Rules for box volume and vent

[giralfino]

Hi all,
I'm thinking of using a Peerless HDS Nomex 830875 as a woofer in a small vented 3-way project. Various modeling programs think that the "ideal" box is around 15L with a 50 Hz tuning. But I found that modeling a bigger box with a lower tuning could give a bit more bass (21-22L, 42-44 Hz tuning).

It is wise to use a box bigger than the Vas and a tuning lower than the Fs? Are there rules about when it is possible or when absolutely not?

Thanks in advance,
Ralf

The T/S parameters of the driver are:
Fs = 48.1 Hz
Qms = 2.67
Qes = 0.45
Qts = 0.39
Vas = 17.6 L
Re = 6.4 Ohm
Le = 1.3 mH
BL = 8.4

[richie00boy]

Have a look at the curves for excursion and group delay or phase response. These will give you an idea of what compromises you are making. The software is showing common used alignments, there are thousands of alignments you can make up, each with their own merits and pitfalls.

[jernejc]

Originally Posted by giralfino

Hi all,
I'm thinking of using a Peerless HDS Nomex 830875 as a woofer in a small vented 3-way project. Various modeling programs think that the "ideal" box is around 15L with a 50 Hz tuning. But I found that modeling a bigger box with a lower tuning could give a bit more bass (21-22L, 42-44 Hz tuning).

It is wise to use a box bigger than the Vas and a tuning lower than the Fs? Are there rules about when it is possible or when absolutely not?

Thanks in advance,
Ralf

The T/S parameters of the driver are:
Fs = 48.1 Hz
Qms = 2.67
Qes = 0.45
Qts = 0.39
Vas = 17.6 L
Re = 6.4 Ohm
Le = 1.3 mH
BL = 8.4

Depending on your wish. Larger volume with lower tunning will produce lower bass, but not as clear. More boomy. In case You increase volume for a litre, maybe two, there won´t be significant boomy effect. If You double it...
I prefer tighter bass, so I would choose smaller volume.
It is your choice.

Here are some useful online calculators for DIYers
mh-audio.nl - Calculations



Jernej

[PeteMcK]

re:'Larger volume with lower tunning will produce lower bass, but not as clear. More boomy' - not necessarily, depends on where the tuning is and how well controlled it is.
What the OP is looking at is an EBS alignment, the price to pay for the lower extension is larger box and a lower output level, as well as what Richie00boy said. Group delay can be bypassed if the tuning is low enough, excursion may be more of a problem if you like lots of low bass loud (depends on the drivers capabilities)...

[rcw]

You can within certain limits "compliance scale" one alignment to another.

In your case for instance you want a 40Hz. out off if you divide the cut off of your current alignment by this then multiply your current box volume by..

(50/40)^2.5, you get around 26litres

If you divide the current tuning frequency by

(50/40)^.5 you get the tuning frequency, around 45 Hz.

Theses alignments are of the Chebashev sort and have ripple.

Overall a ten inch driver is better for 40Hz.
rcw.

[pheonix358]

Originally Posted by richie00boy

there are thousands of alignments you can make up, each with their own merits and pitfalls.

In reality it is a continuum, there are an infinate number of combinations. The so called alignments are only points within the continuum. Don't be afraid of going outside of 'alignments'.

I agree with everyone else, the down side will be an increase in excersion limits and a little less detail in bass and lower midrange. The driver has to work harder and you will hear the difference. It's all about finding the balance that suits you.

Terry