| zenmasterbrian |
This is an extension of a thread Giant Subwoofer.
I had asked about drivers bigger than 18". But a great deal was said about running below fs.
So, I want to separate these two issues so they both can be explored more fully.
Some folks have been extremely helpful here already.
But still, who is running below fs now, or has thought about it, or has some information about it? |
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| zenmasterbrian |
http://sound.westhost.com/project48.htm
I am especially intriqued by the above. He uses a small sealed box enclosure to raise the resonance of a sub woofer.
So he operates only below fs, never above or at it.
He uses eq to contend with the downward slope.
I find this approach very intriquing.
It solves one issue. Previously, you could add more drivers and more power, but it does not lower fs.
Here, he starts below fs. So more drivers and more power do help. |
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| richie00boy |
| And the Linkwitz Transform (P71) is even better. It has the best of both worlds and then some - it equalises below Fs yet also makes use of above Fs so is more efficient and can use a bigger box. Also the upper cutoff frequency is not set in stone. |
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| REK |
There are several listing of giant subwoofer systems that operate below Fs.
http://home.comcast.net/~infinitely...ousaineIB1.html
http://home.comcast.net/~infinitely...IB-Gallery.html
http://home.comcast.net/~klone-audi...3-12Shiva1.html
http://home.comcast.net/~infinitely...IBmanifold.html
They are called infinitely baffled subwoofer, and work this way: If you measure the free air resonance (impedance peak) of a subwoofer, in my case an 18” JBL Professional 2245H, it is approximately 20Hz. When you mount the sub in a manifold, as pictured above, and measure the impedance plot of the system, the impedance peak goes down, in my case to 12.5Hz. This is using 4 of the 2245H’s in a 41” wide by 55” high by 12” deep box, with the top opening in the first floor living room covered by a 12” by 42” open mesh iron grate, and the backs of the subwoofers opening into the basement, hence the name “Infinite Baffle”. The basement is 28’ by 33’ and almost 8’ high, so it is reasonably large. The system is powered by an Ampzilla power amp, feeding two of the 2245’s in parallel on each channel that delivers nearly 400 Watts per channel into 4 Ohms. The system in capable of providing 126dB SPL at 16Hz, at less than 10% THD, at the listening position in the living room, which is 14’ by 22’ by 9’, and has several open doorways into other parts of the house. As mentioned in a previous post, Tom Nousaine wrote up this system in Audio Magazine, in December 1999, in an article. Incidentally, the first link above is on his Infinite Baffle Subwoofer system that Tom Nousaine installed in his house. |
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| zenmasterbrian |
I'm going to check out all the links posted.
Richie00boy, might you have a link for yours? It does sound highly relevant.
We all talked about this on the Giant Subwoofer thread. I'm intriqued, but I'm still reluctant to beleive you can slew through it with no problems.
So I like the Elliot sound approach. But of course I understand that if you don't have to push the resonance up with a small box, then the possibilities are still greater. |
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| richie00boy |
| P71 is on the ESP site, where you have already linked from ;) |
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| zenmasterbrian |
| I'll check it out. Thanks:D |
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| soho54 |
I don't understand what you are looking for? There is a 12db/octave roll-off under Fs. These effects can be negated by EQ, in the form of enclosure size and tuning, or electronic signal manipulation.
EBS and IB subs use the enclosure method. They use large enclosures, which decrease the air spring pressures on the drivers, and drastically increase the power to SPL ratio. Enabling increased output below Fs, with little power needed. The trade-off is max SPL achievable per sweep area, which is why you want high xmas 15"s or greater in this application.
ELF, EAS, and LT circuits electronically modify the input signal. In this case you add EQ to negate the drivers natural roll-off. These designs use smaller enclosures to increase the air spring, which lowers the power to SPL ratio. Massive amounts of power and EQ are used to produce SPL level near a normal sealed sub. The lower you try to go the more power required. +1K levels of power for high SPL applications. A driver with high power handling and high xmas is needed to make the most of these types of subs.
