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Old 7th June 2004, 11:26 AM   #21
navin is offline navin  India
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using box size as a THE deciding factor...a dipole (OB or H frame or otherwsie) seems to the most inefficient method to produce bass. albeit without boom. isobariks are slightly more efficient.

sealed boxes (with Qts < 0.7 and aperiodic) are a bit more efficient than isobariks. horns while being efficient in absolute terms are not so when you factor in box size (db/w per cu. ft of box)

that leaves TL and bass reflex. My guess is that bass reflex produce the most quantity of bass out of a given box size.

now if you are factoring in bass quality just about all these systems if properly designed for their particular enviroments can produce good if not startling results. This I feel is the STRATEGIC advantage of being DIY. We as DIYers can choose what suits our listening tastes, home decor and other requirements.

for example.....
if you have a 12" woofer that can produce 100db in a 3 cu. ft. sealed box, youd need 4 similar woofers to produce the same SPL in dipole.

The same woofer could (given it's T/S parameters are suitable) also produce 100db in a horn with very little wattage but the horn box would be considerably larger than 3 cu. ft. or the F3 would be considerably higher if the horn were to fit in 3 cu.ft.

the same woofer in a well damped BR would produce about 6db more in a box that is maybe 10% larger (this depend a lot on T/S parameters).

horns tend to have "slam", dipoles tend to sound "smooth and natural", bass relfex boxes tend to sound boomy, sealed boxes are somewhere in between.

I think we are all searching for that holy grail. a speaker that has slam and depth, does not boom, sounds natural, fits in with WAF's demands, and to to it costs next to nothing. If we weren't we would not be here.
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Old 7th June 2004, 11:52 AM   #22
Ken L is offline Ken L  United States
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Quote:
Originally posted by paulspencer


Another question:
Horns are often criticised as having coloration. Does this occur in bass horns as well?

This does not occur with modern well executed designs -

This is a fallacy that is a holdover from decades ago.

Horns have moved far beyond this.


Horn loading of the front and rear is something that has been talked about a good bit but is not something I remember anyone.
having done successfully

I am running Lowther DX4's open backed on Azurahorns. There is a small dipole effect from the rear - but since the rear is not horn loaded it is down in output - I have never attempted to measure how much or determine by serious listening the benefit derived from this - Sounds good though _grin_

Regards

Ken L
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Old 7th June 2004, 12:53 PM   #23
Previously: Kuei Yang Wang
 
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Default Re: Horn vs Open baffle bass

Konnichiwa,

Quote:
Originally posted by paulspencer
1. Bass horns have a cardiod polar response pattern (I think)
Only in the region where the horn actually controls dispersion, which is directly determined by the size of the hornmouth. Below this most "domestic" horns operate as resonant systems (TL, Reflex) to produce extended bass, while incorporating room placement gain to boost the LF into place. The result is highly inaccurate LF rendition, with a lot of room mode excitation.

You are in big LF trouble unless you can make a Bass Horn with a mouth surface commesurate to the required wavelenth (eg like here....

Click the image to open in full size.

Quote:
Originally posted by paulspencer
which means that they interact much less with room modes.
Horns are usually corner loaded. As they are not any longer strongly directional below the flare cutoff they will from their position maximally excite all room modes.

Quote:
Originally posted by paulspencer
In addition they have very low distortion, a very good transient response and very high output and efficiency.
All the above holds true for an IDEAL horn with a sufficiently large mouth area. This automatically means architecturally, build in structures with several squaremeters mouth opening. Once you move towards shrunken and foreshortened horns only high output remains, the rest is traded off for (comparably) small size.

Quote:
Originally posted by paulspencer
2. Dipoles have a figure of 8 polar response pattern, with the same advantage regarding room modes.
I would say that dipoles are drastically different from horns in that they operate as velocity transducers, as opposed to pressure transducers (Horns, Sealed Boxes, Reflex or Organpipe reflex [aka TL]). This has implications for room mode excitation that goes far beyond the normally discuused issues.

