Not happy with my DIY Tempest

[kelticwizard]

You [Sreten] seem very knowledgable, do you think its an easy thing to adjust something in the circuit, on a plate amp, that would shift the x-over down a tad? (e.g. I use 50hz, but 45hz might be more apt, as my speakers are still ok to the high forties, and things pile up at 55-60hz, where there is a room mode)

This do you any good?
http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

 

[SimontY]

Smaller the space more gain true - but this is at
frequencies where boundaries have no effect.

Disconnect your main speakers and you should see what I mean.
Even organ pipes will have "bass" but no tone. Most bass sounds
will be unrecognisable.

not easy to do unless the maker will give circuit details.
Simply double all capacitor values in the relevant circuit
section to half the frequency range of the subwoofer.

Most subs have a 2nd order rolloff, Butterworth or Linkwitz/Riley.
24/dB reflex main speaker rolloff makes the frequency setting of
a sub more obvious, but ultimately a 2nd order main speaker
roll-off should integrate with the subwoofer better, especially
for the L/R sub and reflex speaker -> sealed case, out of phase.

Thanks for correcting me on the boundaries.

I have had my sub play by itslef many times, and there simply are notes under 50hz, but I see what you're getting at now - the tone of the note is not there without the harmonics and other sound which is always really over 50hz.

Its a shame it would be hard to fiddle the sub x-over Could I not change the value of the pot which affects x-over, make it a bit smaller or bigger?? (I'd probably break the whole amp mind you)

What you say about slopes makes sense, thanks for pointing it out, but I still reckon in practice a ported speaker will be easier to fit in.

This do you any good?
http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

Thanks for thinking of it, but I use my hi-level input for music, as I have no non-looped pre-out sockets on my hi-fi amp Maybe a giant inductor in series with the plate amp input would work!

 

[JohnSz]

This webpage might be of interest to you: Viper's webpage

The link to JohnKs page does not work. He use to have some very good info posted, as well. It might be hosted, somewhere else, but I don't have a link.

JohnSz

 

[kingdaddy]

Equalizing

The only way you'll ever know what’s going on is to take some SPL measurements, at least every 1/12 octave from 15-100Hz. I bet you'll find a major peak, and at least one null somewhere in that 50-80Hz boomy range. It's time consuming but simple and all you need is a cheep Radio Shack SPL Meter and burn your own Test Tone CD, then use Excel to plot the graph. IMO all subs need at least some equalization, no or configuration is perfect. My dual Maelstrom subs were very boomy at 45Hz and 84Hz I found a 12db peak and there was a serious null at 56Hz on my right sub, but the Left sub had a null at 40 and a peak at 47Hz. After spending $115 on a BFD and about 3 days of measuring and adjusting I have everything within +/-3db from 15Hz to 80Hz, and it sounds so much better, I can’t even think of ever having a un-equalized sub again.

 

[sreten]

Its a shame it would be hard to fiddle the sub x-over Could I not change the value of the pot which affects x-over, make it a bit smaller or bigger?? (I'd probably break the whole amp mind you)

Thanks for thinking of it, but I use my hi-level input for music, as I have no non-looped pre-out sockets on my hi-fi amp Maybe a giant inductor in series with the plate amp input would work!

a) no. you can't just change the pot. You'd need to double the
value of all resistors in that subcircuit to maintain the alignment.
(Its the same effectively as doubling the value of capacitors in
the subcircuit).

b) a line level low pass feed to your subwoofer is easy to
implement with a simple RC filter, you don't need an inductor.
You just need to add a C at the point inside the sub the high
level is reduced to line level for feed into the subamplifier.
This should be easy to trace.

sreten.

 

[SimontY]

Ok, thanks. That's some scary stuff though. That plate amp stopped working on me for a while before, when I put extra psu caps in, then it just worked again, the crazy thing. It's going to be above my head, and this is slightly off-topic, but if I take a photo of the board(s) will you have a glance at it and make a guess of what's what?

edit: as an extra consideration - this extra 6db/oct. will likely make it a closer match for my ported speakers, right? (plate amp uses Linkwitz-Riley, 12 dB/oct) -with maybe the 6db starting at 40hz...??? I could always experiment, once I knew where to throw the cap in.

 

[grampi]

What would removing the polyfill do to the sound? I've been told polyfill makes the driver think it's in a larger enclosure than it actually is. If I were to remove the polyfill, wouldn't this make the bass sound punchier?

 

[CZ Eddie]

Sorry, didn't read the whole thread.


Just wanted to say that I too built the mid-q sealed box. I didn't use any of the internal bracing and my box isn't perfectly sealed, thanks to a poor choice in speaker wire terminals.

I'm powering it with a used Samson S1000 amp, running 250 watts to each voicecoil.

It is NOT boomy in the slightest, and seeing as how I have a pair of Soundstream SPL 12's in a bandpass box in my car, I KNOW what boomy sounds like.

My only dissapointment is that it isn't as dynamic as I'd hoped. I plan to build a ported box for it soon.

 

[kelticwizard]

Grampi:

You can build an aperiodic vent which essentially lowers the Qtc of the box. I can give you links on the board on how to do it. Parts Express sells the vents, but they can be homemade. They essentially let a little of the air out of the box, but the aperiodic vent does not act like a vent in a reflex.

However, I suspect that there are things you can do to reduce boominess before you start cutting into the box. So I do not recommend it for right now, only as a last resort.

If Adire gave you this as a recommended box, I don't think that boominess is the box's fault.

 

[tg3]

Re: PEQ is the answer.

Sounds like room modes to me...

Here's another vote for room modes.

If your room is reasonably rectangular, you may find the Room Response Caculator from the FRC to be helpful.

 

[grampi]

What about removing the polyfill?

 

[kingdaddy]

Removing Stuffing.

If the cabinet was over-stuffed then there could be a significant difference, but if it is properly stuffed then I doubt there would be much benefit in removing the stuffing, but give it a try.

 

[grampi]

The cabinet has 40 oz of polyfill. Is that overstuffed?

 

[kingdaddy]

That sounds about right, but I always go by ear, and this works best for dual or stereo pair so you can compare the sound. I always lightly stuff one enclosure then purposely over-stuff the other, then pan from one to the other with test tones and listen to the difference. This way I have a reference to what to listen for when it is overstuffed. Then I just keep adding stuffing to the lightly stuffed cabinet until I just start to hear the signature sound of the overstuffed reference, then remove a few ounces. Then copy (weight) that amount to the other enclosure. I still think you should do some SPL measurements if you’re really interested in finding out the problem, but by all means try the easy stuff first, I would just remove all the stuffing and see what it sounds like.