Minimum recommended qts for OB use?

[vaughn]

I have a pair of Stephens Trusonic 120FR 12" speakers that I would like to try on an open
baffle. They have a qts of .475 and I am wondering if that is too low for open baffle use?

Looking at the 12" PHY speakers on Madisounds website I see that their qts is .62, not much
higher and yet it states that they are made specifically for open baffle use.

Thoughts?

I should also add that the Fs for the Stephens is listed as 30 hz.

 

[Nelson Pass]

It's a little low. The best overall results I've had with the Eminence
woofers (as a common example) is the Eminence beta with a Qts of
0.58. The Eminence Alpha is preferred by Martin King at 1.26.

It sounds good, but I have a slight preference for the Beta, which has
less of a bump above 45 Hz and more response below.

By contrast, the Gamma has poorer bass response than either of the
others, with a Qts at 0.30

Of course you can EQ this easily enough.

 

[vaughn]

Thank you sir...

I actually did a little experimenting today on some open baffles I had made a la JE Labs. These
are 32" high, 36" wide with wings that taper from 10" up to 5" at the top. I found a pair of
Electro-Voice 12 LT coaxial speakers the other day that appear to have a qts of about 1.6 according to info I could find on the web. The EV's sound great on the open baffles but the
Stephens are not as good at .475. I have no measuring equipment but my ears but the EV's have much better bass than the Trusonics on the baffle.

 

[croat47]

Mr. Pass,

What if one were to use two 15": a Beta and Alpha. On an 18" baffle, the Beta on the lower position and the Alpha on the Higher Position (FR, MT above those, of course). Could they compliment each other and smooth things out for a longer range?

Playing about with XBaffle to compare the two and thought I would ask the question.

 

[dobias]

minimum recommended qts for OB use?

Nelson Pass,
You said, "Of course you can EQ this easily enough."
Would you please direct me to a way to EQ my Wharfedale 12CS-AL speakers?

FS: 26.4 Hz
VAS 11.4 cu.ft.
Qts 0.26
Re 5.3 ohm
Le 1.48 mH
Eff. 95 dB/w/m

Each OB has one full range, augmented with two Super 3 tweeters (5 kHz) & a 12RS-AL mid bass (600 Hz.) I find I still need to have a pair of subs to provide decent bass.
Frank Dobias

 

[Cal Weldon]

What if one were to use two 15": a Beta and Alpha.

Try not to use different drivers to cover the same range. It's like using different tires on your car. One for traction , one for a smooth ride. Doesn't really work.

 

[Cal Weldon]

Re: minimum recommended qts for OB use?

You said, "Of course you can EQ this easily enough."

You can but it puts a heavy demand on your amp. If you can, get a woofer in the range of Q = 1

 

[croat47]

Cal,

Thanks. You could cross between them if you were active, yes? Passive would cost a bit in coils as it would be in the "subwoofer" ranges for crossover. Too complex in the end, I suppose.

 

[Telstar]

In my opinion Qt is not everything. Even 0.4 can work. Xmax is more important, otherwise the driver will distort soon.

Of course a bass augmentation is needed with "thinner" FRs.

 

[ttan98]

In my opinion Qt is not everything. Even 0.4 can work. Xmax is more important, otherwise the driver will distort soon.

Of course a bass augmentation is needed with "thinner" FRs.

If you ask Martin King he will disagree with you, he said Xmax is not that important, look at Alpha 15" its Xmax is low about 3.8mm.

If I am buying woofer I will be looking for Qts no less than 0.65 and low FS equal or less than 40hz. There are a few models from Goldwood drivers range that satisfy this criteria and they are cheap. Buy 2 per side instead of one.

 

[Telstar]

If you ask Martin King he will disagree with you

I know I've read almost anything he wrote.

I was talking about the FR specs. About woofers... mmmh each one is a case apart. T-S parameters are way too approximate.
Strangely enough, I care more on the Qts for the FR than for the woofer. But I agree on the low Fs to reduce the amount of EQ needed.

Martin would have immediately ditched the woofers that I'm using, but they sound wonderful and they are still almost unbroken-in.
Math is not everything.

 

[norman bates]

here is a link to a graph of the silver iris (qts near 1.1) on maybe 2' wide baffle.

It has a good bass hump near 125hz then vanishing, much better than I thought it would be.

http://www.audioasylum.com/forums/hug/messages/14/142635.html

I believe on an open baffle, the speaker rolls off at Fs/qts, regardless of the baffle size.


Norman

 

[Telstar]

I believe on an open baffle, the speaker rolls off at Fs/qts, regardless of the baffle size.

Norman

Yes, and IIRC its a 6db rolloff.

 

[Pano]

Though in practice it often seems to be ~9dB/octave.

The 125Hz for the Iris looks right, at least from the couple of pairs I've heard.

 

[chris661]

I considered buying some 5" Visaton drivers, which has a qts of 1.8 (ish), so this is interesting...

My advice - Qts may not be as important as Xmax, and the moving mass of the driver. If you have low Xmax, you will begin to distort on bass at fairly low volumes. If you have a heavy cone and motor assembly, the driver will more "flop" around, as heavier cones require more damping. OB provides very low (compared to sealed, vented) damping, which is where the Qts comes in, so, a nice balance of the 2 would be more important than one by itself.

Chris

 

[EC8010]

Don't forget that you can always change the Qts of a driver by adding a series resistor. This isn't as wasteful as you might think.

Open baffles are very wasteful so you need a driver that can move a large volume of air. That either means a large linear excursion or a large area (preferably both). Efficiency is useful, too, because you're going to need a lot of equalisation, so all of this points towards professional drivers.

I'm going to use (haven't quite finished the woodworking) a Precision Devices PD184 18" driver with Qts = 0.253 increased to 0.5 by adding a small series resistor...

 

[dpaws]

Yes, and IIRC its a 6db rolloff.

Late night thinking is always a hazard but... as I understand it we also get a roll-off dependant on baffle width (2pi to 4pi radiation) If these two coincide I assume the slopes combine for a steeper roll off? Or would it only be for the first 6db and then the slope would revert to first order again?

Could someone refresh my memory - at what frequency is room gain considered to act from? Also, at what slope is this apparent gain?

Time for a nightcap.... but now you've got me thinking... awwww

 

[dpaws]

Don't forget that you can always change the Qts of a driver by adding a series resistor.

Conversely... does this mean I can lower the Qts by adding resistance in parallel? What would the side effects be? I'm looking for a higher roll off to avoid bass doppler effects from a FR driver....

 

[Telstar]

Late night thinking is always a hazard but... as I understand it we also get a roll-off dependant on baffle width (2pi to 4pi radiation) If these two coincide I assume the slopes combine for a steeper roll off?

Yes, that's additional rolloff, that sums to the baffle step rolloff, which is 6db per octave.
It becomes quite obvious that if we are not using subwoofers we'll need a woofer with Fs lower than our desired minimum range.

Could someone refresh my memory - at what frequency is room gain considered to act from? Also, at what slope is this apparent gain?

I dont remember clearly, but I think that is variable on the room. I dont like the fixed formulas, they do not apply in MY room for instance

 

[dpaws]

Could someone refresh my memory - at what frequency is room gain considered to act from? Also, at what slope is this apparent gain?

More specifically, what is the nett effect when hearing sensitiviity is factored in? A gain or a loss overall and at what rate / slope?

I had in mind a pair of Eton woofers. On an OB, Fs/Qts = 70Hz. If I recall (I do listen guru) room gain may offer +3db from 80Hz - 40Hz & +6db beyond... but hearing sensitivity drops below 200Hz... So overall the predicted response as heard will be ???

Help!!!