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Old 21st February 2016, 11:11 AM   #1
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Location: Manchester
Question 3-Way Build Project - Woofer help

Hi, this first post but have been reading the forum on an off for years. I'm reaching out for help on this occasion

I'm in the process of upgraded my floor-standers and i'm really struggling to find a suitable 6.5" woofer; which has high sensitivity, a reasonably flat response and good low down dB's.

Here's my setup so far.
Tweeter : Dayton Audio PT2C-8 Planar (2,000 - 26,000 94 dB)
Midrange: 6.5" Audax PR170M0 (400Hz to 8kHz 100 dB)
Woofer: ???
X/O : Dayton Audio XO3W-375/3K

I plan on adding some attenuators on the tweeter and the midrange, just to bring the sensitivity inline.

Any help/woofer recommendations would be very much appreciated.

Last edited by spark010; 21st February 2016 at 12:21 PM.
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Old 21st February 2016, 02:04 PM   #2
Draki is offline Draki  Macedonia
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What exactly are you upgrading? a)Are you reusing existing cabs (floorstanders, with cutouts for 2 6,5" and a tweeter) or b) the two drivers you listed were already in, and if yes, what was the third - bass - driver?
I presume it's a).
The generic X/O will most certainly be unusable. You will have to measure and design a x/o to the specific driver combination, in that specific box.
The choice of midrange (which is excellent) is odd here, far too efficient for the tweeter - although it could be dealt with in the xo design.
But the woofer option - being limited to 6,5" - is impossible to find. No 6,5 will match the PR170MO. Dual 8, 10 or even 12.....
The cabinet (again, if that is what you have and are reusing) lends to a 2,5 way with dual 6,5's if it is WWT, or a 2 way D'Appolito (if it is WTW).

Last edited by Draki; 21st February 2016 at 02:16 PM.
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Old 21st February 2016, 03:33 PM   #3
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Quote:
Originally Posted by Draki View Post
What exactly are you upgrading? a)Are you reusing existing cabs (floorstanders, with cutouts for 2 6,5" and a tweeter) or b) the two drivers you listed were already in, and if yes, what was the third - bass - driver?
I presume it's a).
The generic X/O will most certainly be unusable. You will have to measure and design a x/o to the specific driver combination, in that specific box.
The choice of midrange (which is excellent) is odd here, far too efficient for the tweeter - although it could be dealt with in the xo design.
But the woofer option - being limited to 6,5" - is impossible to find. No 6,5 will match the PR170MO. Dual 8, 10 or even 12.....
The cabinet (again, if that is what you have and are reusing) lends to a 2,5 way with dual 6,5's if it is WWT, or a 2 way D'Appolito (if it is WTW).
The existing cab (Mordaunt-Short MS-904) has a tweeter and midwoofer. The plan is to removed a section of the front cab panel, which is large enough to house a 3-way setup. I'd let fabricate some MDF and insert back into the space. From memory the floorstanders only have wadding and there's no complex internal structure. The internal width of the cab is 7", so 6.5" drivers are the limit. The current cab has a nice finish/colour, therefore, my preference is to re-use it. The tweet and midrange are yet to purchased... I wanted to make sure I had my drivers correct before committing.

It's good to hear I've chosen a good midrange! Forgive my lack of understating but why is the tweeter a poor companion for the midrange? I'm happy to build or buy a crossover that fits with the drivers however I have no idea what cross over points would be right. I chose the 375/3k based on looking at the graphs and trying to avoid breakup whilst maintaining a flat-ish response

I'd not considers doubling up some drivers but happy to go that way

Last edited by spark010; 21st February 2016 at 03:43 PM.
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Old 21st February 2016, 04:05 PM   #4
Draki is offline Draki  Macedonia
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I suspect you are better off keeping the MS-904 as is...
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Old 21st February 2016, 04:11 PM   #5
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I suspect you are better off keeping the MS-904 as is...
That's not very DIY Audio though...
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Old 21st February 2016, 05:52 PM   #6
jReave is offline jReave  Canada
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First, I suspect you don't know just how hard this is going to be.

Second, you'll want to stay away from a prefab xo if you want decent sound.

Third, you are pushing that tweeter and woofer combination in terms of the xo point. You are better off crossing higher for the tweeter which means that you should really be using a smaller mid, like just as an example since you picked Audax, the HM100ZO.

But you haven't really provided us with enough info.

Why do you need/want such high sensitivity?
What is the net internal volume for the mid and for the woofer?
What do you mean by "good low down dB's"? What F3 in Hz are you after?
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Old 21st February 2016, 06:48 PM   #7
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Originally Posted by jReave View Post
First, I suspect you don't know just how hard this is going to be.
It's been pretty hard so far and at this point in the project its a bit overwhelming but I like a steep learning curve

Quote:
Originally Posted by jReave View Post
Second, you'll want to stay away from a prefab xo if you want decent sound.

Third, you are pushing that tweeter and woofer combination in terms of the xo point. You are better off crossing higher for the tweeter which means that you should really be using a smaller mid, like just as an example since you picked Audax, the HM100ZO.
I can see that the 4" has different characteristics higher up the frequency range. i.e. less peaks.. Is that the rational for using the 4"? XO of 4 or 5 kHz?

