BSC...can i avoid lowered senstivity?

[boogs]

Long story short...

I've got a pair of Usher 8137A 8" woofers (bought on sale from PE - i couldn't resist), a pair of CSS WR125S 4.5" full range drivers (I'd heard so much about these i thought i should get a pair and have a listen) and a pair of Morel MDT22 tweeters. I had been planning on making a 3 way (ideally with 2 of the WR125S drivers as mids to help with increasing sensitivity) with integral subwoofer, but after plugging everything into various design programs, i'm thinking baffle step correction might make the CSS drivers too quiet for my HT/music room.

Sensitivity ratings are:
Usher 8" 88dB
CSS WR125S 85.6dB
Morel MDT 22 89dB

I don't want to sacrifice any sensitivity, so i'd like to either reduce or eliminate BSC in this design by adding an additional woofer per side to augment bass response and crossover to the mids where baffle step starts so the crossover could help. Ideally i'd be crossing the Ushers to the CSS mids around 400 or 500hz and the mids to the Morels around 4000hz. Cabinet size looks to be about 13.5" wide, 48" tall, 22" deep (there's a TC2+ 15" sub to be mounted in the side of cabinet to bring up the bottom end).

What should i do?

Thanks, Scott

[Pete Schumacher ®]

> Long story short...

> I've got a pair of Usher 8137A 8"
> woofers (bought on sale from PE - i couldn't
> resist), a pair of CSS WR125S 4.5" full
> range drivers (I'd heard so much about these
> i thought i should get a pair and have a
> listen) and a pair of Morel MDT22 tweeters.
> I had been planning on making a 3 way
> (ideally with 2 of the WR125S drivers as
> mids to help with increasing sensitivity)
> with integral subwoofer, but after plugging
> everything into various design programs, i'm
> thinking baffle step correction might make
> the CSS drivers too quiet for my HT/music
> room.

> Sensitivity ratings are:
> Usher 8" 88dB
> CSS WR125S 85.6dB
> Morel MDT 22 89dB

> I don't want to sacrifice any sensitivity,
> so i'd like to either reduce or eliminate
> BSC in this design by adding an additional
> woofer per side to augment bass response and
> crossover to the mids where baffle step
> starts so the crossover could help. Ideally
> i'd be crossing the Ushers to the CSS mids
> around 400 or 500hz and the mids to the
> Morels around 4000hz. Cabinet size looks to
> be about 13.5" wide, 48" tall,
> 22" deep (there's a TC2+ 15" sub
> to be mounted in the side of cabinet to
> bring up the bottom end).

> What should i do?

> Thanks, Scott

Adding the extra woofer is a good idea. However, crossing at 4000Hz to the MDT20 is not the best solution. You'd be better off with a smaller flange tweeter if crossing that high. Knock the XO point down to 2500Hz and you'll be a lot better off.

[boogs]

Hi Pete

Actually the MDT 22 is the small square flange Morel that's pretty much the same as the 20, just smaller (2-1/8" square). I had planned on placing the Morel in typical MTM fashion with the tweeter and woofer flanges touching.

Scott

[lcholke]

> Sensitivity ratings are:
> Usher 8" 88dB
> CSS WR125S 85.6dB
> Morel MDT 22 89dB

I would give the wr125s a good listen with no x-over for a while. This is where they should shine. The TANG BAND W4-1320SB 4" BAMBOO CONE DRIVER is another driver made in the same factory I think. They will need the bass help, but if you are new to the full range sound , you may like it. Then add the morel with a cap for more air. Watch the phase alignment by adjusting along the horizontal axis.

-Linc

[boogs]

Hi Linc

When i first rec'd the CSS drivers, i mounted one in a baffle (maybe 12" x 24") and listened to it alone for a few days. I was shocked at the amount of bass and clarity in a single full range driver. They do miss the top end, though it's not too bad but the sensitivity issue is another matter. I listen to music occasionally at moderately loud levels and i do notice compression with these drivers. I thought using 2 drivers per side would help (and of course it does) but they do need a tweeter and i'd prefer to cross my sub over very low (50 - 80hz) so figured i'd go with a solid midbass performer so i wouldn't stress the CSS drivers too much. Their midrange is too nice to cloud with heavy bass reproduction (IMO).

Scott

[davidyohn]

Why do you need a BSC network? Just pad the tweeter to match the mid and allow the natural sensitivity difference between the woofer and the mid to supply diffraction loss compensation. The Usher is what, about +4db more sensitive than the CSS mid? You may not need any BSC if 4db will do it for your enclosure geometry.

> Long story short...

> I've got a pair of Usher 8137A 8"
> woofers (bought on sale from PE - i couldn't
> resist), a pair of CSS WR125S 4.5" full
> range drivers (I'd heard so much about these
> i thought i should get a pair and have a
> listen) and a pair of Morel MDT22 tweeters.
> I had been planning on making a 3 way
> (ideally with 2 of the WR125S drivers as
> mids to help with increasing sensitivity)
> with integral subwoofer, but after plugging
> everything into various design programs, i'm
> thinking baffle step correction might make
> the CSS drivers too quiet for my HT/music
> room.

