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Design of analog audio filters for individual speaker models in a distributed system

Saranpää, William LU and Alveteg, Simon LU (2025) EITM01 20251
Department of Electrical and Information Technology
Abstract
This thesis investigates the performance and feasibility of passive and active analog frequency compensation filters for audio signal processing in a distributed
speaker system. One passive and one active circuit topology were investigated
more thoroughly and then the active filter was realized on a PCB and evaluated
with electrical, thermal and acoustic measurements.

The work also resulted in two methods of designing frequency compensating
or equalizing filters based on active or passive filters respectively. The design was
partly automated with the use of optimizing algorithms that integrated with a
LTSpice model of different circuits. The active filters were based on a constant-
Q graphic equalizer topology, and performed... (More)
This thesis investigates the performance and feasibility of passive and active analog frequency compensation filters for audio signal processing in a distributed
speaker system. One passive and one active circuit topology were investigated
more thoroughly and then the active filter was realized on a PCB and evaluated
with electrical, thermal and acoustic measurements.

The work also resulted in two methods of designing frequency compensating
or equalizing filters based on active or passive filters respectively. The design was
partly automated with the use of optimizing algorithms that integrated with a
LTSpice model of different circuits. The active filters were based on a constant-
Q graphic equalizer topology, and performed better than the passive bridged-T
based topologies in relation to flattening the speaker's frequency response. The
passive filters had less power dissipation and produced less noise than their active
counterparts, at the expense of lower selectivity as well as a lower output volume
due to the added insertion loss. The design of the active filters was also quicker
and gave more reliable results.

The filters were evaluated on two different speakers with different frequency
responses in order to ensure the generality of the method. The passive filters could
reduce the average deviation from 3.52 dB to 1.68 dB for speaker 1 and from 2.64
dB to 1.58 dB for speaker 2, while the active filter with 16 filter sections could
reduce it to 1.57 dB for speaker 1 and 0.82 dB for speaker 2. Further reduction is
most likely possible, as manual adjustment of just five filter sections brought the
average deviation down from 1.75 dB to 1.63 dB for speaker 1.

Analog filters are a viable option for applications where the power budget, cost
or limitations in signal availability or routing pose challenges. The method created
simplifies the design process of equalizing filters and reduces the engineering time
needed. (Less)
Popular Abstract (Swedish)
Sannolikheten att det finns en högtalare nära dig är hög. De finns där för att spela
musik i en affär, för att meddela att brandlarmet har gått i byggnaden du befinner
dig i eller för att berätta att tåget du ska åka med är inställt. Alla högtalare låter
på lite olika sätt, de har sina egna skavanker som gör att en viss frekvens kanske
låter lite mer än andra. I detta projekt har vi funderat på detta och undersökt
hur man kan kompensera olika högtalares egenheter med analoga filter för att få
ett platt frekvenssvar, det vill säga att alla frekvenser låter lika högt.
Det är nu för tiden vanligt att högtalare frekvenskompenseras digitalt med
något datorchip. Detta kan bli problematiskt för vissa sorters högtalarsystem
där det finns... (More)
Sannolikheten att det finns en högtalare nära dig är hög. De finns där för att spela
musik i en affär, för att meddela att brandlarmet har gått i byggnaden du befinner
dig i eller för att berätta att tåget du ska åka med är inställt. Alla högtalare låter
på lite olika sätt, de har sina egna skavanker som gör att en viss frekvens kanske
låter lite mer än andra. I detta projekt har vi funderat på detta och undersökt
hur man kan kompensera olika högtalares egenheter med analoga filter för att få
ett platt frekvenssvar, det vill säga att alla frekvenser låter lika högt.
Det är nu för tiden vanligt att högtalare frekvenskompenseras digitalt med
något datorchip. Detta kan bli problematiskt för vissa sorters högtalarsystem
där det finns olika typer av begränsningar som exempelvis strömförbrukning eller
kostnad. Därför undersöker detta arbete en lite äldre teknik, nämligen att frekven-
skompensera med analoga filter.

Analoga filter kan delas upp i passiva eller aktiva filter. Passiva filter har
oftast bara komponenter som motstånd, kondensatorer, och spolar medan aktiva
filter även kan innehålla förstärkare. Det visar sig att båda sorterna har för- och
nackdelar, men om man vill platta till frekvenssvaret och hålla ljudvolymen lika
hög, är aktiva filter det bättre valet.

Detta arbete har kommit fram till att det finns situationer där de äldre analoga
filtrena är ett bra val för att filtrera signaler till högtalare. De är ofta billigare,
det går fortare att utveckla dem samt att de kan vara mer energieffektiva. En
annan fördel är att varje högtalare kan byggas på ett enklare sätt, man behöver
inte programmera varje högtalare i rummet för att allt ska låta bra. Digitala filter
presterar bättre i frekvenskompensering jämfört med analoga filter, men ibland
behövs inte all prestanda utan bara tillräcklig. Därför bör den lite äldre tekniken
inte förbises i alla situationer, utan ingå i utvecklingsfasen då det, beroende på
situationen, kan vara det bättre alternativet. (Less)
Please use this url to cite or link to this publication:
author
Saranpää, William LU and Alveteg, Simon LU
supervisor
organization
course
EITM01 20251
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Analog filters, speaker systems, active filters, passive filters
report number
LU/LTH-EIT 2025-1053
language
English
id
9194730
date added to LUP
2025-06-09 10:38:41
date last changed
2025-06-09 10:38:41
@misc{9194730,
  abstract     = {{This thesis investigates the performance and feasibility of passive and active analog frequency compensation filters for audio signal processing in a distributed
speaker system. One passive and one active circuit topology were investigated
more thoroughly and then the active filter was realized on a PCB and evaluated
with electrical, thermal and acoustic measurements.

The work also resulted in two methods of designing frequency compensating
or equalizing filters based on active or passive filters respectively. The design was
partly automated with the use of optimizing algorithms that integrated with a
LTSpice model of different circuits. The active filters were based on a constant-
Q graphic equalizer topology, and performed better than the passive bridged-T
based topologies in relation to flattening the speaker's frequency response. The
passive filters had less power dissipation and produced less noise than their active
counterparts, at the expense of lower selectivity as well as a lower output volume
due to the added insertion loss. The design of the active filters was also quicker
and gave more reliable results.

The filters were evaluated on two different speakers with different frequency
responses in order to ensure the generality of the method. The passive filters could
reduce the average deviation from 3.52 dB to 1.68 dB for speaker 1 and from 2.64
dB to 1.58 dB for speaker 2, while the active filter with 16 filter sections could
reduce it to 1.57 dB for speaker 1 and 0.82 dB for speaker 2. Further reduction is
most likely possible, as manual adjustment of just five filter sections brought the
average deviation down from 1.75 dB to 1.63 dB for speaker 1.

Analog filters are a viable option for applications where the power budget, cost
or limitations in signal availability or routing pose challenges. The method created
simplifies the design process of equalizing filters and reduces the engineering time
needed.}},
  author       = {{Saranpää, William and Alveteg, Simon}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Design of analog audio filters for individual speaker models in a distributed system}},
  year         = {{2025}},
}