HDS 810921 Tweeter with Fullrange Driver (XO-help) - diyAudio
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Old 8th September 2008, 01:17 PM   #1
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Default HDS 810921 Tweeter with Fullrange Driver (XO-help)

Hello friends,

I need help with XO work

I would like to try using my Fostex F200A fullrange driver in a 2-way application with a Peerless HDS tweeter I have. XO to be around 3500Hz. The F200A is truly "fullrange" and it may seem real waste to cut off as low as 3,500Hz. However I want to try it in a 2-way (passive) this time, to escape F200's rising response bump, starting just before 4000Hz.

Unfortunately I am not network guy at all. Is 2:nd order XO for the HDS at 3,500Hz recomendable? Would it be high enough for the HDS?

I am not sure if it possible without lots of measurments etc, but is it possible to recieve (or buy) a suggested network (LP+HP) 2:nd order, for my F200a-HDS configuration? Some details are:

1. Mid+Bass: Fostex F200A, ported alignment. http://www.fostexinternational.com/d.../pdf/f200a.pdf

2. Peerless HDS Tweeter
http://www.tymphany.com/810921

My above speaker is "in-wall" i.e the two element will be flush mounted same level as the wall, in other words no possibility for toe-in. I will constantly listen off-axis (aro 15Degrees). I also have Fostex L-Pad so I could (possibly) also use that one to manually adjust level of tweeter, if necessary.

All comments appreciated.

Thanks in advance

LageB
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Old 8th September 2008, 01:56 PM   #2
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Hello,

2kHz should be a better point of crossover.

To make a good crossover, you should have measurement tools.

But See here : http://www.geocities.com/woove99/Spk...esigningXO.htm

Regards.
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Old 8th September 2008, 08:02 PM   #3
Jay_WJ is offline Jay_WJ  United States
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There's no point doing this with expensive fullrange drivers. You'll lose one of the benefits people attributes to fullrange drivers: low phase distortion. The audibility of phase distortion is a debatable issue, but even so, if I were you I'd never add a tweeter to this driver. I might try an acoustic first order filter to avoid phase distortion, but with a 1" tweeter, the highest xover point for a 1st order rolloff would be greater than 4000 Hz, which nullifies your purpose.

If your sole purpose is to attenuate a hump around 4000 Hz, why not try a notch filter?
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Old 8th September 2008, 08:45 PM   #4
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Thanks for your input Jay & Jerome,

Jay,
Source for 2-way idea for the F200a is coming not only from me, but also others experience, such as http://www.iol.ie/~waltonaudio/fostex.html
or threads like this http://www.diyaudio.com/forums/showthread/t-113223.html

I will listen off-axis so I will in any case need helper tweeter. Then, I thought perhaps worthwhile to try 2-way with somewhat lower XO (aro 3,500-4000Hz) to completely avoid bumpy frequency response of F200 over 4000Hz - especially off axis case.

Maybe notch to tame 5000Hz bump of F200 and then 1:st order XO say 8,000Hz? could it be another idea you think?

LageB
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Old 8th September 2008, 09:05 PM   #5
Salas is offline Salas  Greece
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Quote:
Originally posted by Jay_WJ
There's no point doing this with expensive fullrange drivers. You'll lose one of the benefits people attributes to fullrange drivers: low phase distortion. The audibility of phase distortion is a debatable issue, but even so, if I were you I'd never add a tweeter to this driver. I might try an acoustic first order filter to avoid phase distortion, but with a 1" tweeter, the highest xover point for a 1st order rolloff would be greater than 4000 Hz, which nullifies your purpose.

If your sole purpose is to attenuate a hump around 4000 Hz, why not try a notch filter?

Hello. The main benefit in using a single extended range driver isn't phase distortion per se, but listening naturally from a single source (well as close as it gets to it). This is very audible. We don't integrate 2 relatively large distanced sources or more with our crossover and brain processing collage efforts, but we listen to a single source as in nature. Feels inherently right. Of course it does not create lobes as well, but a competent crossover design can come very near for that too. All other sectors of performance are severely compromised versus a 2 way or a multi way.
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Old 8th September 2008, 09:09 PM   #6
Jay_WJ is offline Jay_WJ  United States
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Quote:
Originally posted by salas



Hello. The main benefit in using a single extended range driver isn't phase distortion per se, but listening naturally from a single source (well as close as it gets to it). This is very audible. We don't integrate 2 relatively large distanced sources or more with our crossover and brain processing collage efforts, but we listen to a single source as in nature. Feels inherently right. Of course it does not create lobes as well, but a competent crossover design can come very near for that too. All other sectors of performance are severely compromised versus a 2 way or a multi way.
Yes, that's why I said "one of the benefits." Your point may be relevant in near-field listening. I don't think we can perceive vertically 5" to 7" distant sources from 3 m or farther away.
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Old 8th September 2008, 09:17 PM   #7
Salas is offline Salas  Greece
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Depends on room treatment, for absolute far field, but our competing crossover speaker must be excellent for integration and lobes. Else, minor cancellations or bad power response give it away even more since we now listen 90% to its dispersion. A perfectly crossed coaxial is our best bet for being indistinguishable from a single source in the far field. Try a line array at a gig. 50metres away you know if its a line array or a ''point source'' system.
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Old 8th September 2008, 09:30 PM   #8
Jay_WJ is offline Jay_WJ  United States
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Quote:
Originally posted by salas
Depends on room treatment, for absolute far field, but our competing crossover speaker must be excellent for integration and lobes. Else, minor cancellations or bad power response give it away even more since we now listen 90% to its dispersion. A perfectly crossed coaxial is our best bet for being indistinguishable from a single source in the far field. Try a line array at a gig. 50metres away you know if its a line array or a ''point source'' system.
We may be able to distinguish between different power responses due to coaxial vs non-coaxial driver placement. But in this case, strictly speaking, what we hear is simply different power responses, not the distant sources per se. And I don't think a dip in power response around the xover point due to driver offset is necessarily a bad thing. Some may find it less fatiguing to their ear.
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Old 8th September 2008, 09:33 PM   #9
Salas is offline Salas  Greece
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P.S. Of course Jay_WJ has strong points in his suggestions. And I agree. Don't bastardize a driver like an alnico Fostex. Go one voice, or typical 2 way. Each school to its own.
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Old 8th September 2008, 09:40 PM   #10
Jay_WJ is offline Jay_WJ  United States
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Quote:
Originally posted by LageB
Thanks for your input Jay & Jerome,

Jay,
Source for 2-way idea for the F200a is coming not only from me, but also others experience, such as http://www.iol.ie/~waltonaudio/fostex.html
or threads like this http://www.diyaudio.com/forums/showthread/t-113223.html

I will listen off-axis so I will in any case need helper tweeter. Then, I thought perhaps worthwhile to try 2-way with somewhat lower XO (aro 3,500-4000Hz) to completely avoid bumpy frequency response of F200 over 4000Hz - especially off axis case.

Maybe notch to tame 5000Hz bump of F200 and then 1:st order XO say 8,000Hz? could it be another idea you think?

LageB
According to the Fostex measurement, a 15 degree off-axis listening shouldn't a problem. Using a (super-) tweeter above 8 k with a single capacitor would be an option if you really want a strong top end response. Otherwise, I'd try a simple notch filter approach first. Below is my quick modeling of a notch filter. A Zobel RC circuit is necessary for the notch filter to work properly. You can adjust notch depth by changing the resistor value in the filter. Lower value for shallower notch and higher value for deeper one.

Click the image to open in full size.

-jAy
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