Net Volume ?

[Alex2507]

I need some clarification here. From what I've gathered net vulume is what's left after you subtract the slotted port, bracing and driver displacement from the total internal volume of the cabinet. Now I need to know that I don't have to further subtract the insulation (OC 703).

TIA,
Alex

 

[Alex2507]

Another thing I need to ask about is woofer placement in relation to the slot vent. In my case both are in the front. The slot is horizontal on the top left and I would like to know if that means that I have to place the woofer on the bottom right? I would rather not but will if I have to.

 

[TLS Guy]

Another thing I need to ask about is woofer placement in relation to the slot vent. In my case both are in the front. The slot is horizontal on the top left and I would like to know if that means that I have to place the woofer on the bottom right? I would rather not but will if I have to.

You are correct. The volume should be Vb plus driver bracing, vent and amp. Do not add the fill.

The driver can be placed near the port.

 

[Alex2507]

Do not add the fill.

Thank you for answering my questions but I have to add the fill to stay true to some cabinet recommendations that WmAx gave me.

 

[mike c]

what does WmAx say about the fill?

if i had to guess, the fill is supposed to get rid of resonance, and does not actually add to the volume. wild guess here.

 

[Alex2507]

what does WmAx say about the fill?

if i had to guess, the fill is supposed to get rid of resonance, and does not actually add to the volume. wild guess here.

Hi mike,

Here's the PM:

http://forums.audioholics.com/forums/private.php?do=showpm&pmid=77032

I asked some not very well thought out questions regarding this PM and haven't heard back from him yet. I'm pretty new to this and figure that if I just stick to the recommendations, I'll end up with as good a result as possible. Planning one of these things is taking up some serious time for me due to limited knowledge and poor drafting skills. But I have time and I'm not looking for the knock out punch in the first round.

Congrats on the mod thing. So, do you get paid? lol

 

[TLS Guy]

Thank you for answering my questions but I have to add the fill to stay true to some cabinet recommendations that WmAx gave me.

If you are using high density Rockwood type panels as recommended by WmAx, then you will have to add that to Vb. Any type of wool natural or synthetic should not be added. I do not regard sound treatment panels as fill, they are a form of treatment for the enclosure walls. I have used bituminous panels in the past, but the sources seem to have dried up now.

 

[mike c]

Hi mike,

Here's the PM:

http://forums.audioholics.com/forums/private.php?do=showpm&pmid=77032

I asked some not very well thought out questions regarding this PM and haven't heard back from him yet. I'm pretty new to this and figure that if I just stick to the recommendations, I'll end up with as good a result as possible. Planning one of these things is taking up some serious time for me due to limited knowledge and poor drafting skills. But I have time and I'm not looking for the knock out punch in the first round.

Congrats on the mod thing. So, do you get paid? lol

thanks. nope i don't but Clint said 'chicks liked mods'.

and private messages really are private, mod or not

if it were me, i'd disregard the fill in the volume computation because you can "fill it in" if there's too much volume, but you can't add to the volume once you build the box. i also still think the fill won't affect the volume by much ... 0.1 cu ft maybe? how big is the box you are planning?

 

[Alex2507]

i also still think the fill won't affect the volume by much ... 0.1 cu ft maybe? how big is the box you are planning?

The net volume is targeted at 3.7'^3. Now the OC 703 recommended would take up quite a lot of that space up. Exactly 2'^3 would be eaten up leaving me with 1.7'^3.

Just to make sure that I'm doing this right let me say that I am using 1728"^3 as a conversion for 1'^3. My internal dimensions start at 14"x24"x26" getting me to 5.06'^3. After the slot port, bracing and driver displacement are subtracted I end up with 3.7'^3.

This is more math than I've done in 25 years. I think I'm doing it right and can only hope that proceeding to stuff the recommended insulation in there is correct. The box can be no bigger for what I want to use these for.

Sorry about the PM thing. I just saw somebody else do it and thought it was all good. Won't happen again and it was too late to edit that out. Can you edit it out for me as a mod?

 

[Alex2507]

If you are using high density Rockwood type panels then you will have to add that to Vb.

