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Old 21st December 2001, 02:56 AM   #21
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Quote:
Is that the answer why my posts are a troll like quality?
Gee I don't know you tell me.....

Quote:
I don't want the 'muddy' sound of the ported box which is suited for home theatre.....I rather have the 'constipated' sound of the sealed box because it is quick and suited to music
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Old 21st December 2001, 04:02 AM   #22
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Most magazines are there for the advertizing revenue. (But what about my subscription price? That pays for the paper it's printed on and the postage to get it to you. The magazine's profit comes from its advertizing content.) Where does that revenue come from? From the companies whose products are being reviewed. This quickly leads to a situation where the reviews are, shall we say, tainted. The manufacturer says,"You gave my last product a bad review. I'm pulling my ads from your magazine."
Blackmail?
No.
Business.
It's a cold, cruel world out there, and magazine reviews sell product for manufacturers. It's basically another form of advertizing. About all most magazines are good for are to let you know that the XYZ company has a new widget out, it looks like this, and sells for a fistful of dollars.
Read the last half dozen issues of whatever magazines you're getting. If the majority of the reviews end in a catch phrase like,"If you're in the market for a new subwoofer, you're cheating yourself if you don't check out the new ABC subwoofer," or, "Another strong effort from the talented engineers at XYZ company. You can't go wrong with this one," cancel your subscription.

Grey
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Old 21st December 2001, 04:21 AM   #23
Wizard of Kelts
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Gum:

Judging by advertising, I guess one could get the idea there are different standards for home theater and music. Why they do that, I don't know.

Here is REL, a well-known subwoofer manufacturer whose subwoofers run into the thousands of dollars. It's better line of subwoofers-they also have "compact" units-sports both sealed and ported models, with the ported being top-of-the-line model.

http://www.rel.net/products/stseries.shtml
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Old 21st December 2001, 09:45 PM   #24
Wizard of Kelts
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Gum:

Now that the notion of ported=home-theater-only has been exploded, I recommend that you run those plots of the Blueprint 1503 in the 120 liter sealed box, and the Blueprint 1503 in the 120 liter ported box, tuned to 16 Hz-or higher, if you wish. Remember to take 15 liters off the ported to compensate for the 5" diameter vent. If you run Boxplot, make Alpha = 1, because Boxplot assumes a 10% reduction plus you are compensating for the port.

The response in the lower bass region jumps 6 dB. Just to give you an idea what that means, you must supply 4 times the power to raise the SPL 6 db.

If we have two Blueprint 1503's, one in a sealed 120 liter box, one in a ported 120 liter box tuned to 16 Hz:

At 16 Hz, 1,000 Watts through the ported box will yield the same SPL as 4,000 Watts thruough the sealed-assuming the excursion does not limit the output of the sealed by itself;

250 Watts through the ported box will yield the same SPL as 1,000 Watts through the sealed, at 16 Hz.

Other low basss frequencies have differentials almost as great.

My point is not that you absolutely must build the ported box. I only wish to make it clear that your decison to NOT port your box is a major one. The quality of the bass coming from the sealed enclosure had better be A LOT better to justify this loss of SPL. That is why I suggested you build the ported box with the plug, so that you may judge for yourself.

The decision is entirely yours. Good luck with your project, either way.
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Old 21st December 2001, 10:16 PM   #25
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kelticwizard

Nice post........

I'll offer one suggestion regarding port tuning for the BPD1503, use 18Hz not 16Hz. The 1503 is much happier doing that given it's relatively high Fs. It results in a smoother overall response curve. Less of a 'saddle' between the port output and the driver's natural oll-off.

And yep your right, the power requirement differences between ported and sealed boxes especially for the high excursion drivers is considerable. For the 1503 it works out to be around 10 dB more output at 20Hz in favor of the ported design.

I didn't save the sim for the 1503, but here's one for the 1203.

Click the image to open in full size.
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Old 22nd December 2001, 12:35 AM   #26
Wizard of Kelts
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Thomas W:

All the time I was writing the post, I had your Aerial Stryke Sub project in the back of my mind. You had written that 18 Hz was as low as you would recommend. You have also written that, as you have bought and used both TC Sounds HE-15 drivers and Blueprint 1503's, you consider them virtually identical.

As the Aerial Stryke Sub is about 6 cubic feet internal volume or so, and you recommended no lower than 18 Hz for that project, I kind of figured I was "pushing it" to speak of 16 Hz tuning for a 4.2 cubic foot subwoofer.

Since PKGum has given numbers down to 15 Hz for the sealed sub, I figured I would use the 16 Hz tuning as a comparison. But I also figured that if he shows any interest in using the ported method, it should be mentioned that a slighly higher tuning is an even better way to go.

