Extrapolating Dave’s baffle step compensation approach?

[otto88]

Dave outlines six methods of dealing with baffle step loss: http://www.t-linespeakers.org/tech/b...intro-bds.html

Baffle step compensation in a typical crossover varies from 3 to 5.5 dB, gaining flat response at the loss of sensitivity. Especially with lower powered amps (tubes, class D) it’s desirable to maximise sensitivity . .

Dave's favorite approach (above) adds a further mid-woofer on the back (bipole).

If BSC was left out of a 2 way's crossover, and instead of adding a mid-woofer, a sub were added with an active crossover (eg a Behringer DCX 2496) having shelf filter abilities, with tweaking of the shelf filter and phase, would you agree that the subs could provide the compensation for the baffle step loss; so the sensitivity could be raised.

Eg with Jay’s MTM Usher 8945P / Peerless HDS http://www.geocities.com/woove99/Spk.../Usher_MTM.htm , sensitivity could be

Usher averages 87 + 6 (two drivers) = 93 dB
Peerless averages 93 dB

A trade off is that 200 Hz is into the range of eg voices. But with
low powered amps to gain 6 dB, that’s not necessarily a major deficit . .
A benefit is that as the bass load of the mid-woofer is greatly reduced, they should preform better . .
A sub would also go deeper.

What do you think?

[GM]

Originally posted by otto88

would you agree that the subs could provide the compensation for the baffle step loss...........

A trade off is that 200 Hz is into the range of eg voices.

Works for me as long as the 'sub' driver has a wide enough BW to be nominally flat through the XO BW with no strong break up modes above it. I do the same thing except with a 500 Hz/2nd order XO.

Not much of a trade-off if you look at how poor our hearing acuity is down low........... I mean look at a phone's BW, its low cut-off is 250 Hz.........

GM

[otto88]

Most want to XO subs at 40 - 80 Hz, that seems a waste.

Most good subs are very clean way beyond that, eg an engineer at the former Peerless (now Tympani) said that the XLS 12 driver with a 4th order XO could be crossed at up to 300 Hz

So i'm right that sensitivity is gained for the mid-woofers . . and there are no other drawbacks?

[sreten]

Hi,

The Watt / Puppy did this yonks ago albeit with stereo subs.
(and proper high pass filtering of the mid unit to boot)

see http://www.deadwaxcafe.com/vzone/david/david.htm

FWIW it is also one of the many ways of implementing a 3-way
speaker. a 3 way can be designed with BSC in the bass, in the
mid, or shared between the two in any ratio. No wonder then
that people get 3 ways so badly wrong, except for sub + sats.

/sreten.

[pjpoes]

I think I must be a little confused. I mean bass is too directional by 300-500hz, thats lower midrange territory. You wouldn't want a single subwoofer centrally placed acting as baffle step. If it was included into the main speakers, then yeah, but at that point, we are talking about a fairly common 3-way approach. I'm thinking I must be misunderstanding what you are asking, so please correct me here.

[badman]

There's a lot to be said AGAINST using subs for 300Hz. In addition to localization issues, there's lobing, poor transient response and breakup suppression concerns, and other stuff.

If you want the bass driver to run that high, a good solution is to pick a passive driver with the extra 3dB of sensitivity, and use it as a woofer proper, with an XO at the bafflestep frequency (assuming passive XO).

But using subs.... just asking for trouble. If you like muddy mids, it's a fine solution. Subs are best crossed LOW LOW LOW, to keep them out of the more sensitive ranges of our hearing, and from interfering with any but the deepest of instrumental fundamentals.

[otto88]

pjpoes
I didn’t say stereo subs, because I thought any (sensible) use of subs over about 80 Hz would be stereo, my oversight.

I only mentioned 300 Hz because a Peerless engineer said that their XLS’s would go that high. I’m assuming for the time being that baffle step would occur around 200 Hz +/- 50 Hz.


Sreten
A tad off topic, but in the Watt / Puppy, what did you mean by *proper high pass filtering of the mid?

badman
> localization issues, there's lobing, poor transient response and breakup suppression concerns, and other stuff
Are you assuming a mono sub: if not, can you elaborate?

The drivers I want to use - because I have them, and they achieve a higher efficiency tube friendly result are:

Tweeter: Peerless HDS 810921 (used in eg the Elsinore and Jay’s systems with Ushers) 93 dB
Mid: a B&C (cant recall model, Fs I know is 117 Hz) ~ 95 dB
“bass/ sub”: Eminence Kappa Pro ~ 95 dB

If used up to say 250 Hz, how would the Eminence muddy the sound?


One thing that’s since occurred to me is that reasonable inductors at say 250 Hz would cost a bit, tho’ I have no idea how much.

[augerpro]

Sounds like the beginings of a typical 3 way, and I would design it as such.

Considering excursion and response capabilities of both woofer and mid, driver placement vs listening position, crossover slopes, baffle size, etc.

[pjpoes]

I actually would consider a 3.5 way or a 3 way. The setup may be too efficient in the bass if designed as a typical three way. If you want higher impedance in the bass, you could wire the woofers in Series, then design as a typical 3 way. But really, I think a 3.5 way would be a potential option.

I don't agree that there will be any problems such as lobing. This design will actually work quite well I think, and you could run those drivers higher if you wanted. I would have no problem running those woofers to 500hz. To be honest, I think they don't begin having lobing problems until around 1khz or maybe just below that.

If you need any help with some overall topologies let me know. I can post some schematics. Without the drivers themselves I couldn't give you exact values for the parts, but it would get you started. If you do have measurements, and just need help with the crossover, then you can send me the files and I can see what I come up with.

[otto88]

Yes my thinking evolved from a 2way with mid-woofer, but it’s a 3 way with the “bottom” active.
So a few 3 ways use the bass driver with a shelf filter for BSC?

pjpoes
Possibly I might end up running those 12” Eminences to 500 Hz, they should handle that easily enough; it’ll be by trial. .

Can anyone throw a rough cost on reasonable inductors at say 250/ 300/ 400 Hz??

Thanks