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Old 13th November 2012, 03:58 PM   #41
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Quote:
Originally Posted by bear View Post
Minor point:

Subs radiate omnidirectionally.

This does not mean that their source can not be determined by a listener. This is something that seems to have gotten confused by an awful lot of people.

_-_-bear
Bear,
Minor point additions to your minor point addition:
Subs radiate omnidirectionally only at very low frequencies, and progressively become more directional at higher frequencies.

The larger the piston diameter, or distance between radiating surfaces, the more directional the sub will be to a lower frequency.

Horn loaded subs are in general more directional than front loaded subs.

The more shallow the crossover slope, the more obvious the directional control the sub has. The "sub" output on many home theater units may have output extending past 500 Hz, octaves above the point where subs are "omnidirectional".

Art
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Old 13th November 2012, 04:00 PM   #42
tb46 is offline tb46  United States
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Just typed "sound pressure level meter" into ebay, first item: Digital Sound Noise Pressure Level Tester 30 130 Decibel DB Meter | eBay , $22.99, and free shipping.

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Last edited by tb46; 13th November 2012 at 04:03 PM.
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Old 13th November 2012, 05:29 PM   #43
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get an analog meter if possible... and actually skip the SPL meter, go directly to freeware FFT software and a cheap measurement mic, DIY per Linkwitz being the starting point. At LF the soundcard in any computer is more than good enough.

regarding the TH (tapped horn) response posted, the lower range looks too flat to be believed, but the upper peaks will require a really sharp filter to get rid of, since they are very sharp and rise >24dB.

A "standard" 4th order won't do it.
A "standard" 8th order will have to come in lower in frequency than desired in order to pull that down enough, which *if* that works in the system might be acceptable.

You'd need some DSP or some trickier filters to tame those peaks, imo.

_-_-bear
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Old 13th November 2012, 06:04 PM   #44
Moonfly is offline Moonfly  Spain
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Quote:
Originally Posted by weltersys View Post
Bear,
Minor point additions to your minor point addition:
Subs radiate omnidirectionally only at very low frequencies, and progressively become more directional at higher frequencies.

The larger the piston diameter, or distance between radiating surfaces, the more directional the sub will be to a lower frequency.

Horn loaded subs are in general more directional than front loaded subs.

The more shallow the crossover slope, the more obvious the directional control the sub has. The "sub" output on many home theater units may have output extending past 500 Hz, octaves above the point where subs are "omnidirectional".

Art
If we are going to be specific, then almost all sound radiates omni-directionally, certainly low/mid frequency sound does. When we speak of a sub being omni directional then we are talking about an inability to locate the source of bass. Our ears can locate the source of sounds down to roughly 100hz, below which they no longer can. I dont agree piston diameter has anything to do with subwoofer directionality. A sub becomes locatable by ear when it produces frequencies high enough to enter the range in which our ears can locate the source of the sound. Typically, this is down to distortion/harmonics etc, but can also be due to very high crossovers. If your going to crossover above 120hz, then its advisable you only do so if you run dual subs that are located very close to your front left and right speakers, as that helps maintain the illusion of being unable to locate the source of bass. Ive used 18 inch subs and had no problems with achieving the invisible sub bass effect.

Last edited by Moonfly; 13th November 2012 at 06:12 PM.
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Old 13th November 2012, 06:04 PM   #45
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Thanks so much guys for all the input.
SNIP....
Regarding one time project or not... Safe to say, I am being sucked to the dark side of DIY. I have always enjoyed screwing around with stuff, and have always had a passion for music. So I am probably in for the long haul. Feel sorry for you guys - you may be stuck with me for ever "evil laugh". In that same vein, is there some "basic DIY survival kit" that I should be looking at acquiring. That would be an awesome other post - or publication, recommendations for equipment for newbies.
SNIP....
Yes,
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Welcome to the dark side.

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Doh.. Had to buy a laptop for my RTA software

Last edited by Shadydave; 13th November 2012 at 06:07 PM. Reason: Keyrect Spellind
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Old 13th November 2012, 06:08 PM   #46
tb46 is offline tb46  United States
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Hi bear,

According to the people who have build the double fold version of the TH the peaks are nowhere near as pronounced as they are in Hornresp. Basically, a 4th order @ 80Hz would do it. If you read through that thread, you'll see, that part of the "smooth" response in the passband is the result of a series 5mH inductor.

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Old 14th November 2012, 12:34 AM   #47
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Quote:
Originally Posted by Moonfly View Post
If we are going to be specific, then almost all sound radiates omni-directionally, certainly low/mid frequency sound does. When we speak of a sub being omni directional then we are talking about an inability to locate the source of bass. Our ears can locate the source of sounds down to roughly 100hz, below which they no longer can. <snip>
I can't fully agree with this.

all sound does not radiate omni-directionally, it is true that as frequencies descend then the radiation becomes more and more omni-directional.

But if one takes the case of a basic dipole woofer, then it's not omni-directional at all... (for example)

and if you move the subs a certain number of ms of delay away from your main speakers you will certainly hear that as an audible discontinuity... similarly, set your sub or subs off to your left and right, have the delay time between them and the main speakers identical to your ears, I expect you will be able to easily detect the positions of the subs...

in my experience, if your system is such that there is continuity in terms of how an impulse is reproduced (things come out in phase and add properly) small differences in delay or position of the subs effects the way that individual instruments are heard - especially things that have LF components. When I say "way" I mean the sonic character and importantly the way that the spatial aspect works and how the sound stage resolves...

the gross frequency response likely varies not enough to register as being significant.

