Transcript
JAZZMAN
Jazzman
Scan Speak 22W/8857T00 + 15W/8530-K00 + Vifa XT25TG30-04 (- or ScanSpeak R2904/832000)
Copyright 2009 © Troels Gravesen
DRIVERS CABINETS CROSSOVER MEASUREMENTS CROSSOVER KIT
3-Way ScanSpeak made by www.snedkeri.dk for Sven Felsby/Denmark Sven Felsby: "This speaker was designed for maximal bass extension on a minimal footprint. As a result we end up with an expected sensitivity of 85dB/2.8V". So far, so good. Same midbass and tweeter as Ellam-XT, only here supplemented by an 8" dedicated bass driver taking us all the way down to 30 Hz. The price to pay is modest sensitivity, but impedance stays above 6.5 ohms and phase angles are modest, so no problem for a good minimum 100 wpc solid state amp.
DRIVERS
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Click here to download specs: 22W/8857T00, 15W/8530K00, R2604/832000
The Cabinet BACK TO INDEX
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Box simulation. Click image to view large. Please note that even LspCAD is wrong about vent length calculation. For Fb = 25 Hz, the vent has to be 70 mm (ID) x 290 mm.
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Bitumen on most internal surfaces. Egg crate foam in midrange chamber, upper bass chamber and on top plate. MDM-3 synthetic wool in midrange chamber and behind tweeter (acting as wave trap) To tune the port to 25Hz, the port has to be placed vertically. Use a flanged port to minimize chuffing. Minimum distance to floor is 40 mm.
Volumes:
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Inner dimension with 4 mm bitumen pads on all internal panels are: 198 mm (W) x 274 mm (D) x 898 mm (H) = 48.7 liters (42.4 liters netto) Port, drivers, bracing and crossover is likely to occupy some 1-2 liters, thus close to 40 liters netto. Midcap outer dimensions: 198 mm (W) x 170 mm (D) x 186 mm(H) = 6.3 liters. Midcab net volume: 206 mm x 148 mm (D) x 154 mm (H) = 4.7 liters.
The Crossover BACK TO INDEX
Due to low efficiency of the bass driver, some attenuation is required for the midrange, hence paralleled 10 watt MOX resistors in midrange section. These will stay cool even at high playback levels.
CROSSOVER KIT BACK TO INDEX
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Complete crossover kit incl. ports available from Jantzen Audio:
[email protected] The crossover made from the very best components is not particularly cheap. The 68 uF in the bass section can be standard MKP. No need to use super caps here. The 32 uF is important and so are the tweeter caps. Sorry, no free ride if you want to squeeze the final micro details out of your recordings. List includes additional 3R9 and 4R7 resistors to fine-tune treble level to personal taste and room conditions. 3.3 mH has to be as low-ohmic as possible. Use a good cored inductor. The 5.6 mH can be from 1 mm wire, cored or air cored and DCR = 0.5-1.5 ohm, no big deal.
Measurements BACK TO INDEX
Measurements may give us an idea of tonal balance of a system, i.e. too much or too little energy in certain areas. Measurements may tell us about bass extension if far-field measurements are merged with near-field measurements. In addition to this ports may contribute to bass extension. Most of us diy'ers do not have access to an anechoic room for fullrange measurements from 20-20000 Hz. What cannot be seen is what kind of bass performance we get in a given room. Bass performance is highly dependent on in-room placement of your speaker and the same speaker can be boomy in one place and lean in another. Actual SPL level at 1 meter distance and 2.8V input is useful for en estimate of system sensitivity and combined with the impedance profile may give an idea of how powerful an amplifier is needed to drive the speaker to adequate levels. What measurements do not tell is the very sound of the speaker unless displaying serious linear distortion. The level of transparency, the ability to resolve micro-details, the "speed" of
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JAZZMAN the bass, etc., cannot be derived from these data. Distortion measurements rarely tell anything unless seriously bad and most modern drivers display low distortion within their specified operating range. Many people put way too much into these graphs and my comments here are only meant as warning against over-interpretation. There are way more to good sound than what can be extracted from a few graphs. I think I speak for all of us doing speaker measurements when I say that we learn new things every time we do one. Every graph needs interpretation in terms of what it means sonically and how it impacts our choice of mating drivers, cabinet and crossover design.
Left: Response from drivers in cap without crossover. XT25 smooth as always. 15W.... remarkable driver. Really goes up to 10 kHz without any trouble. 22W: Doesn't start breaking up until 3-5 kHz. Excellent from an 8" alu cone.
Left: SPL @ 1 meter, 2.8 volts. System sensitivity = 85 dB. Reading merged with bass nearfield response at 250 Hz. Right: Impedance doesn't go below 6.5 ohms. Maybe even a 50+ watt PP valve amp may do well here.
Left: Point of crossover between mid and tweeter is 3200 Hz. Right: Blue = reverse mid polarity at tweeter height, 1 meter distance.
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Point of crossover between bass and mid is around 500 Hz with shallow slopes on both drivers.
Left: Horizontal dispersion at 0, 10, 20 and 30 deg. (red/blue/green/purple) Right: Vertical dispersion at 1 meter from 10 cm above tweeter height (red) to bass height (purple). Overall this speaker provides an even power response. No hot-spot here.
CSD at 20 and 40 dB scaling. BACK TO INDEX
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