There is nothing special about running a driver under Fs. You just have to pick your poison. A large enclosure or huge amps and extra electronics. |
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| soho54 |
| quote: | It solves one issue. Previously, you could add more drivers and more power, but it does not lower fs.
Here, he starts below fs. So more drivers and more power do help. |
I do not understand this. The Fs is not lowered in a EAS sub either. You just use a box with an Fsc above the passband. That way you know the roll-off will be 12db/octave, and you can just use the generic EQ for any box and driver combo. The EAS method is the easy way of creating LT like gains.
More drivers always help with output above and below the drivers Fs.
You can accept a sub operating below an abnormally high Fsc, but not at normal levels?
EDIT: Not trying to flame you. I'm trying to understand where you are coming from. |
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| paulspencer |
Those are some great links.
After reading that Nousaine article, I do wonder why he doesn't consider horn loaded. My simulations indicated you could exceed 120 dB easily @ 20 Hz with two high excursion 12" drivers with much less power than all but the cheapest of plate amps. Required footprint is only about 2 x 0.5m with a large floor to ceiling box. Not that bad really. If I had room I would have done it by now.
When I was working on the design, another who had built a smaller bass horn suggested that it could go well below 20 Hz due to the corner expansion. Given a spare basement, you could also build some very large vented boxes or bandpass boxes to get high SPL @ 10 Hz if unhappy with the extension of the horn.
The horn could actually match the SPL of the IB on the low end, given the same number of drivers. Not that you would pull this off since the horn would be huge then with that many drivers. |
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| kingdaddy |
| I've played 7Hz test tones on my 4-18" Avalanche IB with no problem and still quite strong on the SPL, but the electronics brick wall there and as far as I know you wont find many combinations of electronics that wont stop you somewhere before 5Hz. Also if your looking for any measurements or want to do some real experimenting here I don’t know how you would as I don’t know of any test equipment readably available that will test anything accurately down this low. BTW, why? |
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| Bogie |
| It's fun to hack off the guys at the seismic lab? |
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| AndrewT |
Hi,
I have just downloaded Stig Tangen's article from post4.
Can I assume the content as gospel? or are there any corrections that I should account for?
22Hz performance from a driver with Fs=40Hz seems more than impressive! |
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| zenmasterbrian |
The why is to experiement with infrasonics in music. This thread is a continuation of the Giant Subwoofer thread where this was first broached.
There are 3 pipe organs in the world that have the 64' octave, which has its lowest note, C at 8hz. Is that music, or is it a sound effect?
I am not sure, but I'd like to experiment . I think it is a fascinating subject. If its possible to go lower, OK.
Do you have a link for that 18" Avalanche? I tried to find that once and could not. |
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| 4fun |
| quote: | Originally posted by AndrewT
Hi,
I have just downloaded Stig Tangen's article from post4.
Can I assume the content as gospel? or are there any corrections that I should account for?
22Hz performance from a driver with Fs=40Hz seems more than impressive! |
He has active correction.
Quote:
"The first two sections are the equalizer. The two last 2nd order filters are in combination a 4th order Linkwitz-Riley filter"
The woofer he is using has Qtc around 0.3 so it is possible to have sufficient gain from BR. Tuning is also low. Resulting in a shelf response that he is EQing flat.
The site seems to have lost all pictures that backed up his article.
Edit:
Here's one sim i made with JBL 2226 in 220L box tuned to 22Hz. Not impossible to EQ flat. |
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| AndrewT |
Hi 4fun,
thanks for the clarification.
What about mistakes or rose tinted glasses in the Stig article? |
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| zenmasterbrian |
| qi, IB Cult? I don't know what to make of that. All those boxes with the back side of the woofer exposed? Are those Avalanche? I really never heard of that name and have not been able to find them. |
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| Bogie |
Enough woofs, with enough surface area, and enough xmax, and with a little judicious equalization, you're there. Granted, with a single one, you're not going to be able to rumble loud, but you _can_ rumble... And when you get into the folks who build walls out of them, well...
