Building Modula MT - pls help with bass response

[fvoelling]

I've built and glued the boxes minus the sides, mounted the drivers with a couple of screws (no silicone seal yet), sat the crossovers on the speaker floor and made the connections (just wrapped around the posts, nothing permanent yet). Then I stuffed some polyfill behind the woofer and clamped the speaker side walls (also held by biscuits) for a test run. The inside walls have not been dampened yet.

Firing up some music, everything appears to be working, with the exception of weak or anemic bass response. Is this because I haven't lined the speaker walls with dampening material yet, or due to the joints not being completely sealed yet, or did I maybe screw up the crossovers? FWIW, both speakers sound the same, for better or worse.

The woofers are definitely operating, they visibly move when I crank up the volume, and the bass changes when I use the bass control on the amplifier. Phase appears to be correct as well (would it hurt to change polarity to see if things improve?).

Thx,
Frank

[Paul H]

Frank,

It wouldn't hurt anything to change polarity as a test. Maybe the two speakers have opposite polarity?

I couldn't understand your description of the status of your speaker boxes - do you have the sides and front clamped, but no back installed? That would produce little/no bass ..

[Xander]

Are there visible gaps between the panels? They do have backs, right? Maybe try and crank them up a bit and see if you can feel any air escaping the "box." Not using dampening shouldn't affect bass that much.

[rj45]

break in time, dude!

The Dayton woofers (or mid-woofers) take a couple of
hours to break in. Bass frequencies will become fuller
and deeper in the first 3-6 hours. Mids will take about
10-20 hours and become clearer.

You can easily check woofer polarity with a D or C cell battery.
Positive term on the battery should cause woofer cone to
move outward... ;x(

HTH,
-Don

[fvoelling]

I'll double-check the polarity. The front/back/top/bottom/brace are glued in place, the sides are only held by biscuits/clamps (probably leaving some small gaps).

Regarding break-in, what volume level should I use?

[Xander]

Regarding break-in, what volume level should I use?

I'd use something with enough bass to give the spider and surround a workout to loosen it up. If x-max is 4mm, then just make sure you can visibly seem them moving, without audible distortion of course.

[fvoelling]

Polarity seems ok, I checked with a battery (thx for the tip).

Did some burn-in (maybe 3 hours) and it seemed to help. Also swapped amps just in case, no apparent difference.

Tomorrow I'll hook up one of my better speakers from my HT room and compare its bass to the MT in the same setup. The MTs are just sitting on top of a 4x8 sheet of MDF on top of my workbench in the basement (bare drywall with concrete floors), I'm sure that doesn't help the bass much.

BTW, other than the bass they sound really good so far.

[---k---]

You should post a good photo of the crossover. Someone may be able to tell if something is wired wrong. I would also get those sides glued on the leaks could be throwing your tuning off. You should be able to fit the crossover through the woofer hole, so having the sides glued on shouldn't be an issue.

[servicetech]

Did you build the box w/the same volume and port size as the original plan?

[fvoelling]

I will try to post a picture, and yes, they're built per the original specs.

Ran them for several hours today and then compared a single MT against a single speaker from my HT room (Soliloquy Sat Five, a 5.25" 2-way that retailed for $495/pr). Wasn't even close (MT way better), but not a good way to assess bass performance since the Sat Five only go down to about 60Hz. Then I switched back to the two MTs and did some more listening, and the bass has definitely improved (it seems by quite a bit, but I listened to some bass-heavy material and cranked the volume up more than in my initial test).

I don't want to comment any further on their sound until I have the cabinets fully assembled and placed them on speaker stands in a more suitable location.

[servicetech]

Another thing to think about is many commercially made speakers are strong in the mid bass compared to the accurate sound of the MT. You may be used to a strong mid bass.

[cjd]

Are these sealed or ported?

Are the speakers you're comparing to sealed or ported?

That alone can make a HUGE difference.

C

[fvoelling]

Well, the Sat Five is sealed, the MT is ported.

servicetech, you may have a point re: being used to strong bass, though it's not mid-bass in my case. I most often listen to my office system, which consists of Magnepan MMG W left/right speakers (wall-mounted), augmented by a self-built sub. I'm probably guilty of over-dialing the volume on the sub a bit to make sure I was reaping the benefits of my hard labor.

[Dennis H]

One thing I noticed is your stuffing. Is that the final config? It looks like the backwave has to travel through the stuffing to get to the port and that will reduce the bass a bit. Jon's plans call for lining all the walls with some extra behind the woofer and leaving a clear path between the woofer and the port. You've sorta got the opposite -- nothing on the walls but the two paths to the port are blocked.

