Passive correction for SPL dip?

Tenson · 6th May 2007, 12:40 AM

Hi,

I have built a pair of speakers using the ScanSpeak 12m4631G midrange driver and they sound really good, but there is a noticeable dip around 2-3KHz that makes vocals sound a bit recessed.

I also notice this same dip, though less pronounced, in the response measurements Zaph took of some of these drivers.

I think part of the issue may be that I did not countersink the driver, so I will try that. It is also, however, partly due to having the Xover near-by and the lead-in to the crossover drops that dip down even more

But if it is still an issue after recessing the driver, is there any way to correct for that dip using passive filters?

If the whole level has to go down 3-4dB to do it then so be it (thinking band pass kind of filter). Or maybe I can actually make a resonance at this frequency? But I am not sure exactly how to do all this with passive filters so advice is appreciated please!

I realise I could correct using an active filter between CDP and amp but I don't want to have to do that since I'd like the speakers to be 'stand alone'.

Cheers guys!

Edit: Zaph, can you recall if you countersunk the driver when you took your measurements? ScanSpeak's own PDF does not show this dip.

Geoff H · 6th May 2007, 12:57 PM

Hi Tenson, it's not so much a dip at 2.3k but a rise from 600 - 1.6 k of 3db. See how recessing the driver effects things. A diagram of the crossover would be helpful, with xo freqs.

Geoff

banana · 6th May 2007, 03:37 PM

Hi Tenson. I suggest u to measure off axis response as well. If the dip dissapear off axis, I'll live with it.

Try to correct diffraction issue with EQ, might create power response irregularity.

Svante · 6th May 2007, 08:45 PM

What are the baffle dimensions/driver placement on the baffle? Have you run th baffle through The Edge?

Tenson · 6th May 2007, 09:41 PM

Hi,

Yes I did BD simulations, I don't think it is that. I am beginning to think it is more complex such as phase issues and inconsistencies between the tweeter I first measured and the one I added the network to.

Don't worry about it for now, I must rethink the whole thing I think.

Tenson · 6th May 2007, 11:15 PM

Actually I do have a question if I may.. is it just me who has found SpeakerWorkshop does not model notch filters well? At least, I have tried two different notch filters in this project (at different frequencies and Q) and neither were anywhere near as effective as SpeakerWorkshop made out they would be. I had to use about double the resistor value to even get a noticeable dip in the response.

Ron E · 7th May 2007, 12:34 AM

Are you modeling inductor DCR, and what type of capacitor are you using?

Tenson · 7th May 2007, 12:39 AM

Hi, yeah I was modelling the inductor DCR, it was not big enough to mean I needed double the resistor value anyway though.

I was using standard aluminium electrolytic caps. Are these not suitable?

In fact I have sometimes wondered, since music is AC, surely electrolytic caps, directional as they are, are not suitable? But they do seem to work fine in most cases! I don't like to splash on polyprops or whatever until I know the Xover is working well. ..and sometimes I just don't bother at all!

Geoff H · 7th May 2007, 12:50 AM

Hi Tenson,

We should never use standard electrolytic caps in a xo. If larger values are required use bipolar, or non polarised electro, and if passing higher freqs should have smaller non electrolytic caps in parallel.

A standard electrolytic has a diode type action, and can explode if reversed polarised.

Geoff

Tenson · 7th May 2007, 12:56 AM

I know it is not best practice... but they do seem to work just fine for things like simple tweeter Xovers. In fact I have never had any problems using polarised caps!! Its seems odd to me, but anyone with a good electronics head care to explain why they seem to work fine in most cases?

