Speaker ports

[Les Cargill[_4_]]

Suppose you are designing a ported speaker enclosure. Suppose this
design wants two 2 inch ports @ 0.80 inches.

Suppose also you are using 3/4" plywood.

Must the port extend 0.80 into the internal volume of the speaker box
or would the slightly less than .75 inches of the box material suffice?


--
Les Cargill

[Mike Rivers[_2_]]

On 1/17/2015 9:18 PM, Les Cargill wrote:
>
> Suppose you are designing a ported speaker enclosure. Suppose this
> design wants two 2 inch ports @ 0.80 inches.
>
> Suppose also you are using 3/4" plywood.
>
> Must the port extend 0.80 into the internal volume of the speaker box
> or would the slightly less than .75 inches of the box material suffice?

It depends on the designer and the design. You could glue a piece of 2"
PVC pipe (2.375" OD, 2.05" ID) inside the port and trim it to length for
what you think is the best sound.

Or you could use a cardboard toilet paper roll if you want something
easier to cut. Remember that there's a long history of toilet paper and
NS-10 speakers. ;)

--
For a good time, visit http://mikeriversaudio.wordpress.com

[Don Pearce[_3_]]

On Sat, 17 Jan 2015 14:18:36 -0600, Les Cargill
> wrote:

>
>Suppose you are designing a ported speaker enclosure. Suppose this
>design wants two 2 inch ports @ 0.80 inches.
>
>Suppose also you are using 3/4" plywood.
>
>Must the port extend 0.80 into the internal volume of the speaker box
>or would the slightly less than .75 inches of the box material suffice?

The length of the port is used to determine the mass of air that is
"bouncing" against the spring of the air inside the cabinet, so yes,
that length is the total length of the port as calculated.

Now it gets tricky. The moving mass of port air extends beyond the
physical port for some distance - so called end effect - so you need
to shorten the physical port to allow for it. In your design, that
probably means a physical port length around zero.

You should be able to refine the design parameters you feed into the
programme to end up with a port length of at least a couple of inches
in order to make it physically possible to build. The programme should
be able to give you the end effect lengths that you subtract from the
tube when building it.

d

[Les Cargill[_4_]]

(Don Pearce) wrote:
> On Sat, 17 Jan 2015 14:18:36 -0600, Les Cargill
> > wrote:
>
>>
>> Suppose you are designing a ported speaker enclosure. Suppose this
>> design wants two 2 inch ports @ 0.80 inches.
>>
>> Suppose also you are using 3/4" plywood.
>>
>> Must the port extend 0.80 into the internal volume of the speaker box
>> or would the slightly less than .75 inches of the box material suffice?
>
> The length of the port is used to determine the mass of air that is
> "bouncing" against the spring of the air inside the cabinet, so yes,
> that length is the total length of the port as calculated.
>
> Now it gets tricky. The moving mass of port air extends beyond the
> physical port for some distance - so called end effect - so you need
> to shorten the physical port to allow for it. In your design, that
> probably means a physical port length around zero.
>

That sounds like a feature, not a bug. This then becomes just a hole in
the outer wall of the box. No tube required. I 'd expect a couple
millimeters to not have much effect. If it does, cut a ring out of
something to make it up.

The "chuff" factor - "vent mach" in WinISD parlance - is 0.10; not
bad at all.

> You should be able to refine the design parameters you feed into the
> programme to end up with a port length of at least a couple of inches
> in order to make it physically possible to build. The programme should
> be able to give you the end effect lengths that you subtract from the
> tube when building it.
>

The program is WinISD and it just calculates a port length. I
deliberately chose 2X2" because it has calculated a small - 0.5 cu. ft.
box - that will need to be doubled in volume to actually be able to
hold the speaker in question.

The ports could be in the back, but 2x2" is about all you could afford
for front-mounted ports.

> d
>
--
Les Cargill

[Trevor]

On 18/01/2015 7:18 AM, Les Cargill wrote:
>
> Suppose you are designing a ported speaker enclosure. Suppose this
> design wants two 2 inch ports @ 0.80 inches.
>
> Suppose also you are using 3/4" plywood.
>
> Must the port extend 0.80 into the internal volume of the speaker box
> or would the slightly less than .75 inches of the box material suffice?

The port length includes the baffle thickness, so the easiest way to do
what you want is simply adjust the port diameter slightly to suit the
baffle thickness you have. Even better, cut them undersize and then
adjust their size and thus tuning of the finished box.

Trevor.

[Don Pearce[_3_]]

On Sat, 17 Jan 2015 19:45:37 -0600, Les Cargill
> wrote:

