| Autotuba measurements, plus shiva - Click HERE for Original Thread |
| tiroth |
I've built two versions now of Bill Fitzmaurice's Autotuba design. This is a horn sub with a 7' path, using the MCM 55-2421 8" driver.
The first is the textbook one, with 14.5" outer dimensions. The second is slightly larger, with 16" outer dimensions. Although it doesn't sound like much, the difference in mouth area is significant.
I've attached nearfield measurements taken with Speaker workshop, smoothed 1/10 octave. Behringer ECM-8000 mike, with Claudio's calibration file. These measurements have been adjusted so that the SPL of the tuba and shiva match at 40Hz--this is not showing the absolute sensitivity.
The black and red lines are the 16" tuba--the only difference is the black has 2" legs, the red 5.5" legs.
The brown line is the 14" tuba. For comparison, the yellow line is an Adire Shiva in a sealed 75L box. |
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| tiroth |
I'm interested in any critique of my measurement setup. I was unable to measure any loading differences, whether I located the sub hard in the corner, farther out, or in the middle of the room. Does the nearfield measurement remove the contribution such loading would normally impart?
The Shiva F3 appears to be textbook at ~38Hz, so I am inclined to think that these measurements are spot on.
It looks like the 16" version picks up a few dB over the 14" below 32Hz, and the Shiva definitely is a big winner below 30Hz.
This is only part of the story of course. I will try to post measurements tomorrow indicating relative efficiency, and max SPL at 40, 30, and 20Hz. I'll also include some subjective comments after I've had more time to listen...I don't want to overstate my initial impressions. |
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| tiroth |
| Anyone out there have a summed response nearfield measurement of an EBS (142L) vented Shiva? I'm interested in trying this out, but I'd love to see a graph before building the box. |
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| simon5 |
| I'll try to get a graph from the girl I built the subwoofer for. |
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| tiroth |
| Thanks a lot Simon! |
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| morbo |
| Frankly, from all the talk about the Autotuba being optimized for typical room gain, I expected to see a gradual shallow rolloff rather than a sharp dropoff with a hump at 40 hz. |
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| tiroth |
Sub measurements always seem to be hopelessly optimistic. Grey has been hammering on this for years...the TS equations work, but there is generally a 1st order highpass starting fairly high up that causes problems.
A suggestion was made to measure farfield near the ground plane. This measurement shows the nearfield, on-axis gated farfield, and ungated farfield measurements for Shiva. If room loading is being measured at all with this technique, it isn't helping much. |
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| tiroth |
This graph shows the tuba at various distances from the wall, with 2" and 5.5" legs. There are some variations, but they are subtle for the most part.
I also include the reference Shiva. There were no significant response differences, no matter how far from the wall I moved it. So, it does show that the tuba has some sensitivity to loading.
None of these curves are scaled; that is, each curve is printed as measured, with equal voltage gain. Because the Shiva has much lower impedance, it is drawing anywhere from 2-4 times as much power for the same voltage. (3-6dB) |
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| tiroth |
I also did some SPL tests for 20-40Hz band limited (4th order) pink noise. I turned the output on my sound card up as high as possible, and ended up maxing the controls on the amp as well for this test. (250W MCM plate amp)
Measurements were done with a Radio Shack analog meter, set to C weighting and fast response. I applied a correction factor of +4.5dB.
Shiva was peaking at 109.5dB/1m. Excursion was high, and I was hearing some small louder pops at intervals. I do not think this was bottoming, just loud transients. The lights were dimming noticebly from the current draw.
Autotuba was peaking at 114.5dB/1m. There were some scary loud pops, which were either bottoming or the effect of 115dB LF audio. No dimming of the lights. Autotuba may be cheating due to extra ~80Hz range response.
I still plan to do more power testing, but not tonight. :) |
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| johninCR |
| Not bad for an 8" driver in a horn designed for use in a car. I would like to see a smoother response though. I guess there's no getting around the laws of physics. |
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| mike.e |
If the AT rolls off at 2nd order below 80hz id be glad,since in the car this will yield an approximately flat response - otherwise youd be complaining about how bloated and slow it sounds :D
I expected more change with distance from corner- but remember that you have to consider how acoustically close things are - considering 40hz waves that are 8m long youd have to near 2m from the corner to affect things down here
where as 80hz waves much easier to affect things with a 1m distance from the boundary. |
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| simon5 |
Shiva EBS measurements :
This is not a max SPL chart and this is in the center of a small room, not in the corner.
I don't know if she used the RatShack SPL correction chart on these numbers, I'll ask her.
