Daryl - Sealed alignments

[ktaillon]

Provided Link: Speaker Pics (http://www.flickr.com/photos/hexaudio/sets/)


I've been reading your Sealed Alignments on your web page! Very interesting... I'm in the middle of building a 3-way that will be using two of the RS225 8" woofers per speaker. I've tested these drivers in various sized vented and sealed boxes. I'm leaning towards the sealed because of the smaller box and the way they sound.

I changed out the values of Qe and Re which shows a change of F3 from ~50hz to ~39hz(using your calculations). The only part I see as a draw back is the SPL output. Is there anything that I'm missing? Does the box size need to change?

[Pete Schumacher ®]

> I've been reading your Sealed Alignments on
> your web page! Very interesting... I'm in
> the middle of building a 3-way that will be
> using two of the RS225 8" woofers per
> speaker. I've tested these drivers in
> various sized vented and sealed boxes. I'm
> leaning towards the sealed because of the
> smaller box and the way they sound.

> I changed out the values of Qe and Re which
> shows a change of F3 from ~50hz to
> ~39hz(using your calculations). The only
> part I see as a draw back is the SPL output.
> Is there anything that I'm missing? Does the
> box size need to change?

yes!

Varying series resistance will alter the driver Qts, raising it. Higher Qts and steady Vas will mean that the box will have to be sized up to accommodate the changes in order to reach a desired Qtc.

[ktaillon]

Provided Link: Speaker Pics (http://www.flickr.com/photos/hexaudio/sets/)


> yes!

> Varying series resistance will alter the
> driver Qts, raising it. Higher Qts and
> steady Vas will mean that the box will have
> to be sized up to accommodate the changes in
> order to reach a desired Qtc.

I noticed on his web site that the volume of the boxes for the drivers that he tested were on the small side.
I'm liking the sound of the RS225's in a sealed box but it would be nice to have a little lower F3 without a very large box.

[daryl]

http://img.villagephotos.com/p/2003-4/144711/RS225spl.gif

Provided Link: Daryl's Speaker Stuff. (http://www.villagephotos.com/pubgallery.asp?id_=144711)


Hi Ken,

Using resistance and/or capacitance in series with drivers in sealed enclosures you can gain more control over the result than the 'normal' approach.

A wide range of response shapes are possible.

Even after you have chosen a specific cabinet volume you still can tailor the response considerably just by changing values for R and C.

With the same cabinet volume you can choose a slow early rolloff or an extended sharp rolloff.

Someone a year ago (or so) was wondering about two RS225's and I happen to have the chart still that I modelled back then (below).

It shows two RS225's in a 2ft^3 100%FG fill sealed (purple) and 4.5ft^3 20hz vented (green).

Both of these will net you impressive performance inroom.

[daryl]

http://img.villagephotos.com/p/2003-4/144711/Sealed1.gif

Provided Link: Daryl's Speaker Stuff. (http://www.villagephotos.com/pubgallery.asp?id_=144711)


The most important aspect of custom sealed alignments is system resonance frequency (Ftc).

The rolloff 'knee' will be centered at Ftc with 2nd order systems and with 3rd order systems the knee will be a little below Ftc.

You choose your box volume to set Ftc which also will be related to your rolloff knee.

You then use resistance to bring Qtc up to where you want it (Qtc is how far down the response is at Ftc).

Then you can move in with capacitance (start astronomical and move smaller with your capacitance).

You peak the response up a little with more resistance then move your capacitance smaller which will knock down the peak above Ftc and peak up the response below Ftc moving the knee below Ftc.

Below all of the responses were created by adjusting R and C with the same driver and cabinet.

As you extend the response sensitivity will go down and nominal impedance will go up so it is better to use series resistance with multiple driver systems that might benefit from increased Znom.

[porper]

Let Me Get This Straight - you're putting caps and resists in series with woofers?????????

As I understand, that should just about kill all of the peak current your amp puts out, as well as wreaking havoc with the frequency response. At least that's what I heard.

And, the cap will rolloff the bottom. Why in the world would you do that?

[wingnut]

I hit your link. Nice collection of projects!

I noticed your media center and screen shots. What PJ? I've got the Optoma h31. Love it, but wish I would've waited a bit longer for HD. I've got my eye on the HD70 and the Mitsubishi HD1000U. If the price goes south enough, I might bite the bullet and sell the h31.

I've been experimenting with DIY screens. I much prefer a slightly gray screen (gray flat paint) over titanium white (1.0 gain). Super inky blacks.

Toby

[daryl]

Provided Link: Darl's Speaker Stuff. (http://www.villagephotos.com/pubgallery.asp?id_=144711)


Finally!

Someone who speaks my language.

