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Old 11th October 2010, 03:26 AM   #31
DougL is offline DougL  United States
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I have been following this thread. I was trying to find a diplomatic way to break it to you, but that failed. So I will just say it.
You have conflicting requirements and will never find a solution.
Hoffman's Iron Law basically states that you can't have high efficiency, low F3, and a small box. OB makes that worse, not better.
My recommendation is to find one of the OB calculators and play with a number of likely driver suspects, and input different values for D.
I think you will be appalled how quickly a single 12" reaches Xmec at 40 Hz.

Personally, I think you can get to 60 Hz with your design and go IB with 4 by 15", or go for a sealed sub.

Good luck with your project.

Doug
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Old 11th October 2010, 04:09 AM   #32
DQ828 is offline DQ828  Australia
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Originally Posted by DougL View Post
I have been following this thread. I was trying to find a diplomatic way to break it to you, but that failed. So I will just say it.
You have conflicting requirements and will never find a solution.
Hoffman's Iron Law basically states that you can't have high efficiency, low F3, and a small box. OB makes that worse, not better.
My recommendation is to find one of the OB calculators and play with a number of likely driver suspects, and input different values for D.
I think you will be appalled how quickly a single 12" reaches Xmec at 40 Hz.

Personally, I think you can get to 60 Hz with your design and go IB with 4 by 15", or go for a sealed sub.

Good luck with your project.

Doug
I dont know, that was pretty diplomatic, sounds like Im trying to defy gravity. which is the sort of information I really need to hear. Thanks for the advice,

David
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Old 11th October 2010, 06:42 AM   #33
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Originally Posted by Helmuth View Post
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.
Can't say I've measured a lot of drivers, but I've yet to measure a low end dipole response that would be predictable from the datasheet with good accuracy. So I wouldn't put too much store in simulations, though Linkwitz' power limited SPL spreadsheet is excellent for roughing out driver selection for a given baffle. You'll need to find the balance between SPL and excursion which satisfies your distortion requirements, but the usuable excursion is probably someplace between xmax / 4 and xmax / 10 depending on how much distortion you're willing to accept. Normalization between geometric xmax and 10% THD xmax is desirable when comparing drivers.

Selenium 12PW5 or 15PW5 would be my choice here given the stated constraints, desire for pro efficiency levels, and lack of need to operate below those drivers' Fs. But as a rule of thumb going up a driver size results in about the same SPL boost as doubling a smaller driver or using an H baffle. If you're thinking three 15s you'll probably find using an 18 results in a smaller speaker. Dipole sub selection is usually xmax dominated and the price/performance ratio on the 18SWS1110 is tough to beat. Not many 18s with lower Rms, either.

Last edited by twest820; 11th October 2010 at 06:44 AM.
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Old 11th October 2010, 09:13 AM   #34
DQ828 is offline DQ828  Australia
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Originally Posted by twest820 View Post
Can't say I've measured a lot of drivers, but I've yet to measure a low end dipole response that would be predictable from the datasheet with good accuracy. So I wouldn't put too much store in simulations, though Linkwitz' power limited SPL spreadsheet is excellent for roughing out driver selection for a given baffle. You'll need to find the balance between SPL and excursion which satisfies your distortion requirements, but the usuable excursion is probably someplace between xmax / 4 and xmax / 10 depending on how much distortion you're willing to accept. Normalization between geometric xmax and 10% THD xmax is desirable when comparing drivers.

Selenium 12PW5 or 15PW5 would be my choice here given the stated constraints, desire for pro efficiency levels, and lack of need to operate below those drivers' Fs. But as a rule of thumb going up a driver size results in about the same SPL boost as doubling a smaller driver or using an H baffle. If you're thinking three 15s you'll probably find using an 18 results in a smaller speaker. Dipole sub selection is usually xmax dominated and the price/performance ratio on the 18SWS1110 is tough to beat. Not many 18s with lower Rms, either.
I was hoping to use 2 x 12" per speaker in a H or U frame. I dont need to achieve real LOUD music, I play mostly classical & probably only accasionally play them at preformance levels, also my room isn't huge about 200 square feet or 20m2.

