Measuring Some Vintage Speakers

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Now some big speakers, starting with the biggest of the group. Polk Audio SDA SRS 2.3TL. 6x6.5" woofers, 15" passive radiator, 3x1" trilaminate tweeter. Strong bass, as you would expect.

I had to rebuild a couple of tweeters. It was very delicate work.

 

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Here's an ESS amt1 tower with 10" woofer in transmision line cabinet and the "great heil" air motion transformer tweeter. Strong bass and bright highs. 3 level tweeter setting. I preferred "Soft"

A few more pictures.

 

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Another big multi-driver tower. Definitive Technology BP2000TL. 15" powered subwoofer, 4x6.5" mid-woofers in bipolar D’Appolito array, 2x1" dome tweeter. I could have measured them better. The subwoofer was level was too high and the floor bounce problem at 150Hz was especially bad.

Here's the subwoofer amp and the slotted port. The port is small and was could get noisy at high volumes.

 

[bconline]

One more for today - the ever-contoversial Bose 901 Series VI Version 2. This model was the very last Bose 901. I didn't know how to measure it properly. So I just put it on it's tulip stands and set the mic on axis with the front driver. Othe people have done a much more thorough jobs of measuring the 901's. But here, I can compare it with other speakers under the same testing conditions. It does throw a wall of sound. Suprising amount of bass from small cabinet, if you have enough power.

 

[Head_Unit]

Yamaha NS1000M...a bit shy on bass. I thought about extending the cabinet and porting it, but didn't want to cut up this nice pair.

Definitely not. But if you stuff the enclosure well that would increase the apparent box volume, which plus a low-tuned port would *probably* extend the bass without boom. Ideally you would pull out the woofer and measure the Thiele-Small parameters to allow more concise simulations. How much to stuff? While still sealed, measure the impedance curve. Keep stuffing and measuring until the resonance frequency, after having decreased, starts to go back up. And leave several port diameters clear on the inside of the port. IIRC fiberglass is still kind aside from long hair wool which tends to settle. Pillow stuffing not effective. Acousta-Stuf effective albeit not free. Vance Dickason's Loudspeaker Cookbook had a section on stuffing in the 7th edition, probably in the newer pricier 8th edition as well.

 

[Vladimir Filevski]

I thought about extending the cabinet and porting it,

No! Crossover is the problem here and has to be redesigned.

 

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No! Crossover is the problem here and has to be redesigned.

Troels Gravesen did a complete crossover redesign here.

 

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Definitely not. But if you stuff the enclosure well that would increase the apparent box volume, which plus a low-tuned port would *probably* extend the bass without boom. Ideally you would pull out the woofer and measure the Thiele-Small parameters to allow more concise simulations. How much to stuff? While still sealed, measure the impedance curve. Keep stuffing and measuring until the resonance frequency, after having decreased, starts to go back up. And leave several port diameters clear on the inside of the port. IIRC fiberglass is still kind aside from long hair wool which tends to settle. Pillow stuffing not effective. Acousta-Stuf effective albeit not free. Vance Dickason's Loudspeaker Cookbook had a section on stuffing in the 7th edition, probably in the newer pricier 8th edition as well.

The woofer's T/S parameters have been measured. Those measurements supported a DIY project to extend the cabinet and port it. I was considering duplicating that effort and tried to contact the builder. In the end, I just couldn't cut the cabinets and ended up selling the pair to another NS1000M fan.

 

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Next are 3 small speakers with interesting features. The first is the Kef XQ One. Nice curved cabinets with piano finish. Ported, with 6.5" concentric Uni-Q driver, plus a 3/4" hypertweeter. The hypertweeter is a strange addition and claimed to respond from 15khz to 55khz!

Overall frequency response:

Nearfield of the Uni-Q driver and hypertweeter. Do you think we're going to get 55khz? Comb filtering problems?

 

[bconline]

This is a common Polk RTi6. 6.5" woofer with Power Port and 1" dome tweeter. In stock form, it was too bright. So I added a 3.3 ohm resistor in series with the tweeter. With the resistor, it does's sound bad for a generic old speaker. I like the real wood cherry finish.

Response with and without the 3.3 ohm resistor:

The interesting part is the second port on the front. Polk call it "Acoustic Resonance Control (ARC)". Description from Stereophile:

With Polk's Acoustic Resonance Control technology, a second port on the front of the speaker resonates at the same frequency as the cabinet's internal depth resonance. As the radiation of the front and rear ports are out of phase with respect to the drive-unit output, any resonance peaks are claimed to be suppressed.

I removed the drivers and discovered that the port tubes are about same length, but they are different diameters. What does it do? Here's the zoomed-in response with the ARC port (green) and without it (purple). It does seem to tame a midrange resonance, at the expense of a small amout of bass response.

Here's the near-field response of the driver (red), Power Port (green), and ARC port (blue). These are not scaled for radiating size, so the ARC port shows higher than should be. The two ports have a high resonance at slightly different frequencies. Maybe they are out of phase to cancel each other?

 

[bconline]

Last of the small bookshelf speakers... Klipsch The Sixes. Powered with 6.5" ported woofer and 1" tweeter with Tractrix horns. Strong boomy bass. Maybe using DSP??

People have questioned the quality of the different inputs. Here's the line input (purple), optical (orange), and bluetooth (red). Looks all the same to me.