Re: flat speaker up to 40 kHz
GregS
>Hi everyone,
>I'm currently working in a lab dealing with auditory perception and
>biology. Since I have a very small sound chamber, I need a flat and
>compact loudspeaker with a frequency ranger extending from, say, 125
>Hz or 150 Hz to 40 kHz. The depth of the speaker should not be above 6
>or 7" (15 to 17.5cm). In a nutshell, something like the Fostex PMO.4
>but flatter and slightly shifted to higher frequencies:
>http://www.fostexinternational.com/docs/music_products/pm_series_mkII_spec.shtm
>l
>Do you have an idea ?
>thank you in advance
>Boris
How flat and it must be on axis, right ? How far away ?
I crosposted.
greg
bobopi
> In article <69cd5797-ad91-4fa0-800e-5c99bf2f6...@b1g2000hsg.googlegroups.com>, bobopi <bo...@pi314.net> wrote:
>
> >Hi everyone,
> >I'm currently working in a lab dealing with auditory perception and
> >biology. Since I have a very small sound chamber, I need a flat and
> >compact loudspeaker with a frequency ranger extending from, say, 125
> >Hz or 150 Hz to 40 kHz. The depth of the speaker should not be above 6
> >or 7" (15 to 17.5cm). In a nutshell, something like the Fostex PMO.4
> >but flatter and slightly shifted to higher frequencies:
> >l
> >Do you have an idea ?
> >thank you in advance
> >Boris
>
> How flat and it must be on axis, right ? How far away ?
> I crosposted.
>
> greg
actually, the sound chamber is about less than a cubic meter. The
speaker should be put very close (a few centimeters) to the ear of an
animal (a guinea pig), which should prevent the chamber to
dramatically influence the frequency response, well, at least, I
hope...
The speaker probably has to be passive because powered speakers would
introduce 60 Hz signals within the chamber (we perform
electrophysiological recordings).
A one way speaker would be best, but a two way speaker is likely
possible if we put the tweeter in front of the animal's ear, since low
frequencies have less directional properties I think.
I found this model that may be of interest, what do you think about
it ?:
http://www.tannoy-speakers.com/products/66/CMS%20401%20DCe_Data_File_Web%20V1.06.pdf
Regards,
Boris
GregS
Pretty, almost exactly what you want.
When recording there will be a small amount of magnetic noise from the speaker.
A magnetically shielded speaker is desirable or mandatory. There are way to
shield or partially shield speakers, but its much easier if they are designed that way.
Keep in mind the response is likly to be still ragged. I am going to see if they have a plot on this.
Recording setups are mostly electrostatic sensitive, but magnetics do have effects.
greg
GregS
I might add, I have never worked with a speaker in a test chamber. There are static magnetic fields
from the speaker and if there is movement or vibration it will induce into
the electrodes. The magnets are the prime magenetic source. The actual signal field will be much
smaller. Crossover network coils also radiate.
greg
Jay Kadis
zekf...@zekfrivolous.com (GregS) wrote:
Is the animal restrained? What kind of electrophysiological measurements
are you making?
Electrode/skin impedances are fairly low, although the preamp gain is
substantial for EEG signals with surface electrodes. If you're doing
intracellular recordings, the very high impedances will present a
definite problem with electrical radiation and magnetically-induced
currents. Implanted depth electrodes would fall nearer to the surface
electrode case.
-Jay
--
x------- Jay Kadis ------- x ---- Jay's Attic Studio ----x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x---------- http://ccrma.stanford.edu/~jay/ ------------x
Scott Dorsey
>
>actually, the sound chamber is about less than a cubic meter. The
>speaker should be put very close (a few centimeters) to the ear of an
>animal (a guinea pig), which should prevent the chamber to
>dramatically influence the frequency response, well, at least, I
>hope...
Sort of.
At high frequencies, any driver is very beamy, which means the position the
animal is in will affect the sound.
At low frequencies the box acts like a sealed chamber whose pressure changes
uniformly with excitation.
At some point in the midrange you will have standing wave issues with the
box. You can do the mode calculations for yourself, but making the box
smaller raises the resonance issues.
>The speaker probably has to be passive because powered speakers would
>introduce 60 Hz signals within the chamber (we perform
>electrophysiological recordings).
>A one way speaker would be best, but a two way speaker is likely
>possible if we put the tweeter in front of the animal's ear, since low
>frequencies have less directional properties I think.
In fact, the only way to get reasonably accurate response measurements of
the ear is to use a headphone or something similar, where the ear canal is
sealed or is part of a chamber of fixed volume.
