Thin/dry sound: Too little BSC or too much rockwool lining?

[sorue]

So... i made a pair of zaph zrt 2 way. Had some issues with lack of bass at first but it's been all settled.

The only 'problem' left now is i'm not 100% satisfied with how drum toms sound and in general, rock songs lack some body, for lack of a better word. There's definitely much stronger (< 80 Hz) with the new speakers, but i suspect i'm lacking that midbass punch.

So.. i'm wondering if it's because of the reduced BSC (2.0 mH) i went with that was recommended for my near field usage, throwing off the tonal balance and making the speakers a bit too forward and mid-centric.



Or is it because i have too much mineral wool lining?
I'm using this particular rockwool type
The sound absorption data is as follows:




The back wall is lined with 2" roxul rockwool, side walls lined with 1" and top 2". There is no stuffing at all. I understand fiberglass wool is generally more effective at killing frequencies than acoustic foam/fill, so i don't know if i'm using too much. While googling around i found other people who reported that fiberglass wool killed off the sound too much so maybe i'm in a similar situation?

At the same time, i don't see how i can minimize the lining even more. Maybe reduce the back lining to 1"? But then i'm worried about not attenuating the backwaves enough.

I did change the lining thickness quite a lot but it didn't seem to make much of a difference, this being the bare minimum i thought was necessary. I guess i could continue tweaking the amount of stuffing but if it's a BSC problem then i guess i should be changing that instead?

[jkrutke]

Hello,

I have some recommendations and suggestions. First, your choice of primary inductor and BSC level is probably not the issue. There's still a good amount of BSC in there with a 2.0 inductor.

If you truly are near field, tune much higher. Just as a temporary experiment, try using only the front half of the flared port. That's going to put the tuning at about 45Hz or so. If you like it, mod the front and back port pieces to be shorter. Most of the tuning suggestions assume normal in-room use and are intentionally rolled off so as to not emphasize primary bass nodes of a typical room.

If you have the tower version, be sure to densely pack the bottom 8-10 inches with acoustic damping material. It's very important and I think a lot of people neglect it with this design. This serves several purposes, all of which are needed in this design.

If you really want more midbass kick, consider sealing off the bottom chamber below the port. This wouldn't mean a more accurate response curve, but you will get some peaking in the 80-160 region that may add the body you are looking for. I recognize that a flat extended low end isn't what some people want so don't be afraid to tune to your liking.

[sorue]

Thank you for your advice, John! Certainly appreciate your help on this - it's your design after all.

Will there be a chance that densely stuffing the bottom will result in too much absorption overall resulting in an even drier sound, since i am using rockwool? Or does the stuffing in that region not effect port and woofer response that greatly?

[cjd]

It may be your ears that aren't finding a nice flat response to be "correct" - something stuffing probably can't fix since it's usually between 50 and 200Hz people want their "hump" - stuffing is usually more subtle than this calls for.

Still, doesn't hurt to try.

[sorue]

Interestingly, i tried using EQ to bump up the 50-200Hz region but it didn't increase the 'midbass' in the way i wanted it to - toms still lack that natural and resonant decay. I'm not sure how to describe it but i'll try.

I'm using Bon Jovi - Always for this reference. During the drum fill intro, with my old speakers, the toms sound like the middle and floor tom, the pitch is quite low and thumpy with some decay (not boomy). But with the ZRTs, it sounds like the little tom being struck instead, high-pitched with a fast decay. So i'm wondering if my old speakers accentuated that tone (can we call it distortion?) while the ZRTs don't, or is it something else?

[fbov]

...So.. i'm wondering if it's because of the reduced BSC (2.0 mH) i went with that was recommended for my near field usage ...

BSC and near/far field are different animals.
- BSC involves speaker placement relative to to room surfaces and the degree to which these surfaces reinforce lower frequencies
- near/far field involves driver radiation patterns and multi-way driver integration, relative to listener position.

At listening distances very close to a driver (near field), SPL falls off at -3 dB/double distance, a 1/r relationship. At a distance that varies with frequency and driver size (far field), SPL falls of as 1/r-squared, or -6dB/double distance. These define near and far field extremes, and are separated by a transition region where the truth is somewhere inbetween.

In the near field, speaker output overwhelms room reflections, changing tonal balance. Zaph's suggestion to raise box tuning frequency will reduce low bass output that you're not hearing in the near field, and add mid bass you will hear to give you the impression of greater bass output. The risk is a bit of boominess and loss of extension when not listening near field, since you longer have Zaph's far field optimum bass alignment. Hopefully, these are all subtle tweaks....

Have fun,
Frank