Will an amp significantly alter box volume??

I'm building a 85L traditional vented sub using the plans found on Adire Audio's web site...except, I just reailzed that my sub will be *not* be passive like their design. My amp (Adire AVA250) is in transit, so I don't know how far it will protrude into the box. I really hope that I can still proceed using Adire's design and not have the sound dramatically altered as a result of the amp. What's the consensus out there?? Thanks.

Grant
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
According to the Adire website, your amp measure 10.5" X10.5" X3.5" for a total of 386 cubic inches. That is less than a quarter of a cubic foot. Your 85 liter enclosure is about 3 cubic feet. The amp will occupy less than 8% of your internal space, a completely negligible amount.

Essentially, it makes your 85 liter enclosure a 79 liter enclosure. If you have a loudspeaker program, you can run the two volumes and see how little difference it makes.
 
Volume difference?

Grantbo,

First, your 8% difference is not that much. It depends on you hunger for detail if you want to call this negligible or not. There some parameters the will change by changing the volume.
Changing the volume will change QL (decreases). This results in an earlier roll-off for f3.
There are “unnatural” ways to compensate this QL loss.
The volume calculated in respect to a certain QL depends on the Qts of your speaker. So, if you were in designing a speaker your two anchor points are Qts and QL. Ideally you want to have a QL of 7. If you do not want to change the characteristics of the enclosure, you should stay away form QL. This leaves you no choice to change the Qts of you speaker. This can be done in many ways. Two of which are fairly simple.
1) Change the DC resistance of the speaker coil (Revc).
2) Change the mass of the cone (Mmd).

Anyway. It’s not worthwhile to change any of your speakers parameters. But if you have some spare time and you’re in the position that you can measure you’re speaker changes, it will give you a piece of profound knowledge.

Like a said, it’s for the detail freak :D.

Good luck in building you’re Sub.
 
Thanks for the follow-up guys. Given the small change in volume, I will leave the dimension specs as is. *But*...would it make sense to add a little fiber filling to the box to give it a little boost in "perceived" vol.? Adire's plans do not call for filling in their 85L sub, but from what I've read, it appears to be a very popular option amongst sub builders. Will adding filling (either filling the box or lining the walls) alter the acoustic properties that Adire has
so carefully determined??

Grant
 
Filling can definitely tidy up bass and help reduce "muddle". If its a vented design, you would just want to line the inner walls. If its sealed, you should fill it loosely. Yes, adding stuffing can theoretically "increase" your volume, but it can have a diverse effect on the sound quality if over/understuffed. Your best bet is to play around with the stuffing before sealing up the box for good. I lined the innards of my sonosub with some extremely dense egg crate foam (I get it for free from a local specialty manufacturer), and despite my cuts not being perfect, my tuning frequency was within about 1/2 hz (lower!) than the desired frequency.
 
So, I've cut out the required box panels today, tomorrow night is set aside for routing, the AVA-250 amp and 12" Shiva driver are
on there way...but what is the recommended method/wire/cable to connect:

1. The Shiva-to-amp
2. The amp-to-receiver's RCA subwoofer out?

For #2, would a simple RCA cable with single jacks on each end
suffice, or do I need a T-type cable to connect to two amp jacks?

Grant