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Old 10th October 2010, 10:56 AM   #21
Helmuth is offline Helmuth  Netherlands
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Originally Posted by DQ828 View Post
Yes but unfortunately it is bigger than the 30cm I am trying to limit the woofer size to.
The baffle is wide enough so this isnt the problem. the opening on the front can be small the it acts as a acoustic lens.

You want to make a small baffle and small woofers result no sub-bass. That is obvious the result.


I have the idea you not know what your doing and by asking here if you made the right choice for drivers it fix the lack theoretical back ground.

By buying expensive stuff, raal, bms it gives you the feeling building a super system but you are fooling your self.

What you need isn't expensive drivers but basic knowledge about simulation and XO building when you want to build a high quality system. Other wise it will be a disappointment.
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Old 10th October 2010, 10:56 AM   #22
DQ828 is offline DQ828  Australia
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Originally Posted by Helmuth View Post
Here the simulation of the orion woofer. peerless xls10.

xmax 12,5mm sd=352 moved air max=440 cubic cm



http://www.selenium.com.br/site/asse..._pdfManual.pdf
The selenium xmax 3mm sd=860 moved air max=258 cubic cm


So it performs poorer to the xls 10 what maximum spl concerns within x-max of the motor.
But it perform better what low end cut off concerns due higher Q.

-3dB cut off xls10 = 60Hz

-3dB cut off selenium = 30Hz!!

The selenium is great but you shout use 3 drivers to compensate the limited xmax.
Helmuth

Sorry I didn't realise you where creating those response graphs, thanks, what software are you using to do that?
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Old 10th October 2010, 10:58 AM   #23
Helmuth is offline Helmuth  Netherlands
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Helmuth

Sorry I didn't realise you where creating those response graphs, thanks, what software are you using to do that?
Hornresponse and it is easy to.
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Old 10th October 2010, 11:04 AM   #24
DQ828 is offline DQ828  Australia
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Originally Posted by Helmuth View Post
The baffle is wide enough so this isnt the problem. the opening on the front can be small the it acts as a acoustic lens.

You want to make a small baffle and small woofers result no sub-bass. That is obvious the result.


I have the idea you not know what your doing and by asking here if you made the right choice for drivers it fix the lack theoretical back ground.

By buying expensive stuff, raal, bms it gives you the feeling building a super system but you are fooling your self.

What you need isn't expensive drivers but basic knowledge about simulation and XO building when you want to build a high quality system. Other wise it will be a disappointment.
You are right in saying, "I dont know what I am doing". But I am trying to learn, it doesnt come easily though.

The Raal was recommended, the Saba I already have & love, the bass is the issue..

I assumed that by having an 20cm opening and a 30-38cm driver behind the opening I would get distorted sound because it is pushing thru the opening.

I am happy to use cheaper drivers as long as they do the job.

The BMS was the only driver I could find that went close to the requirements that I thought I needed.

Last edited by DQ828; 10th October 2010 at 11:14 AM.
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Old 10th October 2010, 01:03 PM   #25
Helmuth is offline Helmuth  Netherlands
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You are right in saying, "I dont know what I am doing
I assumed that by having an 20cm opening and a 30-38cm driver behind the opening I would get distorted sound because it is pushing thru the opening.
You can do what you like I only want to warn for decisions that easily could be prefented.


when the sound pressure has to come through a slit smaller than its own wave length it will bent and have a better of axes. It isn't a advantage for low frequency they already have good of axes, but I do not aspect problems with it.
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Old 10th October 2010, 01:10 PM   #26
jwmbro is offline jwmbro  United States
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Originally Posted by Helmuth View Post
The selenium will go down to 20Hz with some room gain so the hole audio spectrum is covered.
Hi, just a small question here. I may be misinformed, but I believe I read somewhere that open-baffle / dipole bass does not benefit from room gain at all? The way I understand it, room gain is a function of wave lengths greater than the room dimensions creating positive pressure. However a dipole creates the same negative pressure at the back as it does positive pressure at the front, thus equaling zero net room pressure. I think. Am I barking up the wrong tree here?
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Old 10th October 2010, 02:35 PM   #27
Helmuth is offline Helmuth  Netherlands
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Hi, just a small question here. I may be misinformed, but I believe I read somewhere that open-baffle / dipole bass does not benefit from room gain at all? The way I understand it, room gain is a function of wave lengths greater than the room dimensions creating positive pressure. However a dipole creates the same negative pressure at the back as it does positive pressure at the front, thus equaling zero net room pressure. I think. Am I barking up the wrong tree here?
I did measure a set of magnepan magnetostatic dipole's there was clear room gain.

you send of sound it will reflect and come back in phase or not depends how far away the back wall is. There is one major advantage of a dipole, at the side of the dipole the radiated power is near null so there are no reflection side effects.

But with room gain I thought at that moment that the woofers are placed near the floor.

Quote:
The way I understand it, room gain is a function of wave lengths greater than the room dimensions creating positive pressure. However a dipole creates the same negative pressure at the back as it does positive pressure at the front, thus equaling zero net room pressure. I think. Am I barking up the wrong tree here?
I am over asked here.

Last edited by Helmuth; 10th October 2010 at 02:45 PM.
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Old 10th October 2010, 03:56 PM   #28
jwmbro is offline jwmbro  United States
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I did measure a set of magnepan magnetostatic dipole's there was clear room gain.
Well, that's one more measurement of dipole bass than I've ever made, so you probably have more experience with the topic than I do. I'm just going off things that I read, and my basic scientific understanding/guesswork of how things work.

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But with room gain I thought at that moment that the woofers are placed near the floor.
I think that's boundary gain, not room gain / cabin gain. Has something to do with the fact that the sound waves are only expanding along a smaller angle of steradians, therefore covering less area. and less area --> more pressure. (p = F/A). Cabin gain on the other hand has something to do with wavelengths exceeding room dimensions, and.... well, that's kind of where my understanding ends.

Perhaps somebody else more knowledgeable on the subject could clear it up for me.
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Old 10th October 2010, 05:58 PM   #29
Rudolf is offline Rudolf  Germany
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Originally Posted by jwmbro View Post
Hi, just a small question here. I may be misinformed, but I believe I read somewhere that open-baffle / dipole bass does not benefit from room gain at all? ... Am I barking up the wrong tree here?
If you had a dipole with VERY small dipole length, this would probably be true. But this dipole would have VERY big difficulties to emit any deep frequency in the first place.
If you have a dipole with a rather large dipole length (say a 15") and your ear is very near to the cone, you can hear very deep frequencies even in a very small room.

So yes it is true that a dipole can't pressurize the whole room like a closed box speaker can below the lowest room mode. But the dipole does not immediately stop to contribute at that frequency either.

John Kreskovsky has looked into the details: roomgain

Rudolf
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Old 11th October 2010, 02:14 AM   #30
DQ828 is offline DQ828  Australia
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. But this dipole would have VERY big difficulties to emit any deep frequency in the first place.

Rudolf
Why do you say that? remember I'm a beginner wanting to learn.

What do you think of the idea of a 38cm driver mounted in a U frame, pushing out thru a 20cm opening infront of the U frame? As I would need to do if I maintained the design I like the most.

Am I correct in saying? that with a passive design, I am better off sticking to a single larger drive (38cm) in a Uor H frame to get the lower frequencies, than using two smaller drivers in a U or H frame?
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