My dipole experiment

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#142
Hi Carlos,

I quit the amplifier scene because I needed to shift my ideas towards getting decent reproduction from their output.

I remember your new room was inducing problems from your boxed loudspeaker drive, and this is what can be substantially overcome when you get rid of the 'box' and go to open baffle; though then you need appropriate bass lift - which you were doing with your NFB loop anyway !!!

The T-bass circuit also helps even more with OB if you could possibly use one of your many power supply transformers to try it ?

Hope all's well with you.

Cheers ......... Graham.
 
#143
Graham Maynard said:
Hi Simon,

You have what looks like 280uF across the woofers.

Do try different values of resistance in series with that.
Same could apply to the circa 10uF across the choke.
Both to prevent independent high 'Q' circuits arising.

Cheers ....... Graham.
Click to expand...

Hi Graham,

I'll try this. I made the woofers' low-pass filter 2nd order and it did improve matters, and measures loads better of course. I then did the high pass on the mid drivers to 2nd order and didn't like the thin, weedy midrange I got. I'm beginning to wonder if this Audax mid can ever sound as I'd like it to. I put it back to first order and left the woofers on 2nd order - this works fine.

My frequency response (other than some fairly minor visible issues) looks good but the upper midrange is audible stronger than the lower midrange. This causes the piano to sound small in scale and tonally incorrect. I did a spectral decay plot, or something like that, in ARTA and saw a long tail in the upper midrange, which corresponds with the issues I hear. Do we think this is an inherent problem with the Audax 4" midranger?

I added a touch more series resistance (13R & 2.2R L-pad now) with the mid driver and this is as close to right as I've found overall. I might look at finding some cheap 4" kevlar midrange drivers as I've always been a fan of the midrange quality of B&W speakers. Any opinions on this?

Thanks,
Simon
 
#144
Hi Simon,

I suggest that your line of 7" drivers could still cause a midrange peak.
Put a blanket over them - is the peak still there ?
If no, you could try fitting an appropriately absorbent grille cloth over them, or try reverse facing them on the front of your baffle.
If yes, it must be related to your mid driver alone and you could try a vertical roll of cloth (hankerchief) in front of the driver.

Driver responses cannot always be as flat as desired, thus we must modify their output to suit, and, as the problems are often related to post-transduction cone/baffle shape, we should try to modify their response using post-transduction methods, not by electrically pre-distorting the waveform fed to the drivers.

Cheers ........ Graham.
 
#145
Graham,

I like your ideas, they seem to make a lot of sense. I don't want to EQ these speakers, and if I ever do it will be after the woofers are driven by a separate amp, so the signal doesn't go through extra stages wholesale.

I tried the speakers in another room/building yesterday and they sounded terrible - hugely droning upper bass output. I hear the effect, only very subdued, at home. More work is needed to match the levels throughout the range. OB speakers are hard to design 😀

Simon
 
#147
Hi SimontY

In the T-bass thread I wrote that I am following this thread with your work. I find your auto-interactive form of writing ery interesting as it describes lots of small problems and solutions, and not only the final picture. I think I will be repeating your steps and methodology soon, but have to conclude some other things first.

Keep on the good and instructive work!

Erik
 
#148
Thanks Erik, I find it useful to come back here and remind myself of things people have suggested or pictures I've uploaded. I hope it will allow others who are thinking about (multiway, passive) OB speakers a bit of insight into how hard it is to do (for a relative beginner).

My next step will be to work on the bass by adding 2.7mH (I have one) in series with the 4.7mH and listen for the bass quality. I should do this tonight. I will try first and 2nd order.

Simon
 
#149
Hi Simon
I've been following the thread since the start and sometimes I think that you've become addicted to change.
Also many of the things you have been doing are to fix problems that exist because the drivers you started with are not OB woofers.
Don't take this wrong, I've learnt a lot from what you have posted.
But if you do have the OB bug what you really need are OB woofers and good ones seem to be few and far between and vintage drivers seem to be best.
Our local supply of new OB woofers has just dried up.
A few things I've gleaned tho, big is better, low Fs is better, high Q is bette,r but you don't find all of these quality factors parcelled with high power handling, even using 6 woofers the best I've been able to model is 106dB because they run out of travel at 20watts and the sound of an overdriven woofer isn't pretty.
But put these parametres through your programs.
Fs 32/ Qms 4.00/ Qes 0.428/Vas 166litres / SD 0.0490M2
Then put 6 of them on a baffle 650 X 1200mm and see what you think.
I haven't built them yet, still playing with something else.
Regards
Ted
 
#152
Ted,

I've noticed some of the same things as you WRT to suitable OB drivers. I was impressed by some Goodmans 12" full rangers I heard once.

I'm not sure what I can do with those specs you gave me. All I've used software-wise in WinISD for passive crossovers, Edge for dipole losses and baffle peaks and ARTA for measuring.

I don't need 106dB in my tiny room, never mind 106dB before room-gain... that's reference home cinema levels!!

Simon
 
#154
Thanks Ted, that's a terrific spreadsheet, it should be an asset to the armoury of tools!

Last night I made a simple change to my woofer xover. I removed the caps and went back to first order, adding 2.7mH in series with the existing 4.7mH.

LOADS better. The integration between drivers is more seamless, the upper bass peak is audibly inconspicuous and, unexpectedly, the imaging and openness of the sound stage is markedly better. Listening at high levels was once again a joy and now exposes no large problems.

I was going to try adding a bigger uF in parallel for 2nd order but I wanted to listen to more music, and turned the soldering iron off 😀

I might try 2nd order tonight (7.4mH & 460uF).

Ultimately, there could still be more mid and lower bass, and there is some resonance here and there, but it's quite close now.... (for a couple of days I'll say that....!!!)

Simon
 
#155
Simon, your'e using woofers series / parallel aren't you??
Try this / add a second inductor in series between first and second woofer / see if it adds to deep bass.
I've only tried it a couple of times worked once, use that 2.7mH between woofers and listen, it may help then again it may not.

It was a suggestion somewhere for baffle step
 
#157
I would say that the woofers closest to the baffle/floor junction are where the low bass should be, at the moment I'm trying to get my wife to agree to a baffle full height --- Floor to ceiling _____ I'm not having much luck so far.

I would say that the DC of the inductor itself needs to be taken into account if doing things "correctly" but I never bothered in my experiments
 
#159
I managed to buy 12 of those cheap drivers I gave you the parametres for, now I want to use them all up,
I will have to compromise, you think your room is small?? if I put these baffles in the lounge room we'd have to go outside to turn around
 
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