| pkgum |
I am making a subwoofer for a very high excursion 15" subwoofer driver called 15"HE manufactured by TC sounds
( http://www.tcsounds.com )This subwoofer must be flat to around 20Hz.
This subwoofer will be used for music, so which type of enclosure is best...ported or sealed?
TCsounds 15"HE Theiele/small parameters
Fs 25Hz
Qts .24 ?20% (I have no idea what '?20%' means)
Vas 132 Litres
Xmax 3 inches peak to peak
SPL 90 ?2dB
Sd 732cm2
There were some problems when designing a sealed enclosure for this driver. The enclosure volume came out very small at 17.2 Litres with a qtc of 0.707 However, the bass-cut off Frequency (F3) was too high at 73.7Hz I want much lower bass than this There must be something wrong
There were also problems when designing a ported enclosure for this driver. The enclosure volume came out small at 33Litres. However, F3 was too high at 47.93Hz. The tuning frequency was also too high at 37.93 Hz. I want a subwoofer that is flat to around 20Hz
Is there a minimum port diameter with a driver that has a Xmax this big? ( 3 inches peak to peak )
all this tech jargon is blinding me |
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| Super |
| First off, what enclosure design program are you using? I dont think that some of those numbers sound right. Also, have you seen the vas for this driver?! 132 liters! This is far beyond the reach of most DIYers for in home use, and it seems that this is strictly a subwoofer designed for in car use. Also, these drivers were designed to be used with a minimum of 500 watts power in mind. It seems that this driver was designed for high SPL output, rather than to go low. Their other 15 inch driver seems to be a far superior choice for in home use, which even still has a vas of well over 200 liters! Not only is it unlikely that you will make this driver linear down to 20 hz, but it is unlikely that you will have success in designing an enclosure, unless you have the driver specs measured, due to the shoddy +- 20% measurements that are given. |
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| ThomasW |
Well what do they say "been there, done that". :) This design is optimized for the HE15 in the smallest possible ported box. Tuning is 18.56Hz, I don't recommend tuning any lower.
If you have LspCAD or BassBox Pro 6, I can email you the model files, if I remember where they are.....
We found the published HE-15 T/S parameters are somewhat 'optimistic', as compared to our measurements of the drivers we received. But the driver still performs quite well. The Fs is really in the 28-29Hz range after extensive break in. The efficiency is closer to 84-86db in most enclosures.
You will need parametric EQ with any alignment. The driver has a pretty good size hump around 70Hz due to the VC inductance, (see the CLIO measurements page on the Klone project site for specifics). A Behringer DSP110P is a good inexpensive choice
I'm working an a klone of the Krell MRS. Will be using 2 BluePrint 1503. These are for all intents and purposes identical in performance to the HE15.
BTW, If you deside to go with a sealed box seriously consider using a Linkwitz Transform circuit to optimize the performance in a smaller box
The AS-15 Project
[Edited by ThomasW on 10-27-2001 at 01:50 PM] |
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| pkgum |
reply to super: First off i dont think these drivers are not just for car use. This is becuase they are used in the $28000 Krell Master Reference Subwoofer, the stryke project, and a "PR" subwoofer in the website below: http://www.diyaudio.com/forums/show...hp?threadid=244
For sealed enclosures, I am using a program called 'AJ Sealed Designer'downloaded from ajdesignsoftware.com
For ported enclosures, I use the website java calculator at:
http://members.tripod.com/XSSpl/Audio/KeeleBox.htm
I cannot use WinISD because it does not list the tc sounds driver in the database.
You are right, the other 15" driver is much easier to design..but it has only 2 inch peak to peak Xmax.I prefer the 15"HE because it has 3 inches Xmax. I can think of no other driver that comes this close in extreme excursion.
Note: I like ultra exursion bass drivers that go low and fast..so can anyone suggest any other driver that can compete with the 3 inch peak to peak Xmax TC sounds 15"HE?
(The NHT 1259 with 26mm peak to peak Xmax does not qualify)
Lastly, are u saying that it is impossible for me to make enclosures for the TC sounds drivers without special equipment because their parameters are not accurate enough?
Reply to thomas: HOW CAN U TUNE THE VENTED BOX TO 18.56hz WHEN MY READINGS SAY THAT THE TUNING FREQ for your stryke 15"HE driver should be 29.95hz? Is there something wrong?
And what is a parametric equaliser?? This is getting really technical |
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| ThomasW |
gum,
The Krell MRS uses a drivers similar to the HE15 that yes are made by TC-Sounds, but they have a less sophisticated design. Here's a pic of an open MRS so you can see their drivers. These are actually closer in design to the BP1053 but with a smaller magnet structure
'Topless' Krell MRS
BP1503
Stryke HE-15
Understand that the tuning of a ported box has nothing to do with the T/S parameters of the driver. The tuning is purely a function of the size of the box, combined with the size of the port and nothing else. The T/S parameters are needed only if you want to 'model' the performance of the driver in the box.
Now do you own a HE-15? If not, I doubt that you'll be able to buy one since the second special purchase was several months ago, and these aren't 'stocked' by Stryke
If you don't own a HE-15 take a look at the 1503 from http://www.blueprintdrivers.com. These have almost identical performance to the HE-15, are much cheaper and are in stock.
Enter the T/S parameters into WinISD. Or for a more accurate model if you have MS Excel download a copy of Unibox from http://www.danbbs.dk/~ko/ubmodel.htm and enter these HE-15 T/S parameters, they are from our testing. Chose 18 or 19Hz as the Fb for the design.
Fs: 28.5 Hz
Qms: 6.0
Qes: .345
Qts: .326
Vas: 106.7 L
Re: 6 ohm
BL: 27.3 Tm
no: .529%
1W SPL: 86 dB
Cms: .145 mm/N
Mms: 257 grams
Rms: 7.0 kg/s
Xmax: 22.85 mm
Sd: 720 cm^2
Vd: 6.5L total
PEmax: ~ 2000W
A parametric EQ is one that has variable frequencies and bandwidths instead of fixed ones like a 1/3 octave EQ.
If your now completely lost I'll help design a cabinet if you own a driver, either the HE-15 or BP-1503.
Hope this helps.....
Regards
Thomas
[Edited by ThomasW on 10-27-2001 at 10:53 PM] |
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| pkgum |
Nope..i havent bought the 15HE
I've decided to go with a vented box...is this a wise decision since the sub will be used for music...not home cinema
lve actually seen the BP1503 before. I thought it was one of those poor quality cheap drivers because of the dramatic price difference..stryke 15HE- $1000 BP1503-$219
what makes the BP so cheap? Can it produce clean bass to 16Hz? If so..i choose the BP..its so much cheaper
If you are saying the tuning of the ported box has nothing to do with T/S parameters, then what is the tuning freqenency used for?
Also...are there any guidelines or reasons that say which frequency you should tune the box to?
