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In Reply to: Ideal Parameters for OB Woofer posted by Joseph Cohen on February 3, 2007 at 12:28:05:
Assuming no EQ (active or passive):Qts needs to be relatively high (depending on relationship of Fs to baffle cutoff frequency)
Fs needs to be high enough so that the baffle can reinforce the resonant frequency to some extent
Follow Ups:
I couldn't think of a reason other than you only wanted to use the driver as a upper bass/lower midrange driver.
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Richard BassNut Greene
Subjective Audiophile 2007
....
This also assumes a 'practicle' F3
Talking a woofer not a 'sub'
For F3 ~ Fs
needed baffle diameter ~ 360 feet / (Qts * Fs)
For instance:
with a 4' baffle and a driver with Qts~2 and Fs~50Hz
you're flat down to 50Hz sans EQ
Now I'm even more confused.Who wants to have a 16 square foot baffle x 2 ... and still need one or two more speakers for the bass under 50Hz.?
Who wants to use a 2.0 Qts. driver?
And would a 2.0 Qts driver on a 16 square foot open baffle really provide a flat frequency response down to 50Hz. without EQ?
If the answer is yes based on measurements of a real speaker, not theories, then I apologize for questioning the use of a 15" driver in a dipole configuration with no EQ.But then you'd still need to add a monopole speaker to fill in the bass under 50Hz. -- and that would make no sense because the greatest advantage of dipole speakers in most rooms is less excitation of bass standing waves (causing a more realistic reproduction of bass instruments). Why use a monopole speaker to reproduce those low frequencies when a dipole speaker would have the greatest inherent sound quality (including room effects) advantage over monopole speakers?
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RBNG - Who wants to have a 16 square foot baffle x 2?Someone who wants their baffle to contribute to the sound as much as the driver?
RBNG - Who wants to use a 2.0 Qts. driver?
Someone who appreciates high levels of driver distortion "enhancing" their "bass"? What if: "Yeah, but it sounds good"?
RBNG - But then you'd still need to add a monopole speaker to fill in the bass under 50Hz. -- and that would make no sense because the greatest advantage of dipole speakers in most rooms is less excitation of bass standing waves (causing a more realistic reproduction of bass instruments). Why use a monopole speaker to reproduce those low frequencies when a dipole speaker would have the greatest inherent sound quality (including room effects) advantage over monopole speakers?
Well here I must disagree with you. A monopole (placed beside/under) crossed at 50hz to a dipole will create a cardioid radiation pattern in the XO region. It will only radiate omni directionally at even lower frequencies where room modes are sparse and room gain from a pressure source is beneficial. Not a bad idea except there will be added GD from the XO, but I'll take a little phase distortion over grotesque IM from an over excursion driver.
cheers,
AJ
The threshold for disproving something is higher than the threshold for saying it, which is a recipe for the accumulation of bullshit - Softky
That's why they are so audible -- not dense enough!Probably three room modes under 50Hz. in a typical room.
Maybe four in a very large room.
These lowest frequency bass resonances are also the most powerful.
You control harmonic distortion by using mutiple high-XMAX drivers for a dipole. Not cheap. Not small. But subjectivelky better bass quality than monopole speakers in most rooms. Especially smaller rooms.
There is no room gain from a pressure source unless the room is unusually sell sealed (like a car with windows closed) which is very rare. You may ask Earl Geddes for details from his experiments.
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Richard BassNut Greene
Subjective Audiophile 2007
RBNG - That's why they are so audible -- not dense enough!
Probably three room modes under 50Hz. in a typical room.Once again, when you combine a dipole with a monopole xo'd @ 50hz, you have cardioid radiation @ 50hz. So yes, a monopole will have very few modes to excite in the below 40hz range. A cardioid will excite different modes than the dipole or monopole, but will maintain DI and still radiate -4.8db less power. An equalized monopole below 35hz is superior in every way a dipoles hopeless ineffeciency below these frequencies. I have linked a 2 part article for you below. Give it a read.
RBNG - You control harmonic distortion by using mutiple high-XMAX drivers for a dipole. Not cheap. Not small. But subjectivelky better bass quality than monopole speakers in most rooms. Especially smaller rooms.
Yes, I've known that for many years first hand. I practice what I preach :-).
RBNG - There is no room gain from a pressure source unless the room is unusually sell sealed (like a car with windows closed) which is very rare. You may ask Earl Geddes for details from his experiments.
.I was there when Earl caused a near riot over on the Mad board (when it was functional) with his own use of the term. Won't rehash that again.
cheers,
AJ
I contend that we are both atheists; I just believe in one fewer god than you. When you understand why you reject all other gods, you will understand why I reject yours
I wouldn't want you to get too excited by saying "You're right!"In a typical 20' x 15' x 8' listening room
Stereo bass speakers summary:
Most benefits from dipoles are likely to be above 50Hz.