16 107,5
18 107
20 107,5
22 108,5
25 109
28 111
31,5 113
36 114,5
40 114,5
45 114
50 114,5
56 113,5
63 111,5
71 112,5
80 113,5
89 111,5
100 110
125 109 |
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| simon5 |
| I know it's not a really fair comparison, but it would be fun if you can include my measurements in your graph. Drop the curve to match the sealed Shiva with a reference point at 70 Hz or so maybe? |
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| simon5 |
| I asked her, and the values are already corrected. |
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| kornmong |
simon5
Could you show you box on this post and tell me the specs of that box, eg how many litres, box dimension, port tuning watt driving the woofer and what shivs model.
because those numbers are unbeleivable:bigeyes: 16HZ at 107db that better then any subwoofer on the planet and its not even corner loaded
your box must be HUGE or somthing
juding from your success if i bought a tempest 15" could i beat those numbers (DB) |
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| GM |
Greets!
It appears you've led a rather sheltered life WRT infrasonic BW output capability from a single driver. ;) 107 dB/16 Hz is rather ho-hum by today's high Xmax/power handling, low Fs driver standards.
GM |
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| johninCR |
| Especially in room and a small room at that. |
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| kornmong |
| It must be me because i have a bigger xmax than a shiva and I dont get 16hz at 100Db! :bawling: even corner loaded |
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| GM |
| I'm not touching this one with a ten foot pole.......... ;) |
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| rcw |
Some years ago an Australian hi-fi magazine did some tests on typical Australian houses for room gain. They concluded that for all the typical room gain you get you may as well set your sound system up in the middle of a field.
Typical Australian houses are brick veneer, plasterboard wall and ceiling, picture windowed creations, that are open plan and leaky. The fact is you are flat out setting up a decent standing wave in them let alone pressurising them.
In short if you live in a typical Australian house your subwoofer has to be flat down to its lower cut off. and if that is 20Hz.it needs to play at least at 103dbm. otherwise you can't hear it. |
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| simon5 |
Wow, some people not believing me here. You can be skeptical if you want to, but this is actual SPL measurements. The room is small so keep that in mind. I can give you room size if you need it, I can ask the owner.
The design is a EBS ported subwoofer following exactly Adire Audio design. It's 142.5 liters or 5.032 cu.ft internal net. It's tuned to 18.34 Hz with a 18 inches long (17 inches effective) 4 inches diameter pipe, flared on both ends.
It was done with a Shiva Mark IV.
It's powered by a Rythmik Audio A250 250W amplifier into 4 ohms.
This amplifier have a rumble filter set at 12 Hz, second order, Q=0.707.
If you look in WinISD, you'll see that the subwoofer achieve 103 dB anechoic at 16 Hz, so I hope you'll agree with me that 4 dB of room gain at 16 Hz is not exagerated at all.
This subwoofer was designed to beat easily the SVS PB10-ISD sold at 470$ USD shipping included. We wanted to beat it with something which would cost less money to build. I can say mission accomplished.
Pictures are following shortly.
Here's all the parameters :
[Driver]
Brand=Adire Audio
Model=Shiva MKIV
Manufacturer=Adire Audio
ProvidedBy=Simon Arsenault
Comment=
DateAdded=20041124
DateModified=20041124
Qts=0,35041267334714
Znom=4
Fs=20,7642474688133
Pe=650
SPL=87,7486071535912
Re=2,9
Le=0,00212
fLe=0
KLe=0
BL=11,3
Xmax=0,0166
Cms=0,00047
Qms=6,5
Qes=0,370379710990481
Rms=2,50895412712862
Mms=0,125
Sd=0,0481
Vas=0,154252658878499
Dia=0
Vd=0,00079846
no=0,00362589642446061
Dd=0,247472871446066
EBP=56,0620542990458
numVC=2
Hc=0
Hg=0
SPLmax=112,87774072002
SPLmaxLF=98,6094748881186
USPL=92,1603558850874
alfaVC=0
Rt=0
Ct=0
gamma=90,4
Rme=44,0310344827586
Mpow=6,63558848051615
Mcost=0
Gloss=0,0347072703313253
VCCon=1
c=343,684120962152
roo=1,20095217714682
Thick=0,01905
Depth=0,130175
MagDepth=0,0381
Magnet=0,136525
Basket=0,2794
Outer=0,3112
Vcd=0,0508
DVol=0,00239926669428466
ParState=CCECEENNEENEECCCEECCNCCENNCCCNNNCCCCNCEEEEEEECNCC |
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| simon5 |
Some pics...
Here's a 4' x 8' sheet of 3/4" plywood, as you can see, you must do some planning to prevent using a second sheet. The design fits very tightly on a sheet. Left is used wood, right is wasted wood.
Here's the box from several angles when finished (or almost) and ready to be painted.
Here's the box with a 2nd layer of stain. (It took 4 layers to achieve the darkness the owner wanted)
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| simon5 |
Some more pictures... (smaller ones heh!)
Here's the finished product, compared with the mighty Klipsch Promedia 5.1 Ultra subwoofer, which looks like a bug compared to this DIY subwoofer.
