Aperiodic for really high Q

[mashaffer]

I have this nice dual cone 10" (see attached) that I wanted to use for a floor monitor but the parameters seem only fit for an open back design. Is there any point in trying an aperiodic loading for it? Some other lossy design maybe? Realy short, wide, stuffed TL?

mike

[kelticwizard]

Vas is 12 cu ft. Fs is 86. Xmax is only 0.12 in, (3 mm). If you put this thing in even a 3 cu ft box you end up with a 7 dB peak at 192 Hz-very audible, and a plunging response under that.

I really don't see this being used in any box smaller than a closet.

You said this was a dual cone speaker. Is it dual cone or dual voice coil? If it is dual voice coil, and these are the specs if only one coil is connected, then this speaker might be usable in a box.

Otherwise, forget it.

[sreten]

Hi,

As stated the Vas of 12 cuft is incredibly high for a 10" driver of 86Hz Fs.

It indicates for an 8.5" diameter cone driver a cone mass of 2g.

http://www.madisound.com/pdf/fostexd...206esr-rev.pdf

Whilst the above has a cone mass of 12g.

If it really is 2g completely forget about a box, must be open backed.

/sreten.

[mashaffer]

That is what I was afraid of.

These parameters seemed extreme to me also so I will remeasure them again before I do anything. My measurement system was definitely jury rigged and I may have not gotten it quite right. However it was from an open baffle application.

mike

[mashaffer]

Back side

[alan-1-b]

mashaffer,

you can use that driver in a floor monitor - I have used 2 different ones of similar type to that one in wedge shaped floor monitors.

Make the floor monitor as large as it can be in the practical application you will be using it for.

Make it a tightly sealed enclosure. Use a gasket around each driver, and around any removeable panels.

Stuff it, but as follows:- use Acoustistuf or similar, or Fibreglass, or Rockwool.
Cut the stuffing to sizes and arrange it in the enclosure so that open cut edges face the back of the driver.
This can include 1 piece {or 2 pieces if it is a thin substance} cut to fit against the inside of the front baffle around the driver and with a round hole cut in for the driver's back to extend through.

Use sufficient number of pieces so that each supports the other firmly so that none can move around, but do NOT stuff too tightly, as that will effectively reduce the internal size Acoustically !

That is, do not heavily compress the pieces, but a little compression only so that all will stay in place and not flop about as a large mass inside the enclosure when the speaker is operating, because any large mass flopping will Load the driver in such way as to reduce its peformance.

Making an Aperiodically damped enclosure is a lot of work and with this high Q, low Xmax, driver it will be very dfficult to predict the results, thus it would be mostly a make-first then find out situation !

TL is even more work, and it will be large size for that driver !

Do NOT attempt to use that driver in a vented enclosure, and I don't think you were intending to ...

If excess bass, then apply some EQ to reduce. It will not give high volume levels at low frequencies, but you will be able to get some audible bass response from it.

What is the Monitor for ... Vocal , midrange & treble ... or bass instruments ?

regards,

[mashaffer]

Alan;

Thanks for the input. I am tempted to put something together to try. BTW I should point out that the specs I included had total guesses for power capability, xmax, inductance and sensitivity. I had to have something in there to do the sims so took default or guessed. I suspect xmax is actually a little bit higher. Original application was the Orbit synth on a wurlitzer organ.

It would be used for a vocalist and will have the vocal and acc in the mix. Should have clean enough bass to not confuse the user but hifi not needed.

I was originally going to use it along with 15" from the same instrument to make a keyboard amp but interestingly the 15 is 8 ohm while this one is 16. It turns out that the organ used the 15 crossed over to a 6x9 for the main channel and used this 10 as a FR for the built in synth.

mike

[mashaffer]

I just came upon this article in which the author used a parallel resistor to lower the Q of a driver. Since the driver I have was free I am tempted to experiment with this in full knowlege that the efficiency will be lowered and the load on the amp greater (though I am starting with a 16 ohm driver).

Does anyone know the math to calculate a target resistance?. I will probably try different values but it would help to have an idea of where to start. I presume that high power non-inductive is the order of the day here.

mike

[sreten]

Originally posted by mashaffer
I just came upon this article in which the author used a parallel resistor to lower the Q of a driver. Since the driver I have was free I am tempted to experiment with this in full knowlege that the efficiency will be lowered and the load on the amp greater (though I am starting with a 16 ohm driver).

Does anyone know the math to calculate a target resistance?. I will probably try different values but it would help to have an idea of where to start. I presume that high power non-inductive is the order of the day here.

mike

Hi,

Not to put too fine a point on it, the parallel resistor will do nothing.
(It will if you have current drive, but then q is far higher anyway.)

The article is written by someone with very limited knowledge.

/sreten.

[bjorno]

sreten:

It indicates for an 8.5" diameter cone driver a cone mass of 2g.

True, and near 105 dB SPL sensitivity (BL= 3.66 N/A) or if the sensitivity actually is 90 dB then Mmd is about = 58 g and Vas about 11 L (0.39 cu feet) BL = 20 N/A. The conclusion is: The T/S data seems to be corrupt.

alan-1-b:

Making an Aperiodic damped enclosure is a lot of work and with this high Q, low Xmax, driver it will be very difficult to predict the results, thus it would be mostly a make-first then find out situation !

I don’t agree prediction can quite easily be done, but first you need consistent data before you can state anything trustworthy or give any rec. how to apply damping to this driver or the actual behaviour in any box size.

TL is even more work, and it will be large size for that driver!

No, Not before we know reliable data, nothing can be estimated and it’s easy to simulate an aperiodic enclosure using MJK: s programs.

Do NOT attempt to use that driver in a vented enclosure, and I don't think you were intending to ...

There is no reason to avoid building a vented enclosure and then turning into any aperiodic type as there is no difference whether you start with a closed or vented box when applying aperiodic damping methods.

Almost any high Qts driver can be tamed in an aperiodic enclosure, Richard Small gives 8 methods to cure the system Q: s;

1. Acoustic Damping of the Driver,
2. The Resistance-Coupled Double-Cavity Closed-Box System,
3. The Leakage -Damped Closed Box System,
4. The Damped –Vent System,
5. The Leakage-Damped Vented-Box System (ARU),
6. The Absorption-Damped Vented Box System,
7. The Damped Box Damped –Vent System (Aperiodic)
8. The Double-Cavity Vented-Box System.

The best methods for low X-max FR/WR drivers are 1 and 3 and all can all be checked out with MJK:s program or by using an acoustic cad tool like sound Easy:s Box-Cad or others.

As damping depends on the material in use the only difference using MJK: s program is often a simple scale- factor and FR dependent attenuation/damping slopes that must be taken into account.

From the pictures it looks that the drivers are stiff and sturdy enough to start trying with acoustic driver damping and if successful stay with this and/or maybe followed by leakage damping of the rest of the enclosure but on the contrary avoiding any suggested absorption damping as this method is more suited to incorporate with heavier cones with large x-max: s.

sreten:
….The article is written by someone with very limited knowledge.

Agree.

b