(Don Pearce) wrote:
>> On Sat, 17 Jan 2015 14:18:36 -0600, Les Cargill
>> > wrote:
>>
>>>
>>> Suppose you are designing a ported speaker enclosure. Suppose this
>>> design wants two 2 inch ports @ 0.80 inches.
>>>
>>> Suppose also you are using 3/4" plywood.
>>>
>>> Must the port extend 0.80 into the internal volume of the speaker box
>>> or would the slightly less than .75 inches of the box material suffice?
>>
>> The length of the port is used to determine the mass of air that is
>> "bouncing" against the spring of the air inside the cabinet, so yes,
>> that length is the total length of the port as calculated.
>>
>> Now it gets tricky. The moving mass of port air extends beyond the
>> physical port for some distance - so called end effect - so you need
>> to shorten the physical port to allow for it. In your design, that
>> probably means a physical port length around zero.
>>
>
>That sounds like a feature, not a bug. This then becomes just a hole in
>the outer wall of the box. No tube required. I 'd expect a couple
>millimeters to not have much effect. If it does, cut a ring out of
>something to make it up.
>
>The "chuff" factor - "vent mach" in WinISD parlance - is 0.10; not
>bad at all.
>
>> You should be able to refine the design parameters you feed into the
>> programme to end up with a port length of at least a couple of inches
>> in order to make it physically possible to build. The programme should
>> be able to give you the end effect lengths that you subtract from the
>> tube when building it.
>>
>
>The program is WinISD and it just calculates a port length. I
>deliberately chose 2X2" because it has calculated a small - 0.5 cu. ft.
>box - that will need to be doubled in volume to actually be able to
>hold the speaker in question.
>
>The ports could be in the back, but 2x2" is about all you could afford
>for front-mounted ports.
>
OK, your reasoning makes sense, but if you have doubled the box volume
(for whatever reason), then you are headed well along the road to an
infinite baffle design, and you probably don't need a port at all.
d

[Dave Plowman (News)]

In article >,
Les Cargill > wrote:

> Suppose you are designing a ported speaker enclosure. Suppose this
> design wants two 2 inch ports @ 0.80 inches.

> Suppose also you are using 3/4" plywood.

> Must the port extend 0.80 into the internal volume of the speaker box
> or would the slightly less than .75 inches of the box material suffice?

I'd generally glue another small square of plywood to the inside to make
up the required length of port - unless very much longer than the
thickness of the baffle. But the thickest baffle I've ever used is 12mm
birch ply. Although never made PA sized speakers.

--
*Do infants enjoy infancy as much as adults enjoy adultery?

Dave Plowman London SW
To e-mail, change noise into sound.

[Scott Dorsey]

In article >,
Les Cargill > wrote:
>
>Suppose you are designing a ported speaker enclosure. Suppose this
>design wants two 2 inch ports @ 0.80 inches.
>
>Suppose also you are using 3/4" plywood.
>
>Must the port extend 0.80 into the internal volume of the speaker box
>or would the slightly less than .75 inches of the box material suffice?

..75 is well within the margin of error anyway. You're going to have to
do some cut-and-try work outdoors with a measurement system and see.
You may even find the thickness of the box material adds too much delay.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Peter Larsen[_3_]]

"Scott Dorsey" > skrev i en meddelelse
...

> In article >,
> Les Cargill > wrote:


>>Suppose you are designing a ported speaker enclosure. Suppose this
>>design wants two 2 inch ports @ 0.80 inches.

>>Suppose also you are using 3/4" plywood.

>>Must the port extend 0.80 into the internal volume of the speaker box
>>or would the slightly less than .75 inches of the box material suffice?

> .75 is well within the margin of error anyway. You're going to have to
> do some cut-and-try work outdoors with a measurement system and see.
> You may even find the thickness of the box material adds too much delay.

I think the design is trying to explain to the designer that he should use
larger and longer ports. A rectangular slit above the unit and one below
comes to mind.

> --scott

Kind regards

Peter Larsen

[Frank Stearns]

(Scott Dorsey) writes:

>In article >,
>Les Cargill > wrote:
>>
>>Suppose you are designing a ported speaker enclosure. Suppose this
>>design wants two 2 inch ports @ 0.80 inches.
>>
>>Suppose also you are using 3/4" plywood.
>>
>>Must the port extend 0.80 into the internal volume of the speaker box
>>or would the slightly less than .75 inches of the box material suffice?

>.75 is well within the margin of error anyway. You're going to have to
>do some cut-and-try work outdoors with a measurement system and see.
>You may even find the thickness of the box material adds too much delay.

The plumbing section of your local home center can be your friend, particularly the
bins of 2"-3" Schedule 40 ABS drain pipe and parts. Pick whichever; then plug that
value into the port field of your speaker box calculation software. (Inside
diameter)

Get a sleeve coupling or two. Use a chop saw to slice through the middle so that you
cut right through the internal stop ridge. Now you have ring(s) that can be
glued into a rough hole in your baffle.

Next, chop up some of the pipe that will fit the sleeves you made. Cut lengths at
what the software indicated, as well as incrementally longer and shorter. Buff off
the really sharp edges. (I use na 1/8" rounding bit in a laminate finishing router
and spun it around the inside and outside of the pipe ends.)

Insert the "ideal" port length. What's handy here is that it slides right in. Take a
measurement. Is it "perfect"? You're done. But you might try some different length
sleeves; see how the different port lengths affect the system.

In this way, you can completely dial in the ideal port length to compensate
for any errors in box volume calculation as well as variances in the drivers.

With that sleeve-and-pipe approach to port tuning it's fairly easy.

Frank
Mobile Audio



--

[Les Cargill[_4_]]