And finally here's the simulated Anechoic SPL curve without room gain. This curve shows a small rolloff to account for room gain which is around 3-4 dB per octave the lower you go according to Adire Audio. This means ideally the subwoofer would exhibit around 112 dB from 18 Hz to 100 Hz or 118 dB in the same range corner loaded.
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| rcw |
| Those are certainly impressive numbers Simon, I just wonder how much of the signal coming out is that which goes in. In its literature on the shival Adire is noticeably coiy about the matter of distortion, a driver with no flux modulation control or d.c. offset compensation making those kind of excursions with that type of input power must have consideralble distortion, and that 20Hz. output may be mostly 60Hz. |
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| simon5 |
I don't have the appropriate material to measure it, but by the ear it can reproduce these frequencies way louder than harmonics. Everything rattles. Your ears are pressurizing, you feel the room pressurizing and your vision is slightly blurred.
It's the best subwoofer I've ever heard and the owner say the same thing. Deep, accurate, loud bass. I'm curious as how this subwoofer would rate against commercial offers. If someone with alot audio knowledge live near or in NY, maybe you could audition it for me and tell me hehe!
Next time, I'll step up to a more serious driver with better SQ, like the AV series from Acoustic Elegance. It'll need a smaller box, too. |
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| kornmong |
That is one impressive sub you built, those pis are huge:bigeyes:
you should be proud of it I would :D |
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| simon5 |
| Yeah, the only problem is I can't afford it, so I built it for someone else who can afford it hehe! :D |
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| johninCR |
RCW,
Are you saying you can hear distortion at 16hz, other than the extra room rattles that distortion in the low frequencies that significant distortion creates? A more valid point is the EBS ported subs are, IMHO, terrible for music, but great for HT due to the extension. Then for music just stuff the port. |
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| simon5 |
| Why IYHO EBS ported subwoofers are terrible for music? |
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| johninCR |
| quote: | Originally posted by simon5
Why IYHO EBS ported subwoofers are terrible for music? |
For lack of a more technical description, they are too loose and sloppy sounding. I have an EBS maelstrom 18. I have it front firing, so I can easily stuff a chunk of foam rubber in the ports for music giving me a great best of both worlds subwoofer. |
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| BassAwdyO |
John, how low is your EBS maelstrom tuned???
In my experience if you tune below 15hz there is no audible difference between sealed and ported enclosures of the same size.
An octave above tuning a port will be at ~-10db and hardly contributing anything. The sensitivity and group delay should be almost the exact same from there on up.
what is a sealed box other than a ported one with 0hz tuning(in other words a port with infinite airmass) |
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| rcw |
It is my opinion that most of what is talked about subwoofers is nonsense.
There is absolutely no physical basis for saying that bass reflex enclosures are "slow" and sealed ones fast, other than the fact that since most reflex systems have a greater setteling time people concluding therefore it must be audible therefore bad, there is no double blind study that I am aware of that has ever shown this.
The fact is that as shown by Floyd Toole, you can transform a slow one into a fast one by removing the room resonance causing the slowness.
It is also true that most so called fast sealed box subwoofers have considerable amounts of third harmonic distortion and d.c. offset caused second harmonic, not to mention flux modulation effects, and the subjective fastness is just that they are not in fact radiating enough power at the relavent frequencies to activate the slow sounding room resonances, and the so called lack of flabiness is in fact nought but good old 60Hz. punch region bass masquerading as low bass. |
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| johninCR |
| quote: | Originally posted by BassAwdyO
John, how low is your EBS maelstrom tuned???
In my experience if you tune below 15hz there is no audible difference between sealed and ported enclosures of the same size.
An octave above tuning a port will be at ~-10db and hardly contributing anything. The sensitivity and group delay should be almost the exact same from there on up.
what is a sealed box other than a ported one with 0hz tuning(in other words a port with infinite airmass) |
It's the Adire recommended enclosure for the original maelstrom for which, if I recall correctly, is tuned to 16hz. It's not on their site anymore.
| quote: | Originally posted by rcw
It is my opinion that most of what is talked about subwoofers is nonsense.
There is absolutely no physical basis for saying that bass reflex enclosures are "slow" and sealed ones fast, other than the fact that since most reflex systems have a greater setteling time people concluding therefore it must be audible therefore bad, there is no double blind study that I am aware of that has ever shown this.
The fact is that as shown by Floyd Toole, you can transform a slow one into a fast one by removing the room resonance causing the slowness.
It is also true that most so called fast sealed box subwoofers have considerable amounts of third harmonic distortion and d.c. offset caused second harmonic, not to mention flux modulation effects, and the subjective fastness is just that they are not in fact radiating enough power at the relavent frequencies to activate the slow sounding room resonances, and the so called lack of flabiness is in fact nought but good old 60Hz. punch region bass masquerading as low bass. |
I'm not getting into a fast/slow debate. I do know for a fact that there is a significant audible difference with the ports stuffed. Same room, same placement, and room modes have nothing to do with it. Sure room modes can affect bass quality, however, anyone who thinks that perceived quality in the region below 100hz, has nothing to do with the alignment has:
A. A screw loose
B. Has never heard good quality bass OR
C. Has poor low frequency hearing (probably from listening to too
much high SPL, highly distorted bass). |
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| rcw |
I assure you Jonin that all of my screws are about as tight as the next mans.