Quote:
Originally Posted by jReave View Post
But you haven't really provided us with enough info.
As a newbie, its hard to know what info to provide

Quote:
Originally Posted by jReave View Post
Why do you need/want such high sensitivity?
What is the net internal volume for the mid and for the woofer?
What do you mean by "good low down dB's"? What F3 in Hz are you after?
Sensitivity: Based on the midrange, I assumed that the other drivers should be just as sensitive, so that I don't get large variations in volume between driver crossover.

Volume: I haven't calculated that yet. I was going to use some design software to help decide the internal structure of the cab.

F3 & and Low Down dB's: I guess as little drop off as possible. So ideally 20-30hz would be relativity high starting point. My only reference for this is the resonance graphs. Some drivers have very low dB's around 20hz where as others are in the 70dB+ range.
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Old 21st February 2016, 08:15 PM   #8
jReave is offline jReave  Canada
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Quote:
Originally Posted by spark010 View Post
I can see that the 4" has different characteristics higher up the frequency range. i.e. less peaks.. Is that the rational for using the 4"? XO of 4 or 5 kHz?
Sort of. The peakiness up higher on woofers is an indication of breakup and you want to stay away from that. But the other reason is directivity, ie. off-axis response. As you go higher in frequency with any driver, at some point the off-axis response starts to diminish in SPL's based on the diameter of the cone - the larger the diameter, the lower in frequency this starts to happen. Ideally, you want to cross over before this effect gets significant. Thus, smaller drivers for higher xo points.

Quote:
Originally Posted by spark010 View Post
Sensitivity: Based on the midrange, I assumed that the other drivers should be just as sensitive, so that I don't get large variations in volume between driver crossover.
It's the woofer which will determine the speaker sensitivity. However in any speaker sitting out into a room, the LF's will lose about 6dB to something called baffle step loss. So it's this level (woofer sensitivity minus 6dB) that the other drivers need to match. If they are higher which is usually the case, they simply get padded down in the xo. So, you basically need to choose your woofer 1st.

Now in order to select a woofer, it's best if you start by defining your needs. Such as:

- minimum sensitivity (how much power do you have available?)
- minimum impedance (what will your amp be happy with?)
- box volume (defined by your present cabs)
- F3 (music, movies or both?)
- and maybe max SPL levels desired too

Then you have to use a box modeling program to see how different drivers will fit those criteria. Just looking at the manufacturer's FR graphs doesn't tell you enough. Nor does just looking at a driver's resonance frequency, Fs. You have to plug in a driver's relevant specs into a modeling program to see how it will perform in the bottom end.

I prefer Unibox but it needs Excel. WinISD is the other popular one. Give 1 or the other a try.

In terms of F3, the minus 3dB point, if the speakers are just for music, around 40Hz is usually good enough (bottom E string on bass guitar). Trying to get below that with a 6.5" driver does in fact get a little hard.

Figure those things out and then we can start to choose some drivers for you.
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Old 21st February 2016, 08:36 PM   #9
Draki is offline Draki  Macedonia
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Join Date: Sep 2010
Quote:
Originally Posted by spark010 View Post
That's not very DIY Audio though...
The advice was good-hearted. You should consider the first DIY project by trying some of the established kits (i.e. Wilmslow or Falcon in UK) rather than irreversibly changing the very nice cabinet, and a perfectly functioning system.
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Old 21st February 2016, 09:23 PM   #10
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Quote:
Originally Posted by jReave View Post
Sort of. The peakiness up higher on woofers is an indication of breakup and you want to stay away from that. But the other reason is directivity, ie. off-axis response. As you go higher in frequency with any driver, at some point the off-axis response starts to diminish in SPL's based on the diameter of the cone - the larger the diameter, the lower in frequency this starts to happen. Ideally, you want to cross over before this effect gets significant. Thus, smaller drivers for higher xo points.



It's the woofer which will determine the speaker sensitivity. However in any speaker sitting out into a room, the LF's will lose about 6dB to something called baffle step loss. So it's this level (woofer sensitivity minus 6dB) that the other drivers need to match. If they are higher which is usually the case, they simply get padded down in the xo. So, you basically need to choose your woofer 1st.

Now in order to select a woofer, it's best if you start by defining your needs. Such as:

- minimum sensitivity (how much power do you have available?)
- minimum impedance (what will your amp be happy with?)
- box volume (defined by your present cabs)
- F3 (music, movies or both?)
- and maybe max SPL levels desired too

Then you have to use a box modeling program to see how different drivers will fit those criteria. Just looking at the manufacturer's FR graphs doesn't tell you enough. Nor does just looking at a driver's resonance frequency, Fs. You have to plug in a driver's relevant specs into a modeling program to see how it will perform in the bottom end.

I prefer Unibox but it needs Excel. WinISD is the other popular one. Give 1 or the other a try.

In terms of F3, the minus 3dB point, if the speakers are just for music, around 40Hz is usually good enough (bottom E string on bass guitar). Trying to get below that with a 6.5" driver does in fact get a little hard.

Figure those things out and then we can start to choose some drivers for you.
That all makes sense. Thank you for going into so much detail! Looks like I've got a bit of home work and research to get on with. Will post back soon
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