My aim is to build a subwoofer that can produce bass with good, strong and clean output to 20Hz..16Hz is even better because it can compete with pipe organs
F3 for the BP1503 is 37.6Hz----does this fulfil my aim?
Fb for the BP is 33.26Hz-----does this fulfil my aim?
Both frequencies are in the thirties...does this mean that it has limited output in the low 20Hz region?
Do you have more specs for the BP? The site does not list its nominal power rating, its Le (so-called Equivalent Voice Coil Inductance), and its "series resistance"
(all this technical jargon and mumble jumble).
[Edited by pkgum on 10-27-2001 at 11:39 PM] |
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| Super |
A vented enclosure can generally go lower than a sealed enclosure, but will tend to trade off "tightness" or speed in the lower octaves. Because of this, several music-only subs are sealed. However, if you want to go deep, I'd stick with the ported enclosure, and often, there is a minimal difference if a quality driver is used. (I use my ported SonoSub for music and HT alike, and found it to outperform many sealed commercial designs, including Velodyne and REL, using only a single Shiva driver)
Also, would you be willing to consider using stereo subs? I've often found that using two drivers that have similar performance to the bigger brother or more expensive drivers can often outperform the "bigger brother" when two drivers are used. If you were able to get your hands on the HE15, its not unlikely that you will get better performance out of two BP1503's, because each driver will only have to do half as much work, thereby decreasing distortion. Heck, for only $219 per driver, you could build four subs for the price of one! The odds of that one driver outperforming 4 drivers of comparable specs is highly unlikely. GRollins, for example, uses SEVERAL 12 inch subs (a LOT more than four), and achieves disgusting SPL's well into the 16hz range and beyond, despite using fairly inexpensive drivers. (Dayton Titanic drivers if I recall correctly)
As for things that make one driver cheaper than another, well, there are several things. Power handling is probably one of the biggies. There is also the amount of material that goes into making the cone, and also the quantity that the drivers are manufactured in. However, whether theres $800 dollars worth of difference is up to you. Personally, I'd go with multiple subs using the more inexpensive drivers.
[Edited by Super on 10-28-2001 at 12:05 AM] |
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| ThomasW |
gum
When the Stryke HE-15 preorder sales are offered the cost of the HE15's are approx $400ea. I paid less for my 2 because I bought in a presale a year ago December. My understanding is that there may be a few HE-15's available for $425ea
The $1000 'list' price is because Audiobahun the German company that buys the largest number of the drivers from TC-Sounds and sells them for $1000; told TC-Sounds that if Stryke stocked and sold the HE15 for $400 as a regular stock item, there would be legal trouble.
The BP10503 don't use custom designed parts and aren't built as a special order item. They use high quality stock off the shelf parts assembled properly. Also they don't have an aluminium cone and dust cap, double spider, or VC leads woven into the spider. So unlike the HE-15 it's not audio jewelry, but it's a very good driver at a very good price.
I dare say that in a A/B comparison (HE-15 vs BP1503) it would be very difficult if not impossible to tell the difference in a shootout. Understand I own both these drivers so I do speak from experience.
Note neither of these drivers will go down flat to 16Hz. They both do fine down to approx 18-19Hz though.
As I stated before the tuning frequency is related to the box not the driver. But you can't randomly choose an Fb and have any driver work well there. That's why both the HE15 and 1503 should be used in a vented box tuned to between 18-19Hz
Here is a copy of the DUMAX testing done on a BP1053
Super
It's important to look closely at the specs of these high excursion drivers. They have a Vd greater than 6 liters, that's equal to multiple 12"s. And they have power handling abilities that are correspondingly high as well. They certainly aren't for everyone's taste. But if a 'portable' sub having the ability to play at rock concert SPL's day in and out is needed, these will do the job. BTW, the sound quality of the AS-15 design is extremely good. I built one of the Stryke cubes with the PR's and wasn't impressed.
Also having 12-12" drivers isn't something exclusive to GRollins. This is my primary sub, a dozen Shiva IB config, just about 2yrs old. It's about 7db down at 10Hz from a reference level output of 100db. Max output is around 130db@20Hz. Measurements were made with a calibrated B&K 4133 using a CLIO system
[Edited by ThomasW on 10-28-2001 at 01:22 AM] |
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| pkgum |
some questions...
My aim is to build a subwoofer that can produce clean strong bass to around 18Hz
F3 of the BP1503 enclosure is 37.6Hz----is this alright?
Fb of the BP1503 enclosure is 33.26Hz-----is this alright?
Both frequencies are in the thirties...does this mean that the subwoofer has small output in the low 20Hz region?
To thomas: How did you know that u should tune the BP1503 enclosure to 18-19Hz?
Are there any guidelines as to what frequency i should choose to tune the vented enclosure?
You said the tuning of the ported box has nothing to do with "T/S parameters" (tech jargon), then what does the tuning freqenency indicate? |
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| ThomasW |
gum
| quote: | | You said the tuning of the ported box has nothing to do with T/S parameters, then what is the tuning freqenency used for? What does it indicate? |
As I've stated, Fb indicates the frequency the box with its port is tuned to. Think of a ported box as something similar to pop bottle, and you're blowing across the top. If the size of the box, combined with the diameter and length of the port are tuned to 18Hz, when you blow across the port a 18Hz tone is produced. Now this is a bit over simplified.....
Fb = Enclosure resonance (usually for bass reflex systems), in Hz
F3 = -3 dB cutoff frequency, in Hz
To better understand this go to the 'Calculate Your Vent Length' section of the website you're using for ported designs
http://members.tripod.com/XSSpl/Audio/VentCal1.htm
Now type in quantity of ports =1
Enter volume of enclosure =8 ft3
Enter desired tuning frequency = 8Hz
Enter desired port diameter =6"
You'll get a port length of 25.01".
This is how you tune a box to 18Hz without having or using any T/S parameters. Now I'm not suggesting that this is how to design a sub. It's just an example of how to tune a box.
All woofers roll off as the frequencies drop. The port in a reflex design only serves to add some additional boost around the tuning frequency (Fb). Where as a sealed box rolls off at a fixed rate.
Depending on the amount of room gain, EQ will most likely be required to get flat response from any sub down to 18Hz.
You might want to pick up a copy of "The Loudspeaker Design Cookbook" by Vance Dickason. This is a good book to get a grasp of the what/why/how of speaker design.