At the monent I have 1 x 15" Altec in a "U" frame and it seems to do almost evervything I need. I haven't got my brain around the measurement side of life yet, so I really dont know what the Altec is achieving, but it sounds mighty fine with the cello playing low notes.
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Old 11th October 2010, 09:34 AM   #35
CLS is offline CLS  Taiwan
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Originally Posted by DQ828 View Post

..Bass: Well this is where it gets tricky, I don’t want to use the 15” bass drives, because of my design & to reduce bulk, but I am having little luck finding smaller drivers (10” if necessary 12”) that are efficient, (95-98dB) & have a usable range to get me down to the 20Hz. ...
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At the monent I have 1 x 15" Altec in a "U" frame and it seems to do almost evervything I need.

1 x 15" v 2 x 12", hmmmm ......

I don't see 2 x 12" is any less bulky. 1 x 15" can be used on very narrow baffle, too.

Using OB, you'd need every bit of cone area. To get similar or better performance, you need at least the same or as big as possible. And I think one big cone is tidier looking than multiple smaller ones. (Of course that's only my personal opinion.)

And, do I get it right? You want to dump Altec and take Selenium?
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Old 11th October 2010, 10:15 AM   #36
DQ828 is offline DQ828  Australia
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Originally Posted by CLS View Post
1 x 15" v 2 x 12", hmmmm ......

I don't see 2 x 12" is any less bulky. 1 x 15" can be used on very narrow baffle, too.

Using OB, you'd need every bit of cone area. To get similar or better performance, you need at least the same or as big as possible. And I think one big cone is tidier looking than multiple smaller ones. (Of course that's only my personal opinion.)

And, do I get it right? You want to dump Altec and take Selenium?
No I dont want to dump Altec, there great, I just that I wanted to go to 12" as per my first post. The other issue I have with Altec, is the pair of 15" I paid a lot of money for & a LOT of postage for get here from the US didn't live up to the description that the seller had on ebay, and he had a 100% reputation. I figure I shouldn't have that issue with new speakers, hopefully

I was hoping two 12" would give me the same response, & maybe be a bit more punchy, I dont always play classical. The other issue is that my design (for the moment) has them firing thru a slot. I was hoping that if Linkwitz could get great sound with 2 x 10". Maybe I could get close with 2 x 12".
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Old 11th October 2010, 03:13 PM   #37
Rudolf is offline Rudolf  Germany
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Originally Posted by DQ828 View Post
Why do you say that? remember I'm a beginner wanting to learn.
Frankly said: In your place I would try to understand a little bit more about dipoles before starting such a project. Apart from the obvious sources like Linkwitz Lab or Music and Design you may download a small PDF from my place: the third download button below the red text.

Rudolf
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Old 11th October 2010, 10:02 PM   #38
DQ828 is offline DQ828  Australia
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Originally Posted by Rudolf View Post
Frankly said: In your place I would try to understand a little bit more about dipoles before starting such a project. Apart from the obvious sources like Linkwitz Lab or Music and Design you may download a small PDF from my place: the third download button below the red text.

Rudolf
I have been trying, reading is one thing, understanding is another, I have read the Linkwitz site front to back & many others, I will keep reading & hopefully it will sink in eventually. A lot is written for people who already have a general understanding, very little is written with the complete beginner in mind.
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Old 11th October 2010, 10:04 PM   #39
DQ828 is offline DQ828  Australia
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Does anyone esle have an opinion on firing a bass driver through a slot, say 38cm (15") driver through a 20cm (8") slot?
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Old 11th October 2010, 10:50 PM   #40
Rudolf is offline Rudolf  Germany
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I would look at it under two aspects:

1. Is the cone area (including the surround), which is hidden outside the slot, less than 20 % of the whole cone area? In that case I would not bother much.

2. At a crossover frequency < 200 Hz I don`t see any danger of interference.

Apart from that, in my POV, here we are talking about wet hair while sinking in the mid of an ocean.

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