The limiting factors are construction of the chamber (the listening room) and how much $$$ you can throw at it. |
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| zenmasterbrian |
From the Tangen article
"My quest for the Almighty Subwoofers really started when I as a teenager heard a rock band play. The band had a huge bass guitar amplifier, and the clean punch from this, far from anything I'd ever heard, made a deep impression on this author. "
Same for me. Bands would come somedays and play at our high school. The strong base went right through my gut and did something to me permanently.
Now I'm interested in even lower frequencies. |
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| Bogie |
Thing is, you let most "audiophiles" at the EQ for a live band, and it's gonna sound flat... For rock, my 0.9Q sealed subs are a LOT better than my 0.7Q subs... But the sevens are a LOT better with "nice" music.
In my basement, "The Bunker," I've got a pair of 15s tuned to 21hz, and the 0.9s sitting under the mains. I can't hear it down under 20s, but I can feel it. |
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| zenmasterbrian |
Is you system running below the driver fs?
Are you running below the resonant frequency in the box? |
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| pinkmouse |
| quote: | Originally posted by zenmasterbrian
Bands would come somedays and play at our high school. The strong base went right through my gut and did something to me permanently.
Now I'm interested in even lower frequencies. |
You shouldn't be. That punch is around 60-80Hz. |
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| zenmasterbrian |
Correct you are. That was in the days when bands were using these short horn boxes, short straight sided horns. They did not go that low.
I was asking about Bogie.
Bogie, are you running below fs?
Are you running below the in box resonance? |
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| pinkmouse |
| quote: | Originally posted by zenmasterbrian
Correct you are. That was in the days when bands were using these short horn boxes, short straight sided horns. They did not go that low. |
90% of PA still doesn't go much lower than 50Hz, and if the boxes are capable of going lower, the FOH engineer usually rolls them off around there to save room problems. |
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| pinkmouse |
| quote: | Originally posted by zenmasterbrian
Are you running below the in box resonance? |
I think you're getting confused. When you run a system below resonance, it means that the box resonant frequency is lower than the Fs of the driver in an infinite baffle. This is why you nedd a ported box or electronics. |
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| Bogie |
In my old sonotubes, I was running the things at 18hz ported... Fs on the drivers is 21hz... System was also running through a Behringer feedback destroyer for equalization... Basically I cut high...
They would move a lot of air pretty low, but I also had a highpass, so I had to throw a lot of signal at it for the low stuff... I'm semi-seriously thinking about getting a few lengths of large PVC for when I rehab that end of the room, and building in a large transmisson line...
When does a ported system become a transmission line?
I'm not going to lose the "thump" speaks tho... I do too many concert DVDs, and I like that 60-100hz bump to be there with 'em... |
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| qi |
| quote: | Originally posted by zenmasterbrian
qi, IB Cult? I don't know what to make of that. All those boxes with the back side of the woofer exposed? Are those Avalanche? I really never heard of that name and have not been able to find them. |
Please stop wasting our time.
You have alot of threads going on this forum, but expect us to do all the work for you.
If you google "IB Cult Avalanche" , you will find the answers to your question above.
If you google "SVS speakers" (your question from another of your threads), you will also easily find that answer... |
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| zenmasterbrian |
pink mouse, normally you don't go below the box resonance, but there are exceptions. In my post number two I show Elliot sound products. He does purposely use a high box resonance, and then runs exclusively below it.
To Be Continued |
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| mike.e |
| quote: | Originally posted by AndrewT
Hi 4fun,
thanks for the clarification.
What about mistakes or rose tinted glasses in the Stig article? |
Tuning that low below Fs is asking for distortion,perhaps becaus ethe unit is relatively clean it isnt objectionable.