Frank Stearns wrote:
> (Scott Dorsey) writes:
>
>> In article >,
>> Les Cargill > wrote:
>>>
>>> Suppose you are designing a ported speaker enclosure. Suppose this
>>> design wants two 2 inch ports @ 0.80 inches.
>>>
>>> Suppose also you are using 3/4" plywood.
>>>
>>> Must the port extend 0.80 into the internal volume of the speaker box
>>> or would the slightly less than .75 inches of the box material suffice?
>
>> .75 is well within the margin of error anyway. You're going to have to
>> do some cut-and-try work outdoors with a measurement system and see.
>> You may even find the thickness of the box material adds too much delay.
>
> The plumbing section of your local home center can be your friend, particularly the
> bins of 2"-3" Schedule 40 ABS drain pipe and parts. Pick whichever; then plug that
> value into the port field of your speaker box calculation software. (Inside
> diameter)
>
> Get a sleeve coupling or two. Use a chop saw to slice through the middle so that you
> cut right through the internal stop ridge. Now you have ring(s) that can be
> glued into a rough hole in your baffle.
>
> Next, chop up some of the pipe that will fit the sleeves you made. Cut lengths at
> what the software indicated, as well as incrementally longer and shorter. Buff off
> the really sharp edges. (I use na 1/8" rounding bit in a laminate finishing router
> and spun it around the inside and outside of the pipe ends.)
>
> Insert the "ideal" port length. What's handy here is that it slides right in. Take a
> measurement. Is it "perfect"? You're done. But you might try some different length
> sleeves; see how the different port lengths affect the system.
>
> In this way, you can completely dial in the ideal port length to compensate
> for any errors in box volume calculation as well as variances in the drivers.
>

I suspect this is outside the envelope of measurement.

Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there
is one hump in the group delay that goes from 4ish to 8ish msec, around
75-80 Hz in the frequency response.

Doubling the box nearly has to be more of a perturbation than 1.25 mm of
port depth.

But then again, ports are critically sensitive elements. Still, I am
skeptical that "just take it outside and measure it" is going to
allow enough accuracy to be able to tell.

(btw, this is not for me; it's for another participant on a different
forum who has a speaker and is fishing for box designs ).

> With that sleeve-and-pipe approach to port tuning it's fairly easy.
>
> Frank
> Mobile Audio
>
>
>

--
Les Cargill

[Peter Larsen[_3_]]

"Les Cargill" > skrev i en meddelelse
...

> Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there
> is one hump in the group delay that goes from 4ish to 8ish msec, around
> 75-80 Hz in the frequency response.

In winisd you can fix any parameter and then see what happens to the design,
so in case the port lenght is silly you try another area. If you err, then
err to the side of the too long a port because the bass units Fs will get a
wee bit lower in use. Do not err to the side of the too high tuning because
it will give a "loose" sound with flappy transients.

Oh, that btw. is the answer to whether a slightly too short port is OK, no,
it is not redesign so that you have more length and lower air speed in port
or make it a bit smaller. I didn't think that mattered so much until
Quali-Fi service here in Denmark suggested that I should double the port
area since I had room for longer ports, it was a surprising sonic
improvement, unexpected because of my generally modest playback spl.

> Doubling the box nearly has to be more of a perturbation than 1.25 mm of
> port depth.

> But then again, ports are critically sensitive elements. Still, I am
> skeptical that "just take it outside and measure it" is going to
> allow enough accuracy to be able to tell.

Measure the impedance curve, what sounds well to me is the setups where the
lower impedance hump is equal to the higher one or larger, ie. generally
systems that are tuned lower than optimally linear.

> (btw, this is not for me; it's for another participant on a different
> forum who has a speaker and is fishing for box designs ).

But, surely, in fishing putting some bait on the hook, such as telling us
what unit and what its parameters are may increase the chance for a good
catch.

> Les Cargill

Kind regards

Peter Larsen

[Les Cargill[_4_]]

Peter Larsen wrote:
> "Les Cargill" > skrev i en meddelelse
> ...
>
>> Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there
>> is one hump in the group delay that goes from 4ish to 8ish msec, around
>> 75-80 Hz in the frequency response.
>
> In winisd you can fix any parameter and then see what happens to the design,
> so in case the port lenght is silly you try another area. If you err, then
> err to the side of the too long a port because the bass units Fs will get a
> wee bit lower in use. Do not err to the side of the too high tuning because
> it will give a "loose" sound with flappy transients.
>

Interesting. I was concerned that too long a port would fight the box.
Still; moving from 20.00 to 1.97 inches diameter ( from 50.8 to 20.038
mm ) seems rather hairsplitting :) That gets it to a length of 0.75 inches.

Since the ideal front design is 14"x14" for a steel guitar speaker,
there was hardly room for a pair of 2" ports.

They'd just have to go in back.

> Oh, that btw. is the answer to whether a slightly too short port is OK, no,
> it is not redesign so that you have more length and lower air speed in port
> or make it a bit smaller. I didn't think that mattered so much until
> Quali-Fi service here in Denmark suggested that I should double the port
> area since I had room for longer ports, it was a surprising sonic
> improvement, unexpected because of my generally modest playback spl.
>

huh. That actually makes sense.

>> Doubling the box nearly has to be more of a perturbation than 1.25 mm of
>> port depth.
>
>> But then again, ports are critically sensitive elements. Still, I am
>> skeptical that "just take it outside and measure it" is going to
>> allow enough accuracy to be able to tell.
>
> Measure the impedance curve, what sounds well to me is the setups where the
> lower impedance hump is equal to the higher one or larger, ie. generally
> systems that are tuned lower than optimally linear.
>

True enough.

>> (btw, this is not for me; it's for another participant on a different
>> forum who has a speaker and is fishing for box designs ).
>
> But, surely, in fishing putting some bait on the hook, such as telling us
> what unit and what its parameters are may increase the chance for a good
> catch.


It's an Eminence EPS-12C. I guessed ( incorrectly ) that this didn't
matter :) It's not a bass driver at all; it's a guitar speaker. Fs is
49.17 Hz. I get the feeling it's really designed for infinite baffle.

http://www.usspeaker.com/Eps12c-1.htm

The gentleman will use it for pedal steel, presumably with a lowest note
of C2 ( 69.4 cycles ).


