PMC twenty.22

mhardy6647

Clipdat wrote: »

Thanks all for the continued discussion about the speaker's performance attributes, and also my room setup and unfortunate placement options.

...

Going back to the 703s for a minute, they do have a slightly accented midbass, but they also have a lot more bass response in general at lower volumes vs the PMCs, at least in my room. I get that different speaker designs will have different levels and types of bass response. However, it just seems that with the PMCs at the lower listening levels that I tend to listen at such as 60-75db, there is just not enough bass to equally match the treble and midrange, as compared to what the 703s were giving me at those same levels. I believe this must be due to the rear ported design of the 703s and how they were only 7" from the front wall. The PMCs are in the same spot very close to the front wall. I do my listening about a foot or so off the back wall.

If I crank the PMCs up to 75-85db they start kicking out amazing sound and the bass begins to more accurately match the level of sound coming from the treble/mid. Maybe they're just voiced/designed to play at these higher levels since a lot of people like to listen loud. However, it's not really realistic for me to listen at this level (especially for extended amounts of time) since I live in an apartment.

They do have a lot of nice characteristics in terms of their treble and midrange performance. It's really no contest vs. the 703s in that regard. The PMCs are much more clear and detailed, without being harsh. It just seems like in general they are capable of resolving the music on a much higher level than the 703s.
...

If you haven't done so, it might be both interesting and informative to do some frequency response measurements (it's 2019 -- all's you need is a phone... although a good, calibrated microphone is handy, too). This could give you a chance to correlate* what you hear, and what you like, with what the two pairs of loudspeakers are doing.

There's more to it than frequency response in-room, of course (dispersion, diffraction, distortion, and decay characteristics are all important to the perceived tone of loudspeakers, I'd say) -- but the bass issue may just boil down to flatness of frequency response from, say, 50 to 200 Hz.

Another thought:

Your description also reminds me of the well-studied Fletcher-Munson "effect". Our ears are much less sensitive to extreme frequencies (high and low) at low SPL. The old "loudness contour" controls were meant to correct for this physiological "given" -- which they did, albeit with differing levels of success

The funny thing is that some hifi component combinations seem (empirically and unscientifically, to me) to be more or less immune to losing fullness and/or dynamics at low SPLs. I have pretty strong opinions about some aspects of the subject, which I've shared -- but there may be a loudspeaker frequency response curve correlation that I (at least) haven't considered.

__________________
* of course, always remember correlation does not imply causation. This has been a public service announcement.

mhardy6647

So, we're talkin' LSiM703 loudspeakers as the comparator?
(please excuse my naivete!)

Good ol' Stereophile reviewed those.

One does detect a small but significant 'midbass' bump in their quantitative (anechoic) analysis. I am sure all y'all know that, but I don't remember looking at it.


https://www.stereophile.com/content/polk-lsiiim703-loudspeaker-measurements


bass bump, midrange bump, and (larger) treble bump.

EDIT: In fairness, JA's conclusion is that the 703 is somewhat overdamped.

There is almost no sign of the usual nearfield boost in the upper bass, which implies that the Polk's woofer alignment is somewhat on the overdamped side, something I tend to prefer—as did Bob, who commented favorably on the speaker's well-defined lows. It will also allow the speaker to be placed close to the wall behind it without its low frequencies becoming overbearing.

mhardy6647

Oh, here's another interesting thought, FWIW.

Have you tried the time-honored knuckle rap test on the enclosures and compared the two loudspeaker models? If not, that might be interesting, too -- even better if you record and post the results!

I have been a bit obsessed with rapping cabinets lately and trying to correlate/understand what I hear then with what I hear when they're... umm... speaking. Maybe that's just me, though...

rooftop59

I personally found the bass response of the 703s overbearing in my 2000 ft3 master bedroom until I got a beefy 200 wpc behind them. Even then, there was a very clear bump that I never quite completely got over. It is possible that you just really prefer this little boast considering the electronic music that you are using as a test. The boast does give the impression that they dig much deeper than they actually do...imho of course...

So, it could be that the PMCs are much more linear, and therefore subjectively sound like the bass doesn't match the output of the mids and highs. As the Doc points out, measurements might provide some insight...

joecoulson

Drew I absolutely concur (as I think I have mentioned exactly this before to you) with @rooftop59
between the LSIM mid bass bump, the rear port vs front TL, and the source music choice - the PMC might not fit the bill - unless a subwoofer (small and quality) is added.

lightman1

mhardy6647 wrote: »

Oh, here's another interesting thought, FWIW.