> Let Me Get This Straight - you're putting
> caps and resists in series with
> woofers?????????

> As I understand, that should just about kill
> all of the peak current your amp puts out,
> as well as wreaking havoc with the frequency
> response. At least that's what I heard.

> And, the cap will rolloff the bottom. Why in
> the world would you do that?

It is just as obvious that if you take a sealed box and poke a hole in it that all the air will run out that the woofer pumps in there and it will completely kill the bass.

Yet all these so called speaker builders (dumbasses) keep on doing it despite my warnings of catastrophic bass failure, sighting their experiences that the opposite is true and bass response is actually extended.

Even Jim Theil and Neville Small have put out numerous vented speakers despite me having already explained to them that they don't work.

You know they don't even deserve to have parameters named after them.

I don't know whom it was or why they decided to name parameters after them anyway but I am writing the AES right now while I'm all worked up.

Let's see if we can get something done about this.

Can I put your name down on my letter?

[daryl]

Provided Link: Daryl's Speaker Stuff. (http://www.villagephotos.com/pubgallery.asp?id_=144711)


That was fun. (It was right?)

Just like a vented system a third order sealed system using a capacitor in series with the woofer causes the bass to rolloff faster than the sealed system.

Before this happens though the extra pole(s) you have added to the system resonate with the already existing reactive elements and lift up the response below Ftc causing an extension (lower) of the cutoff knee and making the ultimate rolloff steeper.

The third order system is in between the second and fourth in terms of rolloff (obviously) and in terms of where it falls in terms of Hoffmans Iron Law.

A third order systems excusion is decreasing below cuttoff which is an advantage over second or fourth order systems.

A third order system uses higher Q's than second or fourth order systems so the smallest possible enclosure will always be the third order.

Also drivers with difficult to manage high Qts's (like the old Dynaudio's and Morel's) will benefit from third order alignments.

[porper]

[daryl]

http://img.villagephotos.com/p/2003-4/144711/Sealed7.gif

Provided Link: Daryl's Speaker Stuff. (http://www.villagephotos.com/pubgallery.asp?id_=144711)


If you place a driver in a sealed cabinet and raise it's Qtc to 1 the response will have a peak above Ftc.

At Ftc the level will return to the flatband level and below that will rolloff at 12db/oct.

By placing a capacitor in series with the driver you can make it's response flat and extend it's cuttoff frequency lower.

This can be explained by considering five important ranges in the drivers response.

First the high frequency range.

In this range the capacitors impedance is insignifigant and the drivers response is unaffected.

Second the region just above Ftc where the drivers response is peaking above the flatband due to the Ftc of 1.

In this region the capacitors reactance is now signifigant and will knock the response peak down to flat.

Third system resonance (Ftc).

In this region the drivers response is level with the flatband due to the Qtc of 1 and the impedance of the driver is very high due to system resonance (impedance peak).

The high impedance of the driver again renders the reactance of the capacitor insignifigant and no signifigant change to the drivers response is effected at Ftc.

Fourth the region just below Ftc.

In this region the capacitors reactance is even greater and the woofers impedance has come down from it's peak and is again comparable to the capacitors.

Even more importantly the woofers impedance in this region is inductive which is opposite to the capacitors reactance which is capacitive (go figure) and they cancel.

Since the capacitors reactance cancels the woofers the impedance becomes lower and consequently more current flows efffecting a BOOST in response just below Ftc.

Fifth is the low frequency region.

In this region the woofers impedance settles to Re and the reactance of the capacitor in conjunction effects a simple highpass function upon the woofers response turning a 12db/oct. cuttoff into an 18db/oct. cutoff.

Study the image below which shows the transfer function of different capacitor values in series with a woofer and reconcile it with the above text.

[ktaillon]

Provided Link: Speaker Pics (http://www.flickr.com/photos/hexaudio/sets/)


> I hit your link. Nice collection of
> projects!

> I noticed your media center and screen
> shots. What PJ? I've got the Optoma h31.
> Love it, but wish I would've waited a bit
> longer for HD. I've got my eye on the HD70
> and the Mitsubishi HD1000U. If the price
> goes south enough, I might bite the bullet
> and sell the h31.

> I've been experimenting with DIY screens. I
> much prefer a slightly gray screen (gray
> flat paint) over titanium white (1.0 gain).
> Super inky blacks.

> Toby

I have the Panasonic AE-900, it's a great 720p unit but now you can get projectors like the HD70 much cheaper.

I did play around with different screens, about 13 different paint mixes, the screen that you see in the pic is a piece of Fashion Gray laminate. It looks great for not much work. I love the gray screens because it still looks good when the lights are on.

