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Get familiar with the reaction system: Introducing the Reaction System
HiVi DM-7500 and DSP . . .
Guys,
Is this mid dome really all that difficult to work with (flattening) if using DSP alone?
Swan/HiVi says the FR looks like this -->
. . . And impedance looks like this -->
JR says it looks like this on his baffle/raw [no XO I assume] -->
Using DSP alone, can this thing not be easily flattened on a 10" wide baffle and crossed around 400 Hz LR2 or LR4 and be just fine?
Comments
Not hard with DSP.
I suspect that MANY drivers are far more suitable using DSP than passives XO's - Thanks, PWRRYD.
Any other thoughts?
DSP is is no better than passive at fixing the directivity issues around 1200-1300hz this driver exhibits.
It is also no good at suppressing the impedance peak required to cross that low.
Otherwise, I would put this mid face to face with the Volt/ATC.
True.
I was watching Erin's Audio Corner this weekend. He described situations where you can not tame some diffraction issues with EQ/DSP. I think it was part of the new Dayton speaker review.
So, which is it then - GTG with DSP or a no-go due to impedance peak?
What happens to directivity and why?
Seems the active folk disagree with JR and I about whether the spike suppression is worth the trouble when using DSP. There was a discussion awhile ago.
InDIYana Event Website
I'm not discounting it, Wolf.
I am merely looking at the sweeps that are unfiltered and asking myself and you guys what the problem is if using DSP alone.
There are no peaks indicated in the FR that need to be dealt with using passive components.
Distortion tends to rise toward self resonance of any dome based driver, at least in my experience.
Suppression of the hill can allow lower Fc and keep HD low without having to attenuate into oblivion and approach a more shallow slope with better blending of the handoff. Very steep slopes hand off without blend where stuff sound discretely with one driver or another, at least to me.
InDIYana Event Website
A couple of tips...
Keep the baffle as skinny as possible. Use large roundovers (LARGE, like 1-1/4 or 1-1/2 inch roundovers) or large chamfers/facets. I used a 10" woofer so my baffle is 12-1/2 inch wide. It would have had to be even wider for large roundovers so I used as large facets as I could (but realistically it would have been better if I could have got even closer to the tweeter and midrange.)
Why are you crossing over so low? I crossed higher and steeper and simply avoided the impedance peak at Fs. My target was LR4 but I just looked at my VituixCAD details and it looks like I was almost exactly an LR6 at 650Hz. (That's not on purpose, I never even experimented with a deliberate LR6.)
This speaker is still in progress, but was well received at InDIYana. Purple line below is LR6 at 650Hz and LR4 at 3.5Khz (I think maybe I'll claim that I was targeting that LR6 slope.)
Raw directivity of DM7500 in cabinet. White on-axis line probably looks a lot like JRs on axis
Directivity of DM7500 with crossover
Crossover for mid-section
Directivity of complete 3-way speaker
Baffle
Since you appear combative tonight, I ask you how do you deal with a tweeter known for Fs peak induced distortion using DSP? Think XT25 and it's monster impedance peak at Fs.
Then study up on the Purifi suggested topology to lower distortion in an active circuit by using passive components.
Active is not a panacea.
And the HiVi requires impedance compensation for maximum return.
No combat indicated.
Simply a question as to how HiVi/Swan plots a graph that looks flat with an unfiltered FR like the above pic?
JR I am interested in the Purifi topology. Can you pls point me to where it is at or a link if possible?
Ani_101 - The Purfi links in this pertinent thread are dead now for some reason --> https://diy.midwestaudio.club/discussion/2157/passive-resonance-suppression-of-drivers-around-fs-vs-dsp-discussion/p1
(Maybe someone can get us some current live links - it was a good write-up/explanation from Purfi, BTW).
After considering the feedback thus far, I suspect that the sweeps I am looking at are on-axis only while the feedback tells me to look at the off-axis response of the driver.
To my mind this is dictated by baffle width and edge diffraction control employed (round-overs) while ignoring the room.
I listen mostly to on-axis to slightly off-axis so My repeated question remains.
This hobby is so subjective to the point of not being worthwhile to seek further feedback just as asking for mixing feedback - if it sounds good to me in my space and on my baffle the rest of it matters not at all.
If I am in error here please let me know and thanks for the favor of your replies, guys!