Have you tried the time-honored knuckle rap test on the enclosures and compared the two loudspeaker models? If not, that might be interesting, too -- even better if you record and post the results!

I have been a bit obsessed with rapping cabinets lately and trying to correlate/understand what I hear then with what I hear when they're... umm... speaking. Maybe that's just me, though...

Stop doing that, Doc....
You'll only drive yourself insane trying to form a conclusion of the direct influence between thumping the cabinets and how it relates to a curve graph....
Drink wine....

Tony M

There's a reviewer of speakers ( I forget what mag. ) that uses a device to measure what frequencies makes the cabinets vibrate.

That's getting deep right there!

mhardy6647

lightman1 wrote: »

mhardy6647 wrote: »

Oh, here's another interesting thought, FWIW.

Have you tried the time-honored knuckle rap test on the enclosures and compared the two loudspeaker models? If not, that might be interesting, too -- even better if you record and post the results!

I have been a bit obsessed with rapping cabinets lately and trying to correlate/understand what I hear then with what I hear when they're... umm... speaking. Maybe that's just me, though...

Stop doing that, Doc....
You'll only drive yourself insane trying to form a conclusion of the direct influence between thumping the cabinets and how it relates to a curve graph....
Drink wine....

Just remember: you can't spell analytical without, well, you know...

FTGV

Tony M wrote: »

There's a reviewer of speakers ( I forget what mag. ) that uses a device to measure what frequencies makes the cabinets vibrate.

That's getting deep right there!

John Atkinson of Stereophile uses an accelerometer to detect cabinet resonance.

Those PMC's should have at least two full width partitions that form the internal structure for the trans line. These are essentially heavy bracing and should make the sides, top and bottom panels quite inert. My TB2's do very well on the knuckle test. However the front baffle and rear panel are not braced.

Clipdat

EndersShadow wrote: »

Sexy KRK's!

They are a set of speakers I'd love to own for my loft someday. Get the Rokit 8's and paired with my MicroPro I'd be done... but where's the fun in being "done"

I find it interesting that there doesn't seem to be any bookshelf speakers available with an 8" woofer.

Anyone know why that is?

halo

Clipdat wrote: »

EndersShadow wrote: »

Sexy KRK's!

They are a set of speakers I'd love to own for my loft someday. Get the Rokit 8's and paired with my MicroPro I'd be done... but where's the fun in being "done"

I find it interesting that there doesn't seem to be any bookshelf speakers available with an 8" woofer.

Anyone know why that is?

Dynaudio DM 2/10 has a 10" woofer

https://whathifi.com/dynaudio/dm-210/review

For further pondering:

https://avsforum.com/forum/89-speakers/825094-where-did-8-inch-woofers-go.html

Clipdat

Switched preamps and listened to the PMCs for a while tonight.

joecoulson

And ? ^

steveinaz

Love the look and build quality. Bet they sound fantastic.

Clipdat

joecoulson wrote: »

And ? ^

Further tube rolling is required. Tried these last night and I'm not completely sold on them: https://www.upscaleaudio.com/collections/preamp-tubes/products/rca-black-plate-5814wa-12au7-triple-mica

Hermitism

Clipdat wrote: »

joecoulson wrote: »

And ? ^

Further tube rolling is required. Tried these last night and I'm not completely sold on them: https://www.upscaleaudio.com/collections/preamp-tubes/products/rca-black-plate-5814wa-12au7-triple-mica

You repurchased from your arch-nemesis again? When I ordered a cable from them, they said to be sure and tell you hello!

Clipdat

Hermitism wrote: »

You repurchased from your arch-nemesis again? When I ordered a cable from them, they said to be sure and tell you hello!

No, they came with the preamp.

halo

Clipdat wrote: »

Hermitism wrote: »

You repurchased from your arch-nemesis again? When I ordered a cable from them, they said to be sure and tell you hello!

No, they came with the preamp.

I see. Give Brent Jessee a call or Andy at Vintage Tube Services if you decide to roll something else.

mhardy6647

Clipdat wrote: »

EndersShadow wrote: »

Sexy KRK's!

They are a set of speakers I'd love to own for my loft someday. Get the Rokit 8's and paired with my MicroPro I'd be done... but where's the fun in being "done"

I find it interesting that there doesn't seem to be any bookshelf speakers available with an 8" woofer.

Anyone know why that is?