> Sensitivity ratings are:
> Usher 8" 88dB
> CSS WR125S 85.6dB
> Morel MDT 22 89dB

> I don't want to sacrifice any sensitivity,
> so i'd like to either reduce or eliminate
> BSC in this design by adding an additional
> woofer per side to augment bass response and
> crossover to the mids where baffle step
> starts so the crossover could help. Ideally
> i'd be crossing the Ushers to the CSS mids
> around 400 or 500hz and the mids to the
> Morels around 4000hz. Cabinet size looks to
> be about 13.5" wide, 48" tall,
> 22" deep (there's a TC2+ 15" sub
> to be mounted in the side of cabinet to
> bring up the bottom end).

> What should i do?

> Thanks, Scott

[cjd]

BSC is there, no matter what you do. I prefer to bake it into the crossover rather than have discrete "BSC" components. BUT. You can't get rid of BSC unless you're going in-wall.

Otherwise, you do other things to bring sensitivity up - like use more drivers wired in parallel. Which was the other half of what you asked.

And, while that midrange does have good response pretty high up, I'd target 2.8k to 3.3k, personally.

C

[damkor]

> Why do you need a BSC network? Just pad the
> tweeter to match the mid and allow the
> natural sensitivity difference between the
> woofer and the mid to supply diffraction
> loss compensation.

Right. You can adjust for the step without using a separate inductor and resistor. I would model the baffle loss/gain curve with "The Edge" and choose the -2-3dB point of that curve as your low xpoint, if possible. That is the best way in terms of simplicity of xover and potential for flattest in-room response.

Typically, we compensate for 3-4dB of loss, because placing the speaker near the wall behind reinforces bass at some frequencies. (If you do 6dB of compensation, the speaker sounds very boomy if put near the walls.)

You can certainly increase sensitivity by placing the speaker closer to the wall behind and doing less compensation. But speakers usually sound more free and open placed a little out into space.

Or, you can increase average dB if you don't adjust for the baffle. But then, the sound is very forward, edgy and not balanced. Also, you can use a subwoofer as well.

If you want higher sensitivity, you need to change the bass driver, or use two of them and put the speaker within a foot or two of the wall behind.

[boogs]

> BSC is there, no matter what you do. I
> prefer to bake it into the crossover rather
> than have discrete "BSC"
> components. BUT. You can't get rid of BSC
> unless you're going in-wall.

> Otherwise, you do other things to bring
> sensitivity up - like use more drivers wired
> in parallel. Which was the other half of
> what you asked.

> And, while that midrange does have good
> response pretty high up, I'd target 2.8k to
> 3.3k, personally.

> C

With regards to the mid-tweeter crossover - are the ranges you've mentioned to help avoid beaming in the higher frequencies from the CSS drivers?

Scott

[boogs]

> Right. You can adjust for the step without
> using a separate inductor and resistor. I
> would model the baffle loss/gain curve with
> "The Edge" and choose the -2-3dB
> point of that curve as your low xpoint, if
> possible. That is the best way in terms of
> simplicity of xover and potential for
> flattest in-room response.

> Typically, we compensate for 3-4dB of loss,
> because placing the speaker near the wall
> behind reinforces bass at some frequencies.
> (If you do 6dB of compensation, the speaker
> sounds very boomy if put near the walls.)

> You can certainly increase sensitivity by
> placing the speaker closer to the wall
> behind and doing less compensation. But
> speakers usually sound more free and open
> placed a little out into space.

> Or, you can increase average dB if you don't
> adjust for the baffle. But then, the sound
> is very forward, edgy and not balanced.
> Also, you can use a subwoofer as well.

> If you want higher sensitivity, you need to
> change the bass driver, or use two of them
> and put the speaker within a foot or two of
> the wall behind.

Thanks for the info! I'm thinking i'll use 2 of the Usher 8" drivers per side though this greatly affects the cabinet size i had planned. I had wanted to have all drivers (subwoofer included) in one cabinet but it's looking like i may need the keep the sub separate afterall.

Scott

[boogs]

> Why do you need a BSC network? Just pad the
> tweeter to match the mid and allow the
> natural sensitivity difference between the
> woofer and the mid to supply diffraction
> loss compensation. The Usher is what, about
> +4db more sensitive than the CSS mid? You
> may not need any BSC if 4db will do it for
> your enclosure geometry.

I had planned on using 2 of the CSS drivers to bring up overall sensitivity but then realized that due to baffle step i'd need to increase mid bass as well. If i use 2 of the Usher drivers per side in addtion to 2 CSS drivers, i hope i wouldn't need much (or any) BSC if i can arrange the crossover frequency between the mid bass and midrange accordingly.

Scott

[curt_c]

> With regards to the mid-tweeter crossover -
> are the ranges you've mentioned to help
> avoid beaming in the higher frequencies from
> the CSS drivers?

Yep! I'm sure that's what Chris is thinking, and I agree with his assessment.

C

[cjd]

> Yep! I'm sure that's what Chris is thinking,
> and I agree with his assessment.

> C

I *knew* there was a good reason to be thinking that.

Yeah, just to say again, um... yes. beaming'n stuff.