Tube Amp Archive

I'm curious how much of an effect dust caps have on the actual frequency response of the speaker. Do they have any significant effect or is it simply a matter of dispersing highs and reducing treble beam.

For example, do the highs actually reach higher with an aluminum dust cap or does it simply sound brighter because the highs aren't spread out as much so they beam more and make it to your ears more easily?

If you had a speaker with a frequency response of 50hz-6000hz, would replacing an aluminum dust cap for a large paper or screen one, for example, reduce the response to something like say, 5500hz? Or is this more a function of the cone/voice coil/etc.

I'd talk to Jim at Scumback Speakers about this.

Russ

My take is it's more a "tizz" from the virbrating aluminum dustcap itself, rather than a beaming effect of pre-existing frequencies. Jim's take on this would be interesting I'm sure given his closeness with speakers!

A customer of mine with very good ears and many years of experience is adamant that a paper dustcap is more natural sounding because it doesn't "tizz". He has in the past replaced aluminum dust caps with paper to de-tizz the speaker.

One of my 1x12s is an Altec 417B and it displays the "tizz" quite noticeably, whereas my other 1x12 with a Celestion Blue does not.

I associate shiny metal dust caps with the Roland JC120 and GK bass amps. Both damn spanky sounding amps. Neither designed for distortion (what about the distortion circuit on the JC120? forgettabouttit!).

It depends a lot on *where* is the cap attached.

Famous Altec and JBL aluminum caps, 4" and 3" diameter respectively, were glued straight to the voice coil, they followed its tiniest movement, and provided an important extension to the high frequency range.

Snappy sound by definition.

Now lots of people saw that and wanted them, on way smaller voice coil speakers.

Manufacturers were eager to glue 3" to 4" diameter aluminum caps to the cone itself , instead of the coil which was smaller, say 1.5" to 2".

In that case the cap at best will follow the cone movement (remember the cone segment between VC and actual dome is somewhat flexible) so it was mostly cosmetic, worst case it would add some "metallic sound" to what was being reproduced because of its own resonances, but not frequency range extension.

So in a nutshell:
* aluminum cap straight on the VC former: higher frequency response, snappy sound.
* oversized aluminum cap glued to the cone, nowhere near the VC: adds a mid highs peak, maybe what's needed or sound shrill.

There must be a reason most everybody abandoned the oversized aluminum cap.
Not the "real" one of course, but that only in expensive speakers which actuall use it for what it's meant originally.

I thought I read somewhere, many years ago, that the aluminum dust cap came about as a means to dissipate heat from the voice coil, thereby increasing the speakers' power handling. Of couse for this to work, I imagine the dust cap needs to be the same diameter as, and directly fastened to the voice coil former.

You are right.

Real aluminum caps have a "lip" all round , just grabbing the voice coil former.

Peavey , in their Black Widow speakers, went as far as making **one piece** caps and coil formers, go figure.

1501DT-4 Black Widow
The 1501DT is a 4 ohm, 15" Black Widow/Super Structure speaker specifically voiced for musical instrument use. A "classic" sound is achieved by using a specially developed high density curvilinear paper cone, and incorporating a one-piece aluminum dust cap and voice coil former. Sustain is enhanced while retaining control of the overall tone. Obvious applications include lead guitar and steel guitar.

Best cooling possible but very difficult to manufacture.

Ted Weber mentions the heat dissipation benefit of aluminum VC covers here http://www.tedweber.com/lets-talk-speakers/
I guess that benefit would only apply for the 'applied to VC' cover, rather than the 'applied to cone' arrangement that Juan describes.

Steve Dallman describes modding the hard paper dust cover used by modern Jensens to a felt type, which he thinks greatly helps to smooth out their high end http://www.fenderforum.com/forum.html/s ... ber=790201