Tuning a speaker

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izzy wizzy
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Tuning a speaker

Post by izzy wizzy » Thu May 10, 2018 12:30 pm

I was hoping to be pointed at information that will help me determine how to tune and damp my Tannoy corner york cabinets. I'll be honest, I haven't looked as there is much info out there but I don't know how valid any of it is. The Tannoy forum hasn't in the past been much help.

I was going to line the walls with thick wool felt carpet underlay. Any favourite types out there?

I have two rubbish bags of baf wadding taken from someone else's York who went for long haired wool so some such (which I cannot afford).

I built these cabinets as a trial in 2004 to see how it all went after living with electrostatics for 20 years but feel now I should do something to get them more right.

I don't mean for anyone to reinvent the wheel by spending ages on this but rather point me in the right direction. Much appreciated.

cheers,

Stephen

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Re: Tuning a speaker

Post by Scottmoose » Thu May 10, 2018 1:07 pm

It depends exactly what you're trying to achieve.

Some points, FWIW

-There are two distinct types of damping materials. Those designed for acoustic damping (absorbing internal reflections &c.), and those intended to damp panels. These are not interchangable. The latter are high mass; bitumen or alternatives, but are functionally reflective, or relatively so.

-There is nothing wrong with BAF wadding, providing it's of the hollow-fibre variety, so don't feel like you have something inferior. There is nothing magical about any acoustical damping material, they all work in intrinsically the same way and differ primarily in efficiency; there are subtle differences between most types in their behaviour at different frequencies, but with few exceptions the key word there is 'subtle'. Fibreglass is typically the most effective, primarily due to the extremely fine nature of the fibres. Long hair wool works well, but is not some kind of magic bullet where it is infinitely superior to other types. It isn't.

-Note that the speed of sound is not significantly reduced in a fibrous tangle. A bit, no more.

-SAE rated felt is the most consistent of the types of felt out there for obvious reasons. That doesn't necessarily mean it's 'the best' (no such thing). F10 & F13 are quite popular for these duties.

-From the proportions of the Corner York, I'd be inclined to lag the top and one sidewall with 12mm - 20mm material, and probably put about 6in of BAF wadding on the bottom of the enclosure to absorb the longitudinal pressure wave. Caveat there. Many people state they want accuracy in advance, then they hear it. At which point they decide a bit of euphonic colouration is their preference. So you may not want to add any material other than an inch or so on the bottom of the cabinet.

-An alternative, if slightly awkward approach is to hang a curtain of damping material at an angle from the top of the box to the bottom. Surprisingly effective, and sometimes done with pipe horns. Personally I wouldn't bother since it's usually easier just to lag one or several walls.

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ed
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Re: Tuning a speaker

Post by ed » Thu May 10, 2018 2:38 pm

I was going to line the walls with thick wool felt carpet underlay. Any favourite types out there?
the 1/2" or 3/8" I have found both to be perfectly adequate. The stuff I've used is multi coloured fleck style.
I have two rubbish bags of baf wadding taken from someone else's York who went for long haired wool so some such (which I cannot afford).
I've used both and my over-riding feeling is that LHW sounds better, but it's only a feeling. I gave away a full 5kg sack when I closed the workshop, and I think I gave it to Steve Shiels...he may have some left if it was he....5kg should be enough for about 10 pairs of tannoys....

if not ask for raw 'Jacobs tops' from any of the commercial wool sellers if you want to decide for yourself. It certainly wasn't expensive 10 years ago.
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Re: Tuning a speaker

Post by steve s » Thu May 10, 2018 3:03 pm

Still got it Ed I have used a bit though..
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Re: Tuning a speaker

Post by izzy wizzy » Thu May 10, 2018 7:32 pm

Thanks for the replies. It seems that there isn't going to be much damping material in there which surprises me. However that does seem to follow pictures I've seen of some Corner Yorks and they don't have much in them. I think all I have in there at the moment is a curtain of ceiling insulation.

I was kinda expecting to hear about sweep tones and resonance and stuff like that but the suggestions are along the lines of minimal damping of the internals. That all sounds good to me as I have an aversion to too much damping as IME it sucks the life out of the music.

So that then gets me thinking along the lines of the cabinet itself. I made it out of MDF coz as I said, it was meant to be a trial. BB ply is what good cabs seem to be made of which I think was the plan after the trial. Is it that much better?