[Xander]

Yeah, always leave the path from the woofer to the port clear of stuffing.

Also may want to consider a bit of eggshell foam behind the woofer to reduce reflections back to the cone that can cause distortion or coloration.

And that is one heck of an inductor in the crossover.

[fvoelling]

[And that is one heck of an inductor in the crossover.]

Exactly my thoughts when I received that monster in the mail, and I'm still a bit concerned that I either ordered or received the wrong one. Here's what my order form says, and it matches with one of the BOMs in the Modula MT thread:

255-434 Jantzen 2.7mH 15 AWG Air Core Inductor

None of the other crossovers I've seen pictured in the MT thread appear to have one that large!?

I'm definitely planning to line the sides, back and top with Sonic Barrier 1/2in Acoustic Foam, and use either polyfill or fiberglass for some additional stuffing around the woofer. Since I cannot put any stuffing behind the tweeter (as it would block the port), and also none at the top of the woofer (as it would block the path between port and woofer), the only area left to stuff is the bottom section behind the woofer, kind of where I have the majority in the picture, correct?

Also, I've read that some people use Whispermat or asphalt tape to line the speaker walls (in addition to acoustic foam or similar). Is that recommended?

And my baffle is just 3/4" MDF, vs. 1" in the PE boxes and 1 1/2" used by many here. Should I double up on my baffle, and if so, should I add the second sheet on the inside (thereby reducing the interior volume slightly), or on the outside (and would that call for more chamfering on the existing baffle, or just increasing the woofer hole a bit on the existing baffle piece and chamfer the 2nd layer)?

Thx for all the advice!

[---k---]

Looking at the photos in Jon's offical thread, it looks like he used a 12ga inductor, not the 15ga you used. That big red one you see is a Solen 12 ga perfect lay from madisound, and it is bigger. The 2.7 12 ga from Madisound get expensive. I looked through some of the BOMs, and it looks like people some people substituted 15ga to save cost. This will reduce the bass some. Though, the way you are talking, I'm not sure if switching the part out will totally satisfy you. Likely you just want over emphasized bass. You can push them closer to the wall to increase the bass.

1/2" Sonic Barrier is probably good, but more is better. I've used the 1" several times. Whispermat is very similar to Sonic Barrier. I wouldn't worry about it. But if you haven't ordered the stuff, consider ordering thicker - it is on sale now.

Baffle thickness, again thicker is better. 3/4" is okay for this small box. At this point, thickening it probably isn't worth the effort.

[Brian Walter]

I've also noticed that your inductors are all laid out such that they may interfere with each other. I realize that this may not be how they will end up, but be sure to get them set at 90 degrees to each other. There is a link around here somewhere showing you how to correctly layout inductors. If they are too close and laid out poorly that could have an affect on your response.

Brian Walter

[fvoelling]

Brian, good point about the inductors. I take it you mean the proximity of the 2 inductors on the woofer and tweeter board in the picture of the 2 crossovers I posted? I had considered the placement guidelines when building the individual crossovers (I hope they're ok), but that is indeed how I tested them (as pictured, of course inside the box). Who knows how I would have installed them if you hadn't reminded me? Could that have contributed to less-than-optimal bass?

Ryan, I'm not really looking for emphasized bass, just true bass. Mainly I'm just concerned that I didn't mess up the crossovers at this point. I'm sure most of what is lacking in bass performance right now is due to the (poor) acoustics of the environment and setup, and the fact that they are unfinished (not dampened and sealed properly).

I already have the 1/2" Sonic Barrier, but looking at PE's site again I notice that their 1.25" 3-layer stuff weighs 4.4lbs vs only .75lbs for the 1/2", so it probably both makes the cabinet more solid and absorbs better. It would cost me another $50 incl. shipping to switch to the 1.25" barrier, that's quite a bit in relation to the rest of the speakers, but it would be worth it to me if it made a detectable difference. Is that 1.25" material worth the cost?

BTW, does anybody know if PE will have free shipping coming up soon?

Thx,
Frank

[dawaro]

The 15g Jantzen inductor is fine. That is what I used when I built my set and I discussed it with Jon prior to ordering it.

From what you have said it really sounds like there is an error in the xover some where. I am not sure if it was discussed here or at the PE board but there was someone that built the in-wall version and brought it to the Iowa DIY. He also complained of a lacking bass response. Come to find out he had misinterpreted the schematic and installed a jumper in the wrong location I believe. Once he fixed that the bass problems went away.

