Help with loose & boomy 1st sub

[Marzen]

I recently assembled my first prototype home theater subwoofer. I used BassBox Pro & SoundEasy for modeling. The graphs look great (to me), but the reality is that above 45hz it sounds boomy; below it sounds very loose and undefined. Generally lacking punch entirely. I have yet to install the zobel network represented in the design link. Consequently, 45hz is about where my impedance spike is located. My parts should be here soon for the zobel as well as some 1.5" egg crate foam. The enclosure has almost no vibration, but is located in a large concrete basement (modes?). Any help in 'tightening up' the speaker would be greatly appreciated. Note: my plate amp is modded for 3.5db boost at 28hz to give a flatter response. Here's the Word Doc link if you have time to take a look: SSBN-210 SUB SPECS

[DcibeL]

Here I will fix your link for you.

Is there lots of bare concrete where you are listening to your sub? Concrete reflects lots of sound and makes anything sound boomy. However, if there is insulation on the walls, and carpet on the floor then there won't be any problems with this. It looks to me like you have a very nice solid design, maybe the driver selection is not the best choise IMO but it looks to me like there are no problems. Have you tried the sub outside of your basement?

[Marzen]

Thanks for the reply & the link fix. As to your question: yes it's all exposed concrete in my basement workshop/brewery. Due to the weight I have to leave it there until someone can help me carry it upstairs. My parts arrived today along with my faux stone laminate. I hope to get it covered & upstairs by Sun night. I think I'll drop the amp Q down to 0db boost at 28hz & add the foam to the short ends & behind each driver. I read minimal damping helps the upper freq's. Because I have large mains, I set my receiver to cross over at 80hz to the sub. At 100-120hz I can hear some voices when I'm not using a DTS source.

[DSP_Geek]

You might want to check your room dimensions since you could be getting some serious standing waves if the workshop is close to square. Also with a concrete workshop you definitely get room gain, which dropping your amp Q would help. That doesn't apply with drywall contruction: room gain with sheetrock walls is lessened due to flexing, and if you have an open plan living room then LF gain is fairly well out the window.


Meanwhile, of course, the room can still develop some lovely standing waves due to parallel walls, so you're not quite out of the woods. Been there, etc. I have one room mode which is driving me nuts now.


Francois.

[paulspencer]

Marzen, you problem is most likely the room, not the sub! In a typical room in which the walls/floor/ceiling are made of drywall/timber you have effectively an envelope that works like a very large panel bass absorber taking energy out of room modes. Even in this case, the bass response is dominated by the room with 12 db peaks and dips being common. In my room I have a dominant 35 Hz peak and 80 Hz dip.

However, your room is an extreme case. There is VERY LITTLE absorption of room modes in your room hence not only will they be less attenuated, you will also have more of them with sufficient energy to be a problem!

The most effective solution is likely to first damp the resonances by means of drywall walls and ceiling with a resilient mounting system. After this I'd then use parametric eq to tame the peaks.

What are your room dimensions?

[micb]

My bet would be that you are using not exactly good car audio subwoofers.

Use a pair of decent home audio drivers and tune a bit lower and you will see a difference.

[Marzen]

Much thanks to all for your suggestions. Certainly the basement as is, IS an accoustic nightmare what with concrete floor & block walls with a plastered ceiling. That can be addressed after I finish the cabinet upgrades in the house (ref: honey do list). My portion of the basement is 28'Wx42'Lx7'H.
My real concern is my driver selection. I had the Punch 10's boxed away & used them to keep the price down on my first project. I think before I apply the Formica laminate ($75), I should take it upstairs and try it in my living room (23'Wx32'Lx8.5'H). The price of the cabinet was only $30 and 3 hrs build time.
Q: Are car subs designed to take into account the cabin gain in the vehicle, or is that a myth? Consequently, should I be looking for a longer throw driver due to my large room size?

[Volenti]

Originally posted by Marzen

Q: Are car subs designed to take into account the cabin gain in the vehicle, or is that a myth? Consequently, should I be looking for a longer throw driver due to my large room size?

As far as a blanket statement goes it's a myth, there's too many variables in vehicles, enclosure location, design and orientation to make a claim as such, it's like saying all home subs are designed to take into account "typical" room gain, which is nonsence.

There are good and bad car audio drivers just as there are good and bad home audio drivers (just look at most of the trash coming from china for examples in both areas)

More swept volume (longer throw) will give you more bass (assuming you have the power to drive it), there's no replacement for displacement

[Marzen]

Well I stayed home Monday to play with the sub. Took it upstairs into the living room & placed it on a carpet covered dolly. Talk about night & day difference. Much smoother, tighter, & less directional. Using the dolly I moved it around the room. From best to worst placement: 1-rooms center area, 2- against a long wall, 3- against a short wall, 4- corner. A usable (WAF) solution was to place it next to a chaise on the long wall about 3' out, used as a table.
Things I learned: a parametric eq for 20-120hz would be great to have. Porcelain angels on glass shelves get itchy feet. I want to finish this and sell it before starting another sub (this could be addicting).
Thanks again for all your input, I'll have pics of the finished product at the link by this weekend.
Cheers,
Marz

[tade]

is there any way to tell if my sub is boomy? I built a wicked one, and have no outward complaints. i could have built it more solidly, but would have had to actually buy lumber. loooove the bass extention.

thanks