My system uses a 15inch driver in a QB5 class II filter assisted box.
I have measured this and it goes down to 25Hz. at 106dbm. with a cone excursion of 5mm. and I cannot measure more than 5-8% THD, and the roll off Q is almost exactly 0.7, and the setteling time is around 4.2milliseconds.
If you stuff up the port the power handling factor reduces from around 6.4, down to .8, in practicle terms it means that the acoustic output for the same cone excursion is reduced by a factor of 8.
If you increase the power input to compensate for this, not only those distortions due to cone excursion are increased, but also those due to power input, and in practice most of the extra output you get is distortion.
Most professional subwoofers use filter assisted alignments of the QB5 class I or II sort, and they do this for good reason, that is that the quality/extension/size equation reaches an optimum with these enclosure types, they are also very careful to eliminate room resonance effects, this is important for this type of subwoofer since for the same cone excursion they are capable of putting out around 8 times the acoustic power in the range below 100Hz. |
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| johninCR |
RCW,
I don't doubt that you have a fine subwoofer for a BR sub. Power handling and acoustical output are perfectly valid reasons that ported systems are used in PA. I'll even concede that THD measurements of speakers may be a good indicator to distinguish between cheap junk equipment and the good stuff. These things are not necessarily evidence of sound quality.
Now you can quote measurements until you're blue in the face and I can explain my real world results likewise, but you will never be convinced until you take an appropriate driver and a sealed enclosure that is large enough to give you the extension you want for music. Then port it to provide the extension and LF output necessary for HT. Put whatever filters you deem necessary and play music both with the ports plugged and open. If you can't hear the difference, then you really should get your hearing checked.
Let's put it in a different perpective for the types who only care about meaurements and how things look on paper. Clear your mind of all the technical stuff. Now just think about how you can possibly take the rear, out of phase, radiation of a driver going into a box, and port it out of the box and still think the acoustical energy coming out of that port does not harm the quality of the acoustical energy radiating from the front of the driver. Guess what, you can't. If you could get a high quality signal coming out of the port, then almost all subwoofers would be bandpass enclosures because it's the easiest way to get significant output over a narrow bandwidth.
If your primary emphasis is output then by all mean build a BR sub, but if SQ is important to you, don't, because what comes out of that port mucks up your sound. |
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| rcw |
Unfortunately Johnin it is impossible to forget technical stuff when one is discussing the reproduction of sound, since it is by nature a technical exercise and as such is goverened by the laws of physics.
The unfortunate thing about these laws is that if you don't like them, and choose to ignore them and substitute your own laws, they just carry on being true anyway, and your laws don't work, we have to accomodate to them, and there is not a thing we can do about it.
The fact is that a Helmholz resonator is inherantly a far more perfect device than a loudspeaker driver, and you provide such a driver with almost a perfect environment for realising its best performance by providing it with a very high acoustic impedance to deliver its energy to, this lowers its excursion and lessens the amount of power we need to put in, both of which greatly reduce the distortion it produces.
We can measure this by comparing the input to the output. The simple fact is that the signal that comes out of a reflex is a much better copy of that one which goes in than you find in a typical sealed box, which in turn means it must sound more like the musician intended it to sound, and as far as I am concerned that is what we are trying to achieve. |
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| johninCR |
RCW,
You may be correct that a helmholtz resonator is a perfect device. If so, then a typical driver is a substandard mechanism to stimulate it. I'm not saying the laws of physics should be ignored. What I am saying is that if you really understood the physics involved to the extent that you think you do you would understand why a BR enclosure produces a less than optimum sound. I'm sorry that I don't understand it enough to explain it to you, but I'll leave you with this thought. With a BR you are combining apples and oranges to increase the total output and pure apple juice tastes better than the blend.
Also, I as stated before (and it is widely accepted), bandpass enclosures produce a substandard quality of sound. If they were perfect as you say, then they would of course dominate.
I've really grown tired of arguing with know-it-alls like yourself. If you'd get out from in front of your computer other than to stick your head in a book and open up your ears and listen more then you'll learn a few things that will make you more useful in the real world. You should take the time to look at Cheever's work as well. There are valid reasons the THD is one of the most meaningless measurements that guys like yourself have ever come up with. |
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| BassAwdyO |
I still find it strange that with 16hz tuning you find a major difference between the sealed and ported maelstrom...
I'm not going to argue which sounds better or worse, but I think I'd have a hard time hearing that difference....