I think you mean subtract it from Vb? (Volume of Box)

Maybe all that was figured into the recommended size to begin with.

 

[mike c]

there's no need Alex, and its no problem at all.

hey WmAx is online now ... perhaps it is easier for Chris to correspond through email rather than PM's.

 

[WmAx]

what does WmAx say about the fill?

if i had to guess, the fill is supposed to get rid of resonance, and does not actually add to the volume. wild guess here.

The high density panels take up very little actual internal volume. If you want the most accurate calculation, you should probably consider 10 percent, at most, of the volume of the panel itself as real displaced volume. So, if you have 1 ft^3 of the volume displaced by the high density fiberglass, then you could consider 0.1 ft^3 as displaced volume. This would be assuming something like OC705, or 8lb rockwool board. If using OC703 or 4lb rockwool board, a compensation of 5 percent would likely be accurate.

Use of these materials has affected my response plots minimally so far as volume effect. The real effect of these very high density materials, when in excess, is the effect of over-dampening the box and/or port resonant spring properties, causing loss of LF output by a mechanism different than that of volume displacement.

-Chris

 

[Alex2507]

The high density panels take up very little actual internal volume. If you want the most accurate calculation, you should probably consider 10 percent, at most, of the volume of the panel itself as real displaced volume. So, if you have 1 ft^3 of the volume displaced by the high density fiberglass, then you could consider 0.1 ft^3 as displaced volume. This would be assuming something like OC705, or 8lb rockwool board. If using OC703 or 4lb rockwool board, a compensation of 5 percent would likely be accurate.

Use of these materials has affected my response plots minimally so far as volume effect. The real effect of these very high density materials, when in excess, is the effect of over-dampening the box and/or port resonant spring properties, causing loss of LF output by a mechanism different than that of volume displacement.

-Chris

Oh. Thanks for the info about the OC 703 and OC 705. I didn't realize there was a density difference. I thought one was 2" and the other 4". Now I know. I assume that the OC 705 is better so that's what I'll track down.

 

[TLS Guy]

I think you mean subtract it from Vb? (Volume of Box)

Maybe all that was figured into the recommended size to begin with.

No, Vb is the volume of air in the box. You therefore have to add anything that displaces air to Vb, to get the total box volume Vt.

Alex where did you get the 3.7 cu ft volume from? The low Qt vented has a Vb of 3.024 cu. ft and the mid Qt vented has a Vb of 4.653 cu. ft.

 

[Alex2507]

No, Vb is the volume of air in the box. You therefore have to add anything that displaces air to Vb, to get the total box volume Vt.

Alex where did you get the 3.7 cu ft volume from? The low Qt vented has a Vb of 3.024 cu. ft and the mid Qt vented has a Vb of 4.653 cu. ft.

I see the confusion. In my mind I am starting with a fixed box size and subtracting anything that I put into it. So I started with 5.06 cu. ft. and ended up with 3.7 cu. ft. It's back wards but still gets you there.

I got WmAx to recommend a cabinet and port size. This is the first time around for me. Qt vented or mid is still outside of my understanding. I'm going to build his recommended box and try to learn the lingo along the way. WmAx was good enough to come up with an answer in this thread regarding my insulation question so I'm good to go. The next subs that I build will be a different matter. This is where it begins for me.

Thanks for your interest,
Alex

 

[TLS Guy]

I see the confusion. In my mind I am starting with a fixed box size and subtracting anything that I put into it. So I started with 5.06 cu. ft. and ended up with 3.7 cu. ft. It's back wards but still gets you there.

I got WmAx to recommend a cabinet and port size. This is the first time around for me. Qt vented or mid is still outside of my understanding. I'm going to build his recommended box and try to learn the lingo along the way. WmAx was good enough to come up with an answer in this thread regarding my insulation question so I'm good to go. The next subs that I build will be a different matter. This is where it begins for me.

Thanks for your interest,
Alex

Well it is important you understand that the Kappa 12 VQ can be three very different speakers.

It has two inserts. With no inserts it has a high Qts of 0.74 and is only suitable for a sealed enclosure.