But if there is a first-order width standing wave with a particular song (bass must be louder in one channel than in the other), then stereo dipoles are a better choice than stereo monopolesMono bass speaker summary:
If there is just one mono bass driver (let's say up to 80Hz.),
then dipole is the best choice
Supporting "armchair analysis" comparing three bass driver choices:
(1) using one mono monopole driver on left side of room, or on right side of room
(2) dual left-right monopole drivers,
(3) dual left-right dipole driversAxial room modes analysis
28.25Hz. first-order length
(1), (2) & (3) = all strongly excite this room mode37.7Hz. first-order width
(1) = strongly excited (a single dipole would be better)
(reduced excitation if woofer is placed halfway between the side walls in the partial null)
(2) & (3) no standing wave forms at all if bass output from both speakers is identical, because the speakers are located out of polarity for this standing wave. But if bass IS louder from one side, there will be at least a weak standing wave, and dipole speakers will excite the standing wave 4.8dB less than monopole56.5Hz. second-order length
(1), (2) or (3) = all strongly excite this room mode
71Hz. first-order height
(1)= strongly excited (a single dipole would be better)
(2)= strongly excited
(3)= 4.8dB less excitation from dipole woofer75.3Hz. second-order width
(1) strongly excited (a single dipole would be better)
(2) strongly excited
(3) 4.8dB less excitation
(but even less excitation can be achieved from either monopole or dipole if woofers can be located at 1/4 and 3/4 of the room's width, in the partial nulls for this room mode)
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Richard BassNut Greene
Subjective Audiophile 2007
> Someone who wants their baffle to contribute
> to the sound as much as the driver?For 'high efficiecy' one would probably want the
whole 'baffle' full of drivers> RBNG - Who wants to use a 2.0 Qts. driver?
What does "RBNG" mean?
> Someone who appreciates high levels of driver
> distortion "enhancing" their "bass"? What if:
> "Yeah, but it sounds good"?You think you would have much distortion with
(from the standpoint of a 4' x 4' baffle)
(only considering the low end)
say 16 8" drivers with a Q ~ 2
(at a moderate level) ???????
HW - For 'high efficiency' one would probably want the
whole 'baffle' full of driversWell, that would certainly be one way to do it. But your picture showed one driver on a very large baffle. That is what generated my comment.
What does "RBNG" mean?
My post was a response to R ichard B ass N ut G reen. Kinda like this response is to H its W are :-).
HW - You think you would have much distortion with
(from the standpoint of a 4' x 4' baffle)
(only considering the low end)
say 16 8" drivers with a Q ~ 2
(at a moderate level) ???????Carefully read what I said. "Someone who appreciates high levels of *driver* distortion."
I said a 2.0 Qts *driver* would have high distortion. Not 20 of them combined LOL. That would certainly help lower distortion! If you were going to take the multi driver approach, use several HE drivers in a vertical array on your sidewalls.cheers,
AJ
I contend that we are both atheists; I just believe in one fewer god than you. When you understand why you reject all other gods, you will understand why I reject yours
Richard---OBs are easier than boxes, often uses one for convenience and calls it's resulting vices virtues. However on a couple of occasions I've heard them sounding pretty decent, especially an EV Wolverine 12 I heard and a Madison 21. God knows what the things were doing but they sounded full and robust.Note that a fella who was once the foremost advocate of OBs around here used lots of EQ to get deep bass from a large OB array, which as you know means it was no longer high efficiency. He was also keen on using a low efficiency box subwoofer with OBs.
Recently I bought a couple of those old Yamaha "ear" speakers which used open backed boxes. They sounded OK. I'm gonna nail the drivers up on the wall in the garage as curiosities.
> Who wants to have a 16 square foot baffle x 2Yes. Pretty big. Options are foldback 'wings' or both
channels on 1 baffle.> Who wants to use a 2.0 Qts. driver?
Me. Any higher and ripple starts to manifest,
but for OB a Q of ~2 is optimum for bass/size> And would a 2.0 Qts driver on a 16 square foot
> open baffle really provide a flat frequency
> response down to 50Hz. without EQ?Yes. I've measured and listened.
Freddyi did a SPL graph of the same
system (big baffle in the pic)
that agrees.> But then you'd still need to add a monopole
> speaker to fill in the bass under 50Hz.
> -- and that would make no sense because the
> greatest advantage of dipole speakers in most
> rooms is less excitation of bass standing waves
> (causing a more realistic reproduction of bass instruments).
> Why use a monopole speaker to reproduce those low
> frequencies when a dipole speaker would have the
> greatest inherent sound quality (including room effects)
> advantage over monopole speakers?I can live with 50Hz myself. Even down to 100Hz OB with
a sealed 'helper woofer' is better than the box colorations
inherent with monopoles. (IMO).........:)
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