What are you crossing at John? Any chance of pipe resonances in the port..... I know a 16hz port is typically rather long
With my setup (for the mids-bass Extremis 6.8 midwoofers in highly stuffed TL's and an adire Tumult in a 6cubic foot enclosure that can be sealed, 10hz tuned 16hz tuned 20hz tuned or 30hz tuned) I dont really hear any audible differences until I get up to the 20hz tuning. The extremises are uncrossed on the low end and have good extension down to at least 50hz. I intregate them by turning the sub down all the way then slowly turning it up until I first notice any difference, then I back off just a hair and leave it there.
The ports have a few bends in them(which I believe damps the pipe resonances somewhat, I may be wrong)
the 20hz port has 2 bends
the 16hz port has 2 bends
the 10hz port has 5 bends |
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| BassAwdyO |
ohh BTW
For RCW
John is talking about an EBS. Hardly comparable to a Quasi-butterworth alignmemnt. The amount of excursion decrease in an EBS is much smaller compared to the quasi butterworth due to the larger enclosure size and lower tuning.
I think to be fair it would also be wise to neglect electronic corrections here |
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| rcw |
Your point is taken Bass, but I too get tired of people who claim some intrinsic mystical superior property for a particular method of loading, that other types don't poses.
The lastest double blind testing data in the AES journal indicates that for a cut off below 50Hz. people can't hear the difference between a fourth and second order system, although of course audio nuts, (including me), all think that they are the exception and they can. The same research incidently shows that 3% thd is audible, and this is the research that the THX standards are based upon.
It is also true that since most horn loaded designs used are too small
the much vaunted superor low bass sound is in fact caused by the horn acting as a much despised bandpass box.
This is why this type of testing is so important in audio, to sort out what people can actually hear from that which they think they should. |
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| mwmkravchenko |
Hello John. I have posted with you and respect your opinion.
Hello RCW. I have read your posts and they have had a decent grounding in theory.
From what I have read there are valid points in both of the posts up untill you both get tired. Please! Your both intelligent men with lots to offer. Don't give in like this.
If you look at things from an objective point of view you come up with this.
1. A sealed enclosure when sized correctly has a better transient response to a signal input than does a bass reflex. It comes to a point of rest more quickly than does a reflex enclosure due to the air in the enclosure not wanting to stay compressed or rarefied for longer than it is forced to. Overall a theoretically better enclosure. They sound sharper and more lifelike if you have been exposed to the instruments you are listening to live and recorded.
2. A reflex enclosure has some things going for it.
For a given size the low end cutoff and the over all efficiency will be lower and higher respectivly. For many applications these are the only determining factors. Louder and lower.
For the part that is of most interest. Actually the part that offers both the most colouration and the most distorsion. Wether you try to think of it with formulas or just in a common sense manner there is a conflict in the output of the systems in a reflex enclosure.
In the region that the port and driver give up and take over there is a real and definite phase ( read time delay actually ) shift. The sound being reproduced actually goes from being produced from a piston firing at you ( the driver ) to a helmholtz resonator ( the port ) firing from inside an enclosure. As the two cross over from each other there is a slight null and then a shift in the time between the signal input and the sound output.
A helmholtz resonator is not magical. It is a derivative of the grand old pipe organ. A system well understood for centuries. It to must be driven. In this case by the driver. Even though the port is producing the bulk of the sound (in the region we are talking about) it still is in the region of 180 degrees out of phase ( same as listening to something face on and then turning your back to it and listening to it again). So where the two are working at producing sound output there are some conflicts! The two sources of sound cause each other to fight over a narrow bandwidth and there is a definite degradation of transient response due to the lag in time between the driving piston and the resonating port. ( there is more and I acknowledge that but for the puposes of this short explantion this is the crux of the matter )
I have built and listened to both and I still like horns better! :D :D :D
Mark |
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| Stocker |
Guys, have a smoke and relax! If each man is happy with his box, let's all be happy with each other!
Of course different boxes sound different. Of course the same box sounds different when the port is open or closed. Physics are physics. The only half-difference I want to make with anyones opinion is that bandpass boxes don't dominate, not because they can't sound good, but because they are difficult to design, and VERY easy to make sound bad. |
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| johninCR |
Ok I apologize to all.
Mark,
Your explanation of the difference resulting from the conflict in output was well stated and the wording for which I was searching. I hestitate to lay the bulk of the blame there, because my dipoles don't exhibit any SQ problem. With front and rear waves both in full play there is the combination of waves with varying phase relationships across the spectrum, which doesn't sound destructive.
It may be that the tonal characteristics of what comes out of the port vs cone radiation are different enough to have a destructive influence in the range where apples and oranges are combined. As an example I'll use my Decware designed Housewrecker which is an isobarik 6th order pandpass with a large sealed aircushion in the isobarik chamber. I compared it to the same drivers in sealed boxes and EQ'd in the same response for both. The housewrecker has a very different presentation in its operating range below 100hz. While I'm sure some will argue that all bass waves are created equal, I don't believe they sound the same with music just like 2 different midrange drivers don't sound the same even if they measure the same.
