View Full Version : ported speaker into sealed?


k-man
09-30-2007, 08:51 PM
I have a pair of 3 way kenwoods from the 70's that I've recapped and I've always found the bass to be a bit too boomy on it. I prefer the sound of sealed enclosures since the sound seems more crisp and clean to me and I don't listen to much music with allot of bass anyways. So until I get enough money to buy a nice pair of dynaco speaker's is it possible to seal off the port in mine and convert it into a sealed speaker or wont this work because it was designed with the port in mind?

Paul C
09-30-2007, 09:03 PM
No, it isn't that easy, unfortunately.

I would suggest retuning the port. You will have to probably remove the woofer to get to the inside, but first try extending the port. Make it longer, but if it approaches 1 diameter from the rear of the speaker cabinet, add an elbow.

So, what is the diameter and length of the port now? What are the dimensions of the cabinet?

k-man
10-01-2007, 12:42 AM
Ok it's a Trio-Kenwood LSK-400D and the cabinet's dimensions are,
22"X12"X9" which is the HWD. The port is 1.75" across and 5" long.

melofelo
10-01-2007, 08:36 AM
a little trick you might try...try stuffing enough drinking straws in the port so that they are held in place under slight compression..then you can vary the length and 'lossiness' of the port as you listen and fine tune the bass...or if you can find a cardboard tube that will just about fit inside..you can experiment with different lengths and tune by ear for a compromise..

fdrennen
10-01-2007, 08:50 AM
a little trick you might try...try stuffing enough drinking straws in the port so that they are held in place under slight compression..then you can vary the length and 'lossiness' of the port as you listen and fine tune the bass...or if you can find a cardboard tube that will just about fit inside..you can experiment with different lengths and tune by ear for a compromise..

Another is to pack a pair of socks in the port.

saltwater
10-01-2007, 08:56 AM
straw trick works, but so do the socks!

bshorey
10-01-2007, 09:01 AM
Ok it's a Trio-Kenwood LSK-400D and the cabinet's dimensions are,
22"X12"X9" which is the HWD. The port is 1.75" across and 5" long.

I agree with Paul, it's not so simple. Bass Reflex enclosures are typically designed so as to allow for a smaller enclosure size than a traditional acoustic suspension enclosure. A small, sealed enclosure will make for a lot of back pressure on the woofer, and raise the resonance (i.e. you'll lose the deeper bass). The woofers themselves are also designed for different applications.

That said, you mentioned that the music you listen to doesn't have a lot of bass, so maybe none of that matters. You could always try duct taping something over the end of the ports, and see if you like the results. Easy enough to undo if it makes things worse.

HTH,

bs

cfranz
10-01-2007, 09:31 AM
Have you tried to attack the problem from the other direction. Add some bracing to the box, some poly-fill, and something to absorb standing waves inside the cabinate. Sometimes felt directly behind the bass speaker will help some. Or try any of the following: http://www.partsexpress.com/webpage.cfm?webpage_id=3&CAT_ID=48&ObjectGroup_ID=137

Switch the polarity of the bass speaker. Mind you, this works better with a 'shouting' tweeter then a bass, but it's cost free and relatively easy.

As a last and finaly resort, you could try to coat the paper of the bass speaker with something to make it a little heavier and stiffer (spray on laquer or something). Base response would slow a little but from what you are saying, this may not be an issue. You would definitely have to play with the port after that, of course, as the FS of the woofer definitely changes. The more I read this idea the less I like it.... But I'll leave it in.

:worried: Warning: any of these could make things worse. Mind you, they might solve the boominess but change the sound of the speaker for the worse.

Also, I really like the straws idea. Hadn't though of it. Someone is too darn clever for their own good.... :yes:

GordonW
10-01-2007, 09:55 AM
Actually, vented speaker enclosures have to almost univerally be LARGER than a sealed enclosure with the same driver!

I have seen some cases, where the vented enclosure was badly tuned (too small of a box, too short of a vent, etc), that simply blocking the port (sock, rubber ball, etc) made the system more listenable. Worth trying, given you can always revert to the original if it doesn't work...

Lengthening the port can also help, if the box is reasonably well-sized to start with. That'll take away some of the midbass ('boom') and transfer the energy to lower bass extension...

Regards,
Gordon.

