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Multi-Way Conventional loudspeakers with crossovers

Low-Cost PMC-inspired TL Monitor with DC130A and DC28F
Low-Cost PMC-inspired TL Monitor with DC130A and DC28F
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Old 30th October 2015, 07:19 PM   #1
xrk971 is offline xrk971  United States
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Low-Cost PMC-inspired TL Monitor with DC130A and DC28F
Default Low-Cost PMC-inspired TL Monitor with DC130A and DC28F

This speaker started as a spinoff from this thread where I was studying the effects of different levels of stuffing/damping in a TL:
PMC TL Stuffing
The speaker that inspired this was the PMC TB-1:
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Which has a 48in long internal path TL with the following damping scheme, which I think provides a borderline critically-damped aperiodic TL based on the measurements I have seen on-line:
Click the image to open in full size.

There was a rather lengthy debate in that thread about whether or not the TB1 follows Bailey's TL approach and whether or not a proper TL should have single or double impedance peak. Rather than debate it, I decided to model it.

I then went on to model and design my own little TL box to study the effect of damping but using drivers I had on-hand: a Dayton Classic Series DC130A-8 5.25in midwoofer and a Dayton DC28F-8 silk dome tweeter. Both of these drivers actually have quite nice published and measured performance specs and are great sounding high-value drivers. You might be hard pressed to find another 5.25in class midwoofer with the same performance for $20. Similarly, the DC28F is an extremely smooth sounding soft dome with low distortion and flat frequency response.

Anyhow, my design constraints were to use approximately the same 48in long TL that the PMC TB-1 has, and about the same physical format. I put the vent in an up-firing position at first, but eventually went with forward firing to gain a few dB of sensitivity in the bass. I also wanted a tuning frequency fb of about 60Hz - 80Hz depending on the damping scheme used.

The design of the TL was as follows with a 6.0in wide internal dimension:

Click the image to open in full size.

The predicted frequency response for this TL depended heavily on the amount of stuffing inside. Here are 3 cases of light, moderate, and dense stuffing. As expected, each case is a tradeoff in bass extension and SPL for light damping with lower group delay and improved transient response with dense stuffing. The predicted impedance curves go from double peak for light stuffing, to single peak for dense stuffing. The dense case tends to an aperiodic TL.

Light stuffing:

Click the image to open in full size.

Moderate stuffing:

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Dense stuffing:

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Here are the corresponding Group Delays for the light to dense stuffing, the GD goes from 16ms down to under 5ms at 50Hz which is about the same as a sealed cabinet, but with deeper bass extension.

Light:
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Dense:
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Here is the predicted impedance for light stuffing:
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Moderate stuffing:
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Dense stuffing:
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The predicted speaker cone excursion goes from a classic double peak 4th order:
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To what you would see in an aperiodic TL or a sealed cabinet:
Click the image to open in full size.

So these plots intrigued me and I decided to go with a prototype build in foam core. I was aiming for the moderate to dense case somewhere in between. I thought it important to get at least a -3dB point at 80Hz to get a sense of some bass output. I redid the model with front exit vent and the stuffing plan closer to how I will implement it using loosely teased out polyfill. Here is the predicted frequency response with a 2kHz XO and baffle step loses included:

Click the image to open in full size.

And here is the predicted GD:
Click the image to open in full size.

If stuffing is added to the final leg, here is the predicted response - about 80Hz f3:
Click the image to open in full size.

With about 7ms GD at 50Hz:
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With a semi-bordering on aperiodic TL impedance peak with a mild double bump:
Click the image to open in full size.

Anyhow that was the goal and here is the build process:

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Stuffing plan (adding stuffing in final leg transforms to aperiodic TL):
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Here is the completed speaker:

Click the image to open in full size.

And here are the measurements using a miniDSP and TPA3116D2 amps for an active 2-way. I am using 1st order electrical HPF at 2kHz on the DC28F and a 4th order BW low pass at 1kHz on the DC130A to get an acoustic XO of about 1350Hz. The slopes are quasi-Harsch and allow somewhat of a time-coherent output. I will refine the XO later but these are just to get started.

Raw measurement of the woofer in the TL running full range:
Click the image to open in full size.

Frequency response showing XO profiles:
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Harmonic Distortion:
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Phase:
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Impulse Response (there is a slight rise and wiggle before the main pulse due to the time delay on the tweeter to get it to be quasi transient perfect with the woofer):
Click the image to open in full size.

Group Delay (with 1/2oct smoothing for clarity) is about 6.7ms at 50Hz:
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I did take impedance sweeps and they look a lot like the mild double bump prediction above.

The TL sounds very nice - the transients are well aligned in time between the two drivers, the bass is clear and precise without the muddiness of a reflex, the mids are articulate and pleasing, and the highs of the DC28F are excellent - very smooth, transparent, engaging, with no sibillance or harshness. I still need to do more work to refine the XO with careful measurements and simulation in PCD, then transfer to miniDSP rather than doing the XO "by eye". I think I might move the XO up towards the 2kHz point but see that there is additional HD from the woofer there to avoid. If I have time, I may even try to design my first passive XO to see how that looks. Of course it won't be transient perfect given the flush baffle.

I am quite happy with how these turned out and am considering a thin 3/16in Sureply wood baffle to permit the drivers a better mount.