In the case of comparing my EBS box with the ports open and closed the sound difference is "loose and sloppy" as I said before, so I believe it's simply a matter of the cone movement stopping more quickly with the ports sealed. At least that's what it sounds like.
With higher tuned BR's like woofers the sonic difference is probably a combination of the factors you mentioned, but there is definitely a sonic difference and not just in the response curve. |
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| BassAwdyO |
I'm no expert.... But might there be some kind of "critically dampened" vented box with perhaps the tuning equal to the FRC of the sealed system of equivilant size which would make the port actually slow down the driver faster? Probably no such thing... but I would think in a rare case the port might actually help slow the driver faster, I may be dead wrong
It is mostly step response that we judge in the bass region as being "fast" or "slow" I believe... The're no such thing as transients down there for sure. Voice coil inductance instantly smoothes a transient into... a non transient |
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| BassAwdyO |
| quote: | | A helmholtz resonator is not magical. It is a derivative of the grand old pipe organ. |
From my understanding a pipe organ is more/less a quarter wavelength pipe with whisle on it to excite the resonance... not a helmholtz resonator... I may be wrong here again |
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| rcw |
I think Stockers point about bandpass boxes is well made.
They are difficult to get right, and they got most of their bad reputation
In the days before computer simulation and the only things to go by were Earl Geddes "calculator bashing' models. People rushed to them because they were a cheap easy to build alternative to horn loaded subwoofers for sound reinforcement, and the results in most cases were woefull.
I do however emphasis my point that there is no intrinsically better way of making a subwoofer, double blind testing indicates that you can't hear the difference between various forms of loading when such things as room resonances and proximity to boundaries is taken into account, and as a scientist I have to trust the research even if it conflicts with prejudices that I might have. |
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| johninCR |
| quote: | Originally posted by rcw
I think Stockers point about bandpass boxes is well made.
They are difficult to get right, and they got most of their bad reputation
In the days before computer simulation and the only things to go by were Earl Geddes "calculator bashing' models. People rushed to them because they were a cheap easy to build alternative to horn loaded subwoofers for sound reinforcement, and the results in most cases were woefull.
I do however emphasis my point that there is no intrinsically better way of making a subwoofer, double blind testing indicates that you can't hear the difference between various forms of loading when such things as room resonances and proximity to boundaries is taken into account, and as a scientist I have to trust the research even if it conflicts with prejudices that I might have. |
I guess all amplifiers with .01% or less THD will sound the same too. Why did you even bother to make a quality sub when the general public can't tell the difference in blind testing? What differences the general public can or can't hear in blind testing is irrelevant because their ears are totally untrained in identifying the sonic differences involved. While of course the effects of the room are very important, they are not the only factor. As a scientist you should understand that, once trained, our ears and brain are far more sensitive in many respects than any manmade instruments. Believe what you want, it is of no consequence to me, however, you are doing yourself a disservice if you don't learn to trust your ears more. |
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| mwmkravchenko |
| quote: | | From my understanding a pipe organ is more/less a quarter wavelength pipe with whisle on it to excite the resonance... not a helmholtz resonator... I may be wrong here again |
Tis not as simple as all that. If you whistle while you work than....
An open pipe or flue pipe sounds at a tone like this. Approximately an 8' pipe sounds at 64 hz a 16' sounds at 32 hz and a 32' sounds at 16hz. They are 1/2 length resonators. There are pipes that do have 1/4 wavelength resonators ( usually reed pippes. Think of a saxophone where there is a reed that vibrates into a column of air ) and there are pipes that are stopped ( the open end is plugged ) and sound an octave lower than their open counterparts ie a 16' stopped pipe will sound at 16hz. Then there are the overblown pipes that sound an octave or two higher depending on the amount of pressure that is being used to make them sqeak.
Crazy man Crazy OR sorry you asked ( in a evil mood :devilr: :bigeyes: :devilr: :D :D
Hey check this out! http://www.sengpielaudio.com/calculator-wavelength.htm
Mark |
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| paulspencer |
I think we should all be a little less certain of the conclusions we are drawing here. A lot less certain and a bit more curious.
John you say your vented sub sounds less musical than the sealed version. Fair enough.
To give a definitive reason for this is not something I believe we can do just yet. There is a lot of theory to back up different points of view, but I don't believe sufficient to come up with definitve answers which all must accept without question. The reason I say this is I don't believe our understanding of what we can measure and how this translates into what we perceive has progressed far enough to be so sure.
example: RCW, you say that 3% THD is audible. However, I've seen some work by Geddes on distortion perception which indicates that THD measurements and our perception of distortion do not necessarily correlate. www.gedlee.com <<< downloadable sampes are available on their website to indicate this, including a brief discussion of a new way of measuring distortion which actually correlates to what we hear.
