[hertz]

I have two questions.

1.In the two ways HT-1 and 1801 (Normal and TL versions), what is the crossover point ?

2.How is transmission line bass different from bass from a usual ported loudspeaker ? I keep hearing different comments about this. I am looking for comments on various aspects like timing, speed, detail etc.. Why do loudspeaker designers choose one method over the other ?

[chlorofille]

Hi Hertz,

I can only answer your 2nd qn :

Ported normally gives a punchier bass than a TL but doesn't extend as low.
The bass of a TL is usually in between a ported and a closed box system. Also in certain rooms, the smooth roll-off of a TL will reduce "boom".

[fsimms]

TL speakers have internal stuffing along their length.  This usualy helps the midrange as any internal box reflections don't come back out through the midrange driver.  It makes the midrange a little bit clearer than the ported box.   

Bob

EDIT:   We didn’t answer the second part of the second question.   In the past, TL’s were much more difficult and expensive to build.  They, also, were much more bulky.  With the newer Mass Loaded TL designs that Jim Salk uses, they are simpler to build and less bulky

[DMurphy]

I have two questions.

1.In the two ways HT-1 and 1801 (Normal and TL versions), what is the crossover point ?

2.How is transmission line bass different from bass from a usual ported loudspeaker ? I keep hearing different comments about this. I am looking for comments on various aspects like timing, speed, detail etc.. Why do loudspeaker designers choose one method over the other ?

The crossover point for both speakers is around 2400 Hz. 

[hertz]

@Dennis,
Is the crossover point the same in the soundscape series of speakers ? I understand the new HT1 and HT1-TL is going the sport the same soundscape tweeters from now on.

@chlorofille,
I am trying to understand your statement; “The bass of a TL is usually in between a ported and a closed box system”
Are you referring to the “smoother roll off” or “the response”. Can you please elucidate?

[DMurphy]

@Dennis,
Is the crossover point the same in the soundscape series of speakers ? I understand the new HT1 and HT1-TL is going the sport the same soundscape tweeters from now on.

The SoundScape is crossed a hair above 1800 Hz.  The RAAL is designed to operate that low, and in the nearly baffleless upper portion of the SS cabinet, there are no diffraction dips or peaks that make a cross that low difficult.  I can't cross quite that low in the speakers with conventional baffles and still maintain a linear response.  But so far (I've finished RAAL versions for the HT2 TL and Songtower RT), I've managed to cross justly slightly above 2k. 

[chlorofille]

@chlorofille,
Are you referring to the “smoother roll off” or “the response”. Can you please elucidate?

Umm I meant the response. Ported might hit 40Hz fairly linearly but drop off sharply after that (24dB/oct roll off rate). Closed box has a rolloff rate of 12dB per octave. TL would be about 18dB/oct. The TL could start rolling off at 45Hz but still have decent output at 30Hz. My room has a 40Hz resonance so if I had a choice I'd go for the TL so as to not excite the room mode too much. Depends on you - how do you like your bass ? Punchy or dry (linear)

[ctviggen]

Umm I meant the response. Ported might hit 40Hz fairly linearly but drop off sharply after that (24dB/oct roll off rate). Closed box has a rolloff rate of 12dB per octave. TL would be about 18dB/oct. The TL could start rolling off at 45Hz but still have decent output at 30Hz. My room has a 40Hz resonance so if I had a choice I'd go for the TL so as to not excite the room mode too much. Depends on you - how do you like your bass ? Punchy or dry (linear)

What if you move?  Seriously, I would never, ever, ever buy a speaker based on room modes.  Heck, you move back 6 inches and your room mode is gone.  Moreover, you're assuming that each speaker will equally excite the 40Hz room mode, which may not be the case. For instance, my Salk HT3s appear to excite a room mode more than did my VMPS RM40s (and I still haven't determined why).  Go for the best speaker in your budget. 

[Paul K.]

The rolloffs you state for a truly vented system and sealed system are correct, but the rolloff for a TL is not necessarily.  All TLs are inherently 4th-order systems but the actual rolloff, say from 40 Hz to 20 Hz, can be 4th-order (which the SongTowers ML-TL pretty much have), 3rd-order, and even 2nd-order.  It all depends on the specific drivers and the spcific TL implementation.
Paul

Umm I meant the response. Ported might hit 40Hz fairly linearly but drop off sharply after that (24dB/oct roll off rate). Closed box has a rolloff rate of 12dB per octave. TL would be about 18dB/oct. The TL could start rolling off at 45Hz but still have decent output at 30Hz. My room has a 40Hz resonance so if I had a choice I'd go for the TL so as to not excite the room mode too much. Depends on you - how do you like your bass ? Punchy or dry (linear)

[zybar]

What if you move?  Seriously, I would never, ever, ever buy a speaker based on room modes.  Heck, you move back 6 inches and your room mode is gone.  Moreover, you're assuming that each speaker will equally excite the 40Hz room mode, which may not be the case. For instance, my Salk HT3s appear to excite a room mode more than did my VMPS RM40s (and I still haven't determined why).  Go for the best speaker in your budget.

Why is it different?

Aren't the woofers at different heights?   

That will absolutely impact how the speaker interacts with the room.

Next time you take measurements, try moving your microphone up or down a few inches - guarantee you won't get the same results.

George

[ctviggen]

Why is it different?

Aren't the woofers at different heights?   

That will absolutely impact how the speaker interacts with the room.

Next time you take measurements, try moving your microphone up or down a few inches - guarantee you won't get the same results.

George

That was my point.  It's useless to buy speakers depending on room modes, because you can't tell how a speaker will interact with room modes.  But it's also useless to measure at a location your head won't be.  When I measured, I measured exactly at my ear height where I would have been sitting had the microphone not been there.  Any lower would be not useful.  Now, moving forward or backward would be a good idea, since my ears might physically be able to meet those positions.  I did measure my RM40s, but never measured the Salks due to room construction (see below for pictures of my room I took this morning).  The Salks however had a bad interaction with my room.  That's why you can't look at a speaker's rolloff characteristics and your measurements of room modes and come up with a reasonable approximation how the speaker will sound.  Furthermore, I never had the chance to move everything around, and perhaps moving the Salks somewhere else would've helped at the listening position.