And so would an MDF box need more damping of tha panels than an BB ply one?

cheers,

Stephen

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Re: Tuning a speaker

Post by Scottmoose » Thu May 10, 2018 11:42 pm

Not exactly. From a technical POV (note caveat), MDF is rotten for bass enclosures due to the miserable MOE. Fine for some midrange & all HF boxes though.

More specifically, it's a physical impossibility to eliminate panel resonances, all you can do is try to control them. What you really want to avoid is placing the panel resonant mode[s] in the main box operating band, where the maximum amount of energy is available to excite them. So you have a choice; push them down, via copious amounts of mass, or up, by increasing the stiffness. Some people get the wrong idea about the latter because the belt the box with their knuckles & it rings like a bell. Which is exactly what it should do. The analogy doesn't hold; giving a box a belt is nothing like the actual operating conditions. Moving panel resonance frequency up is very effective for bass enclosures; if you do it well, there is little energy left to excite panel modes, and those that are are at such a high frequency they are very easy to kill with a small amount of damping. The less damping you need to accomplish a given task, the more efficient the engineering is. By contrast, the high mass approach is OK for some midrange & HF enclosures, but it's a bit of a hiding to nothing with bass boxes. As panel Fs drops, the broader the resonant bandwidth becomes. For a speaker with genuine bass, it's almost impossible to push it sufficiently low not to be excited. It may not be as obvious, but the low-level slow energy release is there, & smears things. Basically, you need concrete or similar, and a lot of it. If your speaker goes down to 40Hz or lower, you're in for a merry time, from a technical POV.

Technically. In practice, the truth is that MDF boxes don't sound half as bad as all that. Yes, a quality ply or similar is preferable. But MDF is a lot better than nothing at all, and it isn't catastrophic. It just isn't as good as some alternatives. We're talking percentage points here, not night & day. For bass enclosures it doesn't need more panel damping (remember, this is different to acoustic damping) per se; what it really benefits from is more bracing -more than something like BB / apple / marine ply which has a higher MOE.

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Re: Tuning a speaker

Post by simon » Fri May 11, 2018 12:03 am

MOE?

Moment of erm???

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Re: Tuning a speaker

Post by Scottmoose » Fri May 11, 2018 2:41 am

Sorry. MOE = Young's Modulus. The measure of stiffness (or elasticity if you prefer). Matron! ;)

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Re: Tuning a speaker

Post by simon » Fri May 11, 2018 10:55 am

Ah! Modulus of elasticity! Or E as we know it in the engineering world. Thanks Scott, that was bugging me.

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Re: Tuning a speaker

Post by izzy wizzy » Sat May 12, 2018 4:56 pm

Thanks Scott. That makes a lot is sense to me and I like the idea of bracing for stiffness than the major mass damping route.

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Re: Tuning a speaker

Post by Scottmoose » Sun May 13, 2018 4:41 pm

Something you may find useful when damping the box. This is the old click test, popular from the '40s - '60s. Cheap, easy, effective. You don't have to add the damping over the vents BTW, you can add more to the walls, in the bottom or whatever.
Attachments
Click Test.gif

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Re: Tuning a speaker

Post by Cressy Snr » Sun May 13, 2018 4:48 pm

Scottmoose wrote:
Sun May 13, 2018 4:41 pm
you can add more to the walls, in the bottom or whatever.
OOH Matron!

cue DTB Kenneth Williams. :D

Sorry Scott, couldn't resist :wink:
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Re: Tuning a speaker

Post by Scottmoose » Sun May 13, 2018 4:53 pm

:lol:

izzy wizzy
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Re: Tuning a speaker

Post by izzy wizzy » Sun May 13, 2018 4:59 pm

Thanks Scott. I do know the damping factor of my amp which is stated as 20 so that's 0.4R not far off what they claim is a good starting point.

Now I just got to get my amps going again and I can put all this into action. Will report back when I do :)

cheers,

Stephen

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Re: Tuning a speaker

Post by izzy wizzy » Tue May 22, 2018 7:47 pm

Below is a pic of the internal of my speaker. Some bracing is probably a good idea. Any suggestios as to what would be a good way of doing this gratefully received.

cheers,

Stephen
tanbuild6.jpg

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