6th May 2007, 12:40 AM	#1
Tenson diyAudio Member Join Date: Feb 2006 Location: Kent	Passive correction for SPL dip? Hi, I have built a pair of speakers using the ScanSpeak 12m4631G midrange driver and they sound really good, but there is a noticeable dip around 2-3KHz that makes vocals sound a bit recessed. I also notice this same dip, though less pronounced, in the response measurements Zaph took of some of these drivers. I think part of the issue may be that I did not countersink the driver, so I will try that. It is also, however, partly due to having the Xover near-by and the lead-in to the crossover drops that dip down even more But if it is still an issue after recessing the driver, is there any way to correct for that dip using passive filters? If the whole level has to go down 3-4dB to do it then so be it (thinking band pass kind of filter). Or maybe I can actually make a resonance at this frequency? But I am not sure exactly how to do all this with passive filters so advice is appreciated please! I realise I could correct using an active filter between CDP and amp but I don't want to have to do that since I'd like the speakers to be 'stand alone'. Cheers guys! Edit: Zaph, can you recall if you countersunk the driver when you took your measurements? ScanSpeak's own PDF does not show this dip.

6th May 2007, 08:45 PM	#4
Svante diyAudio Member Join Date: Feb 2004 Location: Stockholm	What are the baffle dimensions/driver placement on the baffle? Have you run th baffle through The Edge? __________________ Simulate loudspeakers: Basta! Simulate the baffle step: The Edge

7th May 2007, 12:34 AM	#7
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	Are you modeling inductor DCR, and what type of capacitor are you using? __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan

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6th May 2007, 12:57 PM	#2
Geoff H diyAudio Member Join Date: Oct 2006	Hi Tenson, it's not so much a dip at 2.3k but a rise from 600 - 1.6 k of 3db. See how recessing the driver effects things. A diagram of the crossover would be helpful, with xo freqs. Geoff

6th May 2007, 03:37 PM	#3
banana diyAudio Member Join Date: Feb 2003 Location: Hong Kong	Hi Tenson. I suggest u to measure off axis response as well. If the dip dissapear off axis, I'll live with it. Try to correct diffraction issue with EQ, might create power response irregularity.

6th May 2007, 09:41 PM	#5
Tenson diyAudio Member Join Date: Feb 2006 Location: Kent	Hi, Yes I did BD simulations, I don't think it is that. I am beginning to think it is more complex such as phase issues and inconsistencies between the tweeter I first measured and the one I added the network to. Don't worry about it for now, I must rethink the whole thing I think.

6th May 2007, 11:15 PM	#6
Tenson diyAudio Member Join Date: Feb 2006 Location: Kent	Actually I do have a question if I may.. is it just me who has found SpeakerWorkshop does not model notch filters well? At least, I have tried two different notch filters in this project (at different frequencies and Q) and neither were anywhere near as effective as SpeakerWorkshop made out they would be. I had to use about double the resistor value to even get a noticeable dip in the response.

7th May 2007, 12:39 AM	#8
Tenson diyAudio Member Join Date: Feb 2006 Location: Kent	Hi, yeah I was modelling the inductor DCR, it was not big enough to mean I needed double the resistor value anyway though. I was using standard aluminium electrolytic caps. Are these not suitable? In fact I have sometimes wondered, since music is AC, surely electrolytic caps, directional as they are, are not suitable? But they do seem to work fine in most cases! I don't like to splash on polyprops or whatever until I know the Xover is working well. ..and sometimes I just don't bother at all!

7th May 2007, 12:50 AM	#9
Geoff H diyAudio Member Join Date: Oct 2006	Hi Tenson, We should never use standard electrolytic caps in a xo. If larger values are required use bipolar, or non polarised electro, and if passing higher freqs should have smaller non electrolytic caps in parallel. A standard electrolytic has a diode type action, and can explode if reversed polarised. Geoff

7th May 2007, 12:56 AM	#10
Tenson diyAudio Member Join Date: Feb 2006 Location: Kent	I know it is not best practice... but they do seem to work just fine for things like simple tweeter Xovers. In fact I have never had any problems using polarised caps!! Its seems odd to me, but anyone with a good electronics head care to explain why they seem to work fine in most cases?

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