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RE: 10" midbass at limit of Doppler IMD and smooth 90 degree polars

Piano is a devilishly complicated wavefront launching from sound boards up to 30 square feet. The radiator is a travelling wave membrane dipole with one side bounced roughly 90 degrees and shaped by the case curves. The best representation I have heard is the Yamaha AvantGrand, which uses a 4.1 sample/speaker system in a piano shaped case with angled lid to mimic the room interaction. The Steinway speakers use a dipole tweeter with the back wave bounced at the same angle to good effect. These people know pianos, listen and learn.

Setting aside the spatiality, a concert grand balances against a full orchestra broadband, which means 115dB peaks for accurate volumetric reproduction. In terms of commercially available speakers you are talking extreme horn systems, pro gear or the TADs, pretty much a minimum of 97dB efficiency. It is a percussion instrument which means extreme transients as well. Anything steeper than second order Bessel will lesson the impact so you need to move the drivers up in size without pushing uneven polar response or deleterious effects of diaphragm breakup.

Dipole configuration matches the directivity index of the instrument and maintains more consistent polar response than obtainable from either closed boxes or horns. Look for controlled breakup from curvilinear pulp cones like the 604. This produces a characteristic rising response as the mass loading on the voice coil goes down faster with increasing frequency than the effective diameter.

Next you need super low inductance. The Acoustic Elegance (Lambda) TD15M is <.3mH and rises up to 5KHz while maintaining reasonably wide dispersion because of the decreasing radiating area for the upper freqs. The limited Vd is OK because piano bass notes have very weak fundamentals. The cone is modeled after the 604 but it has a heavy Faraday and extended nose cone. These also help with the power compression, but the 15" cone is too floppy to have clear midrange.

The TPL150 is good from 1.5KHz to 5KHz with the back chamber removed but the vertical narrowing and lobing especially with the H model indicate you should cross to a supertweeter, perhaps a Fostex FT17H. This will keep the budget to $1K per speaker for drivers and crossover components.


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  • RE: 10" midbass at limit of Doppler IMD and smooth 90 degree polars - acuvox 21:57:56 04/30/12 (0)

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