[JohnR]

If you check out JohnK's music and design website there is an article on there describing why running pure open baffle below the lowest room mode is not the best idea.

I can't find that... I did find "An additional consideration arises from anecdotal observations which suggest dipole bass just sounds more natural. Research at Music and Design suggests that the primary reason for this observation lies precisely with the inability of a dipole woofer to pressurize a room below the fundamental."

However getting adequate SPL from a dipole at 20 Hz is harder...

[JohnR]

Many people claim the 30-40Hz response is fine for music.  That is nonsense IF you want to hear everything that's on the recording.  Since I've heard response in a music system that reached to 20Hz and below in the studio and at the mastering facility, I could not go back to anything less.  There is relevant musical and environmental content down there.  I have several recordings that have a certain hall ambience and/or rumble that really adds to the width and depth of the soundstage with stereo bass reaching below 20Hz.  Cut off the subs and your perspective shrinks.

I did some experiments today and this seems to be the case for me too. I used sealed subs highpassed at 20 or 25 Hz, and at times adding the subs did add some spaciousness. It wasn't perceivable as "bass" but that change in ambience. Very interesting, more experiments needed.

Are you running your panels full range (no highpass)? I discovered today that highpassing dipole subs at 35 Hz is a terrible idea. I need to look into whether this applies to the main panels as well.

[Tyson]

Why is high passing at 35 hz such a bad idea?

Not that I do it, I'm just curious, mainly.

[studiotech]

I did some experiments today and this seems to be the case for me too. I used sealed subs highpassed at 20 or 25 Hz, and at times adding the subs did add some spaciousness. It wasn't perceivable as "bass" but that change in ambience. Very interesting, more experiments needed.

Are you running your panels full range (no highpass)? I discovered today that highpassing dipole subs at 35 Hz is a terrible idea. I need to look into whether this applies to the main panels as well.

Yes, exactly.  Not necessarily more bass, but more sense of space.  It has to be captured in the recording, but if it's there, it can be a thrill!  I found some AC rumble in a Chesky recording that Bob did not know was in there due to the monitoring not having the capability to play below 20hz.  It was down around 11Hz!  In that case, it did NOT help the recording and I wanted to filter it out.

At the moment I am running the main panels full range, letting the woofer roll off where it naturally wants to and folding the subs in underneath.  In my case, there is no undo strain on the panels woofer since I'm not applying much additive EQ to it, so I let it run all the way down.  I find this best if the driver can handle it.  Running stereo that low seems to help too.  It goes against the whole localization rules we all get beaten over the head with, but those last few % of performance require it to be done.  I have personally NEVER run a single subwoofer in any of my systems.  Always a stereo sub set-up even since college before I knew exactly why it sounded better.

Greg

[jimdgoulding]

May I inquire about your localization and are we talkin placement of speakers localization or localization of instruments in the sound field?  Thanks.

[JohnR]

Why is high passing at 35 hz such a bad idea?

It sounded wrong - I thought I had wired something out of phase. Letting the dipoles run as low as they could was much better. However i'm told I shouldn't generalize... BuT for me at least that's one variable taken out of the equation!

[Tyson]

I find in my setup that using the bass woofers only below 100hz (77hz, to be exact) works best.  Of course, I also have to boost the low end considerably since the woofers are rolling off significantly below 100hz.  The mids on the V2's are rolling off starting at 350hz, so I boost the low end there as well.  But, the cool thing is that if you boost it just right, you don't have to actually use a crossover on the low end of the mids, they just roll off nicely around 80hz, all by themselves.  Same thing in the high end - no need for a crossover, they just roll off.  BUT, most mids have an upper range resonance that you have to measure in order to see.  In my case, it's at 3.4khz, and 4.5khz.  Notch out these resonances and you don't even have to put an upper crossover on them.

But, John R, since I have your attention here   Let me ask you a philosophical OB question - I take two sets of measurements - one is quasi-anechoic, the other is from the listening position - both measurements are radically different - which one should be optimized in your opinion, and why?

[JohnR]

But, John R, since I have your attention here   Let me ask you a philosophical OB question - I take two sets of measurements - one is quasi-anechoic, the other is from the listening position - both measurements are radically different - which one should be optimized in your opinion, and why?

The way I look at it, there are two problems to solve, and two sets of measurements that you can make, that don't quite match those problems.

The first problem is getting the right anechoic response. With a dipole, you can get "constant directivity" from below 100 Hz up to where the tweeter starts beaming too much - say 10 kHz. Assuming you can do that, then it seems reasonable to me to aim for a flat anechoic response.

The second problem is the room. This is most critical at low frequencies, where it's basically all that counts, and gets less so as you move up in frequency.

So my take on it is to firstly optimize the (quasi) anechoic response at the frequencies where you can do so. Then optimize the in-room response at frequencies where that is all you can do. Then to finally adjust the overall response for a) evident room issues and b) subjective performance.

[JohnR]

May I inquire about your localization and are we talkin placement of speakers localization or localization of instruments in the sound field?  Thanks.

Hi Jim, I think Greg was referring to the notion that a subwoofer cannot be localized (i.e. you can tell where the sound is coming from) at low frequencies - he is saying that regardless of what is said in this area he prefers stereo subs all the way down to 20 Hz and below.

My configuration that I'm heading to looks like being mono below 80 Hz, because of limitations with placement. Such it is.

[JohnR]

At the moment I am running the main panels full range, letting the woofer roll off where it naturally wants to and folding the subs in underneath.  In my case, there is no undo strain on the panels woofer since I'm not applying much additive EQ to it, so I let it run all the way down.  I find this best if the driver can handle it.

Where I'm at today (  ), I'm highpassing the woofers in the main panels at 80 Hz. However I think I will try some woofers with a higher Fs and see what happens.

[jimdgoulding]

Hi Jim, I think Greg was referring to the notion that a subwoofer cannot be localized (i.e. you can tell where the sound is coming from) at low frequencies - he is saying that regardless of what is said in this area he prefers stereo subs all the way down to 20 Hz and below.

My configuration that I'm heading to looks like being mono below 80 Hz, because of limitations with placement. Such it is.

Ah so.  Thanks.

[jimdgoulding]

I just remembered a listening session with a friend of mine in (ZZ Top's) LaGrange, an hours drive from where I live.  He has a Roger Sanders electrostatic speaker sound system in a separate structure from his house on a concrete slab built for listening to music (offset double studding and the whole nine yards), and with three of Duke Lejuene's active subs.  And I remember he played something with some very deep bass hits that was not only out of the room, it was outer space!  There was no identifiable source and it was THRILLING, lemme tell you.  His main speakers contain 10" woofers so he was probably crossing over lower than my speakers even go.  I have got to get back out there!

[studiotech]

Ah so.  Thanks.

Correct!  Some may say that poor subs are localizable due to high distortion products that can end up being more audible than the actual input signal, but that good quality subs are not.  I feel that even with goods subs you are better off for localization AND evening out room modes to use 2.  We have had a very large, high quality ATC ( good but way overpriced ) sub at the studio for several years.  Crossed at 50Hz 24dB/oct and you can still tell it's off to the right side of the console.  Took my dual Rythmiks over there for a few weeks.  No contest.  ATC is for sale and dual Rythmiks will be built into the front wall.

Greg

[Poultrygeist]

With OB I always thought the room was the box?

[panomaniac]

Not unless you usually built speakers with the drivers in the middle of the box - and you sit in there too.

[Tyson]

He might be referring to infinite baffle - which does use an entire room as the "enclosure" for it's rear wave.

[panomaniac]

Yes - probably.   But I couldn't resist the joke.