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stuffing speakers

post #1 of 15
Thread Starter 
I have a pair of JBL 800 bookshelf speakers that are getting fixed right now. I should get them back soon and I have a question. My problem is these are kind of bass-head speakers. I have always had to turn the treble to +5 and bass to -5 on my Kenwood integrated amp and this is how I blew one of the tweeters. The woofers are 8" and the tweeters are 1/2 an inch. These are bass reflex type speakers, and when I look in the bass port I can see lots of stuffing in there, I was wondering if stuffing the speakers with even more stuffing will decrease the bass and tighten it up some? How much can I put in?

These speakers sounded not too bad when I had the bass turned down. The bass was pretty deep and tight. I just don't want to have to turn the treble up so much to get them to sound right (this is what blew the tweeter).

Hope someone can help me. Thanks
post #2 of 15
try this stuff and never again worry about them sounding the best they can:

http://www.tnt-audio.com/accessories/deflex_e.html

be sure to completely remove curent stuffing and apply to all inside panels.
post #3 of 15
Thread Starter 
Can you tell me of a place in Canada that I might be able to buy it? I can't buy over the internet (no credit card or anything).
post #4 of 15
yep:

THE PARTS CONNECTION
3535 Laird Road, Unit #16, Mississauga, Ontario CANADA L5L 5Y7
Telephone and Technical Info Line (905) 828-4575 Facsimile (905) 828-4585
E-mail: TPC@partsconnection.on.ca
Toll Free Order Line (order placement only) 1-800-769-0747 (Canada & U.S. only)
post #5 of 15
Quote:
when I look in the bass port I can see lots of stuffing in there, I was wondering if stuffing the speakers with even more stuffing will decrease the bass and tighten it up some?
The foam inside is there to tune the bass of the speakers, I wouln't put anything else inside. but if you want to get rid of the exces bass, try the following.

1. Make sure the speakers are away from the wall, rear bass port about 1m away, front port can be closer. adjust to suit.

2. Try putting a sock in the hole but not inside. I am serious! Some speakers comes with Bass Plugs and it's use to tune the bass to the person's liking. You won't find any for sale as they only come with the speakers when you buy them.

3. Try a bunch of straws, same as above.

4. Put the speakers on a stand, this help tighten the bass significantly.

Now, the reason the tweeter blows is not that you turn the treble up, it's because the amp is not powerful enough to drive the speakers. A few things could be the case, the JBL have a low sensitivty, hense it needs a lot of power. And you probably turned the volumn too high, which cause the amp struggle to dive the speakers and that's how you blow tweeters.

Try not turn the volumn too high when you get the speakers back, and I would advice not to remove the foam inside as they are there for a reason, they help tune the delay of the bass, the frequencies. you might end up with no bass in the end.
post #6 of 15
quikest way to take out a tweeter is amplifier clipping,too much power usually won't do it.Is your amp a good match to the speakers in question ?
If within the power range,what about the damping factor of the amp ?
The mechanical damping techniques mentioned above will do as advertised but will also make the speakers less sensitive or could even slow down the bass.With speakers as in some headphones it all comes down to matching the driver to the driven
post #7 of 15
Try using Radio Shack magnet wire (30 gauge) instead of your usual speaker cable. Just sand a little insulation off the end of the wire.
post #8 of 15
Stuffing is usually a trial-and-error affair. My experience is that over-stuffing tends to decrease the speaker's sensitivity, and it sounds like your amp is already underpowered.

Try using Radio Shack magnet wire (30 gauge) instead of your usual speaker cable. Just sand a little insulation off the end of the wire.
post #9 of 15

The "stuffing" is not there for bass response...

it is to absorb internal reflections in the midrange which would come back out through the woofer and the port. It also helps damp cabinet resonances. Ported speakers (i.e. bass reflex alignments) should not be stuffed, only lined. Stuffing only decreases efficiency. Sealed cabinet alignments can be stuffed, with the effect being that they behave like the cabinet is slightly larger (and improved absorbtion of the out of phase signal).