A dipole will excite room modes maximally in the absolute centre of the room and minimally in a corner. All other speakers maximally excite room modes in the corner and minmally in the room centre.

Quote:
Originally posted by paulspencer
I'm not sure which is better.
This of course depends upon your defintion of "better".

Quote:
Originally posted by paulspencer
* Which deals with room modes most effectively?
Dipole.

Quote:
Originally posted by paulspencer

* Which system is more accurate?
* Which has a better transient response?
A Full Size Horn with a large rear chamber (eg architectural horn) is about level with a dipole, except on distortion for a given SPL with a given driver. Shrunken Horns are much worse than dipoles.

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Old 7th June 2004, 04:24 PM   #24
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Default Re: Re: Horn vs Open baffle bass

Quote:
Originally posted by Kuei Yang Wang

I would say that dipoles are drastically different from horns in that they operate as velocity transducers, as opposed to pressure transducers....
Is this why very cheap drivers can work to such good effect ?


Quote:
Originally posted by Kuei Yang Wang

A dipole will excite room modes maximally in the absolute centre of the room and minimally in a corner. All other speakers maximally excite room modes in the corner and minmally in the room centre.
I guess that once I build high output dipole subs and room treatment becomes more necessary, I will need panel absorbers or slot resonators, and tube traps in the corners would be ineffective.

By the way, thank you very much for stepping in and providing some very interesting information.
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Old 7th June 2004, 04:33 PM   #25
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Default Re: Re: Re: Horn vs Open baffle bass

Konnichiwa,

Quote:
Originally posted by johninCR
Is this why very cheap drivers can work to such good effect ?
I don't THINK so, BWTFDIK.

Quote:
Originally posted by johninCR
I guess that once I build high output dipole subs and room treatment becomes more necessary, I will need panel absorbers or slot resonators, and tube traps in the corners would be ineffective.
No, tubetraps in corners will be as effective with dipoles as they are with normal speakers (eg completely ineffective for standing waves). The point is that near a wall the pressure of the air for sound is high while the velocity of the air is low. In the middle of the room the air velocity is high while preassure is low. Hence the two different ways dipoles and other speakers couple to room modes.

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Old 7th June 2004, 04:55 PM   #26
MBK is offline MBK  Singapore
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Just a short note - if you are concerned with remaining room effects of dipoles, one or 2 easy notch filters (active) will work wonders for the dominant room modes. It's not just that the drone goes away, it's thatthe midrange clears up significantly.

Build your speakers, place them where yu will play them, and then just do a simple FR test, even with continuous tones or 1/3 octave filtered pink noise (test CD). Then you see where your broad peaks are, and their magnitude. For me it was a broad (low q) peak around 90 hz), and one single -6 dB motch filter made a day and night difference.

I also remember KYW's glowing words about the Behringer room EQ (KYW - do you still use it?). That's more accurate of course. But more pricey.
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Old 7th June 2004, 05:28 PM   #27
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KYW,

I don't understand the velocity vs pressure thing.

Please correct me if I'm wrong, but this is my understanding of the difference between dipole and others when it come to room interaction. Dipoles radiate sound primarily in 2 directions front and rear because the sideways and vertical energies cancel each other out since they are out of phase. This results in reflections primarily on the front and back walls. Other speakers radiate sound in all directions and making the early reflections more complex and numerous so where reflecting surfaces meet (a corner) the pressure builds much more than with a dipole.
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Old 7th June 2004, 06:49 PM   #28
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Konnichiwa,

Quote:
Originally posted by johninCR
I don't understand the velocity vs pressure thing.
Think about a wave standing between two surfaces. It matters not if the wave is in liquid, gas or solid. The medium the wave is transmitted through reacts with compression and rarefaction. Now near a surface the rarefaction or compression cannot "move" the medium being compressed or rarified, so hence we experience pressure effects. Equally, to make the medium compress or rarify we need to excert pressure, as no amount of velocity change input will amount to much, as the velocity of movement is near zero.

