Peak cone excursion

[Vikash]

Been doing some plots using the Seas Excel W22EX-001 using Unibox.

I get the following cone excursion graph. How worried should I be? The simulation is at 60w - half the continuous rating of the driver.

I would obviously like it to be within its linear travel all the time which according to Unibox is around 20w max. Am i missing something obvious here?

[Vikash]

On closer inspection, I see 20w input results in 100db spl. which is 8db down on 120w input. I guess thats ok. Someone please confirm these numbers are sane...

Not sure how loud 100db spl is though...

[SY]

100 dB is pretty loud. If minimizing LF distortion is the goal (a laudable one), you'd do well to filter out the stuff below which the cone unloads.

Depending on the alignment, you can often use that filter to get you a flatter response near the LF rolloff.

[kelticwizard]

I haven't simulated this speaker and box myself. But just looking at your chart, I would say that this is what you get when you put in a fairly low excursion 8 inch in a big box and expect it to go down to 30 Hz. Your F3 is listed as 29 Hz.

People tend to forget how low 30 Hz really is. It takes a lot of air to move high SPL's at that frequency, and you have an 8 inch doing it. Fortunately, you ported that 8 inch which increases it's air moving capability at Fb by 4 times.

If 100 dB SPL at 30 Hz sounds inadequate, remember this:

A) Bass notes are generally engineered to be played on equal loudness on two channels-very few times do you hear bass on the left channel and no bass on the right. So two channels will be playing that bass, which will equal 106 dB.

B) You can probably count on 2 dB or so in the room gain, so you are now approaching 108 dB.

C) If you place one or more enclosures near a corner, you get even more. Up to 6 dB more. Let's allow 2 dB if the speakers aren't that close to the corner. That is 110 dB.

D) I don't know what the non-linear travel is, but if you have an extra 50% of bass travel left over after the voice coil leaves the gap, (most speakers have more), then you are now getting near 113 dB.

So maybe you are not in such bad shape around 30 or 40 Hz after all.

[Vikash]

Minimising distortion is above high spl certainly.

Unloading is when the cone is outside its linear excursion right? I calculate that the driver is within linear operating excursion at 20w input down to 26.5Hz(ish), after which it goes crazy (termed unloading i assume), although it is still within its maximum excursion down to 21Hz (10.5mm).

The alignment is a standard QB3 ported design. Is it common to filter out the bottom end to keep within linear excursion (the bit in green below)?

[phase_accurate]

QB5 and B6 would be highpass-filtered reflex alignments. Does unibox support these as well?
If yes, give them a try - since it costs nothing but some of your time.

Regards

Charles

[kelticwizard]

Originally posted by Vikash
Is it common to filter out the bottom end to keep within linear excursion (the bit in green below)?

It is not common but it is extrememly recommended. Most people just take their chances with the ported box.

Most every book or article on the subject recommends you do it if you can, though, for reasons you have just seen for yourself.

You can try a Passive Line Filter if you don't want to build an active filter. I have never used a Passive Line Filter, but the article looks good.

Here is the article from Planet 10's, (our moderator's) site. It always struck me as being good for something like this, but again, I never used one.
http://www.t-linespeakers.org/tech/f...ssiveHLxo.html

[roddyama]

Originally posted by kelticwizard


It is not common but it is extrememly recommended. Most people just take their chances with the ported box.

Most every book or article on the subject recommends you do it if you can, though, for reasons you have just seen for yourself.

Back in the days of the LP, record warp could really be a problem in the subsonic region. You would have found sub-sonic filters on most receivers, pre-amps, and certianly electronic xovers. Only the very "Hi-End" esoteric "straight wire with gain" stuff would forgo the sub-sonic filter. When you turned the filter off, you could watch the woofer cone try to jump out of the box while you were playing an LP.

CD music was not as much of a problem. There's not much sub-sonic music (what would be the point). Now DVD's, that a whole new ballgame. If the intended use is HT, you should get a bigger woofer or put a sub-sonic filter on the one you have, or go closed box alignment.

[SY]

By "unloading," I meant the frequencies below the excursion minimum.