With the mid Insert it has a Qts of 0.47 which is still optimal for a different sealed enclosure, but can be tuned to give good ported performance with a slot vent. With a Vb of 4.67 cu ft it can be a sub with awesome performance.

With the low insert it has a Qt of 0.34 and is suitable for reflex port loading. It will give good performance with a Vb of 3.024 cu.ft. Best performance is with a slot vent, but it can deliver acceptable performance with a tube vent.

So it is vital to know what Qt you are building for, otherwise you will have a mess.

 

[WmAx]

Oh. Thanks for the info about the OC 703 and OC 705. I didn't realize there was a density difference. I thought one was 2" and the other 4". Now I know. I assume that the OC 705 is better so that's what I'll track down.

The OC705 offers no performance over the rockwool board. The OC costs several times more. Unless you get some special deal on the OC - go for the rockwool board and save money.

-Chris

 

[Alex2507]

Well it is important you understand that the Kappa 12 VQ can be three very different speakers.
.

I'm not building for a Kappa 12 VQ. I am using a JBL GTx 10. This is the info that I have found on it:

Freq response: 30Hz-500Hz
Amp. Power Range: 20W-500W
Continious Power Handling: 250W
Peak Power Handling: 450W
Voice Coil dia: 2,0" (51mm)
Nominal Impedance: 4 Ohms
Sensitivity@2.83V RMS@1M: 87dB
Driver Displacement: 0,09 cu.ft. (2,55l)

Thiele-Small Parameters:
Fs = 31Hz
Vas = 1,85 ft² (52,4l)
Qts = 0,43
Qes = 0,45
Qms = 7,55
Re = 3,3Ohms
Le = 0,6mH
Xmax = 0,480 in. (12,2mm)
Xpk = 0,866 in. (22mm)
Sd = 0,3724 Sq. Ft. (0,0346 Sq.M.)
Vd-linear = 0,000422 Cu. M.
Vd-peak = 0,000761 Cu. M.

The OC705 offers no performance over the rockwool board. The OC costs several times more. Unless you get some special deal on the OC - go for the rockwool board and save money.

-Chris

Thanks.

 

[TLS Guy]

I'm not building for a Kappa 12 VQ. I am using a JBL GTx 10. This is the info that I have found on it:

Freq response: 30Hz-500Hz
Amp. Power Range: 20W-500W
Continious Power Handling: 250W
Peak Power Handling: 450W
Voice Coil dia: 2,0" (51mm)
Nominal Impedance: 4 Ohms
Sensitivity@2.83V RMS@1M: 87dB
Driver Displacement: 0,09 cu.ft. (2,55l)

Thiele-Small Parameters:
Fs = 31Hz
Vas = 1,85 ft² (52,4l)
Qts = 0,43
Qes = 0,45
Qms = 7,55
Re = 3,3Ohms
Le = 0,6mH
Xmax = 0,480 in. (12,2mm)
Xpk = 0,866 in. (22mm)
Sd = 0,3724 Sq. Ft. (0,0346 Sq.M.)
Vd-linear = 0,000422 Cu. M.
Vd-peak = 0,000761 Cu. M.




Thanks.

Alex, it really helps to know what driver we are talking about!

I have run complete graphs for your driver with Vb at 2.44 cu. ft and Vb 3.7 cu. ft. and made a pdf file of both. The smaller Vb is really as good as the larger. The larger has an F3 3Hz lower than the smaller. However it is illusory because there is a small hump in the response. Both exceed xmax about 25 Hz and both are down 9 db at 20 Hz. However the performance of both is really very good. However I consider the larger enclosure a waste of material and time. There is no practical advantage to the larger enclosure.
Basically the Fs of a driver determines its useful bass extension. You can go a few Hz below often. The Fs of your driver is 31 Hz, so practically speaking you can extend the F3 to around 27 Hz. Response will start to fall around Fs whatever you do.

I have updated my pdf program and now any useful file exceeds the 100 KB limit by about 17 KB. I will PM you and you can send me your Email and I will Email you both files.

I find this 100 KB limit very confining for educational technical files. It is most frustrating. Even a 25% increase would make a big difference.

 

[Alex2507]

Hey TLS,

I responded to the PM before reading the above post.