BassBox Pro, prototype ?

[AndrewT]

Hi,
looks like I might be going in the right direction.

It's simulation or trial and error.

I'd prefer simulation if I can get my head around what to aim for and which characteristics will give best chance of success.

I could add yet more weight but feel that 89db/W, Fs=31Hz sounds about as low as I want to go, unless I am advised other wise.

I will now add mass to the other driver and fit both back into the standard cabinet. Then it's experimenting with using one or two ports. I still think a single port of 100mm to 150mm diameter should be sufficient, anybody care to comment?

Richie,

there is a danger that somewhere above tuning you might run out of Xmax.

I am aware of this rise and that it is likely to coincide with just where the original was at it's most efficient, but since the originals were capable of 132db but at an unspecified frequency, I think I can chance my arm that 15db below that will be too loud and losing 20db will still be adequate. That's what I said way back in another thread "I can afford to sacrifice max SPL to obtain lower bass".

190 w, is that per channel or in total? Per channel feeding large drivers with limited xmax it might be ok.

I have 4off 190W into 8ohm monoblocks and these drivers are 8ohm.
I am building 6 off Leach clones that should be about 130W to 150W into 8ohm but these are intended for satellite (5.1) use.

Sreten,
the existing mains are Tannoy Reveal 6D, fitted with a switchable 80Hz high pass 2pole filter and a whole series of other switchable filters that make them suitable for building into a mixing desk. I have them flat for use in a room and 80Hz HP when I bring in the sub.
I can tune the sub to any sensible low pass frequency and select 2pole or 4pole rolloff either Butterworth (to match the Reveals) or Linkwitz. Ultimately the sub will be used with Acoustic Energy AE1s if I can't tune in the sub horn. The horn is likely to get the 4off 15inch DC Tannoys out of the Leopards.

 

[REALFLEO]

Hi, your box - note Ql = 5, /sreten.

How is it possible to have a Ql of 5 if my volume is almost twice as big as it should be .... ?

Thanks,

Simon

 

[richie00boy]

Ql is box losses and as such is unrelated to how big your box is compared to what it needs to be.

 

[sreten]

How is it possible to have a Ql of 5 if my volume is almost twice as big as it should be .... ?

Thanks,

Simon

Ql is box losses and as such is unrelated to how big your box is compared to what it needs to be.

Hi,

RB is right. though I think Ql is supposed to be leakage it does just
fine is modelling the damping of foam lining or stuffing. So I set Ql
=5 in those simulations to indicate some box damping is needed.

They are workable alignments in-room but very sensitive to tuning
due to the large box - so use stuffing amount to fine tune bass.
(stuffing airspace behind driver, not near the port )

/sreten.

 

[REALFLEO]

ok I understand what is Ql but is there a way to prove, by mesuring ,that I'm using right volume, filling material, tunning freq., etc ...

Thanks,

REALFLEO

 

[REALFLEO]

I used the technique described in this paper to compute Ql:

http://users.ece.gatech.edu/~mleach/ece4445/downloads/ventedbox.pdf

I was thinking maybe the box volume would have influenced the position of Fl and Fc on the impedance curve ...

Is it a good thing to do that kind of computation ?

Thanks,

REALFLEO

 

[richie00boy]

Ql doesn't really tell you about the 'right' volume, that really comes by listening and frequency response check.

Ql really just tells you the losses in the system so you can adjust your built design to account for real world against theory.

 

[sreten]

I used the technique described in this paper to compute Ql:

http://users.ece.gatech.edu/~mleach/ece4445/downloads/ventedbox.pdf

I was thinking maybe the box volume would have influenced the position of Fl and Fc on the impedance curve ...

Is it a good thing to do that kind of computation ?

Thanks,

REALFLEO

Hmmmm........

Lots of meaningless number crunching in that paper.

Download WinISDpro and enter all your driver data.

Get the modelled response e.g. Fl, Fb Fc and Fh to agree with measured data.

Box volume does affect Fl and Fh, as it increases they reduce.
Fb (port tuning frequency) also changes the Fh frequency.

Simply by playing with Ql get Rl and Rh to agree with measured data.

This is your effective Ql, what does it mean ? who cares ?
By varying the amount of in-box damping Rl and Rh will change.

The alignments I showed earlier are very workable in-room.
There is no point IMO in reducing the box volume.

/sreten.

 

[REALFLEO]

There is no point IMO in reducing the box volume.

You mean there is not point to reduce the box volume to ajust Ql ... ?

Thanks,

REALFLEO

 

[sreten]

Hi, Ql is adjusted by amount of acoustic damping, not box size, /sreten.

 

[REALFLEO]

ok perfect.

Thanks for your patience,

REALFLEO

 

[richie00boy]

However Ql does have an impact on the box size, a lossier box (low number) means you need a bigger box to retain the same theoretical performance.

But to be honest if it sounds ok just leave it. All you are doing by adjusting things is fitting one specific 'documented' theoretical alignment. And there's an infinite number of perfectly fine alignments out there, of which I'm sure your box is one.

 

[REALFLEO]

also if you read the very first posts, can you explain why I mesured a Qts of 0.40 instead of 0.34 as suggest by Vifa ?

Maybe it's due to break-in ... ?

Wich one should I use, 0.34 or 0.40 ?

I used 0.40 to build my first prototype.

Thanks,

REALFLEO

 

[richie00boy]

Could be due to break in as much as manufacturer tolerance or measuring setup tolerance.

I would use what you measured.

 

[REALFLEO]

the thing is if I use what I mesured it means a box twice as big...

 

[v-bro]

Posted this before, but I think the results are always best with manufacturers parameters. They want customers to get good results, so they surely think the enduser gets the best results that way...

I blindly use them most of the times, and have no complaints about the results most of the times... I only have them measured when I can't get my hand on the parameters any other way...(in shops like 'speakerland' or 'speaker&co' in the Netherlands they charge about 15EUR. for a measurement...)

 

[AndrewT]

Hi,
resurrecting this old thread since I see I never reported back on the outcome of modifying the Tannoy B950 to become a sub-bass speaker.

I use Winisd pro as the simulation programme - excellent programme with superb graphic outputs.

Doubled the cone mass by adding 120gms of lead foil to the back of each driver.

Blocked off one port to drop the Fbox by sqrt(2).

This produces a very droopy reponse that falls at about 3db/octave from 100Hz down to 25Hz and then gradually steepens below that.

The overall sound seems to suit my large room.
Plays loud if set up slightly higher than the satellites. Capable of going far too loud if I were to party. With normal set up the sub-bass is using about half the voltage the satellites require.

Male voice sounds quite normal. Music seems not to be exagerated, no sign of boom anywhere in the range. Deep bass is there for sound effects.
Plays well with CD music and film sound tracks (Freeview & DVD) and Nicam TV and FM radio.

Overall, the mods are a success. And cheap, but time consuming going through dozens of alternative alignments and then testing the T/S parameters at each stage.