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Old 18th April 2004, 05:01 PM   #11
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Quote:
So I could get an okay result if I combine the stereosubwoofers with a Linkwitz circuit in a 2,5-way combination with my small loudspeakers?
Absolutely, I`d think so but that`s just me and others may disagree or may have (although I doubt) better suggestion.

Quote:
It is not 110db at 20Hz I am looking for. I am much more interrested in improoving the midrange and add a quick dynamic (but not abyss deep) bass.
Two of those 7" Scan Speaks combined equal more or less one 10" driver with +/- 6,5mm linear excursion.

Just to give You a clue for dimensioning the circuit:
I used Linkwitz transform with a 10" Scan Speak per channel as subwoofer in a sealed box (approximately 40 ltr.) which gave fc of something around 44 Hz (if I recall correctly). I equalised the driver with the Linkwitz to give a new fc=15Hz / Qt=0.5.
I always use a LR 12db (Q also 0.5) high-pass (*) before the LR transform circuit with f3 set to the new fc of the equalised driver.
Now You have -6dB @ 15Hz due to the LR transform and another -6dB @ 15Hz due to the LR 12 db highpass makes for -12dB @ 15Hz.

Due to this arrrangement the beginning of drop off of low frequencies happens quite early as these are low Q filters (as opposed to higher Q filters which cut off steeper or more abruptly). But as I said in my previous post room gain compensates for this mostly and You`ll get deep and more important (IMO) clean bass.

My setup with the 10" Scan speak described above give incredible clean and deep subbass and even when it gets VERY loud they can keep up with the rest of the system (a 8" mid-bass driver!).
Only when it comes to tracks with very weird low frequencies some caution is indicated with the volume.

Two 7" drivers might have even an advantage over one 10" driver as there are two voice coils which can handle power better than one (which is not unimportant when using a LR transform circuit).


(*) I wouldn`t omit an additional high-pass for a very important reason.
LR transform circuits are high-gain circuits when the "old" fc to "new" fc ratio is big. For frequencies towards DC (and some CD`s can contain weird low frequencies) the LR transform gain raise considerable. Without electronic highpass this easily can lead to clipping in the electronic chain already (let alone what happens to Your drivers).
Eventually You could also play with dividing an 12dB high-pass in two 6dB filter parts - one before the LR transform circuit and another at the input of the power amp.


Quote:
From what I can read from the replies so far, It is not entirely impossible for me to reach that goal.... Right?
For me ..no doubt You can (but You should consider a rather powerful amp).
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Old 18th April 2004, 05:37 PM   #12
daniels is offline daniels  Denmark
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Thank you for the much needed reasuring.

I will make my move on the new subwoofers this week and, if the result is what I wanted, I will post a complete step-by-step on the subwoofers.

- And I already have a new amp coming my way. Unfortunalty it is not as powerful as I wished for (Cyrus Power 2x60W) but it will do for now. So I will have a Cyrus Power for mid/high and another for the subwoofers.
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Old 18th April 2004, 05:48 PM   #13
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I will make my move on the new subwoofers this week and, if the result is what I wanted, I will post a complete step-by-step on the subwoofers.
And if it was not to Your liking it would be interesting to know too!
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Old 18th April 2004, 10:48 PM   #14
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I was just throwing in some caution regarding the transform.
Anyway yes I think you should be able to get excellent results from this, there is absolutly no reason why you shouldnt. Let is know how it turms out.
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Old 19th April 2004, 12:45 AM   #15
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Yes, let us know how it turns out. I've never tried a Linkwitz.
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Old 19th April 2004, 01:25 AM   #16
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I've not used the linkwitz, but I have used a simple other active circuit though not as verstile as the linkwitz works really well. This just needs two resistor and a cap.
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Old 19th April 2004, 01:47 AM   #17
daniels is offline daniels  Denmark
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I have planned on beginning the project this week so it should not take to long before the project is complete - well the cabinet anyway... The crossover is going to be more interesting.

I am going to build a matrix cabinet for the subwoofers and brand new cabinets for my small loudspeakers.
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Old 28th April 2004, 10:00 PM   #18
daniels is offline daniels  Denmark
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It seemes like I have to give up on my project. It is no problem making the subwoofers, but I just cannot get "sub" out of them. Below 40 Hz there is not much punch.

It is much easier making the Scan Speak 8545 go below 40 Hz. So that is what I will do. Too bad though.
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Old 28th April 2004, 11:53 PM   #19
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Quote:
Originally posted by daniels
It seemes like I have to give up on my project. It is no problem making the subwoofers, but I just cannot get "sub" out of them. Below 40 Hz there is not much punch.

It is much easier making the Scan Speak 8545 go below 40 Hz. So that is what I will do. Too bad though.
Does that mean there is no output at 40hz? ie they have rolled of very quickly? or is it an excursion problem with the drivers. It sounds a bit odd what you are saying.

Although I cant say stuff below 40hz actually has punch really. With sine waves can it produce low freqs?
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Old 29th April 2004, 12:48 AM   #20
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Quote:
Originally posted by daniels
It seemes like I have to give up on my project. It is no problem making the subwoofers, but I just cannot get "sub" out of them. Below 40 Hz there is not much punch.
Are the drivers unequalized (without LR transform) in a sealed box? If so then this would be just normal but with a correctly adjusted LR transform You should be really able to get sufficient levels below 40Hz.

Maybe You`re just missing that sort of a "boom box" effect?
LR-transform equalized systems with low Qt can sound remarkable clean and therefore in comparison with "ordinary" systems of comparable low frequency capabilities they usually sound rather "slim".
It is not uncommon that this kind of precision in bass sometimes can be mistaken as no or to less bass.


Quote:
Originally posted by 5th element
Does that mean there is no output at 40hz? ie they have rolled of very quickly? or is it an excursion problem with the drivers. It sounds a bit odd what you are saying.
I don`t believe it`s an excursion problem. This are long linear throw drivers and they should handle "normal" listening levels in an average sized listening room.

Quote:
Originally posted by 5th element
Although I cant say stuff below 40hz actually has punch really. With sine waves can it produce low freqs?
I agree, "punch" is not really what frequencies <40Hz sounds like.
Yes I would check with a sine wave generator and if possible with a microphone in near field measurement to reveal what went wrong.
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