Regards
Thomas
[Edited by ThomasW on 10-28-2001 at 09:37 AM] |
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| Super |
Thomas: Just a quick note. I'm well aware of the 12 Shivas Dancing project. I was just referring to multiple drivers in separate cabinets, for a true stereo setup, not necessarily a multi-driver isobaric setup. Sorry for the mistunderstanding :)
Also, I am aware of the displacement of these drivers. However, I think that the use of multiple high quality drivers can be more linear in lack of distortion when EQ'd properly than a single driver being pushed harder. |
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| ThomasW |
Bryan
I certainly agree that multiple drivers in theory are better than one of the high excursion 15's. But I was quite surprised as to how clean the high extension drivers are, even when driven to extreme SPL's. The big IB is of course the best sounding sub I've ever heard, regardless of cost or construction constraints. It's not real 'mobile' though :)
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| blmn |
pkgum,
This woofer seems to me an unity for bass reflex for car SPL use, as Super said. It seems to me you really want to use this unity as well.
So, why don't you use this woofer in a bandpass configuration? Using this configuration some negotiation with volume, efficiency and f3L and f3H is possible. Many computer programs can calculate the best frequency response for you.
Regards, |
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| pkgum |
NOTE
Should I trust the T/S parameters on the DUMAX report or the different parameters on the blueprint website.
...........................................................
question
F3 of the BP1503 enclosure is 26.06Hz...does this mean that the finished subwoofer guadually has small output in the tones below 26Hz? But according to thomas this subwoofer should have good output to 18Hz, but the F3 for the enclosure is higher, at 26.8Hz.
They say that in ported enclosures the output drops sharply below F3. Note..The F3 is calculated using the report thomas supplied
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blmn
Bandpass enclosures are beyond my reach. Theyre harder to make and need more time than ordinary vented enclosures. I like my design to be SIMPLE |
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| ThomasW |
gum
A ported cabinet must be tuned to 18Hz, to get output at 18Hz, forget the F3.
Sorry but I don't have the time or patience to give an extensive online tutorial in basic subwoofer design.
Consider doing one of 2 things, either trust the info I'm giving you, or purchase a good loudspeaker design program that shows the effects of ROOM GAIN on the performance of a sub. I suggest LspCAD $150.
Here's a plot of the Styke cube measured by Tom Nousaine. As the plot shows the HE-15 will have good output to 18Hz. This is VERY similar to what you would get if you build the ported AS-15 design
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| pkgum |
NOTE
Should I trust the T/S parameters on the "DUMAX" report or the different parameters on the blueprint website.
...........................................................
QUESTION
F3 of the BP1503 enclosure is 26.8Hz...does this mean that the finished subwoofer guadually has small output in the tones below 27Hz? But according to thomas this subwoofer should have good output to 18Hz, but the F3 for the enclosure is higher, at 26.8Hz.
They say that in ported enclosures the output drops alot below F3. Note..The F3 is figured out using the DUMAX report that thomas supplied
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| f4ier |
maybe I can help :)
Thomas is right, the resonant frequency of the box does not have anything to do with the driver. You could put any driver in an existing ported box with a particular resonant frequency and it [the box] will still have the same resonant frequency. The T/S params. on the other hand are used by humans/simulators to construct a mathematical or computer model of the driver unit. They also guide you in designing an appropriate box... given your design goals such as (maybe) maximally-flat response.
There is no one "correct" Fb to which your ported box should be tuned -- this should have been mentioned in your book. Ultimately, it will depend on your design goals, which in turn is usually dictated by your listening room's acoustics. If you have calculated an Fb of 33.26Hz, it could be that your book is recommending an SBB4 alignment or maybe it [the book] is based on an enclosure-loss-less set of equations (or something else). The Loudspeaker Design Cookbook that ThomasW has mentioned discusses the SBB4, SC4 and QB3 alignments to name a few. It really is a good book.
Regarding your urgent question. No, not necessarily -- it simply means that the BP1503 on an IB or sealed box will roll off a bit early. But this is where the BP1503's huge Xmax comes in to assist it in going as low as 18Hz. With more amplifier power and a Linkwitz Transform circuit, the BP1503 can go low and loud with sound quality to boot.
http://www.pvconsultants.com/audio/frdgroup.htm is a great link for box simulators including my beta program (I know, that's a shameless plug :D ) and a Linkwitz Transform spreadsheet.
A good program to approximate your room's acoustics is Adire Audio's version of lspCAD, which can be found at http://www.adireaudio.com/software.htm You can use it to plot your room's effect on the sound.
Good luck :)
Isaac |
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| ThomasW |
gum
DUMAX testing is the most accurate loudspeaker testing available.
Also please STOP fixating on the F3. All drivers and alignments roll off. ROOM GAIN helps boost the lowest frequencies. Also you will need to use a parametric EQ to get flat response to 18Hz from the ported enclosure. Linkwitz-Transform circuits are designed for use with a sealed box, they allow adjustment of the Qtc. BTW Look at the before and after EQ CLIO plots on the AS-15 project website. These show how the frequency response is effected by the equalization
FIY, the design team that created the AS-15, (this being JonMarsh and myself) have 75 years of combined loudspeaker design experience. Yes, that does mean that we're old f*rts :) and we certainly know what we're doing!
The AS-15 design, built either with the HE-15 or BP1503 is designed to be the best performing high output 15" ported sub available. There are no compromises what so ever in this design.
Jon is making complete set of AutoCAD drawings for the AS-15, we will post them to the website for download. It will be a couple of weeks before they are completed.
That's all for tonight
Thomas
[Edited by ThomasW on 10-29-2001 at 02:48 AM] |
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| pkgum |
For now i had made my own basic sub
Vb = 2.953cb.ft (bracing, driver displacement, and damping not included yet)
F3 = 26.06Hz
Fb = 18Hz according to thomas
Port diameter = 8 inch (since programs says that minimum port diameter is 7.85inches)tuned to 18Hz
however.....
port length = 135.73 inches....there is something wrong..can anyone tell me what to do |
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| ThomasW |
What's wrong is that you can't make the box any smaller than about 6.5-7 cu ft NET internal volume. And you need to use a 6" dia flared port not a 8" dia one
Did you read the text in the AS-15 project page?. It states the size of the box, the diameter and the length of the ports. And the CLIO testing proves that the design functions at the desired Fb of 18.56Hz.
Making any changes in the design will result in a sub that doesn't perform up to the full potential of the HE15/BP1503
Edit:
Just to avoid any further confusion. The Lightning Audio port flares are the only 6" dia flares available. They need a pipe that has a 6.25" OD for a good fit. The PVC pipe I used has a 6.25" OD and 5.75" ID, so for software modeling purposes use 5.75" as the diameter of the port. The 22.5" long port PVC tube combined with the length of the 2 flares gives a total port length of 25.5". That tunes the AS-15 box to 18.56Hz.
Note, a nominal 6" dia port with flares, will flow virtually as much air as a 8" diameter port without flares, and it can be much shorter.