>I found this model that may be of interest, what do you think about
>it ?:
>http://www.tannoy-speakers.com/products/66/CMS%20401%20DCe_Data_File_Web%20V1.06.pdf
I have never actually used one. I will say that the standard Tannoy
dual-concentric drivers are susprisingly constant directivity, but the
tweeter on this one is very dramatically different than their usual
dual concentrics.
This is not a small speaker, though.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Boris Gourevitch
> In article <g4iuh2$eq1$2...@usenet01.srv.cis.pitt.edu>,
[...]
>
>
> Is the animal restrained?
yes
> What kind of electrophysiological measurements
> are you making?
>
intracellular recordings. I'm concerned with the shielding actually.
> Electrode/skin impedances are fairly low, although the preamp gain is
> substantial for EEG signals with surface electrodes. If you're doing
> intracellular recordings, the very high impedances will present a
> definite problem with electrical radiation and magnetically-induced
> currents. Implanted depth electrodes would fall nearer to the surface
> electrode case.
>
> -Jay
>
Boris
Jay Kadis
Boris Gourevitch <bo...@SUS-AU-SPAMpi314.net> wrote:
Is the animal in ear bars? There are hollow ear bars that allow sound
to reach the ear canal, but I would think there would be resonances in
them that could alter the spectrum of the delivered stimulus.
Intracellular recording means noise if you bring powered speakers into
the shielded enclosure, so you are right about using passive speakers.
Tightly twisting the wires should cancel most of the electric field. I
would try using an ear bud driver attached to the hollow ear bar, but
finding 40 kHz-capable ear buds might be a problem.
You will find that using any speaker in a closed box, even one made of
screen, creates resonances you don't want. That would indicate that a
small driver placed as closely to the the guinea pig's ear as possible
is desirable.
Have you checked the literature for how others have delivered auditory
stimuli for intracellular recording? The guinea pig is a common animal
in auditory studies and I would think someone has worked this through
before.
Scott Dorsey
>Is the animal in ear bars? There are hollow ear bars that allow sound
>to reach the ear canal, but I would think there would be resonances in
>them that could alter the spectrum of the delivered stimulus.
Yes, but it's possible to quantify that.
It's also possible to have in-ear plugs that block the ear canal. Take
a look at the typical custom-molded hearing aid. You can take the same
Kistler or Knowles armature transducers that the hearing aid guys use
and make molds for animals.
Those things are not designed to go above 20 KHz... you might be able
to make it work, though, but you'll need to do some sweep testing.
>Intracellular recording means noise if you bring powered speakers into
>the shielded enclosure, so you are right about using passive speakers.
>Tightly twisting the wires should cancel most of the electric field. I
>would try using an ear bud driver attached to the hollow ear bar, but
>finding 40 kHz-capable ear buds might be a problem.
I'd make a phone call to Knowles. They can do it, though how much it'll
cost I don't know. You will sacrifice some lower frequency performance
if they make the armature smaller.
>You will find that using any speaker in a closed box, even one made of
>screen, creates resonances you don't want. That would indicate that a
>small driver placed as closely to the the guinea pig's ear as possible
>is desirable.
Well, it depends on what frequencies you really care about. Because
as I said earlier, with a sealed box you wind up with good performance
at low frequencies and good performance at high frequencies, and a
range in-between where all hell breaks loose. But you can quantify where
that range is easily.
>Have you checked the literature for how others have delivered auditory
>stimuli for intracellular recording? The guinea pig is a common animal
>in auditory studies and I would think someone has worked this through
>before.
The guinea pig is very small. Not lots of room in there.
bobopi
>
> Intracellular recording means noise if you bring powered speakers into
> the shielded enclosure, so you are right about using passive speakers.
> Tightly twisting the wires should cancel most of the electric field. I
> would try using an ear bud driver attached to the hollow ear bar, but
> finding 40 kHz-capable ear buds might be a problem.
>
> You will find that using any speaker in a closed box, even one made of
> screen, creates resonances you don't want. That would indicate that a
> small driver placed as closely to the the guinea pig's ear as possible
> is desirable.
>
> Have you checked the literature for how others have delivered auditory
> stimuli for intracellular recording? The guinea pig is a common animal
> in auditory studies and I would think someone has worked this through
> before.
>
> -Jay
actually, I've checked that and there are mostly three cases:
- use of two way speakers, sometimes very far from the animal. Want to
avoid that given the room size.
- use of a microphone as a speaker (bruel and kjear 4134 in general).
Don't understand how it can work given the small size of the product.
- use of headphones. I start to think that this is the best solution.
I started a new post about headphones.
