Preliminary IMD measurements for subwoofers (1 Viewer)

[Tom Vodhanel]

snip.

 

[mylan]

Oh shit, here we go again!

 

[Shervin_Sabri]

......

 

[Tom Vodhanel]

Yeah you guys are right, I don't want to sidetrack Ilkka's data with my rant on the sad state of the internet...I'll save it for another time..

Tom V.
SVS

 

[steve nn]

Totally understood, it's nice to see you post none the same Tom.

 

[mylan]

Tom,
I've never met you but I have the utmost respect for you in regards to your being available to answer questions and join in these forums. How many other manufacturing reps do you think are as forthcoming with information as you and the staff at SVS are? Not many. I understand you wanting to set the record straight concerning the technology behind your product, I just wish someone like Peter Marks wouldn't jump in at EVERY opportunity to debate the best way to build a sub, especially since his product was not even mentioned. Debates like this are hardly productive, especially when no one backs down.
At the end of the day,and I might be in the minority here, all I care about is how it sounds, or more precisely, how it feels. I hope you don't think my comment was directed at you, it wasn't. You and many here have already convinced me that my next sub will proudly be an SVS. Thanks, Mylan

 

[steve nn]

I concur, but thats all I better say...you said it just fine. I've been meaning to say that.:b

 

[dave alan]

Please tell me what debate Peter entered into? What is in his post that you find in error or otherwise?

In fact, Peter has very valid points and I wouldn't mind reading the 'debate' that might ensue if you would please butt out and find the 'how it sounds' thread to post in.

This is just another irrelevant TV cheerleader post

Bosso

 

[Peter Marcks]

Dear Robert,


I can't speak for the design goals of other companies, but rather explain our design goals and philosophies with respect to subwoofer design. Remember that the VTF series has been around since the late 1990's, the first variable tuning subwoofer of it's kind. So we have had variable tuning, single driver, ported box subwoofers for so many years now. Other variable tuning ported subwoofers have surfaced since then. The MK2 series is really just a refresh of the VTF technology introduced on the VTF-MK1 subwoofers. The HO series is certainly a bit different though, using more advanced/new technology. The VTF-3 HO is using different driver and porting technology than others in the price range. How that translates to THD and IMD is difficult to say. However, there are plenty of great options in the price range, to satisfy a wide variety of tastes and preferences.

Sincerely,

 

[ScottCarr]

 

[Mark Seaton]

While I don't disagree that there are points to examine within discussion of different manifestations and causes of distortion, Peter has repeatedly stated his/Hsu's "stance." The vague allusion to some source of distortion without any explanation or example, subjective or quantitative, has been offered on his part. I'm sure both TV and I are well aware of modulation issues in high excursion woofers. While hardly the only reason, if TV wasn't, he probably wouldn't have stuck with the Ultra's motor design through the years.

The question that has been posed by forum members many times before is what efforts does Hsu make to keep this under control that might not be done in other designs? Personally I see many more significant differences between various manufacturer's implementations than IMD, even if there are reasons to talk about it.

My 2c.

 

[SteveCallas]

I have to disagree with this. I enjoy when the "pros" chime in to offer their point of view on sub design and what parameters are important. Now I disagree with Peter on this topic, and we have discussed it more than once, but by examining this area and by benefitting from Ilkka's and Ed's work, we are all more intelligent. Sure, Peter was wrong but his initial comments sparked a learning experience.

 

[Peter Marcks]

Good afternoon Steve,


It would certainly be possible to realistically compare a subwoofer with single higher excursion driver versus a subwoofer with multiple lower excursion drivers. This is exactly the situation with the current dual driver ported versus single driver ported subwoofers in the $899 and $1199 price ranges.

Sincerely,

 

[Peter Marcks]

Hello Mark,


Using Ilkka's data on IMD, it actually strongly supports our philosophy - if one uses two 12" woofers similar in design to Thilo's woofer but less Xmax, the IMD generated would be similar to the 115 dB results - each woofer would only need put out 114 dB to get 120 dB total. In other words, the resulting IMD would therefore be cut in half in comparison to the single higher excursion driver, at the same SPL level.

 

[Ilkka R]

As I already told before, unfortunately I am out of subs already, so I asked a good friend to bring his high performance subwoofer into my place for some measurements. Since some people felt it wasn't a right decision to tell the brands/models of the previously tested subwoofers, let's just call this third sub a "Sub C". I will only say its driver can be considered more high excursion than low excursion driver. I won't even tell if it's a retail or DIY sub.

Again same 4" distance between mic and cone was used and subwoofer was tested for IMD and THD at three different levels: 110 dB, 115 dB and 120 dB.

I will not bore you with exact numbers, but post only the graphs instead.











It seems that Sub C has quite similar results with Ultra regarding IMD at lower levels, but actually pulls slightly ahead at higher levels. Regarding THD it's only a tad worse than the Ultra, so IMD+THD levels are almost identical. I must admit I was a bit surprised how well this sub scored. I wasn't expecting this kind of performance, but it's always nice to see some surprises. I'm really excited to start measuring these tests outdoors for different kind of subwoofers. I'm also considering weighting higher frequency components differently than those closer to the two fundamentals.

 

[Ilkka R]

How does the new '3HO carry out this philosophy of yours?

 

[Tom Vodhanel]

Hi all, thanks for the support(cheerleading... I don't want to sidetrack this thread with a rant. But I will repeat...

Ilkka has never worked for SVS, and has never been compensated in any form by SVS...we have never even sent him a t-shirt. I had no idea he was even doing these measurements until I saw them posted on HTF. So if you see anyone saying/implying otherwise...they are flat out lying. (which shouldn't shock anyone when you consider the source(s)...)

We should let Ilkka perform more tests on more woofers before saying anything definitive. He has even labelled this his PRELIMINARY measurement thread and then went on to say he is planning on many more. I'm sure he'll appreciate any constructive criticism/ideas how to make future tests better. I don't think criticizing his data without offering specific suggestions on how to make it better does much good though. There are literally an INFINITE amount of ways you could measure for IMD in this context. So if anyone thinks they know one specific way which would be best/better...by all means...speak up. But I don't think it would be fair to him if a manufacturer just sits back and waits for him to spend countless hours (on test after test after test) only to take a stance of...

"nope, you didn't do it right THIS time either...keep trying and when you finally find ONE way that makes our product look best...we'll say THAT'S IT"..

Tom V.
SVS

 

[Peter Marcks]

Hi Ilkka


This is a forward-looking philosophy. If you read again, notice I said that we would rather not use one "ultra" high excursion driver, but rather more cone area and lower excursion, in order to achieve a given SPL level. This is for various reasons, including lower IMD. I do not consider the VTF-3 HO driver to be an "ultra" high excursion driver. If it had something like 40mm xmax one-way, then I obviously would.

 

[Tom Vodhanel]

>>>While I don't disagree that there are points to examine within discussion of different manifestations and causes of distortion, The vague allusion to some source of distortion without any explanation or example, subjective or quantitative, has been offered.

 

[Peter Marcks]

I do not feel that is it good to attack or harrass anyone on a personal level.