Note that there is no real advantage over using a low Fs driver apart from the fact that the jbl has flux shorting rings and high RMS rating.
I used a 2226 in 175L internal tuned to 33hz for several years.Loved it!
You could use two low fs HT type woofers push pull and achieve some nice lows without an expensive 2226. |
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| mike.e |
| quote: | Originally posted by zenmasterbrian
pink mouse, normally you don't go below the box resonance, but there are exceptions. In my post number two I show Elliot sound products. He does purposely use a high box resonance, and then runs exclusively below it.
To Be Continued |
There are exceptions,and they pay the price with SPL limitations and distortion. |
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| AndrewT |
Hi Mike,| quote: | | there is no real advantage over using a low Fs driver |
surely this is an oversimplification that has become misleading?
The Fs determines the final cabinet low frequency roll off point.
Using an Fs=25Hz driver in a box that performs well down to say 20Hz and then comparing another speaker using an Fs=100Hz driver in a box tuned to give bass response down to a similar low frequency will be severely compromised.
Or, am I wrong? |
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| Bogie |
IMHO, the real limiting factor is displacement, and how well it can be controlled. If all you have to do is control a little for each driver, a multiple driver setup can give you better results below its limits than a single big floppy driver...
I can localize relatively low frequencies... I'd rather listen to several subs spread across front of room than to a single higher xmax one sitting in a corner. |
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| AndrewT |
Hi,
I think we are all agreed that high Xmax as a substitute for Sd compromises the bass quality.
Look at all the small bass/mids with high Xmax relative to their diameter for proof of compromise.
Whether, bass sound quality is different, using multiple low Xmax smaller drivers compared to using a low Xmax large driver is debatable.
But if the bass drivers are being asked to extend up into the mid range then the driver designer will have an easier job extracting exemplary performance from multiple small drivers than from a big floppy coned single driver. I think we could be persuaded to agree this point.
If the cone is not floppy in it's exemplarly part of the passband then we are back to the debatable. Look at the proliferation of concentrically ribbed dual layer bass cones for proof of non floppy construction. |
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| bremen nacht |
I read Rod Elliott's article and on the face of it it's a way of getting deep bass out of a small sealed box.
But would it cause distortion due to compression (the voice coil is going to get hot)?
I have a pair of Tannoy Ardens (15 inch DCs in 200 litre reflexes) that are, sadly, too big for my room and am thinking of making smaller sealed boxes for them. Can I expect to regain that huge clean bass by means of EQ? I realise that headroom will be limited but I don't listen loud anyway. I have neighbours, you see.
Apologies if this is OT, I just saw the Linkwitz reference. |
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| phase_accurate |
If you look at amplitude statistics then most of them will show a significant drop in level below 60 Hz.
My conclusion is then that you can safely use LTF or similar eq-ing to extend frequency response - if your driver is going at least down to 60 Hz already without use of EQ.
If your box doesn't go that low by itself you run the risk of needing EQ where there is already high power demand by nature.
I once used an LTF to tune down a Dynaudio 20W75 in a closed box (prototype active speaker with an MSW). Without EQ it was going down to approx 60 Hz - with LTF it was going down to 30 Hz with a system Q of 0.5. Gues which one sounded better ? I used a chip amp with 2x10 Watts per speaker and it was sufficient for most records. But you'd also have to be aware that I listened in the nearfield.
Regards
Charles |
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| AndrewT |
Hi,
I cannot guess, tell me.
I suspect that EQing to raise the low bass response will introduce a number of sound quality compromises.
That is, in addition to the extra power/ extra Xmax / limited SPL that results from electronic bass extension.
Bremen,
I think you will be dissappointed.
How about a project to change the SHAPE of the Arden cabinet to one that is more domestically acceptable.
I am thinking tall (1000mm to 1200mm) narrow (400mm to 450mm) and deep (600mm to 700mm). Allow about 25mm thickness and you get your 200L. |
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| richie00boy |
| quote: | Originally posted by AndrewT
I suspect that EQing to raise the low bass response will introduce a number of sound quality compromises.