[Edited by ThomasW on 10-29-2001 at 12:56 PM] |
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| pkgum |
The reason why i veered away from the as-15 cabinet is because one cabinet cannot suit two different drivers, in this case, the HE 15 and the BP1503. The two drivers are similar, but they are not identical
Yep, i did look at the as-15 design page...however I need more detail on the design..not construction...so lam waiting for the CAD drawings
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A QUESTION
tell me how you got around 8cb.ft for the as-15 design instead of my calculated 2.953 cb.ft
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Do the ports really need to be flared? I just want to save the money in buying flared ports because lam from a foreign country. If the ports werent flared then what is the port length? |
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| ThomasW |
| quote: | | The reason why i veered away from the as-15 design is because one design cannot satisfy two different drivers, in this case, the HE 15 and the BP1503. The two drivers are similar, but they are not PERFECTLY identical |
Two people have posted in this thread that box tuning had nothing to do with the driver. You are making assumptions based on speculation not facts. The AS-15 box is just fine for either the HE-15 or BP1503.
| quote: | | Yes, i did look at the as-15 design page...however I need more detail on the DESIGN..not construction...so lam waiting for the CAD drawings that you refered to me |
The AutoCAD drawings are specific to the construction.
| quote: | A QUESTION
briefly explain to me how you got around 8cb.ft for the as-15 design instead of my calculated 2.953 cb.ft |
I have no idea how you got your number. But to get a box with a 6" port tuned to 18Hz, a 8cu ft box is needed. The AS-15 box is slightly smaller because the actual port size is 5.75"
| quote: | | Do the ports really need to be flared? I just want to save the hassle and money in buying flared ports because lam from a foreign country. If the ports werent flared then what is the port length? |
If you want the best performance possible use the flared ports. I find it quite odd that you were willing to spend $1000 for a HE-15, but want to save $50 for flares? The port length as I have previously posted is 25.5" with or without flares for the 5.75" ID port in the AS-15 box
Finally, all the info you need has been posted several times to this thread. If you can't comprehend what's posted then you shouldn't be trying to build this subwoofer right now. Buy "The Loudspeaker Design Cookbook" and LEARN the basics about speaker design. Filling in the blanks in a freeware program isn't going to teach you the fundamentals of loudspeaker design theory. The HE-15/BP1503 are sophisticated drivers. They can only be properly modeled with a quality software program and a solid understanding of loudspeaker design.
Regards
Thomas
[Edited by ThomasW on 10-30-2001 at 01:16 PM] |
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| baby_huey0 |
Being an newbie to the world of diy audio I can understand where the confusion can come from....
But Thomas knows what he is talking about, go to his page and there is tons of info there. He has said everything that is needed to build the subwoofer using either driver. Patiences will help in building a great speaker! I learned that quickly in my early design stages talking to Tony Gee. The AutoCAD drawings will most likely depict the exact design and shape of the box. Wait and get those before you try to get the exact internal volume. Considering the approximate external volume of the cabinet is 12ft^3, with the bracing, driver, and port that would bring the internal volume to about 8ft^3. If you still are confused read all the messages in this tread a few times and take the time to think about what was said, that should clear a few things up.
[Edited by baby_huey0 on 10-30-2001 at 11:13 AM] |
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| ThomasW |
Huey
The dimensions stated on the website are OD. The cabinet has 1-1/2" thick walls, except for the front baffle
The ID of the AS-15 cabinet is 15"X26"X32" so it's a little over 7cu ft before deducting for the port,driver,internal bracing, damping, etc.
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| baby_huey0 |
| I'll just stick my foot back in my mouth now... |
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| pkgum |
does the port length include the thickness of the front baffle or do u need to add the thickness of the front baffle to the port length?
Does anyone object to what is being said in the following passage?
For those who prefer ported enclosures what is your reaction to this passage?
PASSAGE
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Q4.15 Some people say Duntech speakers don't produce enough bass, why is that?
If there is no bass in a recording then there should be no bass in the playback. Some speakers seem to produce some bass out of thin air, even while playing a soprano singer. This is because stray bass sounds in the recording are being blown up by the boosted bass. If you look at the measurements of many loudspeakers they splice their low frequency measurements onto the mid and high frequency measurements in such a way as to make it look "right" but when you listen to them you can tell that something is wrong.
The other problem is that many speakers rely on a pure ported output. The correct way to do it is to use a combination of ported and sealed output which Duntech have found is the only way to create satisfying and accurate bass (which is why the entire Gemstone range and the Prince use this operating principle!)
What happens in a pure ported enclosure is that the sound is produced by both the bass driver and the port. The sound from the port is delayed in time because the sound is actually the result of a plug of air in the port "bouncing" on the air in the enclosure. This takes some time to happen and the lower the frequency the greater the delay (in technical terms it is called "group delay"). This delay produces a muddying of the bass. For many people, unused to real music in a real venue, this becomes the "normal" sound of bass and when they don't hear it from a speaker they assume there is not enough bass. The fact of the matter is that our game is to reproduce music, not the distortion of other manufacturer's speakers.
Q4.16 This criticism of ported bass would apply to your speakers too wouldn't it?
Many of our speakers don't have porting at all and use a sealed enclosure. To get very low bass this way you need a really big enclosure. Which is exactly what we do in most of the Classic series.
If you want to make a smaller speaker and still have full range then you need to produce bass another way. This is usually done with a ported arrangement tuned to a rather high bass frequency like 50Hz or 60Hz. The group delay effect which produces a thick pudding like bass is worst at the resonant frequency of the port so this kind of design is fatally flawed.
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| ThomasW |
Of course you add the thickness of the front baffle to the length of the port, if the port is mounted behind it. This is just common sense.
As for the Duntech statement; is there something that makes you think they don't have a marketing agenda like any other mfgr?
As far as GD (group delay) is concerned, it's probably audible if there is enough of it, and it's occurring at the higher bass frequencies. But a properly designed system usually doesn't have lot's of GD; and if it's occurring around 20Hz, I doubt that many people could hear it. But GD certainly isn't the major cause of 'muddy bass'. That's caused by poorly designed drivers (meaning cheap) and or poorly designed cabinets.
Ported systems generally speaking have a higher Qtc as compared to sealed ones. Sealed systems with a proper box (meaning BIG) can be built to a Qtc of 0.5. This is considered critically damped. Now it is possible to make ported systems with low Qtc; but I certainly not going to discuss that here, when there are problems just figuring out how to tune a normal ported enclosure.
Just so you have a basis for understanding my statements; I've been using separate high performance DIY subwoofers since 1972. I used to own a high end audio salon. We sold Magnepan, Mark Levinson, Quad, Accoustat, etc, etc. So I've had 30 years of experience listening to commercial and DIY subs in every price range and every cabinet type. And in that 30 years I never heard a sub that surpasses my big IB (infinite baffle). So naturally I use it's performance as the basis of comparison for any other sub I hear.
