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Discussion Starter #1
Hi!

I've toyed with the idea of sealing my subs. I have two Soundslpinter RL-p15 tuned to 13,5Hz sonotubes, the usual setup for LLT.

I was wondering if some dense foam would be enough to seal the ports to see if I like them better sealed?
 

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Well, I rolled a few towels tightly and jammed them in the ports. Did a quick measurement of the unequalized results...
The results are pretty much spot on according to the simulations. Notice the non-standard graph extension to 5Hz.

SPL



Group delay:



Cone Excursion:



And the measured, unequalized response in my prime listening position:



Waterfall. Notice the significant improvement down low.
 

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15Hz-25Hz it's a smashing for the ported.
Seems like for HT you'd be losing a noticeable amount of output.
Thought you do have some to spare for most normal folks. :)

I see the group delay is lower, but will it be audible?

Below 15Hz is rare territory is it not? Like the movie "Pulse" and almost nothing else, no?
 

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Discussion Starter #5
Well, having only listened to a few songs, I notice a significant drop in level down low, but also what seems to be increased clarity or whatever. Might well be I'm just hearing what I'm expecting. I'll leave them sealed for a while then go back to ported and see.
 

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I would think that the better looking waterfall for the sealed is atleast partially due to the lower output in that range.

I have a theory that the reason sealed sounds better to many people is due to the roll off on the low end which sounds more like what people are acustomed to hearing the bass sound like. The ported has more output at the deeper freq's which cause it to sound a bit boomy or slow. The lower bass frequencies boosted by the port are naturally boomy and slow sounding because bass IS slow. I could be completely wrong though.

I'd like to do an experiment that EQ's down a large ported sub tuned below 20hz to have a response that matches a smaller sealed sub as close as possible using the same amp , xover, room location and driver and see what happens. Possibly follow that with a test that EQ's the smaller sealed sub to match the ported subs FR and listen again.
 

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I have a theory that the reason sealed sounds better to many people is due to the roll off on the low end which sounds more like what people are acustomed to hearing the bass sound like. The ported has more output at the deeper freq's which cause it to sound a bit boomy or slow. The lower bass frequencies boosted by the port are naturally boomy and slow sounding because bass IS slow. I could be completely wrong though.
You are on the right track. Aside from room effects the primary reason sealed subs are often perceived as 'tight' and 'musical' relative to ported ones is because of the extended bass shelf found in ported subwoofers as well as the natural roll off of each design. Through proper use of equalization this perceived boominess can be mitigated, of course that would require doing something drastically different than the popular house curve found on this site.

I'd like to do an experiment that EQ's down a large ported sub tuned below 20hz to have a response that matches a smaller sealed sub as close as possible using the same amp , xover, room location and driver and see what happens. Possibly follow that with a test that EQ's the smaller sealed sub to match the ported subs FR and listen again.
I have done such experiements here is a post regarding my findings:

Using my previously built Kappa VQ subwoofer that was intentionally designed because it is highly linear regardless of output level and contains inaudible distortions well within the pass band within reasonable SPL. Using a high quality equalizer I adjusted the subwoofers response such that it replicated a sealed alignment, passive radiator alignment and also allowed for the third variable of ported (the subwoofers natural alignment).

Using a panel of 10 listeners 5 [self] trained and 5 untrained. All four subwoofers (the VQ, a sealed unit, a different ported unit and a PR unit) were placed in the room and equalized such that in the main listening position intended frequency response was +/- 3dB. No listener was able to differentiate the original alignment (sealed, ported or PR) from the replicated alignment (VQ) in a statistically significant manner using single blinded ABx methodology. Source material consisted of music, movie clips and actual frequency sweeps. Welcome to what I do in my free time... :nerd::coocoo::dumbcrazy:
 

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Discussion Starter #8
Cool, thanks for the info.

It sorta correspond to my own findings. A properly implemented ported system just sounds different from a sealed one. And if you look at the simulation, they are very similar down to where the port starts to work, and most sealed fans report the higher frequencies to be better with sealed than ported. I think I'm going back to ported.. :)
 

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Thanks for the detailed reply Andrew. I'm going to do my own tests too because I feel like I should.

Atledreier,
You could do a simple test easily too. Try to EQ the sealed up sub to match the response with the port open. Then listen to it and switch back to the port open config and turn the EQ off. Report back your findings...
 

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Atledreier,
You could do a simple test easily too. Try to EQ the sealed up sub to match the response with the port open. Then listen to it and switch back to the port open config and turn the EQ off. Report back your findings...
Please note, for properly generalizable results the testing should be done in a blinded circumstance such that the listener is not biased by extraneous variables. Also, it is vital to proper results for the SPLs to be matched.
 

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I think that you are getting a little deeper into it than what I was thinking. I'm talking about for his and my personal benefit using our own equipment and our own ears. No need for double blind listening tests and all that as it's for no ones knowledge but our own and it's not going to be presented as any kind of true study. If there is an obvious difference then it will be heard switching between them. If it's very subtle then that says something too. There shouldn't be that much bias involved because it's our personal equipment. The only difference is one box has a pipe in it the other doesn't. Levels should obviously be matched as close as possible.
 

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Sealed enclosures DO need to be equalized in the lower portion of the FR. The natural drop off of a sealed enclosure's FR is easily changed with a Linkwitz/Riley circuit or PEQ.
 

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Yes but at the expense of headroom and SPL at the lower end unfortunately...
 

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Yes but at the expense of headroom and SPL at the lower end unfortunately...
It's only unfortunate if the difference in SPL/headroom means dropping more than an average 4-6 DB across the lower FR spectrum.
The examples I've seen on this forum and others usually show only a drop from 120DBL to say 116DBL, still well within my own set of performance standards.
 

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It'll depend on the unique situation how much of a headroom difference there is. I'm just interested in the differences in apparent SQ or lack there of between vented and sealed at moderate levels where both are still in their comfort zone.
 

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Well, I rolled a few towels tightly and jammed them in the ports. Did a quick measurement of the unequalized results...
One more thing . . . . . .
Stuffing towels in the ports does not get you anywhere near being sealed, however your set of graphs and the waterfall show how linear a (SEMI)sealed can be.
 
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