That is, in addition to the extra power/ extra Xmax / limited SPL that results from electronic bass extension. |
I vote the opposite choice :D
With the nicer phase and amplitude characteristics of the gentle roll-off and moving the phase change further down the band where there is much less information, I suspect the EQ'd system sounded cleaner and more natural in Charles' situation where blasting SPLs were not required. |
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| 4fun |
Hi richie00boy!
But we introduce additional phase change with EQ that going to sum with box/speaker, right?
Don't we have to look at the whole signal chain if we are going to judge any phase characteristics. |
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| richie00boy |
| No the beauty of the Linkwitz Transform is it corrects phase, it's not EQ as you know it. |
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| 4fun |
| Ah, we are talking Linkwitz transform and closed boxes, agree with you. |
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| 4fun |
But the trade off, small boxes heavily compensated....
Requring great dispacement capability, usually nowdays by high excursion drivers.
By simply looking at BL vs excursion curves of typical drivers there will shure be greater compression/distorsion compared to alignments that require less excursion for a given sound pressure.
Also, if we are going to compensate the low sensitivity of closed boxes at low frequencies a lot of power will be nessesary. Power compression by voicecoil heating is another factor to take into account.
The usually low sensitivity of high excursion drivers due to low ratio of voicecoil in gap will only add to power requirements. |
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| phase_accurate |
| quote: | | With the nicer phase and amplitude characteristics of the gentle roll-off and moving the phase change further down the band where there is much less information, I suspect the EQ'd system sounded cleaner and more natural in Charles' situation where blasting SPLs were not required. |
The candidate has 100 points !!!!
Regarding power demands: Since the driver-box combination already went down to 60 Hz approx and the final Q was only 0.5 the rise in power wasn't very high for normal program material.
Listening to the infamous 1812 Telarc recording or some hip-hop tracks would change things a bit of course.
The important thing (as is true for most engineering tasks): Don't overdo it.
I think everyone can agree that expanding a woofer that is already capable of doing 60Hz down to 30 Hz is less proplematic than EQing a woofer - that does only reproduce 100 Hz by itself -down to 20 Hz.
And yes, LTF does influence group delay distortion. It depends on what one is doing. Transforming to a lower Q means better group delay properties.
Regards
Charles |
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| bibster |
Well, sorry to pop in on this thread, but you're talking about the subject, so I thought....
I have some 'el-cheapo' 10" ers (mabe by some obscure company, and sold under the name of another obscure company) that I put into a WO-36 (Wicked One odd-thinggy) but I don't like it at all... Might be my not so perfect construction, or the fact that the WO is rahter car-oriented, what ever (More over, this huge anumal doesn't fit in my livingroom, so...)
So I thought, given these specs:
Vas =145 liters
Fs = 34 Hz
Qms = 3,6
Qes = 0,52
Qts = 0,45
Sens: 92 bD, 300W
(As claimed by the manufacturer!!!!)
I'd make a 190/200 l box (approx. 122x40x45 cm) But both in, use my cheap sub-plate amp, and a LTF like this
Fo = 54,70 Hz
Qo = 0,70
Fp = 18 Hz
Qp = 0,707 (K = 3,065)
This gives a max gain of 19,31 dB
My question is: Will it work? Will it sound? How can I determine if the drivers a willing to do what I'll ask them to do?
I don't feel like spendig 60 Euros on MDF, just to find out that I can shove it in the stove (Like my WO-36 is goning to end up like)
Cheers, Paul
OH, BTW: It's for music mainly, no high SPL's needed, rather large listening/living room, KEF CS7's as mains (Blame me, I STILL need to paint them after 2 1/2 years...) |
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| AndrewT |
Hi,
that's a lot of gain. Do you realise the message it's telling you.
+19.31db is almost 100times.
