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Old 28th October 2001, 03:42 PM   #11
Super is offline Super  United States
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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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Old 28th October 2001, 06:57 PM   #12
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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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Old 28th October 2001, 10:12 PM   #13
blmn is offline blmn  Brazil
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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.

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Old 29th October 2001, 05:49 AM   #14
pkgum is offline pkgum  Australia
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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
.................................................. ........


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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Old 29th October 2001, 06:32 AM   #15
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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

Click the image to open in full size.
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Old 29th October 2001, 06:57 AM   #16
pkgum is offline pkgum  Australia
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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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Old 29th October 2001, 07:12 AM   #17
f4ier is offline f4ier  Australia
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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 ) 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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Old 29th October 2001, 07:31 AM   #18
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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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Old 29th October 2001, 08:06 AM   #19
pkgum is offline pkgum  Australia
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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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Old 29th October 2001, 03:24 PM   #20
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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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