As built, the AS-15 offers, about 90% of the sound quality of the big IB; and with adequate amplification it will shake my entire 2500 sq ft brick house with an 18Hz tone. This using only a single 15" driver in a relatively small ported box. So does that give you an idea as to how good it is? This opinion BTW is shared by my Klone-Audio design partner JonMarsh, who also was a partner in the audio salon, and is a twice published member of the AES (Audio Engineering Society)
There a many people that believe the Stryke cube (HE-15 with 3 PR's) is the best sub around. I built one and was quite disappointed in the transient response, and the lack of detail in the lower octaves. The AS-15 design came about after careful consideration as to obtain the best performance possible from the HE-15 driver.
[Edited by ThomasW on 10-31-2001 at 01:38 AM] |
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| pkgum |
bits of the passage is still true..which you had answered for me.
dont assume that lm not trusting your info.
Before I start ordering drivers, MDF, etc I try to ask as many questions as i can to people. |
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| pkgum |
Many subs are built as cubes.
I ve heard that cubes are the worst shape to build a loudspeaker
Why doesnt this apply to subs? |
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| BAM |
| In a subwoofer, the wavelengths of the bass notes produced are too long to fit inside the box, so there is so trouble with internal standing waves. Now, if you were to design a full-range box, with a woofer, mid, and tweeter, you would run into some troubles, but not at the bass frequencies produced by the sub. |
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| Super |
| When building a sub, as mentioned, the cubic/rectangular shape isnt of importance. Lack of resonance is the key. Rectangular/cubic shaped boxes are easier to brace and allot a greater amount of bracing than several other types of enclosures. Cylinders are also becoming popular, because the shapes is self supporting. When internal force is exerted, its exerted equally within the enclosure, making it extrememly rigid and with minimal resonances. However, some people may have problems with the entire enclosure moving around the floor (like the HSU subs) because of their relatively light weight. Spherical enclosures would also have their benefits, but they would be particularly large and difficult to couple to the floor. |
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| pkgum |
| can someone tell me detailed web pages that can teach ppl about how to make subwoofer? |
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| f4ier |
If you don't want to spend money for the above-mentioned book by Vance Dickason, try a nearby engineering library or architecture library. They might have a copy of such great books.
Isaac |
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| pkgum |
thomas and issac,
I find Unibox with the box simulator thingy useful. Can only both of them make a good subwoofer?
the Loudspeaker Cookbook costs $75US in my country |
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| ThomasW |
Unibox is a very good and accurate program.
Where are you located?
$75 for 'The Cookbook' seems insane! The current edition is #6. Some suppliers have put older the 5th edition on sale just to clear out inventory.
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| baby_huey0 |
| The only place I could find to buy the cookbook in Nova Scotia was to order it from Solen. It cost about $63 cdn plus shipping and plus taxs(15%in NS). Thats about the same amount I would have to pay. I found it easily at my local library though. |
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| pkgum |
lm from Australia
thomas,
can you tell me the 'Le', the 'series resistance',
and 'the nominal power rating' of the BP1503 to
fill in the blank spaces in the Unibox? I cant find them in the DUMAX report
everyone,
What does UNIBOX mean by 'leakage'...enclosures are supposed to be airtight..aren't they?
And what the heck is alpha?
[Edited by pkgum on 11-01-2001 at 03:36 PM] |
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| f4ier |
I'm from Australia as well :) All loudspeaker-related material (except for Acoustical Society of America journals... last I checked) is now located at the Univ. of Sydney's architecture library since Audio Eng. is taught there. I remember back in '98 seeing non-Univ. of Syd. students being able to borrow books... or maybe my eyes were deceiving me 'cause of multiple exams and assignments at the time :D
The LDC by V. Dickason is only AU$40 (around US$20) at http://www.jaycar.com.au For less than AU$20 (10 cents/page last I checked), you could photocopy the whole book and put it on plastic binders.
| quote: | | I find UNIBOX with the combined box simulator thingy very useful. Can only both of them create a accurate and good sounding subwoofer? |
UNIBOX is a more finalised program and I even think it has already been coded for large signal analysis (as well as small-signal analysis). My box simulator? If so, it is still in its infancy due to school work etc. Large signal analysis, better interface and more features soon. Try lspCAD, which is a powerful simulator, if you haven't already downloaded it.
| quote: | | What does UNIBOX mean by 'leakage'...enclosures are supposed to be airtight..aren't they? |
Even with an airtight enclosure, the driver itself, the port(s), passive radiator(s), speaker terminal(s) etc. can introduce leaks, which lower system performance. Typical values are 5, 7 and 15 -- higher figure being less 'leaky.'
| quote: | | And what the heck is alpha? |
Alpha is usually the driver volume, Vas, to enclosure volume, Vab, ratio.
Isaac
[Edited by f4ier on 11-01-2001 at 06:25 PM] |
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| ThomasW |
Hi
The Le isn't needed for subwoofer designs where there is an active XO. But since I'm such a nice guy I measured one of my 1503s and the inductance is 4.28mh
The power handling is in excess of 1Kw, so for your model just use 1000 watts |
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| pkgum |
BP1503 t/S parameters
fs ...25.52Hz
Re ...3.9ohm
Qms ...4.46
Qes ...0.41
Sd ...737cm2
Vas ...92L
Xmax peak ...25.86mm
Le ...4.28mH
Nomimal power ...1000W
series resistance ... 0.2ohm
basic 18.56Hz tuned subwoofer
port inside diam. ...5.75inches
port area ...167.64cm2
port end correction ... 0.519
desired Physical Vb ...200L
Absorption, Qa ...20
Leakage, Ql ...15
Port, Qp ...140
Alpha, a ... 0.434
Vb ...212L
Fb ...18.56Hz
h ... 0.727
F3 ...17.37Hz
Response peak ...0
Peak at ...none
Port min diameter ...20.14cm
Port length ...61.58
Port 1. resonance ...249Hz
Vb + driver displacement + two large internal braces = 234L
INTERNAL dimensions are 38cm*77cm*80cm (W*D*H)
Flared ports
Parametric EQ
Unibox states that minimum port diameter is 20.14cm while my one was 5.75inch (14.6cm)
Anything seriously wrong or can you just ignore it?
thomas
How is this different to your as-15 subwoofer? |
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| ThomasW |
The design looks ok. I imagine Unibox's bigger port suggestion is to decrease the potential for port compression. Using a port with flares allows a smaller port to flow as much air as a larger one without compression. Using a smaller port means the box itself can be slightly smaller since the port takes up less space.
Ported designs somewhat forgiving, and can tolerate about a 10% 'fudge factor' before there's a major change in performance. I recommend building a prototype; so as to test the real world performance of the design before making serious investemt in finish grade materials. This though time and labor intensive, can save $$$ in the long run, particularly for the novice. |
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| pkgum |
everyone,
How can this design be improved in your opinion?
