robbie010

Bass reflex volume calculation / mathematics??

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Super Wammer

Sorry if this may be a bit long winded and possibly a stupid question, at this stage I don’t know what I don’t know!

I made a set of clone Klipsch La Scala using all original drivers and horns etc. They are great speakers! ⬇️

D242EE13-551F-4E5A-809D-25AE6981D0E3.thumb.jpeg.81cbc9945eea3bea37315d8f6130d99d.jpeg

Having browsed the US Klipsch forum, there are a number of threads that suggest increasing the volume of the bass cab with an additional bass reflex box added to the bottom, apparently, this increases low end extension below 40hz.

Having read a bit and asked a few questions, I am thinking of giving this a go, as it doesn’t involve any alteration the original speakers and can be easily reversed. I have been told how to do this using a box the same width / depth as the speaker and being 10” deep, this is then ported with 2 sections of pipe being 4” in diameter and 7” long and can be tuned to my room by playing around with the length of the pipes. ⬇️

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What I can’t get my hands on is any details or calculations as to the specific volume required for the additional box and whether there is a minimum volume that I could get away with - raising the whole speaker by 10” seems a lot!

Do we have a resident speaker design wiz on the wam that could enlighten me as to how the given volume of a box will effect the outcome?

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Super Wammer

just a quick update here, I have now found the specifications for the woofer driver and worked out the internal volume of the cabinet as-is. Obviously, I can also work out the volume volume of the additional box at various sizes.

Can I use these with some kind of calculator or sim to see the response of the driver with various perameters???

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Try mh-audio.nl for loads of calculators for loudspeaker design inc reflex.

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I'd be amazed if anyone could model that for you, but If others have had success with adding a ported cabinet, maybe best to just give a try.

What are the woofer specs? I could model a ported enclosure to see how low it could go. I would also need to know how high is the woofer off the floor and your room dimensions (length width). Is it a sealed room or open plan?

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Super Wammer
3 hours ago, Fatmarley said:

Oh, and cabinet width and woofer diameter.

Thanks for the help! Here are the details I can provide, be it accurate or guestimate:

The woofer currently sits within the "doghouse", backwards firing and is 300mm off the floor at its centre point. The image below will give you a better idea of what the inside of the doghouse looks like.

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As you can see, the dimensions of the cabinet are a little tricky, however, I have worked out the internal volume of the sealed doghouse, which is 72.7L, this doesn't take in to account the volume lost to the actual driver though.......

Using the measurements I have found online for the additional ported box, which is the same width and depth as the bass cabinet with an internal height of 254mm (10"), the additional volume would be 90.7L, giving a total internal volume of 163.4L.

When I have read other threads where this mod has been done, there is anecdotal evidence that the bass extension reaches down to the 30 Hz range. However, what I am really interested in is knowing is whether the height of the additional bass reflex box has to be 10", could the same be acheived with say a 5" box. 

If it helps, these are the various internal volumes that could be acheived with varying heights of the additional ported box:

25.5cm (~10") Internal height = 90.7L - gives total internal volume of 163.4L

20cm (~8") Internal height = 66.7L - gives total internal volume of 139.4L

15cm (~6") Internal height = 50.04L - gives total internal volume of 122.7L

12.5cm (~5") internal height = 41.7L - gives total internal volume of 114.4L

The Driver Specs Are:

Klipsch K33E - 15" Woofer

Fs = 34.46 Hz
Qms = 7.39
Vas = 301.7 liters
Cms = 0.268 mm/N
Mms = 79.47 g
Rms = 2.328 kg/s
Xmax = 8.2 mm
Xmech = 12.3 mm
P-Dia = 336.6 mm
Sd = 889.6 sq.cm
P-Vd = 0.729 liters
Qes = 0.41
Re = 3.39 ohms
Le = 0.96 mH
Z = 4 ohms
BL = 11.93 Tm
Pe = 150 watts
Qts = 0.388
no = 2.903 %
1-W SPL = 96.78 dB
2.83-V SPL = 100.5 dB

My room dimensions are: 11ft by 16ft with an 8ft ceiling. There is a bay window at one end and one door, the speakers currently fire across the short width of the room.

Edited by robbie010

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Unfortunately I can't model hybrid designs, only ported, but the good news is this driver is capable of producing relatively deep bass. 163ltr tuned to 36hz (2 x 4" diameter x 6" long ports) is about the same sort of low frequency tuning I'd use with my own speakers. Obviously being hybrid means the ports may have to be a different size to achieve the same frequency response.

Here's a model. The grey line is 163ltr, the black line is 116ltr - The software doesn't allow me to model exact volumes (114ltr), but it makes very little difference in reality. I left out room gain in the model because it doesn't show us much. 163ltr looks much better than 116ltr to me, and this is what I'd personally go for.

htHBEmcl.jpg

Edited by Fatmarley
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Oh, another thing that may be relevant is that when you extend the low frequencies, you trade efficiency for low frequency extension, So bass could end up deeper but lighter or with less punch.

Just wondered if the mid and treble horn have any adjustment? If not, an adjustable L-pad on both may help.

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Super Wammer
4 minutes ago, Fatmarley said:

Oh, another thing that may be relevant is that when you extend the low frequencies, you trade efficiency for low frequency extension, So bass could end up deeper but lighter or with less punch.

Just wondered if the mid and treble horn have any adjustment? If not, an adjustable L-pad on both may help.

Thanks for this, its really helpful!

The HF is run through an Autoformer on the crossover, which allows some tweaking I believe. I’ll have to do a little more research. 

👍🏻

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