Polars, phase response, etc.

[jeffbabcock]

For those looking to move beyond basic eq correction, consider posting polar plots and phase plots of your speakers.

EQ can only go so far, and if you have been doing this for long you know that just because a system has a "flat" response does not mean it sounds the same as another or for that matter even sounds good.

If we can collect information about polars and phase of cabinets we can gain lots of useful information relating to how the cabinets will interact with each other, how much off-axis leakage is present at each frequency, etc. With phase data we can examine use of FIR filters and related DSP. There are plenty of discussions and a few devices and software applications that deal with these topics. There are some amazing possibilities here. If you thought your BFM cabs already sound good, think again, we can take them a step even further.

FYI there are many ways to capture phase and polar data.
Download the free demo of smaartlive for a good start. Runs on windows or mac. Do some reading on FIR filters.

If you have built BFM cabs and have a means of posting some of this information, I would encourage you to do so and see where this can go.

Cheers
Jeff

[Mark Fairchild]

Hi,
I have a personal license for WinMLS2000. It has the capabilities of measuring things like phase, group delay, waterfall plots, etc. The only BFM speaker I have access to is a Tuba 24, but my father is working on some DR250s. When he finishes those I can take measurements with my Superlux ECM-999 microphone. It's at least a step up from the behringer measurement microphone. I will take them outside of course.

[jeffbabcock]

As an example of benefits to be had regarding phase, check out the BSS Soundweb stuff. This is just one example of a product that lets you do frequency-specific phase adjustments. Inordinately more useful than a typical phase-reverse button. Such tools have MAJOR potential once we obtain the existing phase plot for a given speaker cabinet.

Cheers
Jeff

[hclague]

Jeff

Here is a screen capture of a transfer fuction in SMAART 5.0 of one of my 8 DR200's. As you can see, there are some phase/time issues that SMAART does not like going on in the overlap region between woofer and piezo's. ( indicated by the relatively poor coherence (red trace on top) in that range ). Setting eq filters based on the midrange readings seemed to be accurate. ( Co-herence is much better ). My next test will be to run the box active 2-way with a dummy load for the Piezo array and see if alignment is possible or makes a significant difference.

http://www.frappr.com/?a=viewphoto&id=3 ... myphotos=1

Hal

[jeffbabcock]

Thanks Hal, great observation. Looking forward to your findings. Interesting, particularly comparing single cab vs stack of 4. Nice looking rig BTW, great building job, bet that puts out some major SPL.
Jeff

[DAVID_L_PERRY]

I used the trial version of smaart when I was working out the problems I had with my first DR290

extcract from my review:-

EQ setting and delay/phase setup

I spent a lot of time with the cabs in order to setup the delay, eq and attempt to sort out the phase settings of the drivers. I have normally only used an RTA (real time analyser) and pink noise for this, however I downloaded the 30day trail version of Smaart to try and assist in setting up the system to the best of my ability. This bit of software in its simplest form can be used for RTA analysis, however it also can be used as an aid in setting up the correct time/phase setting for the speakers amongst other things. Having had no formal training on this software and only using it for a matter of a week I will not include the results as I can not be relied upon to have carried out or interpreted the test results accurately. I was at least happy to obtain a good coherence trace and fairly flat RTA plot.

I only wish I had taken a snap shot of the coherance trace, as I managed to get it fairly flat.

I think that test results would be of value as long as the user can be relied upon to have interpreted the results and carried out the test accurately....In my case the 30 day trial period was not enough, time soon vanished as I could only practically test the rig a couple of times during that period no matter how much time I speant reading and looking through the software at work/home. As you are aware, just establishing correct cab/mic placement is a major part of the testing that many are not aware of (myself inlcuded prior to starting ot carry out some basic testing)

Very important point
It is completely pointless unless you are running digital speaker managment (I do, but not all bands/PA/DJ's are) and as such all that most people can do anything about is the eq curve or possibly global polarity swap....

I am not saying that it was not worth me doing it (it was), just that for a lot of users who are using analogue / passive crossovers it becomes a mute point as they can't do anything about it.

For this reason the main thing that makes a significant effect to the common user is simply eq adjustment.

I look forward to seeing some more test results from more experienced smaart users than myself.

Dave

[jeffbabcock]

Dave,

Thanks for your post. I agree, right now most users won't have the tools to really do much of anything with whatever results they find. Right now the only tools that can do much in the phase domain are BSS Soundweb, Dolby Lake, and EAW UX8800, all of which are cost prohibitive for most users on this forum. However in the next few years I fully expect this will change and these tools will be more widespread.