[Edited by pkgum on 11-02-2001 at 03:44 PM] |
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| ThomasW |
| quote: | | How can this design be improved in your opinion? |
Well IMHO it can't :) |
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| pkgum |
| Do you recommend me start ordering MDF,drivers, etc and start building the subwoofer using this basic design done by Unibox? |
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| ThomasW |
Yes certainly order the driver. Get the Lightning Audio flares, only if you can find PVC that has a 6.25" OD. Now the ID may vary depending on what you have available. So the final port length may need to be altered depending on what size pipe you're able to find. If you can't find PVC with a 6.25" OD, then don't order the Lightning Flares
Don't build the box in advance of having the driver; and until you know you can duplicate the port with flares, or know what size straight port you will be substituting if getting the flares isn't practical.
When deciding on the dimensions of your box, it's important to have the inside opening of the port approx 6" away from the back wall of the cabinet. Height, width, aren't critical, so they can be what you like, as long as the net interior volume is within the needed parameters, and the cabinet depth is be sufficient for 6" of clearance behind the port.
Once you have everything in hand, driver, port, etc, then I'll run LspCAD calculations from the final net internal volume you get. You can compare them to what you get with UniBox. They should be very close.
[Edited by ThomasW on 11-02-2001 at 10:41 PM] |
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| pkgum |
Here is a quote from a previous post:
"Making any changes in the design will result in a sub that doesn't perform up to the full potential of the HE15/BP1503"
I have a very different design. Is the as-15 is the only way to go to get the ultimate performance out of the driver? If so, then give me its physical Vb excluding driver displacement,bracing,damping,losses, etc. From this Vb I'll make a similar as-15 design-- the only difference is that it is simpler in the woodwork.
Or is the design I created with unibox is enough to get the ultimate performance out of the driver?
Say that unibox calculated your port length is 11". The front baffle of your designed subwoofer is 1.5 inches thick. The port is mounted through the hole you cut in the front baffle.
Should the port be cut and mounted in the subwoofer with a finalised length of 12.5"(plus the thickness of the front baffle) OR to a finalised length of 11"(ignoring the thickness of the front baffle)? |
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| ThomasW |
Ok first let's not get too literal....
And second why has this conversation starting over again? You have a design and it's very similar to the AS-15.
The AS-15 was designed to obtain max performance from the smallest reasonable sized box, with no compromises. This goal was achieved.
I already answered the port behind the baffle question. Of course IF the ported is butted to the baffle, the hole in the baffle adds to the length of the port. This is common sense. However it's a better idea to have the port pass through the baffle. This way the baffle gives added support to the port.
The cabinet work for the AS-15 is part of the design to get the best performance. It's not that difficult. The cabinet MUST be sufficiently braced. If not, the driver is so powerful that serious wall flexing will result, and the performance will suffer.
Why? Well if the walls of the box are vibrating, then they are acting like the cone of a speaker, and the sound waves they generate will cancel those made by the woofer.
Also you need to understand I don't have hours and hours of time to walk you through every question you can think up regarding loudspeaker design. That's what books are for. If you want to build a close copy of the AS-15, I'll give you assistance. |
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| pkgum |
I'll try borrow the book 'The loudspeaker Cookbook'
then I start ordering everything and begin the practical work |
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| pkgum |
| Can you buy high power car audio amps to power the subwoofer? Car audio amps are much much cheaper than the samson,qsc,etc amps. |
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| f4ier |
| .... but you'd still need a hefty power supply to satisfy the current demands of a quality car audio amp, which are actually expensive, btw. http://www.jaycar.com.au offers a 40-amp [which is not enough] supply for AU$350. For that price, you could already buy a 200W or so plate amplifier :) |
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| pkgum |
My subwoofer will be used at home, so I have all the power I need..I dont care if the power supply is hefty or not, as long as the thing can power my sub properly
The car audio amps I see are 500W and only cost $150-$200US
I think I need to clarify some things...I need an amp that is preferably around 400watts(no less than 300). The cheapest way to get to this is by an car audio amp. The samson and qsc amps thomasw mentioned are around $350US!!My budget for the whole subwoofer is $600US ($1200AU) and the amp costs $350US!!!
There are many car audio amps around the same power that retail for $200US-a good saving
can anyone suggest good sounding, powerful, amplifiers (plate or professional - but not car) that has 300W+ power, that retails for less than $300US, that can power my low efficient BP1503 sub?
[Edited by pkgum on 11-04-2001 at 02:22 AM] |
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| f4ier |
That's the thing with car amps -- assuming a quality and cheap one is available, for it to perform to its full potential with little distortion, the AC-DC power supply would have to be hefty in terms of ampere rating. Such power supplies are quite expensive thus negating the concept of "cheap" amplifier in the first place :)
AFAIK, http://www.jaycar.com.au is the only one with a 350W @ 4ohms amp for AU$429. I haven't seen anything more powerful than that one which is locally available. Perhaps guitar shops have some more powerful amps (just make sure the amp can reach -3dB at 5Hz or 10Hz). If you're handy with a soldering iron, you could build your own amps -- http://www.sound.au.com
If only the subwoofer you're planning to order (the BP1503?) had dual voice-coils, the Electronics Australia Pro3 stereo power amp would be enough for your needs. I'm not sure though if the same amp is bridgeable, I never had to bridge mine.
Edit:
Also, I seem to remember that it was Silicon Chip magazine which published a 500W amp. Maybe a local library still has a copy of the issue. Dick Smith Electronics used to sell kits of the 500W amps. They were on clearance sale last year for only AU$100.00 each!! I couldn't forgive myself for missing the sale :D
:)
Isaac
[Edited by f4ier on 11-04-2001 at 03:09 AM] |
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| ThomasW |
gum
No don't mess around trying to use a car amp.
The BPD-1503 has a single nominally 4 ohm VC. So any amp that is stable driving a 4 ohm load, and delivers 500+ watts will be fine. It can be a monoblock or stereo amp strapped in to mono, doesn't matter
Start by looking at the pro sound shops in your area for used gear. Crest, Crown, Ashely, Rane, etc, are companies that make excellent gear, and the stuff is built like a tank. I don't know if there are local AU companies that make amps like these, but if there are then certainly consider their products as well.
A dedicated sub amp doesn't need to deliver super clean power. Primarily it just needs to deliver alot of stable power.
Also understand that many of the lower cost pro amps are fan cooled. So if you're bothered by the constant sound of a fan running then buyer beware.
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| Super |
| Dont forget to check out ebay as well. Decent pro sound and high wattage amps are always popping up on there, and can often be had for under $200 US. |
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| f4ier |
I'm not sure of the reputation of those online stores you have mentioned, but if they check out ok, the Fleco amp looks better.
But... the difference between the 350W plate amp I mentioned above and Fleco amp is only 2dB at the most. Then again, there's the issue of headroom (I'm not helping, am I :D ) Personally, I wouldn't go through all that trouble in ordering the amp online. Moreover, if the thing suddenly stops working (Murphy's law?), think of the hassle in returning and chasing up warranty... overseas service even!
