Pioneer SP-BS21-LR - measured/deconstructed/modded

[bkeane1259]

Got my shipment of Pioneer SP-BS21's yesterday ($50/pair at Newegg) and I took some time to dig into one and do some testing and deconstructing. I guess this thread will be more informative than anything else. I have no timeline in mind, but here are my initial objectives:

1) Measure the stock speaker and compare to my reference (Speedsters)
2) Deconstruct
3) Retune the cabinet by lengthening port
4) Remeasure re-tuned cabinet with stock woofer
5) Remeasure re-tuned cabinet with some other 4” woofers

Today I got a couple tests done and I pulled apart one BS21. Before I go on, I just want to toss out some observations.

CABINET:
The cabinet is very decent. It's made of 15mm (0.59") MDF covered in black vinyl laminate (looks like black ash). A knuckle rap test reveals that it could use a bit more bracing. It has a nice square terminal cup with banana binding posts. In order to use bananas, you have to completely unscrew the posts to pop out the little plastic covers. The XO is screwed onto the back of the terminal cup. Upon removing the drivers I discovered that the cutouts are a bit odd, especially for the woofer. The woofer sits in a plastic frame that sits in a 5.65” recess. Dropping test woofers into this will require some custom trim rings. The tweeter sits in a waveguide that is approx. 4.5” round, and the cutout for the tweeter is 3.73”. There is one internal brace from front to rear baffle. There’s some poly-fill in the lower half of the cabinet (just a couple handfuls). There’s no wall lining at all or any stuffing in the top half of the cabinet. The port is 1.5” I.D. x 2.5” with an exit flare.

DRIVERS:
No markings on the drivers at all. I’m not good at describing drivers, so I will let the pictures do the talking there.

LISTENING IMPRESSIONS:
Here’s my initial (very short and sweet) subjective take on the sound of the BS21’s as compared to my reference Speedsters. Immediately the BS21's appear more efficient but it’s mainly louder in the midrange area. They almost feel a bit forward in the vocals as compared to the Speedsters. They dig fairly deep, but definitely not as deep as the Speedsters. The bass is punchy and definitely there and overall, they sound pretty smooth….no real harshness. I say no real harshness, but it’s pretty obvious to my ears that the BS21’s are a bit hot in the mids, at least as compared to the Speedsters. It may be that my ears are tuned to the Fountek ribbons in the Speedsters which are blatently smoother. I've always thought the Speedsters were a bit warmer in the mids too.

VALUE PROPOSTION:
For $100/pair these are worth every penny. For $50/pair, they are a steal, even if you throw out the drivers and XO and reuse the cabinets. I know this will sound biased, but after tinkering with these for a few hours today, I’m not expecting to find a way to make them better than they already are. I’m going to try though.

Measurements next--

[fjhuerta]

Got my shipment of Pioneer SP-BS21's yesterday ($50/pair at Newegg) and I took some time to dig into one and do some testing and deconstructing. I guess this thread will be more informative than anything else. I have no timeline in mind, but here are my initial objectives:

1) Measure the stock speaker and compare to my reference (Speedsters)
2) Deconstruct
3) Retune the cabinet by lengthening port
4) Remeasure re-tuned cabinet with stock woofer
5) Remeasure re-tuned cabinet with some other 4” woofers

Today I got a couple tests done and I pulled apart one BS21. Before I go on, I just want to toss out some observations.

CABINET:
The cabinet is very decent. It's made of 15mm (0.59") MDF covered in black vinyl laminate (looks like black ash). A knuckle rap test reveals that it could use a bit more bracing. It has a nice square terminal cup with banana binding posts. In order to use bananas, you have to completely unscrew the posts to pop out the little plastic covers. The XO is screwed onto the back of the terminal cup. Upon removing the drivers I discovered that the cutouts are a bit odd, especially for the woofer. The woofer sits in a plastic frame that sits in a 5.65” recess. Dropping test woofers into this will require some custom trim rings. The tweeter sits in a waveguide that is approx. 4.5” round, and the cutout for the tweeter is 3.73”. There is one internal brace from front to rear baffle. There’s some poly-fill in the lower half of the cabinet (just a couple handfuls). There’s no wall lining at all or any stuffing in the top half of the cabinet. The port is 1.5” I.D. x 2.5” with an exit flare.

DRIVERS:
No markings on the drivers at all. I’m not good at describing drivers, so I will let the pictures do the talking there.

LISTENING IMPRESSIONS:
Here’s my initial (very short and sweet) subjective take on the sound of the BS21’s as compared to my reference Speedsters. Immediately the BS21's appear more efficient but it’s mainly louder in the midrange area. They almost feel a bit forward in the vocals as compared to the Speedsters. They dig fairly deep, but definitely not as deep as the Speedsters. The bass is punchy and definitely there and overall, they sound pretty smooth….no real harshness. I say no real harshness, but it’s pretty obvious to my ears that the BS21’s are a bit hot in the mids, at least as compared to the Speedsters. It may be that my ears are tuned to the Fountek ribbons in the Speedsters which are blatently smoother. I've always thought the Speedsters were a bit warmer in the mids too.

VALUE PROPOSTION:
For $100/pair these are worth every penny. For $50/pair, they are a steal, even if you throw out the drivers and XO and reuse the cabinets. I know this will sound biased, but after tinkering with these for a few hours today, I’m not expecting to find a way to make them better than they already are. I’m going to try though.

Measurements next--

I'm very curious about those speakers. They seem like the steal of the year at $50!

I wonder if they'll measure like these ones. http://www.stereophile.com/content/p...r-measurements

[bkeane1259]

I am no scientist when it comes to measuring and I have nothing close to an optimal space to do so, however, since this will be a comparison to the Speedsters, the measurements should yield something of value.

