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Old 5th April 2002, 03:10 AM   #21
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Looks like the recommendation from Blaupunkt is for a tuning frequency of 30Hz. Get some 3" PVC pipe and cut it 8.3" long.
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Old 5th April 2002, 08:21 AM   #22
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but can i tune it any lower? would a longer port decrese preformince? because my enclosure is 15.5 in. deep!
can i tune it lower....?
will i tuning it lower affect the preformance in a negitive way?

thanks,

need answers....
keep postin tanks,,,,,
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Old 5th April 2002, 03:54 PM   #23
Wizard of Kelts
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Slicemaster:

The people who have taken the time to respond are trying to help you, not engage in an anti-Blaupunkt conspiracy, as you seem to be saying. It takes a certain amount of effort to make and upload a graph. The response from you should be something besides accusations. Nobody is getting paid for this, you know.

If you must know, there are certain combinations of Qts, enclosure volume and vent tuning, if any, that are considered optimum. According to the database of WinISD, which is normally pretty accurate, the Blaupunkt PCWG 120 has a Qts of .45, and a Vas of 4.3 cubic feet. Normally, for a vented box, the recommended box size would be between 3.5 and 6 cubic feet-considerably larger than the 2 cubic feet you mentioned.

Fact is, for this Blaupunkt and a 2 cubic foot box, most speaker designers would consider a SEALED enclosure the ideal way to go. You are kind of stretching it a little-but not terribly-by going vented. One speaker could be used for both a sealed and a vented enclosure, but the sealed enclosure will be smaller and have not so deep a bass output.

Every woofer in every box will have a cutoff frequency, beneath which the loudspeaker plays less and less loudly the lower you go. If you compare the PCwg120 and the Peerless, you see that at 30 Hz, the Blaupunkt is about 7 dB down from it's normal playing level. The Peerless is about 3 dB down.

If my amplifier is putting out 100 watts, when I hit 30 Hz I would have to feed the Peerless 200 watts to bring it up to normal playing level. I would have to feed the Blaupunkt over 500 watts to do the same thing.

On the other hand, at 37 Hz, the Blaupunkt will be at the same volume level that the Peerless is at 30 Hz. You got that?

Yes, you can make the vent longer. If it hits the back of the box, you can go to Home Depot or some place and get an elbow that will allow the vent to fit into the enclosure. To tune the box to 25 Hz, the 3" diameter vent should be 12 3/4" long. Such a vent would work well in your box, by the way.

I'm going to try it one more time. Following is a graph of the Blaupunkt in a 2 cubic foot box tuned to 30 Hz. Note the position of the response at 30 Hz in relationship to the green line, which is the point at which the response is 3 dB down. Now look at the Peerless, which I showed earlier. The Peerless puts out more at 30 Hz.

To briefly summarize, the Blaupunkt will work okay in a 2 cubic foot enclosure vented to 30 Hz or 25 Hz. The Peerless will work a little better, but if your heart is set on the Blaupunkt, it won't be grossly mismatched in the 2 cubic foot vented enclosure.
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File Type: png blaupunkt pcwg120.png (2.0 KB, 165 views)
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Old 5th April 2002, 09:25 PM   #24
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thank you for all your help...
espechialy kelticwizard..... tank you so much!
i am sorry if i gave you guys the wrong idea about what i was trying to say....
the fact is that i am a little tence about this project ,it being my first ever....

i am relly tankful for you guys here who took the time to help me out....
i am striving to lern more and i hope i did not give you guys the wrong idea about me.

it's just that i want to make an informed desicition about what components i choose and why....

i again that you all for the help and time....

aditional feed back would be nice but never required....

thank you, kelticwizard for helping me get my facts straight....
as you guys can tell i am relly new to the diy cercit.....
this is my first time working indepth with speakers and enclosures. and i am hoping to upgraid the driver to a better quality one when i have the money.....thanks to your advice....

thank you all...
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Old 5th April 2002, 09:29 PM   #25
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Location: CA
note::::
where can i find more info on the other drivers you guys have sugested?

thanks

could you guys post some links if it's not to much truble...
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Old 5th April 2002, 10:17 PM   #26
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one last q....
does it matter how close to the enclosure wall the port comes to?
in other words can the port be 2in away form the back of the box.... if it does matter what type of elbo should i get?
does it matter whitch way the port end is pointing when i put the elbo on......


thanks for all the help....

this is my final q....
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Old 6th April 2002, 12:46 AM   #27
Wizard of Kelts
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Slicemaster:

No need to make that your last question. This forum is all about people asking questions. I ask questions from others who know more about certain audio subjects than myself.