You're absolutely correct re Smaartlive and measurements, it's tough to get accurate measurements, and even in perfect conditions still there may be some variability between cabs just because of somebody making a mistake building the cab or adding/deleting things to the cabinet structure.

For those who will be doing measurements - PLEASE conduct them outside in a large open space if at all possible, with a proper omnidirectional measurement mic. Also go to prosoundweb.com and read through the smaartlive tutorials section. That will be a good start, even if you intend to use software other than smaart.

So right now, the phase stuff is not something most of us can do much about (other than minor adjustments), however we will be able to very soon as new products arrive (and I know of some that are in the works). The coherence stuff is useful to look at. Also the polar plots would be useful right now. From polars we can extrapolate things like what frequency a certain top box will array "nicely" down to, basic pattern control stuff, calculating what will be happening sonically behind a cabinet (ie what will likely bleed onto the stage) etc.

It's also nice to see those who can measure their cabinets vertically arrayed (thanks Hal) to see how the response changes. Hal's DR200's show some quite significant response changes with 4 cabs high vs single.

Essentially I think some of this is useful now, some will be useful later. I just want to encourage users to think about this stuff, and I would imagine that over the next few years we should be able to start putting together a surprising amount of new information.

Dave, was smaart 6 out when you did yours? If not, you can probably get it and do another 30 day demo. You could also install microsoft virtual pc (free download) and create a virtual machine and run smaart from there. That would get you yet another 30 days if you so desired.

Cheers
Jeff

[DAVID_L_PERRY]

Not sure what version of smaart I used (it was on a laptop I borrowed from work as my home PC is desk bound) but it was around Nov/Dec 06 when I downloaded and tried it out.

I will add Smaart to my list of 'must buy and learn' bits of software once I get a laptop.

Dave

[jeffbabcock]

Hey Dave,
Over on PSW there are a number of excellent Smaart tutorials which are worth reading. Actually they are worth reading even for people that have no intention of ever using Smaart or similar tools. Useful stuff.

Cheers
Jeff

[DAVID_L_PERRY]

Hey Dave,
Over on PSW there are a number of excellent Smaart tutorials which are worth reading. Actually they are worth reading even for people that have no intention of ever using Smaart or similar tools. Useful stuff.

Cheers
Jeff

I got lots from the PSW tutorials when I had the last trial of smaart, yes good reading and was of great help when I was testing my DR290's out.

Dave

[haydar]

Dave,

Right now the only tools that can do much in the phase domain are BSS Soundweb, Dolby Lake, and EAW UX8800, all of which are cost prohibitive for most users on this forum. However in the next few years I fully expect this will change and these tools will be more widespread.

Cheers
Jeff

Jeff,
to my poor knowledge, Xilica DLP4080HD has such phase compensation feature to tune phase response, at one-third price compared to major DSP.
now a slight different question,
I was told that HF driver need to be delayed (or pushed back few inches) against LF driver since they're differ in propagation. in contrast, most of mr. Fitzmaurice designs have LF path longer (horn) than HF. is there any explanation about this? I have searched the forum but unlucky yet.
(but I believe in mr. Fitzmaurice whatsoever! I bought OT12 and start building now )

[Bill Fitzmaurice]

I was told that HF driver need to be delayed (or pushed back few inches) against LF driver since they're differ in propagation. in contrast, most of mr. Fitzmaurice designs have LF path longer (horn) than HF. is there any explanation about this? I have searched the forum but unlucky yet.
(but I believe in mr. Fitzmaurice whatsoever! I bought OT12 and start building now )

The brain gives processing priority to whichever information it receives first. If that is low frequencies it will interpret sound as being dull, if that is high frequencies it will interpret sound as being lively. A typical direct radiator woofer and horn loaded tweeter will have the high frequencies delayed, and it will sound dull. Point of fact, the BBE process 'brightens' sound by delaying the lows, compensating for delayd highs. Horn loaded woofers delay the lows, the highs arrive at the ear first, and the sound is therefore perceived as lively, without electronic manipulation.

[Alan Star]

This is something I have been wondering about, as there is the option to build the dr300 for example with a passive crossover (in which case I see no way to delay the HF ?) and so assume that the delay between the HF/LF would not cause any problems, and so is not necessary even when bi-amping to use delay on the HF ?

[Alan Star]

Anyone ?

[Bill Fitzmaurice]

Anyone ?

The topology of a passive crossed DR300 is no different than any of the DRs and no one yet has found the HF lead to be problematic.