[JonP]

Looking at the photos in Jon's offical thread, it looks like he used a 12ga inductor, not the 15ga you used. That big red one you see is a Solen 12 ga perfect lay from madisound, and it is bigger. The 2.7 12 ga from Madisound get expensive. I looked through some of the BOMs, and it looks like people some people substituted 15ga to save cost.

Well, actually it is 14ga wire. It would have been REALLY big with 12ga...

Typically its a fairly subtle difference in changing a tenth of an ohm or two... though this is a strange series (mostly) crossover, it may matter more than it normally does... But as others have said, 15ga isn't a major change.

I'd also suggest looking over the crossovers real closely, it can be amazingly easy to miss some miswiring.

[fvoelling]

I downloaded and played back some test tones, and starting at around 30Hz up I could hear the woofers. Is that confirmation that everything is working ok, or could there still be some error in the crossover wiring?

[Paul H]

I downloaded and played back some test tones, and starting at around 30Hz up I could hear the woofers. Is that confirmation that everything is working ok, or could there still be some error in the crossover wiring?

It's good sign, but only an indicator that there's at least some bass gettng through, not a confirmation that the crossover is wired correctly. If you post some pics of the crossovers we can have a look at it.

[fvoelling]

I double-checked one of the crossover pairs, appears to be ok, but here's some pics just in case. It's kind of difficult to trace the connections by picture, especially on the tweeter crossover, but I'm mainly concerned about the woofer.

Of course, even if the wiring is correct, there's still the possibility that one of the components isn't working properly, but since both speakers pretty much sound the same that's probably not likely.

If the wiring doesn't expose any obvious errors, I will proceed to dampen and finish assembly of the cabinets before conducting further (critical) listening tests in a more appropriate acoustical environment.

Would the placement of the crossover boards as shown in the last pic be ok with respect to inductor proximity? The inductors would be about 6" apart center-to-center (Troels Gravesen shows 4" as problematic and 8" as good, so hopefully it's at least acceptable).

Re: dampening, would it be a worthwhile improvement to step up to the 1.25" thick 3-layer Sonic Barrier from PE vs. the 1/2" 1-layer stuff?

Thx for all the continued help, I really appreciate it!

Frank

[ThomasW]

I downloaded and played back some test tones, and starting at around 30Hz up I could hear the woofers. Is that confirmation that everything is working ok, or could there still be some error in the crossover wiring?

Sounds fine to me. Do you have a SPL meter so you could measure the output? The crossover assembly would have to be really messed up to effect the lowest frequencies coming from the woofer/port.

dampening, would it be a worthwhile improvement to step up to the 1.25" thick 3-layer Sonic Barrier from PE vs. the 1/2" 1-layer stuff?

I see no real benefit to the 1/2" stuff. If you want to keep the costs down and aren't running state-of-the-art playback electronics, just use polyfill or plain old fiberglass batting.

Remove the of poly behind the tweeter it's too close to the port and remove the chunk directly behind the woofer. Put more poly in the cavity surrounding the port tube.

The thing to remember is these little woofers have impressive bass for their size, but they can't produce the kinds of BASS associated with systems having multiple or much larger woofers. It's important to keep these things in perspective....

[fvoelling]

You make a good point, Thomas, it is after all just a single 7" woofer, and if I have to add a sub when it's all said and done, I won't be entirely heartbroken either (good excuse for another project)!

That said, I still want to bring out their full potential, and the playback electronics will be pretty good (though certainly not state-of-the-art). So would the 1.25" 3-layer stuff from PE (to line the walls, in addition to stuffing the rear cavity with polyfill/fiberglass) be a worthwhile improvement over just using polyfill or fiberglass (with no wall liner)?

And yes, I do have a RS SPL meter, but I'm not quite sure about how or what to measure. Here's what I did:

- played the 160Hz test tone on my HT stereo and took the SPL reading at a reference location
- played the 40/50/60Hz test tones at the same volume level on the HT stereo and again took the SPL readings at the reference location
- played the 160Hz test tone on the Modula MT setup and set the volume level on the amp until I had the same SPL output as the corresponding one on the HT stereo, measured at roughly the same distance/orientation as those taken on my HT stereo
- at that same volume level and reference location, played back the 40/50/60Hz test tones and took the corresponding readings

Here are the results:
Tone==HT stereo==Modula MT
160Hz===72======72
60Hz====62======60
50Hz====68======60
40Hz====72======59

So there's definitely a drop-off in output as compared to the HT speakers (2-way 80lbs floorstanders with two 5.25" woofers, rated sensitivity 90dB), but that's probably to be expected given the smaller size and single (albeit bigger) woofer of the MT. I was a bit surprised by the HT speakers' drop-off around 60Hz, is that sort of thing "normal"?