_-_-bear
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Old 14th November 2012, 02:25 AM   #48
MedPed is offline MedPed  United States
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1. Regarding the TH. The graph seems to taper off pretty rapidly below 25 hz, with about 5dB down at 20 Hz. Is this something that a little DSP (or possible in-room acoustics) should take care of - eg. with the inuke 6000DSP to make fairly linear down to about 18 Hz or will that be difficult, and likely too demanding power from the amp
2. Given the peaks etc as you go higher, will crossing over at around 60-70 Hz take care of that?
3. What exactly are the guys on the TH post referring to with inductors and their role in THs.
4. Does the TH design in question need lining in the cabinet? My initial impression is that the design depends on reflection of the sound through the horn, and absorbent lining may defeat the purpose.
5. If I want a fairly linear output to about 18-20 Hz, is this a good first step for me? When I say fairly linear, I mean it doesn't have to be perfect on a graph, as long as it is linear to most the ears.

As posted earlier by tvrgeek, there is no magic recipe for the perfect sub, waiting to be just shared, and built/sold by everyone, but... as someone who values all your opinions, and if you guys convince me to spend up to $1000 or so, I would like to hear your opinions, dollar for dollar, what design should buy me the most linear sub down to about 18 Hz. I realize this is opening can of worms, but keep in mind the suggestions are for someone who has never built a speaker before, and I really would want to hear varying opinions - comparisons.

I get the sense that the sealed sub is not very popular here. Is it because it take too much power to keep it linear as you go lower, and or that it is far more demanding to eq requiring more DSP/processing etc., or both?
Is it much to harder design and construct a ported sub tuned down to about 18-20 Hz (up to about 60-80 Hz), and am I looking at a much larger sub then a comparative sealed unit?
Size is an issue for me. I can stick a vertical TH in the corner, but a box, would have to fit under my main bookshelves without looking to massive - and that is where the ported designs scare me a little.

Funny, I started this post, with an assumption that sealed subs are more linear and musical but now I am entertaining all these other interesting designs. My biggest impression came from a direct comparison of the sealed and ported HSU research subs - I heard the sealed 15" and the VTF 15", and although the HSU VTF ported sub, was notably louder, it couldn't hold a candle to the sealed 15" HSU in terms of musicality and to my ears, linearity. The sealed just went lower, and was far better with transients, without over hang or any appreciable bloat. The ported VTF was no doubt louder at certain freq, but it seemed almost unnatural the way it suddenly dropped off. Almost like something was missing, even though it gets a good 20 Hz output. I am not a speaker designer and can't explain it, as the sub goes plenty low (lower than my current sub which only goes to about 30Hz), but something about the gradual taper vs the steep taper gives the ears the illusion of a more natural and musical presentation. Can't explain it any other way other than an illusion - perhaps some one on this forum can explain it more technically. Or perhaps it was the quickness of the subs that gave that illusion not the gradual taper, and the sealed was more immediate and in control? Dunno, any thoughts?

Now that I have mentioned the HSU subs, how would some of these proposed designs compare to those. My personal impression is that they ran out of steam a little early, as they are a tad underpowered esp when comparing to SVS and other mail order subs, but they were nonetheless a pleasurable listening experience.

Regarding amps - any other suggestions to consider other than the behringer inuke? Or is that sort of the go to amp here. the 6000 DSP can be had for about US$450 on amazon, plus taxes. Good buy? That would leave me about 400-500 for a quality driver (or two) and cabinetry - but I'm guessing it would sound better than any $1000-1500 sub I can buy!
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Old 14th November 2012, 02:35 AM   #49
MedPed is offline MedPed  United States
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My two bits about omni direction...
I always got the impression that subs were difficult to localize due to humans inability to localize sounds below a certain frequency (120Hz). But any harmonics/distortion may make this vary a good bit as that is beyond the control of a crossover or DSP or whatever, as it is produced mechanically by the driver/surround/cabinet etc. Thinking back to high school physics, lower frequency waves have a higher propensity to diffraction, and therefore reflect of nearby surfaces etc. as compared to waves that just push straight forward.
So wasn't sure if the argument is about perception, or true direction of the waves, but they are both sort of correct. Ears have harder time perceiving direction, and, lower frequency waves diffract like a SOB, and are harder to maintain direction.
2cents from the newbie. Feel free to rip up my warped theories!
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Old 14th November 2012, 04:43 AM   #50
MedPed is offline MedPed  United States
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Question about Behringer amps.
On a quick comparison of the spec sheets of inuke and the europower, it seems that the europower might be the better amp - at least on paper. The freq response is better (-0.1db at 20 Hz vs 2db), and the power consumption ratings seem to be more realistic (couple of kW vs 600W).
Does anyone have any experience with those amps?
The power consumption may be misrepresented in the inuke sheet as some of the models were listed at 1/8 power, and I don't know if that was an omission, and the 600W consumption is at 1/8 power.
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