I am taking the liberty of giving the link to your Aerial Stryke project, even though you already gave it in another thread by PKGum. He might decide to go a little larger than the 4.2 cubic feet he has been mentioning.

http://home.att.net/~tom1/page7.html
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Old 23rd December 2001, 12:51 AM   #27
pkgum is offline pkgum  Australia
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I do have an flexible option....Make a ported box with a 'plug'. One moment its a sealed box and another moment its a ported box

But..I don't want to make a 120L Ported box...port length is too long and I want a slimmer tall enclosure...I want to make a 200L one. Therefore if you put the plug in it will become a 200L sealed box with a QTC of 0.385. Is there any problems with such a low QTC?
The book says that QTC outside the range of 0.5 - 1.5 is not recommended.
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Old 23rd December 2001, 10:53 PM   #28
Wizard of Kelts
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Gum:

If you increase the size of the 1503's sealed enclosure to 200 liters-7 cubic feet-you get bass output virtually the same as the 120 liter sealed box.

Run the plot with 120 liter sealed box. Run the plot with the 200 liter sealed box. If you use Boxplot, reduce the size to 180 liters, making Alpha=.5. The curves of the sealed box of 120 liters and the sealed box of 200 liters are virtually identical. From a sealed box standpoint, you will be adding 66 percent more volume to produce no more output.

A woofer with a lower Q will fit into a smaller sealed box, and a much larger ported box. When the Qtc of the sealed box is around .5 or so, that is where they meet. Only in that range can you have a "convertible enclosure".

You can increase the enclosure size to 400 liters and not change the response much.

When a sealed box enclosure becomes much larger than the Vas of the speaker in it, it gets called an Infinite Baffle. The baffle is the board the speaker is mounted on. A true Infinite Baffle is a huge board which function is to prevent the back wave from curling around and cancelling the front wave. The frequency response charts of the unenclosed speakers that you see are from true Infinite Baffles. At least, some speaker manufacturers use them-others use a nearfield microphone.

If you put a speaker in a box with a volume that is much larger than the Vas, the box will affect the Q and the resonance frequency so little, it resembles the situation with an infinitely large board. Hence, the title Infinite Baffle.

Some people erroneously use the expression Infinite Baffle to mean any sealed box, but strictly speaking, that is not true. A sealed box with a volume much less than Vas is called an Acoustic Suspension enclosure.

Anyway, if you want to make a "convertible enclosure", I suggest you stick with the 120 liter size.
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Old 23rd December 2001, 11:14 PM   #29
Wizard of Kelts
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Gum:

I would just like to add that the internal volume of Thomas W's Aerial Stryke project-I gave you the link before-is 204 liters before you deduct for bracing, port, speaker size, etc. If you want to adjust the dimensions to make your box tall and skinny, go ahead. Otherwise I would follow what he has written there.

Since your box will be tall and slender, use an elbow to fit the port into the box. Speaker designers do it all the time.

If the port is too small, there will be chuffing sounds as the speaker hits the low bass notes. Making the port larger eliminates this, as does flaring the port. Thomas W has clearly gone to great lengths to make sure these chuffing sounds do not happen. If box construction is a problem, you can probably eliminate the flares and not get burned too bad. You can even probably use a 5 inch port, (most 15 inchers use a 4 inch), but why mess further with a successful design?
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Old 24th December 2001, 01:36 AM   #30
pkgum is offline pkgum  Australia
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Kelticwizard

I cannot make a 120L convertible (ported and sealed) box because the port length will be too long to be practical.

The Height should be nearly two times the width and the depth can be longer than the width if possible. The woofer should be forward firing. A 200L ported box is practical. (Practically a nearly identical clone of Thomas W's Aerial Stryke Sub)

Therefore I need to make a convertible box with a volume of around 180 - 200L to keep the port's length practical. But according to your last posts this should not be done.
QUOTE:
"A woofer with a lower Q will fit into a smaller sealed box, and a much larger ported box. When the Qtc of the sealed box is around .5 or so, that is where they meet. Only in that range can you have a "convertible enclosure"

Does this mean that I cannot make a convertible box?
The only other option is to stick to a ported box...but I seem to wander towards the Linkwitz Transform Equalised sealed box with better sound quality but with great loss of SPL.

NOTE:
After emailing Pat of BluePrintDrivers he informed that some of the specs on the DUMAX report was wrong because the RE wasn't measured properly. The specs on his website are correct.
The SPL 1W 1Meter is indeed 91Db. To make matters worse, the 120L sealed box does not have a Q of 0.5...according to the different parameters in the BP website a 0.5 Q box for the driver should be at around 74L.
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