BrocLuno
10-01-2007, 11:57 AM
I agree that some boominess can come from cabinet resonances and interior pressure waves being broadcast from the box surfaces. I have worked on (remodeled) one set of Kenwood speakers.

The boxes were pretty thin. I added a back front brace just above the woofer cutout hole. I also added a 3/4 x 3/4 stiffening rib down the center of each side and next to the front back brace on the back (stiffening the long panels).

It helped a lot. They got more musical and the lousy bass became better. I then stuffed them (not tightly at all) with light weight pillow fill (dacron I think as it was the cheapest locally) and they went up another notch. I did not work on port tuning - that was going to be my next "experiment". They got good enough to listen to until I gave them away a year later.

Point being - experiment. Play them loud and run your hands over the cabs. If you feel any flexing or pulsing, brace to kill that first. Then move on to other mods. The drivers are likely OK, just in an under engineered enclosure?

DaveThreshol
10-01-2007, 05:19 PM
I would try it. It can't hurt anything. My guess is that those might have been designed for extra bass anyway, for the initial reaction of consumers when they were on the store shelf. Also the idea of the straws will give a 3rd order response, instead of 4th, (vented) or 2nd order, (sealed). might be worth a try also, but might chuff more at higher volumes.

The ones that I use are huge subs that I made with huge 6" wide ports @ 17 Hz. one day I figured I'll try stuffing them and listening to them, and they sound better, and tighter sealed. My, "advice" for any amateur builder, is to make them large enough to vent, THEN you have the option to close the vents, (with most types of woofs.) That way you have 2 different types of bass for one type of speaker. It is beyond me why speaker makers don't design some of theirs that way. It really is the best of both worlds.

The NEXT ones I design, will be 3 type convertible. 1. Vented, 2. Sealed and 3. Aperiodic.

k-man
10-01-2007, 05:21 PM
thanks for all the great ideas, I'll try some of these and see what it does.

dnewma04
10-01-2007, 05:23 PM
The chances of it working are order of magnitude more likely than making a sealed speaker ported. You will lose some power handling and possibly some bass extension, but I would say it's got a decent probability of working.

Zilch
10-01-2007, 05:52 PM
It is beyond me why speaker makers don't design some of theirs that way. It really is the best of both worlds.The answer is that driver parameters are optimized for vented vs. sealed alignments.

EBP, Efficiency Bandwidth Product, Fs/Qes, is the index. 50 or lower is a closed-box driver, and 100 or higher is vented. In between, it's a continuum of preference.

EBP can be determined for any driver in a matter of seconds using measurement devices such as Woofer Tester from Parts Express.

It takes a bit longer to do it the old-fashioned way with a voltmeter and a resistor, but that works, too.... :thmbsp:

DaveThreshol
10-01-2007, 05:57 PM
The answer is that driver parameters are optimized for vented vs. sealed alignments.

EBP, Efficiency Bandwidth Product, Fs/Qes, is the index. 50 or lower is a closed-box driver, and 100 or higher is vented. In between, it's a continuum of preference.

EBP can be determined for any driver in a matter of seconds using measurement devices such as Woofer Tester from Parts Express.

It takes a bit longer to do it the old-fashioned way with a voltmeter and a resistor, but that works, too.... :thmbsp:Oh yes I know that, but with the speakers that I've tried it with, it works anyway. The EBP is just a guide. I have Leap and LMS to test them with.

Zilch
10-01-2007, 06:12 PM
Oh yes I know that, but with the speakers that I've tried it with, it works anyway. The EBP is just a guide. I have Leap and LMS to test them with.You know the drill, then. Any driver will work either way, just not as well, typically, even if the alignments are correct.

It's not likely anybody's gonna lose an eye or anything by experimenting, tho.... :p:

k-man
10-01-2007, 07:40 PM
Can the impedance of the speakers change if the enclosure is changed? I ask because I'm using a tube amp which are fairly sensitive to speaker impedance.

Zilch
10-01-2007, 07:45 PM
The shape of the curve will change, and the location of the resonance peak(s) with respect to frequency, but not the fundamental impedance....

bshorey
10-01-2007, 09:35 PM
Actually, vented speaker enclosures have to almost univerally be LARGER than a sealed enclosure with the same driver!

Arghhh! You're right, of course. For some reason I was confusing that with the port length and diameter being used to make the bass reflex box smaller.

bs