I don't know much about this specific design, but I have noticed that various manufacturers (JBL included) tune some of their speakers with a bass hump around 50 to 80 hz. This gives the impression of big bass response in a small cabinet. It also sounds boomy after a while. The room placement tricks mentioned above will help, probably a lot. In addition you can fiddle with the tuning of the cabinet. This simply requires lengthening of the port. Start out with an external extension to see if you like the effect. You will trade the efficiency afforded by the bump for deeper bass extension. Use the same port diameter, or slightly larger. The port must remain unblocked (at either end) by objects or damping material. Both the inside and outside end should be at least 1 port diameter away from any object or wall.

I agree that the tweeter probably went due to clipping. Make absolutely certain that the "loudness" button is turned off on your receiver. These things fry a lot of tweeters by dumping all of the power at low frequencies (even inaudible ones) and clipping. The resulting HF mess goes straight through the x-over and makes the tweeter coils glow, briefly. Also turn on the subsonic filter if you have one. This is power conservation with no adverse effects (unless you have a subwoofer hooked up). It also limits the power that goes to the woofers below the tuning frequency, which causes huge cone excursions with no useable output.

What type of tweeter do these speakers use? Does the owners manual mention any sort of protective device on them (usually a back panel fuse, but sometimes hidden)? If not, you may want to add one.

Good luck.
post #10 of 15
Thread Starter 
Thanks for the help everyone. I'm still waiting to get my speakers back, and yes I'm sure they died because of clipping, and my amp probably is a bit underpowered it's over 20 years old. Although I haven't had it turned up over 7.5 out of 10, I've heard the JBL's have weak tweeters (don't know what kind) so this was probably part of the problem.

I will try stuffing a sock into the bass ports and putting the speakers on stands and moving them away from the wall, then I should get a more balanced sound without cranking the treble and volume up. Thanks again.
post #11 of 15
7.5 out of 10 seems high. I second the stuffing the port with a sock, it works great for me (My speakers are very boxy sounding, the socks help a lot). I don't think this is harmful to the speakers, but if I take the sock out when they are playing, the speaker moves significantly, as if it were playing a bass note of some sort, dosen't make a sound though.

I have never turned my amp over 40%, for fear of my ears, and my speakers, and this is only a 65wpc amp.

The socks might pop out from time to time, but I don't think you can beat sticking socks in the ports as a tweak .
post #12 of 15
I hope that they are clean socks. Do you use gym socks for grunge and dress socks for classical?

7.5 out of 10 seems very high on a typical integrated amp. I am used to seeing the onset of clipping at around 5 to 6 with a healthy input source (like a typical CD player).

Some conjecture on the sock: it acts as a resistor in the port, which keeps the cabinet from acting as a resonator. Basically throwing away the extra bass energy associated with a BR design. Kills the nasty bump associated with a peaky system or room resonance, but sacrifices potential bass extension. The speaker will act more like a lossy sealed cabinet.

Xevion, the cone excursions that you describe are probably associated with bass signals below the tuning frequency of your cabinets. Turn on the subsonic filter on your amp or receiver to reduce some of it. It is wasted energy and distortion. In a BR design the cone motion will actually drop to almost zero at the resonance frequency, with significant output from the port. Below that the output drops at 24db/octave and cone motion goes way up. Lengthening the port lowers the cabinet resonance frequency. The response bump will flatten out, the roll off point will go to a lower frequency, and the onset of cone flapping will also move lower. By doing this you will trade the response bump (or boom) for honest bass extension, rather than just throwing it in the sock hamper.

I am not advocating any right or wrong approach here. Speaker-room interaction is a big player in all of this. Tuning the cabinets to trade depth for amplitude is just the way I would approach the problem. It also gives you one more factor to experiment with!
post #13 of 15
Quote:
Turn on the subsonic filter on your amp or receiver to reduce some of it.
Uhh, the subsonic filter? I have an entry level Yamaha reciever, I haven't quite figured out how the remote works (It is truly horrible, the buttons seem to do different things each time I push them), there is no lowpass filter of any sort that I can find in the settings, I have the speakers set to small, for what its worth. The other reciever in the house has a lowpass filter (It is a 70s Akai reciever) and these speakers sound a good bit cleaner with that enabled, but I oculdn't find something similar on my reciever.