Ken

[daryl]

http://img.villagephotos.com/p/2003-4/144711/RS2253rdorder.gif

Provided Link: Daryl's Speaker Stuff. (http://www.villagephotos.com/pubgallery.asp?id_=144711)


Hi Ken,

I cooked up a design for two RS225's in 2ft^3 100% fiberglass fill like before and then added some resistance and capacitance to extend the bass while keeping the same 2ft^3.

The purple curve is the plain sealed system.

Bass extension inroom will be roughly 45hz.

It's sensitivity is <A HREF="mailto:94db@2.83">94db@2.83</A>v

Nominal impedance is 4ohm so efficiency is 91db@1w

Excusion limited power is about 125w@4ohm for a full range system giving an output capability of about 112db@1m

For the third order system I have kept the same enclosure but added 2ohm (two PE# 017-4 resistors) and 1000uf (two PE# 027-378 NPE caps).

The third order system is shown as the green curve.

I have designed the system so that the response droops somewhat at low frequency to complement roomgain and make effective use of recources (these series RC networks make sealed systems response quite flexible).

Inroom bass extension has been increased roughly half an octave to 32hz.

Sensitivity has gone down to <A HREF="mailto:90db@2.83">90db@2.83</A>v for the third order system.

Nominal impedance has gone up to 6ohm for the third order system giving and efficiency of 89db@1w

Excursion limited power for the third order system is about 125w@6ohm for full range use giving a maximum output capability of 110db@1m

[porper]

So easy to understand. So intuitive. Cool.

And - yes, be sure to vent your spleen on those idiots and their so called math with the AES>

[bill]

What a beautiful explanation! It's obvious once explained, but if you've still got your mind wrapped around thinking of an abstract driver as a (mostly) resistive load, completely counterintuitive. Shame on me! I should know better!

Of course, there is a downside, and that's the dip in impedance below Ftc, where the woofer can really suck power out of the amp. You don't get something for nothing.

Thanks for sorting me out. I never really understood this phenomenon before.

Best regards,
Bill

> If you place a driver in a sealed cabinet
> and raise it's Qtc to 1 the response will
> have a peak above Ftc.

> At Ftc the level will return to the flatband
> level and below that will rolloff at
> 12db/oct.

> By placing a capacitor in series with the
> driver you can make it's response flat and
> extend it's cuttoff frequency lower.

> This can be explained by considering five
> important ranges in the drivers response.

> First the high frequency range.

> In this range the capacitors impedance is
> insignifigant and the drivers response is
> unaffected.

> Second the region just above Ftc where the
> drivers response is peaking above the
> flatband due to the Ftc of 1.

> In this region the capacitors reactance is
> now signifigant and will knock the response
> peak down to flat.

> Third system resonance (Ftc).

> In this region the drivers response is level
> with the flatband due to the Qtc of 1 and
> the impedance of the driver is very high due
> to system resonance (impedance peak).

> The high impedance of the driver again
> renders the reactance of the capacitor
> insignifigant and no signifigant change to
> the drivers response is effected at Ftc.

> Fourth the region just below Ftc.

> In this region the capacitors reactance is
> even greater and the woofers impedance has
> come down from it's peak and is again
> comparable to the capacitors.

> Even more importantly the woofers impedance
> in this region is inductive which is
> opposite to the capacitors reactance which
> is capacitive (go figure) and they cancel.

> Since the capacitors reactance cancels the
> woofers the impedance becomes lower and
> consequently more current flows efffecting a
> BOOST in response just below Ftc.

> Fifth is the low frequency region.

> In this region the woofers impedance settles
> to Re and the reactance of the capacitor in
> conjunction effects a simple highpass
> function upon the woofers response turning a
> 12db/oct. cuttoff into an 18db/oct. cutoff.

> Study the image below which shows the
> transfer function of different capacitor
> values in series with a woofer and reconcile
> it with the above text.

[Paul K.]

looking at the response of the RS225s in the sealed enclosure, F3 appears to be ~49 Hz and F6 is ~35 Hz. I find those values difficult to translate into "impressive in-room performance" in spite of the curve's pretty shallow rolloff below F6.
Paul K.

> Hi Ken,

> Using resistance and/or capacitance in
> series with drivers in sealed enclosures you
> can gain more control over the result than
> the 'normal' approach.

> A wide range of response shapes are
> possible.

> Even after you have chosen a specific
> cabinet volume you still can tailor the
> response considerably just by changing
> values for R and C.

> With the same cabinet volume you can choose
> a slow early rolloff or an extended sharp
> rolloff.

> Someone a year ago (or so) was wondering
> about two RS225's and I happen to have the
> chart still that I modelled back then
> (below).

> It shows two RS225's in a 2ft^3 100%FG fill
> sealed (purple) and 4.5ft^3 20hz vented
> (green).