>
>> Les Cargill
>
> Kind regards
>
> Peter Larsen
>
>
>
>

--
Les Cargill

[Don Pearce[_3_]]

On Sun, 18 Jan 2015 21:38:47 -0600, Les Cargill
> wrote:

>Peter Larsen wrote:
>> "Les Cargill" > skrev i en meddelelse
>> ...
>>
>>> Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there
>>> is one hump in the group delay that goes from 4ish to 8ish msec, around
>>> 75-80 Hz in the frequency response.
>>
>> In winisd you can fix any parameter and then see what happens to the design,
>> so in case the port lenght is silly you try another area. If you err, then
>> err to the side of the too long a port because the bass units Fs will get a
>> wee bit lower in use. Do not err to the side of the too high tuning because
>> it will give a "loose" sound with flappy transients.
>>
>
>Interesting. I was concerned that too long a port would fight the box.
>Still; moving from 20.00 to 1.97 inches diameter ( from 50.8 to 20.038
>mm ) seems rather hairsplitting :) That gets it to a length of 0.75 inches.
>
>Since the ideal front design is 14"x14" for a steel guitar speaker,
>there was hardly room for a pair of 2" ports.
>
>They'd just have to go in back.
>
>> Oh, that btw. is the answer to whether a slightly too short port is OK, no,
>> it is not redesign so that you have more length and lower air speed in port
>> or make it a bit smaller. I didn't think that mattered so much until
>> Quali-Fi service here in Denmark suggested that I should double the port
>> area since I had room for longer ports, it was a surprising sonic
>> improvement, unexpected because of my generally modest playback spl.
>>
>
>huh. That actually makes sense.
>
>>> Doubling the box nearly has to be more of a perturbation than 1.25 mm of
>>> port depth.
>>
>>> But then again, ports are critically sensitive elements. Still, I am
>>> skeptical that "just take it outside and measure it" is going to
>>> allow enough accuracy to be able to tell.
>>
>> Measure the impedance curve, what sounds well to me is the setups where the
>> lower impedance hump is equal to the higher one or larger, ie. generally
>> systems that are tuned lower than optimally linear.
>>
>
>True enough.
>
>>> (btw, this is not for me; it's for another participant on a different
>>> forum who has a speaker and is fishing for box designs ).
>>
>> But, surely, in fishing putting some bait on the hook, such as telling us
>> what unit and what its parameters are may increase the chance for a good
>> catch.
>
>
>It's an Eminence EPS-12C. I guessed ( incorrectly ) that this didn't
>matter :) It's not a bass driver at all; it's a guitar speaker. Fs is
>49.17 Hz. I get the feeling it's really designed for infinite baffle.
>
>http://www.usspeaker.com/Eps12c-1.htm
>
>The gentleman will use it for pedal steel, presumably with a lowest note
>of C2 ( 69.4 cycles ).
>
>
>>
>>> Les Cargill
>>
>> Kind regards
>>
>> Peter Larsen
>>
>>
>>
>>

I was going to ask. Why are you porting this at all? Bottom E on a
guitar is 82Hz, and the speaker cone is far better protected and
supported in an IB box.

Vox get away with open backs because their amplifiers are relatively
low power compared to the speaker drivers. And they leave the backs
open deliberately to roll off the bass for a cleaner sound.

d

[Les Cargill[_4_]]

(Don Pearce) wrote:
> On Sun, 18 Jan 2015 21:38:47 -0600, Les Cargill
> > wrote:
>
>> Peter Larsen wrote:
>>> "Les Cargill" > skrev i en meddelelse
>>> ...
>>>
>>>> Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there
>>>> is one hump in the group delay that goes from 4ish to 8ish msec, around
>>>> 75-80 Hz in the frequency response.
>>>
>>> In winisd you can fix any parameter and then see what happens to the design,
>>> so in case the port lenght is silly you try another area. If you err, then
>>> err to the side of the too long a port because the bass units Fs will get a
>>> wee bit lower in use. Do not err to the side of the too high tuning because
>>> it will give a "loose" sound with flappy transients.
>>>
>>
>> Interesting. I was concerned that too long a port would fight the box.
>> Still; moving from 20.00 to 1.97 inches diameter ( from 50.8 to 20.038
>> mm ) seems rather hairsplitting :) That gets it to a length of 0.75 inches.
>>
>> Since the ideal front design is 14"x14" for a steel guitar speaker,
>> there was hardly room for a pair of 2" ports.
>>
>> They'd just have to go in back.
>>
>>> Oh, that btw. is the answer to whether a slightly too short port is OK, no,
>>> it is not redesign so that you have more length and lower air speed in port
>>> or make it a bit smaller. I didn't think that mattered so much until
>>> Quali-Fi service here in Denmark suggested that I should double the port
>>> area since I had room for longer ports, it was a surprising sonic
>>> improvement, unexpected because of my generally modest playback spl.
>>>
>>
>> huh. That actually makes sense.
>>
>>>> Doubling the box nearly has to be more of a perturbation than 1.25 mm of
>>>> port depth.
>>>
>>>> But then again, ports are critically sensitive elements. Still, I am
>>>> skeptical that "just take it outside and measure it" is going to
>>>> allow enough accuracy to be able to tell.
>>>
>>> Measure the impedance curve, what sounds well to me is the setups where the
>>> lower impedance hump is equal to the higher one or larger, ie. generally
>>> systems that are tuned lower than optimally linear.
>>>
>>
>> True enough.
>>
>>>> (btw, this is not for me; it's for another participant on a different
>>>> forum who has a speaker and is fishing for box designs ).
>>>
>>> But, surely, in fishing putting some bait on the hook, such as telling us
>>> what unit and what its parameters are may increase the chance for a good
>>> catch.
>>
>>
>> It's an Eminence EPS-12C. I guessed ( incorrectly ) that this didn't
>> matter :) It's not a bass driver at all; it's a guitar speaker. Fs is
>> 49.17 Hz. I get the feeling it's really designed for infinite baffle.
>>
>> http://www.usspeaker.com/Eps12c-1.htm
>>
>> The gentleman will use it for pedal steel, presumably with a lowest note
>> of C2 ( 69.4 cycles ).
>>
>>
>>>
>>>> Les Cargill
>>>
>>> Kind regards
>>>
>>> Peter Larsen
>>>
>>>
>>>
>>>
>
> I was going to ask. Why are you porting this at all?