I'll take the readings again tomorrow with less background noise (the boiler was running when I measured the MT) and at a higher volume level, just to be sure. If there's a better way to measure, please let me know.

Thx,
Frank

[---k---]

Something there doesn't look right. I don't think that you should have a drop that big between 160 and 60. Some points in between would be helpful to determine exactly where the drop occurred. Checkout realtraps.com for a test CD with tones in 1hz increments.

There has to be something wrong in the crossover. I haven't built these, so I'm not the best to look over them - and photos is hard.

You might want to post your location in your profile. Someone local to you may come out of the woodworks to help you. We have a great community here. If you're in Chicago, there are a couple of us.

[ThomasW]

Measure the nearfield output from the woofer and the port. Those combined will tell what the speaker is doing.

[JonP]

Something there doesn't look right. I don't think that you should have a drop that big between 160 and 60. Some points in between would be helpful to determine exactly where the drop occurred. Checkout realtraps.com for a test CD with tones in 1hz increments.

Another way to go about it, is download WinISD (alpha, not sure if the beta has it) and use the Signal Generator.. It's pretty handy, you can have it generate sweeps, or get a graph up on the screen and run the cursor back and forth to tune it. I was doing this just the other day, while playing with room placement and a set of Modula MT's...

Which leads to room placement. It could be that you have a big room mode null, sucking it out down around 50-80hz, and it seems weak. Probably a peak somewhere else. How are the speakers and you/spl meter placed in the room? Try changing them around, close to wall, 3-5' from the wall, etc... and see what happens...

[fvoelling]

OK, I have the RS SPL meter and I downloaded WinISD (beta version, which does include the Signal Generator), but I have no clue on how to use either to measure anything (aside from the decibel level with the SPL meter).

Any place where I can find more detailed info on how to perform nearfield measurements, and how to measure/check that drivers are in working order?

Thx,
Frank

[JonP]

WinISD has a rather detailed help file. Some areas are rather instructional on general speaker measuring/building info. Not sure if there's a detailed section on the sig generator, but should be enough to get going.

You might use the pink noise generator, and listen while moving your head around see if there's any funny phasing problems going on. (sound will change a lot with small movments. You should be able to detect a speaker terminal pair with backwards polarity. Also, one might sound different if that crossover is miswired or has another problem. (both might be harder to detect)

Sweeping and measuring with the meter can tell you a lot, though sort of tedious.

[Paul H]

...
Any place where I can find more detailed info on how to perform nearfield measurements ...

Essentially with nearfield you're looking to measure sound output very close to the driver - 1/4" - 1/2" away (as close as possible without having the driver touch the microphone). Doing this measures driver output only, and doesn't pick up room reflections, effect of baffle, etc, as they are so much smaller relative to the driver's direct output.

[fvoelling]

Thx, I'll check out that help file for more info.

Re: nearfield, my ignorance is with respect to the reference(s) I'm comparing against. I have a CD with test tones, but how loud do I play them and how do I know what corresponding decibel levels I should expect to measure nearfield from the driver?

[servicetech]

A quick way to check the box/tuning would be to run the system @ 34hz (box tuning frequency). The woofer should move very little while the port produces most of the bass. If you see the woofer moving a lot with little bass coming from the port you have mis-tuned the box somewhere.

[ThomasW]

I have a CD with test tones, but how loud do I play them and how do I know what corresponding decibel levels I should expect to measure nearfield from the driver?

You shouldn't try for reference levels or anything like that. All you're doing is checking to see if the port tuning is correct. That can easily be done at low 80dB output levels.

If you have a computer hooked up to your audio system you can download the freeware NCH tone generator from my website. Run your tests with very short bursts of pink noise, and don't play frequencies below the port tuning.

[fvoelling]

I ran a quick test using the 40Hz test tone that I had downloaded earlier. At the volume level where the woofer measures about 81dB (in the center of the cone, maybe 1/2" or less away), the port measures about 94dB (same distance).

Now does that indicate that the box/port is tuned properly, and what about the woofer working as advertised?

Over the weekend, I'll try to hook up a PC to the Modulas in the workshop and run the NCH tone generator test.

Thx,
Frank