Quote:
In a BR design the cone motion will actually drop to almost zero at the resonance frequency, with significant output from the port.
BR = ported? I know in a ported design a lot of the output can be from the port. The fact that cone motion goes way up after this point, I don't know if that is a major issue, I have the speakers set to small (I think it cuts off at 80Hz, although from the way they sound I bet the port is tuned a bit higher, they don't extend much deeper then that). I am not overly concerned with deep bass reproduction from my bookshelves, as they blend quite nicely with my Polk sub, and are going to be the rears when I finish my setup (I will replace em with something pretty decent along the lines of Paradigm Mini monitors, or some Axioms in the same price range).

So - lengthening the port will reduce boominess and increase deep bass response. This makes sense. But how am I supposed to do it?

I would prefer just having the speakers basically suspended in the air, it would tighten up the sound a lot . Does anyone make any speakers that don't have an entire box around them? I know Legacy Audio does this with some of their speakers to an extent.

I am far from a massively critiquing audiophile, and the socks seem to work very nicely to my ears, but if I could easily extend the length of the ports on the speakers, I might want to try it.
post #14 of 15
Xevion, you have a bit different situation. I don't know how the Yamaha is set up, but in your case it should not be an issue. I suspect that the subwoofer has it's own subsonic filter built into the crossover (I am assuming a powered sub with a built in amp/x-over combination). Do you have your satelites connected from the x-over output on the subwoofer? The high pass in the sub x-over should take care of the high cone motions in the sats. I would not recommend retuning the satelite cabinets in your case. Let the sub do the grunt work. You do need to have a crossover in place (low pass for the sub and high pass for the sats) that is at a frequency at or above the tuning frequency of the BR (bass reflex) satelites. If that fails, go for the sock. Cone excursion = distortion = bad^2.

I will endorse the Paradigm satelites. Great performance for the dollar. I really like their powered reference monitors.

I hope that I don't come across as a massively critiquing audiophile. I try to be humble in my opinions. I am an audio enthusiast verging on the extreme (extreme ends up describing most of my hobbies). As a chronic DIY type, I have learned a lot from my mistakes over the years (e.g. a phillips hard dome tweeter doesn't make any sound at all if you accidentally drop a 300 watt transient on it). I try to share the knowledge.


Extreme Audio... I like the sound of that!
post #15 of 15
Quote:
Xevion, you have a bit different situation. I don't know how the Yamaha is set up, but in your case it should not be an issue. I suspect that the subwoofer has it's own subsonic filter built into the crossover (I am assuming a powered sub with a built in amp/x-over combination). Do you have your satelites connected from the x-over output on the subwoofer? The high pass in the sub x-over should take care of the high cone motions in the sats. I would not recommend retuning the satelite cabinets in your case. Let the sub do the grunt work. You do need to have a crossover in place (low pass for the sub and high pass for the sats) that is at a frequency at or above the tuning frequency of the BR (bass reflex) satelites. If that fails, go for the sock. Cone excursion = distortion = bad^2.
I am using the unfiltered LFE input on the sub (LFE out on the reciever obviously), the cutoff on the LFE output is 160Hz IIRC, and bass localization isn't an issue. The sub integrated better with the sats when I had it placed next to my computer (Like 3 feet away) and ran the speakerwire through it with the crossover at ~110Hz, but I sacrificed a bit of sound quality to save my PC from potentially getting screwed up and stuck the sub in the back corner of the room (It isn't an optimal situation, but it works for me, and imaging isn't the most important part of the sound, also for some odd reason when I wired the sub with the speaker wire, it was somewhat anemic, connected through the LFE input it is a bit boomier, but drastically more powerful when called upon. Although I had never thought my little setup could integrate so well, I seriously couldn't tell the sub was playing, at all. Part of this was because it wasn't playing as deep as it is now, and I have no clue why) Ill just stick with the socks, and a slight reduction on the bass control on the reciever.


I have spent a bit of time demoing the Atoms and I quite like them, they can be a touch boxy at times, but the mids are just sweet, and the treble is a touch bright, just the way I like it in a loudspeaker. I haven't tried listening to the Mini monitor yet, however, and I am under the impression that it might be too bright for my tastes... How does it compare with the Atom? (I don't even know why I am asking this, I could demo the damn things tomorrow ). I figure the biggest reason why I want the minis over the Atoms is because I want something that can play with the sub off and still get me decent bass response, and I figure of the Atoms have a nice midrange, and the Mini monitors are so highly regarded, they must be even better .
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