Edit 10/31/15: Polar data shown has tweeter rebated and brillo pad diffraction reducers installed

Click the image to open in full size.

Edit 10/31/15 - latest Measurements with 2kHz XO and rebated tweeter with brillo pad diffraction control - sounds great and settings are now"locked down" for enjoyment (and to build stereo pair):

XO plot:

Click the image to open in full size.

Phase - +/-23deg over 150Hz to 15kHz :

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Harmonic Distortion - about 1.4% at 50Hz at normal listening levels:

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Impulse Response/Step Response - very nice:

Click the image to open in full size.

Group Delay (8.6ms at 50Hz - increased 2ms due to BW1 HPF at 32Hz):

Click the image to open in full size.

Last edited by xrk971; 31st October 2015 at 07:27 PM.
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Old 30th October 2015, 08:10 PM   #2
Bill poster is offline Bill poster  Thailand
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V nice indeed
want to do something similar with this Faital driver FaitalPRO | LF Loudspeakers | 5FE120
and the Seas 22TFF
Like your Dayton choice v smooth response and about 20 each in the uk.
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Old 30th October 2015, 08:34 PM   #3
xrk971 is offline xrk971  United States
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Low-Cost PMC-inspired TL Monitor with DC130A and DC28F
Quote:
Originally Posted by Bill poster View Post
V nice indeed
want to do something similar with this Faital driver FaitalPRO | LF Loudspeakers | 5FE120
and the Seas 22TFF
Like your Dayton choice v smooth response and about 20 each in the uk.
Good choice! That was my backup driver and have simulated it as well. Very good performer for a TL. Let me see if I can dig up the sims for you - it might be a drop in replacement for DC130A.
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Old 30th October 2015, 08:45 PM   #4
Charles Darwin is offline Charles Darwin  United Kingdom
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I've used it paired with SEAS 19TFF and all I can say is that little Faital driver is a gem.

At 42 the pair incl. delivery an absolute no-brainer.
The little 19mm SEAS has IMO the advantage that it doesn't need any padding when paired with the Faital.
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Old 30th October 2015, 09:44 PM   #5
xrk971 is offline xrk971  United States
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Low-Cost PMC-inspired TL Monitor with DC130A and DC28F
Default TL Design for 5FE120

This driver is basically almost a drop-in fit for this TL design. Just change the internal width to 5.5in (from 6.0) and you are good to go. About the same sensitivity vs the DC130A-8 but with 5mm of xmax so ultimate SPL should be higher. Nice driver - I hope to try one someday soon.

Here is predicted frequency response with moderate stuffing, 67Hz f3:

Click the image to open in full size.

Here is predicted group delay, about 6 to 8ms depending on stuffing:

Click the image to open in full size.

Here is the impedance:

Click the image to open in full size.

I say go for it!
Attached Images
File Type: png PMCTL5-5FE120-Freq.png (31.5 KB, 3019 views)
File Type: png PMCTL5-5FE120-GD.png (8.8 KB, 2987 views)
File Type: png PMCTL5-5FE120-Impedance.png (7.9 KB, 2990 views)
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Old 30th October 2015, 10:39 PM   #6
haf is offline haf  Germany
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Hi xrk971, nicely done!

Could you please post nearfield measurements of the woofer and the port? Great would be a scaled nearfield measurement of port and woofer (adjusted sound pressure using the port and cone surface area). If possible a nearfield mesurement of the CB (with closed port) would be great.

And finally, a impedance measurement of the TL would be great too. I'm curious about the difference of the CB and the TL.

regards,
Armin
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Old 30th October 2015, 11:09 PM   #7
Bill poster is offline Bill poster  Thailand
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Thanks for modelling it!

never noticed that 19mm Seas tweet before, how is it?
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Old 30th October 2015, 11:29 PM   #8
Charles Darwin is offline Charles Darwin  United Kingdom
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I like it.

It kinda disappears which I mean in the best possible sense ie it doesn't draw attention to itself. I've crossed it in at about 3.4kHz, LR2.
I didn't sim anything and designed the crossover (what there is of one) just using manufacturers data. It was just meant as a rough and ready student system for my daughter but when I finished them I couldn't stop listening to them which in my book is a good sign.
In a direct comparison I preferred the Faital/SEAS to my Rogers DB101 which feature a 5" Audax aerogel midwoofer and a cheap mylar tweet crossed 1st order at 5k.
They are about the same size as each other.

Currently building another two pairs.
My better half wants a pair for the bedroom or garden and a mate of mine (a recording musician for what it's worth) also asked for a couple.

Last edited by Charles Darwin; 30th October 2015 at 11:33 PM.
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Old 30th October 2015, 11:33 PM   #9
xrk971 is offline xrk971  United States
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Low-Cost PMC-inspired TL Monitor with DC130A and DC28F
CharlesDarwin,
How were you loading the Faitals for bass? Sealed or BR? The TL with stuffing has a decidedly better bass presentation than BR. I have always been fond of Linkwitz transform on sealed to get extension and low GD, but through my modeling and measurements, have convinced myself that if I were to go with a passive XO, the damped TL provides the depth of the BR but with the low GD of a sealed LT woofer.
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Old 30th October 2015, 11:41 PM   #10
Charles Darwin is offline Charles Darwin  United Kingdom
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BR.

I think they are quite a bit smaller than your TLs. About 5.5L once I subtract driver, ports and xover parts.
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