Now velocity is the opposite. If we now go to the exact "middle" between the two surfaces we will always find a pressure of equilibrium, never a deviation from even pressure. Yet at any given instant we have a lot of displacement of the medium back and forth at this point. So the VELOCITY of the medium is at the maximum, yet the pressure is at a minimum. So no matter how much pressure you excert, you will have little output, but a little velocity will go a long way.

Does that make it at all clearer?

Quote:
Originally posted by johninCR
Please correct me if I'm wrong, but this is my understanding of the difference between dipole and others when it come to room interaction. Dipoles radiate sound primarily in 2 directions front and rear because the sideways and vertical energies cancel each other out since they are out of phase. This results in reflections primarily on the front and back walls.
Room interactions in the DIFFUSE sound zone, yes. The radiation is still of course directional at low frequencies, but directionality alone doies not reduce standing waves (see LF Horns).

Quote:
Originally posted by johninCR
Other speakers radiate sound in all directions and making the early reflections more complex and numerous so where reflecting surfaces meet (a corner) the pressure builds much more than with a dipole.
All of this is related to the "diffuse" mode, not to modal behaviour. The two are distinctly different.

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Old 7th June 2004, 07:18 PM   #29
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Quote:
Originally posted by paulspencer


Magnetar,

Could you elaborate a little more?

Dipoles aren't pressure loaded by a sealed box and this eliminates box coloration and I suspect that this makes them a little more "accurate."

I can't see how dipoles would actually be any better with room modes than horns. If I'm mistaken, then could someone expand on why?

What if an attempt was made to get the best of both. A dipole where both the front and rear wave was horn loaded. Or, perhaps more practical, an Infinite baffle where the front wave is horn loaded.
The dipole is just paddling the air and has a very poor interface with the room air. It relies on using drivers that are overly resonant to overcome this. In all cases these drivers have to have long excursions to pressurize the room (and your ears) to reproduce bass. Our ears are insensive in the lower range and it makes much more sense to use a horn that excels in pressurizing the air. The horn is an impedence transformer -- it will barely be working when the dipole is near it's limit. IOW it will move air with A LOT less work, hence it is a high efficiency device.

Anytime you you put a loudspeaker in a home listening room you will excite room modes -- A properly designed horn is designed from the start to interface with the room -- in fact, it needs the room reinforcement to really do it's job properly. If there is no room to place the horn in then the horn has to be the size of a room to reproduce the deep bass.

I have built dual driver dipole isobaric loaded horns that are front loaded and worked quite well in my room. The main advantage however was the distortion cancellation of the isobaric design not the figure 8 room interface.

IME either method (horn or dipole) can be quite satisfying but when you really get down to it the horn is king at realistic life like reproduction, power, speed and FUN.
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Old 8th June 2004, 07:04 AM   #30
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Thought Iíd post the to & fros from an off-line discussion on the same subject, to re-stir debate:

> horns ain't all about being loud. They sound fantastic at low volumes. When I talk about effortlessness you may equate that to loudness but what it means is a complete lack of strain - strain you wouldn't notice until you don't hear it.
I must hear this.

> The further a loudspeaker cone moves the more distortion it produces.
I've heard that postulated before, but if it has been measured, I havenít seen it. Is there a link??
I can imagine it true nearer the extremes of excursion, but in a good driver find it difficult to accept at say up to 75% of Xmax.

Even if so, the horn will suffer more from room effects. Which is better in sum, lower excursion distortion or less room effects??

Yes the two drivers together must both work harder in a dipole, but unless the above (cone distortion proportional to excursion) is verifiable, is their a problem with higher excursions than other systems?

> Compare it to a properly done horn system (which will be ridiculously large) and there is no comparison.
Two things, most may accept large, eg the Labhorn, but not ridiculously large.
And compare on what criteria, excursion/ efficiency, or clean sound?

I actually seriously considered going horns, was deterred by size, but still think the dipole is a better all round approach for most normal domestic situations.
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