For a 300W driver limit that means the rest of the frequency range is working upto a maximum of 3W when the bass driver hits the +19.3db induced thermal limit.
If the frequency is quite low your driver may run out of Xmax before you even get to 3W. For a midband or upper bass sensitivity of 92db/W then your EQed bass driver runs out of puff before you have reached a peak SPL of 97db. I think you would be very disappointed with that limitation after all your building effort.
I would try for less bass extension and much less gain. Maybe just +10db and see how the numbers stack up. Even 10db less gain will only increase your peak SPL to about 107db. Headbangers will think this is too quiet.
All you speaker heads.
Have I got this right? |
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| phase_accurate |
| quote: | | Have I got this right? |
Definitely.
Apart from that - using a box that is larger than the VAS of a driver doesn't help max SPL either !
Regards
Charles |
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| richie00boy |
Yes Andrew spot on. A pair of cheap 10 inch speakers are not going to hit 18Hz in a sealed box at any worthwhile SPL, certainly not to keep up with some decent main speakers.
Whilst the high gain is not that good, it's not a show-stopper as long as you have the speakers with capabilities to handle the power and SPL requirements. |
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| bibster |
| quote: | Originally posted by phase_accurate
Apart from that - using a box that is larger than the VAS of a driver doesn't help max SPL either !
|
Oups....
I forgot to mention I'd but BOTH drivers in the box... // so I end up having 4 ohms.
(Andrew's values would thus become: 19 dB, 600W, 6W)
I'll fiddle with the LTF S-sheet to obtain some 'reasonable' values.
I don't bang my head quite often :-D Me thinks maybe around 97 or 100 dB'd do the trick for me...
Bye, Paul
(Ow, and, yes, those KEF's are like 87 dBw-1, so....) |
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| AndrewT |
Hi,
see what happens when I rely on my failing memory.| quote: | | Andrew's values would thus become: 19 dB, 600W, 6W |
I must refresh my RAM more frequently. |
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| richie00boy |
| quote: | Originally posted by bibster
I'll fiddle with the LTF S-sheet to obtain some 'reasonable' values.
I don't bang my head quite often :-D Me thinks maybe around 97 or 100 dB'd do the trick for me... |
IMO the place to start when designing an LT system is to look at the max SPL that is available from your driver and box combination. If this does not meet 97dB at your chosen -3dB or (even higher up the range), you will just be wasting time with the LT spreadsheet and it's time to find new drivers or change your box size, usually the former.
If the Kefs are floorstanders and vented, I think you will end up having to buy new drivers for your sub unless you go for an alternative box design.
From recent posts on here of what WinISD says against what people seem to be realising in the actual houses, it would seem that a lot of the SPL predictions are wildly optimistic from numerous software packages. Linkwitz has some equations on his site which seem to be more accurate.
edit: on the Pluto+ page he has two spreadsheets he used to compare the XLS12 and XLS12, either of these can be used. They are extremely comprehensive. |
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| ChocoHolic |
Once upon a time I used this tiny sub:
http://www.diyaudio.com/forums/show...5015&highlight=
But richie convinced me that LT can do the same job as ACE electronics. ACE electronics measure the current in through the speaker and provide by complex feedback any complex output impedance of the amp. Means you can adjust the system to any desired effective Thiele/Small parameters.
LT is less difficult and can deliver the same results. LT is a 4th order filter. Two orders are exactly compensating poles and zeros of your sealed box system without correction. This means also phase shift and group delay ! Cool !! And the 3rd+4th order define any new desired transfer function of the system.
No matter which electronic compensation you use for an undersized box, you will need high power in the low frequencies. Also distorsions usually increase.
y current approach is IRPS with LT. IRPS=in resonance principle speaker. If we look at the efficacy of a sealed box, you are getting quite values around the resonance frequency. The impedance is high, current and power lower, but sonic output strong. Originally I was thinking to add mass on the cone and my measurements indicated even in this situation a better efficacy than living with high natural fres and electronic correction. But in the end I decided to make the enclosure large enough to have a reasonable natural resonance frequency of the sealed box around 40Hz without adding mass. 40Hz is a frequency where still a good portion of bass signal can be found in normal music. In addition I am adding a LT to this natural IRPS system which is changing the resulting roll off frequency down to 12Hz.