I don't know exactly. I suppose he wants a little more bass support.
Steel goes lower than 6 string.

> Bottom E on a
> guitar is 82Hz, and the speaker cone is far better protected and
> supported in an IB box.
>

Agreed.

> Vox get away with open backs because their amplifiers are relatively
> low power compared to the speaker drivers. And they leave the backs
> open deliberately to roll off the bass for a cleaner sound.
>
> d
>


--
Les Cargill

[Peter Larsen[_3_]]

Hi Don,

> I was going to ask. Why are you porting this at all? Bottom E on a
> guitar is 82Hz, and the speaker cone is far better protected and
> supported in an IB box.

It is a very low Qt unit, well into the "suited for horn loading range", so
yes, it should be vented, I think an IB with this unit will sound thin. So
I'll just re-iterate my suggestion of a slit shaped vent above and below the
unit.

A bit of finagling yields something like this as I see it early in the
morning:

box: 25 liters
tuning: 60 Hz
2 vents as slits 30 centimeters long, 1 centimeter wide, 9 centimeters deep.

The response should then be -5 dB at 80 Hz and sloping upwards to -1 dB
around 250 Hz, that is about as much bass as you can get from that unit. It
is not a standard tuning for the box, but as you said, too much bass in a
guitar box can end up muddy.

It is important to ensure a smooth inside finish of the vents. Box inside
walls should probably be felt covered, 1 cm thick felt stapled in place,
somewhat messy, not too flat and tidy. Make the box 32 liters to allow for
it and for the loudspeaker magnet.

Amplifier should if possible be highpassed at 60 Hz to protect loudspeaker
from "hit all strings tranasients", somewhat depending on how powerful it
is, RMS power for the unit is spec'd at 225 watts, the old JBL guideline was
assume 30% for instrument use because of low crest factor and the risk of
weird transients, ie. "somewhat safe to use with 60 watts amplifier".

> d

Kind regards

Peter Larsen

[Don Pearce[_3_]]

On Mon, 19 Jan 2015 06:24:18 +0100, "Peter Larsen"
> wrote:

>Hi Don,
>
>> I was going to ask. Why are you porting this at all? Bottom E on a
>> guitar is 82Hz, and the speaker cone is far better protected and
>> supported in an IB box.
>
>It is a very low Qt unit, well into the "suited for horn loading range", so
>yes, it should be vented, I think an IB with this unit will sound thin. So
>I'll just re-iterate my suggestion of a slit shaped vent above and below the
>unit.
>
>A bit of finagling yields something like this as I see it early in the
>morning:
>
>box: 25 liters
>tuning: 60 Hz
>2 vents as slits 30 centimeters long, 1 centimeter wide, 9 centimeters deep.
>
>The response should then be -5 dB at 80 Hz and sloping upwards to -1 dB
>around 250 Hz, that is about as much bass as you can get from that unit. It
>is not a standard tuning for the box, but as you said, too much bass in a
>guitar box can end up muddy.
>
>It is important to ensure a smooth inside finish of the vents. Box inside
>walls should probably be felt covered, 1 cm thick felt stapled in place,
>somewhat messy, not too flat and tidy. Make the box 32 liters to allow for
>it and for the loudspeaker magnet.
>
>Amplifier should if possible be highpassed at 60 Hz to protect loudspeaker
>from "hit all strings tranasients", somewhat depending on how powerful it
>is, RMS power for the unit is spec'd at 225 watts, the old JBL guideline was
>assume 30% for instrument use because of low crest factor and the risk of
>weird transients, ie. "somewhat safe to use with 60 watts amplifier".
>
>> d
>
> Kind regards
>
> Peter Larsen
>
>

Extra damping on the walls of the box shouldn't be necessary. The
internal Q is set by the driver and the port, so felt on the walls
would be an added and unknown extra source of loss. And of course this
is for sound production, not reproduction, so some character and
resonance is probably to be considered a good thing.

d

[Trevor]

On 18/01/2015 10:10 PM, Dave Plowman (News) wrote:
> In article >,
> Les Cargill > wrote:
>
>> Suppose you are designing a ported speaker enclosure. Suppose this
>> design wants two 2 inch ports @ 0.80 inches.
>
>> Suppose also you are using 3/4" plywood.
>
>> Must the port extend 0.80 into the internal volume of the speaker box
>> or would the slightly less than .75 inches of the box material suffice?
>
> I'd generally glue another small square of plywood to the inside to make
> up the required length of port - unless very much longer than the
> thickness of the baffle. But the thickest baffle I've ever used is 12mm
> birch ply. Although never made PA sized speakers.

Gee that's really doing it the hard way when you consider the port
inertance is a factor of both the cross sectional area and length. So in
this case a lot easier to adjust the port area slightly than length.
When you must use a tube, the reverse is usually the case of course.