This is part of the reason why there appears to be disagreement between measurements and perception - we don't fully understand how the relationship between what we measure and hear.
Regarding sealed vs vented subs:
* vented subs have output in the range most critical for music accuracy coming from the driver itself, the vent contribution is not significant for most of the bass in music
* vented subs have much lower distortion where their entire bandwidth is being used, however the distortion is reduced down low where it is not as critical
* sealed subs have what we consider better transient response, however can we actually perceive this? At which point does this occur? Suppose you are looking at the transient response around 70Hz - will this actually be any different for vented vs sealed, or is the slightly superior (in paper) transient response of sealed boxes down at a point where our ears can't perceive the difference anyway?
* IB subs are considered by many to have the ideal transient response, however, is this the difference that is actually heard? Is it instead that what is heard is a degree of linearity not normally experienced due to the larger number of drivers? Or is it that there is actually a very audible and detrimental impact of a vent, as well as the distortion of a sealed box, but that both problems are eliminated with IB, also with an audible improvement in transient response?
* vented vs sealed subjective comparisons are rarely made in such a way as to coming even close to identifying a clear cause/effect relationship - use of fairly sophisticated eq and outdoors listening with blind AB testing would be a starting point if you really want to begin to argue about the impact of the vent - otherwise perception is coloured by the room, a different frequency response as well as one's expectations
As much as I like the way that a heated debate brings out at times a more in-depth discussion, is it possible for us to proceed without the need to prove which opinion is right? Is it possible that all (or at least most reasonably informed) opinions have a piece of the truth? Is it also possible that we could all learn more if we all put foward our views, subjective experiences as well as our understanding of theory on the table, not in opposition but in collaboration, that we could actually learn more? I think if we ever do get definitive answers, it will only be by learning to reconcile apparent contradictions that appeared to be fighting each other. |
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| rcw |
The thing that I am trying to point out Paul is that if you are going to design something you need a place to start, and a good place to start is a list of priorities.
For instance we have audio pundits banging on enlessly about the superior transient responce of sealed boxes, this is true but testing indicates that if it is below a particular threshold frequency you can't hear it. It is also true that all other things being equall a sealed box produces more distortion than a vented one, and testing indicates that you can hear it, even at the lowest frequencies.
So by touting the superior transient performance of the sealed box as being more desirable you are favouring an abstraction that you can't hear in favour of a real effect that you can, so much for living in the real world.
I could go on further but I wont, there is a point where robust discussion can degenerate into a slanging match, and this one if not quite reaching that level has become perilously close. |
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| johninCR |
RCW,
When you talk about higher distortion with sealed, are you talking about when you are driving that sealed sub into high excursion that you get the obviously high distortion, because that would make sense. It would also help explain my real world results because I never push mine hard at all with music. It would be too loud, since I don't listen to anything with really low LF content like organ music or trance type stuff. I can only go by my real world results. As soon as a built this sub, I loved it for HT but really disliked it for music. At first I just assumed it was tuned too low to work well for music, so I used a switch to use a different sub for music. When I read somewhere about stuffing ports, I tried it and it made a very audible difference. I've hauled the monster outside as well just to see what effect the room had and the difference is in the alignment, not how they interact with my room.
Now it's just a matter of stuffing the ports with big chunks of foam rubber when I listen to music. Occasionally I forget but I quickly notice the sonic difference. That also makes me certain that there's no psycho acoustic BS going on, because whether the ports are stuffed or not isn't visible from where I sit. For HT I forget to switch sometimes because I may not notice it, but never for music. |
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| simon5 |
I tend to side with RCW on this... maybe it's because I'm studying in engineering I guess.
I think you prefer your EBS sealed for music because you don't like the extra low end which is there in the music you listen to that your EBS subwoofer can produce, compared to the missing bass your sealed subwoofer can't produce.
So, the sealed subwoofer have more "punch", because the lower bass is rolled off.
To have a fair comparison, you should compare your EBS to a sealed subwoofer with a parametric equalizer to compensate for the loss of low end. I guess you'll get back your "sloppy bass".
Anyway, that's my opinion, and if you prefer your subwoofer sealed, then seal it hehe! ;) |
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| paulspencer |
RCW, I'm inclined to agree. I'm not convinced there is an audible penalty for the extra output and extension of vented boxes - certainly not one that is purely attributable to the nature of vented boxes which applies in all cases.
I'd like to at some stage conduct a blind AB test of some things like this with a good number of people. Using my Ultracurve outdoors, I could calibrate a sealed and vented sub to exactly the same response. I'm very curious to see if they would be able to pick the difference. I doubt it.
I don't doubt that John can tell the difference with his, but it's not the same kind of comparison.
Some of the best bass I've heard was from a fairly sohpisticated setup which included:
* 3 x M&K subwoofers
* 1 x 15" vented focal audiom in a 200L box
* 1 x 15" vented tumult in a similar 200L box
* Ultradrive DCX for phase correction
* Ultracurve to calibrate them all flat
Now there's more money in calibrating those things than most over here spend on subs!