From my understanding, a big part of the directivity is related to room reflections. If you listen on axis AND nearfield then maybe you are okay. But even if you listen on axis, if you are listening in the farfield you are getting reflections.
If you want a zip file of the off-axis measurements I posted above (0 to 180 degrees in 10 degree increments) let me know.
David, you are on the money.
I listen in near field on all my systems from a critical perspective - rarely in mid to far field as those later listening positions do not require my detailed focus - they are just ambient noise as a distraction while doing other things.
For my needs the off axis stuff is just not that relevant - It's nice to have wide dispersion so that when moving around a listening space I hear both channels and I accept that the room will effect the FR but it is of no critical consequence to me.
I am not making speakers for a designated concert hall with paying clients.
This is not rocket science unless you have an actual need for it to be so. Damn few of us do but we get so caught up in the minutia as to loose perspective.
Your off axis sweeps are sufficient/telling and I thank you for posting them.
I think I found the Purfi link -->
https://purifi-audio.com/blog/app-notes-2/low-distortion-filter-for-ptt6-5x04-naa-11
At the risk of beating a dead horse, I'll repeat Charlie Laub's post in the previous discussion here about this subject:
"The bulk of what Wolf wrote about seemed to center around impedance compensation. That is something totally different than what Lars is doing (he is filtering). Also, the impedance itself does not represent any sort of energy storage, or there would be a peak in the FR as well at Fs. The amount of energy storage is described by the Q of the resonance, and at Fs this means Qts, and that is not typically very high. My take of Wolf' post was that this issue is all about removing the negative influence of the impedance peak on the (passive) crossover network function. THAT is a non-issue when using a DSP system, because the driver impedance doesn't matter. It is only a problem for the passive network that uses the impedance ratio of two branches as a function of frequency to make a voltage divider and pass or block power that is delivered to the driver. If the attenuation is falling off because there is no impedance compensation at Fs then yes you will probably have the driver making some undesirable sounds because (A) the excursion will be higher near Fs compared to higher in frequency and (B) distortion is always higher near Fs for a driver (based on my observations). Undesirable power that reaches the driver at FS will cause excessive motion and distortion products that occur at higher frequencies. But to reiterate, this is a non-issue for DSP."
I felt like that whole discussion was met with Charlie having blinders on.
InDIYana Event Website
You know what?
I'm gonna order me a pair of them there DM-7500's and Dee Eth Pee the holy crap out of them and be happy.
Pics when I am done . . .
Don't order them today, PE will probably have 10-12% off for Memorial Day this weekend.
Thanks for the heads-up/reminder.
After applying the settings to the DSP units that Thanh suggested to the mini towers, I am reconsidering the purchase of those DM-7500's as the existing DMB-A's dig down deep/clean enough to meet the 3" ported SBPFC20's at 500 Hz LR24 without objectionable midrange port leakage just fine now. No passive components required.
For reference/continuity --> https://diy.midwestaudio.club/discussion/2614/fountek-neo3-5h-ribbon-testing#latest
Keep on experimenting, guys!
My curiosity got the better of me so I now have a pair of these drivers inbound - just couldn't pass up the discount during the sale . . .
[Insert evil laugh, here]
Yep just ordered DMB-As for myself. Managed to stay pennies above the free shipping limit so I don't have to burn my own gas.
OK, I am back home - mum has a part time nurse assistance to be with her now and can give her better care than I.
The XO's I was playing with and had out of phase just sounded cool and I have set the mids out 180* from the tweeters as Thanh suggested and everything is fine with a defined center mix.
This sounds great - very punchy:
David (a4eaudio),
You just posted (your) HD graphs for this subject driver on DIY Audio Forums and I have questions concerning the effects of measurement/listening axis vs HD3 - does the sweep change with angle due to the dome shape or remain constant?
How does the angle effect an equivalent cone driver if at all?
[Just my curiosity kicking-in again . . . ] Thanks.
Interesting question, I have never seen anyone present distortion measurements on axis. (My guess based on the image below, this is because it doesn't provide much more useful information).
I try to measure distortion at 86 and 96 db @ 1m, with the actual measurement 96db and 106db at 31.5 cm. This eliminates more of the noise from the measuring environment. BUT...REW does have the distortion data in all of the measurements. The data below is from my off axis SPL measurements, which was about 88db at 1 meter, but I think it shows what you are looking for.