Trevor.

[Trevor]

On 19/01/2015 2:16 AM, Peter Larsen wrote:
> "Scott Dorsey" > skrev i en meddelelse
> ...
>
>> In article >,
>> Les Cargill > wrote:
>
>
>>> Suppose you are designing a ported speaker enclosure. Suppose this
>>> design wants two 2 inch ports @ 0.80 inches.
>
>>> Suppose also you are using 3/4" plywood.
>
>>> Must the port extend 0.80 into the internal volume of the speaker box
>>> or would the slightly less than .75 inches of the box material suffice?
>
>> .75 is well within the margin of error anyway. You're going to have to
>> do some cut-and-try work outdoors with a measurement system and see.
>> You may even find the thickness of the box material adds too much delay.
>
> I think the design is trying to explain to the designer that he should use
> larger and longer ports. A rectangular slit above the unit and one below
> comes to mind.

Why longer? Many designs simply use a hole cut in the baffle. Far easier
when that is appropriate. As I said already, I'd simply cut smaller
holes and tune the box by making them as large as necessary by measurement.

Trevor.

[Peter Larsen[_3_]]

"Don Pearce" > skrev i en meddelelse
...

> On Mon, 19 Jan 2015 06:24:18 +0100, "Peter Larsen"
> > wrote:

....

>>It is important to ensure a smooth inside finish of the vents. Box inside
>>walls should probably be felt covered, 1 cm thick felt stapled in place,
>>somewhat messy, not too flat and tidy. Make the box 32 liters to allow for
>>it and for the loudspeaker magnet.

....

> Extra damping on the walls of the box shouldn't be necessary. The
> internal Q is set by the driver and the port, so felt on the walls
> would be an added and unknown extra source of loss.

If it was primarily or only a bass box I could agree and at least be willing
to try. Felt suggested with the inernal Q in mind. I'll settle for half the
walls, I'm thinking midrange standing waves causing midrange colouration via
the ports, 32 liters is a small box.

> And of course this
> is for sound production, not reproduction, so some character and
> resonance is probably to be considered a good thing.

As long as it is well sounding, yes. One could also use a partial diagonal
bracing wall to break up standing waves so as to lessen any possible problem
and make the midrange that comes out of the ports sound better.

> d

Kind regards

Peter Larsen

[Dave Plowman (News)]

In article >,
Trevor > wrote:
> > I'd generally glue another small square of plywood to the inside to
> > make up the required length of port - unless very much longer than the
> > thickness of the baffle. But the thickest baffle I've ever used is
> > 12mm birch ply. Although never made PA sized speakers.

> Gee that's really doing it the hard way when you consider the port
> inertance is a factor of both the cross sectional area and length. So in
> this case a lot easier to adjust the port area slightly than length.
> When you must use a tube, the reverse is usually the case of course.

Depends, I suppose, on your woodworking skills and facilities.

--
*Why is it that doctors call what they do "practice"?

Dave Plowman London SW
To e-mail, change noise into sound.

[Trevor]

On 19/01/2015 10:38 PM, Dave Plowman (News) wrote:
> In article >,
> Trevor > wrote:
>>> I'd generally glue another small square of plywood to the inside to
>>> make up the required length of port - unless very much longer than the
>>> thickness of the baffle. But the thickest baffle I've ever used is
>>> 12mm birch ply. Although never made PA sized speakers.
>
>> Gee that's really doing it the hard way when you consider the port
>> inertance is a factor of both the cross sectional area and length. So in
>> this case a lot easier to adjust the port area slightly than length.
>> When you must use a tube, the reverse is usually the case of course.
>
> Depends, I suppose, on your woodworking skills and facilities.

Would be funny skills that find it easier to "glue another small square
of plywood to the inside to make up the required length of port", than
to simply cut a different size hole. But I guess I'll take your word for
it that's easier for you. And I'll even assume the cost of extra
material is no consideration in your case.
Others may feel differently however.

Trevor.

[Dave Plowman (News)]

In article >,
Trevor > wrote:
> Would be funny skills that find it easier to "glue another small square
> of plywood to the inside to make up the required length of port", than
> to simply cut a different size hole. But I guess I'll take your word for
> it that's easier for you. And I'll even assume the cost of extra
> material is no consideration in your case.
> Others may feel differently however.

It's relatively easy to alter the length of the port by adding plywood etc
to the back. Provided it's not that long.

Enlarging a hole (bigger than a drill) may prove more tricky for some.

You can buy adjustable length (telescopic) plastic tubes to use with
ports.

All sorts of ways to skin a cat. The best one will depend on the
individual.

--
*Can vegetarians eat animal crackers?

Dave Plowman London SW
To e-mail, change noise into sound.

[Scott Dorsey]

Les Cargill > wrote:
>> In this way, you can completely dial in the ideal port length to compensate
>> for any errors in box volume calculation as well as variances in the drivers.
>
>I suspect this is outside the envelope of measurement.

In that case, it's either not important, or else you need better measurement
hardware in order to a proper design job.

>Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there
>is one hump in the group delay that goes from 4ish to 8ish msec, around
>75-80 Hz in the frequency response.
>
>Doubling the box nearly has to be more of a perturbation than 1.25 mm of
>port depth.
>
>But then again, ports are critically sensitive elements. Still, I am
>skeptical that "just take it outside and measure it" is going to
>allow enough accuracy to be able to tell.