Subjectively speaking, none of the negative comments I've heard about vented subs applied. The bass was clean, loud, low. My first impression was that I wanted more bass, but I think that was in fact the absense of untamed modes, including a typical 35hz room mode which exists in my room.
Now my more humble system has a pair of AV12s sealed and Ultracurve, they are sealed only temporarily since I haven't gotten around to building proper boxes. The aspect of their bass performance I'm least happy with has nothing to do with the difference between how they sound vented vs sealed, but is in fact the upper bass, around 80 Hz at the top of their bandwidth. I'm yet to determine what this is, but it may be that I need something that has a cleaner top end, which brings me back to the original topic ...
I have considered the idea of an 8" driver in a small horn to handle 40 - 80 Hz. Anyone have thoughts on a bass horn vs drivers like the AV12s for this range? or possibly extending up higher ... |
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| rcw |
Modelling my woofer in sealed the two types of shelving alignments in Win ISD, and my own QB5 box shows that in fact the sealed box has slightely better power handling over the range 22-40Hz. than either the shelving alignments have, but not nearly as good as with the QB5.
I think it was Bass who commented that comparing the QB5 box with the shelving box might not be a fair comparison and this is true over the range where you find musical bass since no advantage in power handling is there.
The other thing of note is that you need 4x10.2cm. diameter pipes
88cm. long in order to get the vent air velocity down to around 10m/s, so the vents that people have mentioned will probably produce considerable noise for large outputs.
Overall the shelving box might make loud noises that sound a bit like the original sound effects people intended but if I had one I would probably stuff up the port when listening to music myself. |
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| RobWells |
| quote: | Originally posted by paulspencer
-snip-
Now my more humble system has a pair of AV12s sealed and Ultracurve, they are sealed only temporarily since I haven't gotten around to building proper boxes. The aspect of their bass performance I'm least happy with has nothing to do with the difference between how they sound vented vs sealed, but is in fact the upper bass, around 80 Hz at the top of their bandwidth. I'm yet to determine what this is, but it may be that I need something that has a cleaner top end, which brings me back to the original topic ...
I have considered the idea of an 8" driver in a small horn to handle 40 - 80 Hz. Anyone have thoughts on a bass horn vs drivers like the AV12s for this range? or possibly extending up higher ...
-snip-
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Hi Paul,
As you know I run 3 tempests each in their own 200L cabs. When I had 2x10" scanspeaks in each of my mains crossed to the tempests at 40Hz (24dB/oct) the sound quality was way better than running the tempests up to 80Hz. I'm working on a pair of labhorns to place behind my screen, corner loaded and will use the tempests below ~30Hz. If I wasn't doing the horns I'd be looking at a pair of large (18 or 21") pro drivers to cover the 40-80 Hz range instead. (Have changed my mains to high eff stuff.)
Cheers,
Rob
I posted this question here, but I don't think people took me seriously:D
http://www.diyaudio.com/forums/show...3971&highlight= |
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| rcw |
| The thing that I would consider is that a "small" horn to cover that range is still big, and if you make it smaller by reducing mouth size you are going to get the invitable peaks and valleys caused by the reflected wave, and typically with little room gain the frequecies below mouth cut off will be attenuated since the horn turns into its equivalent single ported bandpass box, overall its a damn complicated way of making a bandpass box. |
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| paulspencer |
Ahhhhhh, don't you hate that? Sometimes it's surprising what people respond to on a forum, and what they don't. |
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| mwmkravchenko |
RobWells
Your idea has a good basis behind it. Most of the slam in music is in the lower end around 40 to 80hz. A horn can when designed properly and not ham strung by over zealous foreshortening produce those bass transients with greater ease than anything else short of stacks of drivers and kilowatts of power. So yeah go for it! It does work and there are plenty of examples in the idustry to support it. THe transition will be tricky. The horn size and placement will have to be well thought out. But it will work.
Mark |
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| johninCR |
Rob,
Maybe you should try something like the Jensen Imperial. With the huge chamber you get the slam in 40-80 range, plus the region below the acts like the bandpass output giving you deep extension as well.
Steve over at Decware is coming out soon with a sub only version of the design with a throat that is open to the air which is loaded via a Kslot at the side making is some kind of Kslot loaded helmholtz resonator with horn loaded output. |
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| RobWells |
Thanks for the interest chaps:)
John - I remember that cabinet coming up a while back in a search I did. I've actually started cutting the wood for my labhorns now. Already have the side panels done for 4 cabinets. (you never know, one day I might have a room big enough!)
As an aside, I'm considering ebs'ing the tempests to lower the eq on them. Figure that below 30Hz I probably won't hear a quality difference as you feel it, not hear it.
Cheers,
Rob. |
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