All together a trade off between size, required power, possible SPL.
Up to now I enjoy this trade off quite much.
I must agree to statement that micronizing the box to exzessive small values and correcting with brute force electronics does sound less impressive than larger sized designs. I definitely hear this by comparing my new design (Two cubes 40cmx40cmx40cm, with one Adire Sadhara driver each) to my older supersmall 12liter/11driver system. The new system offers much more relaxed and impressive bass reproduction also at low signal levels, where the distorsions should low in both systems. Up to now I did not fully analyze the reasons for this difference, but at least my ears tell me very clear...
For my current situation the two IRPS Sadhara cubes with LT are doing a good job and in my living two 12" drivers with+/-27mm lin Xmax are mostly sufficient. I don't want it giant.
Hm,... 8Hz you say... for pipes... I could change the LT to go deeper. But my reason NOT to go so deep was the fact that our human body is sensitive to infrasound. From what I know the most dangerous frequency range of infrasonic weapons is somewhere between 5Hz....10Hz. How can our pope support such things in the church???!!! :scratch: |
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| Bogie |
Da Pope is a basshead...
With enough drivers, and enough equalization, I think that an IB system could be really interesting.
But to avoid the monster distortion, and loud noises from cones ripping themselves loose from voice coils and surrounds, you need a LOT of speakers. |
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| REK |
| In reply to Bogie, you do not need many speakers, and you do not need a lot of equalization to get this sytem to work. I have heard IB systems with only one high Xmax 15" sound very loud very clean, and get down to 16 Hz. I only use one notch filter at 31.5 Hz with 5 dB of cut to get rid of a room resonance. See Audio Magazine December 1999 issue article by Tom Nousaine for review of four IB subwoofers with complete measurements of output, frequency response and distortion. At normal listening levels, my installation has a reasonably flat response down to 6 Hz, with a system impedance peak at 12 Hz, demonstrating a considerable response one octave below fs. |
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| ChocoHolic |
Hi Rek,
great that you are pointing out the room resonances.
Most normal living rooms have their three main modes all in the range of normal music bass.
Even large rooms do not bring down the modes low enough to ignore.
I.e. floor-ceiling 3m: 57Hz
length 7.3m: 23Hz, urghs also double is within normal bass range :bigeyes:
width 7.1m: 24Hz, + double
Altogether causing fat booming between 40Hz..60Hz, if the subs are in the wrong position. Up to now I am fighting the resonances just by finding proper positions for the subs.
But I am thinking about three notch filters (some simple OP amp solutions), which can be adjusted to the room. I do not have pratical experience with them. Normal room resonances have a Q between 5 up to 15. Do you think Q should be adjustable, or is it sufficient to settle it to Q=10 and just have the frequency + attentuation adjustable?
Bye Markus |
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| bremen nacht |
| quote: | Originally posted by ChocoHolic
[B
Altogether causing fat booming between 40Hz..60Hz, if the subs are in the wrong position. Up to now I am fighting the resonances just by finding proper positions for the subs.
But I am thinking about three notch filters (some simple OP amp solutions), which can be adjusted to the room. I do not have pratical experience with them. Normal room resonances have a Q between 5 up to 15. Do you think Q should be adjustable, or is it sufficient to settle it to Q=10 and just have the frequency + attentuation adjustable?
Bye Markus [/B] |
The problem in "curing" room response that way is that you'll end up with one hotspot where it sounds good. Move away from that spot and you'll wonder where all the bass went. Better to treat the acoustics of the room with bass traps (which might just mean strategically placed bookshelves, sofas etc.) |
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| ChocoHolic |
...right.