> Both of these will net you impressive
> performance inroom.

[daryl]

http://img.villagephotos.com/p/2003-4/144711/RS225xgd.gif

Provided Link: Daryl's Speaker Stuff. (http://www.villagephotos.com/pubgallery.asp?id_=144711)


> looking at the response of the RS225s in the
> sealed enclosure, F3 appears to be ~49 Hz
> and F6 is ~35 Hz. I find those values
> difficult to translate into "impressive
> in-room performance" in spite of the
> curve's pretty shallow rolloff below F6.
> Paul K.

Inroom were talking about 45hz extension (conservative).

The quality of the drivers is first rate and the two drivers will move enough air for a strong output level (112db or so).

I do call that impressive performance (20hz extension is cool but not necessary).

The 4.5ft^3 vented systenm extends response to 20hz or so and as you can see below doesn't cause anymore excursion until below the 20hz tuning frequency maintaining the systems output capability.

A few posts below you can see where I came up with a third order sealed system that uses the same 2ft^3 as the plain sealed system but extends inroom response another half octave lower (32hz) and reduces output capability and efficiency about 2db (125w@6ohm for 110db for the 3rd order sealed vs. 125w@4ohm for 112db for the plain sealed and vented).

I don't think these are necessarily as impressive as the two 15" subs I have that displace 2.55l each, achieve 16hz bass extension and have copper sleeves over their pole-pieces.

But were not talking subwoofers and bass extension isn't the most important parameter.

My subs can't do what the RS225's can up in the woofer range.

[Paul K.]

I agree that the RS225 is a darned good woofer, and two of them should be twice as good, so to speak. But, to say in-room extension is 45 Hz, with F3 already at 49 Hz, isn't much of an "extension" in my view. Personally I think an F3 of ~40 Hz is just fine and anything lower is nice but not absolutely necessary for the music I prefer (but the speakers I'm currently building will have an anechoic F3 of 30 Hz!).
Paul

> Inroom were talking about 45hz extension
> (conservative).

> The quality of the drivers is first rate and
> the two drivers will move enough air for a
> strong output level (112db or so).

> I do call that impressive performance (20hz
> extension is cool but not necessary).

> The 4.5ft^3 vented systenm extends response
> to 20hz or so and as you can see below
> doesn't cause anymore excursion until below
> the 20hz tuning frequency maintaining the
> systems output capability.

> A few posts below you can see where I came
> up with a third order sealed system that
> uses the same 2ft^3 as the plain sealed
> system but extends inroom response another
> half octave lower (32hz) and reduces output
> capability and efficiency about 2db
> (125w@6ohm for 110db for the 3rd order
> sealed vs. 125w@4ohm for 112db for the plain
> sealed and vented).

> I don't think these are necessarily as
> impressive as the two 15" subs I have
> that displace 2.55l each, achieve 16hz bass
> extension and have copper sleeves over their
> pole-pieces.

> But were not talking subwoofers and bass
> extension isn't the most important
> parameter.

> My subs can't do what the RS225's can up in
> the woofer range.

[ktaillon]

Provided Link: Speaker Pics (http://www.flickr.com/photos/hexaudio/sets/)


> Hi Ken,

> I cooked up a design for two RS225's in
> 2ft^3 100% fiberglass fill like before and
> then added some resistance and capacitance
> to extend the bass while keeping the same
> 2ft^3.

> The purple curve is the plain sealed system.

> Bass extension inroom will be roughly 45hz.

> It's sensitivity is <A HREF="mailto:94db@2.83">94db@2.83</A> v

> Nominal impedance is 4ohm so efficiency is
> 91db@1w

> Excusion limited power is about 125w@4ohm
> for a full range system giving an output
> capability of about 112db@1m

> For the third order system I have kept the
> same enclosure but added 2ohm (two PE# 017-4
> resistors) and 1000uf (two PE# 027-378 NPE
> caps).

> The third order system is shown as the green
> curve.

> I have designed the system so that the
> response droops somewhat at low frequency to
> complement roomgain and make effective use
> of recources (these series RC networks make
> sealed systems response quite flexible).

> Inroom bass extension has been increased
> roughly half an octave to 32hz.

> Sensitivity has gone down to <A HREF="mailto:90db@2.83">90db@2.83</A> v
> for the third order system.

> Nominal impedance has gone up to 6ohm for
> the third order system giving and efficiency
> of 89db@1w

> Excursion limited power for the third order
> system is about 125w@6ohm for full range use
> giving a maximum output capability of
> 110db@1m

That's the type of roll off I was thinking of. I will be doing some testing soon with these drivers in a few different size boxes, I just need to order some resistors and caps. Thanks for the time and illustration.



(Originally posted by: ktaillon)