Just downloaded the manual for the Blaupunkt 120. It's a better woofer than I thought. It probably is your best choice for your subwoofer after all. Will explain in another post, gotta run for now.
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Old 6th April 2002, 06:03 AM   #28
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ok i will be waiting for your update.....
i will check back later....

thanks
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Old 6th April 2002, 06:33 AM   #29
Wizard of Kelts
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Slicemaster:

Before I can absolutely say that the Blaupunkt is the best speaker for the job, I have to check one thing with their technical department. The Xmax-the back and forth movement of the cone-is listed as .25 inch. For many speaker manufacturers, that means .25" from midpoint to front, then .25" from midpoint to back. However, some speaker manufacturers measure all the way from the back of the speaker's travel to the front. That is quite a difference. I am pretty sure that Blaupunkt measures from center to front, but I want to check. I will do so Monday.

One of the reasons I liked the Peerless woofer so much was that it had a symmetric magnet system. There is more magnet behind the voice coil than in front, in most speakers. As a result, near the tuning frequency in a vented box, most speakers experience "suck-in", that is, they travel all the way to the back of their position, and instead of moving back-and-forth, they just move forward. Essentially, they cannot reproduce half the waveform. Incredibly high distortion.

There are magnet systems that prevent this, but usually the woofers with them are expensive. One reason I like to recommend the Peerless, when appropriate, is that it is inexpensive but it still has that magnet system.

Well, I checked the Blaupunkt's manual. It has a symmetric magnet system too. Very impressive for the price.

The Blaupunkt is a 4 ohm speaker, the Peerless an 8 ohm speaker. Makers of 4 ohm speakers often have a sneaky way of stating their sensivity so that the speaker is listed as 3 dB higher than it really plays. Long story, I'll explain later if you want. Well, the Blaupunkt does not do that, It is a genuine 90 dB@1W/1M. Actually, 89.5 dB, but rounded off it is 90 dB. So the Blaupunkt is about 1.5 dB more sensitive than the Peerless.

Your Parts Express subwoofer amp gives off 250 watts into 4 ohms, and only 150 watts into 8 ohms. That is about 3 dB higher for the 4 ohm speaker-the Blaupunkt. Add to that the 1.5 dB higher efficiency, and the Blaupunkt can be driven to 4.5 dB higher level than the Peerless.

The Parts Express amp has instructions on how to boost the output at 30 Hz, so the Blaupunkt can put out equally to the Peerless at 30 Hz. Above 40 Hz, the Blaupunkt can be driven to 4.5 dB higher than the Peerless. Put another way, throughout most of the bass range, the Peerless would require a 450 watt amp to play as loud as the Balupunkt does on your Parts Express 250 watt amp.

I will contact the tech department of Blaupunkt on Monday to double check the way they measure Xmax, but I am sure it is the center-front, not back-to-front. Assuming it is center-to-front measurement, I would say that, with the Blaupunkt, you selected an excellent woofer for the price. It is one that I will recommend to other people.
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Old 6th April 2002, 06:41 AM   #30
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As for the ports, there is an adjustment to be made if the opening of the port lies along one of the interior walls of the enclosure. You do want to leave a few inches between the port opening and any walls, as well.

The port can lay along the inside wall of the enclosure as long as the opening is a few inches away from any obstruction. The air must be able to enter and leave the port without any blockage or slowdown..

You probably want to line the interior of the walls of the enclosure with stuffing. Just line the walls-don't fill the enclosure as some people do with a closed box. The air must flow freely in a ported box for it to work properly.

Feel free to ask me any question you wish. If I don't hear from you, I will post Monday and let you know about the excursion question I have for Blaupunkt technical department.
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