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Old 5th October 2001, 11:22 PM   #1
BAM is offline BAM
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I was wondering: can I get more bass out of two 4" woofers with a 4mm Xmax if I use a dual-chamber vented box? I'm designing a pair of small floor speakers. I'm not exactly asking for deeper bass, just louder bass.

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Old 30th October 2001, 06:07 AM   #2
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Question Dual Chambered enclosures

BAM, I'm not sure which way you are going by the term 'dual Chambered'? I think, since you are talking about using two drivers that you are referring to a seperate chamber for each driver. If that is what you mean, then there won't be any difference, except the difference in the ohm rating of the system. There is another type of dual chambered enclosure, and that is where one driver uses two different chambers that are each vented. I have made this project almost 10 years ago using a Peerless 1056 8" driver, which has been replaced by the manufactorer. David B Weems published this project in Speaker Builder, during the late 80's and was later put in his 1990 book, entitled "Great Sound Stereo Speaker Manual". This book in most likely in your local Public Library. Don't confuse this with his other book,"Designing, building, and Testing Your Own speaker System". I have both, and the first one is by far the better. The article in the book does not go into the theory like the one in Speaker Builder, but I will try to pull it up from memory. Once the Ideal box size and the diameter and length of the port is calculated, the second chamber is 1/2 that of the other. The port leading into the second chamber and leading out of the second chamber is the same as in the first chamber. This will cause the Fb of the second chamber to be 1/2 octave lower than the first. I have not been able to measure this, but if you put your ear to each port, one is able to tell that the port from the second chamber is indeed lower than the first. I hope that this helps you. If you have any other questions, let me know. John L
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Old 30th October 2001, 07:24 AM   #3
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Default Do you mean double chamber reflex?

Or are you refering to a dual chamber band pass bass reflex?
Either way you'll end up with a much larger enclosure than conventional. Larger means somewhat more bass, but only in the last half octave.
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Old 30th October 2001, 02:37 PM   #4
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Wink Double Chamber BandPass

AE, actually, the dual reflex that I mentioned is a 6th order bandpass. You will not see this anywhere comercially, because Mr. Bose has the patent on this type of enclosure, but it doesn't stop people from using it for their own enjoyment. It really is a shame that it isn't out there comercially, because if a buck is to be made, then you would get a wealth of these things on the market. John L
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Old 30th October 2001, 03:41 PM   #5
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Default Bandpass' are known for their efficiency.

But the trade off is narrower bandwidth and larger enclosure.
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Old 30th October 2001, 04:05 PM   #6
John L is offline John L  United States
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Smile Double Chamber BandPass

AE, yes, you are right. However, if you check out Mr. Bose's work, you will see that he does two things that help him work around this. First, he uses the smallest drivers possible. Second, the T/S values are customed to the use of the smallest enclosure that he can get. Unforunately, you and I cannot pay for mass produced drivers by a major driver manufacter. We have to take each driver and check them out on our favorite computer program. Later, John L
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Old 2nd July 2004, 02:49 AM   #7
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Default 6th order bandpass

WinISD pro Alpha models 6th order bandpass alignments. If you ask me you'd probably be doing just as well to take the air volume of the 2 chambers and add them into 1 larger chamber and just do a regular bass reflex enclosure. A 6th order bandpass isnt of the best sound quality if you ask me. A low pass filter is needed to prevent enclosure wall resonance above the tuning of the front chamber(the higher tuned chamber). anything above the tuning of the front port will be blocked by both sets of ports and contained in the box causing the enclosure to absorb all of the acoustic energy. Bose rarely uses 6th order bandpasses themselves. their designs that i am familiar with usualy use some version of the bandpass where both front and rear chamber are vented into a 3rd chamber that is finally tuned to the outside. Resonance peaks must be hell to get out when working with something like that. sound quality is entirely comprimised for efficiency. Bose just wants to make something thats tiny and booms.
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Old 2nd July 2004, 02:51 AM   #8
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Since you're using small drivers perhaps a TL might work out for you.
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Old 2nd July 2004, 12:08 PM   #9
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A double chamber reflex of the Augspurger-Weems type will cut cone excursion in the bottom octave and the next-to-bottom octave. A single chamber reflex cuts cone excursion in the bottom octave alone.

The single chamber reflex, tuned to 30 Hz, cuts the excursion, (but not the output), from 30 Ha to 60 Hz. After that, you are just like a closed box.

A double chamber reflex, tuned to 30 Hz and 60 Hz, cuts excursion, (but not output), in the 30 Hz to 60 Hz octave, and also in the 60 Hz to 120 Hz octave.

So if you have some loud passages with big output in the 60 Hz to 120 Hz range-not uncommon-the Augspurger-Weems double chamber reflex will not "run out of excursion" in that octave the way the single chamber reflex or a closed box would. It reduces excursion in that 60-120 Hz octave by up to 75%.
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Old 2nd July 2004, 01:37 PM   #10
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Quote:
Originally posted by BAM
I was wondering: can I get more bass out of two 4" woofers with a 4mm Xmax if I use a dual-chamber vented box? I'm designing a pair of small floor speakers. I'm not exactly asking for deeper bass, just louder bass.

Thanks

Yes, but with reservations. The bandwidth/efficiency product constant means that you can tune the enclosure for higher output over a narrow frequency band or for lower output with a wider frequency band. To see for yourself just model the driver in WinISD and then change the box volumes. The most interesting results occur when you use a small chamber tuned high and a large chamber tuned low, and then a small chamber tuned low and a large chamber tuned high.

However, using 4 inch drivers you'll find for the most part that it's going to be hard to get a lot of bass response anyway. If you're making speakers large enoiugh for floorstanding then there's no reason not to use at least 6 1/2" woofers.
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