frequency dependency ...
Maybe someone else wants to enter discussion here ...
But to reduce inductivity and flux modulation a
copper pole piece is usually applied.
If your drivers miss that you could glue some copper
on the pole piece or use a copper phase plug ...
But the effect of the series wiring is not that evil
as you may fear, because the relation between
inductive reactance and VC resistance stays the same
when connected in series compared to the single driver.
The relation stays also the same when wired parallel.
Since the relation between inductive reactance and resistance
is independent from wiring, there is no -additional-
Lowpass effect introduced from series wiring ...
The RC bypass i suggested reduces impedance of the
whole speaker at HF, thereby driving more current through the
upper VC. Interference between drivers will be reduced,
FR will get significantly smoother.
Much quicker effect than milling copper plugs ... and solves
more problems in one single step.
Cheers
do you mean "focused" as being fixed to a certain listening
position, a "sweet spot" ?
Yep. There are two(2) schools of thought on this (maybe more, i dont know).
1. A floor to roof line array where you sit in the Fresnel (near zone). (Ref. Jim Griffin)
2. A focused array where the energies arrive a a given point in a proper time domain.
Drawbacks:
1. You will lose some HF energy at a given vertical position. (makes a case for rising response drivers or another HF center mounted tweet)
2. Makes an exacting sweet spot. but the wave energies across the spectrum are equal and arrive at the same time.
All depends on what the goal is. My study is that a short focused array emulates a SD with greater dynamics, rather like a HE horn or waveguide.
Again, depends on what your goal is.
ron
position, a "sweet spot" ?
Yep. There are two(2) schools of thought on this (maybe more, i dont know).
1. A floor to roof line array where you sit in the Fresnel (near zone). (Ref. Jim Griffin)
2. A focused array where the energies arrive a a given point in a proper time domain.
Drawbacks:
1. You will lose some HF energy at a given vertical position. (makes a case for rising response drivers or another HF center mounted tweet)
2. Makes an exacting sweet spot. but the wave energies across the spectrum are equal and arrive at the same time.
All depends on what the goal is. My study is that a short focused array emulates a SD with greater dynamics, rather like a HE horn or waveguide.
Again, depends on what your goal is.
ron
If you've enjoyed modding your drivers and haven't already tried this, you might put some damping material on your frames. Hold the driver by the magnet and flick the frame with your fingernail to get an idea of the amount of ring and the pitch that you would be damping. It might even out your mids some more.
Did you thin your PVA coat with water? Unless you specifically desire to add mass it's my understanding that this is a common practice.
You could probably benefit from opening up the back side of your speaker cutout with a dremel / file / router as well, if you haven't already.
Did you thin your PVA coat with water? Unless you specifically desire to add mass it's my understanding that this is a common practice.
You could probably benefit from opening up the back side of your speaker cutout with a dremel / file / router as well, if you haven't already.
REC1 said:
Hi, thanks for explanation.
I agree, IMO this is also due to the higher directivity
compared to a small single driver and is not restricted to
focused line arrays solely.
In your enumeration of "schools"
1st : roof to floor array
2nd : focused short array
I am an advocate of a 3rd one:
Adapting the effective height of the array according
to wavelength radiated.
( "shaded line array" , "tapered line array")
IMO this combines the advantages of 1st and 2nd approach.
Focusing is not necessary anymore because the array
is short enough at HF, so it has no problem with smearing
of transients out of the sweet spot.
The transition from far field to near field can be kept more
frequency independent and at a living room convenient
listening distance.
If designed properly, the result is an "indoor farfield array"
with practical minimum listening distance <1.5 m.
Kind regards
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