subwoofer design problem

[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?

[ThomasW]

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.

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.

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"

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]

[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]

[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.

[baby_huey0]

I'll just stick my foot back in my mouth now...

[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]

[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.

[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?

[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.