That's entirely possible. The problem is that the simulation has even less
accuracy in most cases. So either you need better measurement or better
simulation, or else you need to not worry so much and live with the error.

I will say that if you don't have good measurement, you are more likely to
get a design that meets parameters on the first try with a sealed box design
than a ported design.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Les Cargill[_4_]]

(Scott Dorsey) wrote:
> Les Cargill > wrote:
>>> In this way, you can completely dial in the ideal port length to compensate
>>> for any errors in box volume calculation as well as variances in the drivers.
>>
>> I suspect this is outside the envelope of measurement.
>
> In that case, it's either not important, or else you need better measurement
> hardware in order to a proper design job.
>
>> Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there
>> is one hump in the group delay that goes from 4ish to 8ish msec, around
>> 75-80 Hz in the frequency response.
>>
>> Doubling the box nearly has to be more of a perturbation than 1.25 mm of
>> port depth.
>>
>> But then again, ports are critically sensitive elements. Still, I am
>> skeptical that "just take it outside and measure it" is going to
>> allow enough accuracy to be able to tell.
>
> That's entirely possible. The problem is that the simulation has even less
> accuracy in most cases.

This is one of the few times I'd think the simulation is probably more
reliable. In other words, 1.25 mm of port length seems unlikely to make
as much difference as... well, any other uncontrolled factors from a
homebrew design.

If this was for manufacture, it'd be different - you'd be able to buy
the right tooling, make proper jigs, all that.

> So either you need better measurement or better
> simulation, or else you need to not worry so much and live with the error.
>

I suspect the latter will be used... :)

> I will say that if you don't have good measurement, you are more likely to
> get a design that meets parameters on the first try with a sealed box design
> than a ported design.
> --scott
>

Yep.

--
Les Cargill

[hank alrich]

Les Cargill > wrote:

> If this was for manufacture, it'd be different - you'd be able to buy
> the right tooling, make proper jigs, all that.

I was startled when I opened one of my Meyer UPA1A's long ago. He fit as
much into that little cabinet as will go in there, including a special
horn that must certainly have taken "proper jigs, all that". The result
is reflected both in price, and in performance, both of them "up there".

--
shut up and play your guitar * HankAlrich.Com
HankandShaidriMusic.Com
YouTube.Com/WalkinayMusic

[Trevor]

On 21/01/2015 6:48 AM, Scott Dorsey wrote:
> Les Cargill > wrote:
>>> In this way, you can completely dial in the ideal port length to compensate
>>> for any errors in box volume calculation as well as variances in the drivers.
>>
>> I suspect this is outside the envelope of measurement.
>
> In that case, it's either not important, or else you need better measurement
> hardware in order to a proper design job.
>
>> Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there
>> is one hump in the group delay that goes from 4ish to 8ish msec, around
>> 75-80 Hz in the frequency response.
>>
>> Doubling the box nearly has to be more of a perturbation than 1.25 mm of
>> port depth.
>>
>> But then again, ports are critically sensitive elements. Still, I am
>> skeptical that "just take it outside and measure it" is going to
>> allow enough accuracy to be able to tell.
>
> That's entirely possible. The problem is that the simulation has even less
> accuracy in most cases. So either you need better measurement or better
> simulation, or else you need to not worry so much and live with the error.
>
> I will say that if you don't have good measurement, you are more likely to
> get a design that meets parameters on the first try with a sealed box design
> than a ported design.

It's pretty easy for anybody with computer sound to make an impedance
sweep these days, free software readily available, and that's all you
need to tune the box. Not to mention you can also measure the driver for
T/S parameters before you design the box.
But yes, a sealed box is always easier to design and construct if that's
what you want.

Trevor.

[Les Cargill[_4_]]

Trevor wrote:
> On 21/01/2015 6:48 AM, Scott Dorsey wrote:
>> Les Cargill > wrote:
>>>> In this way, you can completely dial in the ideal port length to
>>>> compensate
>>>> for any errors in box volume calculation as well as variances in the
>>>> drivers.
>>>
>>> I suspect this is outside the envelope of measurement.
>>
>> In that case, it's either not important, or else you need better
>> measurement
>> hardware in order to a proper design job.
>>
>>> Between the 1x ( 0.525 cu ft ) box and the 2x ( 1.05 cu ft ) box, there
>>> is one hump in the group delay that goes from 4ish to 8ish msec, around
>>> 75-80 Hz in the frequency response.
>>>
>>> Doubling the box nearly has to be more of a perturbation than 1.25 mm of
>>> port depth.
>>>
>>> But then again, ports are critically sensitive elements. Still, I am
>>> skeptical that "just take it outside and measure it" is going to
>>> allow enough accuracy to be able to tell.
>>
>> That's entirely possible. The problem is that the simulation has
>> even less
>> accuracy in most cases. So either you need better measurement or better
>> simulation, or else you need to not worry so much and live with the
>> error.
>>
>> I will say that if you don't have good measurement, you are more
>> likely to
>> get a design that meets parameters on the first try with a sealed box
>> design
>> than a ported design.
>
> It's pretty easy for anybody with computer sound to make an impedance
> sweep these days, free software readily available, and that's all you
> need to tune the box. Not to mention you can also measure the driver for
> T/S parameters before you design the box.

I have never had problems finding the manufacturer's published T/S
parameters.

> But yes, a sealed box is always easier to design and construct if that's
> what you want.
>
> Trevor.
>
>

--
Les Cargill

[Scott Dorsey]

Les Cargill > wrote:
>
>I have never had problems finding the manufacturer's published T/S
>parameters.

Sometimes those published parameters are pretty fictional.