Testing methodology:
Speaker on edge of table 30” from floor. Ceiling height 10 feet and nearest side boundaries at least 6 feet away. I took two sets of measurements using a quick sweep in TrueRTA, measured with a Cross Spectrum calibrated ECM8000. Both measurements on axis, mic lined up in between tweeter and woofer – 20” away and then 10” away. I also measured port response with the mic right at the port exit.

BS21 - 20"


Speedster - 20"


BS21 - 10"


Speedster - 10"


20" comparison - BS21(green) - Speedster(purple)


10" comparison - BS21(yellow) - Speedster(gold)


BS21 - port


Speedster - port


Port comparison - BS21(blue) - Speedster (green)

[bkeane1259]

DECONSTRUCTION:

Used microscopic screwdrivers to pluck the grills off. They are held in with what appears to be butyl rubber.




Speaker terminal cup with XO attached to back side.


Woofer out – note the plastic frame.





Tweeter removal.



Tweeter removed from waveguide.

[bkeane1259]

Plastic frame for woofer removed. Note the singular baffle brace and the small amount of poly-fill.


Top half of cabinet, looking thru tweeter cutout. Note the 1.5” I.D. x 2.5” port.


Crossover – double-sided on a PCB – 6 elements – uses a NPE and a poly cap, an air core and a steel core inductor and two 5-watt resistors.




Some physical measurements of the cutouts, etc. (in inches on the caliper readout)
Woofer:


Tweeter (recess):


Tweeter (cutout):


Baffle thickness – 0.59” which equates to 15mm MDF.


BS21 in pieces:

[domwilson]

So it looks like the MCM 55-3870 will fit right in there. What tweeter?

What do you think of this one..http://www.parts-express.com/pe/show...number=264-804

[fjhuerta]

Whenever I measure speakers using RTA I get similar looking graphs to yours... it's interesting to see how your perceptions matched the measurements very closely.

[bkeane1259]

I have to learn how to use TrueRTA better.....I don't do smoothing, gating, splicing, etc. And yes, I also noticed that the charts pretty much confirm my listening impressions. I was really happy to see that BTW, as I don't think I have very stellar ears for critical judgement.

Whenever I measure speakers using RTA I get similar looking graphs to yours... it's interesting to see how your perceptions matched the measurements very closely.

[Trap]

I took the following measurements of my pair of SP-BS21's using ARTA several months ago. The on axis wasn't very pretty but that 10K dip and spike smooths out off axis.

On axis:



Off axis, 30 degrees:

[Whitneyville1]

Stupid here. What I was reading with Audessey as a "bump" near 8Khz is really the dip at 9-10Khz. Duh, duh, duh, ah forget a plus in Audessey is ah minus in response, doh, doh, doh. The "BBC" dip looks like an artifact of the XO/driver spacing. It doesn't show the tweeter diffraction I would really have expected. Give me some T/S numbers and I'll sim the speaker/enclosures and if we get some measurements on the XO, we'll get seriously dangerous. A $25 speaker really worth spending time, effort and money on! Someone needs to call Zaph and warn him! I've simmed three possible MCM woofers in +/- 7L, and I'm not whelmed yet. Zaph's ZA14-8 woofer could be good medicine. It's about 139mm in outside diameter...decent numbers. I'll play with it.

[mintos]

very nice... I haven't had time to play with mine yet

[bkeane1259]

Zaph's ZA14-8 woofer could be good medicine. It's about 139mm in outside diameter...decent numbers. I'll play with it.

I have them. Let me know how they sim. The ZA14 might drop right in that cutout without any modification. For the 4" drivers I want to test, I'm going to have to cut trim rings. I don't know why I get myself into goofy projects like this. Simple stuff turns into a nightmare pretty quickly.

[mintos]

the ND-105-4 might drop on to that 5.25" adapter plate

[bkeane1259]

the ND-105-4 might drop on to that 5.25" adapter plate

Yup....I thought about that too. I also happen to have several ND105-8's which will work perfectly.

Keep the ideas rolling

[hipcheck]

Two caps, two Inductors, and a internal brace. These are way overbuilt for "best buy" level audiphiles,

[bkeane1259]

Crap.....the ND105 just barely fits in the factory mounting plate. No chance of screwing it in though and I'd have to use gasket tape to ensure a good seal. Might as well stick this one on the list for the trim rings.

[jsr]

Can one of you guys measure the FR of the woofer and tweeter separately both with and without the xover inline? Curious what the response is of the drivers and xover.
Of the 4" & 5" drivers I simmed, the RS125 had the most extension, but wondering how complex of a xover would be needed for that.
Due to the CTC, xover frequency is limited to about 2.3kHz. I still wonder how they got around lobing issues on the BS41 & FS51 since the CTC on those is greater than the xover frequency.
I'm looking forward to seeing what you guys get with the MCM & ND105 drivers.

Edit: Bryan, what about an ND140?

[bkeane1259]

The ND140 looks like a good candidate actually. It should fit the woofer cutout nicely, but would probably require a trim ring over the ugly flange for aesthetics. Unfortunately I do not have that driver on hand.

[bkeane1259]

Can one of you guys measure the FR of the woofer and tweeter separately both with and without the xover inline? Curious what the response is of the drivers and xover.

I suppose I can do that, but it ain't gonna be this week. I am out of town on Friday for a few days and I am just totally swamped tomorrow. However, just FYI, I have asked ErinH if he would properly measure the Pioneer drivers. I hope to hear back from him tomorrow. I figure we might as well get the full specs on the drivers just for future reference. I see these speakers being around for a long time...yeah, they are that good.

[fjhuerta]

Two caps, two Inductors, and a internal brace. These are way overbuilt for "best buy" level audiphiles,

That's what I was thinking. Way to go, Pioneer!