There certainly used to be, but the designs (drivers, cabinets, and crossovers) were very different in those long-ago times.

Eight inch is a nice size for a broadband midbass driver (IMO), and there've been some really nice ones over the years. The famous EPI (Epicure) drivers fairly leap to mind.

Clipdat

halo wrote: »

I see. Give Brent Jessee a call or Andy at Vintage Tube Services if you decide to roll something else.

Thanks. I'm familiar with and have had conversations with both of those guys.

I thought these looked pretty interesting: https://tubedepot.com/products/black-sable-jj-ecc82-12au7-gold-pin

"The BLACK SABLE process is far more than putting tubes in a chamber and lowering the temperature. The BLACK SABLE process starts with tube selection. Only the best preamp, power and rectifier tubes are chosen to undergo this arduous process. All tubes undergo a 24 hour burn-in under load. The tubes are then placed in the Cryo-Processor where a computer-controlled proprietary system lowers the temperature to -300 Fahrenheit / -184 Celsius for 24 hours and then slowly ascends back to room temperature. Preamp tubes are tested and rated for Gain, Microphonics and Noise. Next, all 7/9 pin tubes have their pins cleaned for a better electrical connection. Power tubes are matched to within 3% for both Ip (Plate Current) and Gm (Transconductance)."

codycatalist

Granted my experience with tubes is VERY limited and I am sure the RCAs you posted before were better than mine but @mhardy6647 gifted me some RCA 12AU7s that were CONN branded. I LOVED those tubes, not warm in my opinion but brought out so much in the music with great separation.

Man I need to pop those back in.

*Take what I say with a grain or two of salt as I have only used tubes in headphone amps.

mhardy6647

I am pretty sure I have some more of the 12AU7 cleartops all it'd cost you is postage, and not even that if it's only a few bucks! PM me if you have any interest at all.

Clipdat

Hey thanks Mark, appreciate that, I'll keep it in mind.

I still have a pair of vintage NOS Amperex as well as a pair of Electro Harmonix and Psvane to evaluate.

mhardy6647

Clipdat wrote: »

Hey thanks Mark, appreciate that, I'll keep it in mind.

I still have a pair of vintage NOS Amperex as well as a pair of Electro Harmonix and Psvane to evaluate.

that'll keep you occupied for a while.

stangman67

Drew, I’ve tried a few sets of au7s in my Rhumba. The rcas were real hot on top and didn’t work well at all for me. I had conn branded clear tops. I bought amperex bugle boys and Mullard “shield logos” from Jesse and the Mullards are the winner. Sweet, warm sound characteristics.

Clipdat

Thanks for the tip, Zach. I tried a set of Mullards that came with it, but they were microphonic so I removed them.

I'm ideally looking for a tube that accentuates bass.

stangman67

Andy suggests trying psvanes although I never went that route. Since you have some on hand, might be a good option. The stock jjs are not worthy but they certainly create plenty of bass

joecoulson

Newer JJ’s or EH will have better lower end IMO
But we already discussed that.

Clipdat

stangman67 wrote: »

Andy suggests trying psvanes although I never went that route. Since you have some on hand, might be a good option. The stock jjs are not worthy but they certainly create plenty of bass

Mine is the "Extreme" version, so it came with the Psvane stock instead of the JJs. I'll give them a go soon.

halo

Clipdat wrote: »

Thanks. I'm familiar with and have had conversations with both of those guys.

I thought these looked pretty interesting: https://tubedepot.com/products/black-sable-jj-ecc82-12au7-gold-pin

"The BLACK SABLE process is far more than putting tubes in a chamber and lowering the temperature. The BLACK SABLE process starts with tube selection. Only the best preamp, power and rectifier tubes are chosen to undergo this arduous process. All tubes undergo a 24 hour burn-in under load. The tubes are then placed in the Cryo-Processor where a computer-controlled proprietary system lowers the temperature to -300 Fahrenheit / -184 Celsius for 24 hours and then slowly ascends back to room temperature. Preamp tubes are tested and rated for Gain, Microphonics and Noise. Next, all 7/9 pin tubes have their pins cleaned for a better electrical connection. Power tubes are matched to within 3% for both Ip (Plate Current) and Gm (Transconductance)."

I would avoid cryo tubes if it were me. @SCompRacer purchased a bunch of them years ago and, IIRC, he said they burned out pretty quickly. Perhaps he can chime in. I think he got them from Tube World. Kühl tubes?