I'm not going to mention any particular manufacturers here, but a quick
sweep in free air to determine Fs by ear will tell you who they are.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Trevor]

On 23/01/2015 2:16 AM, Scott Dorsey wrote:
> Les Cargill > wrote:
>> I have never had problems finding the manufacturer's published T/S
>> parameters.
>
> Sometimes those published parameters are pretty fictional.
>
> I'm not going to mention any particular manufacturers here, but a quick
> sweep in free air to determine Fs by ear will tell you who they are.
> --scott

And when they are not entirely fictional, they are often just ball park
figures which don't allow for individual and batch variations. If I'm
going to the trouble of designing and building a box, I'd rather take
the time to measure the drivers first, and then tune the finished box.
But each to their own.

Trevor.

[Peter Larsen[_3_]]

"Trevor" > skrev i en meddelelse
...

> On 23/01/2015 2:16 AM, Scott Dorsey wrote:

>> Les Cargill > wrote:

>>> I have never had problems finding the manufacturer's published T/S
>>> parameters.

>> Sometimes those published parameters are pretty fictional.

>> I'm not going to mention any particular manufacturers here, but a quick
>> sweep in free air to determine Fs by ear will tell you who they are.

> And when they are not entirely fictional, they are often just ball park
> figures which don't allow for individual and batch variations. If I'm
> going to the trouble of designing and building a box, I'd rather take the
> time to measure the drivers first, and then tune the finished box. But
> each to their own.

I have a rebuilt white D123 made from original spareparts that has never
been used, it is as hard as guitar loudspeaker. Very nice sounding midrange
on home-coming test sans cabinet, seller suggested that a few days of
sinewave might do it good ... not gonna do that, just playing will be fine -
I don't want to loose the stability of the rear suspension but yes, it will
change in use. Fortunately what it means is only that the initial bassreflex
tuning will be on the lowish side.

I think the specs are where they expect(ed) a played in loudspeaker to end
up, do we have the designer (of at least one other D123 version, the worlds
best 12" wideband loudspeaker unit) in the audience?

> Trevor.

Kind regards

Peter Larsen

[Trevor]

On 27/01/2015 6:51 PM, Peter Larsen wrote:
> "Trevor" > skrev i en meddelelse
> ...
>> On 23/01/2015 2:16 AM, Scott Dorsey wrote:
>>> Les Cargill > wrote:
>
>>>> I have never had problems finding the manufacturer's published T/S
>>>> parameters.
>
>>> Sometimes those published parameters are pretty fictional.
>
>>> I'm not going to mention any particular manufacturers here, but a quick
>>> sweep in free air to determine Fs by ear will tell you who they are.
>
>> And when they are not entirely fictional, they are often just ball park
>> figures which don't allow for individual and batch variations. If I'm
>> going to the trouble of designing and building a box, I'd rather take the
>> time to measure the drivers first, and then tune the finished box. But
>> each to their own.
>
> I have a rebuilt white D123 made from original spareparts that has never
> been used, it is as hard as guitar loudspeaker. Very nice sounding midrange
> on home-coming test sans cabinet, seller suggested that a few days of
> sinewave might do it good ... not gonna do that, just playing will be fine -
> I don't want to loose the stability of the rear suspension but yes, it will
> change in use. Fortunately what it means is only that the initial bassreflex
> tuning will be on the lowish side.
>
> I think the specs are where they expect(ed) a played in loudspeaker to end
> up,

There were no T/S specs for that speaker when JBL designed it. (You were
lucky to find the Fs at the time) It was before Neville Thiele had
published his work I think, certainly before it was widely known and
accepted. And IME, and I think according to Dick Pierce's vastly
superior experience, "burn in" is not a one way street anyway. And
fortunately some variations cancel themselves out. What does happen and
is a far bigger problem these days IME is changes in design or materials
between batches that are not accompanied by new T/S specs. That will
*really* affect your box design if not careful. So measurement is always
a good idea IMO.

Trevor.

[Peter Larsen[_3_]]

"Trevor" > skrev i en meddelelse
...

> On 27/01/2015 6:51 PM, Peter Larsen wrote:

>> I have a rebuilt white D123 made from original spareparts that has never
>> been used, it is as hard as guitar loudspeaker ....

>> I think the specs are where they expect(ed) a played in loudspeaker to
>> end
>> up,

> There were no T/S specs for that speaker when JBL designed it. (You were
> lucky to find the Fs at the time. It was before Neville Thiele had
> published his work I think, certainly before it was widely known and
> accepted.

And when it was known nobody in their sane mind would design the white D123
version, according to the specs that come with winisd it should have a 200
liter box, according to the guidelines Duelund taught me - I don't know if
they were his own or had some source - it is a unit for a closed box with
its Qt around 0.45. With a room friendly box version it almost invariably
ends up with a 4 dB boost around 60 Hz or - in a closed box - quite lame
sounding. All assuming those specs are valid of course.

> And IME, and I think according to Dick Pierce's vastly superior
> experience, "burn in" is not a one way street anyway.

Yes, quite well matching that speakers that have been left unused should
have a play in before being evaluated, he did write about this over in
~.tech.

> And fortunately some variations cancel themselves out. What does happen
> and is a far bigger problem these days IME is changes in design or
> materials between batches that are not accompanied by new T/S specs. That
> will *really* affect your box design if not careful. So measurement is
> always a good idea IMO.

Oh yes, most designers would prefer "loudspeaker unit" to be a constant
rather than a variable!

> Trevor

Kind regards

Peter Larsen