When is Baffle step comensation recommended?

[demon2091tb]

Basically the question is in the subject, but would really like a thourough explination, i've searched but just can't find the info i'm looking for, advantages and disadvantages of using baffle step, as well as when they should be considered.....

My cabinet is going to be around 8.5-9" wide, and ported to 38hz, f3 is 51hz, not sure if i need it or not, drivers in question are Seas CA18rnx, and LPG26nafm. CA18 is 88db effecient, LPG 26 is 92db effecient....Just looking for a very high level of SQ for stereo music/TV and occasional movie.

[Magnetar]

What happens is the front baffle of the loudspeaker reinforces the output of the speaker down to a certain point then the speaker rolls off quite a bit - when you 'model' a woofer in a box like you did it does not account for this loss. So your 88 db sensitive woofer with that little baffle soon becomes anemic sounding and maybe only 80 db sensitive below the point the baffle lets go. To fix this you simply pad the woofer's midrange down to the low bass sensitive level (as well as the tweeter to make it linear) with a series resistor and inductor in the woofer and an Lpad on the tweeter. The series resistor and inductor needs to be tuned for the wanted response/sound. You will end up with a real power sucker (like most 'high end' speakers) - If you choose not to do this the low mids/bass will be weak and you will have a speaker that may 'image and soundstage' well and be 'detailed' but not very true or realistic sounding.

A much larger baffle or a three way with a much more sensitive woofer is a better idea.

[BobEllis]

I'll throw in my two bits -

I agree with Magnetar, BSC is very important to a natural sounding speaker.

The magnitude of the baffle step also depends on speaker placement. The closer to the back wall, the less compensation is required, down to zero at flush mounting.

If you plan to back your speakers up against the wall, you may not need any baffle step compensation, or at least be able to reduce it, impacting the sensistivity less.

Other methods to compensate without the sensitivity penalty would be to use a second CA18 rolled off at the baffle step frequency (AKA 2.5 way) or on the back of the cabinet (AKA bipole).

[Dumbass]

Martin King has a very thorough explanation of baffle-step compensation:
http://www.quarter-wave.com/General/BSC_Sizing.pdf
I believe a careful reading of that doc will tell you everything you need to know.

The amount of BSC you need depends a lot on where you place your speakers, and how acoustically dead your room is. If you place them on stands away from walls, the baffle step dropoff could be very close to the theoretical 6dB. If near boundaries, though, the dropoff will be much less.

Making speakers with large front baffles lowers the baffle-step frequency, which means efficiency losses can be minimized (because you need a less intrusive BSC circuit). Many people say that large baffles "ruin imaging", but I believe this is a myth. The largest baffles I have heard (Jordans in VTL) had excellent stereo imagery.

[Dumbass]

Originally posted by BobEllis
on the back of the cabinet (AKA bipole).

I think bipole is an excellent strategy, but of course doubles the woofer budget, also changes the dispersion pattern (for the better IMO, but still changes it).

[DSP_Geek]

Originally posted by BobEllis
Other methods to compensate without the sensitivity penalty would be to use a second CA18 rolled off at the baffle step frequency (AKA 2.5 way) or on the back of the cabinet (AKA bipole).

Using a second driver for BSC works very well indeed, but as mentioned you do need to pad differently with different distances to the back wall. On the other hand, if you're not afraid of building an op-amp circuit or two, you can add the second driver with no padding at all and use a line-level circuit to apply different levels of baffle step loss depending on how far you are from the back wall.

Why go to this trouble, when an L-pad would solve the problem? Having another driver in parallel increases sensitivity, and padding down at line-level means less power goes to the drivers, thus increasing headroom right where music has most of its power.


Cheers,
Francois.

[hongrn]

I use John Murphy's formula at trueaudio.com to calculate baffle step compensation, although I always end up going for a 3 dB compensation versus a full 6 dB. Let me know if you have Microsoft Excel, I'll shoot you a copy of the spreadsheet I made. All you do is enter the baffle width, and the system impedance. It'll calculate the value of the resistor and inductor for the baffle step correction. It also shows the frequency affected by the diffraction.

Hong

[kingdaddy]

So how do you calculate BSC for a baffle-less speaker?

[demon2091tb]

Well the room that i indend on using them in is around 13x20', 13' being the wall where the stereo will sit, about 1' from the side walls, and around 1.5' from the rear wall. I am looking for a very realistic sound as majority of the music that i listen to is along the lines of Pink Floyd, and ambient chill types. I would really love to reproduce these will a ton of accuracy.

Would porting to the rear, in some ways act like the rear driver or a 2.5way??

If i can make the baffle larger while still being extreemly aesthetically pleasing, as well as imaging very well then that would be a plus.

What would you ideally recommend with the single CA18, as far as cabinet size and either ported or sealed, if ported front or back? For the all around best natural response?

Still waiting for a reply from madisound on the xover issue. As they said i probobly would need a good 3-6db to enjoy it, if thats the case then i will do what needs to be done to get the best sound possible. I have 100w @4ohms available.



The new Cabinets will be going just inside of the bookshelfs, or really whereever they image the best, and have the ovreall best response. But thats a good idea of where there going.

EDIT: Oh yea sorry for the mess in the picture, just moved home lol. Good read as well, now i see i actually do either need a good 3-6db bsc or either make a really large baffle....the first of the two being probobly easier.

[Dumbass]

Just looking at your room, I'd build the speakers first, then see if you even need/want a BSC. Even if you knew you wanted a BSC, don't put them inside the cabinets, you want easy access for fine-tuning. In fact, see Martin's article on using a rheostat (adjustable resistor) for on-the-fly adjustment:
http://www.quarter-wave.com/General/BSC_Variable.pdf

Also, with the music you mention, you probably want some sort of subwoofer? There are affordable ones out there, like the Yamaha servo-subs, that people seem to like.