Boris
Dutch Treat
> In article <69cd5797-ad91-4fa0-800e-5c99bf2f6...@b1g2000hsg.googlegroups.com>, bobopi <bo...@pi314.net> wrote:
>
> >Hi everyone,
> >I'm currently working in a lab dealing with auditory perception and
> >biology. Since I have a very small sound chamber, I need a flat and
> >compact loudspeaker with a frequency ranger extending from, say, 125
> >Hz or 150 Hz to 40 kHz. The depth of the speaker should not be above 6
> >or 7" (15 to 17.5cm). In a nutshell, something like the Fostex PMO.4
> >but flatter and slightly shifted to higher frequencies:
> >l
> >Do you have an idea ?
> >thank you in advance
> >Boris
>
> How flat and it must be on axis, right ? How far away ?
> I crosposted.
>
> greg
Look for a speaker with a planar magnetic (flat membrane) tweeter.
They are the only kind of tweeters that have a low enough
reciprocating mass to reproduce 40 KHz.
RD Jones
> Look for a speaker with a planar magnetic (flat membrane) tweeter.
> They are the only kind of tweeters that have a low enough
> reciprocating mass to reproduce 40 KHz.
Not strictly true.
A piezo responds well beyond 40k.
Nowhere near flat, though.
rd
Arny Krueger
news:75996053-9e09-402a...@j1g2000prb.googlegroups.com
> Look for a speaker with a planar magnetic (flat membrane)
> tweeter.
> They are the only kind of tweeters that have a low enough
> reciprocating mass to reproduce 40 KHz.
Yet another audiophile myth. :-(
Examples of one of the other kinds of speakers that use vastly different
construction and reproduce up to and beyond 40 kHz...
http://www.tymphany.com/files/products/pdf/XT25SC60-04.pdf
William Sommerwerck
news:TKmdncFjv-orMxTV...@comcast.com...
> http://www.tymphany.com/files/products/pdf/XT25SC60-04.pdf
That is remarkable performance -- especially from a non-metal driver.
But, Arny, you are (probably unintentionally) parroting the Bose Lie -- that
the mass of a driver doesn't matter, as long as we have sufficient force to
accelerate it.
I don't have to hear this driver to be reasonably certain it's not as good
as an electrostatic or ribbon, and definitely not as good as the
Plasmatronics. The mass (or more accurately, the unit mass) of a driver has
a significant effect on its performance -- that is, how it sounds.
Scott Dorsey
RD Jones <ann...@juno.com> wrote:
The speaker is the least of your worries.
Play back a 10KHz tone on a speaker, and turn your head to the side. Notice
that the level changes dramatically as you move your head.
The same thing happens even more dramatically at 40 KHz, although it is
less of an issue if your ear canal and head is smaller (like that of a
guinea pig).
Arny Krueger
message news:ps6dnZ8oXu7jJxTV...@comcast.com
> "Arny Krueger" <ar...@hotpop.com> wrote in message
> news:TKmdncFjv-orMxTV...@comcast.com...
>> "Dutch Treat" <atdutc...@comcast.net> wrote in message
>> news:75996053-9e09-402a...@j1g2000prb.googlegroups.com
>
>>> Look for a speaker with a planar magnetic (flat
>>> membrane) tweeter.
>>> They are the only kind of tweeters that have a low
>>> enough reciprocating mass to reproduce 40 KHz.
>
>> Yet another audiophile myth. :-(
>> Examples of one of the other kinds of speakers that use
>> vastly different construction and reproduce up to and
>> beyond 40 kHz...
>> http://www.tymphany.com/files/products/pdf/XT25SC60-04.pdf
> That is remarkable performance -- especially from a
> non-metal driver.
> But, Arny, you are (probably unintentionally) parroting
> the Bose Lie -- that the mass of a driver doesn't matter,
> as long as we have sufficient force to accelerate it.
That's not a lie. However there *is* a goodly list of caveats., the biggest
one I discuss a few paragraphs down.
> I don't have to hear this driver to be reasonably certain
> it's not as good as an electrostatic or ribbon, and
> definitely not as good as the Plasmatronics. The mass (or
> more accurately, the unit mass) of a driver has a
> significant effect on its performance -- that is, how it
> sounds.
One of the *big* caveats is that a large piston is far more directional than
a small one.
The Bose 901 drivers have very large diaphragms if they were to be good
tweeters. As you observe, they aren't very good tweeters, even when
equalized for flat on-axis response.
Based on practical experience, the XT25 tweeter is as about as flat as they
claim - on axis. Off-axis they aren't nearly as bad as the Bose 901 drivers,
but all the bad effects are merely shifted up, they don't go away.
Speakers and mics are sold with on-axis response curves, while their
real-world sound quality includes very heavy contributions from their
off-axis response.
William Sommerwerck
What Arny says is largely correct, but it has little to do with the point I
was trying to make.