plugging speaker ports for 'base management'

[Bevan]

here's what i'm wondering:

if i plug the ports of my bookshelves, and thereby change the freq respose from 52hz to something like 70hz, is this any different to using a filter to send only 70hz and above information to the speakers?

i'm wondering this from the amps and speakers point of view, i.e will the amp see an easier load, and will the speakers play louder and clearer and with less chance of clipping.

i'm hoping to effect a kind of base management here, which i seem unable to achieve with the 2 channel/integrated amp setup i have. (the sub i am looking to buy does not have a high pass filter, nor do i want to implement the extra op-amp a subs filter would use).

i'm wanting to go from dynaudio 52's to 52 se's, but am reluctant to make the move without some kind of base management as i read a review on this site mentioning that they can bottom-out at high volume on base heavy tracks. so, would plugging the ports with the foam bungs prevent this from happening??

thanks

bevan

 

[jaxvon]

By plugging the ports you will change the parameters of the box. Yes, it will raise the frequency response (not sure if it'd go up to 70Hz), but it would also result in less output. I suppose that you could try it and try to see how flat the response is with an SPL meter, but I have a feeling that it might generate some large non-linearities due to the fact that the speaker was not engineered to have a foam plug in the port.

As I read your post though, i'm not sure how much good this would do. Unless you implement some kind of crossover on your sub, will you just be feeding it a full-range signal?

Perhaps you should get the Outlaw ICBM. It's not terribly expensive and would allow you great control and bass managment.

 

[j_garcia]

Base management can be handled with sand, lead, or even cat litter. Oh, you mean BASS management...

No, plugging the port will not change the amount of power needed by the speaker. As jaxvon already pointed out, you will lose some output, causing you to potentially actually have to turn it UP slightly. So, while bass response was reduced, it did not actually modify the frequencies being sent to the speaker, so it will still attempt to reproduce them.

The sub shouldn't have a problem with a full range signal as long as it has a low pass filter.

 

[Bevan]

but if the speaker is not reproducing the 52-70hz signals(even though it may be trying to), doesnt this neccessarily mean that the woofer is not extending as far, thereby playing 'safer'?

thanks

b

pardon the spelling

 

[Buckeyefan 1]

but if the speaker is not reproducing the 52-70hz signals(even though it may be trying to), doesnt this neccessarily mean that the woofer is not extending as far, thereby playing 'safer'?

By changing a bass reflex design into a sealed enclosure, you definitely limit the drivers movement. Sealed enclosure type drivers tend to produce a tighter, more controlled bass. When a port is added, the driver's movement is much freer, and more efficient. Think of closing a storm door when the main door is shut. Now open the main door, and see how much easier and faster the storm door closes. What you run into is a design flaw. Your speaker was built to accomodate a port. It (the volume) would need to be much larger to produce the lower frequencies should you turn it into a sealed enclosure. Go ahead and experiment. You'll lose efficiency, low frequency output, and experience lack of power to properly drive this new enclosure.

 

[WmAx]

By changing a bass reflex design into a sealed enclosure, you definitely limit the drivers movement. Sealed enclosure type drivers tend to produce a tighter, more controlled bass. When a port is added, the driver's movement is much freer, and more efficient.

To really know what's going on at a specific frequency in a particular situation, you have to have the T&S parameters of the drivers and the enclosure specifications. As for generalization: a ported enclosure has less excursion for a given SPL as compared to a sealed enclosure using the same driver, when used around the tuned frequency of the port. However, as you go below the tuned port frequency, the excursion becomes greater with the ported design as compared to a typical sealed design, since the port is no longer loading the speaker, and you basicly have a large open hole in the box to allow free movement of air. As for "tighter, more controlled bass", this a function of frequency response of the woofer alignment and the room interaction(s). You can actually manipulate the FR of a ported design to match that of a sealed design, and have the benefit of increased maximum SPL and decreased non-linear distortion, but with the same sound as the sealed design, if one so desired to go through with this effort.

-Chris

 

[Dinkar Rai]

bevan

the 52se comes with port plugs. i have mine actually installed in a bookshelf area. the base was a little boomy due to the bookshelf enclosure. the plugs healped in tightening the base. i also read the post on flattening out on high base. i have not felt anyting like it at all. in fact i fall more in love with the speakers every day. just go ahaed and buy them.

 

[Bevan]

so if i understand correctly, excursion is limited for frequencies bellow the port tuning. this should protect the speaker then against bottoming out trying to reproduce 30hz basslines.

i understand that the speaker and amp would have to work harder trying to produce bass, but with a sub in the picture(and the absence of any high pass filters), i could now set the sub to take over at the new natural rolloff frequency of say 70hz rather than 52hz.

so if i understand correctly, i get the same 'protection' as using a high pass filter as the woofer is not extending as far producing the real low stuff(and hense maybe increased midrange and high freqency clarity if the woofer is moving les), BUT, i dont get the increased spl's that a high pass filter would offer, as the amp is still trying ineffectively to produce the sub bass?

also, it may be that its not just the speakers lower roll-off that is changed by plugging the port. as the speaker was designed to be used unported for the most part, i would not be surprised if the plug has some negative affect the flatness of the entire freq respose curve to some degree? i wish i could test this out but i dont have a spl meter or test tones as yet.

thanks for the input guys

bevan

 

[j_garcia]

so if i understand correctly, i get the same 'protection' as using a high pass filter as the woofer is not extending as far producing the real low stuff(and hense maybe increased midrange and high freqency clarity if the woofer is moving les), BUT, i dont get the increased spl's that a high pass filter would offer, as the amp is still trying ineffectively to produce the sub bass?

Using a high pass filter actually reduces the amount of signal fed to the speaker so it CANNOT even try to reproduce the lower frequencies, thus it will not draw the current needed to try. Running a full range means the speaker will still try its best to reproduce the frequencies sent to it until it naturally rolls off, which means it may try to reproduce frequencies it is not capable of reproducing.

Plugging the port modifies the tuning of the cabinet, which in this case increases the roll off of the low end response of the driver. This is normal with a sealed speaker. It actually may FLATTEN the response of the speaker, because it is now operating in a narrower range, and as was mentioned, response tends to tighten up because there is more "spring" resistance within the enclosure. Most small speakers will work fine with the port plugged or open, depending on the listener's preference.