Exciters
Precautions & Guidelines
Design Manual for Applications using Peerless Exciters.CONTENT:
1. BACKGROUND AND OBJECTIVE
2. GENERAL DESIGN INSTRUCTION
3. TEST INSTRUCTION OF THE EXCITER IN FREE AIR
4. DESIGN SPECIFICATIONS FOR THE HIGH-PASS FILTER
5. OVERLOAD PROTECTION
6. OTHER DESIGNING RULES
7. MOUNTING THE EXCITER ON TO THE PANEL
8. PRECAUTIONS REGARDING TRANSPORTATION
8.1 FREE EXCITER SYSTEM
8.2 GROUNDED EXCITER SYSTEM
8.2.1 Technical description
8.2.2 Mounting instruction
1. Background and objective
The Peerless exciter is a high performance exciter and has very good sound reproduction no matter what panel material you are using even in the high frequency area. One of the reasons for these fine qualities is the special designed and optimized suspension for which you must take some precautions when you are designing the final product. These precautions are described in this document.It is the objective for this design manual to guide the product designer/user in using the 26 mm Peerless exciters in a way that
- the optimized design is reached without damaging the exciter by normal use.
- the exciter in the final product is not damaged during transit.
- the exciter is not damaged during testing before mounting in the final product.
2. General design instruction
It is very important to act up to these guidelines regarding maximum excursion during your design to prevent damaging of the suspension during normal use.Normally when the NXT speaker operates in true DML-mode the excursion between the exciter and panel is very small even at high SPL.
The suspension in the Peerless exciter is
designed for excursion up to 0.1 mm (the lifetime is 8). If the excursion is higher, the lifetime for the suspension will be reduced. It is therefore very important that you, during your
design work, are testing your final product for resonances which can give large excursions between the exciter and the panel. A general procedure is to sweep by sinus soidal the final design and observe or measure the excursion.
3. Test instruction of the exciter in free air
It is very important to act up to these guidelines regarding test to prevent damaging of the suspension.If you test the exciter before mounting it in the final product please pay attention to the fact that testing with large excursion is damaging the suspension.
We recommend a sweep test voltage for the exciter in free air to be
max. 3.5 volt for the 4 ohm exciter (880102)
max. 5.0 volt for the 5/8, 8 and the 16 ohm exciter (880101, 880103 and 880104)
in the frequency area 500-20.000 Hz which corresponds to as excursion up to 0.5 mm. It is very important that this test is done quickly (max 10 seconds).
4. Design specifications for the high-pass filter
It is very important to use a high-pass filter together with the Peerless exciters in the final product as this will prevent damage of the suspension during normal use. The system powerhandling is greatly improved also.Below a certain frequency, the NXT-speaker will begin to act like a piston instead of the true DML-mode and the SPL will drop very fast.
Normally you can use the NXT-speaker from 3x F0 of the panel, where the F0 is the first mode in the panel. F0 is describe in the NXT Designer Manual.
Also the frequency response of the NXT speaker can tell you where the cut off frequency for the high-pass filter has to be placed: The recommendation is exactly where the curve in the low end begins to drop off.
The fundamental resonance of the exciter mounted on a panel is about 55 Hz. At this frequency the excursion of the exciter is large.
The high-pass filter will also protect the exciter from large excursion in the fundamental resonance frequency.
We recommend that the damping in the fundamental resonance is at least 15-20 dB.
The first order filter is 6 dB/oct - if the damping has to be -15 dB at the fundamental resonance the cut-off frequency has to be minimum 220 Hz.
The second order filter is 12 dB/oct - the cut-off frequency has to be minimum 110 Hz.
Examples of high-pass filters to the Peerless exciter 880101 cut-off frequency at 250 Hz:
1'order: C=150F
2'order: C=100F and L=3mH
The high-pass filter will raise the power handling of the exciter by filtering the frequencies where the NXT-speaker acts like a piston and for that reason does not have any acoustical output.
5. Overload protection
It is recommended to build in an overload protection in the NXT speaker e.g. by using a PTC-resistor to prevent the end-user from overloading the exciter.In conventional speakers the limit in power handling is apparent by audible distortion. Normally the user will turn the volume down on the amplifier and thus prevent damaging the speakers. In NXT speakers this limit is not audible apparent, therefore we recommend to build in a PTC-resistor in series with the exciter. The PTC-resistor has to have a cut-off current at 1.0 A (e.g. MF-050 from Bourns Inc. or equivalent).
6. Other designing rules
We recommend that the general designing rules and advises are followed. These are given by NXT during licensee courses, the NXT Designer manual and the application notes given by NXT.If you have any questions to the material or others, please contact us.
7. Mounting the exciter on to the panel
We recommend to use a glue called Loctite 480 + activator or the 3M CA-50 Gel + activator.The 3M one is a gel which is very easy to dose.
It is very importent when CA-glue is used that you do not use to much of the glue and together with an activator.
The activator that we recommend is called TAK-PAK (accelerator #7452) from Loctite.
Mounting the exciter with CA-glue.
1) add the accelerator to the panel in a circle where the exciter has to be mounted.
2) add 8 small dots of glue to the 8 feets of the exciter.
3) place the exciter on to the panel. After 20 seconds the glue is hardened and the exciter sticks to the panel.
8. Precautions regarding transportation
It is our experience that the exciter has to be protected during heavy transportation handling to prevent damaging the suspension or to prevent the panel material to delaminate, where the exciter feets are mounted to the panel. The following describes which precautions you have to take in your design of your NXT-speakers.8.1 Free exciter system
If the exciter is mounted with free magnet system it is very important that the exciter is efficiently secured in both horizontally and vertically during transportation. The securing has to be taken off before use by the end-user.8.2 Grounded exciter system
Another way to secure the exciter is to ground the magnet system to another stable part in the speaker e.g. the back part in the closed back system or a frame in an open back application.The following is a practical example of how to ground the exciter.
8.2.1 Technical description
A mechanical connection between the exciter and the closed back cabinet will increase the mechanical durability of the exciter under heavy transportation circumstances.A seal between the exciter and the closed back cabinet is recommendable because the sealer:
- takes up the tolerances between the frame/panel/exciter.
- is easy and simple to use.
- has compliance.
- can take up the mechanical energy under heavy transportation circumstances.
In this case we have chosen a seal from 3M which is a polyurethane based rubber like material, but similar sealers can be used.
8.2.2 Mounting instruction
Remove the steel plate in the back of the sealer (3M Scotch-Seal 5300) tube and take away the small water absorbing balls.1) Apply the sealer onto the cabinet on the place where it corresponds to the placement of the exciter when the cabinet is closed. Apply the sealer so plentiful that it will reach the back of the exciter when the cabinet is closed.
2) Put the panel with exciter in to the cabinet
3) Make sure that the sealer is reaching the exciter.
The sealer is drying/hardening by the natural humidity in the air. It is possible to test the speaker right after assembling. Droptest can be carried out after 24 hours.