Hi,
I am modeling with VituixCAD some 2.5 speaker. I do have couple of woofer measurements at hand, but the simulation shows that the low end of bassreflex box will be exactly the same if I put 2 woofers lets say in 10L box tuned to 60Hz or separate them into 2 x 5L chambers tuned to 60Hz. The only difference is 2 vents are mandatory then.
Somehow my guts feel that separate chambers will have better isolation of lower woofer diaphragm from mid freq inner bounces of upper woofer and lower overall acoustic crosstalk between them. But on the other side somehow have a feeling that bigger single box has some advantages... But cannot name them. 😀 Maybe none?
So, what would be your choice in every choice?
1. Two separate chambers or single?
2. In case of single chamber and single vent - the best position is probably in the same distance to each woofer? Does it matter?
3. In case of 2 chambers or single chamber with two vents - do they need to be tuned a little different not to have the same resonance?
4. In case of 2 vents - do they need to be in identical position to their relative woofer? If the distance of the vent exit from woofer cone is 5-10cm different between each woofer-vent pair - it can be measured, but can it be heard with ears?
Opinions and facts are welcome. Thank you!
I am modeling with VituixCAD some 2.5 speaker. I do have couple of woofer measurements at hand, but the simulation shows that the low end of bassreflex box will be exactly the same if I put 2 woofers lets say in 10L box tuned to 60Hz or separate them into 2 x 5L chambers tuned to 60Hz. The only difference is 2 vents are mandatory then.
Somehow my guts feel that separate chambers will have better isolation of lower woofer diaphragm from mid freq inner bounces of upper woofer and lower overall acoustic crosstalk between them. But on the other side somehow have a feeling that bigger single box has some advantages... But cannot name them. 😀 Maybe none?
So, what would be your choice in every choice?
1. Two separate chambers or single?
2. In case of single chamber and single vent - the best position is probably in the same distance to each woofer? Does it matter?
3. In case of 2 chambers or single chamber with two vents - do they need to be tuned a little different not to have the same resonance?
4. In case of 2 vents - do they need to be in identical position to their relative woofer? If the distance of the vent exit from woofer cone is 5-10cm different between each woofer-vent pair - it can be measured, but can it be heard with ears?
Opinions and facts are welcome. Thank you!
I personally would prefer two chambers, unless the baffle and driver layout does not allow it:
- the separation board stiffens the enclosure
- shorter interior dimensions makes it easier to dampen longitudinal "standing wave" resonance.
- ports at two different positions may eventually provide a more even interaction with the room.
- stuffing one or two ports allows more flexible adaptation of bass response.
1. See above!
2. Not necessary. The port should be slightly distant from the driver to avoid rear high frequency radiation exiting the port(s)
3. You can tune them slightly different, but you can also rely on not-identical driver TSP or you could vary tuning with the stuffing material quantity.
4. As I mentioned above, bass output will not be affected by exact port positioning. Enclosure resonances and rear radiation from woofer will be, however!
I'll post some links to my port resonance/geometry thread!
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Port on the back has the advantage of much less audible resonances, chuffing and high frequency output from the port. You need a little space behind the speaker (but that's probably the case anyway).
I think that in order to pressurize the room more evenly it may be best to have the ports more distant, for a tower maybe top and bottom.
Regardless of the port length, a single chamber with two vents will have a single Fb (box tuning frequency), but different port lengths will result in different pipe resonances for each. For such short port lengths as your proposed design, pipe resonance is probably not a problem.
Out of phase upper frequency reflections emitted through the port(s) may be a problem with extended bandwidth vented enclosures, rear porting reduces that effect without requiring as much damping material, which reduces the port's low frequency output.
Art
So all of us basically agree that two separate chambers for two woofers have all the advantages and the only disadvantage is tiny bit more building material and tiny bit more of work?
I'd agree the only disadvantages to two separate chambers are more building material and work and a slightly larger cabinet.
Ok, this is getting interesting! 2.5 design is most likely 6-7 inch woofers, 25-29mm tweeter, arranged in TWW. Internal volume of such speaker probably is in 25-50L range. Box with close to golden section ratio dimensions will have at most freedom to have up to ~40cm distance between ports. In stick form factor box we may be talking about ~80cm at most. If the tuning of ports is 50Hz, we may say, that 100Hz note is the highest coming out of it. So 100Hz is ~3.5m of wavelength, and we are spacing ports just at ~1/4-1/5 of wavelength or just 1/8 for 50Hz.
We can talk about ~35mm tweeter and dual 8-10 inch woofers, but that is a bit too much exotic, and still with ~35-40Hz tuning we are at the same ratios.
Is my logic right? Do such relatively small distances matter?
I prefer single chamber but that's because I'm not fully confident I could get both chambers at the same volume and tuning and I'm sure the woofers are not exactly the same either and not sure how that would effect things.
http://zaphaudio.com/commonenclosuretest.html
http://zaphaudio.com/commonenclosuretest.html
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Probably not!
I could be wrong about my assumption regarding distant ports - my guess was that the room modes may not be excited so unevenly (so not directly related to wavelength).
I heard that mounting woofers on different heigths may have benefits, but again I have no experience with that.
But of course the ports have a very limited output bandwidth compared to woofers.
That is way above my knowledge. Common sense says, that room mode at 100Hz has to be somehow related to wavelegth, so is it ~1.7m of peak and ~1.7m of hole?
I tent to disagree on this one: they have -5 to -10dB SPL, but just a single narrow peak (+ some silent leaking artefacts and port resonance), so still matter in the whole
Zaph had this to say about the two chamber vs one chamber question (the third chamber is the crossover). YMMV.
http://www.zaphaudio.com/Waveguidetmm.html
"This enclosure is a three chamber design. I require the woofers to have their own chambers so the backwave of the top woofer's lower midrange does not interfere with the bottom woofer,"
http://www.zaphaudio.com/Waveguidetmm.html
"This enclosure is a three chamber design. I require the woofers to have their own chambers so the backwave of the top woofer's lower midrange does not interfere with the bottom woofer,"
I think the link I posted above superseded his TMM waveguide project and he changed his mind on the need for separate chambers after experimenting.
http://zaphaudio.com/commonenclosuretest.html
I was almost sure, that I know Zaph's site by heart, but do not remember this project. Thanks for reminder!
3 parts(!) crossover on 3 drivers?!!! WHAT???
Yes, still 300EUR/speaker, and probably response will not look that nice on 1/24 smoothing
To be honest - I do not see much difference in those 2 graphs, still there probably is much more comb filtering effects when trying to cross 2 woofers with tweeter than only the upper one.
