A Phase Linear Transmission Line Project

Section 4: Room integration

Room gain is the LF gain that a normal listening room adds to the signal. The gain varies from room to room and with speaker placement. For a free standing speaker, it can look something like the graph in Figure 4.1.

Authors like Ohman, Bacon, and Colloms have described low frequency alignments that would suit the listening room. The alignments differ according to the cut off frequency. High cut off frequencies requires a higher Q for the tonal balance to be neutral. Low cut offs favors lower Q.

Room curves are very similar to the output of a transmission line with the graduall rolloff.

It should be noted that the room response is always significantly different from the on-axis response. Peaks and dips are often of the +-10dB magnitude!

Several measurements were taken for both speakers with increasing distance to the back wall. The listening room of interest is particularly difficult being assymmetrical with a reflecting wall on the left side and a open space on the right side.

The measurements were done using a 20ms window in the preferred listening position.

room3_tn.jpg (20673 bytes)

Figure 4.1. Room gain after Colloms.

Figure 4.2-4.9 covers the right speaker

Figure 4.10-4.14 covers the left speaker

For the right speaker, placement is not very sensitive up to 30 cm from the wall. Distances from 40-70cm sucks out the low frequencies. Greater distances than 70cm still have good lf extension.

wall1_tn.gif (30202 bytes)

Figure 4.2. Right speaker 0 cm from wall.

wall2_tn.gif (30202 bytes)

Figure 4.3. Right speaker 10 cm from wall.

wall3_tn.gif (30202 bytes)

Figure 4.4. Right speaker 20 cm from wall.

wall2_tn.gif (30202 bytes)

Figure 4.5. Right speaker 30 cm from wall.

wall5_tn.gif (30202 bytes)

Figure 4.6. Right speaker 40 cm from wall.

wall6_tn.gif (30202 bytes)

Figure 4.7. Right speaker 50 cm from wall.

wall7_tn.gif (30202 bytes)

Figure 4.8. Right speaker 70 cm from wall.

wall8_tn.gif (30202 bytes)

Figure 4.9. Right speaker 100 cm from wall.


The left speaker is a bit more difficult to place, being in a corner position. 20-30 cm from the back wall gives the best result.

Placing both speakers 20-30cm from the back wall seem to give the best results for the measured listening position in this living room. This agrees closely with listening observations.

(The PLTL is intentionally optimized for a placement rather close to the wall. )

corner1_tn.gif (30202 bytes)

Figure 4.10. Left speaker 0 cm from wall.

corner2_tn.gif (30202 bytes)

Figure 4.11. Left speaker 10 cm from wall.

corner3_tn.gif (30202 bytes)

Figure 4.12. Left speaker 20 cm from wall.

corner4_tn.gif (30202 bytes)

Figure 4.13. Left speaker 30 cm from wall.

corner5_tn.gif (30202 bytes)

Figure 4.14. Left speaker 40 cm from wall.

corner1_tn.gif (30202 bytes)

Figure 4.15. Left speaker 50 cm from wall.

corner7_tn.gif (30202 bytes)

Figure 4.16. Left speaker 70 cm from wall.


[ ContentsIntro | Measurements | Optimization | Integration | Step Compensation | Time Align | Construction ]