Of course, I also play around with arranging the furniture. But possibilties are limited.... also with combination of acceptable furniture set up and sub position I am not always happy. Furniture usually is of limited use, because wave length are much larger than furniture size. You mostly reduce Q, which is already helpful, but does not avoid the room modes. I would need to install two non parallel pseudo walls and hang down the ceiling in a strange way....
That's why I am thinking about filtering the signal.
From my understanding if the room resonances are filtered out, then most of these hot spot effects should be reduced to a low level. Simply because there is almost no signal anymore, which which could power into this resonances. Or does your experience show opposite results? |
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| richie00boy |
Markus, I have been considering an approach much the same as yours, after coming to conclusions much the same as yours. My lounge has to be lived in and I suspect that the floor-ceiling resonance is my main problem as I get a boom about 50Hz. I don't really care too much if using an EQ to tame the peak makes the sound worse elsewhere, as usually the sofa is where people sit.
As the resonance is a vertical one it seems equally bad throughout the room, so I think a bit of EQ should actually sound better for everyone anyway. |
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| REK |
| In reply to Chocoholic, I was lucky that the room resonance that I encountered at my listening position was right at a slider frequency of my 1/3 octave equalizer, 31,5Hz. Careful measurements should be made with a sine wave generator and a microphone that has reliable frequency response at frequencies below 100 Hertz. Many high quality microphones used for recording have intentional low frequency roll offs that can taint the measurements. The Panasonic capsule that Linkwitz uses is really pretty good in that range, and does go down to the 5 to 6 Hz region. I would recommend a parametric equalizer for subwoofer channel so that the room effects can be worked out. I had to modify my 1/3 octave equalizer since it has a 10Hz to 250Hz variable two pole high pass filter that cannot be bypassed. I added capacitors in parallel with the high pass section filters to make it 1Hz to 25Hz instead. I currently have it set at 4Hz. The other thing that you need to know is the actual low frequency roll off of the power amplifier you are using for the subwoofer channel. I had to select among my power amplifiers to get the one with the lowest –3dB frequency. The one I use measures 3dB down at about 1 Hz. This would be an ideal application of the venerable Crown DC300 amplifier that was flat down to DC! There are a few parametric equalizers out there like http://www.rane.com/pe17.html that have center frequency capability at 10Hz. |
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| ChocoHolic |
...back from holidays...
Yes REK, such parametric EQ is looking pretty much what I want to try. I think for my purpose three bandpass/notch filters should be OK.
Up to now I plan to set up that stuff on my own.
BTW: Why is the low cut of the power amp relevant?
As long as it is much lower than the room modes it should not affect the booming. (I think..)
In my case the power section will be a DC coupled class D amp.
Depending on the application, I plan to have a 6th order 1db ripple tschebbychef around 8 or 9 Hz - cutting off the subsonics. And additional may be a 'party power filter', = 2nd order butterworth below 40Hz, in order to allow high SPL without exceeding Xmax of the speakers. |
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| REK |
| quote: | Originally posted by ChocoHolic
...back from holidays...
BTW: Why is the low cut of the power amp relevant?
As long as it is much lower than the room modes it should not affect the booming. (I think..)
In my case the power section will be a DC coupled class D amp.
Depending on the application, I plan to have a 6th order 1db ripple tschebbychef around 8 or 9 Hz - cutting off the subsonics. And additional may be a 'party power filter', = 2nd order butterworth below 40Hz, in order to allow high SPL without exceeding Xmax of the speakers. |
I recommend having flexibility in setting the low frequency cutoff. From my experience, setting the control at a higher frequency than 9Hz removed some of the rumblings and thuds of door slams in CD's and DVD's that I played. There is one DVD movie that I saw that had the woofer cones moving below 4 Hz. If your going to strive for reproducing all that is on the disc, I recommend not limiting yourself to 8 or 9 Hz. There is plenty down there to experience. |
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