I still think the EA Pro3 stereo power amp is the best deal if you're handy with a soldering iron. Ask someone like Rob Evans at EA -- the Pro3 designer, I think -- or someone at Jaycar how the Pro3 could be safely bridged. If not, the 350W plate amp is the second-best thing :)
Isaac |
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| pkgum |
I dont know how to solder an amp..so the EA is out of the question...
I would have bought the jaycar if the frequency response wasn't 20Hz-160Hz. This is absolutley pathetic...My sub sub is destined to reach into the 18Hz area..even 16Hz..and the jaycar can only go to 20Hz
The power amps Ive mention go down to 10Hz +/-3Db |
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| f4ier |
In that case, the Fleco would be number one on that list when comparing RMS ratings :)
Isaac |
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| ThomasW |
You'll want to be careful with the so called 'DJ' amps. Pyle, Pyramid, Speco, GemStar, etc. They inflate the output rating frequently listing peak power instead of RMS.
The Fidek units are ok, they do have a fairly loud fan.
The only reason I mentioned Crown, Crest, and Ashley, is that often those amps can be found used. And they're usually a good buy, given the very high build quality |
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| pkgum |
Someone mention a good cheap model of so-called parametric EQ..preferably sold locally at Australia to avoid shipping costs,etc.
Isaac and everyone who are familiar with Jaycar,
Does Jaycar sell "parametric" equalisers? |
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| ThomasW |
| I assume Behringer products are sold buy the pro audio shops there. If so, the DSP1100P soon to be replaced by the DSP1128P are great buys. In the US there is nothing cheaper than these, US$130 buys a DSP1100P |
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| pkgum |
| will the 'treated' foam surround of the BP1503 rot like normal foam surrounds or is it really durable and wont rot for 15+ years? |
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| f4ier |
I'm totaly oblivious to pro gear here in Australia (or anywhere else for that matter :) ) 'cause I always go the DIY route whenever practical. The only parametric equalizer I know of is in kit form and it is available from http://www.altronics.com.au (it was published in the July '96 issue of Silicon Chip magazine, btw).
The design has three sets of Q, frequency and cut/boost controls and each frequency band can be easily modified for subwoofer duty (the default design is for fullrange duty). The kit retails for AU$45.00 and it requires a +/-15V power supply, metal case etc. I'd say AU$100.00 should be enough to build a working prototype.
Regarding foam, with proper care the speaker can last for quite some time even for 15+ years. However, I doubt that you can resist the urge to build another monster subwoofer within a few years (or months?) after you complete this one :)
Isaac |
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| argo |
Does anybody know how to design variable bass boost and variable phase control? I know many commercial amps use the variable boost and at least some of them also variable phase adjustment control but I have'nt seen any DIY approaches/shematics yet.
argo
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| f4ier |
argo, try this link -- http://www.geofex.com/Article_Folders/EQs/paramet.htm
I could send you schematics and PCB artwork of a graphic equalizer and/or parametric equalizer, if you're interested.
As for information about variable phase control, I haven't seen any yet, sorry.
Isaac |
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| pkgum |
| Is using 2 BP1503's in a sealed isobaric(push-pull) thingy like the sunfire, Krell, and M&K subwoofers a good idea? they say isobaric designs reduce distortion, etc, |
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| argo |
Isaac thanks for the link and PCB artwork offering.
Hmm...the gyrators. Indeed I'm recalling now, that I have heard using something similar before. I just hoped there is some kind of simpler approach, than using simulated inductors.
As for variable phase control, I believe one is used in Apex Senior plate amp or at least that’s what they are claiming. They have schematic of x-over and amp on their web page but I haven’t had possibility to simulate this because I have trashed my old circuit simulator software.
argo
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| f4ier |
argo,
The simplest way, but the most expensive way at that, would be to use actual inductors :D
Which circuit simulator do you use? I found PSPICE (I use Eval 8 version) to be very flexible, its Probe program is especially a powerful tool. But I use Circuit Maker also for its vast device library.
Do you happen to have a direct link to the apex amp schematics
Thanks :)
Isaac |
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| argo |
Yeah but you need to have a variable inductors!?
I have tried various demos like Circuit Maker, Protel etc. With their usage period or/and component quantity/board size limitations, I got tired of them taking up so much hard drive space, so I trashed most of them.
Apex Senior amp schematics I talked about is at: http://www.apexjr.com/Apexsenior.htm
argo
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| f4ier |
Which is why such equalizers with inductors would cost a mint :D Why not use gyrators?
Protel does require a big chunk of HDD space. But PSPICE and Circuit Maker are both well worth the required HDD real estate. Electronic Workbench is a baby compared to the other two -- always complaining about transient and convergence problems.
Thanks for the link! I might check it out now :)
Isaac |
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| ThomasW |
gum
The Krell, M&K, etc, aren't isobaric configurations. And the drivers aren't wired push-pull. If they were push-pull they would cancel each other out since they share the same space.
The primary benefit to a true isobarioc config is the reduction in cabinet size do to the decrease in Vas.
Making a true isobaric config with 1503's would be difficult. They can't simply be bolted together in a 'clamshell' manner because the surrounds are to large. An adapter ring would be necessary to avoid having the surrounds rub together. |
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| BAM |
If you absolutely must fit a woofer box into a really small space, like a car, and must have lots of power handling, then Isobaric might be a nice way to do it. But for large, open listening rooms, or even the occasional bedroom sub, I would not waste my money on more than 1 woofer per hole. I already tried that, and there was no real advantage to having push-pull woofers. It was easier to bottom them out. I would not recommend using isobaric woofers in anything but a sealed box to prevent the woofers from bottoming out so easily.
I'm not lucky enough to have a separate listening room. My listening room/home theater/office is in my bedroom. When I go away to college, that will be my dorm room. My BPD1001 subwoofer will only be 12 inches wide, so it can fit up against the side of my desk or between my bed and the wall, without needing to be an isobaric configuration. |
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| pkgum |
| What actions do subwoofer makers take to reduce distortion? |
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| ThomasW |
Having a 2 driver cabinet with one woofer facing in and one facing out will result in the cancellation of the harmonics. But understand this isn't 'push-pull', nor is it isobaric
Also the current generation of woofers/subwoofers generate very little even order harmonics, so this type of mounting really isn't necessary. |
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| pkgum |
| is it possible to buy an accelerator servo thingy (the one they use in velodyne) and install it in the woofer. Are there any threads or web pages that show you how to do this? |
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| f4ier |
It's probably an easy circuit to implement, though I haven't thought about it much simply because there's a better solution -- build better subs with *quality* drivers... more of these would be better of course :D
I'd set aside such critical thinking for now :) and proceed with building your BP (or Tempest?) subwoofer then compare it with a Velodyne. It is highly unlikely that you'll feel the need for a current limiter after the comparison. :)
Isaac |
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| BAM |
| Why would you want to put a current limiter on a subwoofer with as much raw horsepower as the BPD xx03 series? The velodyne uses paper drivers that probably cost them $40 apiece, so they need current limiters to keep their amps from melting the voice coils right off their formers. |
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| GRollins |
The two common ways to approach servo loops are to use:
1) A piezo element
2) An accelerometer
The piezos have ferocious phase shift, so you'll need to compensate for that, but after that it's pretty straight forward.
The accelerometer chips are available here and there (Digikey has them), but they're damned expensive--about $15-20 per chip. (Compared to piezos for less than a dollar.)
In either case, generally you mount them under the dust cap/center dome.
Phenomenal results can be had from a servo system. Bad drivers sound good. Good drivers sound better. High quality drivers sound magnificent. I've heard several servo (not to be confused with 'feed forward' systems) systems over the years and they all tend to leave you shaking your head, not knowing that subs could possibly sound that deep, fast, and tight.
I've got an optical method that I'm going to try once I can shake free a few hours. I will eventually report on this if I can just get a few more things off my to-do list, as it's a high priority item for me.
Grey |
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| pkgum |
I think theres a misunderstanding. The accelerator thingy is not a so-called 'current limiter'. Its a chip that measures the motion of the speaker cone several thousand times a second. The data is then carried into a processor where it is compared to the original input signal. Any distortion in movement of the cone is corrected -therefore making it sound just better.
The problem is It doesn't sound possible for a ordinary home user |
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| f4ier |
I haven't read anything about such circuitry as used in Velodyne subwoofers... have to admit that :) I think it's a current limiter basically because I think that is its primary function -- throttling back the current once the driver unit is at or past its mechanical/electrical limit (which is, I think, Xmag). I think that once the sub is asked to operate beyond its limits, no amount of signal correction can successfully reshape the output as per the input signal... I think that current in this case will have to be brought back to practical levels. Within the driver's operating range or specifications, however, things are just a little bit nonlinear, so I think this is where all the extra algorithms in those chips come into play to make the sub sound better.
Of course, I could be WAY off in my assumptions, sorry :D
IMO, with high quality drivers such as the ones mentioned in this thred, I myself would not use such circuitry. The money would be better spent on an active sub. crossover with *variable* signal phase (useful), higher order filter(s), parametric equalizer, higher quality opamps/power supply, better power amp and so on...
Isaac
[Edited by f4ier on 11-13-2001 at 12:52 AM] |
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| pkgum |
f4ier
I have read in some magazines and projects that subwoofers using those things produce one of the best bass available.
Im just interested at this way of reducing distortion.
Someone mention a thread or web page that describes in detail how this is done? |
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| ThomasW |
Designing and implimenting a proper servo feedback mechanism isn't a trivial undertaking. There have been numerous Speaker Builder/AudioXpress articles about this. I'm sure back issues are available.
It's interesting that people like Tom Nousaine consider 10% distortion not audible in subs; and use that figure as the testing limit when comparing sub output. |
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| GRollins |
This is one of those points I like to toss in when people get wrung in the withers about whether their amp has .001% distortion or .0001%--when the speakers are running into upper single digits and lower double digits, it seems rather an exercise in applied foolishness to worry about such small amounts in the amp...
The accelerometers I'm familiar with aren't sampling, they're analog. If they're used with a class D amplifier, the feedback signal will have to be sliced and diced just like the input signal, but with all other classes of amplification, they'll just be added in like any other feedback signal.
No, they're not current limiters, any more than any negative feedback loop is designed to function as a current limiter. If an amp is driven into clipping, the feedback loop will try (futilely) to correct the problem. Likewise, if someone exceeds the mechanical limits of their driver, the feedback loop will try to correct the problem. The results will test how well the cone was glued to the basket at the factory. You can add a cutout to keep from overdriving the driver if you're worried about it.
Grey |
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| BAM |
| You know, just to see what it's like. I want to see a cone and voice coil go shooting off into the distance like it happens at car subwoofer competitions. |
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| GRollins |
I've seen it happen. There was this fellow in an electronics course I took years ago who thought it'd be funny to hook the AC line to the speaker outputs. Yeah. Big laughs. A sound like a gunshot when I turned the circuit on and the cone went thataway! Ripped the surround and spider clean out of the basket. The only problem was that just moments before turnon I and another fellow had had our hands all over the output hookups, and the only reason we'd let go was that we had to reach way over sideways to plug the thing in. Otherwise, we'd have gotten a good jolt of AC--after all, the output is usually a safe thing to touch. Unless, of course, you've got some moron with a warped sense of humor.
Not to mention the fact that he ruined a perfectly good speaker.
And no, in case you're wondering, the powers-that-be didn't do a damned thing to him. If it'd been left up to me, I'd have shot him at sunrise.
Grey |
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| kelticwizard |
GRollins:
Please keep us posted about your optical approach to speaker motion control. I have been thinking of a similar idea for some time, but never sat down and tried to implement it.
Is there any good reason a servo system cannot be used on ported or passive radiator systems? Most of the systems that use it are sealed. I admit that there is a complication-you have to design a circuit that compensates for the fact that as the ported system approaches Fb, the cone motion is suppressed, although the sound output is not. But I would think such a compensating circuit would not be so very complex. Anyone have any thoughts or experiences on this ?
[Edited by kelticwizard on 11-16-2001 at 08:22 AM] |
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| walker |
Kelticwizard, the idea of closed loop servo control is to get the best control of the waveform produced. Deep bass notes are a problem because of the intrinsic resonances, masses and inertia/momentum of the driver.
If a ported sub was used it would be very hard to control the port's output.
Thats my take on it.
Regards WALKER |
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| GRollins |
kelticwizard,
I'll be posting here about the optical feedback circuit, just like I did with water cooling and the SOZ w/current sources. My bottleneck is hours in the day. I'm trying to get some writing done (sold two more stories...yeah!), but am woefully far behind on absolutely everything. Incidentally, in case anyone was wondering, that's why the SOZ/current source thread hasn't moved any faster. I got new & improved current source boards etched and populated, but they kinda got conscripted into the front end of my tube amps. I'll need to make up another pair for the SOZ experiment, but haven't had time.
How a feedback circuit would work in a ported cabinet, I don't know. I tend to think that you'd need a pressure sensor (microphone) in the port, then mix the two different modes of feedback. However, I'm not sure whether that would work well due to the phase differences between the driver and the port. Dunno. Let me get the dingus put together and you're more than welcome to try it out on a ported cabinet.
Grey |
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| pkgum |
| what is the best ultra excursion driver u guys have seen? |
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| AudioFreak |
| 1 x BluePrint 1503 is equivalent to 3 x Shivas as far as displacement goes ....... only difference is the shivas would be ~4dB more efficient :) |
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